SOLID-STATE ELECTROLYTE FOR LITHIUM AIR BATTERIES

Abstract

A solid-state electrolyte composition for a lithium battery. The composition includes a polymeric matrix material, inorganic nanoparticles dispersed in or chemically bonded with the polymeric matrix material, and a lithium salt. The nanoparticles are formed of a compound including lithium and a different semi-metal element or metal element. Exemplary inorganic nanoparticles include a Li-rich super ionic conductor having a Li.sub.xM.sub.yP.sub.zS.sub.q structural formula, wherein M refers to the different semi-metal element or a metal element.

Claims

1. A solid-state electrolyte composition for a lithium battery, comprising: a polymeric matrix material; inorganic nanoparticles dispersed within the polymeric matrix material, the nanoparticles formed of a compound including lithium and a different semi-metal element or metal element; and a lithium salt.

2. The composition of claim 1, wherein the different semi-metal element or metal element is selected from the group consisting of silicon (Si), germanium (Ge), arsenic (As), Antimony (Sb), tellurium (Te), molybdenum (Mo), tungsten (W), niobium (Nb), vanadium (V), copper (Cu), and combinations thereof.

3. The composition of claim 1, wherein the polymeric matrix material comprises polyethylene glycol (PEG), polyethylene oxide (PEO), polyethylene (PE), polystyrene-butadiene (SBR), and combinations thereof.

4. The composition of claim 1, wherein said lithium salt comprises bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), lithium bis(fluorosulfonyl)amide (LiFSI), Lithiumtrifluoromethanesulfonate (LiTF), lithium hexafluorophosphate (LiPF.sub.6), and combinations thereof.

5. The composition of claim 1, wherein the inorganic nanoparticles comprise a Li-rich super ionic conductor having a Li.sub.xM.sub.yP.sub.zS.sub.q structural formula, wherein M refers to the different semi-metal element or a metal element, and each of x, y, z, and q is an integer.

6. The composition of claim 5, wherein x is 10, y is 1, z is 2, and q is 12.

7. The composition of claim 5, wherein the different semi-metal element or metal element is selected from the group consisting of silicon (Si), germanium (Ge), arsenic (As), Antimony (Sb), tellurium (Te), molybdenum (Mo), tungsten (W), niobium (Nb), vanadium (V), copper (Cu), and combinations thereof.

8. The composition of claim 5, wherein the inorganic nanoparticles comprise LGPS (Li.sub.10GeP.sub.2S.sub.12), LWPS (Li.sub.10WP.sub.2S.sub.12), LMoPS (Li.sub.10MoP.sub.2S.sub.12), or combinations thereof

9. The composition of claim 5, wherein the polymeric matrix material comprises polyethylene glycol (PEG), polyethylene oxide (PEO), polyethylene (PE), polystyrene-butadiene (SBR), and combinations thereof

10. The composition of claim 5, wherein said lithium salt comprises bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), lithium bis(fluorosulfonyl)amide (LiFSI), lithiumtrifluoromethanesulfonate (LiTF), lithium hexafluorophosphate (LiPF.sub.6), and combinations thereof

11. The composition of claim 5, further comprising a coupling agent bonding the nanoparticles to the polymer matrix material.

12. The composition of claim 1, having 1-10% w/w nanoparticles to total weight of the polymeric matrix material.

13. The composition of claim 1, wherein the composition is fixed on a gas diffusion layer material.

14. A cathode for a lithium battery, comprising: a gas diffusion layer including a catalyst coating; and the solid-state electrolyte composition applied on the gas diffusion layer.

15. The cathode of claim 14, wherein the solid-state electrolyte composition is applied on the gas diffusion layer with an average thickness of 1-1000 nm.

16. An all solid-state lithium battery comprising an anode, a cathode, and the solid-state electrolyte composition of claim 1 between the anode and the cathode.

17. The battery of claim 16, wherein the solid-state electrolyte composition is applied on a gas diffusion layer of the cathode.

18. A method for producing the solid-state electrolyte composition of claim 1, comprising steps of: dissolving a polymer material in an organic solvent; dispersing the inorganic nanoparticles in the organic solvent; dissolving the lithium salt in the organic solvent to obtain an electrolyte solution; and applying the electrolyte solution to an electrode surface.

