Unlocking the Potential of Li‐Rich Mn‐Based Oxides: Surpassing 300 mAh g−1 at Room Temperature in All‐Solid‐State Batteries

This study presents a comprehensive assessment of the temperature‐dependent electrochemical performance of LiNbO 3 ‐coated lithium‐rich manganese‐based oxide (LRMO) cathodes in all‐solid‐state batteries (ASSBs). The effects of temperature and activation on the performance of LRMO cathodes are systematically investigated through electrochemical characterization and X‐ray diffraction and X‐ray absorption near‐edge structure analyses. LRMO activation significantly improves electronic conductivity by facilitating lithium intercalation within the sulfide‐based solid electrolyte (SE). This conductivity enhancement reduces cell resistance more effectively than an elevation in temperature alone. Because of the low conductivity of LRMO at room temperature (≈10 −6 S cm −1 ), improving the composite cathode's conductivity is critical for reducing cell resistance and enabling LRMO activation. Two strategies are proposed to achieve this: the addition of carbon additives to enhance the electronic conductivity and the application of a LiNbO 3 coating to stabilize the interface between the cathode active material and the SE, thereby minimizing resistance. With these improvements, LiNbO 3 ‐coated LRMO cathodes with conductive additives achieve a high discharge capacity of over 300 mAh g −1 after 30 cycles at 25 °C. These findings provide valuable insights into optimizing next‐generation LRMO‐based cathodes and advancing high‐performance energy storage systems for ASSBs.