Highly Crystalline Lithium Titanium Oxide Sheets Coated with Nitrogen-Doped Carbon enable High-Rate Lithium-Ion Batteries

摘要

Sheets of Li4Ti5O12 with high crystallinity are coated with nitrogen- doped carbon (NC-LTO) using a controlled process, comprising hydrothermal reaction followed by chemical vapor deposition (CVD). Acetonitrile (CH3CN) vapor is used as carbon and nitrogen source to obtain a thin coating layer of nitrogen-doped carbon. The layer enables the NC-LTO material to maintain its sheet structure during the high-temperature CVD process and to achieve high crystallinity. Doping with nitrogen introduces defects into the carbon coating layer, and this increased degree of disorder allows fast transportation of lithium ions in the layer. An electrode of NC-LTO synthesized at 700 degrees C exhibits greatly improved rate and cycling performance due to a markedly decreased total cell resistance and enhanced Li-ion diffusion coefficient (D-Li). Specific capacities of 159.2 and 145.8 mAhg(-1) are obtained using the NC-LTO sheets, at charge/discharge rates of 1 and 10 C, respectively. These values are much higher than values for LTO particles did not undergo the acetonitrile CVD treatment. A capacity retention value as high as 94.7 % is achieved for the NC-LTO sheets after 400 cycles in a half-cell at 5 C discharge rate.