In situ generating poly ionic liquid composite electrolytes supported by mesoporous silica–modified PP separator enabling stable lithium-ion batteries

Solid polymer electrolytes (SPEs) are flexible and safer, but inferior ionic conductivity, electrode/electrolyte interface and mechanical strength limit their use for lithium-ion batteries. Herein, we design and prepare a high ionic conductivity, low internal resistance, stable SPE by in situ polymerization of vinylene carbonate and 1-vinyl-3-pentyl cyano imidazole (trifluoromethanesulfonyl) imide in the mesoporous silica-modified polypropylene separators. Mesoporous silica modified polypropylene separators could efficiently adsorb polymer precursor before in-suit polymerization and inhibit lithium dendrite growth during cycling, improving the mechanical strength of SPEs. The poly ionic liquid with many polar groups could effectively promote the dissociation of lithium salts, while its crosslinked network provides Li⁺ transport channels to facilitate the migration of Li⁺. Meanwhile, in situ polymerization leads to robust electrode/electrolyte interfaces, which reduce the internal resistance and improve the stability of batteries. The optimized SPE (KCE) has a room temperature ionic conductivity of 8.04 × 10⁻⁴ S cm⁻¹ and an electrochemical window of 4.5 V. Assembled Li//KCE//Li cell could run stably at a current density of 0.1 mA cm⁻² for 1000 h. Furthermore, the capacity retention rate of LFP//KCE//Li battery after 500 cycles can maintain over 90% and NCM811//KCE//Li battery shows a capacity retention rate of 86.5% after 100 cycles. The LFP//KCE//Li soft pack battery can light an LED bulb and has an open circuit voltage of 2.95 V, showing great potential in the flexibility field. This work provides a workable strategy for improving the performance of solid polymer electrolytes.