A siloxane-based self-healing gel electrolyte with deep eutectic solvents for safe quasi-solid-state lithium metal batteries

Due to the safety problems caused by the use of flammable organic electrolytes in lithium batteries, it is urgent to develop new solid electrolytes with higher safety. Deep eutectic solvent (DES), as a very promising flame-retardant electrolyte system, has limited its application due to its liquid properties and poor compatibility with lithium metal. Herein, we report a DES-based self-healing polymer (DSHP) electrolyte for quasi-solid-state lithium metal batteries. The electrolyte was prepared by in-situ polymerization of bis (3-amino-propyl)-terminated polydimethylsiloxane (PDMS-NH2) and toluene 2,4-diisocyanate (TDI) monomers in a DES-based electrolyte with fluoroethylene carbonate (FEC) as an additive. The polymer network effectively improves the compatibility of DES with lithium metal and maintains a high ionic conductivity (0.60 mS cm−1 at 30 °C). At the same time, the well-designed siloxane-based DSHP electrolyte not only exhibits self-healing property, but also demonstrates non-flammability advantage with a wide electrochemical voltage window (4.5 V vs Li / Li+) and a high Li+ migration number (0.69). Therefore, the symmetric Li | DSHP | Li cell exhibits long-term cycle stability (>1400 h). The quasi-solid-state lithium battery with DSHP electrolyte coupled with lithium anode and LiFePO4 cathode demonstrates a high specific capacity of 151.6 mA h g−1. More importantly, the DSHP-based pouch cell exhibits excellent flexibility during the deformation process. This work provides a valuable method to design high safety and high energy quasi-solid-state lithium batteries.