A cleverly designed asymmetrical composite electrolyte via in-situ polymerization for high-performance, dendrite-free solid state lithium metal battery

In-situ polymerized gel polymer electrolytes have been considered as the most promising alternative to liquid electrolyte owing to their high ionic conductivity, improved safety, simple and environmentally friendly manufacturing process, and good interfacial compatibility with electrodes. However, their poor mechanical properties are not able to prevent the Li dendrites growth in batteries. Inspired by the composite electrolytes, an asymmetrical gel electrolyte (A-PGCE) consisting of cellulose membrane-supported gel electrolyte and LLZTO-rich layer on one side is fabricated by a facile one-step in-situ polymerization method. The well-designed A-PGCE not only exhibits excellent properties such as superior flexibility, good thermal stability and wide electrochemical window (5.13 V), but also possesses high ionic conductivity (1.25 × 10-3 S cm−1) and Li+ transference number (0.57). Furthermore, the introduced LLZTO-rich layer demonstrates excellent ability in guiding uniform Li+ deposition and suppressing Li dendrite growth, which enables the symmetrical Li-Li cells with such electrolyte to run stably for over 1750 h at 0.1 mA cm−2 and 450 h at 0.2 mA cm−2. Benefiting from these advantages of A-PGCE, the assembled Li metal battery with high-voltage LiCoO2 (LCO) cathode shows high initial capacity of 157.6 mAh g−1 in the cutoff voltage of 4.3 V, and the capacity retention is 90.7% after 200 cycles at 0.2C, indicating a superior cyclic stability. The cleverly designed asymmetrical A-PGCE shows great potential in boosting the development of lithium metal batteries with high energy density and safety.