10-Min Fast Charging of Automotive Li-Ion Batteries at an Elevated Temperature

Abstract

Fast charging technology is widely recognized as a critical factor in bolstering consumer appeal of battery electric vehicles (BEVs). The U.S. Department of Energy (DOE) has set a goal of developing extreme fast charging (XFC) battery technology that can recharge a 200-mile BEV in 10 minutes. A key barrier to XFC of automotive Li-ion batteries is the issue of lithium plating, which drastically deteriorates battery life and even induces hazardous consequences. Fundamentally, lithium plating is affected by the rate capability of ion transport in the electrolyte, intercalation reaction at graphite surface, and solid-state diffusion in graphite particles. Research in the literature, accordingly, has been focusing on improving electrolyte transport properties, enhancing charge transfer kinetics, or utilizing smaller particles. Li-ion battery is well known for its trade-off nature. Improving one property without sacrificing others is always challenging. An alternative approach to suppressing lithium plating is to elevate charge temperature. Indeed, an increase in temperature can boost the rate capability of the above three processes simultaneously. However, an elevated temperature, on the other hand, accelerates the solid-electrolyte-interphase (SEI) growth. Owing to the interplay between lithium plating and SEI growth, it is universally believed that Li-ion batteries have an optimal life at room temperature. [1] In 2018, our group presented a numerical study revealing that the optimal temperature of a Li-ion battery, in contrary to the conventional wisdom, actually increases with an increase of charge rate and/or energy density.[2] Enlightened by this finding, we proposed a heated-charge method [2, 3] to charge a Li-ion cell at an elevated temperature of 40-60oC to enable XFC without Li plating. Very recently, Tesla has applied this concept in its V3 superchargers. Using an ‘On-route Battery Warmup’ strategy, Tesla vehicles are designed to arrive at a fast charging station at a temperature of ~40oC, demonstrating the commercial viability of charging a BEV at an elevated temperature. Nevertheless, a potential issue of Tesla’s on-route warmup strategy is the slow heating speed, making a battery stay at a high temperature for a long period of time and hence incurring excessive SEI-induced degradation. Currently, we are developing an XFC battery based on the heated-charge method. With a novel structure, our battery has >100x faster heating than conventional external heating methods, thereby limiting the duration of heating to a matter of seconds. More profoundly, we will present in this talk that our battery, having an energy density of 210 Wh/kg, could sustain 2,000 cycles of 10-min (6C) charge to 80% state of charge with only 7% capacity loss.