Solid-State Battery Electrolyte Having Increased Stability Towards Cathode Materials

Abstract

Disclosed are electrochemical devices, such as lithium ion battery electrodes, lithium ion conducting solid-state electrolytes, and solid-state lithium ion batteries including these electrodes and solid-state electrolytes. Also disclosed are composite electrodes for solid state electrochemical devices. The composite electrodes include one or more separate phases within the electrode that provide electronic and ionic conduction pathways in the electrode active material phase. A method for forming a composite electrode for an electrochemical device is also disclosed. One example method comprises (a) forming a mixture comprising (i) a lithium host material, and (ii) a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure; and (b) sintering the mixture, wherein the dopant is selected such that the solid-state conductive material retains the crystal structure during sintering with the lithium host material.

Claims

1. An electrode for an electrochemical device, the electrode comprising: a lithium host material; and a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure, the solid-state conductive material retaining the crystal structure during sintering with the lithium host material.

2. The electrode of claim 1, wherein the crystal structure having the dopant has a higher fraction of a cubic structure after sintering relative to the crystal structure having no dopant.

3. The electrode of claim 1, wherein the crystal structure having the dopant has a lower fraction of a tetragonal structure after sintering relative to the crystal structure having no dopant.

4. The electrode of claim 1, wherein the dopant is a transition metal cation.

5. The electrode of claim 1, wherein the dopant is pentavalent or hexavalent.

6. The electrode of claim 1, wherein the dopant comprises tantalum.

7. The electrode of claim 1, wherein the dopant comprises niobium.

8. The electrode of claim 1, wherein the dopant is present in the crystal structure at 1 to 20 weight percent based on a total weight of chemical elements in the crystal structure.

9. The electrode of claim 1, wherein the solid-state conductive material has a lithium ion conductivity that is greater than 10.sup.5 S/cm at 23 C.

10. The electrode of claim 1, wherein the solid-state conductive material has a lithium ion conductivity that is greater than 10.sup.4 S/cm at 23 C.

11. The electrode of claim 1, wherein the solid-state conductive material has a formula of Li.sub.wA.sub.xM.sub.2Re.sub.3yO.sub.z wherein w is 5-7.5, wherein A is selected from B, Ga, In, Zn, Cd, Y, Sc, Mg, Ca, Sr, Ba, Co, Fe, and any combination thereof, wherein x is 0-2, wherein M is selected from Zr, Hf, Nb, Ta, Mo, W, Sn, Ge, Si, Sb, Se, Te, and any combination thereof, wherein Re is selected from lanthanide elements, actinide elements, and any combination thereof, wherein y is 0.01-0.75, wherein z is 10.875-13.125, and wherein the crystal structure is a garnet-type or garnet-like crystal structure.

12. The electrode of claim 1 wherein: the electrode is a cathode for the electrochemical device, and the lithium host material is selected from the group consisting of lithium metal oxides wherein the metal is one or more aluminum, cobalt, iron, manganese, nickel and vanadium, and lithium-containing phosphates having a general formula LiMPO.sub.4 wherein M is one or more of cobalt, iron, manganese, and nickel.

13. The electrode of claim 1, wherein the lithium host material has a formula LiNi.sub.aMn.sub.bCo.sub.cO.sub.2, wherein a+b+c=1, and wherein a:b:c=1:1:1 (NMC 111), 4:3:3 (NMC 433), 5:2:2 (NMC 522), 5:3:2 (NMC 532), 6:2:2 (NMC 622), or 8:1:1 (NMC 811).

14. The electrode of claim 1, wherein the lithium host material is selected from LiCoO.sub.2, LiNiO.sub.2, Li(NiCoAl).sub.1.0O.sub.2, Li(MnNi).sub.2.0O.sub.4, LiFePO.sub.4, LiCoPO.sub.4, LiNiPo.sub.4, or LiVO.sub.3, and any combination thereof.

15. The electrode of claim 1, wherein: the electrode is an anode for the electrochemical device, and the lithium host material is selected from the group consisting of graphite, lithium titanium oxides, hard carbon, tin and cobalt alloy, or silicon and carbon.

