Operando Analysis of Lithium Plating in Lithium-Ion Cells
The widespread commercialization of electric vehicles is currently hindered by their inability to compete with conventional gasoline-powered vehicles in terms of refueling time. The main barrier to achieving fast charge of lithium-ion batteries is the plating of metallic lithium on the surface of the graphite negative electrode, which is known to occur most prevalently at high C-rates, low temperatures, and high states of charge (SOC). While it is accepted that the lithium plating process is largely reversible, the factors affecting the reversibility of lithium plating have not been thoroughly investigated. This work seeks to determine the most influential factors affecting the reversibility of lithium plating in order to devise strategies to mitigate long-term damage to the cell if lithium plating has been detected. It was determined that the temperature during the rest phase following plating has the most significant influence on plating reversibility, with cells undergoing rest at 30 ℃ exhibiting nearly twice the Coulombic inefficiency of cells undergoing rest at 0 ℃. Additionally, a novel technique was developed to observe the relaxation processes directly in a graphite electrode just after lithium plating has occurred. The occurrence of electrochemical stripping and the dissolution of overshooting phases in graphite were verified through direct in-situ observation. A two-part model is presented to describe the progression of the relaxation processes in graphite after lithium plating occurs under high rate operation.