State-of-the-art carbon coatings are sought to protect high-capacity silicon anodes, which suffer from low conductivity, large volume change and fast degradation. However, this approach falls short when handling physical-electrical disconnections between carbon shells and silicon microparticulate (SiMP) with drastic size variations. Here, a strategy of covalent coating is developed to establish a robust encapsulation structure. The obtained covalent Si-C bonds enable an effectively dynamic connection between the electrochemically deforming SiMP and the sliding graphene layers, preventing the evolution of gaps between SiMP and the carbon shell and maintaining persistent electrical connections as well as mechanical toughness. As a result of high structure reversibility, the cycling stability of thick SiMP anodes is greatly improved, up to a high areal capacity of 5.6 mAh cm −2 and volumetric capacity of 2564 mAh cm −3 . This interface bonding effect demonstrates the great potential for suppressing deformation involved degradation of high-capacity materials through coating strategies.

Composite polymer electrolytes (CPEs) are subject to interface incompatibilities due to the space charge layer of ceramic and polymer phases. The intensive dehydrofluorination of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) incorporating Li7La3Zr2O12 (LLZO) significantly compromises electro‐chemo‐mechanical properties and compatibilities with electrodes. Herein, this study addresses the challenges by precisely phosphatizing LLZO surfaces through a surface Li2CO3 mediated chemical reaction. The designed neutral chemical environment of LLZO surfaces ensures high air stability and effective suppression of PVDF‐HFP dehydrofluorination. This greatly facilitates the uniform distribution of ceramic and polymer phases, and fast interfacial Li+ exchange, establishing high‐throughput ion percolation pathways and distinctly enhancing ionic conductivity and transference number. Moreover, the dramatically reduced formation of dehydrofluorination products and an in situ formed interphase layer between phosphatized surface and a Li metal anode stabilize the Li/CPE and cathode/CPE interfaces, which provide a symmetric Li/Li cell and solid‐state Li/LiFePO4 and Li/LiNi0.8Co0.1Mn0.1O2 cells an exceptional cycling performance at room temperature. This study emphasizes the vital importance of achieving electro‐chemo‐mechanical compatibilities for CPEs and provides a new waste to wealth route.