An all-solid-state battery (also referred to herein as “a solid-state battery”) includes a solid anode, a solid cathode, and a solid electrolyte disposed between the anode and the cathode. Compared to a conventional battery that uses a liquid electrolyte, a solid-state battery may achieve a higher energy density due, in part, to the solid electrolyte occupying a smaller volume, thus enabling the battery to be packaged more compactly. The energy density of the solid-state battery may be further enhanced by using a pure alkali metal anode. For example, the theoretical gravimetric capacity of pure lithium (Li) is 3861 mAh/g, which is ten times larger than the theoretical gravimetric capacity of conventional graphite anodes at 372 mAh/g. Although the density of Li (0.534 g/cm3) is lower than graphite (1.6 g/cm3), the volumetric capacity of Li (3861 mAh/g×0.534 g/cm3=2062 mAh/cm3) is still three times larger than graphite (372 mAh/g×1.6 g/cm3=600 mAh/cm3). Furthermore, the solid-state battery may be safer and more durable than a conventional battery because (1) the solid electrolyte may be formed from materials that are less flammable and less toxic than conventional liquid electrolytes and (2) the solid electrolyte does not leak unlike a liquid electrolyte.
Disclosed herein is a mixed ionic-electronic conductor (MIEC). Embodiments of the MIEC include a material having a bandgap less than 3 eV. The material includes an end-member phase directly connected to an alkali metal by a tie-line in an equilibrium phase diagram. The material is thermodynamically stable with a solid electrolyte. The MIEC includes a plurality of open pores, formed within the MIEC, to facilitate motion of the alkali metal to at least one of store the alkali metal in the plurality of open pores or release the alkali metal from the plurality of open pores. The solid electrolyte is ionically conductive to ions of the alkali metal. The solid electrolyte has an ionic conductivity to ions of the alkali metal greater than 1 mS cm−1, a thickness less than 100 μm, and includes at least one of a ceramic or a polymer. In one embodiment, the material may exclude any lanthanides and/or any rare earth metals.
In an embodiment, the solid electrolyte includes the polymer. The polymer may include at least one of a polyethylene, a polypropylene, a polyethylene oxide, a polyacetal, a polyolefin, a poly(alkylene oxide), a polymethacrylate, a polycarbonate, a polystyrene, a polyester, a polyamide, a polyimide, a polyamideimide, a polyarylate, a polyarylsulfone, a polyethersulfone, a polyphenylene sulfide, a polyvinyl chloride, a polysulfone, a polyimide, a polyetherimide, a polytetrafluoroethylene, a polyetherketone, a polyether etherketone, a polyether ketone, a polybenzoxazole, a polyphthalide, a polyanhydride, a polyvinyl ether, a polyvinyl thioether, a polyvinyl alcohol, a polyvinyl ketone, a polyvinyl halide, a polyvinyl nitrile, a polyvinyl ester, a polysulfonate, a polysulfide, a polythioester, a polysulfone, a polysulfonamide, a polyurea, a polyphosphazene, a polysilazane, a polyethylene terephthalate, a polybutylene terephthalate, a polyurethane, an ethylene propylene diene rubber, a polytetrafluoroethylene, a fluorinated ethylene propylene, a perfluoroalkoxyethylene, a polychlorotrifluoroethylene, or a polyvinylidene fluoride.
In another embodiment, the solid electrolyte includes the ceramic. The ceramic may include at least one of Li7La3Zr2O12; Li3OX wherein X is at least one of Cl, Br, or I; Li3SX wherein X is at least one of Cl, Br, or I; Li1.3Al0.3Ti1.7(PO4)3; Li6PS5Cl; Li10MP2S12 wherein M is at least one of Ge, Si, or Sn; Li3PS4: Li7P3Sn; Li3N; Li2S; LiBH4: Li3BO3; Li2S—P2S5; Li2S—P2S5-L4SiO4; Li2S—Ga2S3—GeS2; Li2S—Sb2S3—GeS2; Li3.25—Ge0.25—P0.75S4; (La1−xLix)TiO3 wherein 0<x<1; Li6La2CaTa2O12; Li6La2ANb2O12 wherein A is at least one of Ca, Sr, or Ba; Li6La3Zr1.5WO12; Li6.5La3Zr1.5TaO12; Li6.625Al0.25La3Zr2O12; Li3BO2.5N0.5; Li9SiAlO8; Li1+xAlxGe2−x(PO4)3; Li1+xAlxTi2−x(PO4)3; Li1+xTi2−xAlxSiy(PO4)3−y wherein 0<x<1 and 0≤y<1; LiAlxZr2−x(PO4)3; LiTixZr2−x(PO4)3 wherein 0<x<2; Li6PS5X, wherein X is at least one of Cl, Br, or I; Li2InxSc0.666−xCl4 wherein 0≤x≤0.666; or Li3−xE1−xZrxCl6 wherein E is at least one of Y or Er.
In another embodiment, the solid electrolyte may include at least one of a polyether solid electrolyte, a thiophosphate solid electrolyte, or a garnet-type solid electrolyte. The solid electrolyte may include the polyether solid electrolyte, which may include polyethylene oxide (PEO). The solid electrolyte may include the thiophosphate solid electrolyte, which may include Li10GeP2S12 (LGPS) or Li6PS5X, wherein X is at least one of Cl, Br, or. The solid electrolyte may include the garnet-type solid electrolyte, which may include Li7La3Zr2O (LLZO).
Another embodiment of the present technology includes an anode. The anode includes the MIEC described above, where the MIEC does not reversibly store and release the alkali metal. The anode's MIEC may have a thickness of about 0.5 μm to about 67 μm. The MIEC may have a porosity greater than 45%. The anode may have an areal capacity of about 6±0.5 mAh cm−2. The anode may include the alkali metal. Another embodiment of the present technology includes a battery. The battery includes the anode described above and the solid electrolyte described above.
Another embodiment of the present technology includes an anode including a MIEC. The MIEC includes at least one of AxBy, AxByC, or AxByCzDw and a plurality of open pores, formed within the MIEC, to facilitate motion of an alkali metal to at least one of store the alkali metal in the plurality of open pores or release the alkali metal from the plurality of open pores. The MIEC does not reversibly store and release the alkali metal. The at least one of AxBy, AxByCz, or AxByCzDw includes an end-member phase directly connected to an alkali metal by a tie-line in an equilibrium phase diagram. A is an alkali metal. At least one of B or C is at least one of an alkaline earth metal, a group 13 element, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg, C, N, Si, Sn, Pb, Bi, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, or Yb. X, y, z, and w each have a value of about 1 to about 149.
Both B and C may be at least one of an alkaline earth metal, a group 13 element, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg, C, N, Si, Sn, Pb, Bi, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, or Yb. B may be an alkaline earth metal. B may be a group 13 element. B may be a period 4 transition metal. B may be a period 5 transition metal. B may be a period 6 transition metal. B may be a lanthanide.
Another embodiment of the present technology includes an anode. The anode includes the MIEC described above, and a plurality of open pores, formed within the MIEC, to facilitate motion of an alkali metal to store the alkali metal in the plurality of open pores and/or release the alkali metal from the plurality of open pores. The MIEC does not reversibly store and/or release the alkali metal. The alkali metal may include at least one of lithium (Li), sodium (Na), or potassium (K).
Another embodiment of the present technology includes an anode. The anode MIEC including TiwAlxCyNiz and a plurality of open pores, formed within the MIEC, to facilitate motion of an alkali metal to store the alkali metal in the plurality of open pores and/or release the alkali metal from the plurality of open pores. W, x, y, and z each have a value less than or equal to 8.
Another embodiment of the present technology includes a battery including the anode described above and a solid electrolyte. The solid electrolyte is coupled to a portion of the MIEC. The solid electrolyte includes polyethylene oxide (PEO).
It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.
The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements).
The diffraction spots located on the red dashed circle correspond to the lattice spacing for (110) BCC Li planes of 0.248 nm. The scale bar is 5 nm−1.
The scale bar is 2 nm.
The scale bar is 2 nm.
The scale bar is 2 nm.
The scale bar is 500 nm.
Following below are more detailed descriptions of various concepts related to, and implementations of, an anode that includes a mixed ionic-electronic conductor (MIEC) forming an open pore structure to facilitate the transport of an alkali metal during charging or discharging of a battery. It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in multiple ways. Examples of specific implementations and applications are provided primarily for illustrative purposes so as to enable those skilled in the art to practice the implementations and alternatives apparent to those skilled in the art.
