Reinforcing concentrated phosphate electrolytes with in-situ polymerized skeletons for robust quasi-solid lithium metal batteries

Current lithium metal batteries are haunted by stability issues and safety concerns that are critically linked to the growth of dendritic lithium. A quasi-solid electrolyte is designed that is non-flammable and is capable of suppressing dendrites by in-situ polymerizing a poly (methyl methacrylate) skeleton to support phosphate-based electrolytes with high salt concentrations. By varying the polymer-to-electrolyte ratio, we reveal that there is a strong interplay between the mechanical strength, the ionic conductivity, and the ability to suppress dendrites. A carefully chosen composition leads to a quasi-solid electrolyte with a high ionic conductivity of 0.11 mS cm−1, a wide electrochemical window up to 4.8 V vs. Li/Li+, and the ability to suppress lithium dendrites at high current densities. Stable lithium plating and stripping is achieved using such electrolyte at a current density of 1.2 mA cm−2, a two-fold increase compared with its liquid counterpart. A lithium-metal battery using a LiFePO4 cathode with a high active material loading of ~15 mg cm−2 based on the quasi-solid electrolyte is demonstrated which exhibits high specific capacity of over 100 mAh g−1 and is able to be cycled 150 times without obvious capacity decay. The current work offers a practical solution to the safety concerns as well as the stability issues of lithium metal batteries.