A cathode for an all-solid state lithium battery

Abstract

Disclosed herein is a cathode for an all-solid state lithium battery, the cathode comprising a cathode active material, a sulfide-containing inorganic solid electrolyte material, and an oxygen-functionalised conductive carbon material; wherein the oxygen-functionalised conductive carbon material comprises from about 0.5 wt.% to about 20 wt.% of oxygen atoms, based on the total weight of the oxygen-functionalised conductive carbon material. Also disclosed herein is an all-solid state lithium battery comprising the cathode.

Description

A cathode for an all-solid state lithium battery FIELD OF THE INVENTION

[0001] The invention relates to a cathode for an all-solid state lithium battery, and a battery containing said cathode. However, it will be appreciated that the invention is not limited to this particular field of use. BACKGROUND

[0002] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] All-solid-state lithium batteries (ASSLBs) are of significant interest in the field of energy storage technologies, for reasons such as their potential advantages in safety and energy density. They differ from commercial Li-ion batteries (LIBs) in their use of a solid Li-ion conducting electrolyte instead of a liquid organic electrolyte containing lithium salts. The resistance to self- ignition in the case of inorganic solid electrolytes alleviates the thermal stability and flammability concerns that may otherwise threaten the widespread acceptance of electric vehicles employing LIBs. Greater thermal stability can also allow substantially faster charging. Furthermore, ASSLBs also promise an enhanced energy density, courtesy of their densely packed structure and the bipolar design that reduces the use of inactive materials. The use of high-energy Li metal anodes and Si anodes, which solid electrolytes (SEs) could potentially enable, may also boost the energy density of ASSLBs significantly.

[0004] Aside from engineering challenges regarding the scalable design of ASSLBs, some critical technical hurdles remain, and the electro-chemo-mechanical instability of different solid- solid interfaces is one of them. SEs can have limited thermodynamic stability, and thus, they may undergo reductive and oxidative degradations at the anode and cathode interface, respectively. In the cathode, the SE can directly react with the cathode active material (CAM) particles, but it can also degrade electrochemically. The latter, for example, for sulfide-type SEs, can occur by promotion of the SE redox kinetics by the conductive carbon, leading to the increasing formation of reactive polysulfides, which in turn can degrade the CAM surface. Nonetheless, deploying carbon additives brings forth complex interactions across various interfaces and subsequently influences the long-term capacity retention behavior of ASSLBs.

[0005] Studies into the nature of the NMC (LiNixCoyMnzO2), interfacial degradation with sulfide-type solid electrolytes like Li3PS4 and Li6PS5Cl in the presence of conductive carbon have shed light on the detrimental influence of carbon on the corresponding cathode performance. Thus, even though carbon may be important to furnishing a seamless electron percolation pathway in the cathode composite and achieving fast cathode redox kinetics, it is often avoided to suppress cathode interfacial degradations. However, due to CAM particles like NMCs being weak electronic conductors (e.g. NMC111: 5.2 × 10−8S cm-1), carbon’s absence may negatively impact the rate capability and, thus, the attainable capacity and energy density at even moderately high currents.

[0006] To overcome carbon’s dilemma, coating of the CAM particles with a thin layer of an electronic insulator but poor Li-ion conductor such as Li2CO3, LiNbO3, LiAlO2, Li4Ti5O12, Li2SiO3, Li2BO3-Li2CO3, and more, has been proposed. This approach seeks to create a protective artificial stable interphase that can enhance the stability of the cathode / sulfide-SE interface in the cathode composite. While this strategy can render good interfacial stability, inferior Li-ionic conductivity of the coating layer and the formation of a nonuniform and thick layer can result in high charge transfer impedance and large voltage polarization, which may impact the obtainable specific capacity and rate capability. Other approaches have included coating the carbon with organic polymeric semiconductors and inorganic insulators, respectively, to minimize carbon-catalyzed degradation of the sulfide SE and, hence, the cathode composite. A considerable challenge for this approach can be the synthetic hurdle of achieving a nanoscopic thin film of the insulator, as otherwise, carbon’s beneficial effect may not be realized.

[0007] There is a need to provide new cathodes that can provide enhanced stability of the cathode / sulfide-SE interface while retaining good capacity and recharge rate, and in particular with the ability to provide stable cycling of ASSLB cells in a manner that can provide good thermal stability, rate capability, and / or high Coulombic efficiency.

[0008] It is an object of the present invention to overcome or ameliorate one or more the disadvantages of the prior art, or at least to provide a useful alternative. SUMMARY OF THE INVENTION

[0009] The inventors of the present application have surprisingly found that by using oxygen- functionalised conductive carbon materials in cathodes with particular amounts of oxygen atoms, the resulting cathodes may promote the formation of a robust sulfate and phosphate-rich thin cathode interphase at the carbon-electrolyte interface. Without being bound by theory, the inventors of the present application postulate that this interphase may prevent or ameliorate SE and cathode interfacial degradations, otherwise perpetuated by bare conductive carbon, whilemaintaining the benefit of the electron percolation network furnished by the conductive carbon additive in the cathode. The inventors of the present application have surprising found that cathodes containing carbon additives (e.g. rGO) with particular amounts of oxygen functionality can lead to highly stable cycling of ASSLB cells with excellent thermal stability, rate capability, and / or high Coulombic efficiency.

[0010] In a first aspect of the invention there is provided a cathode for an all-solid state lithium battery, the cathode comprising: a cathode active material; a sulfide-containing inorganic solid electrolyte material; and an oxygen-functionalised conductive carbon material; wherein the oxygen-functionalised conductive carbon material comprises from about 0.5 wt.% to about 20 wt.% of oxygen atoms, based on the total weight of the oxygen-functionalised conductive carbon material.

[0011] The following options may be used in conjunction with the first aspect, either individually or in any combination.

[0012] In certain embodiments, the oxygen-functionalised conductive carbon material comprises oxygen and carbon, with substantially no other atoms.

[0013] In alternative embodiments, the oxygen-functionalised conductive carbon material comprises oxygen and carbon, with other (i.e. non-oxygen and non-carbon) atoms, e.g., one or more selected from the group consisting of nitrogen, sulfur and boron. The non-oxygen and non- carbon atoms may be, e.g. doped into the oxygen-functionalised conductive carbon material. The weight percentage of the non-oxygen and non-carbon atoms in the oxygen-functionalised conductive carbon material may be may be from about 0.0001 wt.% to about 5 wt.%, or from about 0.00028 wt.% to about 5 wt.%, about 0.00046 wt.% to about 5 wt.%, about 0.00064 wt.% to about 5 wt.%, about 0.00082 wt.% to about 5 wt.%, about 0.001 wt.% to about 5 wt.%, about 0.1 wt.% to about 5 wt.%, about 0.2 wt.% to about 5 wt.%, about 0.3 wt.% to about 5 wt.%, about 0.4 wt.% to about 5 wt.%, about 0.5 wt.% to about 5 wt.%, about 0.6 wt.% to about 5 wt.%, about 0.7 wt.% to about 5 wt.%, about 0.8 wt.% to about 5 wt.%, about 0.9 wt.% to about 5 wt.%, about 1 wt.% to about 5 wt.%, about 0.0001 wt.% to about 4.6 wt.%, about 0.0001 wt.% to about 4.2 wt.%, about 0.0001 wt.% to about 3.8 wt.%, about 0.0001 wt.% to about 3.4 wt.%, about 0.0001 wt.% to about 3 wt.%, about 0.0001 wt.% to about 2.6 wt.%, about 0.0001 wt.% to about 2.2 wt.%, about 0.0001 wt.% to about 1.8 wt.%, about 0.0001 wt.% to about 1.4 wt.%, about 0.0001 wt.% to about 1 wt.%, about 0.001 wt.% to about 1 wt.%, about 0.2 wt.% to about1 wt.%, about 0.4 wt.% to about 1 wt.%, about 0.6 wt.% to about 1 wt.%, about 0.8 wt.% to about 1 wt.%, about 0.001 wt.% to about 0.8 wt.%, about 0.001 wt.% to about 0.6 wt.%, about 0.001 wt.% to about 0.4 wt.%, or about 0.001 wt.% to about 0.2 wt.%. It may be greater than or equal to about 0.0001 wt.%, 0.00019 wt.%, 0.00028 wt.%, 0.00037 wt.%, 0.00046 wt.%, 0.00055 wt.%, 0.00064 wt.%, 0.00073 wt.%, 0.00082 wt.%, 0.00091 wt.%, 0.001 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, or 0.4 wt.%. It may be less than or equal to about 5 wt.%, 4.6 wt.%, 4.2 wt.%, 3.8 wt.%, 3.4 wt.%, 3 wt.%, 2.6 wt.%, 2.2 wt.%, 1.8 wt.%, 1.4 wt.%, 1 wt.%, 0.9 wt.%, 0.8 wt.%, 0.7 wt.%, or 0.6 wt.%. In certain embodiments, it may be, for example, about 0.0001 wt.%, 0.00019 wt.%, 0.00028 wt.%, 0.00037 wt.%, 0.00046 wt.%, 0.00055 wt.%, 0.00064 wt.%, 0.00073 wt.%, 0.00082 wt.%, 0.00091 wt.%, 0.001 wt.%, 0.051 wt.%, 0.1 wt.%, 0.15 wt.%, 0.2 wt.%, 0.25 wt.%, 0.3 wt.%, 0.35 wt.%, 0.4 wt.%, 0.45 wt.%, 0.5 wt.%, 0.55 wt.%, 0.6 wt.%, 0.65 wt.%, 0.7 wt.%, 0.75 wt.%, 0.8 wt.%, 0.85 wt.%, 0.9 wt.%, 0.95 wt.%, 1 wt.%, 1.8 wt.%, 2.2 wt.%, 2.6 wt.%, 3 wt.%, 3.4 wt.%, 3.8 wt.%, 4.2 wt.%, 4.6 wt.%, or 5 wt.%.

[0014] The weight percentage of the oxygen atoms in the oxygen-functionalised conductive carbon material may be from about 0.5 wt.% to about 20 wt.%, or from about 0.6 wt.% to about 20 wt.%, about 0.7 wt.% to about 20 wt.%, about 0.8 wt.% to about 20 wt.%, about 0.9 wt.% to about 20 wt.%, about 1 wt.% to about 20 wt.%, about 1.4 wt.% to about 20 wt.%, about 1.8 wt.% to about 20 wt.%, about 2.2 wt.% to about 20 wt.%, about 2.6 wt.% to about 20 wt.%, about 3 wt.% to about 20 wt.%, about 3.4 wt.% to about 20 wt.%, about 3.8 wt.% to about 20 wt.%, about 4.2 wt.% to about 20 wt.%, about 4.6 wt.% to about 20 wt.%, about 5 wt.% to about 20 wt.%, about 0.5 wt.% to about 18 wt.%, about 0.5 wt.% to about 17 wt.%, about 0.5 wt.% to about 16 wt.%, about 0.5 wt.% to about 14 wt.%, about 0.5 wt.% to about 12 wt.%, about 0.5 wt.% to about 11 wt.%, about 0.5 wt.% to about 9.5 wt.%, about 0.5 wt.% to about 8 wt.%, about 0.5 wt.% to about 6.5 wt.%, about 0.5 wt.% to about 5 wt.%, about 1 wt.% to about 5 wt.%, about 1.8 wt.% to about 5 wt.%, about 2.6 wt.% to about 5 wt.%, about 3.4 wt.% to about 5 wt.%, about 4.2 wt.% to about 5 wt.%, about 1 wt.% to about 4.2 wt.%, about 1 wt.% to about 3.4 wt.%, about 1 wt.% to about 2.6 wt.%, or about 1 wt.% to about 1.8 wt.%. It may be greater than or equal to about 0.5 wt.%, 0.55 wt.%, 0.6 wt.%, 0.65 wt.%, 0.7 wt.%, 0.75 wt.%, 0.8 wt.%, 0.85 wt.%, 0.9 wt.%, 0.95 wt.%, 1 wt.%, 1.4 wt.%, 1.8 wt.%, 2.2 wt.%, or 2.6 wt.%. It may be less than or equal to about 20 wt.%, 18 wt.%, 17 wt.%, 16 wt.%, 14 wt.%, 12 wt.%, 11 wt.%, 9.5 wt.%, 8 wt.%, 6.5 wt.%, 5 wt.%, 4.6 wt.%, 4.2 wt.%, 3.8 wt.%, or 3.4 wt.%. In certain embodiments, it may be, for example, about 0.5 wt.%, 0.55 wt.%, 0.6 wt.%, 0.65 wt.%, 0.7 wt.%, 0.75 wt.%, 0.8 wt.%, 0.85 wt.%, 0.9 wt.%, 0.95 wt.%, 1 wt.%, 1.2 wt.%, 1.4 wt.%, 1.6 wt.%, 1.8 wt.%, 2 wt.%, 2.2 wt.%, 2.4 wt.%, 2.6 wt.%, 2.8 wt.%, 3 wt.%, 3.2 wt.%, 3.4 wt.%, 3.6 wt.%, 3.8 wt.%, 4 wt.%, 4.2 wt.%, 4.4 wt.%, 4.6 wt.%, 4.8 wt.%, 5 wt.%, 8 wt.%, 9.5 wt.%,11 wt.%, 12 wt.%, 14 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, or 20 wt.%. In certain embodiments, the oxygen-functionalized conductive carbon material comprises from about 0.5 wt.% to about 15 wt.% of oxygen atoms, from about 1 wt.% to about 10 wt.% of oxygen atoms, from about 1 wt.% to about 5 wt.% of oxygen atoms, or about 2 wt.% of oxygen atoms, based on the total weight of the oxygen-functionalised conductive carbon material.

