The Synthesis And Electrochemical Performances Of Li₄Ti₅O₁₂and Li₂Ti₃O₇Anode Materials For Lithium Ion Batteries

In this paper, we adopted the molten salt-assisted solid-state method、sol-gelmethod and microwave method to synthesize the spinel Li4Ti5O12、Li4Ti5O12/C andthe goethite-type Li2Ti3O7, respectively. What is more, the effects of technologicalconditions on the structures, morphologies and electrochemical performances of theas-prepared samples were all investigated.The high temperature solid-state method, the primary industrial synthesis ofLi4Ti5O12, is a simple route. However, the sluggish solid-solid diffusion rate, longdiffusion distance and compositional inhomogeneity all require a high-temperaturesintering for a long time (8-24h) which inevitably generates high energy consumption,and the as-prepared powder exhibits low capacity and bad rate performance becauseof the large particle size. In an attempt to overcome the above-mentioned signifcantdrawbacks, the low-temperature molten salt LiNO3-LiOH·H2O has been introducedinto the reaction system as lithium sources and dispersion medium to speed up the iondiffusion rate, shorten the ion diffusion paths, accelerate the reaction rate and improvethe electrochemical performances of the as-prepared samples. The optimal synthesisparameters are shown in follow: the precursor was pre-heated at250℃for3h andsubsequently sintered at600℃for4h in air. Finally, the pre-heated powder wasground, pressed into pellets, and sintered at800℃for1h to obtain the Li4Ti5O12powder. The as-prepared sample had a high degree of crystallinity, uniform particlesize distribution. Its average particle diameter is~200nm. At the rate of3C、5C、10C and20C, the initial charge capacities is147.06mAh g-1、137.80mAh g-1、130.89mAh g-1and110.0mA h g-1，the capacity retention rates after800cycles is97.5%,96.8%,95.1%and94.9%, respectively.In order to improve the electrical conductivity of Li4Ti5O12, the carbon coatedLi4Ti5O12had been prepared by sol-gel method. The investigation results show thatthe samples via pre-sintering at600℃for4h and then sintering at800℃for12hhad the best electrochemical performance. What is more, the influence of calcinationatmospheres on the structures, morphologies and electrochemical performances of theas-prepared samples were also investigated. At the rate of1C, the as-prepared samples sintered at the air condition and N2condition exhibited the initial chargecapacities of145.73mAh g-1and132.94mAh g-1, respectively.The Li2Ti3O7/C anode material had been firstly prepared via microwave methodusing rutile TiO2and0.38LiOH·H2O-0.62LiNO3as the raw materials. The influenceof microwave power and treatment time on the structures, morphologies andelectrochemical performances of the as-prepared samples were obvious because of themicrowave heating is uniform and instantaneous. The Li2Ti3O7/C anode materials viamicrowave heating at640W for20min has the best electrochemical. At the rate of0.2C、1C、3C and5C, the initial charge capacities of the sample were145.68mAh g-1、132.78mAh g-1、112.78mAh g-1and102.73mAh g-1, respectively.