Multidimensional Molecular Welding Engineering of In Situ Polymerized Electrolytes Enables Stable 4.6 V LiCoO ₂ Quasi Solid‐State Batteries

ABSTRACT Practical application of LiCoO ₂ ‐based 4.6 V class lithium ion batteries suffers from severe issues, including electrolyte decomposition, electrode/electrolyte interface degradation and lattice structure deterioration. Herein, ethoxylated trimethylolpropane triacrylate, acrylonitrile, trifluoroethyl methacrylate are copolymerized to crosslink the liquid component fluoroethylene carbonate (FEC), which constructs a ternary crosslinked in situ polymerized electrolyte (EATF). Benefiting from this complementary design, molecule segments of EATF are welded though multiple hydrogen bonds to constitute a physical network that enhances intrinsic mechanical stability, improves the Li ⁺ conductivity (1.9 mS cm ⁻¹ ) and expands the electrochemical window (5.32 V). Concurrently, inner Helmholtz plane reconstruction at LCO/EATF interface induces the formation of a thin and uniform inorganic‐rich cathode electrolyte interface. Crucially, cyano groups within EATF and Co in LCO surface are welded to form direct lattice coupling effect, modulating the electron spin state of Co to inhibit irreversible phase transition. These synergistic effects stabilize the LCO structure during operation under 4.6 V, enabling LCO/EATF/Li batteries with excellent electrochemical performance. Ah‐level LCO/Gr pouch cells demonstrate cycling stability after 100 cycles at 0.2C rate with 91.6% capacity retention. This work provides new insights into combining physical network with lattice coupling effect to boost 4.6 V LCO/Li quasi solid‐state batteries.