The figures and example implementations described below are not meant to limit the scope of the present implementations to a single embodiment. Other implementations are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the disclosed example implementations may be partially or fully implemented using known components, in some instances only those portions of such known components that are necessary for an understanding of the present implementations are described, and detailed descriptions of other portions of such known components are omitted so as not to obscure the present implementations.
In the discussion below, various examples of a MIEC, a solid electrolyte, an anode formed from the MIEC, an open pore structure, and a battery formed from the anode and the solid electrolyte. It should be appreciated that one or more features discussed in connection with a given example may be employed in other examples according to the present disclosure, such that the various features disclosed herein may be readily combined in a given system according to the present disclosure (provided that respective features are not mutually inconsistent).
An Exemplary Anode with a Mixed Ionic-Electronic Conductor (MIEC)
The MIEC 1110 may be electrically conducting and ionically conducting with respect to an alkali metal ion 1310 in order to facilitate a reduction and/or oxidation reaction of the alkali metal 1300 during a charge or discharge process, respectively. For example, when the battery 1000 is being charged, alkali metal ions 1310 will be transported from a cathode (not shown), across the solid electrolyte 1400, and into the anode 1100 through the second opening 1114 of the MIEC 1110. A power source (not shown), such as a voltage source, may supply electrons 1320 to the anode 1100 through the current collector 1140. The electrons 1320 and the alkali metal ions 1310 may be transported by the MIEC 1110, resulting in the reduction of the alkali metal ion 1310 to a neutral alkali metal 1300, which is then stored within the open pore structure 1120. As the battery 1000 is charged, the amount of alkali metal 1300 in the open pore structure 1120 may increase, thus occupying a larger portion of the open pore structure 1120. In some implementations, the alkali metal 1300 may have a front (e.g., a surface on the alkali metal 1300 that interfaces the inert gas in the open pore structure 1120) that progressively moves within the open pore structure 1120 as the alkali metal 1300 backfills the open pore structure 1120.
When the battery 1000 is being discharged, the alkali metal 1300 undergoes an oxidation reaction that results in the generation of an electron 1320 and an alkali metal ion 1310. The electrons 1320 are transported out of the MIEC 1110 through the current collector 1140. The tendency for electrons 1320 to preferentially flow towards the current collector 1140 is based, in part, on the solid electrolyte 1400 being electrically insulating. The alkali metal ions 1310 are transported out of the MIEC 1110 towards the cathode and solid electrolyte 1400 through the second opening 1114. As alkali metal ions are transported from the anode 1100 to the cathode, the amount of alkali metal 1300 stored within the open pore structure 1120 may decrease, resulting in a retraction of the front of the alkali metal 1300.
The reserved pore space in the open pore structure 1120 may help relieve the stresses generated by the alkali metal 1300 (hydrostatic and deviatoric) by allowing the alkali metal 1300 to backfill. In this manner, the likelihood of fracturing the anode 1100 when cycling the battery 1000 may be substantially reduced while maintaining electronic and ionic contact. In some implementations, the transport of alkali metal 1300 may also be aided by alkaliphilic capillary wetting of the open pore structure 1120.
As described above, the open pore structure 1120 may be used to transport the alkali metal 1300 into and/or out of the MIEC 1110 for storage when charging the battery 1000 and/or release when discharging the battery 1000. The shape and dimensions of the open pore structure 1120 formed by the MIEC 1110 may thus affect the capacity and the charge/discharge rate of the battery 1000.
Generally, the open pore structure 1120 may include a plurality of pores that form percolation pathways extending across the MIEC 1110. The pores and/or percolation pathways may be separated by a portion of the MIEC 1110 (e.g., a wall). The plurality of pores may be substantially open to allow the alkali metal 1300 to enter and/or leave the MIEC 1110 through the solid electrolyte 1400 when cycling the battery 1000. In some implementations, the percolation pathways may intersect with one another. For example, two or more percolation pathways may merge into a single pathway and/or one percolation pathway may split into two or more percolation pathways. More generally, the tortuosity of the open pore structure may be small (e.g., about 1 corresponding to highly aligned percolation pathways) or large (e.g., greater than 1 corresponding to highly twisted percolation pathways).
The open pore structure 1120 may be a substantially isotropic structure where the orientation of the percolation pathways is distributed uniformly about a 4π solid angle space. For instance, the open pore structure 1120 may be a foam-like structure comprising a plurality of spherical cavities joined together to form the percolation pathways through which the alkali metal 1300 is deposited/stripped.
The open pore structure 1120 may be a substantially aligned array of cylindrical cavities that extend from a first end 1112 of the MIEC 1110 to a second end 1114 of the MIEC 1110. In some implementations, the first end 1112 and the second end 1114 may be disposed on opposite sides of the MIEC 1110, hence, the array of cylindrical cavities may be substantially straight. In some implementations, the first end 1112 and the second end 1114 may be disposed on sides of the MIEC 1110 that are not parallel. Thus, the array of cylindrical cavities may be uniformly curved or bent such that the respective ends of the cylindrical cavities terminate at the first end 1112 and the second end 1114. In this manner, the MIEC 1110 and/or the open pore structure 1120 may be shaped to conform to the form factor of the battery 1000 (e.g., a flat planar cell or a cylindrical cell).
The MIEC 1110 may be fabricated using various approaches including, but not limited to a growth process (e.g., the open pore structure 1120 is formed during the growth of the MIEC 1110 from a substrate) and/or an etching process (e.g., the MIEC 1110 is deposited onto a substrate as a homogenous medium and the open pore structure 1120 is then formed by etching into the MIEC 1110). For example, the aligned tubules 1210 shown in
In some implementations, the battery 1000 may be cycled by applying alternating negative and positive overpotentials. This may cause the alkali metal 1300 to move into and/or out of the open pore structure 1120 in a similar manner to a mechanical pump, resulting in a cyclical load applied to the MIEC 1110 that may cause fatigue. The MIEC 1110 and the open pore structure 1120 should thus be designed to have walls 1200 with a sufficiently large mechanical strength and ductility to accommodate the stresses generated by PLiMetal and capillarity thereby reducing the risk of fracture and/or fatigue in the MIEC 1110.
Generally, the pores of the open pore structure 1120 may vary in size and shape. However, in some implementations, it may be preferable for the pores (e.g., the tubules 1210) to be substantially uniform in terms of size, shape, and/or alkaliphilicity to reduce the formation of dead lithium and/or provide spatially uniform transport of the alkali metal 1300.
Prior to the alkali metal 1300 infiltrating the open pore structure 1120, the open spaces of the open pore structure 1120 may be evacuated and/or contain an inert gas phase. For ease of manufacture, it may be preferable for the open pore structure 1120 to initially contain a gas phase at Pgas=1 atm (105 Pa). The solid electrolyte 1400 should preferably form a hermetic seal on the second end 1114 of the MIEC 1110, otherwise the alkali metal 1300 may readily plate or flow through the solid electrolyte 1400 causing an electrical short with the cathode. The current collector 1140 should also preferably form a hermetic seal on the first end 1112 of the MIEC 1110. As a result, the deposition of the alkali metal 1300 in the open pore structure 1120 may compress the inert gas phase, resulting in a local Pgas that increases as more alkali metal 1300 is deposited. The rise in Pgas may be proportional to the compression ratio of the gas (e.g., Pgas may be about 10 atm for a compression ratio of about 10×).
The rise in Pgas generally does not affect the transport of the alkali metal 1300. For example, the pressure generated by Li, PLiMetal, may be about 102 MPa according to the Nernst equation, which is substantially larger than Pgas. In other words, the alkali metal 1300 may readily act as a piston to compress the gas. However, heterogeneities within the open pore structure 1120 may cause the alkali metal 1300 to be deposited non-uniformly. The non-uniform plating of the alkali metal 1300 may give rise to a pressure difference ΔPgas between adjacent tubules 1210, which may bend or, in some instances, burst the wall 1200 of the MIEC 1110. Thus, in some implementations, the wall 1200 of the MIEC 1110 may be designed to be non-hermetic to allow Pgas to equilibrate from cell to cell. In this manner, the internal pressure of the MIEC 1110 may be more homogenous, thus reducing the likelihood of one tubule 1210 expanding and collapsing a neighboring tubule 1210.
