Patent Application
20190280330
The present invention comprehends an all solid-state, Li-ion battery (“LIB”) including a, mechanically flexible ceramic solid-state electrolyte and the manufacturing methods to make it.
The electric vehicle (EV) battery pack performs the same function as the gasoline tank in a conventional vehicle; it stores the energy needed to operate the vehicle. Battery packs usually contain 10-52 individual 6, 8, or 12 volt batteries similar to the starter battery used in gasoline vehicles. Gasoline tanks can store the energy to drive the vehicle 300-500 miles before refilling; however, current generation batteries only offer capacities of 50-200 miles in affordable vehicles and up to a maximum of 335 miles in expensive large luxury vehicles.
Thus, EVs require 30-40 kWh battery packs for a reasonable mileage range and must possess a long cycle life. This imposes practical needs for high energy density and cycle lifetime. United States Advanced Battery Consortium LLC (USABC) targets for EV battery pack performance are listed in Table I, below:
LIBs and Li-metal polymer batteries (LMPBs) are the most advanced commercial energy storage technologies to-date. However, the combined requirements of energy density and power density, cost, and safety for real applications have not been met. Significant improvement towards one of these requirements often compromises the others. Indeed all high-energy density LIBs suffer from infrequent catastrophic failure as well as poor cycle performance. As LIBs increase in energy and power densities, there is a continuing mandate to develop Li+ electrolytes that operate under extremely harsh conditions.
LIBs are the most promising technology for the widespread use of EVs. However, current industry strategies (e.g., high voltage and high capacity active materials) to achieve high gravimetric and volumetric energy densities accelerate degradation mechanisms, capacity loss, capacity fade, power fade, and voltage fade. These are caused by solid-electrolyte interphase (SEI) growth, cathode structure phase changes, gassing, and parasitic side reactions at anodes and cathodes. High capacity anodes such as silicon anodes experience excessive volume changes on cycling, ≈300% compared to 10% for graphite, in addition they suffer from rapid mechanical degradation.
Li metal anodes offer very high energy densities, 3860 mAh/g; however, safety and cyclability remain limitations that must both be addressed for them to be deployed in any practical systems.
Disclosed herein is an all solid-state Li-ion battery comprising a mechanically flexible, ceramic, solid-state electrolyte having a lithium-conducting oxide composition selected from the group consisting of perovskite-type oxides, NASICON-structured lithium electrolytes, and garnet-type structures containing transition metal oxides and the manufacturing methods to make them. As is known in the art NASICON generally refers to sodium super ionic conductors. As known to those of skill in the art a perovskite is any material with the same type of crystal structure as calcium titanium oxide (CaTiO3). They have the general chemical formula of ABX3, wherein A and B are cations having very different sizes from each other and X is an anion that binds to both A and B.
Per one aspect of the invention, the NASICON-structured lithium electrolytes comprise LiM2(PO4)3, where M=Ti, Zr, or Ge.
Per another aspect, the garnet-type structures containing transition metal oxides comprise Li5La3M2O12, where M=a transition metal.
According to another aspect of the invention, the garnet-type structures containing transition metal oxides comprise amorphous LiPON or LiSi—CON.
Per still another aspect, the garnet-type structures containing transition metal oxides comprise lithium ion-conducting sulfides selected from the group consisting of Li2S—P2S5 glass, Li2S—P2S5—Li4SiO4 glass, Li2S—SiS2 glass, Li2S—Ga2S3—GeS2 glass, Li2S—Sb2S3—GeS2 glass, Li2S—GeS2—P2S5 glass, Li10GeP2S12 glass, Li10SnP2S12 glass, Li2S—SnS2—As2S5 glass, and Li2S—SnS2—As2S5 glass-ceramic.
The solid-state electrolyte according to the present disclosure can be formed by one of the methods selected from casting, freeze casting, sublimation, and sintering of slurries that are based on nanoparticles of the ceramic superfast ionic conductor electrolytes described herein and having conductivities (a) comparable to liquid electrolytes at working temperatures, i.e., 10−6<σ<10−1 S·cm−1, and activation energies that are <0.6 eV.
