Thermal Annealing of Graphite for Enhanced Electrochemical Performance in All‐Solid‐State Lithium Batteries

The advancement of sulfide‐based all‐solid‐state lithium batteries (ASSLBs) is frequently constrained by the low initial Coulombic efficiency and interfacial degradation of graphite anodes, phenomena that predominantly originate from surface impurities of organic origin. In this work, we introduce a facile yet highly effective thermal purification strategy for industrial‐grade graphite (SG‐17), enabling the restoration of its intrinsic electrochemical properties. Multimodal spectroscopic and microscopic characterizations demonstrate that annealing at 500°C under an inert atmosphere effectively eliminates oxygenated surface species while preserving the crystalline architecture of graphite. When deployed in sulfide solid‐state configurations, the purified graphite exhibits a substantially improved initial coulombic efficiency (94.6% vs. 86.3%), enhanced Li + diffusion coefficients, suppressed charge–transfer resistance, and remarkable cycling stability with 81% capacity retention over 300 cycles. Distribution of relaxation time analyses further elucidates the critical role of surface purification in mitigating interfacial impedance growth and promoting efficient ion transport. These findings not only provide fundamental mechanistic insight into impurity‐driven interfacial phenomena in ASSLBs but also establish a scalable and cost‐effective pathway to advance graphite anodes for next‐generation solid‐state energy storage technologies.