Solid-state nanofiber polymer multilayer composite electrolytes and cells
A solid-state electrolyte for a multilayer solid-state electrochemical cell is described herein. The electrolyte comprises a lithium electrolyte salt and nanofibers of a cubic phase lithium lanthanum zirconium oxide (c-LLZO), and a polymer interspersed with the nanofibers and electrolyte salt. Electrochemical cells comprising the solid-state electrolyte, and solid-state cathodes comprising the nanofibers of c-LLZO are also described herein.
1. A multilayer solid-state electrochemical cell comprising a multilayer sheet in the following layer order, in the direction from anode to cathode:
(a) an anode current collector layer;
(b) an anode layer comprising an anode active material;
(c) a solid-state electrolyte layer comprising a lithium electrolyte salt, at least about 55 wt % nanofibers of a first cubic phase lithium lanthanum zirconium oxide (c-LLZO), and a first polymer interspersed with the nanofibers and electrolyte salt; wherein the nanofibers of the first c-LLZO are interconnected in a three-dimensional network, and the lithium salt is present in a ratio of the polymer to Li + of about 5:1 to 30:1 based on moles of polymer monomer units and of Li + ;
(d) a cathode layer comprising a cathode active material dispersed in a second polymer; and
(e) a cathode current collector layer;
wherein adjacent layers in the sheet contact each other and adhere together to form the solid-state electrochemical cell; and the cathode comprises nanofibers of the cathode active material; particles of the cathode active material; nanofibers of a second c-LLZO; and particles of a carbon material; all of which are dispersed in a polymeric matrix.
2. The electrochemical cell of claim 1 , wherein the first c-LLZO is selected from the group consisting of an Al-doped cubic phase Li 7 La 3 Zr 2 O 12 , undoped cubic phase Li 7 La 3 Zr 2 O 12 , Ti-doped Li 7 La 3 Zr 2 O 12 , and Ga-doped Li 7 La 3 Zr 2 O 12 .
3. The electrochemical cell of claim 1 , wherein the second c-LLZO is selected from the group consisting of an Al-doped cubic phase Li 7 La 3 Zr 2 O 12 , undoped cubic phase Li 7 La 3 Zr 2 O 12 , Ti-doped Li 7 La 3 Zr 2 O 12 , and Ga-doped Li 7 La 3 Zr 2 O 12 .
4. The electrochemical cell of claim 1 , wherein the lithium electrolyte salt is selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imidate (LiTFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI), lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA), lithium trifluoromethanesulfonate (LiTf), lithium perchlorate (LiClO 4 ), lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 or “LiBOB”), lithium difluoro(oxalato)borate (LiF 2 BC 2 O 4 or “LiDFOB”), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium thiocyanate (LiSCN), lithium bis(fluorosulfonyl)imidate (LiFSI), lithium bis(pentafluoroethylsulfonyl)imidate (LiBETI), lithium tetracyanoborate (LiB(CN) 4 ), lithium nitrate, and a combination of two or more thereof.
5. The electrochemical cell of claim 1 , wherein the first polymer is selected from the group consisting of PEO, PVDF, PMMA, PC, PAN, and CMC; and the second polymer is selected from the group consisting of PAN, PVDF, PMMA, and CMC.
6. The electrochemical cell of claim 1 , wherein the cathode active material is selected from the group consisting of (a) LiNi x Mn y Co z O 2 (NMC) wherein x+y+z=1, 0<x<1, 0<y<1, and 0<z<1, (b) LiNi 0.5 Mn 1.5 O 4 (LNMO), (c) LiMn 2 O 4 (LMO), (d) LiFePO 4 (LFP), (e) lithium nickel cobalt aluminum oxide (NCA), (f) lithium nickel manganese aluminum oxide, (g) lithium cobalt oxide (LCO), (h) Li 3 V 2 (PO 4 ) 3 , and (i) Li-S.
7. The electrochemical cell of claim 1 , further comprising a first interfacial polymer layer between the anode layer and the solid-state electrolyte layer; and a second interfacial polymer layer between the solid-state electrolyte layer and the cathode layer.
8. The electrochemical cell of claim 7 , wherein the first interfacial polymer layer comprises PEO and the second interfacial polymer layer comprises PAN.
9. The electrochemical cell of claim 1 , wherein the anode current collector layer comprises a copper foil or a carbon material selected from the group consisting of carbon nanofibers, graphite sheets, carbon paper, carbon nanotubes, and graphene; and the cathode current collector layer comprises an aluminum foil or a carbon material selected from the group consisting of carbon nanofibers, graphite sheets, carbon paper, carbon nanotubes, and graphene.
10. The electrochemical cell of claim 1 , wherein the nanofibers of the first c-LLZO have a fiber diameter in the range of about 100 nm to about 10,000 nm.
11. The electrochemical cell of claim 1 , wherein the nanofibers of c-LLZO are substantially evenly dispersed through the cathode, and the nanofibers of the cathode active material are asymmetrically dispersed within the cathode such that the concentration of the cathode active material is higher near one surface of the cathode and lower at an opposite surface of the cathode.
12. The electrochemical cell of claim 1 , wherein the nanofibers of the cathode active material have a fiber diameter in the range of about 100 nm to about 10,000 nm.