In-situ thermal polymerization of rechargeable lithium batteries with poly(methyl methacrylate) based gel-polymer electrolyte

By heating the admixture of a commercial liquid electrolyte (LB302, 1 M solution of LiPF₆ in 1:1 EC/DEC), methyl methacrylate (MMA) and benzoyl peroxide (BPO, initiator), a poly(methyl methacrylate) (PMMA) based gel-polymer electrolyte (GPE) was obtained. AC impedance spectroscopy and cyclic voltammetry were used to evaluate its ionic conductivity and electrochemical stability window. Rechargeable cells LiNi_0.8Co_0.2O₂/Li and LiNi_0.8Co_0.2O₂/graphite with this MMA based GPE were also fabricated via the in-situ thermal polymerization process. This GPE exhibits a high ionic conductivity (over 10⁻³S cm⁻¹) at room temperature. It is stable in the voltage range between 0 and 4.2 V (vs. Li⁺/Li). A phenomenon of large initial cell impedance (LICI) was observed for the LiNi_0.8Co_0.2O₂/Li cells but not in LiNi_0.8Co_0.2O₂/graphite cells. After the first several cycles, the cell impedance decreases substantially and reversible charge–discharge capacity can be obtained. This in-situ polymerization method provides a way to produce GPE cells.