The Role of Surface Coatings on the Strain Evolution in Li-Ion Cathode Electrodes during Electrochemical Cycling

Abstract

Rechargeable Li-ion batteries (LIBs) have been successfully commercialized for portable electronics in the last two decades. Although there has been a great interest to use LIBs in more demanding applications such as electric vehicles, adoption of LIBs has been hindered by capacity loss and poor performance. The current stage of the cathode performance is a limiting factor for the development of higher performance LIBs. Cathode electrodes suffer from significant capacity fade with cycling due to continuous volumetric changes, unstable cathode-electrolyte interface and active material dissolution. Lithium intercalation induces considerable volumetric changes in the electrode and even small strain can cause particle fractures in brittle cathode materials. Surface modification of the cathode electrodes has been used to improve the capacity retention and cycling stability of the electrodes at higher charge/discharge rates by minimizing active material dissolution and stabilizing the electrode-electrolyte surface layer. Although various surface modification techniques were utilized to improve the performance of the electrodes, the underlying mechanism of surface modification has not been elucidated yet. In this work, we investigated the role of surface coatings on the strain generation in lithium manganese oxide (LMO) composite electrodes. Full-field strain measurements based on digital image correlation (DIC) is carried out to measure strain evolution in LMO electrodes1. Scalable electrolysis deposition method was performed to coat LMO particles with Au shell2. LMO composite electrodes were fabricated with a composition of 8:1:1 weight ratio of LMO, carboxymethyl cellulose binder and carbon black. Electrodes were cycled with cyclic voltammetry technique at different scan rates (between 10 and 100μV/s). As expected, composite electrodes expanded during delithiation when lithium is inserted into the electrode and contacted during lithiation when lithium is removed. Capacity was calculated to understand relationship between strain evolution with amount of lithium ions in the electrode at a given scan rate. Interestingly, The LMO electrode without coating undergoes larger strain generation at higher scan rates compared to LMO electrode with surface coatings. Volumetric expansion of LMO (without coating) electrode changes dramatically depending on scan rate whereas strain evolution in the gold-coated LMO electrode is primarily function of capacity, regardless of scan rate. The role of the surface coatings on the mechanical and electrochemical performance of the LMO electrodes will be discussed. References Ö. Ö. Çapraz, S. Rajput, S. White, and N. R. Sottos, Exp Mech, 15, 1182–11 (2018).J. L. Esbenshade, M. D. Fox, and A. A. Gewirth, J. Electrochem. Soc., 162 (1), A26 (2015). Acknowledgement This work was supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.”