[0015] The oxygen-functionalised conductive carbon may be selected from the group consisting of oxygen functionalized carbon black, graphene, carbon nanotube, carbon fiber, and graphite. In certain embodiments, the oxygen-functionalised conductive carbon material comprises reduced graphene oxide.

[0016] In certain embodiments, the oxygen-functionalised conductive carbon material comprises reduced graphene oxide (rGO). The reduced graphene oxide may be an annealed graphene oxide which has been annealed at a temperature which may be from about 300 ºC to about 1500 ºC, or from about 340 ºC to about 1500 ºC, about 380 ºC to about 1500 ºC, about 420 ºC to about 1500 ºC, about 460 ºC to about 1500 ºC, about 500 ºC to about 1500 ºC, about 550 ºC to about 1500 ºC, about 600 ºC to about 1500 ºC, about 650 ºC to about 1500 ºC, about 700 ºC to about 1500 ºC, about 750 ºC to about 1500 ºC, about 800 ºC to about 1500 ºC, about 850 ºC to about 1500 ºC, about 900 ºC to about 1500 ºC, about 950 ºC to about 1500 ºC, about 1000 ºC to about 1500 ºC, about 300 ºC to about 1400 ºC, about 300 ºC to about 1400 ºC, about 300 ºC to about 1400 ºC, about 300 ºC to about 1300 ºC, about 300 ºC to about 1200 ºC, about 300 ºC to about 1200 ºC, about 300 ºC to about 1200 ºC, about 300 ºC to about 1100 ºC, about 300 ºC to about 1000 ºC, about 300 ºC to about 1000 ºC, about 500 ºC to about 1000 ºC, about 600 ºC to about 1000 ºC, about 700 ºC to about 1000 ºC, about 800 ºC to about 1000 ºC, about 900 ºC to about 1000 ºC, about 500 ºC to about 900 ºC, about 500 ºC to about 800 ºC, about 500 ºC to about 700 ºC, or about 500 ºC to about 600 ºC. It may be greater than or equal to about 300 ºC, 320 ºC, 340 ºC, 360 ºC, 380 ºC, 400 ºC, 420 ºC, 440 ºC, 460 ºC, 480 ºC, 500 ºC, 550 ºC, 600 ºC, 650 ºC, or 700 ºC. It may be less than or equal to about 1500 ºC, 1400 ºC, 1400 ºC, 1400 ºC, 1300 ºC, 1200 ºC, 1200 ºC, 1200 ºC, 1100 ºC, or 1000 ºC. In certain embodiments, it may be, for example, about 300 ºC, 320 ºC, 340 ºC, 360 ºC, 380 ºC, 400 ºC, 420 ºC, 440 ºC, 460 ºC, 480 ºC, 500 ºC, 520 ºC, 550 ºC, 580 ºC, 600 ºC, 620 ºC, 650 ºC, 680 ºC, 700 ºC, 720 ºC, 750 ºC, 780 ºC, 800 ºC, 820 ºC, 850 ºC, 880 ºC, 900 ºC, 920 ºC, 950 ºC, 980 ºC, 1000 ºC, 1100 ºC, 1200 ºC, 1300 ºC, 1400 ºC, or 1500 ºC. In certain embodiments, the reduced graphene oxide is an annealed reduced graphene oxide which has been annealed at a temperature of from about 300 ºC to about 1500 ºC, from about 300 ºC to about 1200 ºC, from about 500 ºC to about 1100 ºC, or about 1000 ºC. The annealed reduced graphene oxide may have been annealed for a time offrom about 30 min to about 5 h, or from about 45 min to about 5 h, about 1 h to about 5 h, about 1.3 h to about 5 h, about 1.5 h to about 5 h, about 1.6 h to about 5 h, about 1.8 h to about 5 h, about 2 h to about 5 h, about 2.2 h to about 5 h, about 2.4 h to about 5 h, about 2.6 h to about 5 h, about 2.8 h to about 5 h, about 30 min to about 4.8 h, about 30 min to about 4.6 h, about 30 min to about 4.3 h, about 30 min to about 4.1 h, about 30 min to about 3.9 h, about 30 min to about 3.7 h, about 30 min to about 3.4 h, about 30 min to about 3.2 h, about 30 min to about 3 h, about 30 min to about 2.8 h, about 53 min to about 2.8 h, about 1.3 h to about 2.8 h, about 1.6 h to about 2.8 h, about 2 h to about 2.8 h, about 2.4 h to about 2.8 h, about 53 min to about 2.4 h, about 53 min to about 2 h, about 53 min to about 1.6 h, or about 53 min to about 1.3 h. It may be greater than or equal to about 30 min, 40 min, 50 min, 1 h, 1.3 h, 1.5 h, or 1.6 h. It may be less than or equal to about 5 h, 4 h, 3 h, 2.5 h, or 2 h. In certain embodiments, it may be, for example, about 30 min, 35 min, 45 min, 50 min, 1 h, 1.2 h, 1.5 h, 2 h, 2.5 h, 3 h, 4 h, or 5 h. In certain embodiments, the annealed reduced graphene oxide has been annealed for at least about 30 minutes or at least about 1 hour, in an inert atmosphere.

[0017] The weight percentage of the oxygen-functionalised conductive carbon material based on the total cathode weight may be from about 1 wt.% to about 15 wt.%, or from about 1.9 wt.% to about 15 wt.%, about 2.8 wt.% to about 15 wt.%, about 3.7 wt.% to about 15 wt.%, about 4.6 wt.% to about 15 wt.%, about 5.5 wt.% to about 15 wt.%, about 6.4 wt.% to about 15 wt.%, about 7.3 wt.% to about 15 wt.%, about 8.2 wt.% to about 15 wt.%, about 9.1 wt.% to about 15 wt.%, about 10 wt.% to about 15 wt.%, about 1 wt.% to about 14 wt.%, about 1 wt.% to about 13 wt.%, about 1 wt.% to about 12 wt.%, about 1 wt.% to about 11 wt.%, about 1 wt.% to about 10 wt.%, about 2.8 wt.% to about 10 wt.%, about 4.6 wt.% to about 10 wt.%, about 6.4 wt.% to about 10 wt.%, about 8.2 wt.% to about 10 wt.%, about 1 wt.% to about 8.2 wt.%, about 1 wt.% to about 6.4 wt.%, about 1 wt.% to about 4.6 wt.%, or about 1 wt.% to about 2.8 wt.%. It may be greater than or equal to about 1 wt.%, 1.9 wt.%, 2.8 wt.%, 3.7 wt.%, or 4.6 wt.%. It may be less than or equal to about 15 wt.%, 14 wt.%, 13 wt.%, 12 wt.%, 11 wt.%, 10 wt.%, 9.1 wt.%, 8.2 wt.%, 7.3 wt.%, or 6.4 wt.%. In certain embodiments, it may be, for example, about 1 wt.%, 1.4 wt.%, 1.9 wt.%, 2.4 wt.%, 2.8 wt.%, 3.2 wt.%, 3.7 wt.%, 4.2 wt.%, 4.6 wt.%, 5 wt.%, 5.5 wt.%, 6 wt.%, 6.4 wt.%, 6.8 wt.%, 7.3 wt.%, 7.8 wt.%, 8.2 wt.%, 8.6 wt.%, 9.1 wt.%, 9.6 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, or 15 wt.%.

[0018] In certain embodiments, the cathode active material comprises one or more selected from the group consisting of lithium nickel manganese cobalt oxides, lithium manganese oxides, lithium nickel manganese oxides, lithium iron phosphates, lithium manganese iron phosphates, and doped and / or substituted and / or coated variants thereof, optionally which are doped and / orsubstituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca. In certain embodiments, the cathode active material is a lithium nickel manganese cobalt oxide (NMC) cathode active material, which is optionally doped and / or substituted and / or coated, optionally which is doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

[0019] In certain embodiments, the NMC cathode active material has the general formula: LiNixMnyCo1-x-yO2, wherein x and y are independently between 0 and 1. In certain embodiments, x is from about 0.05 to about 0.5, or about 0.1 to about 0.4, or about 0.2 to about 0.4; and y is from about 0.05 to about 0.5, or about 0.1 to about 0.4, or about 0.2 to about 0.4.

[0020] In certain embodiments, the NMC cathode active material comprises one or more selected from the group consisting of LiNi1 / 3Mn1 / 3Co1 / 3O2 (NMC111) LiNi0.5Mn0.3Co0.2O2 (NMC532), LiNi0.6Mn0.2Co0.2O2 (NMC622), and LiNi0.8Mn0.1Co0.1O2 (NMC811), each of which is optionally doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca. In certain embodiments, the NMC cathode active material comprises LiNi1 / 3Mn1 / 3Co1 / 3O2 (NMC111), optionally which is doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

[0021] The weight percentage of the cathode active material based on the total cathode weight may be from about 50 wt.% to about 95 wt.%, or from about 55 wt.% to about 95 wt.%, about 60 wt.% to about 95 wt.%, about 65 wt.% to about 95 wt.%, about 65 wt.% to about 90 wt.%, about 60 wt.% to about 90 wt.%, about 55 wt.% to about 90 wt.%, about 50 wt.% to about 90 wt.%, about 50 wt.% to about 85 wt.%, about 55 wt.% to about 85 wt.%, about 60 wt.% to about 85 wt.%, about 65 wt.% to about 85 wt.%, about 65 wt.% to about 90 wt.%, about 70 wt.% to about 90 wt.%, about 75 wt.% to about 90 wt.%, about 80 wt.% to about 90 wt.%, about 50 wt.% to about 89 wt.%, about 50 wt.% to about 88 wt.%, about 60 wt.% to about 80 wt.%, or about 70 wt.% to about 80 wt.%. It may be greater than or equal to about 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, or 70 wt.%. It may be less than or equal to about 95 wt.%, 95 wt.%, 85 wt.%, 80 wt.%, or 75 wt.%. In certain embodiments, it may be, for example, about 50 wt.%, 52 wt.%, 55 wt.%, 58 wt.%, 60 wt.%, 62 wt.%, 65 wt.%, 68 wt.%, 70 wt.%, 72 wt.%, 75 wt.%, 78 wt.%, 80 wt.%, 82 wt.%, 83 wt.%, 84 wt.%, 85 wt.%, 86 wt.%, 87 wt.%, 88 wt.%, 89 wt.%, 90 wt.%, or 95 wt.%.