Nanoparticles that can be used for forming the solid-state electrolytes of the present invention can be fabricated by any of a variety of methods including, without limitation, sol-gel synthesis, plasma spray, ultrasonic assist spray synthesis, fluidized bed reaction, atomic layer deposition (ALD) assisted synthesis, chemical vapor deposition (CVD), physical vapor deposition (PVD), gas phase decomposition, detonation, flame spray pyrolysis, co-precipitation. However, it is preferred to start with nanoparticles having a spherical aspect ratio and bell-shaped size distributions that improve the packing density of the “green” films and result in lower sintering temperatures with final electrolyte film densities above 95%.
Suitable precursor nanoparticle materials for the method of manufacture of the present disclosure include, for instance: super fast ionic conductors with garnet, olivine, perovskite, or NASICON crystal structures, or sulfide or phosphate-based glasses and having enhanced ionic conductivities, e.g. c-LLZO (cubic-lithium lanthanum zirconium oxide) or lithium phosphate.
Suitable solvents for the nanoparticle based slurries can be selected from, but not limited to, water, tert-butyl alcohol (TBA), butanol isomers, poly(vinyl alcohol) (PVA), polyvinyl butyral (PVB) and polyvinyl formal (PVF) or any water-soluble synthetic polymer compatible with the solid-state electrolyte nanoparticles. Preferably the solvent used is water as it is inexpensive, works well, can be rapidly frozen and sublimated via freeze casting to produce films having the desired porosity and density. The solvent is preferably used at a level of from 50 to 70% by weight of the slurry.
In some embodiments the nanoparticle based slurries may optionally include a surfactant or dispersing agent to facilitate the nanoparticle suspension in the solvent. Examples of these surfactants and dispersing agents include, but are not limited to, sodium polynaphthalene sulfonate, sodium polymethacrylate, ammonium polymethacrylate, sodium polyacrylate, sodium lignosulfonate, polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, and Triton X-100 (C14H22O(C2H4O)n).
In one embodiment, the precursor ceramic nanoparticle powder has a composition with a general formula ABO3 with “A” representing an alkaline or rare earth metal ion and “B” representing a transition metal ion, e.g. Li3xLa2/3xTiO3 (perovskite).
In another embodiment, the precursor nanoparticle compounds have a general formula of AM2(PO4)3 where “A” represents an alkali metal ion (Li+, Na+, K+) and “M” represents a tetravalent metal ion (Ge4+, Ti4+, Zr4+), e.g. Li1.5Al0.5Ge1.5(PO4)3 (NASICON).
In another embodiment, the precursor nanoparticle compounds have a general formula Li7A3B2O12 where “A” represents an eight coordination cation and “B” represents a six coordination cation, e.g. Li7La3Zr2O12 (garnet). Ionic conductivity of these materials could be further enhanced by substitution of “A” cations with Ta, Nb, Al, Ga, In or Te and substitution of “B” cations with Y, Ca, Ba, Sr.
Per one feature, the solid-state electrolyte may be a c-LLZO-Li3.4Si0.4P0.6O4 (“LSPO”) composite.
Per yet another feature, the solid-state electrolyte may be a metal substituted c-LLZO with a general formula of Li7La(3-x)MxZr2O12 (garnet), wherein the metal M is selected from the group but not limited to Al, Ga, Ta, W, and elements in group III and IV of the periodic table and wherein “x” has a value of from 0 to 3, thus x can be a whole number or any fraction thereof.
Per yet another feature, the solid-state electrolyte may be a metal substituted c-LLZO with a general formula of Li7La3Zr(2-x)MxO12 (garnet), wherein the metal M is selected from the group but not limited to Sc, Y, Ti, or another transition metal and x can have any value from 0 to 2. In yet another embodiment, the precursor materials are crystalline or amorphous nanoparticles of solid sulfide-based electrolytes, such as those of the Li2S—SiS system or those having compositions of the format Li4-xGe3x PxS4, where x is a number between 0 and 1.
