| Lithium ion batteries(LIBs)has been widely used in portable electronic products like mobile phones,notebook computers,digital cameras,because of their high work voltages,high energy densities,good cycling stabilities.However,the available LIBs still cannot meet the requirements of electric vehicles,hybrid vehicles,and intelligent power grids.In existing electrode materials,as a type of lithium transition metal oxides,Li-M-0(M = transition metal)have attracted much attention and extensively studied as electrode materials for LIBs,this is due to the fact that transition metals contain many valence states,which can guarantee the electrical neutrality of lithium ions during charge and discharge.In addition,the compounds containing lithium generally have a high open circuit voltage.Some of them can be used both as cathode and anode materials.Nowadays,Li-M-0 electrode materials still have the problems of volume expansion and rapid capacity decay.In order to solve these problems,we used facile solid state synthesis methods to combine carbon with Li-M-0 materials to suppress volume expansion.To improve the electrochemical performance of Li-M-O electrode materials,we also tried to develop lithium-rich electrode materials with high energy density by a mechanical ball milling technique.(1)y-LiFeO2and a-LiFeO2/C were prepared by one-step in-situ solid state methods.The XRD results indicate that y-LiFeO2 is pure,The sizes of y-LiFeO2 are around 100-300 nm,The first discharge capacity of y-LiFeO2 can reach to 1055.3 mAh/g,and the capacity retention ratio can reach nearly to 80%of that for the second cycle.The size of a-LiFeO2 become smaller.a-LiFeO2/C has the particle sizes of around 20～100 nm,and α-LiFeO2 particles disperse on the surface or interior of porous carbon.Compared with pure a-LiFeO2,a-LiFeO2/C has higher cycling capacity and excellent rate performance.The first discharge capacity of a-LiFeO2/C can reach to 1830.4 mAh/g,there is still a discharge capacity of 792.3 mAh/g after 120 cycles.At 1 C,the first discharge capacity of a-LiFeO2/C is 1820 mAh/g,and there is still 572.1 mAh/g capacity remained after 120 cycles.The residual capacity also shows good a cyclic stability at high rates.The synthetic method is simple and easily scalable prepared,demonstrating strong commercial potential.(2)The electrochemical study of LiFeTiO4/CNTs composite.Compared with other iron-based polyanionic cathode materials,LiFeTiO4 is relatively less developed.Its low potential is probably one of the reasons for this phenomenon.Fe can realize the transition of Fi3+/Fe4+ below 5 V.Therefore,the discharge capacity of LiFeTiO4/CNTs can reach to more than 200 mAh/g after 100 cycles.At 0.1,0.2,0.4,1,2,4,and 8 C,the discharge capacities are 253,167,125,87,62,37,and 15 mAh/g,respectively.With the increase of current density,the discharge capacity decreases gradually.When eventually returning to 0.1 C,the capacity can still be restored to 193 mAh/g,indicating that the material has a good rate performance.LiFeTiO4/CNTs is a very competitive cathode candidate for LIBs.It can lay the foundation for the future study of high energy density electrode materials.(3)A novel lithium-rich Li4Co2Os material was synthesized by mechanical ball milling technique.According to its wide XRD peaks,its size is small and its crystallinity is not perfect.It has a flower-like structure formed by polymerization,and there are some flocculent carbon black coated around it.We have explored the reaction mechanism of Li4Co2O5 and found that its theoretical capacity is as high as 475 mAh/g.The following C-V curves are close to overlapped,implying that the material has an excellent cycling stability.At 0.1 C,the actual discharge capacity is close to 300 mAh/g,which shows its great potential.Although the study on the material is in infancy,it is necessary to explore more to address all the problems it encounters now. |
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