16. The electrode of claim 1, wherein the electrode comprises a conductive additive.

17. The electrode of claim 16, wherein the conductive additive is selected from graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, metallic powders, conductive whiskers, conductive metal oxides, and mixtures thereof.

18. A method for forming an electrode for an electrochemical device, the method comprising: (a) forming a mixture comprising (i) a lithium host material, and (ii) a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure; and (b) sintering the mixture, wherein the dopant is selected such that the solid-state conductive material retains the crystal structure during sintering with the lithium host material.

19. The method of claim 18, wherein step (a) comprises casting a slurry including the mixture on a surface to form a layer, and step (b) comprises sintering the layer.

20. The method of claim 18, wherein step (b) further comprises sintering the mixture at a temperature between 20 C. and 1400 C.

21. The method of claim 18, wherein step (b) further comprises sintering the mixture between 1 minute and 48 hours.

22. The method of claim 18, wherein the dopant is pentavalent or hexavalent.

23. The method of claim 18, wherein the dopant comprises tantalum.

24. The method of claim 18, wherein the dopant comprises niobium.

25. The method of claim 18, wherein the dopant is present in the crystal structure at 1 to 20 weight percent based on a total weight of chemical elements in the crystal structure.

26. The method of claim 18, wherein: the solid-state conductive material has a formula of Li.sub.wA.sub.xM.sub.2Re.sub.3yO.sub.z wherein w is 5-7.5, wherein A is selected from B, Ga, In, Zn, Cd, Y, Sc, Mg, Ca, Sr, Ba, Co, Fe, and any combination thereof, wherein x is 0-2, wherein M is selected from Zr, Hf, Nb, Ta, Mo, W, Sn, Ge, Si, Sb, Se, Te, and any combination thereof, wherein Re is selected from lanthanide elements, actinide elements, and any combination thereof, wherein y is 0.01-0.75, wherein z is 10.875-13.125, and wherein the crystal structure is a garnet-type or garnet-like crystal structure.

27. The method of claim 18 wherein: the electrode is a cathode for the electrochemical device, and the lithium host material is selected from the group consisting of lithium metal oxides wherein the metal is one or more aluminum, cobalt, iron, manganese, nickel and vanadium, and lithium-containing phosphates having a general formula LiMPO.sub.4 wherein M is one or more of cobalt, iron, manganese, and nickel.

28. The method of claim 18 wherein: the lithium host material is a ceramic material having a formula LiNi.sub.aMn.sub.bCo.sub.cO.sub.2, wherein a+b+c=1, and wherein a:b:c=1:1:1 (NMC 111), 4:3:3 (NMC 433), 5:3:2 (NMC 532), 6:2:2 (NMC 622), or 8:1:1 (NMC 811).

29. The method of claim 18 wherein: the lithium host material is selected from LiCoO.sub.2, LiNiO.sub.2, Li(NiCoAl).sub.1.0O.sub.2, Li(MnNi).sub.2.0O.sub.4, LiFePO.sub.4, LiCoPO.sub.4, LiNiPo.sub.4, or LiVO.sub.3, and any combination thereof.

30. The method of claim 18 wherein: the electrode is an anode for the electrochemical device, and the lithium host material is selected from the group consisting of graphite, lithium titanium oxides, hard carbon, tin and cobalt alloy, or silicon and carbon.

31. The method of claim 18 wherein: the electrode comprises a conductive additive.

32. The method of claim 31 wherein: the conductive additive is selected from graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, metallic powders, conductive whiskers, conductive metal oxides, and mixtures thereof.

33. An electrochemical device comprising: a cathode; an anode, and a solid-state electrolyte configured to facilitate the transfer of lithium ions between the anode and the cathode, wherein one or both of the cathode and the anode comprises a lithium host material and a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure, the solid-state conductive material retaining the crystal structure during sintering with the lithium host material.

34. The electrochemical device of claim 33, wherein the crystal structure having the dopant has a higher fraction of a cubic structure after sintering relative to the crystal structure having no dopant.

