Enabling a Co-Free, High-Voltage LiNi_0.5Mn_1.5O₄ Cathode in All-Solid-State Batteries with a Halide Electrolyte

Abstract

One approach to increase the energy density of all-solid-state batteries (ASSBs) is to use high-voltage cathode materials. The spinel LiNi0.5Mn1.5O4 (LNMO) cathode is one such example, as it offers a high reaction potential (close to 5 V). Moreover, it is a Co-free cathode system, which makes it an environmentally friendly and a low-cost alternative. However, several challenges must be addressed before it can be properly adopted in ASSB technologies. Herein, we reveal that lithium argyrodite (Li6PS5Cl), a sulfide solid-state electrolyte (SSE), possesses intrinsic chemical incompatibility with the LNMO cathode. We demonstrate the necessity of using a halide SSE, Li3YCl6 (LYC), through careful analysis of the LNMO/SSE interface. Moreover, we emphasize the necessity of applying a protective coating layer to LNMO particles, even when halide SSEs are used. Furthermore, the chemical phenomena involving LYC in the oxidative environment of LNMO are analyzed, including a comparison between coated and uncoated LNMO particles.

LiNi0.5Mn1.5O4 Cathode Microstructure for All-Solid-State Batteries

“…The enhanced capacity retention of the film-type composite cathode can be attributed to the ability of the PTFE fibrils to maintain the contact between LPSCl, Al 2 O 3 –H-LNMO, and VCF upon cycling. The areal capacities of pellet- and film-type composite cathodes were 1.51 and 2.46 mAh cm –2 , respectively, which were 7–10× higher than those of previously reported SSBs composed of LNMO and a sulfide electrolyte, ,,− thus confirming the importance of microstructure engineering cathode secondary particles to achieve high areal capacities and long-term cyclability in SSBs (Figure d and e and Table S2).…”

Toward Optimization of the Chemical/Electrochemical Compatibility of Halide Solid Electrolytes in All-Solid-State Batteries

“…; X = Cl, Br, and I). They show high ionic conductivity (∼1 mS/cm) and high oxidative stability (>4 V vs Li + /Li) as predicted by density functional theory (DFT) calculations while offering easy fabrication via either solid-state or solution processes. − This enhanced stability was confirmed experimentally by noting greater ASSB performances, relying on the use of Li 3 YCl 6 rather than sulfides, especially when cycled at high potentials. , A culminant demonstration along that line is the remarkable rate capability, long-term cycling performance, and electrochemical stability up to 4.8 V vs Li + /Li recently achieved with the use of scandium-based ionic conducting phases (Li 2 Sc 2/3 Cl 4 and Li 2 Sc 1/3 In 1/3 Cl 4 ). , However, the main drawbacks pertaining to halides are high cost and density as well as their poor electrochemical stability in reduction, preventing their direct use against Li or Li x In y layers in ASSBs . This requires the design of dual SE separators with halides and sulfides facing the positive and negative electrodes, respectively, with the inconvenience of creating more interfaces .…”

“…20−25 This enhanced stability was confirmed experimentally by noting greater ASSB performances, relying on the use of Li 3 YCl 6 rather than sulfides, especially when cycled at high potentials. 26,27 A culminant demonstration along that line is the remarkable rate capability, long-term cycling performance, and electrochemical stability up to 4.8 V vs Li + /Li recently achieved with the use of scandium-based ionic conducting phases (Li 2 Sc 2/3 Cl 4 and Li 2 Sc 1/3 In 1/3 Cl 4 ). 28,29 However, the main drawbacks pertaining to halides are high cost and density as well as their poor electrochemical stability in reduction, preventing their direct use against Li or Li x In y layers in ASSBs.…”

Advances in Solid-State Batteries, a Virtual Issue, Part II

“…The interface and compatibility between the electrodes and solid electrolytes are also essential to ensure excellent electrochemical properties of solid-state cells . LiNi 0.5 Mn 1.5 O 4 is found to be incompatible with Li 6 PS 5 Cl electrolyte but suitable for a solid halide electrolyte, Li 3 YCl 6 . The compatibility and interfacial issues as well as electro-chemo-mechanics interaction and transport-kinetics dichotomy are key fundamental challenges for SSBs during fast charging .…”

“…23 LiNi 0.5 Mn 1.5 O 4 is found to be incompatible with Li 6 PS 5 Cl electrolyte but suitable for a solid halide electrolyte, Li 3 YCl 6 . 24 The compatibility and interfacial issues as well as electro-chemo-mechanics interaction and transport-kinetics dichotomy are key fundamental challenges for SSBs during fast charging. 25 In addition, a proper electrode fabrication process with appropriate binders such as poly(tetrafluoroethylene-co-perfluoro(3-oxa-4-pentenesulfonic acid)) lithium salt 26 and elastic polymer "Spandex" 27 is critical for the performance of SSBs.…”