Characteristics of a thin film lithium-ion battery using plasticized solid polymer electrolyte

Synthesis was performed on a three-dimensional cross-linked material comprising principal chains of a random copolymermade of ethylene oxide and propylene oxide as a solid polymer electrolyte, which was plasticized by an organic solvent. This solid polymer electrolyte has an ionic conductivity of 1.5 × 10−3 S cm−1 at 20 °C and good temperature properties. The solid polymer electrolyte is high in mechanical strength and thermal stability because of the three-dimensional crosslinking. We have manufactured successfully a lithium-ion battery of film form and card size with a thickness of 0.45 mm by using this solid polymer electrolyte. Positive electrodes of the battery use LiCoO2 as an active material, and negative electrodes use a less highly graphitized carbon material. The battery has an average voltage of 3.6 and a discharge capacity of about 100 mAh. In a 0.3C cycle test at 20 °C, the battery was shown to have retained a capacity of about 90% of the initial capacity at the 300th cycle.