19. The method of claim 18, wherein the polymer material, inorganic nanoparticles, and lithium salt are formed in separate solutions using the organic solvent, and then the separate solutions combined to obtain the electrolyte solution.

20. A solid-state electrolyte composition for a lithium battery, comprising: a polymeric matrix material including a combination of polyethylene oxide (PEO) and polyethylene glycol (PEG); inorganic nanoparticles dispersed within the polymeric matrix material, the nanoparticles formed of a compound including lithium and a different semi-metal element or metal element; a silane coupling agent bonding the nanoparticles to the polymer matrix material; and a lithium salt dispersed within the polymeric matrix material.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] FIG. 1 shows a representative battery cell, according to one embodiment of this invention.

[0017] FIG. 2 shows a comparison of (a) potential gap and (b) energy efficiency for an example SSE of this invention and a control comparison non-aqueous liquid electrolyte lithium-air battery systems. Hexagons represent the performance of the SSE system and circles show the performance of the control liquid electrolyte system.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The invention provides and/or incorporates a solid-state electrolyte composition for a lithium battery, and specifically, the use of such composition in a lithium air battery. The invention includes the method of producing said composition and making an all solid-state lithium battery.

[0019] FIG. 1 shows a representative electrolytic cell 10, such as for use in a battery to provide power to load 15. The cell 10 includes an anode 20 and a cathode 22. The anode 20 is generally a lithium anode and the cathode 22 can be a carbon material. The cathode 22 is desirable an air permeable gas diffusion layer including a catalyst coating 24. The catalyst can be any suitable catalyst, applied as needed, such as shown or otherwise coating or impregnating portions of the gas diffusion layer. FIG. 1 additionally shows a solid-state electrolyte 30 according to this invention, between the anode 20 and the cathode 22.

[0020] The solid-state electrolyte of this invention is desirably fully solid, such that there is no liquid or gel component. In embodiments of this invention, the solid-state electrolyte composition includes a polymer material, an inorganic nanoparticle, and a lithium salt. The polymer material forms a matrix for supporting the active parts of the electrolyte. The polymer material is desirably a film forming material that can be applied as a liquid and solidifies on a surface when dried. Exemplary polymer materials for use in this invention include, without limitation, polyethylene glycol (PEG), polyethylene oxide (PEO), polyethylene (PE), polystyrene-butadiene (SBR), and combinations thereof.

[0021] In embodiments of this invention, the inorganic nanoparticles desirably are or include a lithium-rich super ionic conductor. Exemplary nanoparticles have a Li.sub.xM.sub.yP.sub.zS.sub.q structural formula, where each of x, y, z, and q is an integer and M refers to either a semi-metal element such as silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) or a metal element such as molybdenum (Mo), tungsten (W), niobium (Nb), vanadium (V), copper (Cu), etc. In presently preferred embodiments, x is 10, y is 1, z is 2, and q is 12. Exemplary inorganic nanoparticles include, without limitation, LGPS (Li.sub.10GeP.sub.2S.sub.12), LWPS (Li.sub.10WP.sub.2S.sub.12), LMoPS (Li.sub.10MoP.sub.2S.sub.12), and combinations thereof.

[0022] Inclusion of a lithium salt provides benefits such as, without limitation, making the electrolyte ionically conductive, and providing the electrolyte with enough lithium ions for transfer during battery charge and discharge. The lithium salt also can lower the degree of crystallinity of the polymer matrix and increase the amorphicity, which improves the ionic conductivity. The lithium salt is not chemically bound to any other compound, but is dissociated inside the matrix. Exemplary lithium salts include, without limitation, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), lithiumtrifluoromethanesulfonate (LiTFS), lithium hexafluorophosphate (LiPF.sub.6), and combinations thereof.

[0023] In embodiments of this invention, a combination of two or more polymer materials is used. In some embodiments, PEO is a preferred base polymer due to its molecular weight. A combination of PEO and PEG can be used. PEO can have a molecular weight (Mw) between 600 k and 2000 k, whereas PEG is a short-chain version and has a Mw about 2000. Adding PEG in combination provides several benefits, such as: (i) the PEG material provides more -OH groups to facilitate the chemical bonding (using a silane coupling agent) used to bind the nanoparticles (such as Li.sub.10GeP.sub.2Si.sub.2); (ii) PEG has a similar structure to that of PEO, therefore it does not cause any phase segregation issue; and (iii) in certain molecular weight ranges, PEG provides faster Li+ ion transport and higher Li+ transference number.