In some implementations, the height, h, of the open pore structure 1120 and the MIEC 1110 may include a reserved space for the inert gas phase to be compressed without generating exceedingly large Pgas. For example,
The current collector 1140 may be formed from various electrically conductive materials including, but not limited to copper, aluminum, silver, and gold. In some implementations, the current collector 1140 may be a film that is deposited onto the MIEC 1110 or a substrate from which the MIEC 1110 is grown and/or deposited.
The solid electrolyte 1400 may have an ionic conductivity to ions of the alkali metal greater than or equal to 1 mS cm−1 (e.g., 1 mS cm−1, 2 mS cm−1, 5 mS cm−1, or 10 mS cm−1) and a thickness less than or equal to 100 μm (e.g., 1 μm, 5 μm, 10 μm, 20 μm, 50 μm, 80 μm, or 100 μm).
The solid electrolyte 1400 may be formed from various materials including, but not limited to polymers and/or ceramics. The polymer may include at least one of a polyethylene, a polypropylene, a polyethylene oxide, a polyacetal, a polyolefin, a poly(alkylene oxide), a polymethacrylate, a polycarbonate, a polystyrene, a polyester, a polyamide, a polyimide, a polyamideimide, a polyarylate, a polyarylsulfone, a polyethersulfone, a polyphenylene sulfide, a polyvinyl chloride, a polysulfone, a polyimide, a polyetherimide, a polytetrafluoroethylene, a polyetherketone, a polyether etherketone, a polyether ketone, a polybenzoxazole, a polyphthalide, a polyanhydride, a polyvinyl ether, a polyvinyl thioether, a polyvinyl alcohol, a polyvinyl ketone, a polyvinyl halide, a polyvinyl nitrile, a polyvinyl ester, a polysulfonate, a polysulfide, a polythioester, a polysulfone, a polysulfonamide, a polyurea, a polyphosphazene, a polysilazane, a polyethylene terephthalate, a polybutylene terephthalate, a polyurethane, an ethylene propylene diene rubber, a polytetrafluoroethylene, a fluorinated ethylene propylene, a perfluoroalkoxyethylene, a polychlorotrifluoroethylene, or a polyvinylidene fluoride. Any of the compounds listed above may be the sole component of the solid electrolyte or may be used in combination.
The ceramic may include an antiperovskite structure having the formula Li3OX and/or Li3SX3 wherein X is at least one of Cl, Br, or I, or a super halide such as BH4 or BF4. An exemplary antiperovskite is Li3OCl.
The ceramic may include a phosphate-type solid electrolyte such as a NASICON structure of the general formula Li1±xM1xM2−x(PO4)3, wherein M is Al, Ga, In, Sc, Cr, Fe, Ta, or Nb; M2 is Ti, Zr, Hf, Si, or Ge, and wherein the number of moles of lithium per formula unit is 0<x<2, 0.2<1±x<1.8, 0.4>1±x<0.6. For example, the NASICON structure can be LiTi2(PO4)3, Li1+xAlxGe2−x(PO4)3 (LAGP), Li1+xAlxTi2−x(PO4)3 (LATP), Li1+xTi2−xAlxSiy(PO4)3−y, Li1−xTi2−xTax(PO4)3 wherein 0<x<1 and 0≤y<1, LiAlxZr2−x(PO4)3, and/or LiTiXZr2−x(PO4)3 wherein 0<x<2.
The ceramic can also include an oxide-type solid electrolyte such as a perovskite structure having the general formula (La1−xLix)TiO3 (LLTO)) wherein 0<x<1 The ceramic can also include a sulfide or glassy sulfide such as Li6PS5X wherein X is Cl, Br, or I, Li10MP2S12 wherein M is Ge, Si, or Sn; Li2S—P2S5, Li2S—P2S5-L4SiO4, Li2S—GeS2, Li2S—Sb2S3—GeS2, Li3.25—Ge0.25—P0.75S4, or Li1PS4, Li7P3S11. The ceramic can also include Li—N, Li2S, LiBH4, or Li3BO3, optionally including derivatives with dopants on the cation or anion sites. The ceramic can be a garnet-type oxide, e.g., Li7La3Zr2O12. Optionally, the garnet-type oxide can further include one or more dopants, for example selected from Al, Ge, Ga, W, Ta, Nb, Ca, Y, Fe, or a combination thereof, wherein the dopant, if present, is contained in an amount of greater than 0 to 3 moles per formula unit in the unit formula Li7La3Zr2O12 on the La-site, and greater than 0 to 2 moles per formula unit on the Zr site. The ceramic may also include a lithium mixed-metal chlorospinel, e.g., Li2InxSc0.666−xCl4 wherein 0≤x≤0.666; or Li3−xE1−xZrxCl6 wherein E is at least one of Y or Er. Any of the compounds listed above may be the sole component of the solid electrolyte or may be used in combination.
In some embodiments, the deposition metal can be sodium, and the solid electrolyte can include an oxide-type solid electrolyte such as sodium β-Al2O3 or NASICON (Na1+xZr2SixP3−xO12, 0<x<3); a sulfide type (e.g., Na3PS4); a closo-borate; or a polymer electrolyte such as poly(ethylene oxide) with a dissolved salt such as NaAsF6.
For example, the solid electrolyte may include Li7La3Zr2O12; Li1.3Al0.3Ti1.7(PO4)3; Li6PS5Cl; Li10MP2S12 wherein M is at least one of Ge, Si, or Sn; Li3PS4; Li7P3S11; Li3N; Li2S; LiBH4; Li3BO3; Li2S—P2S5; Li2S—P2S5-L4SiO4; Li2S—Ga2S3—GeS2; Li2S—Sb2S3—GeS2; Li3.25—Ge0.25—P0.75S4; (La1−xLix)TiO3 wherein 0<x<1; Li6La2CaTa2O12; Li6La2ANb2O12 wherein A is at least one of Ca, Sr, or Ba; Li6La3Zr1.5WO12; Li6.5La3Zr1.5TaO12; Li6.625Al0.25La3Zr2O12; Li3BO2.5N0.5; Li9SiAlO8; Li1+xAlxGe2−x(PO4)3; Li1+xAlxTi2−x(PO4)3; Li1+xTi2−xAlxSiy(PO4)3−y wherein 0<x<1 and 0≤y<1; LiAlxZr2−x(PO4)3; LiTixZr2−x(PO4)3 wherein 0<x<2; Li6PS5X, wherein X is at least one of Cl, Br, or I, or a combination thereof.
As another example, the solid electrolyte may include a polyether, a thiophosphate, and/or a garnet-type material. Examples of polyether solid electrolytes include polyethylene oxide (PEO). Examples of thiophosphate solid electrolytes include Li10GeP2Si2 (LGPS), Li6PS5X with X being at least one of Cl, Br, or I), and Li3PS3 (LPS). Examples of garnet-type solid electrolytes include Li7La3Zr2O (LLZO). The interface between the MIEC 1110 and the solid electrolyte 1400 is where the alkali metal 1300 is typically deposited first (when charging the battery 1000) and, hence, where PLiMetal is initiated. Thus, the way the solid electrolyte 1400 is coupled to the MIEC 1110 may affect the durability of the battery 1000. In some implementations, the tubules 1210 of the MIEC 1110 may be partially inserted and/or planted into the solid electrolyte 1400 as shown in
In some implementations, the solid electrolyte 1400 may be a composite formed from multiple materials. For example, the solid electrolyte 1400 may include both ceramic and polymer materials, thereby taking advantage of the respective benefits of each of these types of solid electrolytes. As an example, a polymer solid electrolyte may have favorable mechanical properties like a high ductility, but a lower ionic conductivity; and a ceramic solid electrolyte may have less favorable mechanical properties like brittleness, but a higher ionic conductivity. For example,
The charge/discharge rate of the battery 1000 depends, in part, on the manner in which the alkali metal 1300 is transported through the open pore structure 1120. In some implementations, the alkali metal 1300 may be transported as a solid-phase (e.g., a creep mechanism) within the open pore structure 1120. For many applications, it may be preferable to operate the battery 1000 at near room temperature (e.g., between about −20° C. and about 60° C.). At such temperatures, the alkali metal 1300 is typically a solid phase.
