Synthesis, Preparation And Modification Of Lithium Manganate Cathode Materials

Lithium-ion batteries have been widely used in portable electronic products,new energy electric vehicles and energy storage devices because of their high energy density,low self-discharge,high working voltage and long cycle-life.Cubic spinel Li Mn₂O₄has become one of the most potential cathode materials for lithium-ion batteries because of its high working voltage,environment-friendly,low cost,rich resources and good safety performance.However,due to the poor cycling performance and rapid capacity attenuation of Li Mn₂O₄ cathodes,the scope of market application is seriously limited.In this paper,Li Mn₂O₄ cathode materials were prepared by high temperature solid method for changing the sintering temperature and holding time,and the doping and coating methods were used to modify this cathode material to improve the electrochemical performance.The details are as follows:(1)The effects of sintering temperature(700?,800?,900?)on the microstructure and electrochemical properties of Li Mn₂O₄ cathode materials were investigated by using Mn₃O₄and LiOH as raw materials.The results reveal that the sample sintered at 800?exhibits good crystallinity and truncated octahedral morphology,and the comprehensive electrochemical performance of the sample is better than that of the samples sintered at other temperatures,which displays the highest initial discharge specific capacity(128.7 m Ah g^-1)and Coulomb efficiency(92.86%)at 0.2C.(2)The effects of holding time(6 h,8 h,10 h,12 h)on the microstructure and electrochemical properties of Li Mn₂O₄ cathode materials were investigated.The results indicate that the samples prepared at different holding time exhibit good crystallinity and no other impurity phases.The sample held at 800?for 10 h exhibits a discharge specific capacity of 133.1 m Ah g^-1 and a Coulomb efficiency of 94.80%,excellent cycle stability and rate capability,better symmetry of CV curve and higher reversibility of reactions.(3)The effects of doping amounts(0,0.01,0.03,0.05)on the microstructure and electrochemical properties of Li Mg_(x)Mn_(2-x)O₄ cathode materials were studied with Mg as the doping element.The results indicate that the doping of Mg²⁺could not change the inherent cubic spinel structure of the samples.When x is 0.03,the Li Mg_0.03Mn_1.97O₄sample exhibits a higher initial discharge specific capacity,the highest first Coulomb efficiency(98.44%),and good cycle stability,the capacity retention rate is as high as92.62%;the sample can still exhibit the specific capacity of 119.3 m Ah g^-1 at 5C high rate.(4)The effects of Ag nanoparticles(Ag NPs)with different coating ratios(0wt%,3wt%,5wt%,8wt%,10wt%)on the microstructure and electrochemical properties of Li Mn₂O₄ cathode materials were studied by using Ag NPs as coating material.The results indicate that the Ag NPs-coating can not only improve the reversibility of the redox reaction and reduce the polarization,but also act as a conductive bridge,which effectively promotes the charge transfer of the reactions.The sample with a coating content of 8wt%exhibits excellent electrochemical performance,which delivered discharge specific capacities of 118.4 m Ah g^-1 and 120.5 m Ah g^-1 after 500 cycles at0.5C and 100 cycles at 1C,respectively,and the capacity retention rates were 90.2%and 95.4%,respectively.