35. The electrochemical device of claim 33, wherein the crystal structure having the dopant has a lower fraction of a tetragonal structure after sintering relative to the crystal structure having no dopant.

36. The electrochemical device of claim 33, wherein the dopant is a transition metal cation.

37. The electrochemical device of claim 33, wherein the dopant is pentavalent or hexavalent.

38. The electrochemical device of claim 33, wherein the dopant comprises tantalum.

39. The electrochemical device of claim 33, wherein the dopant comprises niobium.

40. The electrochemical device of claim 33, wherein the dopant is present in the crystal structure at 1 to 20 weight percent based on a total weight of chemical elements in the crystal structure.

41. The electrochemical device of claim 33, wherein the solid-state conductive material has a lithium ion conductivity that is greater than 10.sup.5 S/cm at 23 C.

42. The electrochemical device of claim 33, wherein the solid-state conductive material has a lithium ion conductivity that is greater than 10.sup.4 S/cm at 23 C.

43. The electrochemical device of claim 33, wherein the solid-state conductive material has a formula of Li.sub.wA.sub.xM.sub.2Re.sub.3yO.sub.z wherein w is 5-7.5, wherein A is selected from B, Ga, In, Zn, Cd, Y, Sc, Mg, Ca, Sr, Ba, Co, Fe, and any combination thereof, wherein x is 0-2, wherein M is selected from Zr, Hf, Nb, Ta, Mo, W, Sn, Ge, Si, Sb, Se, Te, and any combination thereof, wherein Re is selected from lanthanide elements, actinide elements, and any combination thereof, wherein y is 0.01-0.75, wherein z is 10.875-13.125, and wherein the crystal structure is a garnet-type or garnet-like crystal structure.

44. The electrochemical device of claim 33 wherein: the cathode comprises the lithium host material and the solid-state conductive material, and the lithium host material is selected from the group consisting of lithium metal oxides wherein the metal is one or more aluminum, cobalt, iron, manganese, nickel and vanadium, and lithium-containing phosphates having a general formula LiMPO.sub.4 wherein M is one or more of cobalt, iron, manganese, and nickel.

45. The electrochemical device of claim 33, wherein the cathode comprises the lithium host material and the solid-state conductive material, and the lithium host material has a formula LiNi.sub.aMn.sub.bCo.sub.cO.sub.2, wherein a+b+c=1, and wherein a:b:c=1:1:1 (NMC 111), 4:3:3 (NMC 433), 5:2:2 (NMC 522), 5:3:2 (NMC 532), 6:2:2 (NMC 622), or 8:1:1 (NMC 811).

46. The electrochemical device of claim 33, wherein the cathode comprises the lithium host material and the solid-state conductive material, and the lithium host material is selected from LiCoO.sub.2, LiNiO.sub.2, Li(NiCoAl).sub.1.0O.sub.2, Li(MnNi).sub.2.0O.sub.4, LiFePO.sub.4, LiCoPO.sub.4, LiNiPo.sub.4, or LiVO.sub.3, and any combination thereof.

47. The electrochemical device of claim 33, wherein: the anode comprises the lithium host material and the solid-state conductive material, and the lithium host material is selected from the group consisting of graphite, lithium titanium oxides, hard carbon, tin and cobalt alloy, or silicon and carbon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] FIG. 1 is a schematic of a lithium ion battery.

[0065] FIG. 2 is a schematic of a lithium metal battery.

[0066] FIG. 3 shows Al:LLZO (LLZO doped with aluminum) before (bottom) and after (top) co-sintering with a lithium nickel cobalt manganese oxide (NMC) cathode at 700 C. for 30 minutes. The (112) peak is increased in intensity compared to the (211), indicating increased fraction of the low-conductivity undesirable tetragonal LLZO phase.

[0067] FIG. 4 shows Ta:LLZO (LLZO doped with tantalum) before (bottom) and after (top) co-sintering with lithium nickel cobalt manganese oxide (NMC) at 900 C. for 30 minutes.

