Double-layer solid-state electrolyte enables compatible interfaces for high-performance lithium metal batteries

Solid-state lithium metal batteries are promising next-generation batteries for both micro-scale integrated electronic devices and macro-scale electric vehicles. However, electrochemical incompatibility between electrolyte and electrodes causes continuous performance degradation. Here, we report a unique design of a double-layer composite solid-state electrolyte(D-CSE), where each layer, composed of both polymer and ceramics, is electrochemically compatible with its contacting electrode(Li anode or LiCoO2cathode). The D-CSE has a small thickness(50 μm), high thermal stability(up to 160 °C without noticeable deformation), and good flexibility even at a high ceramics content(66.7 wt%). Large-area selfstanding film can be obtained by a facile coating route. The electrolyte/electrode interface can be further enhanced via forming a soft interface by in-situ polymerization. Quasi-solid-state Li|D-CSE|LiCoO2coin cells with the cathode-supported D-CSE can deliver a high initial discharge capacity of 134 mAh g-1and a high capacity retention of 83% after 200 cycles at 0.5 C and 60 °C. Quasi-solid-state Li|D-CSE|LiCoO2pouch cells(designed capacity 8.6 mAh) with the self-standing D-CSE have a high retention of80% after 180 cycles at 2 mA charge and 4 mA discharge. At a high cathode loading(19.1 mg cm-2),the Li|D-CSE|LiCoO2pouch cell still can be stably cycled, and can withstand abuse tests of folding, cutting and nail penetration, indicating practical applications of the D-CSE.