<p>The increasing upper voltage limit of LiCoO₂ (LCO) cathodes is an effective strategy to boost the energy density of lithium-ion batteries (LIBs); however, it also exacerbates structural degradation. Conventional doping strategies employing high-mass low-diffusion elements often reduce crystal growth kinetics, resulting in polycrystalline secondary particles with compromised performance. In this study, an innovative grain boundary engineering approach using Li₂WO₄ (LWO) as a modifier is presented to stabilize high-voltage LCO (W@LCO). During annealing, WO₃ transforms into highly conductive LWO, which is strategically localized at grain boundaries to serve as efficient “bridges” for enhanced performance. This modification yields three key advantages: (1) effective suppression of the irreversible O3-to-H1-3 phase transition occurring at high voltages, (2) significant improvement in valence stability of Co, and (3) maintenance of fast Li⁺ diffusion kinetics during prolonged cycles. Consequently, the optimized W@LCO cathode exhibits exceptional electrochemical performance, achieving 158.9 mAh·g⁻¹ (84.4% capacity retention, 1C) after 200 cycles. This grain boundary enrichment strategy establishes a new paradigm for designing durable high-voltage layered cathodes, providing essential insights for the exploration of high-energy-density LIBs.</p> Graphical abstract <p></p>