[0024] In embodiments of this invention, such as the PEO/PEG mixture discussed above, a coupling agent is used to bond the nanoparticles to the polymer matrix. An exemplary coupling agent is a silane coupling agent. The bonding occurs via chemical bonding of sulfur atoms in Li.sub.2S clusters of the nanoparticles and the Si atoms in the silane coupling agent. This helps alleviate the interfacial instability of the nanoparticles in contact with both the lithium metal anode and the air due to the similarity between O-H and S-Li bonds. In embodiments of this invention, the silane coupling agent has a general formula of R-Si-(OCH.sub.3).sub.3 where R is a hydrocarbon chain or alkyl halide hydrocarbon, where the halide can be chlorine, bromine, fluoride, and/or iodine elements. Exemplary coupling agents include 2-[Methoxy(polyethyleneoxy)6-9 propyl]trimethoxysilane, chloropropyl trimethoxy silane, and similar compounds.

[0025] The solid-state electrolyte composition of this invention can be prepared by dissolving polymers in an organic solvent, such as acetonitrile, tetrahydrofuran, dimethylformamide, etc. The polymer to solvent ratio can vary between 0.1:99.9 to 99.9:0.1 w/w. The inorganic nanoparticles (e.g., LGPS) can be dispersed in the same solvent as for the polymeric part. The lithium salt (e.g., LiTFSI) can also be dissolved in the same solvent as for the polymeric part with salt to solvent weight ratio of 0.1:99.9 to 99.9:0.1. Once all solutions are prepared, they are added together. The final solution can then be applied on the intended surface(s), such as a catalyst coated gas diffusion layer (GDL) to form a cathode-electrolyte structure for a lithium-air battery. Any suitable application method can be used, such as a solution casting method. Desirably the final solid coating has an average thickness of 1-1000 nm. In embodiments of this invention the electrolyte has a final polymer to lithium molar ratio of 0.1:9.9 to 9.9:0.1, with 1-100% w/w LGPS to total weight of the polymer. More desirably, the molar ratio of the polymer repeating units to lithium, such as [EO]:[Li] for PEO, is 1:8-1:32. These ratios can be tuned for higher ionic conductivity and/or improved mechanical strength.

[0026] The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

[0027] An exemplary SSE was prepared by dissolving PEG and PEO polymers in an organic solvent, such as acetonitrile, tetrahydrofuran, dimethylformamide, etc. Inorganic LGPS nanoparticles were separately dispersed using the same solvent as for the polymeric part. The lithium salt LiTFSI was also dissolved using the identical solvent. Once all solutions were prepared, they were added together. The final solution was then be applied on the intended surfaces. A GDL-SSE architecture was used with a lithium metal anode in a custom-designed lithium-air battery for electrochemical testing purposes. For ionic conductivity measurements and mechanical strength tests, the solution was casted on a stainless-steel disc and a glass watch, respectively.

[0028] FIG. 2 shows a performance of the SSE lithium-air battery (hexagons) compared to a control non-aqueous liquid electrolyte counterpart with the same catalyst coating on the cathode part (circles) and the same current density and capacity of 1000 mA/g and 1000 mAh/g. As it can be seen in FIG. 2, the potential gap in the SSE lithium-air battery system is 34.5 mV at the first cycle that is stable over 100 cycles (68.5 mV at the 100th cycle). The observed potential gap in the SSE lithium-air battery system (34.5 mV) was more than 15 times smaller than that of the non-aqueous liquid electrolyte lithium-air battery (533.2 mV) at the first cycle, confirming the superiority of the SSE. Similarly, the energy efficiency of the SSE lithium-air battery system was 99.42% at the first cycle and stable over 100 cycles (98% at the 100th cycle) whereas the energy efficiency for the non-aqueous liquid electrolyte lithium-air battery system is 89.27% at the first cycle that decays to 78% over 100 cycles, suggesting the better performance of the SSE compared to non-aqueous liquid electrolyte medium.

[0029] Thus, the invention provides an improved solid-state electrolyte composition for a lithium battery. The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

[0030] While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.