Preparation And Electrochemical Properties Of Sm-Modified LiMn₂O₄

LiMn₂O₄ cathode material has the advantages of good safety and low raw material cost,so it is a potential cathode material for lithium ion battery.However,there are still many problems in LiMn₂O₄,such as poor electrical conductivity and rate capability.In this paper,LiMn₂O₄ was synthesized by solid phase method,and the modification of LiMn₂O₄ was studied by gas penetration and solid phase doping.XRD,SEM,TEM,FTIR,ICP,XPS and other characterization methods were used to investigate the resistivity,morphology,structure and electrochemical properties of LiMn₂O₄ prepared under different modification conditions.The commercial LiMn₂O₄ was modified by rare earth gas phase penetration method,and the effects of penetration height and penetration temperature on the structure and electrical conductivity of Sm-modified LiMn₂O₄ were discussed.The technological conditions of Sm-modified LiMn₂O₄ were determined as follows:water as penetration solvent,penetration height was H5,penetration temperature was 300℃,penetration concentration was 60 g·L^-1 and the drip rate was 80 d·min^-1.The results of electrochemical impedance spectroscopy test showed that Sm modification can effectively reduce the SEI film resistance and charge transfer resistance,and increase the charge transfer rate of the material.XRD and TEM results showed that Sm-modified LiMn₂O₄ was pure spinel phase,Sm³⁺entered the Mn 16d site of the spinel LiMn₂O₄ structure,and the bond energy of Sm-O bond was stronger than that of Mn-O bond,which stabilized the spinel structure and improved the electrical conductivity and rate capability of LiMn₂O₄.Under these conditions,the resistivity of Sm-modified LiMn₂O₄ was the lowest,which was1.15×10⁵Ω·cm.The specific discharge capacity of Sm-modified LiMn₂O₄ were91.4 m Ah g^-1,76.0 m Ah g^-1 and 53.6 m Ah g^-1 at large rates of 5 C,10 C and 15 C,respectively.Furthermore,LiMn₂O₄ was synthesized by solid phase method,and the effects of sintering temperature on the structure and electrical conductivity of LiMn₂O₄were investigated.The optimal sintering temperature for solid phase synthesis of LiMn₂O₄ was determined to be 700℃.On this basis,the effects of Sm doping amount on the electrical conductivity and electrochemical properties of Li Sm_xMn_2-xO₄ cathode materials were discussed,among them,the resistivity of Li Sm_0.01Mn_1.99O₄ was the lowest,which was 1.88×10⁵Ω·cm.The discharge specific capacity of Li Sm_0.01Mn_1.99O₄ was 114.8 m Ah g^-1 after first cycle and 101.7 m Ah g^-1after 300 cycles at 1 C.Finally,the secondary modification of Li Sm_xMn_2-xO₄ was studied by Sm gas penetration method.The resistivity of Sm-penetrated Li Sm_xMn_2-xO₄ all decreased,and the resistivity of Sm-penetrated Li Sm_0.01Mn_1.99O₄was the lowest,which was 8.88×10⁴Ω·cm,and the initial specific discharge capacity of Sm-penetrated Li Sm_0.01Mn_1.99O₄ was 127.7 m Ah g^-1 at 0.1 C.The specific discharge capacity of Sm-penetrated Li Sm_0.01Mn_1.99O₄ was 118.0 m Ah g^-1after first cycle and 103.9 m Ah g^-1 after 300 cycles at 1 C.The specific discharge capacity of Sm-penetrated Li Sm_0.01Mn_1.99O₄ were 98.4 m Ah g^-1,80.1 m Ah g^-1 and53.4 m Ah g^-1 at large rates of 5 C,10 C and 15 C,respectively.It was found that Sm gas-solid co-doping improved the electrical conductivity and rate capability of LiMn₂O₄ cathode material effectively.