Synthesis And Modification Of Li-rich Mn-based Layered Cathode Materials For Lithium-ion Batteries

Since lithium ion batteries（LIBs）were first commercialized,this kind of energy storage system has attracted intensive attention attributing to its high energy,power density and long life,and has been used widely in military and civilian fields.Lithium-rich manganese-based layered cathode material has attracted much attention due to high specific capacity and has been considered as one of the most promising cathode materials.However,there are numerous serious issues with this class of cathode materials:poor rate performance,high initial irreversible capacity losses,discharge capacity and voltage fading.With those problems,we report a urea-based hydrothermal method followed a heat treatment to synthesize three-dimensional micro/nano-hierarchical Li-rich layered materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂.Furthermore,the structure and morphology of the precursor particles could be tailored by controlling of reaction to improve cycling performance and performance.Also,surface modification of cathode materials had been done to improve electrochemical performance and ease voltage fading partly.Firstly,Li-rich layered cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13Mn_1.5O₂ was prepared by hydrothermal method.The influence of synthetic process on the properties of products was investigated.Furthermore,the structure and morphology of the precursor particles could be tailored by controlling of reaction time,reaction solvent,and precipitator.Precursors were mixed with Li salt and then calcined to obtained Li-rich layered materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂.Fusiform precursors were acquired in urea-based hydrothermal reaction in ammonium acetate solution and the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particle prepared from the carbonate precursors can maintain the morphology of precursors and the cathode powders are well-crystallized,showing excellent cyclic performance.This study investigates such influence of hydrothermal temperature and ammonium acetate solution on elecchemical performance of cathode powders.The influence of synthetic process on the properties of products was investigated.The fusiform powders prepared in ammonium acetate solution showed an excellent cycling performance.It delivers a reversible capacity of 232mAh·g^-1 capacity after 50 cycles.It could be attributed to unique hierarchical micro/nano structure and preferred orientation growth of the active（110）plane.The fusiform powders prepared in ammonium acetate solution at 220℃showing an excellent rate performance.The discharge capacity is260mAh·g^-1、224mAh·g^-1、201mAh·g^-1、166mAh·g^-1、92mAh·g^-1 at 0.2C、0.5C、1C、2C、5C.Also,the fusiform powders showed an excellent cycling performance at0.5C rate.Compound modification was used to improve electrochemical performance of fusiform powders.The method of mixing Li-rich layered cathode materials and spinel cathode materils and surface spinel modification were adopted.This study investigates influence of technological conditions on modified cathode materials.The results showed that the two methods could both improve the cycling performance of cathode materilas.Suface spinel modification played better results because of synergistic effect of layered cathode materils spinel cathode materils.The750℃heated sample delivers a reversible capacity of 220mAh·g^-1 capacity after cycles.While the amount of（CH₃COO）₂Mn was 10%～13%of mole of layered cathode materials,samples could make the balance between equity capacith and cycling performance and delivers a reversible capacity of 220～230mAh·g^-1 capacity after cycles while the the voltage drop is about 0.3V.