DETAILED DESCRIPTION OF THE INVENTION

[0068] In one non-limiting example application, an electrode according to embodiments of the invention can be used in a lithium ion battery as depicted in FIG. 1. The lithium ion battery 10 of FIG. 1 includes a current collector 12 (e.g., aluminum) in contact with a cathode 14. A solid state electrolyte 16 is arranged between the cathode 14 and an anode 18, which is in contact with a current collector 22 (e.g., aluminum). The current collectors 12 and 22 of the lithium ion battery 10 may be in electrical communication with an electrical component 24. The electrical component 24 could place the lithium ion battery 10 in electrical communication with an electrical load that discharges the battery or a charger that charges the battery.

[0069] A suitable active material for the cathode 14 of the lithium ion battery 10 is a lithium host material capable of storing and subsequently releasing lithium ions. An example cathode active material is a lithium metal oxide wherein the metal is one or more of aluminum, cobalt, iron, manganese, nickel and vanadium. Non-limiting example lithium metal oxides are LiCoO.sub.2 (LCO), LiFeO.sub.2, LiMnO.sub.2 (LMO), LiMn.sub.2O.sub.4, LiNiCoMnO.sub.2 (NMC), LiNiO.sub.2 (LNO), LiNi.sub.xCo.sub.yO.sub.2, LiMn.sub.xCo.sub.yO.sub.2, LiMn.sub.xNi.sub.yO.sub.2, LiMn.sub.xNi.sub.yO.sub.4, LiNi.sub.xCo.sub.yAl.sub.zO.sub.2, LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 and others. Another example of cathode active materials is a lithium-containing phosphate having a general formula LiMPO.sub.4 wherein M is one or more of cobalt, iron, manganese, and nickel, such as lithium iron phosphate (LFP) and lithium iron fluorophosphates. Many different elements, e.g., Co, Mn, Ni, Cr, Al, or Li, may be substituted or additionally added into the structure to influence electronic conductivity, ordering of the layer, stability on delithiation and cycling performance of the cathode materials. The cathode active material can be a mixture of any number of these cathode active materials.

[0070] In some non-limiting embodiments, the lithium host material is selected from the group consisting of lithium metal oxides wherein the metal is one or more aluminum, cobalt, iron, manganese, nickel and vanadium, and lithium-containing phosphates having a general formula LiMPO.sub.4 wherein M is one or more of cobalt, iron, manganese, and nickel. In some non-limiting embodiments, the lithium host material has a formula LiNi.sub.aMn.sub.bCo.sub.cO.sub.2, wherein a+b+c=1, and wherein a:b:c=1:1:1 (NMC 111), 4:3:3 (NMC 433), 5:2:2 (NMC 522), 5:3:2 (NMC 532), 6:2:2 (NMC 622), or 8:1:1 (NMC 811). In some non-limiting embodiments, the lithium host material is selected from LiCoO.sub.2, LiNiO.sub.2, Li(NiCoAl).sub.1.0O.sub.2, Li(MnNi).sub.2.0O.sub.4, LiFePO.sub.4, LiCoPO.sub.4, LiNiPo.sub.4, or LiVO.sub.3, and any combination thereof.

[0071] The cathode 14 may include a conductive additive. Many different conductive additives, e.g., Co, Mn, Ni, Cr, Al, or Li, may be substituted or additionally added into the structure to influence electronic conductivity, ordering of the layer, stability on delithiation and cycling performance of the cathode materials. Other suitable conductive additives include graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, metallic powders, conductive whiskers, conductive metal oxides, and mixtures thereof.

[0072] A suitable active material for the anode 18 of the lithium ion battery 10 is a lithium host material capable of incorporating and subsequently releasing the lithium ion such as graphite, a lithium metal oxide (e.g., lithium titanium oxide), hard carbon, a tin/cobalt alloy, tin/aluminum alloy, or silicon/carbon. The anode active material can be a mixture of any number of these anode active materials. The anode 18 may include one or more of the conductive additives described above.

