Patent Application
20200075960
This disclosure relates to batteries with solid state electrolytes. More particularly, the disclosure relates to solid state batteries having a unique solid state electrolyte and combinations of materials, and methods of making such batteries.
Lithium ion batteries (LiBs) have the highest volumetric and gravimetric energy densities compared to all other rechargeable batteries making LiBs the prime candidate for a wide range of applications, from portable electronics to electric vehicles (EVs). Current LiBs are based mainly on LiCoO2 or LiFePO4 type positive electrodes, a Li+ conducting organic electrolyte (e.g., LiPF6 dissolved in ethylene carbonate-diethyl carbonate), and a Li metal or graphitic anode. Unfortunately, there are several technological problems that exist with current state-of-the art LiBs: safety due to combustible organic components; degradation due to the formation of reaction products at the anode and cathode electrolyte, interfaces (solid electrolyte interphase—SEI); and power/energy density limitations by poor electrochemical stability of the organic electrolyte. Other batteries based sodium, magnesium, and other ion conducting electrolytes have similar issues.
Sulfur is a promising cathode for lithium batteries due to its high theoretical specific capacity (1673 mAh/g), low cost and environmental friendliness. With a high theoretical specific energy density of 2500 Wh/kg that is 10 times greater energy density than conventional Li-ion battery, Li—S battery hold great potential for next-generation high energy storage system. However, wide-scale commercial use is so far limited because of some key challenges, such as the dissolution of the intermediate discharge product (Li2Sx, 2<X<8) in conventional liquid electrolytes, remained unsolved. On the other hand, all-solid-state batteries (SSB) are considered to be ultimate power supply for pure electric vehicles (EVs). SSB system demonstrates a new approach for novel Li—S battery. Replacing the organic electrolyte with solid state electrolyte (SSEs) will intrinsically eliminate the dissolution of polysulfide. However, all of the solid state Li—S batteries incorporating current state-of-the-art SSEs suffer from high interfacial impedance due to their low surface area.
Provided is a solid-state, ion-conducting battery comprising: (a) cathode material or anode material; (b) a solid-state electrolyte (SSE) material comprising a porous region having a plurality of pores, and a dense region, where the cathode material or the anode material is disposed on at least a portion of the porous region and the dense region is free of the cathode material and the anode material, and a current collector disposed on at least a portion of the cathode material or the anode material.
In one embodiment, the SSE material comprises two porous regions, the battery comprises a cathode material and an anode material, wherein the cathode material is disposed on at least a portion of one of the porous regions forming a cathode-side porous region and the anode material is disposed on at least a portion of the other porous region forming an anode-side porous region, and the cathode-side region and the anode-side region are disposed on opposite sides of the dense region, and wherein the battery further comprises a cathode-side current collector and an anode-side current collector.
In one embodiment, the cathode material is a lithium-containing material, a sodium-containing cathode material, or a magnesium-containing cathode material. In another embodiment, the cathode material comprises a conducting carbon material, and the cathode material, optionally, further comprises an organic or gel ion-conducting electrolyte. In another embodiment, the lithium-containing electrode material is a lithium-containing, ion-conducting cathode material selected from LiCoO2, LiFePO4, Li2MMn3O8, wherein M is selected from Fe, Co, and combinations thereof. In another embodiment, the sodium-containing cathode material is a sodium-containing, ion-conducting cathode material selected from Na2V2O5, P2-Na2/3Fe1/2Mn1/2O2, Na3V2(PO4)3, NaMn1/3CO1/3Ni1/3PO4, and Na2/3Fe1/2Mn1/2O2 graphene composite. In another embodiment, the magnesium-containing cathode material is a magnesium-containing, ion-conducting cathode material. In another embodiment, the magnesium-containing cathode material is a doped manganese oxide.
In one embodiment, the anode material is a lithium-containing anode material, a sodium-containing anode material, or a magnesium-containing anode material. In another embodiment, the lithium-containing anode material is lithium metal. In another embodiment, the sodium-containing anode material is sodium metal or an ion-conducting, sodium-containing anode material selected from Na2C8H4O4 and Na0.66Li0.22Ti0.78O2. In an embodiment, the magnesium-containing anode material is magnesium metal.
In one embodiment, the SSE material is a lithium-containing SSE material, a sodium-containing SSE material, or a magnesium-containing SSE material. In another embodiment, the lithium-containing SSE material is a Li-garnet SSE material. In another embodiment, the Li-garnet SSE material is cation-doped Li5La3M12O12, where M1 is Nb, Zr, Ta, or combinations thereof, cation-doped Li6La2BaTa2O12, cation-doped Li7La3Zr2O12, and cation-doped Li6BaY2M12O12, where cation dopants are barium, yttrium, zinc, iron, gallium or combinations thereof. In an embodiment, the Li-garnet SSE material is Li5La3Nb2O12, Li5La3Ta2O12, Li7La3Zr2O12, Li6La2SrNb2O12, Li6La2BaNb2O12, Li6La2SrTa2O12, Li6La2BaTa2O12, Li7Y3Zr2O12, Li6.4Y3Zr1.4Ta0.6O12, Li6.5La2.5Ba0.5TaZrO12, Li6BaY2M12O12, Li7Y3Zr2O12, Li6.75BaLa2Nb1.75Zn0.25O12, or Li6.75BaLa2Ta1.75Zn0.25O12.
In one embodiment, the current collector is a conducting metal or metal alloy.
In one embodiment, the dense region of the SSE material has a thickness of 1 μm to 100 μm. In another embodiment, the porous region of the SSE material that has the cathode material disposed thereon has a thickness of 20 μm to 200 μm. In another embodiment, the porous region of the SSE material that has the anode material disposed thereon has a thickness of 20 μm to 200 μm.
In one embodiment, the ion-conducting cathode material, the ion-conducting anode material, the SSE material, the current collector form a cell, and the solid-state, ion-conducting battery comprises a plurality of the cells, each adjacent pair of the cells is separated by a plate. In one embodiment, the plate is a bipolar plate.
Also provided is a solid-state, ion-conducting battery comprising a solid-state electrolyte (SSE) material comprising a porous region of electrolyte material disposed on a dense region of electrolyte material, the SSE material configured such that ions diffuse into and out of the porous region of the SSE material during charging and/or discharging of the battery. In one embodiment, the SSE material comprises two porous regions disposed on opposite sides of the dense region of the SSE material.
In some embodiments, the battery comprises a dense central layer. The dense central layer comprises a dense electrolyte material, and has a first surface and a second surface opposite the first surface. A first electrode is disposed on the first surface of the dense central layer. The first electrode comprises a first porous electrolyte material having a first network of pores therein, and a cathode material infiltrated throughout the first network of pores. The cathode material comprises sulfur. Each of the first porous electrolyte material and the cathode material infiltrate the first electrode. A second electrode is disposed on the second surface of the dense central layer. The second electrode comprises a second porous electrolyte material having a second network of pores therein, and an anode material infiltrated throughout the second network of pores. The anode material comprises lithium. Each of the second porous electrolyte material and the anode material infiltrate the second electrode. Each of the dense electrolyte material, the first porous electrolyte material, and the second porous electrolyte material are independently selected from garnet materials.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, each of the dense electrolyte material, the first porous electrolyte material, and the second porous electrolyte material are the same.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, each of the dense electrolyte material, the first porous electrolyte material, and the second porous electrolyte material are different.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the dense central layer has a thickness of 1 to 30 microns, the first electrode has a thickness of 10 to 200 microns, and the second electrode has a thickness of 10 to 200 microns.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, each of the dense electrolyte material, the first porous electrolyte material, and the second porous electrolyte material are independently selected from canon-doped Li5La3M12O12, where M1 is Nb, Zr, Ta, or combinations thereof, cation-doped Li6La2BaTa2O12, cation-doped Li7La3Zr2O12, and cation-doped Li6BaY2M12O12, where cation dopants are barium, yttrium, zinc, iron, gallium and combinations thereof.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, each of the dense electrolyte material, the first porous electrolyte material, and the second porous electrolyte material are independently selected from Li5La3Nb2O12, Li5La3Ta2O12, Li7La3Zr2O12, Li6La2SrNb2O12, Li6La2BaNb2O12, Li6La2SrTa2O12, Li6La2BaTa2O12, Li7Y3Zr2O12, Li6.4Y3Z1.4Ta0.6O12, Li6.5La2.5Ba0.5TaZrO12, Li6BaY2M12O12, Li7Y3Zr2O12, Li6.75BaLa2Nb1.75Zn0.25O12, or Li6.75BaLa2Ta1.75Zn0.25O12, and combinations thereof.
In some embodiments, the anode material is lithium metal.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the cathode material is selected from the group consisting of: S and Li—S compounds (Li2S2 Li2S2, Li2S3, Li2S4, Li2S6, Li2S8), and combinations thereof. In some embodiments, the cathode material is S. In some embodiments, the cathode material is selected from the group consisting of: Li2S, Li2S2, Li2S3, Li2S4, Li2S6, and Li2S8, and combinations thereof.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the cathode further comprises a conductive material comprising carbon.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the conductive material is selected from the group consisting of conductive polymers, carbon nanotubes, and carbon fibers.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the anode material and the conductive material comprising carbon together fill 40 to 60 percent of the volume of pores in the a first porous electrolyte.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the anode material has a density of 0.4 to 0.6 mg/cm2 in the first electrode, and the conductive material comprising carbon has a density of 0.4 to 0.6 mg/cm2 in the first electrode.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, a method of fabricating a battery having a solid state electrolyte is provided. A scaffold is provided, the scaffold comprising: a dense central layer comprising a dense electrolyte material, the dense central layer having a first surface, and a second surface opposite the first surface; a first porous layer comprising a first porous electrolyte material, the first porous layer disposed on the first surface of the dense central layer, the first porous electrolyte material having a first network of pores therein; wherein each of the dense electrolyte material and the first porous electrolyte material are independently selected from garnet materials. Carbon is infiltrated into the first porous layer. Sulfur is also infiltrated into the first porous layer.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed after infiltrating carbon into the first porous layer.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating carbon into the first porous layer comprises exposing the first porous layer to carbon nanotubes in suspension or solution.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating carbon into the first porous layer comprises exposing the first porous layer to graphene flakes in suspension or solution.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating carbon into the first porous layer comprises: exposing the first porous layer to a solution of polyacrylonitrile in dimethylformamide, and subsequently carbonizing the polyacrylonitrile by exposure to heat.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the polyacrylonitrile is carbonized by exposure to a temperature of a temperature of 500 to 700° C. for a time period in the range 30 minutes to 3 hours.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, carbon nanofibers are grown inside the first porous layer by microwave synthesis.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed by a vapor deposition.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed by exposure to gaseous sulfur.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed by exposure to gaseous sulfur in an inert atmosphere or vacuum for a time period of 30 minutes to 6 hours.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed by exposure to gaseous sulfur in an inert atmosphere or vacuum for a time period of 30 minutes to 6 hours at a temperature of 225 to 700° C.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, exposing the first porous layer to gaseous sulfur during infiltrating sulfur into the first porous layer comprises exposing the first porous layer to gaseous sulfur in an argon atmosphere at a temperature of 200 to 300° C. for a time period in the range 30 minutes to 2 hours.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer is performed by contacting the first porous layer with a sulfur-containing liquid.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, infiltrating sulfur into the first porous layer comprises contacting the first porous layer to a solution of S dissolved in CS2.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the method further comprises, after contacting the first porous layer to a solution of S dissolved in CS2, evaporating the CS2 by vacuum drying.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, after infiltrating carbon into the first porous layer and infiltrating sulfur into the first porous layer, the anode material and the conductive material comprising carbon together fill 40 to 60 percent of the volume of pores in the a first porous electrolyte.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, after infiltrating carbon into the first porous layer and infiltrating sulfur into the first porous layer, the anode material has a density of 0.4 to 0.6 mg/cm2 in the first electrode, and the conductive material comprising carbon has a density of 0.4 to 0.6 mg/cm2 in the first electrode.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the scaffold further comprises a second porous layer comprising a second porous electrolyte material, the second porous layer disposed on the second surface of the dense central layer, the second porous electrolyte material having a second network of pores therein. And, the method further comprises infiltrating lithium into the second porous layer.
