Enhancing Interfacial Contact in Solid‐State Batteries with a Gradient Composite Solid Electrolyte

Abstract Solid‐state batteries promise to meet the challenges of high energy density and high safety for future energy storage. However, poor interfacial contact and complex manufacturing processes limit their practical applications. Herein, a simple strategy is proposed to enhance interfacial contact by introducing a gradient composite polymer solid electrolyte (GCPE), which is prepared by a facile UV‐curing polymerization technique. The high‐Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO)‐content side of the electrolyte exhibits high oxidation resistance (5.4 V versus Li + /Li), making it compatible with a high‐voltage cathode material, whereas the LLZTO‐deficient side achieves excellent interfacial contact with the Li metal anode, facilitating uniform Li deposition. Benefiting from the elaborate composition and structure of GCPE films, the symmetric Li//Li cell exhibits a low‐voltage hysteresis potential of 42 mV and a long cycle life of >1900 h without short‐circuiting. The Li//LiFePO 4 solid‐state batteries deliver a capacity of 161.0 mA h g −1 at 60 °C and 0.1 C (82.4% capacity is retained after 200 cycles). Even at 80 °C, the cell still shows an outstanding capacity of 132.9 mAh g −1 at 0.2 C after 100 cycles. The design principle of gradient electrolytes provides a new path for achieving enhanced interfacial contact in high‐performance solid‐state batteries.