[0073] A suitable solid state electrolyte 16 of the lithium ion battery 10 includes an electrolyte material having the formula Li.sub.uRe.sub.vM.sub.wA.sub.xO.sub.y, wherein

[0074] Re can be any combination of elements with a nominal valance of +3 including La, Nd, Pr, Pm, Sm, Sc, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, and Lu;

[0075] M can be any combination of metals with a nominal valance of +3, +4, +5 or +6 including Zr, Ta, Nb, Sb, W, Hf, Sn, Ti, V, Bi, Ge, and Si;

[0076] A can be any combination of dopant atoms with nominal valance of +1, +2, +3 or +4 including H, Na, K, Rb, Cs, Ba, Sr, Ca, Mg, Fe, Co, Ni, Cu, Zn, Ga, Al, B, and Mn;

[0077] u can vary from 3-7.5;

[0078] v can vary from 0-3;

[0079] w can vary from 0-2;

[0080] x is 0-2; and

[0081] y can vary from 11-12.5.

[0082] In another non-limiting example application, an electrode according to embodiments of the invention can be used in a lithium metal battery as depicted in FIG. 2. The lithium metal battery 110 of FIG. 2 includes a current collector 112 in contact with a cathode 114. A solid state electrolyte 116 is arranged between the cathode 114 and an anode 118, which is in contact with a current collector 122. The current collectors 112 and 122 of the lithium metal battery 110 may be in electrical communication with an electrical component 124. The electrical component 124 could place the lithium metal battery 110 in electrical communication with an electrical load that discharges the battery or a charger that charges the battery. A suitable active material for the cathode 114 of the lithium metal battery 110 is one or more of the lithium host materials listed above, or porous carbon (for a lithium air battery), or a sulfur containing material (for a lithium sulfur battery). The cathode 114 may include one or more of the conductive additives described above. A suitable active material for the anode 118 of the lithium metal battery 110 is lithium metal. A suitable solid state electrolyte material for the solid state electrolyte 116 of the lithium metal battery 110 is one or more of the solid state electrolyte materials listed above.

[0083] The present invention provides embodiments of an electrode that provide improved electronic and ionic conduction pathways in the electrode active material phase (e.g., lithium host material) of a cathode or an anode suitable for use in the lithium ion battery 10 of FIG. 1 or the lithium metal battery 110 of FIG. 2. In one non-limiting example, we describe how dopant control within the garnet-LLZO solid electrolyte system can dramatically improve the stability of the high ionic conductivity cubic phase when co-sintering with common cathode materials.

[0084] Transition metal (e.g., Ta, Nb) doped LLZO can be produced by direct solid state reaction of transition metal oxides or a transition metal and LLZO during synthesis. In another embodiment, one or more additional transition metal cations (such as cobalt) can be diffused into the LLZO at a temperature (e.g., 600-1000 C.) from a transition metal or transition metal oxide species in the gas phase. Although tantalum and niobium are used as examples, it is expected that other dopants including transition metal cations, preferably pentavalent or hexavalent, can similarly prevent the conversion of cubic LLZO to tetragonal LLZO during co-sintering of LLZO with lithium host materials.

Composite Electrodes

[0085] In one embodiment, the invention provides a composite electrode for an electrochemical device. The electrode may be a cathode or an anode. The electrode comprises a lithium host material having a structure (which may be porous); and a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure. The dopant is selected such that the solid-state conductive material retains the crystal structure during sintering with the lithium host material.

[0086] In a composite electrode of the present disclosure, one non-limiting example solid-state conductive material is Li.sub.6.5La.sub.3Zr.sub.1.5Ta.sub.0.5O.sub.12, in which the dopant level of tantalum is 12.5 wt. % Ta.sub.2O.sub.5 or 10.3 wt. % Ta elemental. The dopant may be present in the crystal structure of the solid-state conductive material at 0.05 to 20 weight percent based on a total weight of the chemical elements in the crystal structure, or the dopant may be present in the crystal structure at greater than 0.01 weight percent based on a total weight of the chemical elements in the crystal structure, or the dopant may be present in the crystal structure at 1 to 20 weight percent based on a total weight of the chemical elements in the crystal structure, or the dopant may be present in the crystal structure at 5 to 15 weight percent based on a total weight of the chemical elements in the crystal structure. For example, transition metal doping of garnet LLZO phase can ensure that ionic conductivity is minimally changed. Tantalum and niobium, in particular, readily dope the LLZO structure. The transition metal cation dopant (e.g., tantalum and niobium) may be from any appropriate transition metal containing source.