For example, the alkali metal 1300 may be Li, which is a soft metal at room temperature with a melting point of TM=180° C. At a temperature of 300 K (e.g., room temperature), the homologous temperature for Li metal is T/TM=0.66. Thus, the alkali metal 1300 may exhibit an appreciable creep strain rate {dot over (ε)}(T,σ) where σ is the deviatoric shear stress. The creep strain rate applied to a solid alkali metal 1300, such as Li at T=300 K, may deform the alkali metal 1300 to such an extent that the alkali metal 1300 may be viewed as behaving like an incompressible work fluid. Said in another way, the creep strain rate may deform the alkali metal 1300 thereby causing the alkali metal 1300 to advance and/or retract within the open pore structure 1120 as if the alkali metal 1300 were a fluid with an effective viscosity of η≡σ/{dot over (ε)}(T,σ). The creep strain rate may be caused by various creep mechanisms including, but not limited to a diffusion mechanism (e.g., an interfacial-diffusion Coble creep mechanism, a bulk-diffusion Nabarro-Herring creep mechanism), a dislocation slip mechanism, and a combination of a diffusion and dislocation mechanism.
A purely diffusional creep mechanism, such as lattice-diffusional Nabarro-Herring creep or interfacial-diffusional Coble creep, may exhibit a strain rate of {dot over (ε)}(T,σ)∂σ. Thus, the viscosity q depends on T and grain size, but not on a. The alkali metal 1300 thus behave like a Newtonian fluid when viewed from a continuum mechanics viewpoint. In contrast, a dislocation creep mechanism, such as power-law creep, may exhibit a viscosity η∂σ1-n with n>1. This implies the alkali metal 1300 behaves like a shear-thinning, non-Newtonian fluid. Both types of mechanisms, however, may be used to transport the alkali metal 1300 within the open pore structure 1120 with the driving force being the chemical potential gradient −Ω∇PLiMetal(x), which is related to the pressure gradient.
Although different transport mechanisms (e.g., dislocation vs. diffusion creep, interfacial Coble creep vs. bulk Nabarro-Herring creep) may be used to transport the alkali metal 1300 in the open pore structure 1120, the transport rate of the alkali metal 1300 may vary between the different mechanisms. In other words, the type of transport mechanism used may influence the overall transport rate of the alkali metal 1300, which in turn affects the current density and charge/discharge rate of the battery 1000. The contribution of different creep mechanisms on the transport rate of the alkali metal 1300 may depend on various factors including, but not limited to the grain size of the alkali metal 1300, the shape of the open pore structure 1120, and the size of the open pore structure 1120 (e.g., a characteristic width along a cross-section of a pore in the open pore structure 1120).
For example, a Coble creep mechanism typically contributes substantially to the transport of alkali metal 1300 when the characteristic width of the pores in the open pore structure 1120 are less than about 300 nm and the homologous temperature of the alkali metal 1300 is about T/TM≈⅔. The creep strain rate due to the Coble creep may be estimated as follows,
where {dot over (ε)} is creep strain rate due to the Coble creep mechanism, K is a dimensionless constant, δI is the nominal interfacial diffusion layer thickness, DI is the interfacial diffusion diffusivity, Ω is the atomic volume, D is the diameter size, kB is Boltzmann constant, T is temperature, and σ is the yield stress.
As shown in Eq. (1), the yield stress σ∂D3 or σ=kD3 for a fixed creep strain rate. Thus, the stress that arises from Coble diffusional creep, which is applied to the portions of the MIEC 1110 forming the open pore structure 1120 (e.g., the walls of the MIEC 1110) by the alkali metal 1300, decreases as the characteristic width of each pore in the open pore structure 1120 and the alkali metal 1300 contained therein becomes smaller. By using a smaller pore to reduce the mechanical stress applied to the MIEC 1110, mechanical degradation of the MIEC 1110 and the solid electrolyte 1400 covering the MIEC 1110 may be substantially reduced. However, the thickness of the walls of the MIEC 1110 should remain sufficiently thick (e.g., between about 1 nm to about 30 nm) to sustain electrochemically generated mechanical stress.
Eq. (1) also shows that the creep strain rate {dot over (ε)} scales with D−3 for a fixed stress. Thus, as D decreases, the creep strain rate may increase substantially. The transport of alkali metal 1300 is primarily driven by the Coble creep mechanism if the pores in the open pore structure 1120 have a diameter less than about 300 nm.
The “rail-guided” behavior may also be used to transport alkali metal 1300 even when internal obstructions/obstacles are present within the open pore structure 1120. For example,
The diffusion rate of the alkali metal 1300 may also vary depending on whether a coherent or incoherent boundary is formed between the alkali metal 1300 and the wall 1200 of the MIEC 1110 and/or the surface of the obstruction 1220.
In some implementations, the MIEC 1110 may support multiple types of phase boundaries. For example, a MIEC 1110 formed from lithiated carbon and a lithiophilic coating (Li2O) may have two phase boundaries: (1) a phase boundary between the Li metal and the Li2O crystal (a few nanometers thick) and (2) a phase boundary between Li metal and lithiated carbon. In some implementations, the phase boundary between Li and Li2O crystals may not exhibit a matched lattice due, in part, to the Li2O being nanocrystalline, resulting in an incoherent boundary with a fast diffusion rate. Additionally, a MIEC 1110 formed from carbon may contain a mixture of graphite and amorphous carbon. As a result, the phase boundary between the Li metal and the lithiated carbon may have a free volume that spatially varies (i.e., not sharply localized at a certain site) between clusters of amorphous carbon, which may also increase the diffusion rate.
The local diffusion path length of the alkali metal 1300 may also vary based on the shape of the wall 1200 and/or the obstruction 1220 since the alkali metal 1300 follows the topology of a surface during deposition.
In some implementations, the process of stripping alkali metal 1300 from the MIEC 1110 may generate a void plug 1350 (also referred to herein as “void space”) that grows between residual alkali metal 1300 and the solid electrolyte 1400. The presence of the void plug 1350, however, may not prevent the remaining alkali metal 1300 from being stripped. Rather, the void plug 1350 may continue to grow as more residual alkali metal 1300 is stripped from the MIEC 1110 by transporting the alkali metal 1300 along the interface and/or surface of the MIEC 1110.
In some implementations, it may be preferable to design the open pore structure 1120 to preferentially increase contributions from a particular creep mechanism. For example, the shape and dimensions of the open pore structure may be chosen such that the alkali metal 1300 is driven primarily by a fast interfacial-diffusion creep mechanism, thereby achieving a desired current density through the MIEC 1110. In some implementations, an interfacial diffusion mechanism may also render the transport of alkali metal 1300 less dependent on the material used to form the MIEC 1110.
To illustrate the impact different transport mechanisms may have on the design and material choice of the MIEC 1110, the following example describes a MIEC 1110 applied to a Li battery. However, it should be appreciated that other alkali metals and performance metrics may be used depending on the application of the battery 1000. Batteries used in industrial applications should preferably exhibit an areal capacity Q about 3 mAh/cm2 and a current density J≡dQ/dt about 3 mA/cm2. In implementations where the alkali metal 1300 is Li, a typical Li-containing anode (LMA) may have an overpotential Uversus Li+/Li of approximately 50 mV.
As described above, the open pore structure 1120 formed by the MIEC 1110 may include multiple percolation pathways (e.g., about 1010 tubules) for alkali metal 1300 to flow through the MIEC 1110. The large number of percolation pathways may lead to heterogeneities within the MIEC 1110 that cause transport and reactions (e.g., an oxidation reaction, a reduction reaction) to vary spatially across the MIEC 1110. Additionally, an overpotential may be applied to the alkali metal 1300 to drive an electric current through the battery 1000. However, the overpotential may also cause the alkali metal 1300 to generate a pressure applied to the MIEC 1110 forming the open pore structure 1120. Due to the presence of heterogeneities within the MIEC 1110, the pressure produced by the alkali metal 1300 may vary spatially, resulting in an unbalanced load that may cause portions of the MIEC 1110 to deform or, in some instances, fracture.
The pressure generated by Li when subjected to an overpotential may be expressed as maxPLiMetal [MPa]=7410U[V]. Thus, a larger overpotential directly results in a larger pressure applied to the MIEC 1110, which may lead to more rapid mechanical degradation of the MIEC 1110. For reference, an overpotential U=50 mV produces a pressure maxPLiMetal=370 MPa according to the relation above.
