Achieving Durable Three Li‐ion Storage in Cation‐disordered Rock‐salt Li _x V ₂ O ₅ Cathodes for all‐solid‐state Thin Film Lithium Batteries

ABSTRACT All‐solid‐state thin‐film lithium batteries (TFBs) are ideal power sources for next‐generation microelectronics and the Internet of Things. However, their development is constrained by conventional cathodes that require high processing temperatures (≥500°C) and offer limited specific capacity, hindering on‐chip integration. Here, we demonstrate phosphate‐doped cation‐disordered rock‐salt Li _x V ₂ O ₅ (LVO‐PO) nanosheet arrays as a high‐performance cathode, processed at a low temperature of 200°C and enabling durable three Li ⁺ storage. This unique structure is fabricated through an in situ interfacial reaction between V ₂ O ₅ nanosheet arrays and a LiPON electrolyte, followed by electrochemical activation, resulting in LiPON embedded within the LVO‐PO domains. This architecture establishes a 3D ion‐diffusion network and an intimate electrode/electrolyte interface for rapid Li ⁺ transport. Phosphate doping further enhances the structural stability by forming a reinforced framework resilient to repeated Li ⁺ (de)intercalation and lowers the Li ⁺ diffusion barrier. Consequently, the LVO‐PO/LiPON/Li TFB delivers a high specific capacity of 416 mAh g ⁻¹ at 0.2C, good rate capability (147 mAh g ⁻¹ at 2C), and stable cycling (67.9% capacity retention after 220 cycles), outperforming the undoped analogue and previously reported V ₂ O ₅ ‐based cathodes. This work provides a novel design strategy for high‐capacity, low‐temperature‐processable thin‐film electrodes, advancing the development of on‐chip integrated energy storage.