Research and development of all-solid-state lithium polymer secondary batteries

All-solid-state lithium polymer secondary batteries (LPBs) have been studied for the purpose of developing large-scale batteries for electric power load leveling devices. First, we prepared LPBs using a thin-film cathode, and the 'polymer/ceramic composite concept' of the LPBs was confirmed. Next, the degradation mechanism of powder-type cathode LPBs was investigated using a combination of several electrochemical methods. It was possible to quantitatively separate the resistances in the LPBs. It was revealed that the degradation of the LiCoO2 cathode/solid polymer electrolyte interface is dominant. Therefore, ceramic electrolyte coated cathode powder was prepared by a mechanical coating technique. As a result, it became clear that the oxidative decomposition, which takes place at the cathode/electrolyte interface, can be controlled by a coating of ceramic electrolyte on cathode powder.