In practice, it is preferable to limit the overpotential U in order to reduce the mechanical load applied within the MIEC 1110. However, the overpotential U, which is a global parameter for the battery 1000, should still be sufficiently large to provide a desired global average current density J. Based on the typical overpotential U=50 mV, the average transport conductance of the MIEC 1110 may be estimated to be equal to or greater than about 3 mA/cm2/50 mV=0.06 S/cm2.
For purposes of illustration, the open pore structure 1120 may be a honeycomb structure with substantially aligned tubules. The effective transport conductance of the MIEC 1110 with a honeycomb open pore structure 1120 may be expressed as (κMIEC/h)×w/(w+W), where κMIEC [S/cm] is an effective Li conductivity, and w/(w+W) is the fill factor by the MIEC 1110 assuming substantially straight pores and a tortuosity=1.
κMIEC×w/(w+W)>0.06 S/cm2×20 μm=0.12 mS/cm (2)
Various mechanisms may contribute to the effective transport conductance, κMIEC, of the MIEC 1110. For example, bulk diffusion of the alkali metal 1300 may occur within the MIEC 1110. The bulk diffusivity, κMIECbulk, may be expressed as follows,
κMIECbulk˜e2cLiDLLibulk/kBT (3)
where cLi (unit 1/cm3) is the Li atom concentration, kB is the Boltzmann constant, and DLibulk is the tracer diffusivity of Li atom in bulk MIEC 1110.
Based on Eq. (3), the contribution of bulk diffusion to the conductance of the MIEC 1110 may depend on the bulk diffusivity, DLibulk, which may vary for different materials. Additionally, the MIEC 1110 should be compatible with the alkali metal 1300, which may be accomplished by alkaliating the material forming the MIEC 1110. For example, the MIEC 1110 may be compatible with Li when lithiated to below 0 V vs Li+/Li. Several anode materials may be used to form the MIEC 1110 including, but not limited to graphite or hard carbon (e.g., LiC6), silicon (e.g., Li22Si5), and aluminum (e.g., Li9Al4). These materials are commonly used as anodes in previous Li batteries. Additional materials may be used to form the MIEC 1110 based on their electrochemical stability as will be described in further detail below. The bulk transport properties of carbon, silicon, and aluminum may be estimated to be the following: (1) LiC6 has a cLi=1.65×1022/cm3 and an optimistic DLibulk about 10−7 cm2/s, (2) Li22Si5 has a cLi=5.3×1022/cm3 and an optimistic DLibulk about 10−11 cm2/s, and (3) Li9Al4 has a cLi=4×1022/cm3 and an optimistic DLibulk about 10−9 cm2/s.
Using Eq. (3), lithiated aluminum, Li9Al4, exhibits a κMIEC(Li9Al4) about 0.25 mS/cm, which is sufficient to satisfy the condition in Eq. (2). The MIEC fill factor is thus
about 0.5. For a 100 nm wide pore, w=W about 100 nm. In other words, the width of the tubules and the walls of the MIEC 1110 should be comparable in size. For lithiated silicon (Li22Si5), the bulk diffusivity of DLibulk about 10−11 cm2/s results in κMIEC(Li22Si5) about 0.003 mS/cm, which does not satisfy the condition in Eq. (2).
Lithiated carbon, LiC6, exhibits the largest cLiDLibulk amongst the three materials yielding a κMIECbulk(LiC6) about 0.01 S/cm based on Eq. (3). These estimates are based on previous diffusivity data, which exhibited large uncertainties. For a more conservative estimate, the diffusivity may thus be assumed to be DLibulk about 10−g cm2/s, resulting in κMIECbulk(LiC6) about 1 mS/cm. For LiC6, the fill factor of the MIEC 1110 should preferably be equal to or greater than
about 0.1. For a tubule width W about 100 nm, the thickness of the wall of the MIEC 1110 should thus be at least about w about 10 nm. These dimensions are similar to conventional graphite or hard carbon anodes used in Li-ion batteries (LIB), which typically have a film thickness of about 100 μm and are known to support a current density of 3 mA/cm2 at an overpotential of about 50 mV.
However, an industrial LIB graphite anode typically operates near borderline conditions. A current density greater than about 3 mA/cm2 through the LIB graphite anode may cause the local potential to drop below 0V vs Li+/Li. Under these conditions, Li metal would precipitate out of the anode resulting in the generation of new SEI when the Li metal contacts the flooding liquid electrolyte in the battery. The precipitation of Li metal and the generation of new SEI may severely degrade the cycle life and safety of LIB anodes.
Unlike conventional LIB graphite anodes, it is actually preferable for the alkali metal 1300 in the anode 1100 to “spill out” from the open pore structure 1120 of the MIEC 1110. The difference between the anode 1100 and previous anodes is the open pore structure 1120 formed by the MIEC 1110 enables a more controlled flow of alkali metal 1300. As described above, the open pore structure 1120 may substantially reduce or, in some instances, prevent a buildup of pressure PLiMetal, which may otherwise crack the solid electrolyte 1400. Additionally, the MIEC 1110 may be electrochemically stable against the alkali metal 1300, thus substantially reducing or, in some instances, preventing the generation of new SEI since the expanding and/or shrinking portions of the alkali metal 1300 are in contact with only the MIEC 1110.
The above example shows that in implementations where the alkali metal 1300 is transported primarily by bulk diffusion in the MIEC 1110, the materials used to form the MIEC 1110 should preferably exhibit a sufficiently large diffusivity to meet a desired current density. For example, the MIEC 1110 should be formed from a material having DLibulk at least about 10−8 cm2/s to achieve a desired current density of J about 3 mA/cm2.
However, bulk diffusion is not the only mechanism that may contribute to the transport of alkali metal 1300 within the MIEC 1110. Interfacial transport of alkali metal 1300 may also occur along the surfaces of the MIEC 1110 (e.g., the interface between the MIEC 1110 and the open pore structure 1120). In some implementations, the contribution of interfacial transport to the overall transport conductance of the MIEC 1110 may be substantial, particularly for smaller sized tubules (e.g., tubules with a width W=100 nm and a wall thickness w=10 nm) where the surface area is large relative to the volume of the MIEC 1110. In some implementations, the MIEC 1110 may support fast-diffusion paths of width δinterface (typically taken to be 2 Å) at the phase boundary between the MIEC 1110 and the alkali metal 1300 (e.g., the red/gray interface in
κMIEC=κMIECbulk×(1+2DLiinterfaceδinterface/DLibulkw) (4)
The surface diffusivity of alkali metal 1300 may be estimated using empirical formulations. For example, the surface diffusivity of Li on a BCC Li metal may be estimated as follows,
D
Li
surface=0.014 exp(−6.54TM/T)[cm2/s] (5)
Eq. (5) has been shown to accurately predict the diffusivity of monatomic metals. At room temperature, Eq. (5) predicts DLisurface=7×10−7 cm2/s in BCC Li, which is 70× larger than DLibulk about 10−8 cm2/s in LiC6 in the previous example. The geometric factor, 2δinterface/w, is approximately 4 Å/10 nm= 1/25. If DLiinterface is assumed to be similar to DLisurface, the contribution of interfacial diffusion to the overall conductance may still be 3× larger than bulk diffusion within the MIEC 1110 for LiC6.
Generally, the phase boundary between the MIEC 1110 and the alkali metal 1300 may have a lower atomic free volume compared to a free alkali metal surface. Thus, DLiinterface may be smaller than DLiinterface=7×10−7 cm2/s. For example, experimental diffusivity data suggests that DLiinterface≈2×10−7 cm2/s, which is still comparable to the bulk diffusivity of LiC6. For Li9Al4 and Li22Si5, DLiinterface is several orders of magnitude larger than DLibulk. In particular, the ratio DLiinterface/DLibulk is 200 for Li9Al4 and 20,000 for Li22Si5, which is substantially larger than the geometric factor 2δinterface/w ( 1/25 for w=10 nm). As a result, the contribution of bulk diffusion in the MIEC 1110 for these materials may be treated as being negligible. Thus, interfacial diffusion alone may yield an effective 1MIEC about 1 mS/cm, which satisfies the conditions in Eq. (2). The MIEC fill factor is thus w/(w+W)=0.1.