[0022] In certain embodiments, the sulfide-containing inorganic solid electrolyte material comprises one or more selected from the group consisting of lithium phosphorous sulfides, lithium phosphorous sulfide halogens, and lithium metal phosphorous sulfides. In certainembodiments, the sulfide-containing inorganic solid electrolyte material comprises one or more selected from the group consisting of Li3PS4 and Li6PS5Cl.

[0023] The sulfide-containing inorganic solid electrolyte material may comprises particles having a particle size distribution d50 of from about 100 nm to about 20 µm, or from about 120 nm to about 20 µm, about 140 nm to about 20 µm, about 160 nm to about 20 µm, about 180 nm to about 20 µm, about 200 nm to about 20 µm, about 1.2 µm to about 20 µm, about 2.2 µm to about 20 µm, about 3.1 µm to about 20 µm, about 4.1 µm to about 20 µm, about 5.1 µm to about 20 µm, about 6.1 µm to about 20 µm, about 7.1 µm to about 20 µm, about 8 µm to about 20 µm, about 9 µm to about 20 µm, about 10 µm to about 20 µm, about 100 nm to about 19 µm, about 100 nm to about 18 µm, about 100 nm to about 17 µm, about 100 nm to about 16 µm, about 100 nm to about 15 µm, about 100 nm to about 14 µm, about 100 nm to about 13 µm, about 100 nm to about 12 µm, about 100 nm to about 11 µm, about 100 nm to about 10 µm, about 200 nm to about 10 µm, about 2.2 µm to about 10 µm, about 4.1 µm to about 10 µm, about 6.1 µm to about 10 µm, about 8 µm to about 10 µm, about 200 nm to about 8 µm, about 200 nm to about 6.1 µm, about 200 nm to about 4.1 µm, or about 200 nm to about 2.2 µm. It may be greater than or equal to about 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 1.2 µm, 2.2 µm, 3.1 µm, or 4.1 µm. It may be less than or equal to about 20 µm, 19 µm, 18 µm, 17 µm, 16 µm, 15 µm, 14 µm, 13 µm, 12 µm, 11 µm, 10 µm, 9 µm, 8 µm, 7.1 µm, or 6.1 µm. In certain embodiments, it may be, for example, about 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 690 nm, 1.2 µm, 1.7 µm, 2.2 µm, 2.7 µm, 3.1 µm, 3.6 µm, 4.1 µm, 4.6 µm, 5.1 µm, 5.6 µm, 6.1 µm, 6.6 µm, 7.1 µm, 7.6 µm, 8 µm, 8.5 µm, 9 µm, 9.5 µm, 10 µm, 12 µm, 13 µm, 14 µm, 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, or 20 µm. In certain embodiments, the sulfide-containing inorganic solid electrolyte material comprises particles having a particle size distribution d50of from about 0.1 µm to about 10 µm, from about 0.5 µm to about 2 µm, or about 1 µm.

[0024] The weight percentage of the sulfide-containing inorganic solid electrolyte material based on the total cathode weight may be from about 3 wt.% to about 50 wt.%, or from about 6 wt.% to about 50 wt.%, about 7 wt.% to about 50 wt.%, about 8 wt.% to about 50 wt.%, about 9 wt.% to about 50 wt.%, about 10 wt.% to about 50 wt.%, about 14 wt.% to about 50 wt.%, about 18 wt.% to about 50 wt.%, about 22 wt.% to about 50 wt.%, about 26 wt.% to about 50 wt.%, about 30 wt.% to about 50 wt.%, about 34 wt.% to about 50 wt.%, about 38 wt.% to about 50 wt.%, about 42 wt.% to about 50 wt.%, about 46 wt.% to about 50 wt.%, about 3 wt.% to about 55 wt.%, about 3 wt.% to about 50 wt.%, about 3 wt.% to about 40 wt.%, about 5 wt.% to about 45 wt.%, about 5 wt.% to about 40 wt.%, about 10 wt.% to about 50 wt.%, about 18 wt.% toabout 50 wt.%, about 26 wt.% to about 50 wt.%, about 34 wt.% to about 50 wt.%, about 42 wt.% to about 50 wt.%, about 10 wt.% to about 42 wt.%, about 10 wt.% to about 34 wt.%, about 10 wt.% to about 26 wt.%, or about 10 wt.% to about 18 wt.%. It may be greater than or equal to about 3 wt.%, 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, 7.5 wt.%, 8 wt.%, 8.5 wt.%, 9 wt.%, 9.5 wt.%, 10 wt.%, 14 wt.%, 18 wt.%, 22 wt.%, or 26 wt.%. It may be less than or equal to about 50 wt.%, 45 wt.%, 42 wt.%, 38 wt.%, or 34 wt.%. In certain embodiments, it may be, for example, about 3 wt.%, 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, 7.5 wt.%, 8 wt.%, 8.5 wt.%, 9 wt.%, 9.5 wt.%, 10 wt.%, 12 wt.%, 14 wt.%, 16 wt.%, 18 wt.%, 20 wt.%, 22 wt.%, 24 wt.%, 26 wt.%, 28 wt.%, 30 wt.%, 32 wt.%, 34 wt.%, 36 wt.%, 38 wt.%, 40 wt.%, 42 wt.%, 44 wt.%, 46 wt.%, 48 wt.%, or 50 wt.%.

[0025] In certain embodiments, the mass ratio of cathode active material to the sulfide-containing inorganic solid electrolyte material is from about 55:45 to about 95:05, or about 70:30.

[0026] In certain embodiments, the mass ratio of the sum of the cathode active material and the sulfide-containing inorganic solid electrolyte material, to the oxygen-functionalised conductive carbon material, is from about 100:20 to about 100:1, from about 100:10 to about 100:2, or about 100:6.

[0027] In certain specific embodiments, the cathode comprises: from about 1 wt.% to about 15 wt.%, or about 1 wt.% to about 10 wt.%, or from about 2 wt.% to about 8 wt.%, or from about 5 wt.% to about 7 wt.%, or about 5.7 wt.%, of the oxygen-functionalised conductive carbon material, optionally reduced graphene oxide, optionally reduced graphene oxide having a weight percentage of oxygen of from about 0.5 wt.% to about 20 wt.%, or from about 0.6 wt.% to about 20 wt.%, about 0.7 wt.% to about 20 wt.%, about 0.8 wt.% to about 20 wt.%, about 0.9 wt.% to about 20 wt.%, about 1 wt.% to about 20 wt.%, about 1.4 wt.% to about 20 wt.%, about 1.8 wt.% to about 20 wt.%, about 2.2 wt.% to about 20 wt.%, about 2.6 wt.% to about 20 wt.%, about 3 wt.% to about 20 wt.%, about 3.4 wt.% to about 20 wt.%, about 3.8 wt.% to about 20 wt.%, about 4.2 wt.% to about 20 wt.%, about 4.6 wt.% to about 20 wt.%, about 5 wt.% to about 20 wt.%, about 0.5 wt.% to about 18 wt.%, about 0.5 wt.% to about 17 wt.%, about 0.5 wt.% to about 16 wt.%, about 0.5 wt.% to about 14 wt.%, about 0.5 wt.% to about 12 wt.%, about 0.5 wt.% to about 11 wt.%, about 0.5 wt.% to about 9.5 wt.%, about 0.5 wt.% to about 8 wt.%, about 0.5 wt.% to about 6.5 wt.%, about 0.5 wt.% to about 5 wt.%, about 1 wt.% to about 5 wt.%, about 1.8 wt.% to about 5 wt.%, about 2.6 wt.% to about 5 wt.%, about 3.4 wt.% to about 5 wt.%, about 4.2 wt.% to about 5 wt.%, about 1 wt.% toabout 4.2 wt.%, about 1 wt.% to about 3.4 wt.%, about 1 wt.% to about 2.6 wt.%, or about 1 wt.% to about 1.8 wt.%; from about 3 wt.% to about 50 wt.%, or about 5 wt.% to about 50 wt.%, or from about 20 wt. % to about 40 wt. %, or from about 25 wt.% to about 35 wt. %, or about 28.3 wt.%, of the sulfide-containing inorganic solid electrolyte material; and from about 50 wt.% to about 95 wt. %, or from about 50 wt.% to about 80 wt.%, or from about 60 wt.% to about 70 wt.%, or about 66 wt.%, of the cathode active material.

[0028] In certain specific embodiments, the cathode comprises: from about 1 wt.% to about 15 wt.%, or about 1 wt.% to about 10 wt.%, or from about 2 wt.% to about 8 wt.%, or from about 5 wt.% to about 7 wt.%, or about 5.7 wt.%, of reduced graphene oxide; from about 3 wt.% to about 50 wt.%, or about 5 wt.% to about 50 wt.%, or from about 20 wt. % to about 40 wt. %, or from about 25 wt.% to about 35 wt. %, or about 28.3 wt.%, of Li6PS5Cl; and from about 50 wt.% to about 95 wt. %, or from about 50 wt.% to about 80 wt.%, or from about 60 wt.% to about 70 wt.%, or about 66 wt.%, of NMC111.

[0029] In a second aspect of the invention there is provided a battery, comprising the cathode according to the first aspect.

[0030] The following options may be used in conjunction with the second aspect, either individually or in any combination.

[0031] In certain embodiments, the battery is an all-solid state lithium battery. The all-solid state lithium battery may comprise a cathode, and anode and a solid electrolyte. The anode may be, for example, a LixIn anode wherein x is from about 0.5 to about 1.

[0032] In certain embodiments, the battery comprises an electrolyte region distinct from the cathode, wherein said electrolyte region comprises a sulfide-containing inorganic solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The patent or application file contains at least one drawing executed in colour. Copies of this patent or patent application publication with colour drawings will be provided by the Office upon request and payment of the necessary fee (if appropriate).

[0034] Figure 1: Room temperature (22°C) galvanostatic cycling of the NMC111 ASSLB cells with different carbon additives. (a) Cycling performance of Li0.5In|Li6PS5Cl|NMC111 cells with different carbon additives measured at a 0.1 C (15 mA g-1) current rate in 2.0-3.7 V (vs. Li0.5In) window with an average CAM Loading ~10-12 mg cm-2. The first cycle Coulombic efficiency is shown in Table 2. The color coding for the different carbon additive-based samples is noted above the figure. Cell voltage profiles at selected cycles are shown here for (b) Super-P and (c) rGO-1000. The difference in initial polarisation behavior for the first two cycles is highlighted in the corresponding figure inset. (d) The corresponding cumulative inefficiency plot for the ASSLBs is represented with an identical color scheme.

[0035] Figure 2: X-ray photoelectron spectroscopy (XPS) investigation of the cathode interphases. Cathode composites with different carbon additives were probed by XPS before and after (25 cycles) cycling. The left panel represents the sulfur (S) 2p region, and the right panel depicts the phosphorus (P) 2p region. For the S 2p region, the pristine and cycled samples are indicated by Super-P (a, b); rGO-1000 (c, d); rGO-600 (e, f), and rGO-200 (g, h), respectively. Similarly, for the P 2p region, the corresponding samples are represented as Super-P (i, j); rGO- 1000 (k, l); rGO-600 (m, n); and rGO-200 (o, p), respectively. In the fitted XPS spectra, black data points = experimental data, red line = overall fitted data, other shaded regions = fitted individual components as indicated in (a, b) for the S 2p region and in (c, d) for the P 2p region.