Electrochemical Devices

[0087] In one embodiment, the invention provides an electrochemical device, such as the lithium ion battery 10 of FIG. 1 or the lithium metal battery 110 of FIG. 2. The electrochemical device comprises a cathode, an anode, and a solid-state electrolyte configured to facilitate the transfer of ions between the anode and the cathode. The cathode can comprise a lithium host material having a first structure (which may be porous). The anode can comprise a lithium metal, or a lithium host material having a second structure (which may be porous).

[0088] In the electrochemical device, a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure fills at least part (or all) of the first structure in the lithium host material of the cathode and/or a second structure of the lithium host material of the anode (in the case of a lithium ion battery). Typically, the lithium host materials are sintered. The dopant is selected such that the solid-state conductive material retains the crystal structure during sintering with the lithium host material.

[0089] In some embodiments, the solid-state conductive material has lithium ion conductivity that is greater than 10.sup.5 S/cm at 23 degrees Celsius, or that is greater than 10.sup.4 S/cm at 23 degrees Celsius.

Methods for Forming a Composite Electrode

[0090] In one embodiment, the invention provides a method for forming a composite electrode for an electrochemical device. The method comprises: (a) forming a mixture comprising (i) a lithium host material, and (ii) a solid-state conductive material comprising a ceramic material having a crystal structure and a dopant in the crystal structure; and (b) sintering the mixture, wherein the dopant is selected such that the solid-state conductive material retains the crystal structure during sintering with the lithium host material. In certain non-limiting versions of the method, the mixture may be sintered at a temperature between 20 and 1400 C. for a time period between 1 minute and 48 hours, or between 1 minute and 1 hour.

[0091] In one non-limiting embodiment, the method may comprise casting a slurry including the mixture on a surface to form a layer, and step (b) may comprise sintering the layer. The slurry to be cast may include optional components. For example, the slurry may optionally include one or more sintering aids which melt and form a liquid that can assist in sintering of a cast slurry formulation of the invention via liquid phase sintering. Example sintering aids can be selected from boric acid, boric acid salts, boric acid esters, boron alkoxides phosphoric acid, phosphoric acid salts, phosphate acid esters, silicic acid, silicic acid salts, silanols, silicon alkoxides, aluminum alkoxides and mixtures thereof.

[0092] The slurry may optionally include a dispersant. One purpose of the dispersant is to stabilize the slurry and prevent the suspended active battery material particles from settling out. The dispersant may be selected from the group consisting of salts of lithium and a fatty acid. The fatty acid may be selected from lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, and behenic acid.

[0093] The slurry may optionally include a plasticizer. The purpose of the plasticizer is to increase the workability of the as-cast tape. Preferably, the plasticizer is a naturally derived plant based oil. The plasticizer may be selected from the group consisting of coconut oil, castor oil, soybean oil, palm kernel oil, almond oil, corn oil, canola oil, rapeseed oil, and mixtures thereof.

[0094] The slurry formulation may optionally include a binder. Non-limiting examples of the binder include: poly(methylmethacrylate), poly(vinylacetate), polyvinyl alcohol, polyethyleneoxide, polyvinylpyrrolidone, polyvinyl ether, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, polyethylene, polypropylene, ethylene-propylene-diene terpolymers (EPDM), cellulose, carboxymethylcellulose, starch, hydroxypropylcellulose, and mixtures thereof. The binder is preferably a non-fluorinated polymeric material.

[0095] The slurry may optionally include a solvent is useful in a slurry formulation to dissolve the binder and act as a medium for mixing the other additives. Any suitable solvents may be used for mixing the active battery material particles, dispersant, and binder into a uniform slurry. Suitable solvents may include alkanols (e.g., ethanol), nitriles (e.g., acetonitrile), alkyl carbonates, alkylene carbonates (e.g., propylene carbonate), alkyl acetates, sulfoxides, glycol ethers, ethers, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, or a mixture of any of these solvents.

