Enabling Extreme Fast Charging through Control of Li Deposition Overpotential on Graphite Electrodes

Abstract

Currently produced electric vehicles (EVs) rely on the use of lithium ion battery technology due to its high energy and power density.1 However, a major barrier facing the adoption of electric vehicles is that currently utilized Li-ion batteries take significantly longer to recharge (~ 30 minutes) compared to the time necessary to refuel vehicles powered by internal combustion engines (< 10 minutes). Thus, the need to develop Li-ion batteries which can be charged in approximately 10 minutes (6 C rate) without sacrificing range, cost, or cycle life is critical for the widespread implementation of EVs. The major barrier preventing extreme fast charging of Li-ion batteries is the occurrence of Li plating at the graphite anode, which operates at a working potential between 0.05 – 0.1 V vs. Li/Li+.2-4 When the anode is polarized below 0V, Li deposition on the graphite surface is favored over intercalation, and plating occurs. Because of the high reactivity of Li metal, subsequent reaction with the electrolyte occurs, consuming some of the active lithium and resulting in cell capacity loss. To suppress Li plating, multiple strategies have been demonstrated with only limited effectiveness, and new approaches are needed to enable cycling at extreme fast charging rates. In contrast to previous approaches for suppressing Li plating, in this project we utilized an entirely new concept where the overpotential for Li metal deposition at the electrode surface was deliberately increased, thus inhibiting Li metal deposition during extreme fast charging. This was be accomplished by coating graphite electrodes with ultrathin metal coatings which have high overpotentials unfavorable for lithium deposition. The nanometer scale thickness of the metal coatings enabled the function of the graphite electrode to be maintained and preserve state of the art energy density. Published results probed the properties of the metallic surface coatings and their effectiveness at suppressing Li deposition and reducing capacity fade under XFC.1,2 Batteries incorporating graphite electrodes with high metal film loadings exhibited an improvement in capacity retention after 500 fast (10-minute) charge cycles of ~9% compared to uncoated anodes. Li metal deposition quantified by X-ray diffraction supported these findings, with higher loading metal films exhibiting enhanced Li plating suppression compared to lower loading films. The results highlight the use of nanoscale functional surface coatings for prevention of Li plating during battery fast charging. These results establish an effective method using interfacial modification to achieve deliberate control of Li-metal deposition overpotential and reduction of lithium plating on graphite.