Tapping the True Potential of Carbon By Stabilized Li Plating: High Gravimetric / Areal Capacity Systems

Abstract

With the advent of high-capacity lithium - sulfur chemistry, lithium – O2 system and the industrial impetus on increasing the areal loading of oxide-based cathode systems to improve the energy density of existing batteries, efficient and stable lithium plating/deplating in liquid electrolyte still remains the key for all these technologies to come into practical utilization or improve the existing commercial systems.The major electrochemical performance issues with lithium metal plating are poor coulombic efficiency of plating/deplating, the erratic voltage fluctuations which are reflected due to undesired plating morphology (high surface area lithium growth, mossy Li plating, dendritic lithium plating) and the decomposition of electrolyte on the growth sites (solid electrolyte interphase, SEI) during the plating process. The fundamental phenomena which dictate these issues are the electron transfer at the plating interface and the Li+ flux in the system. Subsequently, the reversibility of Li plating is determined by the stability of the deposition structure on the substrate along with that of solid electrolyte interface (SEI) upon repeated plating/deplating.Stabilization of lithium metal plating in liquid electrolyte is a critical barrier for high energy density and high-rate capability lithium-ion batteries. Carbon – based system with a high gravimetric capacity of 2500mAh/g – 3000mAh/g is developed surpassing intercalation chemistry by stabilizing the plating of lithium metal in liquid electrolytes to compete with that of silicon and graphite-based electrodes. Anode architecture utilizing carbon structures as the active material with the ability to control / restrict the Li plating sites as well as the morphology has been developed which improves the reversibility of the Li plating in the system.The innovative testing methodology developed reflects the true performance of the system with accuracy compared to the traditional coincell testing. The carbon-based nanostructured electrodes show a high theoretical capacity sustaining areal capacities of ~6mAh/cm2 for over 600 cycles with a high coulombic efficiency of ~99.75 – 99.94%. The system can sustain cathodes at areal capacity of 2 – 5 mAh/cm2 and areal current densities of 1mA/cm2 – 6mA/cm2 with good rate capability without sacrificing gravimetric capacity and energy density.A detailed testing protocol has been develped to distinguish the phenomenon of Li reaction and Li metal plating on the anode. A modified coin cell testing has been developed to control the Li plating to record accurate electrochemical signal. Results of these studies along with the electrode architecture, extensive electrochemical characterization including electrochemical impedance, rate capability and SEM analysis of the electrodes will be presented and discussed. Acknowledgement: The authors gratefully acknowledge the Department of Chemical and Petroleum Engineering, Energy Innovation Center, Nano Fabrication and Characterization Facility at University of Pittsburgh for their support.