Application Of Micro-nano Hollow Structure In Lithium-ion Battery Cathode Material

In order to meet the development of new energy products such as new energy vehicles,we urgently need to develop a new generation of lithium-ion batteries with higher energy density,higher rate capability and higher cycle performance.As we all know,the research of cathode material is closely related to the development of lithium-ion battery,and there are two basic methods to increase the energy density of cathode material:one is to increase the actual capacity of the materials;the other is to increase the potential voltage of the battery.Based on this,we have selected high theoretical capacity cathode materials Li₂MnSiO₄ and Li₂FeSiO₄ and high potential voltage material LiNi_0.5Mn_1.5O₄.However,due to some problems such as low electronic conductivity,low diffusion coefficient of lithium-ion,and structural damage,it is difficult for these materials to develop further.Therefore,in view of the above problems,we have prepared a composite material with a micro-nano hollow structure by using the template method.Through reasonable control of its structure,we can obtain higher electrochemical performance.The main contents are as follows:1)In order to improve the electronic conductivity and lithium-ion diffusion rate and ease the dissolution of transition metal ions in the electrolyte,we have designed and synthesized the nano-hollow structure CNT@Li₂MnSiO₄@C cathode material by using the hard template method.The material has a uniform core-shell structure,and the electronic conductivity of the electrode material is improved by double carbon compound,and the thickness of the Li₂MnSiO₄ layer is precisely controlled to achieve the increase of the lithium-ion diffusion rate.The outer carbon coating is also effective reduced dissolution of manganese ions.Finally,the actual capacity of the obtained nano-hollow structure CNT@Li₂MnSiO₄@C cathode material reached more than 225 mAh/g.When the charge and discharge rate was 0.2 C,the discharge capacity remained above 80%after 50 cycles.2)Although Li₂FeSiO₄ and Li₂MnSiO₄ belong to the same polyanion cathode materials,its theoretical capacity?166 mAh/g?is only half of the Li₂MnSiO₄,and the conductivity and pure lithium-ion diffusion coefficient of pure Li₂FeSiO₄ are very low,which is not conducive to electrochemical reactions.The nano-hollow structure of CNT@Li₂FeSiO₄@C has solved this problem,and its actual capacity,cycle performance and rate performance have been optimized to a certain extent.The nano-hollow CNT@Li₂FeSiO₄@C material with the same structure is much better than CNT@Li₂MnSiO₄@C in cycle energy and rate performance.When the charge-discharge rate is 0.2 C,the discharge capacity remains above 80%after 150 cycles.3)In order to promote the transfer of lithium-ions/electrons and reduce the structural damage caused by the volume change,we have used self-template synthesis method to prepare micrometer hollow rectangular cuboid LiNi_0.5Mn_1.5O₄ through solvothermal reaction and lithiation process.This method is convenient controlling the formation of its morphology and size,the resulting micrometer hollow cuboid structure can improve the cycle performance and rate performance of the high potential voltage LiNi_0.5Mn_1.5O₄cathode material of the spinel structure.When the discharge rate is 1 C,the discharge capacity can reach 125 mAh/g;when the discharge rate is up to 30 C,the discharge capacity is still 109 mAh/g,and the discharge capacity retention rate can reach 94.4%after 900 cycles.