According to another feature, the solid-state electrolyte is formed by casting nanoparticles of precursor materials made via spray pyrolysis of liquid precursors or by another suitable method, into a film followed by sintering the film wherein the sintering takes place at temperatures below approximately 1,100° C.
According to another feature an electrolyte scaffold, meaning a porous electrolyte structure, can be manufactured by freeze-casting nanoparticle based slurries of the precursor materials described herein. In some embodiments the freeze-casting may be followed by a sintering step at temperatures below 1,100° C.
In another embodiment the sintering step is further assisted by optical heating methods, e.g. laser, photonic, or flashing of suitable wavelength light. In another embodiment the sintering step is further assisted by IR irradiation or by an equivalent bulk heating method. Alternatively, the sintering is assisted by electrical or electromagnetic fields, wherein the sintering takes place within seconds of exposure and at temperatures below 1,000° C., preferably at temperatures between 90° C. and 700° C.
In certain embodiments of the present invention the anode, cathode or electrolyte material can be formed into a film and the films can include a thin-film coating buffer layer applied to their surface before or after sintering and interfacing one or all of the individual layers. This facilitates lithium ionic mobility between layers and reduces or prevents layer-to-layer contact resistance, a hindrance that typically plagues solid state lithium batteries. Moreover, such a buffer layer may prevent anode, cathode and electrolyte materials interdiffusion and promote adhesion between layers of dissimilar composition, crystal structure and mechanical properties. Suitable materials for such a buffer layer may be selected from, without limitation, compounds from the group including Li2O, B2O3, WO3, SiO2, Li3PO4, P2O5, Fe3(PO4)2, CO3(PO4)2, Ni3(PO4)2, Mn3(PO4)2 and mixtures thereof.
In yet another embodiment the thin-film coating buffer layer applied to anode, cathode or electrolyte layers consists of a polymeric material or a polymer electrolyte material based on a material selected from the group consisting of polyethylene oxide (PEO), poly(vinyl alcohol) (PVA), aramids, and polyaramid polyparaphenylene terephthalamide.
Any of the solid-state electrolyte precursor nanoparticles or the sintered film, the cathode precursor nanoparticles or the sintered film, and the anode precursor nanoparticles or the sintered film may be infiltrated or pre-coated with, respectively, an intermediate phase between the electrolyte and a secondary or tertiary compound, a catholyte, or an anolyte selected from, without limitation, the group consisting of Li, Li2O, B2O3, WO3, SiO2, Li3PO4, P2O5, Fe3(PO4)2, CO3(PO4)2, Ni3(PO4)2, Mn3(PO4)2, lithium phosphorous oxy-nitride (“LiPON”) and LaTiO3.
In yet another embodiment the catholyte, the anolyte or both are essentially made from a solid state electrolyte. The solid state electrolyte precursor particles can be mixed with the cathode or anode active materials particles to create a composite. Alternatively the catholyte and anolyte materials could be incorporated in the cathode and anode slurries as powders during the mixing operation and before casting or they could be infiltrated into the porous electrode structure after the anode and cathode electrodes are formed.
Per a still further feature, the solid-state electrolyte includes a lithium phosphorous oxy-nitride (“LiPON”) coating applied to the surface of the films either pre-sintering or, alternatively, after sintering and before calandering.
In yet another embodiment the electrolyte film prepared according to the present disclosure includes a polymer coating applied after sintering and before anode or cathode layers are bonded to the electrolyte or the electrolyte scaffold.
According to yet a further feature, Li is melt-infiltrated into the solid-state electrolyte prepared according to the present disclosure. Further embodiments comprise a composite electrolyte film with lithium infiltrated between the composite grains or as an intermediate electrolyte phase acting as an anolyte or a catholyte infiltrated in between the composite grains or the active material grains, e.g. in the cathode. Such an intermediate electrolyte phase comprises at least two components resulting from the reaction of the lithium or the cathode materials with the electrolyte forming a binary or tertiary intermediate phase.
