Preparation And Modification Of Lithium-rich Cathode Material For Lithium-ion Batteries

Improving the properties of the active cathode materials can promote the development of LIBs.Li-rich layered oxide materials,xLi2MnO3(1-x)LiMO2(M=Mn,Ni,Co,etc.0<x<1),which have been regarded as one of the most promising candidates for the next generation cathode materials.They have alreadly attracted significant interest because of their high capacities(>250 mAh/g)under high operating voltages of above 4.6 V and excellent electrochemical and thermal stabilities.However,Li-rich materials have faced new fundamental challenges of poor rate capability,signficant initial irreversibility capacity loss,and severe decrease in the discharge voltage plateau upon cycling.In an attempt to enhance the electrochemical performance of the Li-rich material,the porous-rodlike micro-nanostructured Li-rich spinel/layered oxide and micro/nano structure design have been adopted in this dissertation.And the primary research tasks are as follow:1.Li-rich material 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 with layered/spinel heterostructure is synthesized by a simple strategy.Based on structure and morphology analyses,it reveals the as-prepared Li-rich material possesses both porous micro-nano structure and integral layered-spinel heterostructure.Moreover,the obtained layered-spinel cathode material possesses prominent electrochemical characteristics,especially the rate capability.The initial discharge capacity of the as-prepared material is 269 mAh/g with a high coulombic efficiency of 90.3%.The material delivers discharge capacities of 239 mAh/g at 0.5 C,195 mAh/g at 5 C,and 175.8 mAh/g even at 10C.Besides,the capacity retention of cell is still as high as 80%at high current density(5C)after 200 cycles.The addition of spinel can inhibit the collaps of material structure and voltage fading upon the cycling.The 3D spinel Li4Mn5O12 phase in Li-rich compound could provide fast Li+ diffusion pathway and the porous micro-nano structure which are the key parameters for the remarkable excellent electrochemical performance of the as-prepared cathode material.2.By changing the rich precursor synthesis reaction temperature in the process of lithium-ion battery anode materials,surface active agent,reaction time,solvent and the choice of precipitant can control the morphology of material and the size of the grain size.The four types of materials are cubes(L-LLNCM),spheres(Q-LLNCM),sheets(P-LLNCM)and short bars(D-LLNCM).Due to the morphology of P-LLNCM is flake,the site of Li+ insert/take off has greatly increased.Then,the kinetic parameters of material is improved.In addition,the crystallinity of P-LLNCM is high and has a good layered structure.Therefore,P-LLNCM has the best electrochemical performance in the four materials.