Preparation of SiO2 grafted polyimidazole solid electrolyte for lithium-ion batteries

Solid electrolytes have emerged as a promising alternative to liquid electrolytes for application in solvent-free lithium rechargeable batteries. Composite polymer electrolytes based on polymer and nanoparticle exhibit acceptable ion conductivity due to the interaction between nanofillers and polymer. However, the application of composite polymer electrolytes is hindered by the agglomeration of nanofillers at high concentration. Herein, in this study, the polymer electrolytes with branched polyimidazole were synthesized by radical polymerization based on functionalized SiO2 nanoparticles and imidazole monomers. Different from the reported methods of blending ceramic particles with polymers, we introduce an in situ synthesis of branched polymer electrolyte based on functionalized SiO2 nanoparticles. The stronger chemical interactions between SiO2 nanospheres and polymer chains could significantly suppress the aggregation of the nanoparticles and improve temperature stability. Among all of the electrolyte films, SiO2-MOBIm6-BF4 shows the best ion conductivity of 5.96 × 10−5 S cm−1 at 25 °C and the value reaches to 9.54 × 10−4 S cm−1 at 95 °C. This is mainly due to the long methylene chain increasing the flexibility of the chain segment and the molecular mobility, which is benefit to lithium-ion transportation. The electrochemical stabilization window can reach 4.85 V at room temperature, and the LiFePO4/SiO2-MOBIm6-BF4/Li battery was assembled with the electrolyte based on SiO2-MOBIm6-BF4. The first discharge capacity can reach 158.3 mAh g−1, and the batteries show good cycle performance.