Spinel Lithium Manganese Oxide Preparation And Performance

The development of electronic materials for lithium ion batteries were reviewed in this paper.Based on analysis of a large number of studies on spinel LiMn₂O₄ at abroad and home,it is well known that the deficiency of spinel LiMn₂O₄ lies in inhomogeneity,motley phase,instability as well as poor electrochemical performance.High tap density manganese oxide were prepared by a route of two step sintering with electrolytic manganese powder as raw material.The effects of oxidation temperature,dwelling time and calefactive velocity on physical-chemistry property of manganese oxide were studied,and the results showed that the material property was poor which was obtained with one stage oxidation,while the material property which was obtained with two stage oxidation was excellent.Increasing temperature and dwelling time,oxygen content increased and primary particle grown up.And heat treatment system of high tap density is as follows:Heat electrolytic manganese powder from room temperature to 700℃by 2℃/min,dwelling 9h,and cool at radium speed,mill the product till D₅₀≈3.0μm,sift out,and collect under product of sifter. then heat the collected powder from room temperature to 1050℃by 2℃/min, dwelling for 7h,and cool at radium speed,mill the powder till D₅₀≈4.0μm,sift out, and collect under product of sifter,namely,manganese oxides.X-ray-diffraction spectra indicated that the manganese oxides were the mixture of Mn₃O₄ and Mn₂O₃, and its tap density is 2.70g·cm^-3(D₅₀≈4.0μm).LiMn₂O₄ was prepared with high tap density manganese oxides as precursor and Li₂CO₃ as Li sources through the mechanical activation-high temperature solid state sintering route.TG-DSC curves indicated that the endothermic phenomenon occurred and the mixture lose weight evidently at 500℃,and this is to say LiMn₂O₄ formed at 500℃,and at 930℃exothermic phenomenon occurred and cubic spinel LiMn₂O₄ transforms to square structure.SEM and XRD analysis showed that materials prepared under 650℃concluded Mn₂O₃,materials prepared at 650～900℃exhibited a cubic pure spinel structure.With the raising of temperature,particle size and lattice parameter(a) became bigger.The heat temperature had more effects on morphology, particle morphology was poor when temperature was below 650℃,octahedral morphology appeared with increasing otemperature,but sample prepared at 850～900℃can easily be found breaking of grain.With the increasing of heat temperature,initial discharge specific capacity increased and then decreased,and at 750℃initial discharge specific capacity reached maximum.Increase dwelling time can enhance initial discharge specific capacity in a way.Li content had remarkable effect on initial discharge specific capacity and electrochemical performance,the initial specific capacity was small and electrochemical property was poor when Li was lack,and the initial specific capacity was big and electrochemical property was good when Li was rich.And the initial discharge specific capacity of Li_1.015Mn₂O₄ is 111.25mAh·g^-1(0.1C,4.2V,vs.C) and is the maximum among the different Li/Mn molar ratio,and has a high capacity retention of 95.03%after 30 cycles.Lithium manganese oxides of Li_1.015Mn_2-xM_xO₄(M=Co,Ni,Ti,Zr) were prepared with Co₃O₄,NiO,TiO₂,ZrO₂ as dopant.Effects of the Li_1.015Mn_2-xM_xO₄ on structure, morphology and electrochemical property were investigated,and the results indicated that Li_1.015Mn_2-xM_xO₄(M=Co,Ni,Ti,Zr;x≤0.1) exhibited a cubic pure spinel structure, except Li₍1.015_Mn_1.9Zr_0.1O₄.Cation order was optimized.With the increasing of dopant content,initial specific capacity deceased and electrochemical performance was enhanced.Initial specific capacity deceased unnotably when x≤0.01 but notably when x≥0.1.Particle sizes became smaller and tap density decreased in a way with the import of substituted ions.Li deintercalation/intercalation process from spinel LiMn₂O₄ was studied by means of AC impedance measurement.It was found that the exchange current density(i₀) and diffusion coefficient(D_Li+) were changed with delithiation voltage,and the maximum value of exchange current density(93.5mA·g^-1) and diffusion coefficient (0.66×10^-12cm²·s^-1) were obtained near the voltage plateau of 4V.Moreover,both of them were affected by doping modification.