Synthesis And Characterization Of LiMO₂(M=Ni,Co,Mn) Cathode Materials For Lithium Ion Battery

In the revolution of energy, LIB (lithium ion battery) holds an important position byits advantages. It has gotten the rapid development and wide application in theproduction and life of the human. Now LIB has penetrated into every field of our life,such as electronic products: mobile phone, computer, MP₃, MP₄etc. In terms oftransportation, application of lithium-ion battery is not to be underestimated.. Nowmany countries pay more attention to research and development of EV (electricvehicles) and HEV (hybrids electric vehicles), developed countries spend hugeamounts of money to support and promote the development of EV. In France, theUnited States, Japan, the EV enterprises have been successfully listed. In Paris and LaRochelle, EV charging station networks have been built. Although starting lately inChina, the EV research has become the focal supporting project. In space, the batteryusing in the spacecraft is solar battery, so it has certain limitation, it can't workproperly when sunless. At this time, energy storage equipment with high reliability, Inthe low temperature with good performance, long cycle life, higher energy density isneeded. LIB occurs in not only national defense communications but alsosophisticated weapons. In the energy storage, LIB moreover becomes the first choice.Cathode materials as important component for LIB have become the focus ofresearch. In recent years, mixed transition metal layered compound,has attracted moreattention. Li NixCo₁-xO₂material has high specific capacity, good cycle performance, low cost but poor thermal stability. Li-Ni-Co-Mn-O₂material is the complex ofLiCoO₂, LiNiO₂and LiMnO₂, it inherited the advantages of three kinds of ions andinhibit defects greatly. However, the morphology of its homologue is difficult tocontrol. Some products with non stoichiometric ratio don't meet the usingrequirements. The prepared material using low temperature technology for example,sol-gel method, combustion method and co-precipitation method own more excellentcycle performance. Liquid phase synthesis makes ionic mix more fully and reactionactivity increase, it is helpful to get the pure phase of the product. In addition, themethod uses the lower calcining temperature, so that the product has smaller particle,higher specific surface and better crystal lattice strain.This paper mainly uses the synthesis route combining the hydrothermal method andsolid phase method to prepare the layered compounds of Li-Ni-Co-O₂andLi-Ni-Mn-Co-O₂, and do the structure characterization and electrochemical propertiestest for the two series of compounds separately.1, we prepare the compounds of LiNi_0.5Co_0.5O₂and LiNi_0.6Co_0.4O₂by thehydrothermal method and high temperature calcination method. The sample structure,valence state and morphology are characterized. The compounds have relativelyuniform particle size, good dispersion and good layered structure, the valences of Niand Co element are+3valence. In the constant current charge and discharge test, theinitial capacity of our sample is very close to the theoretical capacity. The capacityretention reached86%, this also illustrates our sample has excellent electrochemicalperformance.2, The manganese source compounds, the nickel source compounds and cobaltsource compound lithium and lithium hydroxide aqueous solution are mixed andconduct hydrothermal reaction to get manganese, cobalt, nickel oxide precursor; thenget Li(Ni_1/3Mn_1/3Co_1/3)O₂and LiNi0.4Mn0.4Co0.2O₂compounds after the precursor800℃baking10h. We do a series analysis on the target products. Based on theelectrochemical performance test of the sample, sample capacity is relatively high at acurrent density of20mA/g, voltage within2.5-4.4v. After50charge-discharge cycles,the capacity retention is above160mAh/g. Li(Ni_1/3Mn_1/3Co_1/3)O₂has good electrochemical reversibility and structural stability. At the same time, samples haverelatively stable voltage platform.