In some embodiments, in addition to the features described in any combination of the preceding paragraphs, the sulfur infiltrated into the first porous layer is S, Li2S, and combinations thereof.
The following figures are given by way of illustration only, and thus are not intended to limit the scope of the present disclosure.
The present disclosure provides ion conducting batteries having a solid state electrolyte (SSE). For example, the batteries are lithium-ion, solid-state electrolyte batteries, sodium-ion, solid-state electrolyte batteries, or magnesium-ion solid-state electrolyte batteries. Lithium-ion (Li+) batteries are used, for example, in portable electronics and electric cars, sodium-ion (Na+) batteries are used, for example, for electric grid storage to enable intermittent renewable energy deployment such as solar and wind, and magnesium-ion (Mg2+) batteries are expected to have higher performance than Li+ and Na+ because Mg2+ carries twice the charge for each ion.
The solid-state batteries have advantages over previous batteries. For example, the solid electrolyte is non-flammable providing enhanced safety, and also provides greater stability to allow high voltage electrodes for greater energy density. The battery design (
The solid state batteries comprise a cathode material, an anode material, and an ion-conducting, solid-state electrolyte material. The solid-state electrolyte material has a dense region (e.g. a layer) and one or two porous regions (layers). The porous region(s) can be disposed on one side of the dense region or disposed on opposite sides of the dense region. The dense region and porous region(s) are fabricated from the same solid-state electrolyte material. The batteries conduct ions such as, for example, lithium ions, sodium ions, or magnesium ions.
The cathode comprises cathode material in electrical contact with the porous region of the ion-conducting, solid-state electrolyte material. For example, the cathode material is an ion-conducting material that stores ions by mechanisms such as intercalation or reacts with the ion to form a secondary phase (e.g., an air or sulfide electrode). Examples of suitable cathode materials are known in the art.
The cathode material is disposed on at least a portion of a surface (e.g., a pore surface of one of the pores) of a porous region of the ion-conducting, solid-state electrolyte material. The cathode material, when present, at least partially fills one or more pores (e.g., a majority of the pores) of a porous region or one of the porous regions of the ion-conducting, solid-state electrolyte material. In one embodiment, the cathode material is infiltrated into at least a portion of the pores of the porous region of the ion-conducting, solid-state electrolyte material.
In an embodiment, the cathode material is disposed on at least a portion of the pore surface of the cathode side of the porous region of the ion-conducting, SSE material, where the cathode side of the porous region of ion-conducting, SSE material is opposed to an anode side of the porous region of ion-conducting, SSE material on which the anode material is disposed.
In an embodiment, the cathode material is a lithium ion-conducting material. For example, the lithium ion-conducting cathode material is, lithium nickel manganese cobalt oxides (NMC, LiNixMnyCozO2, where x+y+z=1), such as LiCoO2, LiNi1/3Co1/3Mn1/3O2, LiNi0.5Co0.2Mn0.3O2, lithium manganese oxides (LMOs), such as LiMn2O4, LiNi0.5Mn1.5O4, lithium iron phosphates (LFPs) such as LiFePO4, LiMnPO4, and LiCoPO4, and Li2MMn3O8, where M is selected from Fe, Co, and combinations thereof. In an embodiment, the ion-conducting cathode material is a high energy ion-conducting cathode material such as Li2MMn3O8, wherein M is selected from Fe, Co, and combinations thereof.
In an embodiment, the cathode material is a sodium ion-conducting material. For example, the sodium ion-conducting cathode material is Na2V2O5, P2-Na2/3Fe1/2Mn1/2O2, Na3V2(PO4)3, NaMn1/3Co1/3Ni1/3PO4 and composite materials (e.g., composites with carbon black) thereof such as Na2/3Fe1/2Mn1/2O2 graphene composite.
In an embodiment, the cathode material is a magnesium ion-conducting material. For example, the magnesium ion-conducting cathode material is doped manganese oxide (e.g., MgxMnO2.yH2O).
In an embodiment, the cathode material is an organic sulfide or polysulfide. Examples of organic sulfides include carbynepolysulfide and copolymerized sulfur.
In an embodiment, the cathode material is an air electrode. Examples of materials suitable for air electrodes include those used in solid-state lithium ion batteries with air cathodes such as large surface area carbon particles (e.g., Super P which is a conductive carbon black) and catalyst particles (e.g., alpha-MnO2 nanorods) bound in a mesh (e.g., a polymer binder such as PVDF binder).
It may be desirable to use an electrically conductive material as part of the ion-conducting cathode material. In one embodiment, the ion-conducting cathode material also comprises an electrically conducting carbon material (e.g., graphene or carbon black), and the ion-conducting cathode material, optionally, further comprises a organic or gel ion-conducting electrolyte. The electrically conductive material may separate from the ion-conducting cathode material. For example, electrically conductive material (e.g., graphene) is disposed on at least a portion of a surface (e.g., a pore surface) of the porous region of the ion-conducting, SSE electrolyte material and the ion-conducting cathode material is disposed on at least a portion of the electrically conductive material (e.g., graphene).
The anode comprises anode material in electrical contact with the porous region of the ion-conducting, SSE material. For example, the anode material is the metallic form of the ion conducted in the solid state electrolyte (e.g., metallic lithium for a lithium-ion battery) or a compound that intercalates the conducting ion (e.g., lithium carbide, Li6C, for a lithium-ion battery). Examples of suitable anode materials are known in the art.
The anode material is disposed on at least a portion of a surface (e.g., a pore surface of one of the pores) of the porous region of the ion-conducting, SSE material. The anode material, when present, at least partially fills one or more pores (e.g., a majority of the pores) of the porous region of ion-conducting, SSE electrolyte material. In an embodiment, the anode material is infiltrated into at least a portion of the pores of the porous region of the ion-conducting, solid-state electrolyte material.
In one embodiment, the anode material is disposed on at least a portion of the pore surface of an anode-side porous region of the ion-conducting, SSE electrolyte material, where the anode side of the ion-conducting, solid-state electrolyte material is opposed to a cathode side of the porous, ion-conducting, SSE on which the cathode material is disposed.
In one embodiment, the anode material is a lithium-containing material. For example, the anode material is lithium metal, or an ion-conducting lithium-containing anode material such as lithium titanates (LTOs) such as Li4Ti5O12.
In one embodiment, the anode material is a sodium-containing material. For example, the anode material is sodium metal, or an ion-conducting sodium-containing anode material such as Na2C8H4O4 and Na0.66Li0.22Ti0.78O2.
In one embodiment, the anode material is a magnesium-containing material. For example, the anode material is magnesium metal.
In one embodiment, the anode material is a conducting material such as graphite, hard carbon, porous hollow carbon spheres and tubes, and tin and its alloys, tin/carbon, tin/cobalt alloy, or silicon/carbon.
The ion-conducting, solid-state electrolyte material has a dense regions (e.g., a dense layer) and one or two porous regions (e.g., porous layer(s)). The porosity of the dense region is less than that of the porous region(s). In one embodiment, the dense region is not porous. The cathode material and/or anode material is disposed on a porous region of the SSE material forming a discrete cathode material containing region and/or a discrete anode material containing region of the ion-conducting, solid-state electrolyte material. For example, each of these regions of the ion-conducting, solid-state electrolyte material has, independently, a thickness (e.g., a thickness perpendicular to the longest dimension of the material) of 20 μm to 200 μm, including all integer micron values and ranges there between.
The dense regions and porous regions described herein can be discrete dense layers and discrete porous layers. Accordingly, in an embodiment, the ion-conducting, solid-state electrolyte material has a dense layer and one or two porous layers.
The ion-conducting, solid-state electrolyte material conducts ions (e.g., lithium ions, sodium ions, or magnesium ions) between the anode and cathode. The ion-conducting, solid-state electrolyte material is free of pin-hole defects. The ion-conducting solid-state electrolyte material for the battery or battery cell has a dense region (e.g., a dense layer) that is supported by one or more porous regions (e.g., porous layer(s)) (the porous region(s)/layer(s) are also referred to herein as a scaffold structure(s)) comprised of the same ion-conducting, solid-state electrolyte material.
In an embodiment, the ion-conducting solid state electrolyte has a dense region (e.g., a dense layer) and two porous regions (e.g., porous layers), where the porous regions are disposed on opposite sides of the dense region and cathode material is disposed in one of the porous regions and the anode material in the other porous region.
