Electrochemical properties of surface-modified hard carbon electrodes for lithium-ion batteries

Current methods for improving the electrochemical properties of lithium-ion battery electrode materials demand an understanding of its surface property and chemistry. We investigate the electrochemical property of a thin-film Li₄Ti₅O₁₂ (LTO) layer on a hard carbon (e.g., glass-like carbon) ideal model electrode and propose that its unique properties make it an effective protective coating layer to improve the performance and stability of commercially obtained hard carbon powder. The LTO layer displayed a varying degree of coverage with the number of coatings, which minimized the initial reversible capacity loss because of the continuous electrolyte reduction due to the surface film formation on the GC electrode surface and improved reversibility. With the successful addition of the protective coating layers, the total resistances for interfacial charge transfer was significantly decreased. Using an in situ technique to probe the surface film's electrochemical characteristics, we systematically reveal that the LTO layer functioned as an inner, compact layer with its in situ surface film formation on the surface and resulted in a stable interface and displayed exemplary coverage and shielded most of the direct contact between the GC electrode and electrolyte solution. Furthermore, the LTO layer displayed a notable increase in current density, indicating the increased lithium-ion activity (a_Li+) at the interface between the GC electrode and the LTO layer resulting in outstanding cyclability and rate performance.