In yet another embodiment a lithium or lithium alloy ribbon, foil or other suitable metallic film form is laminated onto the electrolyte layer to form the anode. Between the electrolyte and the metallic lithium anode there may be an intermediate layer interposed made of, but not limited to, compounds from the group including Li2O, B2O3, WO3, SiO2, Li3PO4, P2O5, Fe3(PO4)2, Co3(PO4)2, Ni3(PO4)2, Mn3(PO4)2 and mixtures thereof.
In yet another embodiment the thin-film intermediate layer consists of a polymeric material or a polymer electrolyte material based on a material selected from the group consisting of PEO, PVA, aramids, and polyaramid polyparaphenylene terephthalamide.
An embodiment will now be described, by way of example only, with reference to the accompanying drawings, wherein:
Disclosed herein is an all solid-state, mechanically flexible Li-ion battery (LIB) having a ceramic, mechanically flexible solid-state electrolyte formed by freeze-casting or casting, preferably in combination with sintering, of nanoparticle slurries of ceramic, superfast ionic conductors prepared according to the present disclosure. The nanoparticle slurries are formed into thin films by casting, preferably followed by sintering at temperatures below 1,100° C. and then further formed into structures within a LIB. They preferably have conductivities comparable to liquid electrolytes at working temperatures, i.e., 10−6<σ<10−1 S·c−1, and activation energies that are <0.6 eV.
Disclosed herein is an all-solid-state, mechanically flexible LIB including ceramic solid-state electrolytes comprising a lithium-conducting oxide composition selected from the group consisting of perovskite-type oxides, NASICON-structured lithium electrolytes, and garnet-type structures containing transition metal oxides.
In one form, the solid-state electrolyte is cubic-Li7La3Zr2O12 (“c-LLZO”). Per one feature, the solid-state electrolyte may be a c-LLZO-Li3.4Si0.4P0.6O4 (“LSPO”) composite.
Per yet another form, the solid-state electrolyte may be a metal substituted c-LLZO with a general formula of Li7La(3-x)MxZr2O12 (garnet), wherein the metal M is selected from the group but not limited to Al, Ga, Ta, W, and elements in group III and IV of the periodic table and wherein x has a value of from 0 to 3.
Per yet another form, the solid-state electrolyte may be a metal substituted c-LLZO with a general formula of Li7La3Zr(2-x)MxO12 (garnet), wherein the metal M is selected from the group but not limited to Sc, Y, Ti, and another transition metal and wherein x has a value of from 0 to 2.
In one form, the battery designed according to the present disclosure may be a 12V (nominal voltage) LIB made with such mechanically flexible solid-state electrolytes, wherein the solid-state electrolytes are made using scalable casting and sintering methods based on metal-oxide nanoparticle powders. More specifically, the solid-state electrolyte membranes (e.g. <30 um thick) may be fabricated using nanoparticle powders that have sizes ranging from 20-900 nanometers synthesized by flame-spray pyrolysis, co-precipitation or other solid-state or wet chemistry nanoparticle (“NPs”) fabrication routes.
Nanoparticles that can be used for the invention can be synthesized by any of a variety of methods including, without limitation, plasma spray, ultrasonic assist spray synthesis, fluidized bed reaction, atomic layer deposition (ALD) assisted synthesis, direct laser writing (DLW), chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), microwave plasma enhanced chemical vapor deposition (NPECVD), pulsed laser deposition (PLD), physical vapor deposition (PVD), gas phase decomposition, detonation, flame spray pyrolysis, co-precipitation, sol-gel synthesis, sol-gel dipping, spinning or sintering. As described they preferably have an average particle size of from 20 to 900 nm, more preferably from 200 to 600 nm.
