Nanostructured Electrode Materials for High Rate, Large Format Lithium Ion Batteries 2005-01-1895
Lithium ion batteries are superior to NiMH batteries in energy density, but have been excluded from the highest power density applications due to safety and cost limitations. The cathode materials in conventional lithium ion cells are based on metal oxide materials, typically containing nickel or cobalt. These nickel and cobalt based cathode materials are expensive and reactive with the electrolyte. Metal oxides are electronic insulators, which can limit the rate performance of lithium ion cells. The open circuit potential of conventional metal oxide electrodes is relatively high. This limits the charge acceptance rate, since the polarization under high rate charging (> 10C) can exceed the potential limit of the electrolyte. Similarly, the open circuit potential of conventional graphitic anode materials is close to the lithium plating potential which also limits high charge rate acceptance. T/J Technologies has developed and demonstrated new bulk energy storage concepts based on nanostructured composite metal oxide anode and metal phosphate cathode electrodes. The composite design provides for high electronic conductivity, and the nanostructure limits the lithium transport distance. The open circuit potentials for these materials are displaced from the lithium plating and electrolyte decomposition potentials. These features contribute to high rate capability. In these systems, up to 25% of the C/10 capacity is retained at charge/discharge rates of >100 C. These cells have improved thermal stability and electrolyte oxidation resistance, excellent cycle life, high capacity retention at high rates, and potentially low cost for high volume/large format applications. With much higher energy density than ultra capacitors or hybrid battery/capacitors, these ultra-high rate lithium batteries are ideally suited for hybrid electric vehicles (Future Combat System).