Self-supporting carbon-encapsulated TiNb2O7 electrode as anode for improved Li-ion batteries: Experimental and theoretical studies

Titanium Niobate (TiNb2O7, TN), exhibiting the Wadsley-Roth phase, is regarded as a promising candidate for lithium-ion batteries (LIBs) due to its substantial theoretical capacity and safe operating potential. However, its commercial application is impeded by poor electronic conductivity and slow ionic diffusion kinetics. In this study, carbon-encapsulated TiNb2O7 particles (TNC) were investigated as viable anodes for LIBs. In contrast to the conventional binder-based electrode fabrication method, the anode is produced using a 'binder-free' technique, yielding a 'self-supporting' flexible electrode suitable for diverse applications. A thorough electrochemical evaluation shows that TNC self-supported composite electrode exhibits improved reaction kinetics and enhanced specific capacities, reaching 334 mA h/g at 0.1 C. Additionally, it demonstrates improved rate capabilities, and long-term cyclic performance by retaining similar to 82 % of its capacity and maintaining nearly 100 % Coulombic efficiency even after 2000 cycles at 10 C. Moreover, the role of carbon encapsulation has been thoroughly examined via experimental studies and vigorously supported by theoretical calculations using density functional theory (DFT). Additionally, a full-cell LIB is configured using TNC and LiFePO4 composite electrodes as anode and cathode, respectively. The full cell shows excellent electrochemical performance, high capacity, and promising potential for practical applications. The full-cell battery maintains around 79 % of its capacity and attains 98 % Coulombic efficiency after 500 cycles. Additionally, it exhibits a high energy density of 255 W h/kg and a substantial power density of 1,409 W/kg. These findings unequivocally indicate that the TNC composite material is a highly promising anode candidate for safe, high-capacity, and stable flexible LIBs.