When interfacial diffusion is substantial, the MIEC 1110 may achieve a desired current density even when formed from materials with a poor bulk diffusivity, such as Li9Al4 and Li22Si5, since the diffusion flux along the δinterface≈2 Å MIEC/metal incoherent interface and/or MIEC surface is substantially larger than the bulk diffusion through the wall of the MIEC 1110. As a result, the ionic transport within the open pore structure 1120 may depend solely on the dimensions of the open pore structure 1120, which allows the MIEC 1110 to be formed from a broader range of electrochemically stable materials. For example, the MIEC 1110 may be formed from a material that exhibits desirable mechanical properties (e.g., toughness, yield strength, ductility) despite having a low bulk diffusivity.
As described above, the MIEC 1110 may be formed from typical anode materials such as carbon, silicon, and aluminum. More generally, the MIEC 1110 may be formed from a material that is electrochemically stable against the alkali metal 1300 such that the MIEC 1110 does not decompose to form fresh SEI at the interface between the MIEC 1110 and the alkali metal 1300. The alkali metal 1300 may be various types of metals including, but not limited to lithium, sodium, and potassium. In some implementations, only the MIEC 1110 (and not the solid electrolyte 1400) may be formed of an electrochemically stable material since the front 1340 of the alkali metal 1300 remains in contact with only the MIEC 1110 when extending into the open pore structure 1120 or receding from the open pore structure 1120. In this manner, no new SEI is formed as the battery 1000 is cycled. In some implementations, the MIEC 1110 and the solid electrolyte 1400 may both be formed of an electrochemically stable material, thus eliminating the generation of SEI during cycling and initial charging of the battery 1000. It should be appreciated that if the MIEC 1110 crumbles into pieces that are then embedded into the alkali metal 1300, electronic and ionic percolation is still possible since the MIEC 1110 is electrically and ionically conductive.
The MIEC 1110 may be made compatible with the alkali metal 1300 by alkaliating the MIEC 1110. Referring to the above example, a MIEC 1110 used in a Li battery may be lithiated to below 0V vs Li+/Li to form compounds such as LiC6 using carbon, Li22Si5 using silicon, and Li9Al4 using aluminum. Electrochemical stability of the MIEC 1110 may be evaluated on the basis that a thermodynamically stable compound is formed between the MIEC 1110 and the alkali metal 1300.
For example,
As evidenced by the phase diagrams of
For example, the MIEC 1110 may be formed from a material having a large mechanical toughness (e.g., the material absorbs a large amount of energy before fracturing) to withstand the mechanical stresses generated by the alkali metal 1300 when cycling the battery 1000. In another example, the MIEC 1110 may be formed from a material that has an incoherent boundary/interface with the alkali metal 1300 to increase the free volume of the phase boundary and, in turn, increase the diffusion transport rate. In another example, the MIEC 1110 may be formed from a passive material (e.g., TiN) that does not store and/or release the alkali metal 1300 when cycling the battery 1000. For such materials, the alkali metal 1300 is primarily stored and/or release from the open pore structure 1120 formed by the MIEC 1110.
In some implementations, the surfaces of the MIEC 1110 forming the open pore structure 1120 may also be coated with an alkaliphilic coating to increase the electrical and ionic conductance between the MIEC 1110 and the alkali metal 1300. For example, a thin ZnOx film (e.g., about 1 nm) may be deposited onto the surfaces of the open pore structure 1120 in cases where the alkali metal 1300 is Li. The deposition of Li metal onto the ZnOx coating may cause a layer of Li2O to form at the interface between the MIEC 1110 and the alkali metal 1300. The Li2O film may increase the wettability of the Li metal to the MIEC 1110, ensuring contact is maintained as more alkali metal 1300 is deposited in the open pore structure 1120. The alkaliphilic coating may thus provide a deformable, wetting, and lubricating film to enhance contact and transport of the alkali metal 1300 in the MIEC 1110.
A First Exemplary Demonstration with a Single Carbon Hollow Tubule (CHT)
A demonstration of the MIEC 1110 will now be described. Specifically, the transport of the alkali metal 1300 through the open pore structure 1120 was observed and characterized by performing experiments where Li metal was transported through individual carbon hollow tubule (CHT).
The nanobattery 1000 included an anode 1100 comprising one or more CHT's 2100. The CHT's 2100 were coupled to a transmission electron microscope (TEM) copper grid 2140 using silver conductive epoxy. Thus, the CHT's 2100 served as the MIEC 1110 and the copper grid 2140 served as the current collector 1140. The nanobattery 1000 also included a counter-electrode 2200 comprising a tungsten probe 2210, which was coated with Li metal 2220 in a glove box filled with Ar gas. A solid electrolyte 1400 comprising poly (ethylene oxide) (PEO) and Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were dissolved in 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (ionic liquid). The Li metal 2220 on the tungsten probe 2210 was then coated with an approximately 50 μm thick film of the solid electrolyte 1400 inside the glove box filled with Ar gas.
The nanobattery 1000 was placed in a TEM (JEOL 2010F) for in situ imaging and characterization at 200 kV. Specifically, the TEM included a Nanofactory STM/TEM holder, which held the counter-electrode 2200 via the tungsten probe 2210. The anode 1100 was mounted to a sample holder. After loading the counter-electrode 2200 and the anode 1100 into the TEM, the STM/TEM holder supporting the counter-electrode 2200 was moved until the solid electrolyte 1400 contacted the free ends of the CHT's 2100, thus completing the assembly of the nanobattery 1000.
The voltage source 2500 was used, in part, to electrically control the transport of Li metal into and/or out of the MIEC 1110. Specifically, lithium plating and stripping in the CHTs 2100 were realized by applying −2 V and +2 V with respect to the lithium metal.
The CHT's 2100 were synthesized using the following steps: (1) obtaining a solution by dissolving 1 g of polyacrylonitrile (PAN, Aldrich) and 1.89 g of Zn(Ac)2.2H2O in 30 mL of dimethylformamide (DMF, Aldrich) solvent, (2) synthesizing PAN/Zn(Ac)2 composite fibers via electrospinning by using the solution of (1) at 17 kV of working voltage, 0.05 mm/min of flow rate, and 20 cm of electrospinning distance, (3) forming a layer of Zeolitic Imidazolate Framework (ZIF-8) on the surface of the composite fibers by adding the fibers into an ethanol solution containing 2-methylimidazole (0.65 g, Aldrich), and (4) heating the synthesized core-shell composite fibers at 600-700° C. for 12 h to obtain the CHTs with some lithiophilic ZnOx. In step (3), a trace amount of cobalt acetate was introduced into the composite fibers to improve the degree of the graphitization of the synthesized CHTs.
The in-situ TEM experiments were performed under conditions that reduced electron beam damage. Li metal is sensitive to electron beam irradiation in a TEM due, in part, to the elastic and inelastic scattering between the incident electron beam and the sample. The elastic interactions from electron-nucleus scattering may lead to sputtering damage. The inelastic interactions from electron-electron scattering may cause damage due to specimen heating and radiolysis. When taking images and/or video of the nanobattery 1000, an electron beam current of about 1.5 mA/cm2 was used to reduce damage. Images were also acquired at a slight underfocus condition to enhance the contrast. The electron beam was also banked prior to imaging the sample and the exposure time (e.g., for taking a video) was limited to 2 minutes. The electron beam was also blanked while plating and stripping Li, except when making observations, to reduce the effect of electron beam impinging on the sample.
The nanobattery 1000 was also characterized by other instruments including a high-resolution TEM (HRTEM), a field emission scanning electron microscopy (FESEM, FEI Helios 600 Dual Beam FIB), an energy-dispersive X-ray spectroscope (EDX, oxford), and an X-ray photoelectron spectroscopy (XPS, PHI5600).
As previously described, multiple types of creep mechanisms (e.g., interfacial diffusion, power-law dislocation) may contribute to the transport of alkali metal 1300 in the open pore structure 1120. To distinguish between the two creep mechanisms, experiments were performed based on the schematic of
The mechanism for transporting alkali metal 1300 across a single pore in the open pore structure 1120 is scalable. For example,
where t stands for the thickness, λ stands for effective mean free path, It is the intensity integrated over the EELS spectrum, and Jo is the intensity integrated under a zero loss peak.
The accelerating voltage, semi-convergence, and semi-collection angles previous described and the atomic number, Zeff, was used to calculate X. Before Li plating, Zeff=6 for the CHT. After Li plating, Zeff may be estimated based on a mixture of Li and CHT at the location where the EELS signal was recorded. For example, an atomic ratio between Li and C may be estimated to be 0.56:1 based on the observed geometry of the tubule (e.g., an inner diameter of about 100 nm and a wall thickness of about 28 nm). Thus, Zeff may be estimated using the following,
Based on Eq. (7) and the above values, Zeff=5.1 after Li plating.
