Preparation and capacitance performance of nitrided lithium titanate nanoarrays

Nitrided lithium titanate (N-Li4Ti5O12) nanoarrays with nanowire and nanotube structures were designed as the electrode materials of lithium-ion supercapacitor for electrochemical energy storage. Two types of TiO2 nanoarrays were used as the precursor which involved TiO2 nanowire array prepared by hydrothermal process and TiO2 nanotube array prepared by anodization process. Li4Ti5O12 nanoarrays were formed through hydrothermal reaction or sonochemical reaction of TiO2 nanoarrays with lithium hydroxide and then calcination treatment process. Finally, N-Li4Ti5O12 nanoarrays were formed through nitriding treatment of Li4Ti5O12 using ammonia as nitrogen source. The electroactive N-Li4Ti5O12 nanowire array and nanotube array exhibited the specific capacitance of 607.2 F g−1 and 814.4 F g−1 at a current density of 1 A g−1, respectively. The corresponding capacitance retention was determined to be 92.1% and 94.2% after 1000 cycles at high current density of 5 A g−1. The corresponding capacitance still kept 182.9 and 352.1 F g−1 at much higher current density of 20 A g−1, presenting reasonable rate capability for N-Li4Ti5O12 nanoarrays. The improved capacitance performance of N-Li4Ti5O12 nanotube array was ascribed to the more amount of TiN and more accessible nanotube surface area, which contributed to the improved conductivity and fast diffusion of electrolyte ions on the surface of electrode. Both N-Li4Ti5O12 nanowire array and nanotube array with well-aligned integrative structure exhibited an excellent cycling stability during continuous charge/discharge process. Well-designed N-Li4Ti5O12 nanoarrays with high capacitance, good cycling stability and rate capability presented the promising application as feasible electrode materials of lithium-ion supercapacitors for the energy storage.