[0036] Figure 3: ToF-SIMS investigation of the nature and origin of the CEI and CnEI. ToF- SIMS spectra for negatively charged fragments representing the cathode composite before and after cycling (25 cycles) in a Li0.5In|Li6PS5Cl|NMC111 ASSLB cell with the different carbon additives (Super-P, rGO-200, and rGO-1000) at room temperature. The fragments present here are: (a) NiS- and (b) NiSO- representing the CAM particle surface degradation; (c) LiPO2- and (d) LiSO2- representing Li6PS5Cl interface degradation; (e) SOC- and (f) S2CO-, SO2CO- / SOCO2- representing carbon-SE interface degradation. Three mass spectra were measured for each sample, as represented by three spectral lines, to confirm the observation.

[0037] Figure 4: Probing cathode interfacial evolution by in situ EIS. Distribution of relaxation time (DRT) evolution as calculated from the Nyquist EIS data for Li0.5In|Li6PS5Cl|NMC111 ASSLB cells, collected in situ in the discharged or 0% SOC (100% DOD) state over 100 cycles during 0.1 C constant current cycling with: (a) Super-P, (b) rGO-1000, (c) rGO-600 and (d) rGO-200 as the carbon additive in the cathode. The corresponding 3D evolution of the PCathode-MF region is shown in (e-h), and the PCathode-LF region is shown in (i-l).

[0038] Figure 5: Impact of the stable vs degrading CEI on long-term and high-temperature cycling. (a) Comparison of the Li0.5In|Li6PS5Cl|NMC111 ASSLB galvanostatic cycling stabilitybetween Super-P and rGO-1000 based cathode at a 1 C rate at 60°C with an active NMC loading of ~10-12 mg cm-2. (b) The corresponding capacity retention and cumulative inefficiency plots and (c, d) corresponding charge-discharge profiles every 10 cycles from the 1stto 100thcycle. (e) Nyquist impedance profile before and after cycling. Rate-capability of Li0.5In| Li6PS5Cl|NMC111 ASSB cells with (f) Super-P and (g) rGO-1000 based cathode at 60°C. (h) Long-term cycling stability at a 4C (600 mA / g) rate for 60°C temperature for Li0.5In |Li6PS5Cl |NMC111 cell with rGO-1000 and rGO-600 based cathode.

[0039] Figure 6: Working principle and comparison of performance. (a) Scheme illustrating the CEI evolution for bare and surface oxygen functionalized conductive carbon in Li6PS5Cl (sulfide) SE-based all-solid-state battery cathode. (b) Comparison of the capacity retention (%) and cycle life for the rGO-1000 based cathode with other CEI modifications for sulfide SE-based (Li3PS4,Li6PS5Cl, LGPS etc.) ASSBs with high-voltage transition metal cathodes (LCO, NMC etc.). The asterisk (*) marked works represent the modification solely on conductive additives, whereas the rest of the works represent protective surface coating on cathode particles as a strategy for modifications. Table 4 provides the data represented in the figure. The rGO-1000 data in (b) incorporates some room temperature cycling data presented in Figure 24.

[0040] Figure 7: (a- e) Ex situ Raman spectra of various carbon additives. The x (bottom) axis corresponds to the Raman shift in wavenumber (cm-1) as noted in the figure. One notable observation is that rGO samples display strong Raman scattering and better signal-to-noise ratio owing to the surface-enhanced Raman scattering. Furthermore, the D band intensity first decreases with annealing temperature but again increases for the 1000°C annealed sample owing to the formation of carbon vacancies. (f) C, H, N, S, O composition analysis of the various carbon additives used in this study. As expected, the oxygen content decreases with increasing annealing temperature, and the observed values are consistent with other reports.

[0041] Figure 8: Carbon 1s XPS spectra for different carbon additives: a) Super-P, b) rGO-200, c) rGO-600 and d) rGO-1000. In the fitted XPS spectra, gray data points = experimental data, red line = overall fitted data, other shaded regions = fitted individual components as indicated on the top panel of the figure. The comparison of relative contributions of Carbon 1s components for e) C=C or sp2carbon; f) C-C / C-H sp3carbon; g) sum of all C-O components; h) individual C-O components. The evolution of the nature of the functional group on the rGO is consistent with other studies. Upon 1000°C annealing, the oxygen on rGO is predominantly carbonyl (C=O) and ether (C-O-C) types.

[0042] Figure 9: Powder X-ray diffraction (XRD) pattern for a) Li6PS5Cl sourced from Ampcera® (MSE Supplies) b) as obtained NMC 111 (MSE Supplies), c) NMC 111 after 24 hrs drying at 200°C under vacuum, d) pelletized composite with the composition of NMC111 (70): Li6PS5Cl (30): Super-P (6), where the number in parentheses represents the corresponding weight% or weight ratio.

[0043] Figure 10: Powder XRD powder pattern for pelletized composite with the composition of NMC111 (70): Li6PS5Cl (30): Carbon (6), for different carbon additives: a) Super-P, b) rGO- 200, c) rGO-600 and d) rGO-1000, where the number in parentheses represents the corresponding weight% or weight ratio.

[0044] Figure 11: Cycling performance of a representative Li|LiPF6(EC:DMC)|NMC111 coin cell (type 2032, Al current collector for the cathode side) at different C-rate (0.1C, 0.2C, 0.3C, 1C, 2C), where 1C= 150 mAh g-1, within 2.7-4.3 V (vs. Li) voltage window at room temperature (22oC) with a CAM Loading of 3.5 mg cm-2.

[0045] Figure 12: Galvanostatic polarization profiles of Li0.5In|Li6PS5Cl|NMC111 ASSLB cells at selected cycles at a 0.1C rate for a) rGO-600 and b) rGO-200 based cathode. The difference in initial polarisation behavior for the first two cycles is highlighted in the corresponding figure inset.

[0046] Figure 13: Comparison of three statistical parameters with the possibility of correlating progress in degradation with cell electrochemical irreversibility, i.e. Coulombic efficiency (%): (a) Summation of Efficiency (y-axis plotted at a logarithmic distance); (b) Running Average Efficiency (%), (c) Cumulative Inefficiency.

[0047] Figure 14: X-ray photoelectron spectra (XPS) comparing the O 1s binding energy of the cathode composite before and after cycling (25 cycles) in Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with different carbon additives. The pristine and cycled samples are designated as Super-P (a, b), rGO-1000 (c, d), rGO-600 (e, f) and rGO-200 (g, h), respectively.

[0048] Figure 15: ToF-SIMS spectra for negatively charged fragments representing the cathode composite before and after cycling (25 cycles) in Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with the different carbon additives (Super-P, rGO-200, rGO-600, and rGO-1000). The figure shows the evolution of the CAM particle surface degradation product: a) NiS2- and b) MnS2-.

[0049] Figure 16: ToF-SIMS spectra for negatively charged fragments representing the cathode composite before and after cycling (25 cycles) in Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with the different carbon additives (Super-P, rGO-200, rGO-600, and rGO-1000). The figureshows the evolution of a) MnS- and b) MnSO- representing the CAM particle surface degradation product.

[0050] Figure 17: ToF-SIMS spectra for negatively charged fragments representing the cathode composite before and after cycling (25 cycles) in Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with the rGO-600 as the carbon additive. Evolution of the fragment a) NiS- and b) NiSO- correspond to the CAM particle surface degradation; c) LiPO2-, d) LiSO2- fragment represents Li6PS5Cl interface degradation; e) SOC-, f) S2CO-, SO2CO- / SOCO2- represent carbon-SE interface.

[0051] Figure 18: ToF-SIMS spectra for negatively charged fragments representing the cathode composite before and after cycling (25 cycles) in Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with the different carbon additives (Super-P, rGO-200, rGO-600, and rGO-1000). The figure shows the evolution of the CAM-SE interfacial degradation product: a) LiS2- and b) LiS-.

[0052] Figure 19: Nyquist impedance evolution of Li0.5In|Li6PS5Cl|NMC111 ASSB cells with the different carbon additives during 0.1 C rate constant current rate cycling at room temperature. EIS was recorded in the discharged state or at 0% SOC every 10 cycles over 100 cycles to probe the evolution of the CEI contribution. Cells were probed with a) Super-P, b) rGO-1000, c) rGO-600 and d) rGO-200 as the carbon additive in the cathode.

[0053] Figure 20: (a) DRT evolution of a representative Li0.5In|Li6PS5Cl|NMC111 ASSLB cell with rGO-1000 carbon in the cathode composite during cycling at 0.1C at room temperature (22°C). Temperature dependence of the DRT evolution for the two symmetric configurations: (b) Li0.5In|Li6PS5Cl|Li0.5In and (c) NMC111+Li6PS5Cl|Li6PS5Cl|NMC111+Li6PS5Cl. The DOD / SOC dependence of the DRT evolution of PCathode-MF, PCathode-LF regions for (d, e) rGO- 1000 and (f, g) Super-P conductive additive-based Li0.5In|Li6PS5Cl|NMC111 cell during discharge at a 0.1 C equivalent current rate.

[0054] Figure 21: Comparison of cycling-stability of Li0.5In|Li6PS5Cl| NMC111 ASSLB cells with rGO-1000 measured at different constant current rates within 2.0-3.7 V (w.r.t. Li0.5In) voltage window at elevated temperature (60°C) with an average CAM Loading ~10-12 mg cm-2: a) 1 C (150 mA g-1); b) 8 C (1200 mA g-1).

[0055] Figure 22: (a) Comparison of the Li0.5In|Li6PS5Cl|NMC111 ASSLB cell galvanostatic cycling stability between Super-P and rGO-600 based cathode at a 1 C rate at 60oC with an active NMC loading of ~10-12 mg cm-2. (b) The corresponding capacity retention and cumulative inefficiency plots, (c) corresponding charge-discharge profiles every 10 cycles from the 1stto 100thcycle, and (d) the corresponding rate capability.

[0056] Figure 23: Li0.5In|Li6PS5Cl|NMC111 ASSLB cell galvanostatic cycling data for the carbon free NMC cathode composite. The cell was cycled at a 1 C rate at 60oC with an active NMC loading of ~10-12 mg cm-2. All other conditions are identical to the rest of the cells.

[0057] Figure 24: Comparison of cycling-stability of Li0.5In|Li6PS5Cl|NMC111 ASSLB cells with rGO-1000 measured at different constant current rates within 2.0-3.7 V (w.r.t. Li0.5In) voltage window at room -temperature (22°C) with an average CAM Loading ~10-12 mg cm-2: a) 0.2 C (30 mA g-1); b) 0.5 C (75 mA g-1). DEFINITIONS

[0058] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting.

[0059] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

[0060] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process or method.

[0061] The transitional phrase “consisting of” excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consisting of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0062] The transitional phrase “consisting essentially of” is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting essentially of” occupies a middle ground between “comprising” and “consisting of”.

[0063] Where applicants have defined an invention or a portion thereof with an open-ended term such as “comprising”, it should be readily understood that (unless otherwise stated) the description should be interpreted to also describe such an invention using the terms “consisting essentially of” or “consisting of”. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of” or, alternatively, by “consisting essentially of”.

[0064] Other than in the claims or operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention.

[0065] In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”.

[0066] The terms “predominantly”, “predominant”, and “substantially” as used herein shall mean comprising more than 50% by weight, unless otherwise indicated.

[0067] As used herein, with reference to numbers in a range of numerals, the terms “about,” “approximately” and “substantially” are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth.

[0068] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0069] As used herein, the term “oxygen functionalized conductive carbon material” means a material which predominantly comprises carbon, has a conductivity of at least about 0.1 S / cm, and includes oxygen containing functional groups such that its oxygen content is at least about 0.5 wt.%. In certain embodiments “oxygen functionalized conductive carbon material” may comprise at least about 50 wt.%, 60 wt.%, 70 wt.%, or 80 wt.% carbon.

[0070] As used herein, the term “cathode active material” means a material which is capable of being the active component of a cathode in an all-solid state lithium battery. That is, a material which is reduced when used in the cathode of an all-solid state lithium battery during its discharge. Examples of cathode active materials include, but are not limited to, lithium nickel manganese cobalt oxides, lithium manganese oxides, lithium nickel manganese oxides, lithium iron phosphates, lithium manganese iron phosphates, and doped and / or substituted and / or coated variants thereof.

