Synthesis And Doping Modification Of Li₄Ti₅O₁₂ Anode Materialfor High Rate Lithium-ion Battery

The property of “zero strain” has endowed the spinel lithium titanate(Li4Ti5O12) with electrochemical characteristics of high reversibility, safetyand stability, which means there will be no volume and nature changeduring discharge/charge process. And thus, Li4Ti5O12is considered aspromising anode material for lithium-ion battery for energy storage andvehicle devices. However, the insulation property limits its large-scaleapplication due to the low electronic conductivity and poor rateelectrochemical performance. In order to overcome the shortcoming,several methods have been introduced from two aspects which include thereduction of particle size to nano-scale and the increase of conductivity. Inthis paper, a modified sol-gel method was introduced to reduce the particlesize and metal ions were doped into the spinel structure to raise its abilityof conductivity.Li4Ti5O12was synthesized by a modified and facile sol-gel methodwith ethylene diamine tetraacetic acid (EDTA) and citric acid (CA) as abi-components chelating agent. Nano-scale Li4Ti5O12oxides, with a highphase purity and good stoichiometry, could be obtained at the calcinationtemperature of750℃and higher. The Li4Ti5O12nanoparticle shows anetwork morphology with high dispersion and its particle size is about150~400nm. The Li4Ti5O12anode material also has good electrochemicalperformances, which reaches a capacity of164and108mAh g-1at1C and10C discharge rate, respectively. The result of the cycling performanceshows a high capacity maintenance ratio of97%and its discharge capacityremains160mAh g-1at1C and25℃after1000cycles. On the basis of the modification of the traditional sol-gel method,La3+and Sc3+were doped into A and B sites of Li4Ti5O12respectively toimprove its ability of conductivity and rate performance.The dopant of La3+can greatly reduce the charge transfer resistanceand alleviate the electrode polarization of anode material. Theelectrochemical performances are influenced by two factors. The positiveone is that the impurity material of La0.625Li0.125TiO3can improve theability of conductivity; the negative one is that the free La3+outside thecrystal structure squeezes the transfer path of Li+and thus reduces the Li+diffusion rate. The electrochemical performances of La3+-doped Li4Ti5O12are worse than the pristine one due to the combined effect of the above twofactors.The dopant Sc totally enters into the16d sites of the spinel structureof Li4Ti5O12, and then further affects its morphology and property. TheLi4Ti4.95Sc0.05O12powder exhibits a3D network morphology and its grainsize is about200nm. The Li4Ti4.95Sc0.05O12electrode material exhibitsexcellent initial discharge capacities of174and94mAh g-1at1C and40C, respectively. The reversible capacities of Li4Ti4.95Sc0.05O12at differentcurrent rates remain nearly100%after50cycles, which are compared withthe capacities of the second cycles. Sc3+doping can greatly improve theelectronic conductivity of Li4Ti5O12which is demonstrated byelectrochemical impedance spectroscopy. Cyclic voltammetrymeasurements also reveal that Li4Ti4.95Sc0.05O12has small polarizationresistance due to the high electrical conductivity and Li-ion apparentdiffusion rate.