The nanoparticles that can be used for preparing the solid-state electrolytes according to the present disclosure in certain embodiments can be coated, treated at the surface or throughout the bulk or in any open porosity by one or multiple layers of solid electrolyte materials or intermediate phases between solid electrolyte and anode or cathode active materials, e.g. a catholyte or anolyte suitable compound using one or more sequential deposition processes selected from, without limitation, plasma treatment, ultrasonic assist spray, fluidized bed reaction, atomic layer deposition (ALD), direct laser writing (DLW), chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), microwave plasma enhanced chemical vapor deposition (NPECVD), pulsed laser deposition (PLD), physical vapor deposition (PVD), gas phase decomposition, detonation, flame spray pyrolysis, co-precipitation, sol-gel synthesis, sol-gel dipping, spinning or sintering, sputtering, radio frequency magnetron sputtering, nanoimprint, ion implantation, laser ablation, spray deposition.
It is preferred, but not strictly necessary, to start with nanoparticles having a spherical aspect ratio and bell-shaped size distributions that improve the packing density of the green films formed and result in lower sintering temperatures with final film densities above 95% for incorporation into a LIB design.
Suitable precursor nanoparticle materials include, for instance, ionic conductors with garnet, olivine, perovskite, or NASICON crystal structures, or sulfide or phosphate based glasses and having enhanced ionic conductivities, e.g. c-LLZO or lithium phosphate as described herein.
In one embodiment, the precursor ceramic nanoparticle powder has a composition with a general formula ABO3 with “A” representing an alkaline or rare earth metal ion and “B” representing a transition metal ion, e.g. Li3xLa2/3xTiO3 with a perovskite type oxide structure.
In another embodiment, the precursor compounds have a general formula of AM2(PO4)3 where “A” represents an alkali metal ion (Li+, Na+, K+) and “M” represents a tetravalent metal ion (Ge4+, Ti4+, Zr4+), e.g. Li1.5Al0.5Ge1.5(PO4)3 (NASICON structured lithium electrolyte).
In another embodiment, the precursor compounds have a general formula Li7A3B2O12 where “A” represents an eight coordination cation and “B” represents a six coordination cation, e.g. Li7La3Zr2O12, a garnet type structure including a transition metal oxide. Ionic conductivity of these materials could be further enhanced by substitution of “A” cations with Ta, Nb, Al, Ga, In or Te and substitution of “B” cations with Y, Ca, Ba, Sr.
In yet another embodiment, the precursor materials are crystalline or amorphous nanoparticles of solid sulfide-based electrolytes, such as those of the Li2S—SiS system or those having compositions of the format Li4-xGe1xPxS4, where x has a value between 0 and 1.
The batteries produced using the approaches disclosed in the present invention will have superior performance to any of the existing lithium ion or other battery chemistries. Additionally, they will have distinct performance from any of the emerging battery technologies as outlined in
The nanoparticles used to form the slurries in the present disclosure may be conditioned using one of the three approaches shown in
According to another feature, the solid-state electrolyte is formed by casting into a film and then sintering of nanoparticles of precursor materials made via spray pyrolysis of liquid precursors, or another suitable method, wherein the sintering takes place at temperatures below approximately 1,100° C.
The basic process steps in the present disclosure are shown in
In some embodiments the nanoparticle based slurries may optionally include a surfactant or dispersing agent to facilitate the nanoparticle suspension in the solvent. Examples of these surfactants and dispersing agents include, but are not limited to, sodium polynaphthalene sulfonate, sodium polymethacrylate, ammonium polymethacrylate, sodium polyacrylate, sodium lignosulfonate, polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, and Triton X-100 (C14H22O(C2H4O)n).
The slurries are then cast into a film using one of the processes shown in
In another embodiment the sintering is assisted by optical heating methods, e.g. laser, photonic, or flashing of suitable wavelength light. Alternatively, the sintering is assisted by electrical or electromagnetic fields, wherein the sintering takes place within seconds of exposure and at temperatures below 1,100° C., preferably at temperatures between 90° C. and 700° C., see for example
The anode, cathode or electrolyte films may include a thin-film coating buffer layer applied to their surface before or after sintering and interfacing one or all of the individual layers. This facilitates Lithium ionic mobility between layers and reduces or prevents layer-to-layer contact resistance, a hindrance that typically plagues solid-state lithium batteries. Moreover, such a buffer layer may prevent anode, cathode and electrolyte materials interdiffusion and promote adhesion between layers of dissimilar composition, crystal structure and mechanical properties. Suitable materials for such a buffer layer may be selected from, without limitation, compounds from the group including Li2O, B2O3, WO3, SiO2, Li3PO4, P2O5, Fe3(PO4)2, Co3(PO4)2, Ni3(PO4)2, Mn3(PO4)2, and mixtures thereof.
