Investigation of Novel Polymeric Solid Electrolyte for Lithium Secondary Battery

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Novel polymeric solid electrolyte, poly (ethylene oxide) -grafted poly (methyl methacrylate) with a lithium salt and polar solvents (propylene carbonate (PC) and/or polyethylene glycol (PEG)) was investigated for lithium secondary batteries.1. The polymeric solid electrolyte was prepared by UV irradiation to mixture of monomer, lithium salt, solvent and photo initiator. Electric conductivity of the resulted film was ca. 10^<-4> S cm^<-1> at room temperature.Improvement of conductivity to 3.5 x 10^<-3> S cm^<-1> was accomplished by dipping the film into a liquid electrolyte (lithium salt, for an example LiClO_4 / PC) after heat treatment.2. The electrode reaction of lithium in the polymeric solid electrolyte was studied. The charge transfer rate at the lithium electrode/polymeric electrolyte was high and the ion transfer in the bulk electrolyte was rate determing at high cathodic polarization.3. Insertion and removal of lithium ions at an advanced manganese oxide electrode in the polymeric solid electrolyte was confirmed by cyclic voltammetry. This material can be used as positive material for a lithium secondary battery.4. According to results from 1 to 3, a model lithium secondary cell was constructed. The model cell had 140 - 200 mAh g^<-1> (per gram of positive material) as discharge capacity and excellent cycle performance.