Electronic transport properties in lithium cobalt oxide battery electrode material studied in ion-gated transistor configuration

Li-ion battery (LIB) electrode materials feature mixed electronic-ionic transport. Their electronic conductivity is expected to depend on the degree of de-lithiation/lithiation, but it is challenging to evaluate such dependence as disentangled from ionic conductivity. Herein, we use the Ion-Gated Transistor (IGT) configuration to study the dependence of the electronic conductivity of lithium cobalt oxide (LiCoO₂ or LCO)-based composite cathode material. LCO-based composite is employed as transistor channel interfaced with the ionic liquids: 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PYR₁₄][TFSI]), both without and with lithium bis(trifluoromethane)sulfonimide salt (LiTFSI). The gate-source bias controls the degree of lithiation/de-lithiation in the LCO composite-based IGT. We observed an increase in the drain-source transistor current upon the application of a gate-source bias, i.e., upon Li⁺ de-intercalation from the LCO composite cathode material. Our results pave the way for the in operando evaluation of the state-of-charge (SOC) of LIB electrode materials, crucial for their efficient and sustainable use.