Per a still further feature, the solid-state electrolyte includes a lithium phosphorous oxy-nitride (“LiPON”) coating applied to the surface of the films pre-sintering or, alternatively, after sintering and before calandering.
In yet another embodiment, active material nanoparticles are mixed with a glass or glass ceramic solid state electrolyte, e.g. a lithium ion-conducting sulfide with Li3PS4 (LPS), and the precursor nanoparticles are infiltrated and coated by means of heating above the glass transition temperature of the glass electrolyte, bringing the solid electrolyte to a super cooled liquid state as shown in
The inventive LIBs disclosed herein are made economical via manufacture using a low pressure sintering method and the replacement of existing separator materials, liquid electrolytes, and temperature management peripherals. In
In another embodiment of the present invention the individual layers or the whole stack can be formed via casting, freeze-casting or any other viable method that is capable of forming a thick film of the precursor nanoparticle material. After the casting and the solvent removal by drying or sublimation, the film may undergo a sintering step as shown.
The present invention also comprehends several avenues to improve c-LLZO films to enable Li cycling without shorting, to generate solid ion conductors that can prevent dendrite growth, self-discharge, and to promote safety, power and cycle life.
A major challenge for wide deployment of c-LLZO is processing feasibility at thicknesses similar to existing ion conducting membranes (ICMs) and polyolefin separators, i.e. 20-30 μm, such that the substitution of liquid with solid-state electrolyte comes with no performance loss. While numerous reports are available regarding the fundamental properties of c-LLZO based on pellet forms, the accumulated knowledge has not been translated to solid-state continuous films due to energy/equipment-intensive sintering of c-LLZO. Prolonged sintering times of 10-40 hours and lithium loss at temperatures >1000° C. greatly impede obtaining single-phase c-LLZO solid-state films with properties matching pellet counterparts due to higher surface/volume ratios, thereby accelerating Li loss during heating. Only hot-pressing has been successful in reducing the sintering duration but requires specialized and costly equipment, hindering mass-production at commercial scales. Also, thin film formability by hot-pressing has yet to be demonstrated.
Solid-state ion conductors, e.g. newly developed mechanically flexible c-LLZO combined with high energy density cathodes and Li anodes according to the present disclosure represent innovations that remove the tradeoffs between energy and cycle life. Novel, mechanically flexible c-Li7La3Zr2O12 ion-conducting solid-state films made by freeze-casting and low-pressure-sintering of nanoparticles according to the present disclosure can overcome most of the existing technical gaps in solid-state electrolytes and can attain ionic conductivities comparable to liquid electrolytes see
Previously it has been demonstrated that c-LLZO and LiTi2(PO4)3 Li+ conducting films by processing NPs can provide films <30 μm thick with ion conductivities ˜1 mS cm−1. Details are described, for instance, in Eongyu Yi et al., “Flame made nanoparticles permit processing of dense, flexible, Li+ conducting ceramic electrolyte thin films of cubic-Li7La3Zr2O12 (c-LLZO),” J. Mater. Chem. A, 2016, 4, 12947-12954. These prior art films suffers from several deficiencies including: they have very little to no conductivity at temperatures of 0° C. or less; they require high sintering temperatures well above 1,110° C. and very long sintering times. All of these drawbacks make these films impractical for use in commercial batteries.