[0071] As used herein, the term “all-solid state lithium battery” means a lithium battery composed of all non-liquid components, in particular having a solid or substantially solid electrolyte.

[0072] As used herein, the term “sulfide-containing inorganic solid electrolyte material” means an inorganic non-liquid material containing a sulfide which is suitable for use as an electrolyte in an all-solid state lithium battery. Examples of sulfide-containing inorganic solid electrolyte materials include, but are not limited to, lithium phosphorous sulfides, lithium phosphorous sulfide halogens, and lithium metal phosphorous sulfides. ABBREVIATIONS

[0073] All-solid-state lithium batteries (ASSLBs); cathode active material (CAM); cathode- electrolyte interface (CEI); interphase at the oxygen-functionalised conductive carbon-solid electrolyte interface (CnEI); distribution of relaxation time (DRT); electrochemical impedance spectroscopy (EIS); Li-ion batteries (LIBs); solid electrolytes (SEs); lithium nickel manganese cobalt oxide (NMC), reduced graphene oxide (rGO); time of flight secondary ion mass spectrometry (ToF-SIMS); X-ray photoelectron spectra (XPS); X-ray diffraction (XRD).

[0074] Preferred features, embodiments and variations of the invention may be discerned from the following Examples which provides sufficient information for those skilled in the art to perform the invention. The following Examples are not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. EXAMPLES Experimental Section / Methods Materials

[0075] Li(Ni0.33Co0.33Mn0.33)O2or NMC 111 and Ampcera®Li6PS5Cl were purchased from MSE Supplies LLC (AZ, USA). Li6PS5Cl with a D50 value of 80 µm (150 mesh, bulk conductivity of 3-4 mS cm-1) was utilized as the bulk solid electrolyte or solid electrolyteseparator layer. Li6PS5Cl, with a D50 value of 1 µm exhibiting bulk conductivity in the range of 1.2-1.5 mS cm-1,was used for cathode composite preparation. Super P®(TIMCAL), widely used in the battery industry for its exceptional electronic conductivity, was selected as the reference carbon material. Meanwhile, rGO (provided by NiSiNa Materials, Japan ) was chosen as the source of functionalized carbon for the ease of controlling the extent of functional groups by thermal treatment. Preparation of Conductive Additives

[0076] To remove any residual surface oxygen functionalities, Super P was annealed at 1000oC for 1 hour with a 10°C min-1heating ramp under the 20 mL min-1argon flow in a tube furnace. Similarly, rGO was annealed at 200oC, 600oC, and 1000oC to create three variations of conductive additive with different surface functionalities and electronic conductivity. The goal was to design the highest surface functionalities and lowest extent of graphitization in the case of rGO annealed at 200 (termed as rGO-200) and the highest extent of graphitization and least amount of surface functionalities in rGO-1000. The rGO-600 exhibits a conductivity and surface functional group density between these two. Preparation of Cathode and Anode

[0077] NMC111 was vacuum dried at 200oC overnight in a Buc̈hi oven before use. X-ray diffraction and scanning electron microscopy were performed before and after the thermal pretreatment to confirm the phase purity and morphology of the NMC material. The cathode composite was prepared by hand grinding NMC111 with Li6PS5Cl in 70:30 weight ratio in an agate mortar.100 mg of this mixture was then ground with 6 mg of the carbon additive, resulting in the final composition of NMC111: 66 wt%, Li6PS5Cl: 28.3 wt% and Conductive additive: 5.7 wt%. LixIn (0.5<x<1) anode was prepared by pressing and rolling Li and In foils together. Uniform 100-150 μm thick and 8 mm diameter LixIn coins were punched out (average Li content of 1.5-2 mg) and used as the anode. Fabrication of the All-Solid-State Battery (ASSB) Cells

[0078] The ASSBs were fabricated inside an argon-filled glovebox maintained at H2O < 0.1 ppm and O2 < 1 ppm. An in-house designed cell (die internal diameter: diameter 12 + / - 0.02 mm) set-up was used, capable of applying the fixed assembly and stack pressure. To fabricate the cell, 90-100 mg of solid electrolyte (SE), i.e., Li6PS5Cl (150 mesh, D50~ 80 μm), was first uniaxially pressed at ~256 MPa for 1 minute to prepare the SE layer. Subsequently, 15-20 mg freshly prepared cathode composite was introduced on top of the SE and pressed under an uniaxial pressure of ~512 MPa for 1 minute. Finally, the LixIn coin was placed on the other sideof the SE layer to complete the electrode stack. Anode and cathode plungers fitted with O rings ensured hermetic sealing throughout the cell cycling. Cells were removed from the glove box and placed under an in-house designed compression jig and electrochemically cycled under a steady uniaxial stack pressure of 45-49 MPa. Electrochemical Cycling

[0079] Electrochemical testing was performed at room temperature (22 + / - 1oC) and an elevated temperature of 60oC using the VMP3 (BioLogic) electrochemical potentiostat / galvanostat. Some of the room-temperature galvanostatic cycling data were also collected on the LAND CT3002A battery cycler. Galvanostatic cycling was carried out with a charging voltage limit of 3.70 V (w.r.t. LixIn, where 0.5 ≤ x ≥ 1.0) and a discharge cut-off of 2.00 V (w.r.t. LixIn). EIS data was collected in the 1 MHz - 10 μHz frequency range by applying a 50 mV signal amplitude. The EIS spectra were analyzed and fitted using the EC Lab Zfit software package. For EIS measurement during cycling at 100% depth-of-discharge, cells were rested for 30 minutes before AC signal perturbation. Distribution of Relaxation Time (DRT) Analysis

[0080] The Python-based pyDRTtools software developed by Ciucci’s lab was utilized for the deconvolution of EIS data, employing second-order Gaussian radial basis functions (RBF) with shape factor control between 0.75 to 1.0 and a regularization parameter of 0.001. The RBFs are defined as RBFs used by pyDRTtools was ϕμ(x)=exp(-(μx)2), where ^^ = |ln τ- ln τ^^| and μ is the shape factor. A more detailed outlook of the method and its significance, along with the segment assignment, is provided at the end of the experimental section. Time-of-Flight Secondary-Ion Mass Spectrometry

[0081] Time-of-flight secondary ion mass spectrometry was performed with a TOF.SIMS 5 instrument (IONTOF GmbH) equipped with a 30 keV Bi3+cluster primary-ion gun for analysis down to 100 nm lateral resolution and Angstrom-resolution depth profiling (low energy cesium, oxygen, and argon-cluster ion beams for sputtering). Samples were transferred under an argon atmosphere, and the sample surface was cleaned with 1 keV Cs+sputter gun for 1 minute to eliminate contamination. All ToF-SIMS measurements were performed in negative ion mode to probe the chemical nature of the degradation products.

[0082] Bi3+ions with an energy of 30 keV were utilized as the primary-ion species, and the analysis area of (100 × 100) μm2was rasterized with the primary-ion dose-measuring limit of 1.66 × 1014ions cm-2to achieve equivalent measuring conditions. To confirm the reproducibilityof the results, three mass spectra were collected per sample from three distinct analysis areas while keeping all other parameters constant. X-ray photoelectron spectroscopy (XPS)

[0083] XPS data was collected using a Thermo Scientific™ ESCALAB™ 250Xi XPS Microprobe instrument. Monochromatic Al Kα radiation (1486.6 eV) with 120 W power was used as the radiation source for the analysis. The beam voltage was maintained at 13.8 kV. The beam spot size was 500 μm, and the chamber vacuum was maintained at lower than 2x10-9bar. All samples were transferred to the XPS vacuum chamber under an argon atmosphere and the sample surface was cleaned with an Ar+(1 keV) for 1 minute. All X-ray photoelectron (XP) spectra were calibrated with the binding energy value for Au 4f7 = 83.96 eV, Ag 3d5 = 368.21 eV, Cu2p3 = 932.62 eV w.r.t the binding energy reference of adventitious carbon at 284.8 eV. CasaXPS software was used to fit the obtained XPS spectra. For C 1s, O 2s, and P 2p spectra, a Shirley-type background was applied, while the S 2p spectra were fitted using a Touggard-type background. The fitting functions chosen were Gaussian-Lorentzian (GL) or Asymmetric Lorentzian (LA) lineshapes. Results and Discussion

[0084] In efforts to probe the influence of surface oxygen functionalized carbon, reduced graphene oxide (rGO) was chosen as a model carbon material due to its well-documented reproducibility in surface functional modifications under various annealing temperatures, which engineer both the electronic conductivity and the nature and content of the surface functional groups. Commercial rGO powder (provided by NiSiNa Materials, Japan) was annealed at three different temperatures, resulting in three distinct carbon additive materials labeled rGO-200, rGO-600, and rGO-1000, where numerical labels correspond to the annealing temperature. Higher-temperature annealing facilitated graphitization, improving electronic conductivity (Table 1), and reducing the prevalence of oxygen-containing surface functional groups (Figures 7-8) on the carbon. For example, the 1000°C annealed rGO displayed an electronic conductivity of ~2 S cm-1and an oxygen content of ~2 weight%. Furthermore, the evolution of the functional groups as a function of annealing temperature, e.g., predominant ether (C-O-C) and carbonyl (C=O) functionality (Figure 8), after 1000°C annealing was also consistent with previous studies.

[0085] Despite its moderate specific capacity, NMC111 was chosen as the CAM due to its unique atomic composition, characterized by equal proportions of Ni, Mn, and Co, and the well- documented susceptibility of high-nickel-containing NMCs to significant degradation, often attributed to the evolution of oxygen from the NMC lattice. The low nickel-containing NMCallowed the effective investigation of and ability to address interfacial degradation in the cathode resulting from facile electron percolation rendered by conductive carbon additives.

[0086] Conductive carbon Super-P, a leading carbon black applied in cathode composite formulations, was employed as the control conductive additive. Based on insights from a prior study, the commercially sourced Super-P was annealed at 1000°C under an argon atmosphere to remove any oxygen impurities or functionalities (Figure 7a). Prior to electrochemical performance evaluation, the chemical and phase purity of the NMC111 and Li6PS5Cl and the cathode composites, obtained upon mixing NMC11, Li6PS5Cl, and the conductive carbon was confirmed by X-ray diffraction analysis (Figures 9 and 10). Table 1: Measurement of Electronic Conductivity of carbon additives.Room temperature (22°C) galvanostatic cycling

[0087] First, the ASSLB cells were galvanostatically cycled at a 0.1C current rate, which is a moderate rate suitable for achieving the maximum specific capacity for charge storage. The cells were charged-discharged for 100 cycles by employing a relatively high or practical CAM loading of approximately 12 mg (±2 mg) cm-2. This meant an areal current density of 0.15-0.2 mA cm-², considering 1C = 150 mA g⁻¹ for the NMC111 cathode (Figure 11). As shown in Figures 1a-c and 12 and summarised in Table 2, the Super P cathode exhibited the highest initial specific capacity of 135 mAh g-1, with around 89% retention or 121 mAh g-1after 100 cycles (Figure 1b). For rGO cathodes, the initial discharge capacity correlated well with the degree of graphitization and the electronic conductivity of the cathode composite (Table 3), with a similar initial capacity for rGO-1000 and rGO-600 at 122 mAh g-1and 119 mAh g-1, respectively. However, rGO-1000 demonstrated the best capacity retention of nearly 97% after 100 cycles (Figure 1c), surpassing rGO-600 (85%). As expected, the rGO-200 cathode, due to its lower conductivity and substantially high (Figure 7a) oxygen-containing surface functionalities (24 wt%), lead to a modest initial discharge capacity of 90 mAh g-1with retention (84%) close to that of rGO-600. Interestingly, even though the Coulombic efficiency (C.E.)values were close, rGO-200 lead with an average C.E. of 99.91%, followed by rGO-1000, rGO- 600, and Super-P at 99.79%, 99.76%, and 99.64%, respectively. Table 2. Summary of the galvanostatic cycling data of the ASSLB cell with different carbon additives in the cathode.Table 3. Measurement of electronic conductivity of cathode composites.

