Design,Synthesis And Electrochemical Performance Of Ti-Based Anode Materials For Lithium-Ion Battery

Along with the rising demand of actual production and living for energy storage equipment,the existing battery technology can not meet the needs of people very well,the anode material is the decisive factor which limits the development of lithium battery industry.And Li₄Ti₅O₁₂anode material is concerned by researchers because of its low discharge voltage,high lithium storage capacity,and in the process of charging and discharging,it is not easy to generate SEI film and volume change.However,due to the low conductivity of the such titanium anode material and the higher cost because of lithium content is higher,in this paper,Li₂MTi₆O₁₄（M=2Na,Ba）anode materials with lower cost and lower discharge voltage are synthesized（1.3-1.5 V）,in addition,doping,coating and composite modification methods were carried out to improve the electron and ion migration rate and electrochemical cycle performance of Li₂MTi₆O₁₄（M=2Na,Ba）.A series of BaLi_2-xNa_xTi₆O₁₄（0≤x≤2）compounds were synthesized by solid phase method,the XRD Rietveld results show that the Bragg position is corresponded to BaLi₂Ti₆O₁₄and proved the successful preparation of this series of materials.The unit cell volume of the BaLi₂Ti₆O₁₄compound after Na⁺ion doping is larger than that of the original material,because the ion radius of Na⁺is 55%larger than that of Li⁺.SEM images show that BaLi_2-xNa_xTi₆O₁₄（x=0,0.5 and 1）samples are between 500and 1000 nm,which are irregular particles of similar shape.However,BaLi_2-xNa_xTi₆O₁₄（x=1.5,2）are rod-shaped powder.Compared with other samples,BaLi_0.5Na_1.5Ti₆O₁₄has higher reversible capacity,better rate capacity and superior recycle ability.The lithium capacity of BaLi_0.5Na_1.5Ti₆O₁₄at 50,100,150,200,250,300 m A·g^-1are 162.1,158.1,156.7,152.2,147.3,and 142 m Ah·g^-1,respectively.All the test results show that BaLi_0.5Na_1.5Ti₆O₁₄has the highest lithium storage capacity of all samples and the largest lithium ion diffusion coefficient.At the same time,BaNa₂Ti₆O₁₄also shows acceptable electrochemical performance as anode material.In the experiment we carried out physical characterization and electrochemical tests.The results of such tests show that the BaLi_2-xNa_xTi₆O₁₄（0≤x≤2）samples display different topography though prepared by the same method,and the Li sites are successfully replaced by Na,all the elements are uniformly distributed in the material.BaLi_0.5Na_1.5Ti₆O₁₄has the highest capacity for lithium storage and the largest lithium ion diffusion coefficient,that is to say,the electrochemical performance of BaLi_0.5Na_1.5Ti₆O₁₄is optimal.All the results of this experiment also proved that BaNa₂Ti₆O₁₄can also be used as anode material for lithium ion batteries.Na₂Li₂Ti₆O₁₄pure sample were prepared by solid state method and then was modified with CeO₂coating.The materials are composed of particles with an average particle size of about 1μm,and there is no significant difference between the morphology and particle size of the three samples.At 50 m A·g^-1,the initial charge capacities of CeO₂（0,5 and 10 wt.%）-Na₂Li₂Ti₆O₁₄are 213.5,259.8 and 206.6m Ah·g^-1,respectively.After 100 cycles under 500 m A·g^-1,the discharge capacities are122.7,157 and 138.4 m Ah·g^-1,and the corresponding capacitance retention rates are70.1%,89.7%and 76.5%.All the results show that CeO₂（5 wt.%）-Na₂Li₂Ti₆O₁₄has the optimal cyclic reversibility and the best lithium storage capability of all,and CeO₂coating can improve the lithium ion diffusion coefficient of pure sample.Na₂Li₂Ti₆O₁₄pure sample with spherical morphology was prepared by solvothermal method,and then it was added into the raw material of Li₄Ti₅O₁₂.Then different composite ratios of Na₂Li₂Ti₆O₁₄-Li₄Ti₅O₁₂dual-phase composite materials were prepared successfully by hydrothermal method method.The results of XRD test prove that the Na₂Li₂Ti₆O₁₄and Li₄Ti₅O₁₂in as-synthesized composite materials are of high purity,which is consistent with the analysis results of HRTEM and SAED diagrams.The SEM diagram shows that Na₂Li₂Ti₆O₁₄pure sample has the shape of the strawberry,and Li₄Ti₅O₁₂is of multilayer sheet structure,and the composite samples are a spherical particle with a surface of multiple layers,indicating that the Li₄Ti₅O₁₂wafer is attached to the surface of Na₂Li₂Ti₆O₁₄.The results of the CV test along with the charge-discharge results of the samples under the multiple ratio and the single magnification show that NLTO-LTO（1:2）has the optimal cyclic reversibility and rate capability.The results of EIS test show that NLTO-LTO（1:2）has the smallest migration resistance among all samples.