The porous region (e.g., porous layer) of the ion-conducting, solid-state electrolyte material has a porous structure. The porous structure has microstructural features (e.g., microporosity) and/or nanostructural features (e.g., nanoporosity). For example, each porous region, independently, has a porosity of 10% to 90%, including all integer % values and ranges there between. In another example, each porous region, independently, has a porosity of 30% to 70%, including all integer % values and ranges therebetween. Where two porous regions are present the porosity of the two layers may be the same or different. The porosity of the individual regions can be selected to, for example, accommodate processing steps (e.g., higher porosity is easier to fill with electrode material (e.g., charge storage material) (e.g., cathode)) in subsequent screen-printing or infiltration step, and achieve a desired electrode material capacity, i.e., how much of the conducting material (e.g., Li, Na, Mg) is stored in the electrode materials. The porous region (e.g., layer) provide structural support to the dense layer so that the thickness of the dense layer can be reduced, thus reducing its resistance. The porous layer also extends ion conduction of the dense phase (solid electrolyte) into the electrode layer to reduce electrode resistance both in terms of ion conduction through electrode and interfacial resistance due to charge transfer reaction at electrode/electrolyte interface, the later improved by having more electrode/electrolyte interfacial area.
In an embodiment, the solid-state, ion-conducting electrolyte material is a solid-state electrolyte, lithium-containing material. For example, the solid-state electrolyte, lithium-containing material is a lithium-garnet SSE material.
In an embodiment, the solid-state, ion-conducting electrolyte material is a Li-garnet SSE material comprising cation-doped Li5La3M′2O12, cation-doped Li6La2BaTa2O12, cation-doped Li7La3Zr2O12, and cation-doped Li6BaY2M′2O12. The cation dopants are barium, yttrium, zinc, iron, gallium, or combinations thereof and M′ is Nb, Zr, Ta, or combinations thereof.
In an embodiment, the Li-garnet SSE material comprises Li5La3Nb2O12, Li5La3Ta2O12, Li7La3Zr2O12, Li6La2SrNb2O12, Li6La2BaNb2O12, Li6La2SrTa2O12, Li6La2BaTa2O12, Li7Y3Zr2O12, Li6 4Y3Zr1.4Ta0.6O12, Li6.5La2.5Ba0.5TaZrO12, Li6BaY2M12O12, Li7Y3Zr2O12, Li6.75BaLa2Nb1.75Zn0.25O12, or Li6.75BaLa2Ta1.75Zn0.25O12.
In an embodiment, the, solid-state, ion-conducting electrolyte material sodium-containing, solid-state electrolyte, material. For example, the sodium-containing, solid-state electrolyte is Na3Zr2Si2PO12 (NASICON) or beta-alumina.
In an embodiment, the, solid-state, ion-conducting electrolyte material is a, solid-state electrolyte, magnesium-containing material. For example, the magnesium ion-conducting electrolyte material is MgZr4P6O24.
The ion-conducting, solid-state electrolyte material has a dense region that free of the cathode material and anode material. For example, this region has a thickness (e.g., a thickness perpendicular to the longest dimension of the material) of 1 μm to 100 μm, including all integer micron values and ranges there between. In another example, this region has a thickness of 5 μm to 40 μm.
In one embodiment, the solid state battery comprises a lithium-containing cathode material and/or a lithium-containing anode material, and a lithium-containing, ion-conducting, solid-state electrolyte material. In an embodiment, the solid state battery comprises a sodium-containing cathode material and/or a sodium-containing anode material, and a sodium-containing, ion-conducting, solid-state electrolyte material. In another embodiment, the solid state battery comprises a magnesium-containing cathode material and/or a magnesium-containing anode material, and a magnesium-containing, ion-conducting, solid-state electrolyte material.
The solid-state, ion-conducting electrolyte material is configured such that ions (e.g., lithium ions, sodium ions, or magnesium ions) diffuse into and out of the porous region(s) (e.g., porous layer(s)) of the solid-state, ion-conducting electrolyte material during charging and/or discharging of the battery. In one embodiment, the solid-state, ion-conducting battery comprises a solid-state, ion-conducting electrolyte material comprising one or two porous regions (e.g., porous layer(s)) configured such that ions (e.g., lithium ions, sodium ions, or magnesium ions) diffuse into and out of the porous region(s) of solid-state, ion-conducting electrolyte material during charging and/or discharging of the battery.
One of ordinary skill in the art would understand that a number of processing methods are known for processing/forming the porous, solid-state, ion-conducting electrolyte material such as high temperature solid-state reaction processes, co-precipitation processes, hydrothermal processes, sol-gel processes.
The material can be systematically synthesized by solid-state mixing techniques. For example, a mixture of starting materials may be mixed in an organic solvent (e.g., ethanol or methanol) and the mixture of starting materials dried to evolve the organic solvent. The mixture of starting materials may be ball milled. The ball milled mixture may be calcined. For example, the ball milled mixture is calcined at a temperature between 500° C. and 2000° C., including all integer ° C. values and ranges there between, for least 30 minutes to at least 50 hours. The calcined mixture may be milled with media such as stabilized-zirconia or alumina or another media known to one of ordinary skill in the art to achieve the prerequisite particle size distribution. The calcined mixture may be sintered. For example, the calcined mixture is sintered at a temperature between 500° C. and 2000° C., including all integer ° C. values and ranges therebetween, for at least 30 minutes to at least 50 hours. To achieve the prerequisite particle size distribution, the calcined mixture may be milled using a technique such as vibratory milling, attrition milling, jet milling, ball milling, or another technique known to one of ordinary skill in the art, using media such as stabilized-zirconia, alumina, or another media known to one of ordinary skill in the art.
One of ordinary skill in the art would understand that a number of conventional fabrication processing methods are known for processing the ion-conducting SSE materials such as those set forth above in a green-form. Such methods include, but are not limited to, tape casting, calendaring, embossing, punching, laser-cutting, solvent bonding, lamination, heat lamination, extrusion, co-extrusion, centrifugal casting, slip casting, gel casting, die casting, pressing, isostatic pressing, hot isostatic pressing, uniaxial pressing, and sol gel processing. The resulting green-form material may then be sintered to form the ion-conducting SSE materials using a technique known to one of ordinary skill in the art, such as conventional thermal processing in air, or controlled atmospheres to minimize loss of individual components of the ion-conducting SSE materials. In some embodiments of the present invention it is advantageous to fabricate ion-conducting SSE materials in a green-form by die-pressing, optionally followed by isostatic pressing. In other embodiments it is advantageous to fabricate ion-conducting SSE materials as a multi-channel device in a green-form using a combination of techniques such as tape casting, punching, laser-cutting, solvent bonding, heat lamination, or other techniques known to one of ordinary skill in the art.
Standard x-ray diffraction analysis techniques may be performed to identify the crystal structure and phase purity of the solid sodium electrolytes in the sintered ceramic membrane.
The solid state batteries (e.g., lithium-ion solid state electrolyte batteries, sodium-ion solid state electrolyte batteries, or magnesium-ion solid state electrolyte batteries) comprise current collector(s). The batteries have a cathode-side (first) current collector disposed on the cathode-side of the porous, solid-state electrolyte material and an anode-side (second) current collector disposed on the anode-side of the porous, solid-state electrolyte material. The current collector are each independently fabricated of a metal (e.g., aluminum, copper, or titanium) or metal alloy (aluminum alloy, copper alloy, or titanium alloy).
The solid-state batteries (e.g., lithium-ion solid state electrolyte batteries, sodium-ion solid state electrolyte batteries, or magnesium-ion solid state electrolyte batteries) may comprise various additional structural components (such as bipolar plates, external packaging, and electrical contacts/leads to connect wires. In an embodiment, the battery further comprises bipolar plates. In an embodiment, the battery further comprises bipolar plates and external packaging, and electrical contacts/leads to connect wires. In an embodiment, repeat battery cell units are separated by a bipolar plate.
The cathode material, the anode material, the SSE material, the cathode-side (first) current collector (if present), and the anode-side (second) current collector (if present) may form a cell. In this case, the solid-state, ion-conducting battery comprises a plurality of cells separated by one or more bipolar plates. The number of cells in the battery is determined by the performance requirements (e.g., voltage output) of the battery and is limited only by fabrication constraints. For example, the solid-state, ion-conducting battery comprises 1 to 500 cells, including all integer number of cells and ranges there between.
In an embodiment, the ion-conducting, solid-state battery or battery cell has one planar cathode and/or anode electrolyte interface or no planar cathode and/or anode electrolyte interfaces. In an embodiment, the battery or battery cell does not exhibit solid electrolyte interphase (SEI).
The following examples are presented to illustrate the present disclosure. They are not intended to limiting in any manner.
The following is an example describing the solid-state lithium ion batteries of the present disclosure and making same.
The flammable organic electrolytes of conventional batteries can be replaced with non-flammable ceramic-based solid-state electrolytes (SSEs) that exhibit, for example, room temperature ionic conductivity of ≥10−3 Scm−1 and electrochemical stability up to 6V. This can further allow replacement of typical LiCoO2 cathodes with higher voltage cathode materials to increase power/energy densities. Moreover, the integration of these ceramic electrolytes in a planar stacked structure with metal current collectors will provide battery strength.
Intrinsically safe, robust, low-cost, high-energy-density all-solid-state Li-ion batteries (SSLiBs), can be fabricated by integrating high conductivity garnet-type solid Li ion electrolytes and high voltage cathodes in tailored micro/nano-structures, fabricated by low-cost supported thin-film ceramic techniques. Such batteries can be used in electric vehicles.
Li-garnet solid-state electrolytes (SSEs) that have, for example, a room temperature (RT) conductivity of ˜10−3 Scm−1 (comparable to organic electrolytes) can be used. The conductivity can be increased to ˜10−2 Scm−1 by increasing the disorder of the Li-sublattice. The highly stable garnet SSE allows use of Li2MMn3O8 (M=Fe, Co) high voltage (˜6V) cathodes and Li metal anodes without stability or flammability concerns.
Known fabrication techniques can be used to form electrode supported thin-film (˜10 micron) SSEs, resulting in an area specific resistance (ASR) of only ˜0.01 Ωcm−2. Use of scaleable multilayer ceramic fabrication techniques, without need for dry rooms or vacuum equipment, provide dramatically reduced manufacturing cost.
Moreover, the tailored micro/nanostructured electrode support (scaffold) will increase interfacial area, overcoming the high impedance typical of planar geometry solid-state lithium ion batteries (SSLiBs), resulting in a C/3 IR drop of only 5.02 mV. In addition, charge/discharge of the Li-anode and Li2MMn3O8 cathode scaffolds by pore-filling provides high depth of discharge ability without mechanical cycling fatigue seen with typical electrodes.
