Fast Charging of Li-Ion Cells: Part IV. Temperature Effects and "Safe Lines" to Avoid Lithium Plating

Fast charging of lithium-ion batteries that does not compromise cell performance and durability is critical for wider adoption of electric vehicles. Raising cell temperature is one approach to enable fast charge; the higher temperature facilitates charge migration and lowers electrode polarization limited by the rates of diffusion and interfacial transport. In this study we examine the behavior of cells subjected to constant current and pulse current charging, at rates from 1C to 8C in the 30 °C to 55 °C range. To demonstrate safe charge conditions that averts Li metal plating on the anode, we use a microprobe reference electrode to continuously monitor the electrode potentials during tests. We then adopt a state-of-the-art multiphase electrochemical model to extrapolate the anode reference potential to the anode surface potential, which determines the overpotential for Li plating. For constant current charging, the results suggest that safe charging at 6C to 80% full capacity would be untenable for all but the thinnest electrodes. For pulse charging, the safe conditions depend on cell voltage, temperature, and the rate/duration of the pulse. The "safe lines"established in this study can help define charging protocols that enable higher charge rates, while minimizing losses in cell performance over time.