The Mechanism of Li Plating on Graphite Particles

Abstract

Lithium ion battery is the mainstream technology that is powering most of mobile applications (consumer electronics, power tools etc.) and in the future, our transportation by electrifying the vehicles. Current lithium ion battery can only support 1C charging (~50 mins for 80% charge), which is much longer than refilling gasoline car ( < 5 min). Extreme fast charging ( <10 min for 80%) is a very attractive technology that can address this problem. However, Li plating happens in graphite at high charge currents or low temperature, which causes battery performance degradation or even safety hazard (short-circuit, thermal runaway and even fire).The core of addressing Li plating problem lies in understanding its mechanism. Despite Li ion battery has been invented for 30 years, a systematic understanding on the onset and growth of Li in graphite anode is still lacking. In this work, we elucidate the mechanism of Li plating, by investigating the interplay between Li intercalation and Li plating on a single graphite particle using in-situ optical microscopy coupled with electrochemical test. The results show Li plating happens when the surface of graphite saturates which shuts down the intercalation reaction. The saturation can happen much earlier than full lithiation of graphite particle due to solid diffusion limitation, resulting in severe under-utilization. The discovery sheds light on directions and guidelines of materials innovation or electrode design for achieving extreme fast charging.