Solid electrolyte separator bonding agent
Set forth herein are electrochemical cells which include a negative electrode current collector, a lithium metal negative electrode, an oxide electrolyte membrane, a bonding agent layer, a positive electrode, and a positive electrode current collector. The bonding agent layer advantageously lowers the interfacial impedance of the oxide electrolyte at least at the positive electrode interface and also optionally acts as an adhesive between the solid electrolyte separator and the positive electrode interface. Also set forth herein are methods of making these bonding agent layers including, but not limited to, methods of preparing and depositing precursor solutions which form these bonding agent layers. Set forth herein, additionally, are methods of using these electrochemical cells.
1. An electrochemical stack, comprising:
a lithium metal (Li) negative electrode, a positive electrode, an electrolyte separator film comprising a lithium-stuffed garnet, and a bonding layer; wherein the bonding layer comprises a lithium salt, a polymer, and a solvent;
wherein the polymer in the bonding layer is selected from PAN, PVDF-HFP, PVDF-HFP and PAN, PMMA, PVC, PVP, PEO, polyethylene carbonate, polyphenylene sulfide, polypropylene carbonate, and a combination thereof; and
wherein the bonding layer is characterized by a thickness about 1 nm to about 5 μm;
wherein the electrolyte separator film is characterized by a thickness of about 0.1 μm to about 100 μm;
wherein the electrolyte separator has a density greater than 95% of its theoretical density as determined by scanning electron microscopy;
wherein the electrolyte separator film is in direct contact with the Li metal negative electrode; and
wherein the bonding layer directly contacts, and is positioned between, the electrolyte separator film and the positive electrode; wherein the electrolyte separator has a surface directly contacting the lithium metal, wherein the surface only includes material which is the same as the material in a bulk of the electrolyte separator.
2. The electrochemical stack of claim 1 , wherein the Li negative electrode comprises a layer of Li metal having a thickness from 1 nm to 30 μm in the fully discharged state.
3. The electrochemical stack of claim 1 , wherein the Li metal negative electrode comprises a layer of Li metal having a thickness from 1 μm to 50 μm in the fully charged state.
4. The electrochemical stack of claim 1 , wherein the electrolyte separator film has a surface flatness of 0.1 μm to about 50 μm.
5. The electrochemical stack of claim 1 , wherein the polymer in the bonding layer is polyacrylonitrile (PAN) or polyvinylidene fluoride hexafluoropropylene (PVDF-HFP).
6. The electrochemical stack of claim 4 , wherein the electrolyte separator is nearly 100% dense electrolyte and has a planar surface.
7. The electrochemical stack of claim 1 , wherein the lithium salt in the bonding layer is selected from the group consisting of LiPF 6 , LiBOB, LiBETI, LiTFSI, LiBF 4 , LiClO 4 , LiAsF 6 , LiFSI, LiI, LiBF 4 , and a combination thereof.
8. The electrochemical stack of claim 1 , wherein the solvent in the bonding layer is selected from the group consisting of ethylene carbonate (EC), diethylene carbonate or diethyl carbonate (DC), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), tetrahydrofuran (THF), γ-Butyrolactone (GBL), fluoroethylene carbonate (FEC), fluoromethyl ethylene carbonate (FMEC), trifluoroethyl methyl carbonate (F-EMC), fluorinated 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane(F-EPE), fluorinated cyclic carbonate (F-AEC), propylene carbonate (PC), dioxolane, acetonitrile (ACN), succinonitrile, adiponitrile, hexanedinitrile, pentanedinitrile, acetophenone, isophorone, benzonitrile, dimethyl sulfate, prop-1-ene-1,3-sultone (PES), dimethyl sulfoxide (DMSO), ethyl-methyl carbonate, ethyl acetate, methyl butyrate, dimethyl ether (DME), diethyl ether, propylene carbonate, dioxolane, glutaronitrile, gamma butyl-lactone, and combinations thereof.
9. The electrochemical stack of claim 8 , wherein the amount of solvent in the bonding layer is the minimum amount of solvent required to solvate the lithium salt.
10. The electrochemical stack of claim 1 , wherein the interfacial impedance between the electrolyte separator film and the positive electrode is less than 50 Ω·cm 2 at 50° C.
11. The electrochemical stack of claim 1 , wherein the positive electrode further comprises a catholyte.
12. The electrochemical stack of claim 11 , wherein the catholyte is a gel electrolyte; wherein the positive electrode comprises a gel catholyte which has the same composition as the bonding layer.
13. The electrochemical stack of claim 11 , wherein the positive electrode comprises a gel catholyte comprising:
a solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), methylene carbonate, and combinations thereof;
a polymer selected from the group consisting of PVDF-HFP, PAN, and combinations thereof; and
a salt selected from the group consisting of LiPF 6 , LiBOB, and LiTFSI.
14. The electrochemical stack of claim 1 , wherein the bonding layer does not comprise components which volatilize and diffuse around the electrolyte separator film to contact the Li metal negative electrode.