Climate-Immune Extreme Fast Charging of High Energy Li-Ion Batteries

Abstract

Fast charging is the enabler of mainstream adoption of electric vehicles (EVs). There is a race worldwide for building fast charging stations with the power up to 350kW, which are able to charge a 200-mile-range EV at 6C (10 minutes). State-of-the-art EV batteries (cell-level energy density >200 Wh/kg) could only withstand 2C (30 minutes) charging due to the issue of lithium plating. Even worse, the charge rate must be dramatically reduced at low temperatures to prevent lithium plating. Most recently, our group presented a controllable cell structure that enables lithium plating free (LPF) fast charging at all temperatures. [1] The key is to charge a cell always above a temperature that can prevent lithium plating. A rapid heating step will be performed before charging if the cell temperature is low. It is demonstrated that a 9.5Ah pouch cell with an energy density of 170 Wh/kg could be charged by 80% state of charge in 15 minutes even at -50oC, an extremely low temperature at which all conventional Li-ion cells would cease to work. Furthermore, the LPF cell sustained 4500 cycles of 15-min fast charging at 0oC with <20% capacity loss, which is equivalent to >12 years and >280,000 miles of EV lifetime, whereas a baseline conventional cell at the same condition only survived 50 cycles. Based on the LPF cell structure, we proposed an approach to enable 10-min extreme fast charging (XFC) of high energy EV cells. By numerical analysis, we revealed that the optimal temperature for Li-ion battery charging increases with the increase of charge rate and energy density. [2] Thus, we are now partnering with the U.S. Department of Energy (DOE) to develop an XFC battery that is charged at high temperatures (>60oC). The target is to achieve 6C charging of >225 Wh/kg cells with a life of >1000 cycles at <20% capacity loss. In this talk, we will give a comprehensive discussion of the LPF cell structure and operating strategy. We will also share our latest progress on the development of XFC cells.