Exploring the Opportunity Space For High-Power Li-Ion Batteries in Next-Generation 48V Mild Hybrid Electric Vehicles 2017-01-1197

48V battery packs, with rated power capabilities on the order of 8-16kW, are rapidly becoming a new standard in the automotive industry. Improving on their 12V counterparts (2-5kW), 48V Mild Hybrid Electric Vehicles (MHEV) allow for extended start-stop and regenerative braking functionalities, providing fuel economy benefits of up to 10-15% in standard passenger vehicles.

New and relatively unexplored opportunities exist to further increase the fuel economy and performance of 48V systems. Improvement in battery power (to ~25kW) would further enable hybridization to near-HEV levels as well as engine downsizing, thus paving the way to fuel economy improvements beyond the current 10-15% MHEV limit. Additionally, new electrified features may be added, such as electric turbo/supercharging, electric traction, electric power steering, electric suspension and electric air conditioning. Vehicle electrification topology and strategy are investigated with respect to their impact on sizing, including a fuel-economy-oriented strategy based on a belt-integrated starter generator, a P4 “through-road” hybrid, and a 48V variant with electrified accessories.

In this paper, we explore the various opportunities for novel, advanced 48V systems and link these capabilities with requirements at the battery level. We conclude that future-looking vehicle features and high levels of fuel economy benefit require the development of 48V battery packs with a high power-to-energy ratio. 48V batteries with strong power (up to ~25kW) and HEV-level energy capabilities (<200Wh for most scenarios) are needed to enable the technologies explored in this work, demanding batteries with power-to-energy ratios between 30 and 160. To serve these power and energy needs, we present a high-power, lithium-iron-phosphate chemistry with excellent rate capabilities. Our conclusions suggest that a family of batteries based on high-power lithium-iron-phosphate (LFP) can meet the needs of advanced 48V architectures, providing new features to consumers and excellent fuel economy.