Simultaneous Near‐Surface Trace Doping and Surface Modifications by Gas–Solid Reactions during One‐Pot Synthesis Enable Stable High‐Voltage Performance of LiCoO₂

Abstract LiCoO₂ (LCO) with a high theoretical capacity of 274 mAh g^–1 can rarely achieve a high practical capacity even at an upper cutoff voltage of 4.6 V due to severe structural instability and interface side reactions. Herein, an in situ strategy of gas–solid modifications during synthesis is proposed to improve the performance of LCO using sulfocompound‐contained expanded graphite (EG) as templates. In situ generated SO₂ gas from EG enables the Co‐coating of coherent spinel Li_xCo₂O₄ and Li₂SO₄ and the trace doping of high‐valence S mainly in the near‐surface regions via its reactions with the precursors. The modified LCO possesses excellent structural reversibility, interfacial stability, slight dissolution of Co²⁺, high diffusion coefficients of Li⁺, and low O 2p band top. This endows LCO with remarkably improved high‐voltage performance, 222 and 143 mAh g^‐1 at 0.1 and 20 C, respectively, and 88% capacity retention over 100 cycles at 1 C for LCO/Li half cells between 2.8 and 4.6 V, and 202 mAh g^–1 at 1 C and 87% capacity retention over 1000 cycles between 2.8 and 4.5 V for LCO/graphite full cells. This study provides a unique, simple, and upscalable strategy for performance improvement of electrode materials.