At ˜170 micron/repeat unit, a 300V battery pack would only be <1 cm thick. This form factor with high strength due to Al bipolar plates allows synergistic placement between framing elements, reducing effective weight and volume. Based on the SSLiB rational design, targeted SSE conductivity, high voltage cathode, and high capacity electrodes the expected effective specific energy, including structural bipolar plate, is ˜600 Wh/kg at C/3. Since bipolar plates provide strength and no temperature control is necessary this is essentially a full battery pack specification other than the external can. The corresponding effective energy density is 1810 Wh/L.
All the fabrication processes can be done with conventional ceramic processing equipment in ambient air without the need of dry rooms, vacuum deposition, or glove boxes, dramatically reducing cost of manufacturing.
For the all solid-state battery with no SEI or other performance degradation mechanisms inherent in current state-of-art Li-batteries, the calendar life of the instant battery is expected to exceed 10 years and cycle life is expected to exceed 5000 cycles.
Solid-state Li-garnet electrolytes (SSEs) have unique properties for SSLiBs, including room temperature (RT) conductivity of ˜10−3 Scm−1 (comparable to organic electrolytes) and stability to high voltage (˜6V) cathodes and Li-metal anodes without flammability concerns.
Use of SSE oxide powders can enable use of low-cost scaleable multilayer ceramic fabrication techniques to form electrode supported thin-film (˜10 μm) SSEs without need for dry rooms or vacuum equipment, as well as engineered micro/nano-structured electrode supports to dramatically increase interfacial area. The later will overcome the high interfacial impedance typical of planar geometry SSLiBs, provide high depth of discharge ability without mechanical cycling fatigue seen with typical electrodes, as well as avoid SEI layer formation.
The SSE scaffold/electrolyte/scaffold structure will also provide mechanical strength, allowing for the integration of structural metal interconnects (bipolar plates) between planar cells, to improve strength, weight, thermal uniformity, and form factor. The resulting strength and form factor provides potential for the battery pack to be load bearing.
Highly Li+ conducting and high voltage stable garnet type solid electrolytes can be made by doping specific cations for Ta and Zr in Li5La3Ta2O12, Li6La2BaTa2O12 and Li7La3Zr2O12, to extend RT conductivity from ˜10−3 to ˜10−2 Scm−1. Compositions having desirable conductivity, ionic transference number, and electrochemical stability up to 6V against elemental Li can be determined.
Electrode supported thin film SSEs can be fabricated. Submicron SSE powders and SSE ink/paste formulations thereof can be made. Tape casting, colloidal deposition, and sintering conditions can be developed to prepare dense thin-film (˜10 μm) garnet SSEs on porous scaffolds.
Cathode and anode can be integrated. Electrode-SSE interface structure and SSE surface can be optimized to minimize interfacial impedance for targeted electrode compositions. High voltage cathode inks can be made to fabricate SSLiBs with high voltage cathode and Li-metal anode incorporated into the SSE scaffold. The SSLiB electrochemical performance can be determined by measurements including CV, energy/power density and cycling performance.
Stacked multi-cell SSLiBs with Al/Cu bipolar plates can be assembled. Energy/power density, cycle life, and mechanical strength as a function of layer thicknesses and area for the stacked multi-cell SSLiBs can be determined.
Li-Stuffed Garnets SSEs. Conductivity of Li-Garnet SSEs can be improved doping to increase the Li content (“stuffing”) of the garnet structure. Li-stuffed garnets exhibit desirable physical and chemical properties for SSEs including:
Li+ conductivity of garnet SSEs can be further increased. The Li ion conductivity of garnet is highly correlated to the concentration of Li+ in the crystal structure.
In another approach, we can substitute M2+ cations (e.g., Zn2+, a 3d° cation known to form distorted metal-oxygen octandera) for the M5+ sites in Li6BaY2M2O12. ZnO is expected to play a dual role of both further increasing the concentration of mobile Li ions in the structure and decreasing the final sintering temperature. Each M2+ will add three more Li+ for charge balance and these ions will occupy vacant Li− sites in the garnet structure. Thus, further increase Li+ conduction can be obtained by modifying the garnet composition to control the crystal structure, Li-site occupancy, and minimize the conduction path activation energy.
Due to the ceramic powder nature of Li-garnets, SSLiBs can be fabricated using conventional fabrication techniques. This has tremendous advantages in terms of both cost and performance. All the fabrication processes can be done with conventional ceramic processing equipment in ambient air without the need of dry rooms, vacuum deposition, or glove boxes, dramatically reducing cost of manufacturing.
The SSLiBs investigated to date suffer from high interfacial impedance due to their low surface area, planar electrode/electrolyte interfaces (e.g., LiPON based SSLiBs). Low area specific resistance (ASR) cathodes and anodes can be achieved by integration of electronic and ionic conducting phases to increase electrolyte/electrode interfacial area and extend the electrochemically active region farther from the electrolyte/electrode planar interface. It is expected that modification of the nano/microstructure of the electrolyte/electrode interface (for example, by colloidal deposition of powders or salt solution impregnation) can reduce overall cell area specific resistance (ASR), resulting in an increase in power density relative to identical composition and layer thickness cells. These same advances can be applied to decrease SSLiB interfacial impedance. The SSLiB will be made by known fabrication techniques Low-cost, high-speed, scaleable multi-layer ceramic processing can be used to fabricate supported thin-film (˜10 μm) SSEs on tailored nano/micro-structured electrode scaffolds. ˜50 and 70 μm tailored porosity (nano/micro features) SSE garnet support layers (scaffolds) can be tape cast, followed by colloidal deposition of a ˜10 μm dense garnet SSE layer and sintering. The resulting pinhole-free SSE layer is expected to be mechanically robust due to support layers and have a low area specific resistance ASR, for example, only 0.01 Ωcm−2. Li2MMn3O8 will be screen printed into the porous cathode scaffold and initial Li-metal will be impregnated in the porous anode scaffold (
Another major advantage of this structure is that charge/discharge cycles will involve filling/emptying of the SSE scaffold pores (see
Moreover, there will be no change in overall cell dimensions allowing for the batteries to be stacked as a structural unit. Light-weight, ˜40 micron thick Al plates will serve not only as current collectors but also provide mechanical strength. ˜20 nm of Cu can be electrodeposited on the anode side for electrochemical compatibility with Li. The bipolar current collector plates can be applied before the slurry is fully dried and pressed to improve the electrical contact between bipolar current collector and the electrode materials.
Compared to current LiBs with organic electrolytes, the SSLiB with intrinsically safe solid state chemistry is expected to not only increase the specific energy density and decrease the cost on the cell level, but also avoid demanding packing level and system level engineering requirements. High specific energy density at both cell and system level can be achieved, relative to the state-of-the-art, by the following:
The energy density is calculated from component thicknesses of device structure (
The corresponding total energy is Etot=C×V=5.13 mAh×6 V=30.78 mWh. The total volume is 1.7×10−5 L for 1 cm2 area. Therefore, the theoretical effective specific energy, including structural bipolar plate, is ˜603.29 Wh/kg. As calculated below, the overpotential at C/3 is negligible compared with the cell voltage, leading to an energy density at this rate close to theoretical. Since the bipolar plate provides strength and no temperature control is necessary this is essential the full battery pack specification other than external can. (In contrast, state-of-art LiBs have a ˜40% decrease in energy density from cell level to pack level.) The corresponding effective energy density of the complete battery pack is ˜1810 Wh/L.
A desirable rate performance is expected with the SSLiBs due to 3-dimensional (3D) networked scaffold structures, comparable to organic electrolyte based ones, and much better than traditional planar solid state batteries. The reasons for this include the following:
To calculate the rate performance, the overpotential of SSLiB, shown in
The porous SSE scaffold achieves a smaller interfacial impedance by: 1/Zinterface=S*Gs, where S is the interfacial area close to the porous SSE and Gs is the interfacial conductance per specific area. The interfacial impedance is expected to be small since the porous SSE results in a large electrode-electrolyte interfacial area. For ion transport impedance through the entire SSE structure: ZSSE=Zcathode−scaffold+Zdense−SSE+Zanode−scaffold; and Z=(ρL)/(A*(1−ε)), where ρ=100 Ωcm, L is thickness (
Desirable cycling performance is expected due to the following advantages:
The SSLiB is an advancement in battery materials and architecture. It can provide the necessary transformational change in battery performance and cost to accelerate vehicle electrification. As a result it can improve vehicle energy efficiency, reduce energy related emissions, and reduce energy imports.
Since garnet SSEs can be synthesized as ceramic powders (unlike LiPON) high-speed, scaleable multilayer ceramic fabrication techniques can be used to fabricate supported thin-film (˜10 μm) SSEs on tailored nano/micro-structured electrode scaffolds (
The ˜6.0 volt cathode compositions (Li2MMn3O8, M=Fe, Co) have been synthesized. These can be combined with SSE scaffold & graphene to increase ionic and electronic conduction, respectively, as well as to reduce interfacial impedance. Li2MMn3O8 can be screen printed into the porous cathode scaffold and Li-metal impregnated in the porous anode scaffold.
Bipolar plates can be fabricated by electroplating ˜200 Å Cu on ˜40 μm Al. Given the 3× lower density of Al vs. Cu the resulting plate will have same weight as the sum of the ˜10 μm Al and Cu foils used in conventional batteries. However, with 3× the strength (due to ˜9× higher strength-to-weight ratio of Al vs. Cu). Increases in strength can be achieved by simply increasing Al plate thickness with negligible effect on gravimetric and volumetric energy density or cost. The repeat unit (SSLiB/bipolar plate) can be stacked in series to obtain desired battery pack voltage (e.g., fifty 6V SSLiBs for a 300V battery pack would be <1 cm thick).
In terms of performance and cost:
The energy density of SSLiBs shown in
The calculation for energy density in Table 3 does not include packing for protection of thermal runaway and mechanical damage as this is not necessary for SSLiBs. If 20% packaging is included, the total energy density is still 500 Wh/kg.