[0088] The effect of the conductive carbon and the degree of its functionalization become particularly apparent from the cumulative inefficiency plot, as shown in Figure 1d. This parameter, defined below, provided a cumulative measure of the Coulomb loss and better quantified the progress of degradation with cycling (additional discussion and comparison with similar statistical parameters have been provided at the end of the experimental section).100 - Coulombic efficiency (%) Inefficiency = 100 Cumulative inefficiency = ∑ Inefficiency

[0089] The cumulative inefficiency aligned inversely with the average efficiency trend, showing the steepest growth in inefficiency for Super-P and the lowest slope for rGO-200. Notably, rGO-200 started with the highest inefficiency but quickly stabilized, whereas Super-P showed the second highest starting inefficiency (Figure 1b, d, and Table 2) and maintained the steepest cumulative inefficiency slope throughout. On the other hand, rGO-600 and rGO-1000 started with the least inefficiency – or best efficiency during the first few cycles – and exhibited a similar slope of the inefficiency growth that is in between rGO-200 and Super-P.

[0090] In the cathode, aside from the degradation of the SE, especially at high voltages, CAM-SE and carbon-SE interfacial reactions can contribute to the Coulombic inefficiency. Capacity loss, on the other hand, can primarily stem from the loss of the active cathode due to degradations and increasing polarization (impedance) arising from the side reactions. Although carbon additives like Super P have been shown to accelerate capacity decay in ASSLBs and are commonly avoided (at least in > 2 wt%) in cathode composite preparation, the capacity retention of 89% after 100 cycles at room temperature (22°C) appeared promising. The high starting inefficiency (Figure 1d) and the highest cumulative inefficiency slope, however, suggested significant underlying degradation that may prove detrimental to long-term and high-temperature stability. Oxygen-containing functional groups on rGO are expected to trigger distinct reactions with the sulfide solid electrolyte and furnish an interphase located at the carbon-SE interface, referred to as CnEI (contrary to CEI for the CAM-SE or NMC-SE interphase) here, which may play a role in slowing down cumulative inefficiency growth with cycling. These reactions are expected to be chemical in nature and may occur as soon as the SE and the carbon are mixed for the cathode composite formation and during the electrochemical cycling of the cell. rGO-200, with a large extent of functional groups, is expected to furnish a thick and resistive CnEI that helps attain the highest average C.E. and the lowest cumulative inefficiency after 100 cycles but compromises the obtainable capacity and capacity retention. rGO-1000 and, to a good extent, rGO-600 appear to strike a good balance between CnEI formation and associated stabilization. Further, its high electronic conductivity ensures a high capacity. Probing cathode interphases by X-ray photoelectron spectroscopy (XPS)

[0091] Before delving into the impact of the CEI and CnEI on long-term cathode cycling, it was important to elucidate the chemical nature of the interphases - formed for functional group- free carbon (Super-P) and oxygen-functionalized carbon (rGOs). This was first investigated byX-ray photoelectron spectroscopy (XPS) analysis of the cathode before and after cycling. From the cumulative inefficiency plot (Figure 1d), it appears that a large extent of degradation occurs during the first 10-25 cycles, depending on the carbon additive. Therefore, cathodes were probed after 25 charge-discharge cycles when the degradation slowed down, and the chemistry of the interphase became steady. To mitigate the impact of ageing, ASSLB cells were fabricated immediately with the same pristine composite that was used for the spectroscopic analysis. The samples were transferred to the XPS vacuum chamber under an argon atmosphere, and the sample surface was cleaned by sputtering with Ar+beam (1 keV) for 1 minute.

[0092] In the pristine state, all cathode composites exhibited nearly identical S 2p and P 2p signals, especially corresponding to the PS43-species (Figure 2). Here, the S 2p signal for PS43-has been designated as SOx,1. The higher binding energy shoulder to SOx,1– labeled as SOx,2– is typically ascribed to the formation of oxidized polysulfide-type species such as P2Sy and Li2Sy. The broadness of the SOx,2signal suggests variation in the nature of the higher oxidation state sulfur species and P-[S]n-P chain length. Besides, there is a lower binding energy signal (161.2 ± 0.2 eV) that is attributed to the S2-species, which may arise due to the presence of the Li2S phase.

[0093] All three sulfur component signals observed for the uncycled cathode corresponded well with the S 2p spectra of pure Li6PS5Cl. The pristine rGO-200 composite displayed a higher binding energy shoulder to SOx,2, albeit very small, which is absent for Li6PS5Cl and other composites, suggesting the formation of S*SOxor thiosulfate species, plausibly arising from the chemical reaction of abundant surface oxygen functionalities of rGO-200 with Li6PS5Cl. Notably, rGO-600, rGO-1000, or Super P composites exhibited no obvious differences except for the slight variation in the S2-species signal.

[0094] In contrast, the cycled composites presented a different story. What stood out immediately was the marked difference in the changes in relative intensity of the PS43-S 2p signal (Sox,1) across composites. Aside from a much diminished PS43-S 2p signal (Figure 2b), a noteworthy increase in the S2-contribution and a rise in the high binding energy P-Sy-P or S0(Sox,2) species and S*SOx species suggested a significant interfacial degradation for the Super P cathode upon cycling. An equally heightened interfacial degradation was observed for the rGO- 200 cathode after cycling (Figure 2h).

[0095] Analogous to Super P, there was a more pronounced reduction in PS43-signal, and a strong increase in the S2-component. However, in contrast to Super P or other rGO composite cathodes, the escalation in S*SOxand sulfate type (SOx) species may underscore the effect of the oxygen-rich surface of rGO-200 in shaping the CnEI. Both rGO-600 and rGO-1000 showed onlya slight decrease in the relative intensity of the PS43-S 2p signal. In fact, for rGO-1000, there were very little changes upon cycling. Except for the appearance of S*SOx component in the 163 – 165 eV region, the rest of the spectra remained nearly unchanged. rGO-600 displayed a small increase in the Sox,2component corresponding to the P-Sy-P species, along with the appearance of the S*SOx signal. The relative intensity of the S2-signal also remained nearly unchanged upon cycling for both rGO-600 and rGO-1000.

[0096] P 2p region of the XPS spectra closely followed the trend observed in the S 2p region, characterized by a reduction in PS43-component contribution and an increase in secondary components corresponding to P2Sy, POx, or phosphate species. These changes were pronounced for the Super-P and rGO-200 cathode. O 1s XPS region evolution (Figure 14) upon cycling showed an increase in the phosphate O 1s signal and a decrease in the O 1s component corresponding to the lattice oxygen in metal oxide, especially for Super-P and rGO-200 cathodes. rGO-200 showed a large increase in O 1s signal upon cycling, which likely corresponded to the formation of LixO type species. The heightened weakening of the S 2p and P 2p signal intensity corresponding to PS43-unit of the Li6PS5Cl SE and the oxide lattice O 1s signal upon cycling for Super-P and rGO-200 cathode composite may be ascribed to the formation of a large amount of interfacial degradation product or a thick CEI and CnEI. The XPS being a surface-sensitive technique with a small sampling depth (< 10 nm), even a thin CEI / CnEI can mask the signal from the SE and the cathode, as observed for rGO-600 and rGO-1000.

[0097] Based on the XPS data analysis, the inventors of the present application postulate that conductive carbon Super-P may leaded to significant interfacial degradation, leading to the formation of polysulfide-type species along with some fraction of sulfate and phosphate-type products. This observation is consistent with previous studies, which have shown that the polysulfide forms upon electrochemical oxidation of Li6PS5Cl. Meanwhile, sulfate and phosphate species can form upon the reaction of polysulfides with the NMC surface oxygen. With a large extent of oxygen-containing surface functional groups on carbon, the carbon-SE interfacial degradation becomes prominent, and sulfate and phosphate species become dominant in the CnEI, as observed for rGO-200. A controlled amount of surface oxygen functionality strikes the right balance, i.e., it does not lead to an aggressive reaction with the Li6PS5Cl, and the thin layer of sulfate-phosphate CnEI may protect the Li6PS5Cl from oxidative degradation. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) investigation of the cathode interphase evolution

[0098] ToF-SIMS analysis of the cathodes shed further light on the chemical composition of the CEI / CnEI and the likely origin of the degradation. For each sample, data were collected atmultiple spots to ensure uniformity and reproducibility. To minimize the effect of current collector-induced degradation on the cathode surface, the cathode surface was cleaned by cesium ion sputtering (1 keV Cs+) before data collection.

