The paper presents an in-situ polymerization strategy for gel polymer electrolyte (GPE) to enhance the performance of Si||Ni-rich lithium-ion batteries. The Si anode, combined with a nickel-rich cathode (LiNiₓMnᵧCo₁₋ₓ₋ᵧO₂, x ≥ 0.8), faces challenges such as mechanical instability, cathode collapse, and severe leakage current. The proposed GPE reinforces the mechanical integrity of the Si anode and chelates with transitional cations to stabilize the interfacial properties. By integrating the conformal GPE encapsulation with spatially arranged Si anodes and NMC811 cathodes, a 2.7 Ah pouch-format cell achieved a high energy density of 325.9 Wh kg⁻¹, 88.7% capacity retention over 2000 cycles, self-extinguishing properties, and wide temperature tolerance. The GPE design balances adhesion strength, ionic diffusivity, stable SEI and CEI formation, cross-talk effect suppression, and flame retardancy, addressing the multiscale interfacial stability and controlled electro-chemo-mechanics of the electrodes.The paper presents an in-situ polymerization strategy for gel polymer electrolyte (GPE) to enhance the performance of Si||Ni-rich lithium-ion batteries. The Si anode, combined with a nickel-rich cathode (LiNiₓMnᵧCo₁₋ₓ₋ᵧO₂, x ≥ 0.8), faces challenges such as mechanical instability, cathode collapse, and severe leakage current. The proposed GPE reinforces the mechanical integrity of the Si anode and chelates with transitional cations to stabilize the interfacial properties. By integrating the conformal GPE encapsulation with spatially arranged Si anodes and NMC811 cathodes, a 2.7 Ah pouch-format cell achieved a high energy density of 325.9 Wh kg⁻¹, 88.7% capacity retention over 2000 cycles, self-extinguishing properties, and wide temperature tolerance. The GPE design balances adhesion strength, ionic diffusivity, stable SEI and CEI formation, cross-talk effect suppression, and flame retardancy, addressing the multiscale interfacial stability and controlled electro-chemo-mechanics of the electrodes.