Preparation of Li4Ti5O12/C–C with super long high-rate cycle properties using glucose and polyurethane as double carbon sources for lithium ion batteries

Abstract

Li4Ti5O12/C–C (using glucose and polyurethane as double carbon sources) microspheres with particle sizes ranging from 200 to 300 nm were fabricated with a spray drying method, followed by a solid-state reaction. Compared with pure Li4Ti5O12 and Li4Ti5O12/C (using glucose as single carbon source), Li4Ti5O12/C–C exhibits higher rate performance and better cycling properties. The initial discharge capacity of Li4Ti5O12/C–C can reach 152.6 mA h g−1 at 5.0 C, which is much higher than the discharge capacity of pure Li4Ti5O12 (124.7 mA h g−1) and Li4Ti5O12/C (141 mA h g−1). Li4Ti5O12/C–C delivers a reversible capacity of 152.1 mA h g−1 (99.7% of capacity retention) during a cycle test at 5.0 C (400 cycles). This capacity is much higher than that of pure Li4Ti5O12 (118.5 mA h g−1, 95.1%) and Li4Ti5O12/C (140 mA h g−1, 99.3%). What is more gratifying is that the discharge capacity of Li4Ti5O12/C–C is still 131 mA h g−1 after another 1600 cycles, and the Coulombic efficiency remains close to 100%, indicating the crystal structure remains stable. These excellent electrochemical properties are attributed to the different carbon content and contribution from the double carbon source coating, which increases electronic conductivity, the diffusion coefficient of lithium ions, and the effective polarization reduction. In our work, Li4Ti5O12/C–C exhibits excellent rate capacity and super long high-rate cycle properties by improving lithium ion diffusion coefficient (DLi) and reducing the charge transfer resistance (Rct) which comes from the higher carbon content and double carbon sources.