Solid‐state electrolytes (SSEs) show potential in addressing the safety issues of liquid batteries, but the poor interface contact between them and the electrodes hinders practical applications. Here, coordination chemistry of nitrile groups based on succinonitrile (SCN) and polyacrylonitrile (PAN) is studied on the surface of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) SSE to build the chemical bonded electrolyte/electrode interfaces. The coordination of the nitrile group and LLZTO is clarified. A deformable PAN‐modifying SCN electrolyte (PSE) interphase with stable ionic conductivity (10−4 S cm−1) and high lithium‐ion transference number (0.66) is fabricated on the surface of LLZTO electrolyte based on the coordination competition of nitrile groups. Once applied to SSBs, it endows low interface resistance and strong bonding for the electrolyte/electrode interfaces so that the initial Coulomb efficiency reaches 95.6 % and the capacity remains 99 % after 250 cycles at 25 °C. A nitrile group‐induced coordination interphase on the surface of the LLZTO electrolyte stabilizes the electrolyte/electrode interface.