In situ initiator-free gelation of highly concentrated lithium bis(fluorosulfonyl)imide-1,3-dioxolane solid polymer electrolyte for high performance lithium-metal batteries

The safety concern on the uncontrollable growth of lithium dendrites in liquid electrolytes is the main challenge for high performance lithium-metal batteries. The traditional ex situ solid electrolytes can solve these issues to a great extent but are still plagued by low ionic conductivity, low Li+ transference number, and high interfacial impedance. Herein, a solid polymer electrolyte (SPE) with highly concentrated (3.5 M) lithium bis(fluorosulfonyl)imide (LiFSI) in 1,3-dioxolane (DOL) is developed via a simple in situ initiator-free gelation route at room temperature. This simple and ingeniously designed in situ SPE integrates a high ionic conductivity (7.9 mS cm−1 at room temperature), high Li+ transference number (0.82), and low interface impedance. As a result, the in situ 3.5 M LiFSI-DOL SPE demonstrates a superior lithium dendrite-free behavior, which enables the Li|Li symmetric battery to be stably stripped/plated for more than 1000 cycles with a low overpotential of 45 mV at 5 mA cm−2 and 5 mAh cm−2. Moreover, the Li|Cu battery with the in situ 3.5 M LiFSI-DOL SPE also exhibits a high coulombic efficiency (CE) up to 98.0% at 5 mA cm−2. In addition, the in situ 3.5 M LiFSI-DOL SPE used in the Li|LiFePO4 battery leads to superior cycle life (500 cycles), CE (98.8%), rate performance, and good mechanical flexibility. Remarkably, the Li-S batteries with the in situ 3.5 M LiFSI-DOL SPE also show good compatibility and stability. This work shows tremendous prospect toward high performance solid-state lithium-metal batteries by combining the in situ polymerization and high concentration electrolyte.