The SSE materials can be synthesized using solid state and wet chemical methods. For example, corresponding metal oxides or salts can be mixed as solid-state or solution precursors, dried, and synthesized powders calcined between 700 and 1200° C. in air to obtain phase pure materials. Phase purity can be determined as a function of synthesis method and calcining temperature by powder X-ray diffraction (PXRD, D8, Bruker, Cukα). The structure can be determined by Rietveld refinements. Using structural refinement data, the metal-oxygen bond length and Li—O bond distance can be estimated to determine role of dopant in garnet structure on conductivity. In-situ PXRD can be performed to identify any chemical reactivity between the garnet-SSEs and the Li2(Fe, Co)Mn3O8 high voltage cathodes as a function of temperature. The Li ion conductivity can be determined by electrochemical impedance spectroscopy (EIS-Solartron 1260) and DC (Solartron Potentiostat 1287) four-point methods. The electrical conductivity can be investigated using both Li+ blocking Au electrodes and reversible elemental Li electrodes. The Li reversible electrode measurement will provide information about the SSE/electrode interface impedance in addition to ionic conductivity of the electrolyte, while the blocking electrode will provide information as to any electronic conduction (transference number determination). The concentration of Li+ and other metal ions can be determined using inductively coupled plasma (ICP) and electron energy loss spectroscopy (EELS) to understand the role of Li content on ionic conductivity. The actual amount of Li and its distribution in the three different crystallographic sites of the garnet structure can be important to improve the conductivity and the concentration of mobile Li ions will be optimized to reach the RT conductivity value of 10−2 S/cm.
Sintering of low-density Li-garnet samples is responsible for a lot of the literature variability in conductivity (e.g., as shown in
Cathode and anode integration. Nanosized (˜100 nm) cathode materials Li2MMn3O8 (M=Fe, Co) can be synthesized. With the SSE that is stable up to 6V, a specific capacity of 300 mAh/g is expected. Slurries of cathode materials can be prepared by dispersing nanoparticles in N-Methyl-2-pyrrolidone (NMP) solution, with 10% (weight) carbon black and 5% (weight) Polyvinylidene fluoride (PVDF) polymer binder. The battery slurry can be applied to cathode side of porous SSE scaffold by drop casting. SSE with cathode materials can be heated at 100° C. for 2 hours to dry out the solvent and enhance electrode-electrolyte interfacial contact. Additional heat processing may be needed to optimize the interface. The viscosity of the slurry will be controlled by modifying solids content and binder/solvent concentrations to achieve a desired filling. The cathode particle size can be changed to control the pore filling in the SSE. In an example, all of the mobile Li will come from cathode (the anode SSE scaffold may be coated with a thin layer of graphitic material by solution processing to “start-up” electronic conduction in the cell). In another example, a thin layer of Li metal will be infiltrated and conformally coated inside anode SSE scaffold. Mild heating (˜400° C.) of Li metal foil or commercial nanoparticles can be used to melt and infiltrate the Li. Excellent wetting between Li-metal and SSE is important and was obtained by modifying the surface of the SSE scaffold (
Multi-cell (2-3 cells in series) SSLiBs with Al/Cu bipolar plates can be fabricated. The energy/power density and mechanical strength can be determined as a function of layer thicknesses and area.
In some embodiments, 3D Li—S batteries are based on a tri-layer solid state electrolyte structure. This battery configuration is shown in
Battery 900 includes a tri-layer solid state scaffold 910. Tri-layer solid state scaffold 910 includes a dense central layer 911, a first porous electrolyte material 912 having a first network of pores therein, and a second porous electrolyte material 913 having a second network of pores therein. Dense central layer 911 has a first surface on which first porous electrolyte material 912 is disposed, and a second surface opposite the first surface on which second porous electrolyte material 913 is disposed.
A cathode material 920 is infiltrated throughout the first network of pores. A carbon material 925, for example carbon nanofibers, is also infiltrated throughout the first network of pores. Collectively, first porous electrolyte material 912, cathode material 920, and carbon material 925 form a first electrode 950. Each of first porous electrode material 912 and cathode material 920 percolate through first electrode 950—in other words, there are conduction pathways through first electrode 950 in each of first porous electrode material 912 and cathode material 920. In some embodiments, cathode material 920 is a solid material, preferably S or Li2S. As the battery charges and discharges, Li ions move through scaffold 910. So, in a charged state, cathode material 920 may be S, and in a discharged state, cathode material may be Li2S.
An anode material 930 is infiltrated throughout the second network of pores.
Collectively, second porous electrode material 913 and anode material 930 form a second electrode 960. Each of second porous electrode material 913 and anode material 930 percolate through second electrode 960—in other words, there are conduction pathways through second electrode 960 in each of second porous electrode material 913 and anode material 930. In some embodiments, anode material 930 is Li.
Battery 900 may include other features, such as a first current collector 970, a second current collector 980, and a third current collector 990. These current collectors may be made of any suitable material, for example Cu and Ti for first current collector 970 and second current collector 980, respectively.
Dense central layer 911 may have a thickness of 5 to 30 microns, preferably 10 to 30 microns. At smaller thicknesses, the likelihood of an undesirable pinhole or pathway through the layer increases. At greater thicknesses, the resistance across the battery may undesirably increase without any corresponding benefit. The most desirable thickness may be affected by factors such as the specific electrolyte material used in dense central layer 911, and the density of that material the layer.
First electrode 950 may have a thickness between 20 and 200 microns. The energy density of the first electrode increases with thicknesses. At lower thicknesses, the energy density may be undesirably low. But, if the thickness is too high, ions may have difficulty migrating across the electrode, which undesirably increases resistance. Second electrode 960 may have a thickness in the same range, for the same reasons. But, the thicknesses of the first electrode 950 and second electrode 960. The thicknesses of first electrode 950 and second electrode 960 may be adjusted such that the two electrodes have similar energy densities. As illustrated in
The 3D Li-S batteries are based on a tri-layer structure with the following attributes: The battery consists of three components: tri-layer solid state electrolyte, cathode, and lithium metal anode. The tri-layer solid state electrolytes have a supported thin-film dense layer in the middle, and a thicker porous scaffold support layer on the cathode side and anode side, respectively. The porous scaffold on the cathode side is designed to host sulfur based materials, which can be solid cathode (S, Li2S), or liquid cathode (polysulfide Li2Sx, 8>x>2). The infiltration method could be liquid penetration or gas infusion. In the anode side, Li metal is infiltrated into the pores of scaffold. This highly porous scaffold provides large interface area to enable better contact with cathode and anode, which can significantly decrease cell impedance. This solid state Li—S battery can effectively increase the energy density of batteries, and prevent lithium dendrite penetration through the dense solid state electrolyte. Conductive contents are added in the two outer layers of SSE scaffold to improve electron transport. These conductive materials can be conductive polymer or porous carbon nanotubes (CNT)/fibers, or other conducting carbon materials. Charge/discharge cycles in the 3D networked SSE scaffolds occur by pore filling/emptying thus removing electrode cycling fatigue and allowing for tight cell dimensional tolerances since electrodes don't expand or shrink when cycled. An exemplary cell was fabricated. The cell had a triple layer ceramic lithium conductor Li7La2.75Ca0.25Zr1.75Nb0.25O12 with liquid cathode (polysulfide and single-walled CNT) infiltrated in cathode and Li metal infiltrated in anode. The cell was fabricated following the below procedures: Synthesized the Li7La2.75Ca0.25Zr1.75NbO0.25O12 powder by solid state reaction. Fabricated the trilayer SSE by tape casting method and firing at 1050° C. in O2 to achieve ideal structure. Infiltrated Li metal by pressing lithium foil onto one side of the trilayer SSE and heating at 300° C. for 1 hour. The whole process was carried out in an argon-filled glove box.
The cell was tested in a voltage window between 1˜3 V with a current density of 1 mA/mg-S. The cycling performance of the cell for 30 cycles is shown in
In some embodiments, a Li-garnet enabled Li—S battery has several advantages which are desirable for practical energy storage application including superior coulombic efficiency, high power density and wide operating temperature and pressure capability. In some embodiments, batteries described herein may be used in: electric vehicles (EVs), consumer electronics (cell phone, camera, laptop, etc.), drones (unmanned aerial vehicle, UAV), and stationary energy storage for renewable energies (wind, and solar).
A “Very High Specific Energy Device” of some embodiments is shown in
The use of garnet SSEs provides several desirable advantages: high RT bulk conductivity (˜10−3 S/cm)5-6 comparable to liquid/polymer electrolytes, but ceramic SSE is inflammable. High electrochemical stability from Li metal to high voltage (6 V). Excellent chemical stability in contact with elemental and molten Li anodes up to 400° C. Wide operating temperature capability, maintaining appreciable conductivity below 0° C. and increasing with temperature reaching 0.1 Scm−1 at 300° C.
Further, the trilayer garnet structure provides additional desirable advantages: the porous SSE scaffold on either side of trilayer provides structural support for fabrication of very thin dense center layer with corresponding low area specific resistance (2 Ω·cm2). The porous 3D networked SSE scaffold layers provide dramatically increased electrolyte/electrode contact area thus decreasing electrode interfacial impedance. Charge/discharge cycles in the 3D networked SSE scaffolds occur by pore filling/emptying thus removing electrode cycling fatigue and allowing for tight cell dimensional tolerances since electrodes don't expand or shrink when cycled. The supported dense ceramic SSE layer prevents dendrite shorting.