It has already been demonstrated in the literature how to produce thin LLZO films of <30 μm thick and a few cm2 in size. While this is a notable achievement, translating to thinner films of <15 μm with larger area dimensions of >30 cm2 raises more processing challenges. The present disclosure process has overcome these processing challenges by: utilizing precursor particles having a nanometer size with D50 particle size of 20 to 900 nm, more preferably 200 to 600 nm and most preferably approximately 400 nm while the prior art utilized particles having a size of greater than 1 micron; by assisting the casting process steps with other techniques including freeze-casting and sublimation of the slurry solvents; and by controlling electrode and electrolyte microstructure and porosity by using proper casting temperature and times/speed. As described herein preferably in one embodiment the porosity is greater than 50%, with uniform pores having a size of 5 microns or larger and uniform direction of the pores. The sensitivity of LLZO sintering to numerous parameters is notable and raises concerns in obtaining large area films with uniform microstructures and phase compositions. Even >90% uniformity may actually be insufficient. Open pores, generated by partial over- or under-exposure during sintering will likely be avenues for Li dendrite propagation. Thus, temperature variations within the furnace require control of all processing conditions. Alternately, any defective areas, e.g. open pores, may be safely protected/blocked with a very thin solid state amorphous electrolyte, e.g. LiPON, or polymer based solid-state electrolyte overcoat as described herein.
In another embodiment the LLZO film can be cast on a flat bed and the solvent removed via freezing through a sublimation process then followed by a sintering step as shown in
The present invention lowers sintering temperatures to ≈1000° C. to expand the optimal processing window resulting in higher tolerance to temperature variations during sintering. Compounds in the Li2O—P2O5—SiO2—B2O3(“LPSB”) system have been used widely as sintering aids for LLZO, showing moderate improvements in reducing the required energy input for densification when mixed with micron sized particles. For example, others have sintered Ta:LLZO-Li3BO3 (10 vol. %) composites to 90% density at 790° C. with ambient ionic conductivity of 0.36 mS cm−1. Still others have processed Al:LLZO-Li3BO3 (13 vol. %) composites to 92% density by sintering at 900° C. with conductivities of 0.1 mS cm−1 at 30° C. The drop in net ionic conductivity is not significant compared to neat LLZO, considering ˜10 vol. % addition of low ionic conductivity secondary phase and low relative densities. However, Li3BO's low Tm of 700° C. prevents sintering composites at higher temperatures due to volatility, limiting accessible densities. According to our disclosed process the sintering temperatures are lower than in the past which reduces costs and the sintering times are much shorter. In addition, films produced according to the present disclosure are very dense, on the order of greater than 95%, this makes the films much stronger. Unlike the prior art the dense films according to the present disclosure do not require pressure to produce the dense films. Also as shown in
The present invention, in one embodiment, employs LLZO-LPSO composites to reduce sintering temperatures, targeting thin films >95% dense. LSPO has higher conductivity, 4.3×10−3 S cm−1 and a Tm of ˜1070° C. compared to Li3BO3, so higher net conductivities and densities can be achieved by sintering at >900° C.
The film processing disclosed herein can theoretically result in non-uniform microstructural and phase compositional distributions, deteriorating overall performance. Hence, the present invention comprehends introducing solvents, described herein, that can be easily removed via freezing (sublimation) after or during the films coating operation and use of sintering aids to lower the sintering temperatures, widening the optimal sintering window to increase overall uniformity of sintered large area films
The present invention comprehends fabricating electrolyte/anode composite layers as an alternative approach to increase interfacial areas in order to reduce the interfacial resistance on the cathode side.
Many different (electro)chemical approaches have been proposed to prevent dendrite formation. One suppression method involved adding saccharin or bubbling hydrogen to reduce formation of Ni or Zn dendrites. Magnetic fields have been used to manipulate dendrites morphology during electrodeposition of Cu, suppressing it to some degree. Such measures cannot work for commercial batteries. Other methods include additives to liquids, or gel electrolytes as possible routes to improve LIB stability/performance. Different solid electrolytes have been investigated in production, but these present problems of their own eventually translating to alternative safety concerns and energy losses. Surface microstructural control and surface flattening have been shown to promote a homogeneous distribution of Li current as well as Li/LLZO contact, such that non-uniform dissolution/deposition of Li, i.e. dendrites, and interfacial resistance are reduced, resulting in higher critical current densities.
