A thermoresponsive composite separator loaded with paraffin@SiO2 microparticles for safe and stable lithium batteries

Abstract

Lithium-ion batteries (LIBs)-related accidents have been reported for years and safety issues are stumbling blocks for the practical applications of lithium metal batteries (LMBs) with higher energy density. More effective strategies to shut down the battery at the early stage of thermal runaway with less side effects on the electrochemical performance are greatly desired. In this work, the core–shell structural paraffin@SiO2 microparticles were synthesized by in situ emulsion interfacial hydrolysis and polycondensation and the paraffin@SiO2-loaded separator (PSS) was prepared by a facile filtration method. The introduction of hydrophilic silica shells in paraffin@SiO2 enhanced the wettability of carbonate electrolyte with the composite separator and improved the processability of soft paraffin. As a result, when used in LMBs at room temperature, the cell with PSS inside had a more uniform deposition of lithium, a much lower overpotential and a more stable electrochemical performance than the cell with the blank separator or the conventional pure paraffin-loaded separator inside. More significantly, when a heating stimulation (i.e. 115 ℃) was subjected to the cell with PSS inside, the paraffin in the core of paraffin@SiO2 could be released, blocking the gaps between particles and the pores in the separator and efficiently stopping the transportation of Li+ between two electrodes, resulting in the thermally-induced shutdown of the cell below the melting temperature of PE (~135 ℃) in the Celgard2325 separator. The core–shell structure of paraffin@SiO2 enables the maintaining of each component’s benefits while avoiding each one’s drawbacks by elaborating microstructural design. Therefore, the conventional dilemma between the electrochemcial performance and safety of LMBs could be solved in the future.