Development of Safe and High Power Batteries for HEVs

Safety is one of the most important concerns for lithium-ion batteries due to the high energy density of the cells. In battery packs for HEV, PHEV, or EV applications, there exist dozens of lithium-ion cells that are connected in series and/or parallel to create a pack with high voltage and that is capable of discharging and charging with high currents. Managing such a battery pack therefore requires increased safety management compared to a cellphone or laptop battery. Not only is the management of the safety important during usage of the pack but also during assembly and maintenance. The high voltage conditions (>100V) that exist in HEV battery packs can pose potential hazards for workers and auto mechanics. The need for increased safety controls increases with higher voltage systems. Therefore, improving the safety of the lithium-ion battery via the cell chemistry can lead to a reduction of cost for the HEV, PHEV, and EV battery by eliminating the need for costly battery management and cooling systems.
In order to improve the safety of lithium-ion batteries for use in HEV, PHEV, and EV applications, EnerDel has investigated various battery active materials using 2Ah sized prototype cells. These cells were tested according to the U.S. Advanced Battery Consortium (USABC) test FreedomCAR manual. The tests included power capability, cycle life, calendar life, and cold cranking tests. In addition to the tests in the FreedomCAR test manual, some abuse tests such as overcharge and nail penetration were also carried out.