The Synthesis And Modification Of Spinel LiMn₂O₄ For Lithium-Ion Battery Cathode Material

The spinel LiMn2O4 is promising material as cathodes for Li-ion batteriy, due to their relatively high energy density, low cost and low toxicity. However, the capacity of spinel LiMn2O4 fades rapidly in the charge-discharge cycle process. It has suggested that the capacity fading in the 3V region is due to Jahn-Teller distortion and in the 4V region due to dissolution of spinel into the electrolyte and decomposition of the electrolyte.In this dissertation, LiMn2O4 and doping LiMn2O4 are synthesized by modifying sol-gel method using citric acid as a chelating agent. The favored synthesis temperature is found by TGA(thermogravimetric analysis), DSC(differential scanning calorimetry) and charge/discharge test. The favored mole ratio of citric acid to metal ions is found by charge/discharge test for different mole ratio of citric acid to metal ions. The synthesis process is not only simplified, but also the discharge capacity increases for this method. For more work, we synthesized LiMn2O4 doped by anion and cation, and coated by LiCoO2 and Al2O3.The process of doping LiMn2O4 is putting the corresponding cation or anion salt (some mole ratio vs LiMn2O4) to the solution contained lithium carbonate, manganese nitrate and citric acid in the process of LiMn2O4 synthesis. Electrochemical behavior of doped LiMn2O4 is characterized by galvanostatic charge/discharge test and cycle voltammetry method. The structure of doped LiMn2O4 is characterized by X-ray diffractometry (XRD). The doping ions are well-proportioned distributing in the main LiMn2O4 spinel. The doped sample exhibited higher discharge capacity.LiMn2O4 is coated by LiCoO2 or Al2O3 using modified sol-gel method with citric acid as a chelating agent. Electrochemical behavior of coated LiMn2O4 is characterized by galvanostatic charge/discharge test and cycle voltammetry method. The structure of coated LiMn2O4 is characterized by XRD. LiCoO2 or Al2O3 coated on the surface of LiMn2O4 enhanced stableness of the structure and suppressed the dissolution of manganese into electrolyte.