Modification And Electrochemical Performances Of TiO₂ Negative Electrode Materials

Nowadays,the world is facing two major problems,energy crisis and environment pollution.The key of sustainable development is how to overcome these problems.Electrochemical energy is one of the effective ways to solve these problems at present.Lithium ion batteries?LIBs?as an electrochemical energy storage device,because of their excellent energy density,safety,cycle performance and environmental friendliness,LIBs have been widely apply to many fields,such as portable electronic products,electric vehicle,communication equipment and aerospace applications.Lithium ion batteries are considered as the most promising energy storing devices in the field of energy storage in the future.Electrode materials are the core of LIBs,which determine the capacity and life of battery at a large part.At present,the cathode material of commercialized LIBs is graphite electrode materials,the unavoidable problem is the formation of Li dendrite at lower discharge platform of this kind of material,which brings about serious problems in terms of safety and cyclical stability,such as battery explosion or fire when the separator punctured by Li dendrite.In addition,the solid electrolyte interface?SEI?film will generate during first cycle,which leads to large irreversible capacity loss and low initial coulomb efficiency.Among the many compounds,titanium dioxide?TiO₂?is environmental friendliness and easily prepare.Also,TiO₂ has higher discharge voltage as LIBs negative electrode,and smaller volume effect during charge-discharge process.The most significant fault of TiO₂as an active material is its low electron conductivity and ion conductivity which affects its electrochemical performance.In this paper,TiO₂ were chosen as the object of study,and the effect of doped element on the electrochemical properties were investigated.The main research contents of this paper are as follow:?1?Mo-doped TiO₂ nanoparticles were synthesized by hydrothermal reaction.The Mo-doped TiO₂@C were prepared by coating PANI on the Mo-doped TiO₂ after annealing at 500?.The phases of as-prepared TiO₂ and Mo-TiO₂@C are anatase phase.The results of electrochemical testing shows that Mo-TiO₂@C displayed excellent electrochemical performance.The reversible capacities of as-prepared TiO₂ and Mo-TiO₂@C after 100cycles at the current of 0.5 C were 142.08 and 372.15 mAh g^-1,respectively.After 200cycles at the high current of 5 C,Mo-TiO₂@C could be obtained the reversible capacity of153.4 mAh g^-1,which is high than that of TiO₂(52.89 mAh g^-1).For rate performances,the average capacities of undoped TiO₂ nanoparticle electrode are 242.93,147.55,117.76,97.48,64.59,49.86 and 43.41 mAh g^-1 at rates of 0.2,0.5,1,2,5,8 and 10 C,respectively.In contrast,the Mo-TiO₂@C electrode delivers a stable capacity of 574.07,410.44,335.74,273.38,173.41,114.47 and 88.68 mAh g^-1 at the rates of 0.2,0.5,1,2,5,8 and 10 C,respectively.Obviously,the cycling stability and rate performance of Mo-TiO₂@C electrode are excellenter than anatase TiO₂.The average Li⁺diffusion coefficient of oxidation and reduction process is 2.15×10^-9 cm² s^-1 and 2.33×10^-9 cm² s^-1 by calculation from cyclic voltammetry curves.The contribution of pseudocapacitance contribution was also estimated by analyzing the cyclic voltammetry data at various sweep rates,the capacitive contribution for Mo-TiO₂@C is 26.56%,39.13%,47.41%,58.73%and 73.07%at scan rate of 0.2,1,2,5 and 10 mV s^-1,respectively.?2?Amorphous sphericals TiO₂ precursors were prepared by hydrolysis of titanium isopropanol,and AT-Sn-TiO₂ could be synthetised through ion adsorption–incorporation.Then the polydopamine was coated on the surface of the AT-Sn-TiO₂ sphere,and obtained rutile Sn-TiO₂@C by annealed at high temperature.Sn-TiO₂@C displayed the reversible capacity of 267 mAh g^-1 after 200 cycles at the current of 0.5 C,which was much higher than that of TiO₂(88 mAh g^-1).And the average capacities of undoped spherical TiO₂electrode were 276.61,179.68,142.44,102.97,50.74 and 31.77 mAh g^-1 at the current density of 0.2,0.5,1,2,5 and 10 C,respectively.In contrast,the Sn-TiO₂@C electrode delivers a stable capacity of 435.67,339.16,312.61,275.91,205.18 and 140.92 mAh g^-1 at different current density of 0.2,0.5,1,2,5 and 10 C,respectively.Obviously,rutile Sn-TiO₂@C electrode showed excel ent cycling stability and rate performance.