A composite polymer electrolyte based on an ionic liquid, Li salt and polymeric ionic liquid that included PIL-functionalized mesoporous silica nanoplates is prepared through a simple solution-casting method. A PIL-functionalized mesoporous silica content (8wt.%) optimized composite polymer electrolyte possesses high ionic conductivity, a high Li ion transference number, and good interfacial stability characteristics superior to those of a plain PIL-based electrolyte or incorporating PIL-functionalized silica nanoplates. The incorporation of porous structured silica nanoplates leads to the creation of a continuous and interconnected conductive network, and weakens the anionic and cationic interactions of the IL and Li salts, thereby improving ionic mobility and charge carrier concentration. Also, the PIL-functionalized mesoporous silica nanoplates effectively improves the electrochemical stability and interfacial stability of the polymer electrolyte with the Li metal electrode and anode electrode, due to its large surface area and the high affinity resulting from porous structures and grafted PIL. Accordingly, Li/LiFePO4 cells with composite polymer electrolyte and PIL-functionalized mesoporous silica nanoplates exhibit remarkably improved discharged capacities and cyclabilities, compared to cells with plain PIL-based polymer electrolyte,displaying a higher average specific capacities at 40 and 60°C, approximating to 228% and 152% enhancements after 100 cycles, respectively.