A novel gel polymer electrolyte based on trimethylolpropane trimethylacrylate/ionic liquid via in situ thermal polymerization for lithium-ion batteries

Gel polymer electrolytes (GPEs) based on trimethylolpropane trimethylacrylate (TMPTMA) are in situ polymerized using lithium bis(trifluoromethane)sulfonimide (LiTFSI), dimethylcarbonate (DMC) and ionic liquid (IL)-tributylmethylammonium bis(trifluoromethanesulfonyl) imide (N_1,4,4,4TFSI). The GPEs presented both the liquid-like ionic transport and solid-like features. The N_1,4,4,4TFSI can effectively dissociate the lithium salts to boost ionic transport, and thus delivers a high ionic conductivity of 6.15 × 10⁻³ S cm⁻¹ at 25 °C. The interfacial resistance between ionic liquid and lithium metals was reduced, resulting in the benign interfacial contact with Li metal electrode. Lithium ion batteries are assembled based on TMPTMA-based cross-linked gel polymer electrolytes (with LiCoO₂ as positive electrode and lithium as negative electrode). The results suggest that the GPEs modified with ionic liquid presented improved cycling performance (with a discharge capacity of 111.1 mA h g⁻¹ after 100 cycles) and good capacity retention of 80%. Also, the GPEs hold favorable compatibility with the LiNi_0.8Co_0.1Mn_0.1O₂ positive electrode, exhibiting an initial discharge capacity of 183.1 mA h g⁻¹ as well as a stable capacity of beyond 149 mA h g⁻¹ after 100 cycles. The GPEs enable the assembled LiCoO₂/Li and Li_1.2Ni_0.8Co_0.1Mn_0.1O₂/Li batteries for well operating within a wide C rate range (0.1–2.0 C). The improved cycling behaviors can be attributed to the suppressed growth of the cell impedance and stable interface compatibility toward lithium metal negative electrode .