[0096] The slurry formulation may include other additives. For example, the cathode or anode active battery material particles may be mixed with other particles, such as conductive particles. Any conductive material may be used without particular limitation so long as it has suitable conductivity without causing chemical changes in the fabricated battery. Examples of conductive materials include graphite; carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers and metallic fibers; metallic powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0097] Any suitable method may be used to mix the slurry components into a uniform slurry. Suitable mixing methods may include sonication, mechanical stirring, physical shaking, vortexing, ball milling, and any other suitable means.

[0098] After the uniform slurry is obtained, the formulation is cast on a substrate surface to form a cast tape layer. The substrate may include any stable and conductive metals suitable as a current collector for the battery. A suitable metallic substrate may include aluminum, copper, silver, iron, gold, nickel, cobalt, titanium, molybdenum, steel, zirconium, tantalum, and stainless steel. In one embodiment, the metal substrate is aluminum.

[0099] The slurry layer cast on the surface may have a thickness in the range of a few micrometers to a few centimeters. In one embodiment, the thickness of the cast slurry layer is in the range of 10 micrometers to 150 micrometers, preferably 10 micrometers to 100 micrometers. After the slurry is cast on the substrate surface to form a tape, the green tape can be dried and sintered to a composite electrode having a thickness in the range of 10 micrometers to 150 micrometers, preferably 20 micrometers to 100 micrometers, more preferably 50 micrometers to 100 micrometers. Optionally, multiple layers can be cast on top of one another. For example, the anode can be cast first on the metal substrate, followed by casting the solid electrolyte on the anode, and finally casting the cathode on the electrolyte. Alternatively, the cathode can be cast first on the metal substrate, followed by the solid electrolyte, and finally the anode. The multi-layer green tape can be dried and sintered at a temperature in a range of 600 C. to 1100 C., or in a range of 800 C. to 1000 C., to achieve the necessary electrochemical properties.

EXAMPLE

[0100] The following Example has been presented in order to further illustrate the invention and is not intended to limit the invention in any way.

[0101] We have shown that replacement of the Al:LLZO (LLZO doped with Al to stabilize the cubic crystal structure at room temperature) with that of pentavalently doped LLZO, such as Ta:LLZO (LLZO doped with Ta to stabilize the cubic crystal structure at room temperature) or Nb:LLZO (LLZO doped with Nb to stabilize the cubic crystal structure at room temperature) prevents reaction of the LLZO electrolyte with the cathode phase. As such, the LLZO retains the cubic-LLZO structure at room temperature which is desirable for high lithium ion conductivity. Whereas Al:LLZO is unstable during co-sintering with NMC or LCO at 700 C., Ta:LLZO or Nb:LLZO are stable with both cathodes to processing temperatures >1000 C. This innovation is key in enabling processing of LLZO based composite cathodes for all solid-state batteries.

[0102] FIG. 3 gives a plot of an XRD pattern for Al:LLZO before and after co-sintering with lithium nickel cobalt manganese oxide (NMC) at 700 C. The Al:LLZO was present at 51% by weight in the NMC. The (112) peak intensity increases with respect to the (211) peak after co-sintering, indicating increased tetragonal LLZO fraction. FIG. 4 gives XRD patterns for Ta:LLZO sintered with lithium nickel cobalt manganese oxide (NMC) to 900 C. The Ta:LLZO was present at 51% by weight in the NMC. Unlike Al:LLZO as shown in FIG. 3, there is no peak splitting in FIG. 4 to indicate phase transformation of the cubic LLZO phase after co-sintering.

[0103] Thus, the invention provides electrochemical devices, such as lithium ion battery composite electrodes, and solid-state lithium ion batteries including these composite electrodes and solid-state electrolytes. The composite electrodes include one or more separate phases within the electrode that provide electronic and ionic conduction pathways in the electrode active material phase. The solid state electrochemical devices have applications in electric vehicles, consumer electronics, medical devices, oil/gas, military, and aerospace.

[0104] Although the invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.