Stable interface of a high-energy solid-state lithium metal battery via a sandwich composite polymer electrolyte

All solid-state composite polymer electrolyte (CPE) is considered to be the key to solving the high safety and long life of solid Li metal batteries (LMBs), but there are few CPEs that can suppress the side reactions of the cathode and achieve dendrite-free plating simultaneously. Here, a sandwiched structure CPE (SCPE) is prepared through a layer-by-layer coating process. Oxidation resistant polyacrylonitrile (PAN) and reduction resistant polyethylene oxide (PEO) are used to contact with cathode and anode respectively to protect "polymer-in-ceramic" (PIC)-CPE in SCPE. In which, PAN-CPE contacts with LiNi0.8Mn0.1Co0.1O2 (NCM811) to form a stable interface, and PEOCPE contacts with lithium (Li) to avoid reduction, thus ensuring high-voltage tolerance. More importantly, the synergistic effect of different CPEs in SCPE significantly facilitates high Li ion conductivity, wide electrochemical window, strong mechanical property and stable electrolyte/electrode interface. As a result, the Li symmetric cell using SCPE can be cycled over 500 h without voltage hysteresis. The NCM811/Li battery assembled with SCPE exhibits excellent cycle stability (88% after 500 cycles), and high Coulombic efficiency (over 99.2% after 500 cycles). This work proposes an approach to develop a low-cost, safe, and promising CPE to achieve high safety LMBs.