Preparation Of TiO₂ Nanotubes By Anodic Oxidation And Application In Energy Storage Field

The conventional lithium-ion batteries are limited by the inherent energy density,and has been difficult to meet the needs of production and life.Lithium-sulfur(Li-S)battery with high theoretical specific capacity(1675 mAh g^-1),is hoped to break through the capacity bottleneck of the energy storage system as a new type of secondary battery.However,the large-scale application of Li-S batteries has also been hindered by the inherent shortcomings,eg.the lithium polysulfides shuttle effect leads to low charge/discharge efficiency,the poor conductivity of the active material sulfur hinders electron transport,the volume expansion of sulfur cathode during charge and discharge is severe,and the chemical reaction is slow under high sulfur loading.In order to solve the above problems,a reasonable design on the sulfur cathode is needed.Some transition metal oxides can effectively adsorb polysulfides and have a catalytic effect,when they are used as cathode materials,they can significantly improve the electrochemical performance of Li-S batteries.In this paper,a simple anodization process is used to prepare oxide layer with a nanotube array structure on the surface of the Ti foil,and then the oxide layer worked as sulfur host,and together with the Ti foil substrate,it is applied as cathode after a hot-melt process.The effect of morphology of TiO₂ nanotubes on the electrochemical performance of the cathode was investigated by adjusting the anodic oxidation voltage.Ti-TiO_2-x,which is rich in oxygen atom vacancies and can be used as an effective adsorption/catalytic support,was also prepared under argon-hydrogen heat treatment,and the effect of sulfur loading on discharge capacity was explored.The main research results are as follows:(1)TiO₂ nanotubed oxide layers with different morphologies and structures were prepared on the surface of Ti foil by controlling the anodic oxidation voltage.The effects of anodic oxidation voltage on the morphology,pore size distribution,and sulfur loading of the TiO₂ nanotubed oxide layer were investigated,and the electrochemical performance of the prepared S/Ti-TiO₂ cathode was measured.The results show that the Ti-TiO₂-50 host prepared at 50 V anodizing voltage has a uniform surface morphology and an average inner diameter of 60.3 nm,and the percentage of sulfur in the prepared S/Ti-TiO₂-50 cathode is 41.7%.The constant current charge-discharge test showed that the S/Ti-TiO₂-50 cathode reached an initial specific discharge capacity of1238.6 mAh g^-1 at a rate of 0.1 C,and still had a specific discharge capacity of 944.3mAh g^-1 after 100 cycles.(2)The Ti-TiO₂ host prepared under the optimum anodizing voltage,was subjected to argon-hydrogen heat treatment to obtain a Ti-TiO_2-x host rich in oxygen atom vacancies.The formation of a large number of oxygen atoms was confirmed by XPS and EPR tests,the morphological and structural characteristics of the Ti-TiO_2-x support were analyzed by SEM and TEM,and the effect of sulfur loading per unit area on the electrochemical performance of S/Ti-TiO_2-x cathode was also explored.The results have shown that 1.13-S/Ti-TiO_2-x cathode with a sulfur loading of 1.13 mg cm^-2 has the superior excellent electrochemical performance,the initial and final discharge capacities at 0.1 C separately reached 1.23 mAh cm^-2 and 0.96 mAh cm^-2,and has excellent long-cycle performance and rate performance.