As further demonstration of the scalable nature of the MIEC 1110 mechanisms described herein,
As previously mentioned, the transport of the alkali metal 1300 may be primarily driven by the Coble creep mechanism when the characteristic width of each pore in the open pore structure 1120 is less than about 300 nm. For example,
For
As described above, the open pore structure 1120 formed by the MIEC 1110 may be coated with an alkaliphilic coating that increases wettability towards the alkali metal 1300, thus increasing ionic and electrical contact with the MIEC 1110. Experiments were performed to characterize the interface between the BCC Li metal (the alkali metal 1300) and a Li2O coating (the alkaliphilic coating) formed, in part, by coating the CHT with ZnOx, which results a conversion/alloying reaction of ZnOx+(2x+y)Li=ZnLiy+xLi2O. Due to challenges in observing the Li2O coating inside the CHT, the Li metal was intentionally over-plated during deposition in order to increase the pressure PLiMetal(x) until Li metal whiskers were extruded out of the CHT. The Li whiskers, which included the Li2O coating, were then analyzed.
The Li2O layer has an FCC crystal structure, thus the {110}BCC//{111}FCC orientation relationship is similar to the Kurdjumov-Sachs orientation relationship (OR) in various steels. Both the {111}FCC and {110}BCC are slip planes, thus the orientation relationship may be formed due to minute local slippage. The OR provides strong adhesion between the Li and Li2O phases, thus enabling the Li2O crystalline layer to remain attached to the Li metal as a lubricant layer. The lateral growth of the Li2O layer by interfacial diffusion was observed on a thicker Li metal nanostructure outside the tubule.
Based on the results above, a few-nm thick Li2O layer may function as a ‘lubricant’ by enabling slight slippage between the Li and Li2O surfaces, which increases the mechanical durability and provides strong adhesion between the Li metal and the MIEC, thus ensuring lithiophilicity on the MIEC wall.
In some implementations, the thin lubricant layer may spread onto at least one of the current collector 1140 and/or the solid electrolyte 1400. Once this occurs, a thin wetting layer of Li metal may follow, forming an atomically-thin, but effective ionic and electronic conduction channel (“composite interfacial MIEC”). The thin wetting layer of Li metal may ensure any Li metal in the open pore structure 1120 (e.g., the Li metal beads α, β, and γ in
Cycling tests were also performed on a single CHT where Li metal was continually transported into and out of the CHT.
The experimental demonstrations described above have focused on using Li as the alkali metal 1300 in the MIEC 1110. However, it should be appreciated that the transport mechanisms and the designs for the MIEC 1110 and open pore structure 1120 are general and may be applied to other materials including, but not limited to sodium (Na) and potassium (K). For example,
A Second Exemplary Demonstration with a Carbonaceous MIEC Beehive
The previous demonstration evaluated the transport of alkali metal 1300 through a single (or few) tubules representing the MIEC 1110. To demonstrate the scalability and use of the MIEC 1110 in a practical device, a large scale MIEC was fabricated and integrated into a cm×cm all-solid-state full cell battery. Specifically, a carbonaceous MIEC beehive was fabricated with about 1010 aligned tubules where each tubule had an aspect ratio on the order of about 102. A half-cell and a full-cell were then assembled with the carbonaceous MIEC beehive for use with Li metal. It should be appreciated the techniques previously described may also be used to characterize the carbonaceous MIEC beehive.
The carbonaceous MIEC beehive was synthesized as a Li host using the following steps: (1) growing a layer of carbon onto the inner surface of an anodic aluminum oxide (AAO) template using chemical vapor deposition (CVD) with a C2H2 gas flow rate of 90 sccm at 640° C., (2) depositing a layer of Pt onto the bottom of the AAO template as the current conductor via sputtering, (3) etching the AAO template using a 3M NaOH aqueous solution with a small amount of ethanol to obtain the carbonaceous MIEC beehive, and (4) depositing a 1 nm-thick ZnO layer onto the inner-surface of MIEC beehive using atomic layer deposition (ALD) to enhance the lithiophilicity of the MIEC beehive.
Nanoindentation tests were performed to evaluate whether the carbonaceous MIEC beehive can sustain a gas-pressurized environment.
This hardness is sufficient to sustain at least a gas pressure of about 101 MPa (i.e., a compression ratio of 10×) when the gas is compressed by Li metal deposition in the MIEC.
A half-cell 3000 was assembled that included the carbonaceous MIEC beehive, a solid electrolyte, and a Li metal counter-electrode. First, a about 200 nm thick layer of lithium phosphorus oxynitride (LiPON) was deposited onto the MIEC beehive via sputtering deposition to obstruct the open pores, thereby reducing the inflow of polymeric solid electrolyte into the MIEC beehive during testing at 55° C.
A full-cell was also assembled and tested using the carbonaceous MIEC beehive. The full-cell included a LiFePO4 cathode, which was constructed from the active material LiFePO4 (60 wt %), polyethylene oxide (PEO, 20 wt %), LiTFSI (10 wt %), and carbon black (10 wt %). The mass loading was 4-6 mg (LiFePO4)/cm2.
These results show that a practical full-cell device may be constructed using the MIEC 1110 according to theoretically derived design parameters (h=10-100 μm to ensure capacity, W about 100 nm to ensure interfacial Coble creep, w about 10 nm to ensure mechanical robustness, and hermetic soft SE cap for pressurization).
A Third Exemplary Demonstration with a Non-Carbonaceous MIEC Beehive
The MIEC 1110 may be formed from a broad range of materials that are electrochemically stable against the alkali metal 1300. In particular, the MIEC 1110 and the open pore structure 1120 may be configured to transport alkali metal 1300 primarily by an interfacial diffusion mechanism. As described above, this allows for greater flexibility when selecting the material to construct the MIEC 1110 because the electronic and ionic transport properties depend primarily on the structure and dimensions of the open pore structure 1120 rather than the material composition of the MIEC 1110.
To demonstrate the general applicability of the designs and mechanisms described herein, another exemplary MIEC 1110 was fabricated from titanium nitride (TiN). As shown in the equilibrium phase diagram of
A TiN honeycomb MIEC was synthesized by reacting anodized TiO2 template with ammonia gas as shown in
A half-cell 3000 was assembled with the TiN MIEC using a similar architecture to the carbonaceous MIEC previously described. The half-cell 3000 was tested at 55° C.
An all-solid-state full-cell was also assembled using the TiN MIEC. Specifically, the full cell comprised (1× excess) Li predeposited TiN MIEC beehive/SE/LiFePO4 battery. A 1×excess amount of Li metal was predeposited electrochemically inside the TiN MIEC beehive before the full cell was cycled.
MIEC Chemical Compositions
In some implementations, any of the MIECs described above may be formed from various binary, tertiary, or quaternary compound materials having a particular set of properties. These properties include electronic conductivity (>106 S/m), electrochemical stability against the alkali metal, and electrochemical stability against the solid electrolyte. Electrochemical stability of the MIEC against the alkali metal reduces or substantially prevents the MIEC from decomposing to form fresh SEI at the interface between the MIEC and the alkali metal. Electrochemical stability of the MIEC against the solid electrolyte reduces or substantially prevents the MIEC from decomposing to form fresh SEI at the interface between the MIEC and the solid electrolyte. Electrochemical stability may be evaluated based on thermodynamic stability.
The MIEC material may be computationally chosen from a database (e.g., The Materials Project: A materials genome approach to accelerating materials innovation) using the property criteria above. Specifically, a list of binary, tertiary, and quaternary compounds was generated. From this list, to screen for materials that are electronically conductive, any materials having a bandgap smaller than 3 eV were selected. Electrochemical stability of the MIEC against the alkali metal was screened using equilibrium phase diagrams. Materials with an end-member phase directly connected to an alkali metal by a tie-line in an equilibrium phase diagram were selected. Electrochemical stability of the MIEC against the solid electrolyte was screened using equilibrium phase diagrams and/or through experimentation. Materials with an end-member phase directly connected to the solid electrolyte by a tie-line in an equilibrium phase diagram were selected. Electrochemical stability against the solid electrolyte was screened experimentally by measuring the impedance over time of a bilayer of MIEC and solid electrolyte. Any materials having an impedance change over time less than 20% per hour were selected. The resulting list includes MIEC materials that have all three properties.
