Enhancing the Cycling Performance of High Voltage (4.5 V) Li/LiNi0.5Mn0.3Co0.2O2 Cell by Tailoring Sulfur-Derivative Cathode Passivation Film

Abstract

A sulfur-based compound, 1,3,2-dioxathiolane-2,2-dioxide (DTD) is utilized as a cathode film forming additive for high voltage (4.5 V) Li/LiNi0.5Mn0.3Co0.2O2 cell. Electrochemical performance of Li/LiNi0.5Mn0.3Co0.2O2 cell with 1.0 M LiPF6 EC/EMC (3/7, v/v) with/without DTD additive electrolyte has been evaluated. Linear sweep voltammetry (LSV) result demonstrates that DTD is preferably oxidized on the cathode surface to the LiPF6/carbonate bulk electrolyte. After 100 cycles at high voltage (4.5 V, vs. Li/Li+), the discharge capacity retention of the Li/LiNi0.5Co0.2Mn0.3O2 cell with baseline electrolyte is 68%, whereas the cell with 2.0 wt% DTD added electrolyte maintains 84% of its initial discharge capacity. Moreover, the cells with DTD additive exhibits superior rate performance and negligible self-discharge behavior. Ex-situ surface analysis on the cycled cathode and lithium metal was conducted with multiple advanced-techniques, including scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma spectroscopy (ICP-MS) and transmission electron microscope (TEM) as well. Ex-situ surface analysis of the cathode after cycling confirms that the improved electrochemical performances of the cells can be ascribed to more stable and robust surface layer built-up on cathode surface via the sacrificial decomposition of the DTD additive. This tailored stable and robust cathode layer can effectively prevent the detrimental reactions on the cathode/electrolyte interface, mitigate electrolyte decomposition on the cathode surface, and inhibit transition metal dissolution from the bulk cathode material upon cycling at high voltage.