Synthesis And The Lithium Storage Properties Of TiO₂ And Nb₂O₅

With the increasing environmental pollution and energy crisis,it is important to make full use of renewable clean energy to replace fossil fuels.In recent years,the expansion of consumer electronics market and transportation requires the development of high capacity,high power energy storage and conversion device.Rechargeable lithium-ion batteries（LIBs）and supercapacitors（SCs）are the main targets in the existing energy storage devices.However,there are some problems:i)the rechargeable LIBs have limited application because of slow charging and discharging rate,low power consumption,short lifetime and volume expansion.ii)SCs are not fully used in electric devices for the lower energy density.To explore the high energy/power density energy storage device,utilizing pseudocapacitive effect is one of the most prominent methods to enhance the lithium storage performance.On the other hand,developing the novel capacitive energy storage device or optimizing device system is critical.Finally,improved LIBs and optimized SC performance are achieved.The main research contents are as follows:（1）Utilising pseudocapacitive effect is one of the most efficient methods to enhance the lithium storage rate performance.In our work,H-TiO₂@C nanospindles are synthesized in a simple hydrothermal process and later by an annealing treatment with a carbon coating（506 epoxy resin）in H₂/Ar atmosphere.The hydrogenation treatment can introduce rich oxygen vacancies on the TiO₂ surface.The H-TiO₂@C as the anode material for LIBs exhibits remarkable cycling durability and rate performance,which delivers 310 mAh/g（0.1 A/g）and 126 mAh/g（1 A/g）reversible capacity.The pseudocapacitive contribution is calculated of 63.9%from the cyclic voltammetry test.Such well electrochemical performance could be attributed to the synergistic effect of the carbon coating and oxygen vacancies for enhancing the pseudocapacitive effect.The work may afford a new strategy to improve effectively pseudocapacitive performance of the metal oxides.（2）Increasing the energy density,power density as well as widening the operation voltage are essential to electrochemical capacitors for the energy demands.Herein,a novel flexible quasi-solid-state dual-ion asymmetric supercapacitor（ASC）with Ni（OH）₂ and Nb₂O₅ nanosheets grown on stainless steel mesh is assembled.In such dual-ion ASC,Nb₂O₅ negative and Ni（OH）₂ positive electrodes react with Li⁺and OH^-respectively in alkaline gel electrolyte to store energy,quite different from conventional alkali metal ion SCs and alkaline SCs.The as-assembled flexible device has an extended working voltage（1.7 V）and shows a specific capacitance of 19.32 mF/cm²,a maximum energy/power density of 0.52 mWh/cm³ and 170 mW/cm³,respectively.The device exhibits good capacitance retention after long cycling.Moreover,our device can light up a LED light efficiently upon fast charging.The proposed quasi-solid-state dual-ion ASC has potential applications in future portable electronics and flexible energy storage devices.