Safety performance for phosphate based large format lithium-ion battery

The use of lithium-ion batteries in many of today´s electronic consumer products has increased significantly due to the advantages of high energy density, high cell voltage, and longer shelf life over that of comparable battery chemistries. The cell chemistry of conventional lithium-ion batteries has been limited by the choice of suitable lithium liberating cathode materials i.e. the three oxide electro active materials: LiMn₂O₄, LiCoO₂ and LiNiO₂ (lithium-manganese, lithium-cobalt, and lithium-nickel respectively). These materials are generally found to offer high electrochemical performance at the expense of poor thermal stability. The three lithium oxide´s thermal instability when over-charged has limited the application of these materials to small and relatively low capacity lithium-ion batteries. The novel use of a phosphate-based material in the cathode has been found to offer many of the advantages of traditional lithium-ion chemistries without sacrificing the safety necessary in a large format application. In this paper, the results of safety testing comparing phosphate-based cells and the most popular of the three lithium oxide materials (lithium-cobalt), is presented. Test data will show that the safety circuitry used in popular lithium-cobalt 18650 cylindrical cells will not prevent an event or propagation of an event if thermal runaway occurs within one cell in a battery pack. In contrast, abuse testing of phosphates based cells shows no thermal events under identical conditions.