In some embodiments, various desirable features are incorporated into a battery. These desirable features include:
1. Higher Conductivity and Lower Sintering Temperature Garnet Compositions
In some embodiments, specific garnet-type SSE are used. Several garnet-type
SSE compositions were developed to both lower the sintering temperature and improve the ionic conductivity. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) was successfully synthesized by solid state reaction and sol-gel methods. It was demonstrated that LLCZN can be sintered at significantly lower temperature (1050° C.) and still yield high Li-ion conductivity (˜0.4 mS/cm at room temperature). The lower LLCZN sintering temperature reduces lithium loss and improves the trilayer fabrication process. Higher ionic conductive Li-based garnets were developed by La3+-sites substitution with Ba2+ and Zr4+-sites with Ta5+ and Nb5+. As shown in
In some embodiments, trilayer (porous-dense-porous) garnet SSEs (consistent with
In some embodiments, an interface layer is used to reduce Limetal-Garnet Interfacial Impedance. While there is tremendous interest in solid-state batteries and progress has been made on increasing the lithium ion conductivity of SSEs, there has been little success on the development of high-performance batteries using these SSEs. A major issue is the high interfacial impedance between SSEs and solid electrode materials. This interfacial impedance between Li metal and the garnet SSE may be reduced using an ultrathin Al2O3 interface layer, deposited by atomic layer deposition (ALD), as illustrated in
Two dense (150 μm thick) garnet pellets were prepared, one with and one without the ALD Al2O3, and a Limetal foil applied to both sides of each pellet,
In some embodiments, a high current density (3 mA/cm2) and high depth of discharge (95%) cycling of Limetal across trilayer (porous-dense-porous) garnet SSE structures has been demonstrated with a ˜17 μm dense center layer and ˜50 μm porous layer on either side (See
In some embodiments, sulfur (S) and carbon (C) were successfully infiltrated in porous garnet SSEs using both vapor (600° C. under vacuum) and liquid (2 M Li2S8 with PAN in DMF) infiltration methods. Sulfur infiltrated using liquid Li2S-PAN in DMF is co-infiltrated with C. A uniform distribution of the three phases: electronically conductive C, Li-storage S, and ionically conductive garnet, has been achieved (See
The sulfur and carbon infiltration into a porous garnet SSE described herein may be advantageously used as a cathode in combination with a wide variety of battery structures. Such structures include, but are not limited to, batteries with a lithium-containing anode. Such structures include, but are not limited to, batteries with an anode comprising an anode material infiltrated into a porous structure. For example, an anode without a porous structure may be used. In a preferred embodiment, which exhibits unexpectedly superior performance, a solid state battery has the structure shown in
Working cells with Li—S chemistry and the garnet SSE trilayer structure have been demonstrated. In some embodiments, the garnet surface was ALD coated to improve Limetal wetting. A sulfur cathode was them infiltrated on one side, followed by infiltration of a Limetal anode on the other side. A thin carbon nanotube sponge was placed between metal foil current collectors and the garnet to improve electrical contact.
In some embodiments, full format cells with a dimension of 10 cm×10 cm may be fabricated, with an energy density of 541 Wh/kg. Scalable processes may be used to fabricate these full format cells. Current collector, sealing, and packaging features may be added. Multi-cell stack of full format cells may be fabricated. Packs may be designed. SOFC fabrication techniques may be used for cell scale-up. Table B shows the dimensions and thickness of the layers for some embodiments. Due to the excellent mechanical strength and safety of the Li—S batteries with garnet SSE, the performance at the battery pack level is expected to be similar to the value at the cell level. In some embodiments, 14 cells may be stacked in series to achieve 28 V stacks (See
Solid-state batteries have the potential to provide a transformative solution to crucial energy storage needs for multiple mission applications associated with both robotic science and human exploration of space. Garnet electrolytes are highly conductive across a wide temperature range. It is expected that solid-state batteries described herein will be able to operate over a wide temperature range, far exceeding a desired range of −10 to 30° C., especially at the upper end, without the need for cumbersome and complex temperature control, thus uniquely providing the large operating temperature range needed for multiple space related applications. In terms of energy density, solid-state Li−S energy storage technology described herein is expected to exceed desirable parameters. For example, the projected energy density of some embodiments is 541 Wh/kg at the cell level (See Table B). Moreover, due to the garnet SSE materials lack of need for temperature control, as well as designs described herein that utilize the intrinsic garnet SSE strength, the projected energy density at the Pack level will be essentially the same, far exceeding desirable parameters. In addition, our unique design allows the Limetal anode and S cathode to expand and contract inside the porous garnet scaffold during cell cycling, resulting in no volume change on the macroscopic battery scale. This provides not only exceptional cycling stability, but also a disruptive solution for space related applications where dimensional tolerances are critical.
In some embodiments, the following results are achieved: synthesis of highly conductive garnet SSEs; fabrication of trilayer porous/dense/porous SSE structures; modification of the SSE surface to negate interfacial impedance; infiltration of porous SSE layer with Limetal-anode and ability to cycle Li repeatedly with no degradation or dendrite growth; infiltration of porous SSE layer with C and S-cathode; and demonstration of working solid-state Li—S battery.
As shown conceptually in
Trilayer Fabrication Process—While numerous trilayer SSE structures have been made, a systematic investigation may improve the process and increase its reproducibility. For example, improvements may increase yield by decreasing trilayer from curling and cracking during sintering. This includes improving tape formulation and firing conditions of sintering ramp rate (1 to 10° C./min), firing time (10 min to 12 h) and gas ambient (Ar, O2 and air), followed by structural (XRD, SEM, TEM, and FIB/SEM) and compositional analysis (XRD, ICP, EDS).
Porous Layer Structure—Each of the porous layers in the asymmetric trilayer SSE may have different parameters in terms of pore volume and thickness to balance Li/S capacity. Pore size and distribution may be adjusted to improve initial electrode filling as well as charge/discharge rate and mechanical strength.
Large Batch Processing—Reproducibility and quantity may be improved in each batch to ensure sufficient supply for full cell investigations and cell scale-up.
The uniform distribution of S, C, and garnet in the cathode contributes to high energy and power density, due to negligible ionic and electronic conductivity of S. S and C have been uniformly infiltrated within the porous layer using vapor and liquid methods (as shown in
Improved Solution Based S and C Co-Infiltration—The Li2S8 and PAN solution composition may be adjusted to to achieve balanced ionic and electronic conductivity in the porous garnet and high S loading. The porosity of the garnet SSE, and the relative amount of Li2S8 and PAN in the DMF solution may be adjusted to balance S loading, electronic/ionic conduction, and resident porosity. For example, it is desirable to balance S loading in the cathode to accommodate a large S volume change (79%) during discharge. The PAN carbonization temperature may also be adjusted to obtain a highly electronic-conductive infiltrated carbon, without reacting with the garnet during carbonization.
Improved Vapor-Based S and C Co-Infiltration—C may be infiltrated in the porous garnet SSE layers to obtain sufficient electronic conductivity. Then, the amount of infiltrated S as function of temperature, pressure, and duration may be determined to obtain improved C and S infiltration.
Evaluation of S and C Co-Infiltrated Cathodes—The ionic and electronic conductivity of S-C-infiltrated garnet SSE cathodes may be determined using EIS and blocking electrodes. The electrochemical performance of S-C-garnet cathodes may be evaluated in Li/garnet/S-C-garnet coin cells, and related to ionic/electronic conductivity, garnet pore structure, and S/C loading. The structure-performance relationships may be used to improve the S cathodes.
In some embodiments, an interface layer may be used to effectively negate the Limetal-garnet interfacial impedance (as shown in
Conformal Coating of Nano-Carbon Inside Porous Garnet—The carbonization of PAN inside porous garnet process in terms of conductivity and structure/mesopore filling may be improved by adjusting ink concentration, drying time, and temperature.
Improvement of Al2O3 Layer—The effect of Al2O3 thickness may be determined using an ALD process. Al2O3layer deposition using sol-gel may be more scalable. For example, aluminum sulfate may be dissolved in isopropanol followed by immersion of garnet pellets in the above solution and vacuum infiltration. The wetted garnet pellets may then be dried at room temperature and sintered at 750° C. for 3 hours. The coating layer thickness may be controlled by the precursor solution concentration.
Improvement of Li Metal Filling of Porous Garnet—Li metal filling is a function of garnet SSE pore structure and Li infiltration conditions. Li metal foil may be applied under varying pressure as Al2O3 coated garnet SSE is heated up to 200° C. SEM, EIS and current cycling may be used to characterize the Li anodes.
In some embodiments, full coin cells include garnet SSE, Limetal-anode and S-cathode.
Assemble Full Cells—Starting with trilayer garnet, pores on one side may be filled with a S/C-cathode, and pores on the other side of the dense central layer may be filled with Limetal-anode. Ti is electrochemically stable for both Li and S. So, Ti foil current collectors may be be attached on both Li anode and S/C cathode sides. To improve electrical contact between electrodes and current collectors, a thin compressible CNT-sponge layer may be applied.
Full Cell Testing—The electrochemical performance of the coin cell may be evaluated by cyclic voltammetry, galvanostatic charge-discharge at different rates, and cycling performance at C/10. EIS, from 1 MHz to 0.1 mHz, may be used determine any sources of device impedance, and reveal the interfacial impedance between the cathode and SSE by comparing the EIS of symmetrical cells with Limetal electrodes. The energy density, power density, rate capability, and cycling performance of each cell may be characterized as a function of SSE, electrode, SSE-electrolyte interface, and current collector-electrode interface. The electrode-electrolyte interface, and its role in cell impedance and battery degradation, may be characterized using EIS, SEM, and TEM of dissembled cells to understand any degradation mechanisms. Electrochemical performance tests may be conducted in an environmental chamber with a temperature range of −10° C. to 30° C.
In some embodiments, working Li-S batteries are provided, using full format cells with an energy density of 540 Wh/g, and 80% retention of capacity after 200 cycles. Battery cells described herein may be scaled-up into full format (10 cm×10 cm) cells to achieve such results, as follows:
Fabricate 10 cm×10 cm Trilayer Garnet Cells—In some embodiments, scaled up the cells with dimensions of 10cm×10cm may be fabricated, as illustrated in
Infiltration of S Cathode and Li Metal Anode—The vacuum and solution methods for S infiltration described herein may be scaled up. For the vacuum process, S infiltration can be done for 10 cm×10 cm garnet by simply increasing the tube size. The uniformity and amount of S infiltration may be evaluated after scaling up. After S infiltration, scaled up Li metal infiltration may be done by pressure contacting a 10 cm x 10 cm size commercial Li foil on top of the anode side of the garnet trilayer and heating to 200° C.
Test Full Format Cells—After successfully integrating Limetal-anode and S-cathode in the trilayer garnet, Ti current collectors may be applied to ensure good electric contact. Electrochemical performance may be evaluated at a rate of C/10 in an environmental chamber with a temperature range of −10° C. to 30° C.
In some embodiments, packaging, bipolar plates and contacts may be used for stacking the cells in series. For example, commercial heat sealable pouch cells may be used. Or, custom 3D printed packaging may be used to pack the cells (see
In some embodiments, Ti foils with a thickness of 10 μm may be used as the bipolar plates, i.e. as current collector for both anodes and cathodes. The Ti tabs will extend out as outsides electrical leads. Due to intrinsic thermal stability of garnet in large range of temperatures, no thermal management is required for a garnet Li—S battery.
Stacking of 3 Cells (10 cm×10 cm)—In some embodiments, many cells may be stacked in series to form a battery pack. For example, a 28 V battery pack with a total weight of 100 Kg may be formed by stacking 3 full format (10 cm×10 cm) cells in series.
Test Stacked Cells (−10° C. to 30° C.)—Electrochemical characterization tests (as described above for coin cells) may be performed in an environmental chamber over −10° C. to 30° C. temperature range.