[0099] Figure 3a shows the evolution of the NiS- fragment mass spectra upon cycling. For Super-P and rGO-200, there was a considerable increase in the signal, but for rGO-1000 the signal intensity decreased slightly. The same trend was observed for other transition metal sulfide fragments like NiS2-, MnS-, and MnS2- (Figures 15 and 16). Unlike rGO-1000, the rGO- 600 cathode showed an increase in the intensity of these sulfide fragments (Figures 15-17), but the increase was much less than that for rGO-200. LiS- and LiS2- fragments showed a strong increase for Super-P and rGO-200 cathodes compared to a small (LiS2-) to almost no (LiS-) increase for rGO-600 and rGO-1000 (Figure 18). The observations for the transition metal sulfide and lithium sulfide fragments were consistent with the XPS results, which showed a sharp increase in S2--type species intensity upon cycling for the Super-P and rGO-200 cathode. [000100] Despite the very different carbon surface chemistry, the same intensity trend for lithium and transition metal sulfide species across the four carbon samples indicated that those may have occurred via the same degradation pathway or byproduct. Given that the XPS revealed a significant rise in polysulfide-type species for Super-P and rGO-200 cathodes upon cycling, it is plausible that the reactive polysulfides react with the metal oxide surface, leading to partial degradation of the active cathode surface in the form of transition metal sulfide. Lithium sulfide fragments, observed in ToF-SIMS spectra, on the other hand, may originate from lithium polysulfide type species. For rGO-200, though, the lithium sulfide species can also arise from the reaction of Li6PS5Cl with -O.H. and -COOH-type functional groups on rGO. [000101] When comparing NiSO- (Figure 3b) and MnSO- (Figure 15b) fragments, the increase in the intensity was most prominent for rGO-200 cathode, followed by that for Super P. Intriguingly, for the rGO-1000 cathode, the relative intensity of both fragments changed only slightly upon cycling. An identical intensity evolution was observed for LiPO2-, and LiSO2- fragments upon cycling (Figures 3c, d), which corresponded to lithium phosphate and lithium sulfate-type byproducts. The observation of phosphate and sulfate fragments by ToF-SIMS further corroborated the XPS results presented in Figure 2. [000102] The greater intensity of LiSO2- compared to LiPO2- was consistent with the 5:1 atomic ratio of S and P in the L6PS5Cl electrolyte. Notably, the Super-P cathode showed the lowest pre- cycled intensity for LiPO2-, and LiSO2- fragments, and for the rGO cathodes, the pre-cycled intensity increased with increasing oxygen functional groups on carbon. Upon cycling, Super-P showed a fivefold increase in LiSO2- fragment intensity, followed by a three-fold increase forrGO-200 and a one-fold increase for rGO-600 and rGO-1000. However, rGO cathodes, especially rGO-200 and rGO-600, showed a much higher intensity for the LiPO2- and LiSO2- fragments both before and after cycling. These observations can be rationalized by different reactions leading to the formation of the phosphate and sulfate species. For rGOs, the reaction of Li6PS5Cl with the oxygen functional groups on rGO resulted in those species (as the CnEI), and for the Super-P cathode, the reaction of polysulfides with the metal oxide surface (forming as the CEI) may be the responsible mechanism. [000103] The intensity evolution of fragments such as SOC- (Figure 3e), S2CO-, and SOCO2- / SO2CO- (Figure 3f) may present insight into the carbon- Li6PS5Cl interface. A much lower intensity for all fragments for the Super-P cathode both before and after cycling was expected due to the lack of oxygen functional groups on Super-P. With the highest oxygen density (groups like -O.H. and -COC-) on its surface (Figure 8), rGO-200 exhibited high SOC- and S2CO- intensity even in the pre-cycled condition. The large extent of the degradation product may shut down further reactions, leading to only a small intensity change for those fragments after cycling. The observation was reversed for rGO-1000, which again may be explainable by the smaller extent of functional groups and continuation of rGO-Li6PS5Cl interfacial reaction over a more extended period. [000104] Overall, the findings from ToF-SIMS analysis suggested that the carbon-SE interface accumulates electrically and ionically insulating and chemically stable (unreactive) lithium phosphate / sulfate and SOC / S2CO / SO2CO containing byproducts for rGO, which help arrest the carbon-mediated degradation of the SE and cathode-SE interfacial reactions facilitated by the electron conductive network furnished by carbon. rGO-200 results in too much of these insulating byproducts, which compromises its already poor electronic conductivity, resulting in significantly low utilization of the active NMC in the electrochemical process and hence delivering inferior capacity. Inhibition of the CEI degradation beyond the initial cycles, however, leads to the lowest Coulombic inefficiency. On the other hand, an optimal amount of insulating byproducts at the carbon-SE interface for rGO-1000 and rGO-600 not only apprehends the conductive carbon’s detrimental role in continuing cathode interfacial degradation during the cathode cycling as manifested by the lower Coulombic inefficiency but also appears to uphold the required conductive network to engage the majority of the NMC particles electrochemically toward achieving higher capacity. For Super-P, the insulating byproducts primarily arise at the active NMC-SE interface but are unlikely to grow conformally on the NMC surface, which could lead to some extent of stabilization as can be rendered by the ex situ insulating coating of NMCparticles.]As a result, CEI degradation prevails for the Super-P carbon cathode, as reflected by the highest cumulative inefficiency slope during cycling (Figure 1d). In situ EIS evaluation of the impact of cathode interfacial degradations [000105] EIS was conducted in situ for the full cell by performing EIS every 10 cycles during galvanostatic cycling. The measurement was done at the end of discharge after an hour of resting at the open circuit voltage. The Nyquist diagrams, as presented in Figure 19, show only one depressed semicircle for Super-P and all rGOs, but the size and shape of the semicircle vary with carbon and with cycling. Deconvolution of the EIS data by DRT (distribution of relaxation times) transformation in the relaxation time space, as shown in Figure 4, unravels the processes contributing to the overall impedance and how those evolve for different carbons with cycling. [000106] The presence of several processes immediately becomes apparent from multiple DRT peaks (Figure 4a-d), which were assigned based on the DRT analysis of a few carefully designed experiments involving symmetric cells (for Li0.5In and NMC111) and the full-cell DRT analysis as a function of the state of charge or SOC (Figure 20 and accompanying discussion). The contributions in the mid-frequency (10-4to 10-1s in τ scale) and low-frequency (>1 s in τ scale) regions correspond to the overall cathode (including CEI and CnEI) impedance (labeled as PCathode-MF) and cathode interfacial charge transfer impedance (labeled as PCathode-LF), respectively. [000107] The highly stable LixIn-SE interface contributed to components in the 10-2to 10-1τ range (Figure 19), but these were relatively weak compared to the cathode contributions and do not evolve with cycling. The component (Pcathode-MF) in the 10-4< τ > 10-1range, the evolution of which for the different cathodes are highlighted in Figures 4e-h, also shows variation in the frequency / τ scale as a function of the SOC (Figures 19d-g) and thus may be linked to a cathodic process. [000108] Super-P showed the largest contribution for this component, likely corresponding to the impedance of the byproduct accumulated at the NMC-SE interface through the reaction of reactive polysulfides, originating from Li6PS5Cl, with the NMC particle surface (see above). All rGO cathodes showed a comparable contribution (resistance) for this component, even though the rGO-200 cathode showed a high extent of polysulfide formation and its reaction with the NMC particles in XPS and ToF-SIMS analysis. It is likely that the considerably lower active material utilization for the rGO-200 cathode, as evident from the obtained low specific capacity (Figure 1), leads to a comparatively lesser extent and nonuniform interfacial degradation and byproduct accumulation, resulting in the relatively low PCathode-MF component. However, the rGO-200 cathode displayed a particularly large contribution (resistance) for the PCathode-LFcomponent (Figures 4d, l), followed by Super-P (Figures 4c, i) and rGO-600 (Figures 4c, k),corresponding to the charge transport across CAM-carbon-SE interfaces, through the thick and insulating byproduct layer furnished by the reaction of oxygen functional groups on rGO with Li6PS5Cl (rGO200) or the reaction of the active NMC particle surface with polysulfides. [000109] The rGO-1000 cathode showed the smallest contribution for this component (Figures 4b, j), which is in agreement with the XPS and ToF-SIMS analysis. The charge transfer component was also highly stable for rGO-1000 over the probed 10 to 100 cycles. For rGO-600, this component decreased with cycling, indicating the formation of a uniform CEI / CnEI with a relatively small charge transport barrier. Conversely, Super-P showed a steep increase for both PCathode-LFand PCathode-MFcomponents with cycling, suggesting continuous CEI (CAM surface) degradation-mediated resistive byproduct accumulation. Stable CEI / CnEI enables stable long-term cycling [000110] The EIS evolution, along with thorough XPS and ToF-SIMS investigation, has shown that rGO-1000 and rGO-600 based cathodes have superiority in terms of cathode interfacial stability with cycling compared to that with super-P and rGO-200. However, the trend in interfacial (CEI / CnEI) evolution was not evident from their room temperature (22°C) macroscopic galvanostatic behavior (Figure 1), except in the cumulative inefficiency data. Therefore, to unveil the true impact of the stable vis-à-vis degrading interface, galvanostatic cycling was performed at a higher temperature so as to amplify the degradation kinetics. Figure 5a compares the specific capacity retention data for the rGO-1000 cathode against the Super-P cathode at 60°C at 1C. [000111] While ramification of the NMC interfacial (CEI) degradation with Super-P is apparent from the steady deterioration of the capacity with cycling and nearly 50% capacity decay after 100 cycles, stable cycling with ~100% retention for the rGO-1000 (Figures 5a, 21a) and rGO- 600 cathode (Figure 22a) highlights the impact of stable CEI furnished by oxygen functional groups on the carbon. Notably, while cycling data of the carbon-free cell under the same condition (no carbon in the cathode mix), as shown in Figure 23, indirectly confirms that it is indeed the conductive carbon super P that promotes cathode degradation and associated capacity decay, the need of carbon to ensure high capacity and current capability is clear. [000112] Differences, not only in terms of capacity retention, but also were observed with respect to Coulombic efficiency and cumulative inefficiency evolution. The super-P cathode displayed a C.E. of ~98.9% compared to the very high ~99.8% C.E. observed for both rGO-1000 and rGO-600 (Figures 5b and 22b). Cumulative inefficiency evolution with cycling, as shown in Figure 5b, agreed with the average C.E. values, and revealed a much faster interfacial degradation for the Super-P cathode at 60°C. This result for the Super-P cathode also becameapparent from the increasing polarization of the galvanostatic charge-discharge voltage profiles with cycling (Figure 5c), which resulted in rapid capacity fading. [000113] Interestingly, interface evolution for the rGO-1000 (Figure 5b) and rGO-600 (Figure 23b) cathode suggested a significantly subdued interfacial degradation or the formation of a more stable cathode interphase at 60°C than at room temperature. The effect is directly evident from the extremely stable voltage polarization profile, as shown in Figure 5d and Figure 22c. This may seem counterintuitive, but the inventors postulate that the chemical reaction of the oxygen functional groups on rGO with the Li6PS5Cl, responsible for furnishing the stable CnEI in rGO-1000 and rGO-600 cathodes, may progress faster at higher temperatures and furnish a stable interphase before considerable deleterious electrochemical degradations can kick in. [000114] Notwithstanding this, the formation of a stable CnEI and fast interfacial charge transport (as revealed by EIS / DRT analysis) for the rGO-1000 cathode also became evident from the impedance evolution from the 0thto 100thcycle (Figure 5e). The overall resistance component dropped from ~200 Ohms to ~120 Ohms upon cycling, which was consistent with the voltage polarization profile evolution. As expected, the Super-P cathode, on the other hand, displayed a significant rise in overall resistance from ~150 Ohms to ~400 Ohms, explaining the large increase in voltage polarization upon cycling. [000115] A comparison of the rate capability data between Super-P (Figure 5f) and rGO-1000 (Figure 5g) cathode further highlighted the impact of stable and lowly resistive cathode interphases that sustain the benefit of the conductive carbon additive. At a 0.5C, 1C, 2C, 4C, and 8C rate, the rGO-1000 cathode displayed a stable and reversible capacity of 139.5, 122.5, 108.5, 87, 46.5 mAh g-1, which, except for at 0.5 C and 1C rates, was higher than that for the Super-P cathode. Despite the Super-P cathode composite having a higher electronic conductivity than the rGO-1000 cathode, higher specific capacities displayed by the rGO-1000 cathode at high current rates may be rationalized by the lowly resistive and stable interphases furnished by rGO-1000. For Super-P, its high electronic conductivity is compromised by the resistive and degrading interface, rendered by carbon-mediated degradation. [000116] Irrespective of the rate, the rGO-1000 cathode displayed a very high average C.E. of 99.8% (1C). rGO-600 showed a slightly inferior rate capability (Figure 22d) compared to rGO- 1000, which is not surprising considering the slightly higher extent of CEI degradation with rGO-600 (Figure 4c), leading to relatively impeded charge transport across rGO-600 cathode interfaces than for the rGO-1000 cathode. [000117] The same effect was observed during long-term cycling (Figure 5h) at a 4C rate, i.e., rGO-1000 cathode displays a higher capacity of ~ 94.5 mAh g-1compared to the highest capacityof ~ 67.5 mAh g-1observed for rGO-600. The cells were cycled at a 0.5 C rate for 20 cycles prior to the high-rate cycling. Both cells display exceptional capacity retention of ~100% over 1000 cycles and >90% after 2000 cycles for rGO-1000, which has rarely been demonstrated for solid- state batteries, especially at elevated temperatures where interfacial degradation kinetics lead to rapid capacity decay. Even when the rate was increased to 8C, the rGO-1000 cell showed excellent stability with 100% retention over 1000 cycles (Figure 21b). Without being bound by theory, the inventors postulate that the performance demonstrated for rGO-1000 may be ascribed to optimal oxygen functionalities on the carbon (rGO) surface, facilitating in situ generation of a stable and thin CnEI, which arrests interfacial degradation when the high electronic conductivity of the carbon ensures enhanced electron percolation and thus high active material utilization and fast charge transport. Such a balance of interfacial stabilization with fast electron percolation enabled by surface-engineered carbon may lead to the high rate and long-term stable cycling of the NMC cathode, which has remained elusive to others performing research in this area. The superiority of the Cumulative Inefficiency parameter [000118] The different statistical parameters, as depicted in Figure 23, are represented in the following manner: I. Summation of Inefficiency = ∑ Coulombic Efficiency (%)Coulombic EfficiencyII. Running Average Efficiency (%) = (%) ^^^^ℎ ^^^^^^^^^^ III. Cumulative Inefficiency = ∑ Inefficiency100-Coulombic Efficiency (%) Inefficiency = 100 [000119] Although all three inherit the same property mathematically when represented, the visually cumulative inefficiency parameter conserves both minute changes in the efficiency value along the macroscopic trend. Thus, the cumulative inefficiency is presented herein as a more suitable statistical parameter to monitor long-term battery performance regarding its degradation kinetics or growing irreversibility. Distribution of Relaxation Time (DRT) Analysis (Methodology) [000120] Due to the complexities associated with Nyquist plots, The EIS data were deconvoluted from frequency to time domain, yielding a Distribution of Relaxation Time (DRT) diagram to differentiate the physicochemical processes or interfacial interactions by their contributory size / area, denoted by γ(τ) and time constant in the relaxation time domain, represented by τ. (Figure 4a-l, 20a-g)[000121] The raw data collected from EC lab software after appropriate formatting were utilized as the input files for the Python-based pyDRTtools software, which is available as open source. The primary objective of the DRT is to ascertain the distinctive distribution of standard EIS timescales. To achieve this, the experimental data Zexp, measured at specific frequencies, was compared to a model ZDRT derived from the subsequent expression: Equation 1:where R∞ is the ohmic resistance and ^^(^^) is a suitable function that describes the time relaxation characteristics of the electrochemical system studied. Expression (1) can be interpreted as an equivalent Voigt circuit. Put simply, the impedance model of the DRT consists of an Ohmic resistance (at f→∞) along with a summation of an infinite series of parallel resistors with capacitors (RC circuits). Since the frequency in impedance data collection is logarithmically spaced, the logarithmic correlation of ^^(^^) can be established with ^^ with the following equation: Equation 2:[000122] In the software, the combined ZRe and ZIm data were used after inductance data were discarded during fitting. For discretization, second-order Gaussian radial basis functions (RBF) were used with shape factor control between 0.75 to 1.0. The regularization method was controlled by the Generalized cross-validation (GCV) function, and the regularization parameter was set at 0.001 for the second-order regularization derivative. The RBFs used by pyDRTtools wasthe shape factor. [000123] This methodology ensured a semi-empirical mathematical representation of the impedance data, allowing identification and analysis of the distinct timescales present in the electrochemical system. Assignment of Components in DRT Analysis [000124] A series of experiments were conducted to verify the DRT components assignment (Figure 20a; a representative full-cell DRT profile), involving the following scenarios. Two symmetric all-solid-state battery (ASSB) cells were prepared with the following configurations: Li0.5In|Li6PS5Cl|Li0.5In cell and NMC111+Li6PS5Cl+Super- P|Li6PS5Cl|NMC111+Li6PS5Cl+Super-P cell. The impedance response was measured in the 1MHz to 10 μHz frequency range at varied temperatures ranging from 30°C (303 K) to 60°C (333 K), and the corresponding DRT profile is shown in Figure 20b and 20c, respectively. [000125] In accordance with previous work on DRT deconvolution of impedance spectra for solid-state batteries with Li6PS5Br SE, the present Li6PS5Cl-based Li0.5In symmetric cell exhibited a temperature dependence of its major component in the 0.01 (10-2) to 0.1 (10-1) τ range (Figure 20b). Due to the stable Li0.5In - Li6PS5Cl interface and the absence of any significant DRT component in the low to lower mid τ range for the symmetric Li0.5In cell, which was also noted by others previously for Li₆PS₅Br, it was concluded that the anode-electrolyte interfacial impedance may be significantly low as to not prominently appear in the full-cell DRT. [000126] Similarly, in the cathodic symmetric configuration (Figure 20c), the variation observed in the DRT plot was confined to the high τ or low-frequency region, which has been assigned to signify the changes associated with the cathodic charge transfer component. [000127] Further, the DRT deconvolution as a function of SOC / DOD in the case of rGO-1000 and Super-P-based cells after 10 cycles (Figures 20d-g) highlights that the majority of the contribution in the mid-frequency (10-4to 10-1s in τ scale) and low-frequency (> 1 s in τ scale) regions manifests from the overall cathode (including CEI) impedance and impedance associated with the cathode interfacial charge transfer, respectively. [000128] It is important to note that DRT, being a mathematical tool for inverse Fourier analysis of the impedance response, can overestimate or underestimate the number of deconvolution characteristic components corresponding to the electrochemical interaction components in an actual physical system. Conclusion [000129] These experiments represent a highly significant and facile approach to addressing the cathode interfacial degradation in sulfide electrolyte-based ASSLBs through optimally surface oxygen functionalized conducting carbon additive. In accordance with previous observations, in- depth XPS and ToF-SIMS analyses reveal that the electron percolation rendered by conductive carbon (Super-P) facilitates the degradation of Li6PS5Cl SE into reactive polysulfides, which reacts with the active NMC (cathode) particles leading to continuous degradation of the CEI (Figure 6a). This CEI degradation is reflected in high cumulative inefficiency growth with cycling at room temperature and rapid capacity fading at a high temperature. A large extent of surface oxygen functionality on the carbon (rGO-200; 24 wt% oxygen content), on the other hand, leads to the accumulation of a large amount of insulating byproducts at the carbon-SE interface, which enables interfacial stabilization but worsens the already poor electron transportin the cathode from poorly conductive highly functionalized carbon. This leads to only partial utilization of the active NMC in the electrochemical process and hence delivers inferior specific capacity. A moderate to low surface oxygen functionality, as embodied by rGO-600 (~13 wt% oxygen content) and rGO-1000 (~2 wt% oxygen content), leads to a thin layer of sulfate and phosphate type insulating byproducts at the carbon-SE interface, which stabilizes the cathode interface while upholding the conductive network furnished by conductive carbon (Figure 6a). Consequently, the corresponding cathode demonstrates low cumulative inefficiency growth, stable cycling both at room temperature (22°C) and high temperature (60°C), high rate capability, and high Coulombic efficiency exemplified by >90% retention after 2000 cycles at a 4C rate at 60°C which is unparalleled in the art (Figure 6b, Table 4). Table 4. Complementary data comparison of this work with other work in CEI engineering among sulphide solid electrolyte-based ASSBs with high-voltage transition metal cathodes.[000130] Notably, the experiments disclosed herein describe intriguing variations in the chemical nature of CEI and CnEI evolution under the influence of different types of conductive additives, with macroscopic electrochemical performance manifesting only under elevatedtemperature cycling. This underscores the importance of incorporating high-temperature cycling in testing cathode interfacial degradation in solid-state batteries. Finally, the inventors of the present application postulate that the presented oxygen functionalized carbon mediated in situ interfacial engineering for enabling stable high performance ASSLBs can be extended to other sulfide electrolytes beyond Li6PS5Cl and NMC cathodes of different compositions, as well as different forms of oxygen functionalized conductive carbon beyond rGO. In fact, this work can potentially inspire carbon surface functionalization as a facile and scalable approach for the in situ designing of robust interphases for highly durable ASSLB cathodes. [000131] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. In particular, features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.