In some implementations, the list of MIEC materials is additionally screened to select inexpensive chemical elements. Materials that only include inexpensive chemical elements may be cheaper to produce and may be preferably for large scale production. In one implementation, inexpensive chemical elements may be screened by excluding any lanthanide elements. In another implementation, inexpensive chemical elements may be screened by excluding any rare earth metals. In another implementation, inexpensive chemical elements may be screened by excluding any compounds that include any of the following elements: beryllium, scandium, vanadium, gallium, germanium, krypton, niobium, technetium, ruthenium, palladium, gold, indium, tellurium, xenon, hafnium, tantalum, rhenium, osmium, iridium, platinum, silver, thallium, praseodymium, neodymium, promethium, terbium, dysprosium, thulium, and lutetium.
The accompanying APPENDICES constitute part of the present disclosure. The APPENDICES 1-3 include lists of MIEC materials that may be used as anodes in lithium, sodium, and potassium-based batteries, respectively. The APPENDICES include the chemical formulas, Materials Project identification number (“Material ID”), bandgaps (eV), density (g/cm3), price (USD), number of atoms in the compound, and price per atom for each of the MIEC materials. Compound price was calculated using prices of each element in in the compound. For example, if the prices of elements A and B are PA and PB, respectively, the price for A2B3 is 2×PA+3×PB. The price per atom is the compound price divided by the number of atoms in the compound's chemical formula. For example, for the compound A2B3, the price per atom is (2×PA+3×PB)/(2+3). The price per atom is a way of comparing prices between compounds with different numbers of atoms, since a compound with a fewer number of atoms will likely have a lower compound price, as calculated here, than a compound with a higher number of atoms.
All of the materials in the APPENDICES have an energy above hull equal to zero, indicating thermodynamic stability.
The MIEC material may include an aluminum (Al) alloy. For example, the MIEC material may be formed from aluminum alloyed with nickel, cobalt, iron, molybdenum, or vanadium.
The MIEC material may include a barium (Ba) compound. For example, the MIEC material may be formed from a barium compound including sodium, mercury, lead, boron, carbon, copper, lithium, or strontium.
The MIEC material may include beryllium (Be) or a beryllium compound. For example, the beryllium compound may include carbon or copper.
The MIEC material may include a calcium (Ca) compound. For example, the calcium compound may include gallium, copper, nitrogen, silicon, zinc, boron, beryllium, copper, magnesium, or nickel.
The MIEC material may include cerium (Ce) or a cerium compound. For example, the cerium compound may include carbon, gallium, silicon, aluminum, boron, copper, gallium, nitrogen, or zinc.
The MIEC material may include cobalt (Co) or a cobalt compound. For example, the cobalt compound may include nickel, tungsten, or boron.
The MIEC material may include chromium (Cr) or a chromium compound. For example, the chromium compound may include carbon, boron, silicon, or nickel.
The MIEC material may include cesium (Ce) or a cesium compound. For example, the cesium compound may include carbon.
The MIEC material may include erbium (Er) or an erbium compound. For example, the erbium compound may include aluminum, carbon, gallium, boron, or nitrogen.
The MIEC material may include europium (Eu) or a europium compound. For example, the europium compound may include nitrogen, gallium, silicon, boron, carbon, or mercury.
The MIEC material may include iron (Fe) or an iron compound. For example, the iron compound may include cobalt, boron, cobalt, silicon, boron, or nickel.
The MIEC material may include gadolinium (Ga) or a gadolinium compound. For example, the gadolinium compound may include boron, carbon, indium, aluminum, boron, gallium, or nitrogen.
The MIEC material may include hafnium (Hf) or a hafnium compound. For example, the hafnium compound may include nitrogen or carbon.
The MIEC material may include holmium (Ho) or a holmium compound. For example, the holmium compound may include aluminum, carbon, gallium, or boron.
The MIEC material may include potassium (K) or a potassium compound. For example, the potassium compound may include carbon.
The MIEC material may include lithium (Li) or a lithium compound. For example, the lithium compound may include indium, chromium, nitrogen, lead, tin, silicon, aluminum, calcium, nitrogen, cerium, europium, gallium, gadolinium, tellurium, hafnium, holmium, neodymium, samarium, ytterbium, yttrium, zinc, copper, zirconium, cadmium, mercury, scandium, titanium, molybdenum, manganese, boron, beryllium, cobalt, erbium, magnesium, and/or nickel.
The MIEC material may include a magnesium (Mg) compound. For example, the magnesium compound may include copper or nickel.
The MIEC material may include manganese (Mn) or a manganese compound. For example, the manganese compound may include carbon, boron, chromium, cobalt, niobium, silicon, iron, aluminum, nickel and/or vanadium.
The MIEC material may include molybdenum (Mo) and/or sodium (Na).
The MIEC material may include niobium (Nb) or a niobium compound. For example, the niobium compound may include boron, nitrogen, cobalt, chromium, iron, nickel, vanadium, and/or tungsten.
The MIEC material may include neodymium (Nd) or a neodymium compound. For example, the neodymium compound may include boron, carbon, cobalt, gallium, silicon, aluminum, copper, nitrogen, or zinc.
The MIEC material may include nickel (Ni) or a nickel compound. For example, the nickel compound may include boron, molybdenum, or tungsten.
The MIEC material may include rubidium (Rb) or a rubidium compound. For example, the rubidium compound may include carbon.
The MIEC material may include scandium (Sc) or a scandium compound. For example, the scandium compound may include iron, silicon, aluminum, carbon, cobalt, gallium, indium, boron, copper, nitrogen, and/or zinc.
The MIEC material may include samarium (Sm) or a samarium compound. For example, the samarium compound may include boron, carbon, gallium, silicon, aluminum, boron, copper, or nitrogen.
The MIEC material may include strontium (Sr) or a strontium compound. For example, the strontium compound may include lithium, mercury, cobalt, nitrogen, tellurium, lead, chromium, calcium, silicon, tin, or magnesium.
The MIEC material may include tantalum (Ta) or a tantalum compound. For example, the tantalum compound may include aluminum, beryllium, nitrogen, silicon, or tungsten.
The MIEC material may include titanium (Ti) or a titanium compound. For example, the titanium compound may include manganese, carbon, cobalt, copper, gallium, manganese, iron, nickel, nitrogen, zinc, aluminum, and/or boron.
The MIEC material may include vanadium (V) or a vanadium compound. For example, the vanadium compound may include boron, carbon, chromium, iron, nickel, cobalt, silicon, and/or tungsten.
The MIEC material may include tungsten (W) or a tungsten compound. For example, the tungsten compound may include carbon.
The MIEC material may include yttrium (Y) or an yttrium compound. For example, the yttrium compound may include nickel, carbon, cobalt, gallium, lead, silicon, tin, aluminum, boron, copper, iron, magnesium, manganese, zinc, or nitrogen.
The MIEC material may include ytterbium (Yb) or an ytterbium compound. For example, the ytterbium compound may include carbon, gallium, silicon, nitrogen, boron, indium, tellurium, aluminum, copper, or mercury.
The MIEC material may include zirconium (Zr) or a zirconium compound. For example, the zirconium compound may include carbon, copper, beryllium, nitrogen, silicon, iron, scandium, manganese, or nickel.
While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.
As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.
This application is a continuation-in-part application of U.S. nonprovisional application Ser. No. 16/499,656, filed on Sep. 30, 2019, entitled “METHODS AND APPARATUS TO FACILITATE ALKALI METAL TRANSPORT DURING BATTERY CYCLING, AND BATTERIES INCORPORATING SAME,” which in turn claims priority to U.S. Provisional Application No. 62/734,564, filed on Sep. 21, 2018, entitled “RAIL-GUIDED Li METAL PLATING/STRIPPING FOR SOLID-STATE Li BATTERIES.” Each of the aforementioned applications is incorporated herein by reference in its entirety.
This invention was made with Government support under Grant No: DE-SC0002633 awarded by Department of Energy (DOE) and Grant No. ECCS-1610806 awarded by the National Science Foundation (NSF). The Government has certain rights in the invention.
Number | Date | Country | |
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62734564 | Sep 2018 | US |
Number | Date | Country | |
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Parent | 16499656 | Sep 2019 | US |
Child | 17694174 | US |