Thermal Expansion, Bipolar Plate and Contact Issues—Organic electrolyte systems may have a wide range of thermal challenges. For the Limetal-anode and S-cathode in the trilayer garnet structures described herein, thermal challenges are more limited, and include expansion mismatches between cells, bipolar plates and packaging.
Thermal Related Issues—Dimensional change vs. temperature may be measured using a dilatometer (See
Methods to Address Contact Issues—In some embodiments, interface problems between current collector and the Li-anode/S-cathode may be addressed in a variety of ways. For example, a fast, microwave method may be used to grow vertical carbon nanofibers on metal foil within a minute (See
Package a Full Format Multi-Cell Stack—2 full format multi-cell battery stacks have been successfully fabricated and packaged.
To overcome issues related to liquid organic electrolytes, such as safety and degradation, numerous solid-state inorganic Li+ electrolytes, including perovskite Li0.36La0.55
Moreover, solid state Li-ion batteries (SSLiBs) incorporating these solid state electrolytes (SSEs) suffer from high interfacial impedance due to their low surface area, planar electrode/electrolyte interfaces.
A group of materials usable for SSE is Li-Garnet-type metal oxides, such as Li5La3M2O12 (M=Nb, Ta). The conductivity of these SSEs has been greatly improved by us and ether groups through judicious doping to increase the Li content (“stuffing”) of the Garnet structure. These Li-stuffed Garnets exhibit promising physical and chemical properties for SSEs including:The highest known RT bulk conductivity (for example, about 10−3 S/cm for cubic Li7La3Zr2O12). Highly electrochemical stability for high voltage cathodes (up to 6 V), about 2 V higher than current liquid organic electrolytes and about 1 V higher than the most desirable LiPON. Excellent chemical stability in contact with elemental and molten Li anodes up to 400° C., unlike NASICON-type LiTi2P3O12 and perovskite-type La(2/3)-xLi3x
However, challenges exist in Garnet based electrolytes, which has previously limited the success of Garnet electrolytes. These challenges include:
In some embodiments, a Li—S battery configuration includes Garnet electrolytes, as shown in
The first demonstration of all-solid-state Li-S batteries with Garnet electrolytes is described herein. While there are many challenges as seen in other solid-state battery chemistries, in some embodiments porous Garnet and Li—Li2MnFe3O8 chemistry overcome such challenges. Table B shows the dimensions and thickness of the layers of some embodiments.
Energy storage technology based on solid-state Li—S chemistry is well-suited for, inter alia, robotic science and human exploration of space. As shown in Table B, the theoretical energy density is 1212 Wh/kg. Current efforts are directed to demonstrating a working full cell with an energy density of 600 Wh/kg, which exceeds the energy density needed for some space exploration efforts. Solid state storage will be desirable for multiple mission applications associated with both robotic science and human exploration of space. Garnet electrolytes are highly conductive across a wide temperature range, and solid-state batteries should operate over a wide temperature range as well.
During device operation, Li metal anode and S cathode expands and contracts inside the carbon nanofibers (CNFs) filled Garnet scaffold, with the CNFs and Garnet scaffold maintaining electronic and ionic conduction, while the space in the carbon-Garnet scaffold accommodates the respective volume changes. This process results in no volume change on the macroscopic battery scale, thus an excellent cycling stability is expected.
In some embodiments, synthesis of pore-dense-pore triple layer Garnet SSEs using scalable tape casting methods may be used. In some embodiments, a Li/Garnet/S structure is used. Li/Garnet/S has much higher energy density than Li/Garnet/Li2MnFe3O8. In some embodiments, a S cathode is used. Sulfur infiltration, interface engineering and electrochemical performance evaluation are desirable aspects of such a S cathode. Short-chain S2/C composite cathodes may be used to completely avoid the shuttle reaction of liquid organic electrolytes, thus achieving high Coulombic efficiency and long cycling stability. This unique S cathode delivers 600 mAh/g capacity for 4020 cycles (0.0014% loss per cycle) in liquid carbonate electrolyte, with 100% Coulombic efficiency and the absence of self-discharge. Based on the success in liquid electrolyte Li—S cell, this S2/C technology may be transferred to all-solid-state Li—S batteries by infusing S2 gas into the CNF filled porous garnet layer in vacuum at 600° C. Experiments demonstrate that Garnet does not react with S even at 600° C. in vacuum as evidenced by XRD measurement (See
As shown in
Various compositions of lithium conductive garnets have been investigated. Preferred compositions include: Li7La3Zr3O12 (LLZ) and Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN). LLZ has a higher conductivity, close to 10−3 Scm−1 when sintered at temperature around 1200° C. However, lithium loss during high sintering temperature can be an issue when densifying the structure. By using nanosized LLZ particles, high density at lower temperature. In comparison, LLCZN shows lithium ion conductivity half of that of LLZ (4*10−4Scm−1). The advantage of LLCZN is a lower sintering temperature of 1050° C., which will reduce lithium loss making it easier to fabricate the triple-layer structure.
Fabrication of Dense Layer In some embodiments, garnet powders are prepared by solid state reaction and sol-gel methods.
The synthesized LLCZN dense electrolyte layer shows the cubic garnet phase and a wide electrochemical window up to 5.5 Volt as illustrated in
Fabrication of Porous Layers Porous garnet anode supports for 1 inch diameter button cells may be fabricated using technologies available for the synthesis of SOFC's. Such supports may be scaled up to 10 cm×10 cm. Relevant parameters include slurry composition, tape casting procedures, and sintering conditions. Tape slurries of SOFC materials generally begin with well-milled materials in their desired phase. For this reason, fully calcined LLZ was used as a starting material. This starting material was added with fish oil as a dispersant to toluene & ethanol. Polyvinyl butyral (PVB) and butyl benzyl phthalate (BBP) were added as binder and plasticizer and allowed to mill overnight. Varying the amount of binder and solvent in relation to the amount of garnet ultimately led to the desired rheology. To eliminate bubbles, tape slurries were degassed by stirring in a vacuum chamber for two hours immediately prior to casting. The slurry was poured into a holding chamber with a 330 um slot through which the slurry was pulled on a mylar sheet. After casting, the tape was dried on a 120° C. bed for one hour.
The microstructure of a porous LLCZN support layer is shown in
Scalable Fabrication of Garnet Triple Layers In some embodiments, finished porous and dense tapes may be laminated together to form the desired porous-dense-porous triple layer and then co-sintered. The porous layers may be formed from thicker tapes with pore former. The dense center layer may be formed from a very thin tape without pore former. These layers may be pressed, for example, at 160° C. and 50 MPa for ten minutes. Shrinkage during sintering occurs at a similar rate for all layers because they are all formed from the same garnet material. After sintering, the trilayer has the desired microstructure and is ready for anode and cathode infiltration.
Tape casting and laminating are inexpensive and scalable industrial processes. Even on a lab scale, tapes are commonly two meters long, allowing for the creation of an entire 28V stack of 10 cm×10 cm cells with one tape of each layer. On an industrial level, flexible tapes enable roll-to-roll processing which could theoretically produce a continuous line of tape. Individual cells may then be punched from the tape before sintering.
Methods In some embodiments, S may be filled into Garnet pores. Suitable methods include S gas vacuum infusion at 600° C., and liquid S-CS2 penetration at room temperature. Due to the low electronic and ionic conductivity of S and sulfides, a highly electronic conductive CNF-web (carbon nano-fiber web) will be formed in the pores of the highly ionically conductive Garnet scaffold before S infusion to enhance the utilization of S and reaction kinetics. Due to the large volume change (˜80%), it is preferred to fill the S—C composite to only about 50% by volume of the porous Garnet on the cathode side to accommodate the volume change upon charging.
Conformal Nanocarbon Coating in the Cathode and Anode Pores: In some embodiments, a porous, conformal conductive coating is formed on porous Garnet. Suitable methods include use of solution based carbon nanotube, and use of graphene. Since the pore size of Garnet electrolyte is larger than the size of short carbon nanotube (CNTs) or graphene flakes, CNTs and graphene solution can easily penetrate into the pore of garnet scaffold layer. CNTs have been successfully filled into a garnet scaffold layer. In some embodiments, a microwave synthesis method may be used to grow CNF, which is cheaper than CNT and graphene, inside pores of Garnet electrolyte before filling S cathode and Li metal anode.
Sulfur Cathode in Porous Garnet: In some embodiments, S may be infiltrated into porous Garnet that was previously filled with CNF or nanotubes. Suitable S infiltration methods include vacuum and solution methods.
One suitable way to infuse S gas under vacuum uses a sealed vacuum glass tube technique. Sulfur powder and the garnet scaffold are added into a one-end sealed glass tube. The resulting glass tube is evacuated with a vacuum pump over a 6 h period. The vacuumed glass tube is then sealed by melting the open-end with a high temperature flame. The sealed glass tube is transferred to an oven for annealing at 600° C. for 3 h, and then cooled to room temperature. Afterwards the sulfur is infiltrated into the Garnet pores, and the sealed glass tube is opened. This method has been used to successfully infiltrate S into porous CNT-Garnet, as shown in
One suitable way to infuse liquid S involves dissolving S into CS2 to form a solution. The S-CS2 solution may be dip impregnated into the pores of Garnet scaffold at room temperature, followed by CS2 evaporation. The S loading can be manipulated by multiple dip impregnations. The formed sulfur integrated porous garnet is then ready for battery tests. The porous anode side of the triple-layer Garnet electrolyte may be sealed during these processes.
In some embodiments, the cathode may be evaluated using a gel electrolyte on the anode side to minimize anode interfacial impedance. The inventors have recently successfully demonstrated that a gel-electrolyte can effectively decrease the impedance resistance of Li metal anodes in Garnet based batteries. In some embodiments, a full cell may be fabricated that uses S/carbon filled porous garnet as cathode, dense Garnet as the electrolyte and Li metal as the anode. These cells may be used to evaluate interfacial impedance between S cathode and Garnet electrolyte, and the electron transport with CNFs fabricated with different microwave conditions, S loading, and thermal treatment. It is expected that the impedance between electrode and electrolyte will decrease after initial conditioning.
In some embodiments, Li-metal may be used as a high capacity anode in a high energy density battery. The Li anode may be filled inside the porous Garnet with minimized interfacial impedance. A thin layer of conductive carbon such as CNFs may be conformally coated on porous Garnet electrolyte. Relevant parameters include infiltration temperatures, and surface modifications before Li filling to the pores of the anode side of triple-layer Garnet electrolyte.