The present invention comprehends several avenues to either mechanically block Li dendrites or maximize distribution of the Li+ current by increasing Li/electrolyte interfacial areas to enhance tolerable current densities with a target performance >3 mA/cm2 at ambient temperature.
To mechanically and thermodynamically block Li metal dendrites from growing and penetrating through the mechanically flexible electrolyte layer, we disclose a novel route to coat a thin-film layer of solid-state electrolyte, e.g. LiPON, or PEO based electrolyte via coating with polymer precursors allowing facile coating of a thin-film having a thickness of <400 nm on pre-sintered c-LLZO membranes see
According to yet a further feature, Li metal can be melt-infiltrated into the solid-state electrolyte scaffold to form a solid anode structure. To promote Li current distribution, a Li/electrolyte composite layer is processed by melt-infiltrating Li into a porous electrolyte layer to increase Li/electrolyte interfacial area, see
As discussed above, thin film LIBs have successfully cycled at practical levels. However, the cathode layer is only several μm thick, limiting the attainable energy density. For bulk battery systems, thicker (several tens μm) cathode layers are required. The present invention comprehends cathode/electrolyte or anode/electrolyte composite layers formed by infiltrating cathode or anode active materials into the solid-state electrolyte scaffolds to maximize the utilization of the active materials (cathode and anode) and to accelerate the ionic conductance on charge/discharge. See
LLZO readily reacts with common cathode materials such as LiCoO2, LiMn2O4, LiCoPO4 at temperatures as low as 500-700° C. Resulting tertiary phases are often passive, exacerbating the battery performance. LLZO seems unlikely to serve as the catholyte, based on recent reports.
Binary or ternary compounds in the Li2O—P2O5—SiO2—B2O3(“LPSB”) system with moderate ionic conductivities (up to 3-4×10−3 mS cm−1, composition selective) and thermodynamic compatibility with LLZO and cathode materials are utilized to form LPSB/LLZO and LPSB/cathode composites. Bonding of the two layers will reduce LLZO/cathode contact area and increase “active” contact of cathode and electrolyte. Benefits of this approach are shown in
Among other features, the present invention comprehends: purchasing from commercial suppliers nanoparticles of c-LLZO or other solid-state electrolytes and Li(NxMyCz)O2 cathode materials, with x+y+z=1, x:y:z=4:3:3 (NMC433), 5:3:2 (NMC532), 6:2:2 (NMC622), and 8:1:1 (NMC811) cathode NPs or using one of the described high-throughput methods to synthesizing these NPs materials at rates higher than 100 g/h.
Fabricating several tens cm2 c-LLZO/LSPO composite films <10 μm thick, with conductivities of 0.5-1 mS/cm using any of the manufacturing methods shown in
Fabricating several tens cm2 Li(NxMyCz)O2/LSPO wherein x+y+z=1 composite films 20-40 μm thick using any of the manufacturing methods shown in
Fabricating several tens cm2 bilayer c-LLZO/LSPO-LCO/LSPO films <60 μm thick using any of the manufacturing methods shown in
In addition using polymer-derived interfacial coatings based on LiSiOx, LiPON and LiBOx for these fabricated layers.
Such all-solid-state LIBs as disclosed hereinabove eliminate thermal management systems and allow use of Li-metal anodes, providing batteries with higher volumetric/gravimetric energy densities, as well as the ability to safely operate at higher temperatures with faster charge/discharge rates that enable further flexibility in LIB designs.
Although an exemplary embodiment of the present invention has been described and illustrated, it will be apparent to those skilled in the art that numerous modifications and variations can be made thereto without departing from the scope of the invention as defined in the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 62/419,423 filed on Nov. 8, 2016, and which is incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/060546 | 11/8/2017 | WO | 00 |
