Development of 10 Wh class lithium secondary cells in the ‘New Sunshine Program’

The LIBES member companies have developed 10 Wh class lithium secondary cells in 1996. Through the Phase 1, the member companies developed elementary technologies and reflected these into a 10 Wh class cell. The 10 Wh class cells have substantially fulfilled the targets of the first interim evaluation for capacity, energy density and specific energy. Some of these cells have not satisfied the targets of cycle life, therefore, it was obvious that the cycleability should be set at 3500 cycles for the long life type and at 500 cycles for the high energy density type, respectively. It appeared that the solid polymer electrolyte type 10 Wh cell implied the importance of the interface control between active materials and solid polymer electrolyte and improved ionic conductivity, and that the lithium metal system needs to restrain the lithium reaction with electrolyte. The incompleteness of cycle life seems to come from the selection of the active materials, the capacity balance of the materials and the volume of the electrolyte involved. Further R&D on cell design and material development are necessary in the cell system for the final targets in 2001.