Infiltration of Li in Porous Garnet In some embodiments, a conformal coating of lithium is infiltrated into a porous CNT (or CNF) filled Garnet scaffold to fabricate of a Li-S battery. The CNTs in the garnet pores is to maintain the electronic pathway (conduction) even when the Li is consumed during deep discharge, thus enhancing Li utilization. A major challenge of solid state batteries is the interfacial resistance between electrodes and electrolyte. It is desirable that melted lithium not only fully penetrate each pore, but remain in contact with the garnet surface and CNTs after cooling. The low surface energy of ceramics presents a difficulty. When lithium was melted onto a 70% porosity pellet in an argon atmosphere, the lithium formed a bead and did not penetrate. There are, however, some strategies that can be employed to increase lithium infiltration. For example, heating the Garnet scaffold in an argon atmosphere for an extended period of time before applying the lithium has been demonstrated to enable the lithium to quickly penetrate the porous scaffold. And, good contact was maintained after cooling. See
Characterizations Characterization of the Li-Garnet interface assists in understanding the stability of Garnet electrolyte against Li metal, and the contributors to interfacial impedance at the anode. Impedance may be measured with varying scaffold porosities to estimate interfacial impedance per real surface area. Interface surface engineering methods such as various ALD materials (e.g., Al2O3) and thickness may be evaluated to decrease interface resistance. CV may be used to evaluate the electrochemical stability of Garnet electrolyte when contacting with Li metal anode. Measured results indicate that Li metal is very stable with Garnet up to 5.5 V. See
In some embodiments, full cells are fabricated and evaluated. Contact resistance between current collectors and the electrode materials may be minimized. Mechanical properties may be improved to ensure high mechanical device strength. The interface between the SSE and the electrode may be improved to achieve stable cycling performance. Energy density, power density, rate performance, cycling, degradation performance, etc. of lab scale solid state batteries may be determined through electrochemical measurements. In some embodiments, working Li-S batteries have 10 cm by 10 cm dimensions and an energy density of 600 Wh/g, and 80% retention of capacity after 200 cycles.
Full Cell Assembly In some embodiments, a triple-layer Garnet is used as a membrane. S cathode is vacuum filled on one side, followed by Li metal on the other side. After successfully filling the scaffold pores with Li anode and S cathode in the lab scale, Ti foil coated with 20 nm Cu may be used for the current collectors and bipolar plate. These plates may be assembled in a battery stack to achieve high voltage. To improve the electrical contact between electrodes and current collectors, a thin graphene layer may be applied. For example, low-cost graphene ink may be used. The finished device may be heated up to 100° C. for 10 minutes to further improve the electrical contact between layers.
Full Cell Testing In some embodiments, the electrochemical performance of the SSLiB may be evaluated by cyclic voltammetry, galvanostatic charge-discharge at different rates, electrochemical impedance spectroscopy (EIS), and cycling performance at C/3. EIS in a broad frequency range, from 1 MHz to 0.1 mHz, may be used to investigate the various contributions to the device impedance, and reveal the interfacial impedance between the cathode and SSE by comparing the EIS of symmetrical cells with Limetal electrodes. The energy density, power density, rate dependence, and cycling performance of each cell may be fully characterized as a function of SSE, electrode, SSE-electrolyte interface, and current collector-electrode interface. Structure-process-property relationships may be analyzed and improved to achieve the best performance SSLiBs. The electrode-electrolyte interface and its role in cell impedance and battery degradation may be characterized using EIS, SEM, and TEM of dissembled cells to better understand any degradation mechanisms.
Battery Stack: In some embodiments, a battery stack is made using 10 cm by 10 cm cells. For example, 14 cells may be stacked in series as a stack to achieve 28 V. See
Table A shows one set of parameters for a battery cell similar to battery cell 1902. Table B shows a set of parameters a battery device 1930 made up of the cells of Table A. Table C shows another set of parameters for a battery cell similar to battery cell 1902. Table D shows a set of parameters a battery device 1930 made up of the cells of Table C.
One issue is large interfacial resistance between electrodes and Garnet electrolytes. Various interface-engineering methods such as atomic layer deposition (ALD) or gel electrolytes may be used to improve the charge transport between the interfaces and improve the mechanical integrity during battery charging/discharging processes.
A two step method was developed to co-integrate Sulfur and Carbon into one porous layer of porous-dense-porous triple-layer garnet electrolyte. The method may also be used to co-integrate Sulfur and Carbon into a porous layer of any garnet electrolyte, for example a garnet electrolyte having only one porous layer into which Sulfur and Carbon are integrated, and a non-porous interface with the anode.
PAN (polyacrylonitrile) in DMF as the source of carbon was prepared, infiltrated into the porous-dense-porous triple layer porous garnet electrolyte and carbonized at 600° C. for 1 hour. Sulfur was then successfully infiltrated into the triple layer porous garnet electrolyte at 250° C. for 1 hour in argon atmosphere furnace. According to elemental mappings, sulfur and carbon were uniformly distributed in the cathode side of porous garnet electrolyte, shown in
A sulfur-cathode and lithium-anode garnet electrolyte battery was fabricated, and assembled in a coin cell with carbon sponge for deformable contact. The electrochemical performance was tested in an Arbin instrument at a current density of 50 uA/cm2. The procedure for assembling the coin cell was the following:
Step 1, Cathode fabrication: Carbon was infiltrated to improve electrical conductivity of cathode. 10% PAN with concentration of 10% in weight was dissolved in DMF solution, stirring overnight in glove box, then coated onto cathode side of the triple-layer porous garnet electrolyte several times with a paint brush, keeping in vacuum after coating each time. The PAN/DMF coated garnet sample was heated up to 600° C. with 2-5° C./min rate, and annealed for 1-2 hours in argon-filled glove box for carbonization. Sulfur/carbon disulfide (S/CS2) solution with a concentration of 1 mol/L was prepared for the sulfur infiltration, stirring for 1-2 hours. The solution was dropped onto the carbonized porous garnet electrolyte sample, followed by drying in vacuum for 1-2 hours.
Step 2, Anode fabrication: Lithium foil was attached to the anode side of the triple layer garnet electrolyte and covered with a stainless steel disk. The sample was heated at 150° C. for 10-30 minutes, then heated at 300° C. for 10-30 minutes in an Argon-filled glovebox for lithium penetration into the porous anode garnet layer.
Step 3, Assembling coin cell: the triple layer garnet electrolyte with sulfur-carbon cathode and lithium anode was packaged in a coin cell. Carbon sponges were attached to the cathode for better electrical contact and to protect the garnet electrolyte from mechanical pressure. The coin cell was then sealed in argon-filled glove box using Epoxy Adhesive (AB Glue) for isolation from air.
In this cell, the mass density of sulfur loaded into the cathode side of the triple layer garnet was 0.5mg/cm2, the mass density of carbon infiltrated was 0.5 mg/cm2, lithium foil was 15 mg, and the garnet electrolyte was 100 mg. The 3rd, 4th, 5th and 10th charge-discharge curves of lithium-sulfur garnet electrolyte battery are shown in
Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the interfacial resistance of the sulfur cathode and garnet electrolyte. A lithium∥triple layer garnetHlithium symmetric cell was fabricated to test the interface resistance between lithium and triple layer garnet. However, this was done without the ALD Al2O3 layer that was demonstrated previously to negate the Li-garnet interfacial impedance. Lithium foil was attached to both sides of the triple layer garnet pellet, and the symmetric electrodes were assembled in a Swagelok cell module. The EIS measurement was performed with a Gamry instruments EIS and tested from 1MHz to 0.02Hz.
A lithium∥triple layer garnet∥sulfur-carbon cell electrode was then fabricated to measure the interface resistance of the sulfur cathode and the triple layer garnet electrolyte. Lithium foil was attached onto the anode side of a triple layer garnet pellet, and the sulfur and carbon were co-infiltrated into the cathode side of the garnet electrolyte, then the cell electrode was assembled in Swagelok cell module. The EIS measurement was performed as before.
Cell No. 1 was fabricated with mass loading of sulfur was 0.2 mg, carbon mass was 0.6 mg, lithium foil mass was 16.7 mg, and garnet electrolyte mass was 100 mg. The cell performance examination was pre-conducted over 27 cycles, and the initial performance is shown in
Cell #2
Cell No. 2 was fabricated according to the methods described above in the section “Assembling coin cell and testing the electrochemical performance of Li—S garnet electrolyte battery.” The mass loading of sulfur was 0.5 mg, carbon mass was 0.5 mg, lithium foil mass was 13.0 mg, and garnet electrolyte mass was 100 mg. The cell performance examination was pre-conducted for 2 cycles, and the charge-discharge curves are shown in
As used herein, a “dense” layer of an electrolyte material does not have any pathways through the dense layer, such as a pinhole or series of pores extending from one surface of the dense layer to an opposite surface. This may be achieved, for example, by creating a layer where the amount of electrolyte material present in the layer is not less than 95% of the maximum theoretical amount of electrolyte material that could fit in the volume of the dense layer.
As used herein, “S” refers to elemental sulfur. For example, S may have the chemical formula S8 at 1 atm pressure at 25° C.
As used herein, “comprising” is an open-ended transitional phrase. A list of elements following the transitional phrase “comprising” is a non-exclusive list, such that elements in addition to those specifically recited in the list may also be present.
Where a range of numerical values is recited herein, comprising upper and lower values, unless otherwise stated in specific circumstances, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the claims be limited to the specific values recited when defining a range. Further, when an amount, concentration, or other value or parameter is given as a range, one or more preferred ranges or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether such pairs are separately disclosed. Finally, when the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. When a numerical value or end-point of a range does not recite “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.”
While various embodiments have been described herein, they have been presented by way of example only, and not limitation. It should be apparent that adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It therefore will be apparent to one skilled in the art that various changes in form and detail can be made to the embodiments disclosed herein without departing from the spirit and scope of the present disclosure. The elements of the embodiments presented herein are not necessarily mutually exclusive, but may be interchanged to meet various needs as would be appreciated by one of skill in the art.
The following documents are incorporated by reference in their entirety: U.S. Appl. 62/260,955, filed on Nov. 30, 2015. U.S. Pub. No. US 2014/0287305, filed on Mar. 21, 2014.
The invention was made with government support under NNC14CA27C awarded by NASA. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/064232 | 11/30/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62260955 | Nov 2015 | US |
