Solution Process for the Li Carboranes Solid-State Electrolyte Preparation and Its Inverse Pressure Dependence

Lithium-ion battery (LIB) use in electric vehicles (EV) continues to grow. However, conventional LIBs use flammable liquid electrolytes that are prone to failure in EV applications. To solve this problem, solid-state electrolytes have emerged as a non-flammable alternative to conventional liquid electrolytes with a higher theoretical energy density than liquid electrolyte batteries due to stability of certain solid electrolytes against metallic lithium anodes. Among the various solid-state electrolytes, a mixture of LiCB₉H₁₀ and LiCB₁₁H₁₂ has shown to exhibit very high ionic conductivities. Specifically, an optimal 7 to 3 ratio of LiCB₉H₁₀ / LiCB₁₁H₁₂ (mixed carboranes) demonstrated ionic conductivities of 6.7 mS cm^-1 and 85 mS at 25 ^oC and110 ^oC respectively. Herein, we have prepared the mixed-phase Li carborates with a different solution-based processing method to improve scalability and enhance synthetic control beyond typical ball milling methods.
Conventional solid electrolytes typically exhibit increasing ionic conductivities as cell stack pressures increase, which is caused by improved interfacial contacts between the solids. Herein we also report that the pressure-dependent ionic conductivity of Li carboranes exhibits the opposite trend, where ionic conductivity decreases as a function of cell stack pressure.