Negative‐Thermal‐Expansion Strategy Enables Hard Carbon With Tuned Heat/Strain Tolerances for Sodium Storage

ABSTRACT The thermal/stress runaways pose a risk to the safety and industrialization of sodium‐ion battery (SIB), which hence requires external management equipment. Actually, the thermal/stress generation originates from the repetitive Na + intercalation within carbon interlayers and pore‐filling in the initial stage. Herein, we propose a regulation strategy of “in situ thermal strain relief” to achieve internal thermal and stress managements of SIB hard carbon (HC) anode by incorporating negative thermal expansion oxide ZrW 2 O 8 . The results indicate that the heat and strain were reduced obviously after cycling, leading to rapid diffusion kinetics and enhanced sodium storage capacity. Moreover, the microstructure and efficient electron/ion transport within HC were preserved, demonstrating excellent capacity stability even after high‐rate and long‐term cycling over wide operating temperature ranges (−20°C to 60°C). This study provides a new approach for thermal and stress management inside the battery, which may play a joint effort with the conventional management equipment outside the battery and beyond.