Competitive Adsorption and Structural Reinforcement Synergy Stabilizes High‐Voltage Quasi‐Solid‐State Batteries

Quasi‐solid‐state batteries (QSSBs) employing high‐voltage cathodes promise high energy density and safety, yet suffer from unstable cathode/electrolyte interfaces and cathode degradation. Here, we propose a competitive adsorption and structural reinforcement synergy (CASR) strategy to address these challenges. Specifically, a Cu‐centered self‐adsorption molecule is incorporate into the polymer electrolyte, which preferentially adsorbs at the cathode/electrolyte interface through competitive adsorption against solvent molecules, thereby reducing the solvent content on the cathode surface while promoting anion enrichment. This process induces the formation of a uniform F‐rich cathode/electrolyte interphase with a LiF‐rich outer layer and an inner layer containing Cu─F bonds, thereby effectively suppressing cathode degradation. Cathode structural stability is further reinforced through dynamic Cu doping into TM‐deficient lattice sites during cycling. Under low‐loading coin‐cell conditions (2.0 mg cm −2 ), the resulting Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 QSSBs retain 80% of their initial capacity after 400 cycles at 4.6 V, and achieve 80% capacity retention over 1000 cycles under 10C and 4.5 V. A 1 Ah‐level pouch‐cell tested under 4.3 V and 1C charge/0.5C discharge conditions supports the potential of the CASR strategy. This work provides a promising pathway for synchronously stabilizing cathode/electrolyte interface and cathode structure in high‐voltage QSSBs.