Accelerated Degradation of All‐Solid‐State Batteries Induced through Volumetric Occupation of the Carbon Additive in the Solid Electrolyte Domain

Abstract The accelerated oxidative degradation observed in all‐solid‐state batteries (ASSBs), particularly focusing on the argyrodite solid electrolyte in conjunction with Ni‐rich positive electrode surfaces is demonstrated. The formation of oxidative intermediates of the solid electrolyte oxidation process increases the amount of oxidation on the NCM surface with conductive carbon. The introduction of high‐weight‐composition conductive carbon additives results in a reduction of solid electrolytes within the positive electrode and the amount of solid electrolytes retained after formation. Consequently, cells with high concentrations of carbon additives demonstrate a decrease in both the cycle and power performances of ASSBs. The energy density of ASSBs is significantly limited by the fundamental failure mechanism induced by conductive carbon, particularly pronounced in cells with high active material contents. Consequently, this study provides pivotal insights for the design of high‐energy‐density ASSBs with NCM electrodes and high active material contents. To mitigate failure induced by high‐volumetric‐occupied carbon additives, carbon fiber‐type additives are further utilized to interconnect the NCMs by decreasing the occupation of the solid electrolyte domain by carbon. Morphological alteration of the carbon additive significantly improves the electrochemical performance of ASSBs by preventing the deterioration of the electrode structure even after prolonged cycling and suppressing electrolyte degradation.