Claims

Claims:

1. A cathode for an all-solid state lithium battery, the cathode comprising: a cathode active material; a sulfide-containing inorganic solid electrolyte material; and an oxygen-functionalised conductive carbon material; wherein the oxygen-functionalised conductive carbon material comprises from about 0.5 wt.% to about 20 wt.% of oxygen atoms, based on the total weight of the oxygen-functionalised conductive carbon material.

2. The cathode of claim 1, wherein the oxygen-functionalised conductive carbon material comprises oxygen and carbon, with substantially no other atoms.

3. The cathode of claim 1 or 2, wherein the oxygen-functionalized conductive carbon material comprises from about 0.5 wt.% to about 15 wt.% of oxygen atoms, from about 1 wt.% to about 10 wt.% of oxygen atoms, from about 1 wt.% to about 5 wt.% of oxygen atoms, or about 2 wt.% of oxygen atoms, based on the total weight of the oxygen-functionalised conductive carbon material.

4. The cathode of any one of claims 1 to 3, wherein the oxygen-functionalised conductive carbon material comprises graphene oxide.

5. The cathode of any one of claims 1 to 4, wherein the oxygen-functionalised conductive carbon material comprises reduced graphene oxide (rGO).

6. The cathode of claim 5, wherein the reduced graphene oxide is an annealed reduced graphene oxide which has been annealed at a temperature of from about 300 ºC to about 1500 ºC, from about 300 ºC to about 1200 ºC, from about 500 ºC to about 1100 ºC, or about 1000 ºC.

7. The cathode of claim 6, wherein the annealed reduced graphene oxide has been annealed for at least about 30 minutes or at least about 1 hour, in an inert atmosphere.

8. The cathode of any one of claims 1 to 7, wherein the cathode active material comprises one or more selected from the group consisting of lithium nickel manganese cobalt oxides, lithium manganese oxides, lithium nickel manganese oxides, lithium iron phosphates, lithium manganese iron phosphates, and doped and / or substituted and / or coated variants thereof, optionally which are doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

9. The cathode of claim 8, wherein the cathode active material is a lithium nickel manganese cobalt oxide (NMC) cathode active material, which is optionally doped and / or substituted and / or coated, optionally which is doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

10. The cathode of claim 9, wherein the NMC cathode active material has the general formula: LiNixMnyCo1-x-yO2, wherein x and y are independently between 0 and 1.

11. The cathode of claim 9 or 10, wherein the NMC cathode active material comprises one or more selected from the group consisting of LiNi1 / 3Mn1 / 3Co1 / 3O2 (NMC111) LiNi0.5Mn0.3Co0.2O2 (NMC532), LiNi0.6Mn0.2Co0.2O2(NMC622), and LiNi0.8Mn0.1Co0.1O2(NMC811), each of which is optionally doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

12. The cathode of any one of claims 9 to 11, wherein the NMC cathode active material comprises LiNi1 / 3Mn1 / 3Co1 / 3O2(NMC111), optionally which is doped and / or substituted and / or coated with one or more selected from the group consisting of Al, Ti, Zr, Mg, B, F, W, Mo, Ga, Nb, and Ca.

13. The cathode of any one of claims 1 to 12, wherein the sulfide-containing inorganic solid electrolyte material comprises one or more selected from the group consisting of lithium phosphorous sulfides, lithium phosphorous sulfide halogens, and lithium metal phosphorous sulfides.

14. The cathode of any one of claims 1 to 13, wherein the sulfide-containing inorganic solid electrolyte material comprises one or more selected from the group consisting of Li3PS4 and Li6PS5Cl.

15. The cathode of any one of claims 1 to 14, wherein the sulfide-containing inorganic solid electrolyte material comprises particles having a particle size distribution d50of from about 0.1 µm to about 10 µm, from about 0.5 µm to about 2 µm, or about 1 µm.

16. The cathode of any one of claims 1 to 15, wherein the mass ratio of cathode active material to the sulfide-containing inorganic solid electrolyte material is from about 55:45 to about 95:05, or about 70:

30.

17. The cathode of any one of claims 1 to 16, wherein the mass ratio of the sum of the cathode active material and the sulfide-containing inorganic solid electrolyte material, to the oxygen-functionalised conductive carbon material, is from about 100:20 to about 100:1, from about 100:10 to about 100:2, or about 100:6.

18. The cathode of any one of claims 1 to 17, comprising: from about 1 wt.% to about 15 wt.%, or about 0.1 wt.% to about 10 wt.%, or from about 2 wt.% to about 8 wt.%, or from about 5 wt.% to about 7 wt.%, or about 5.7 wt.%, of the oxygen-functionalised conductive carbon material; and / or from about 3 wt.% to about 50 wt.%, or about 5 wt.% to about 50 wt.%, or from about 20 wt. % to about 40 wt. %, or from about 25 wt.% to about 35 wt. %, or about 28.3 wt.%, of the sulfide-containing inorganic solid electrolyte material; and / or from about 50 wt.% to about 95 wt. %, or from about 50 wt.% to about 80 wt.%, or from about 60 wt.% to about 70 wt.%, or about 66 wt.%, of the cathode active material.

19. A battery, comprising the cathode of any one of claims 1 to 18.

20. The battery of claim 19, which is an all-solid state lithium battery.

21. The battery of claim 20, comprising an electrolyte region distinct from the cathode, wherein said electrolyte region comprises a sulfide-containing inorganic solid electrolyte.

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