Liquid Prepared By Lithium-ion Battery Cathode Materials Of Limn <sub> 2 </ Sub> The O <sub> 4 </ Sub> And Its Doping Research

Rapid Progresses have been made in the research on lithium-ion batteries due to its superior properties for recent years. These properties, however, are greatly affected by the selection and preparation of the materials, such as the cathode materials, the anode materials, and the electrolytes, particularly the cathode materials. The research on cathode materials is focused on layered compounds LixMO2 and spinel compounds LixM2O4 (M=Co, Ni, Mn and other transition metal ions). The shortage of the cobalt resources results in the high price of LixCoO2 as cathode material. The cathode material of LixNiO2 with perfect crystal structure is very difficult to be prepared. The capacity of LixMn2O4 fades with cycling in practice. If the factors of price and comprehensive electrochemical properties are considered, the cathode materials of lithium manganese oxides should be recognized as the most potential cathode materials for lithium-ion batteries.In this paper, lithium manganese oxide with superior properties synthesized by the solution process is studied; the preparing technological parameters, and synthesizing doped lithium manganese oxide are discussed, and some electrochemical properties of the products are measured as cathode materials for lithium-ion batteries. The main results are as follows:(1) LiMn2O4 ultrafine powder has been successfully synthesized by the solution process. The products show higher degree of crystallinity, prefect spinel structure, and regular grain shope. And the products have high purity and fine particles with 500nm in average size. Have been measured as cathode materials for lithium-ion batteries, the products show good electrochemical properties. The first discharge capacity of the cathode is 125.79mAh g-1, and the capacity maintenances 111.81mAh g-1 after one charge/discharge cycle. The specific capacity is 107.14mAh g-1 after 10 cycle, only fading 14.83% contrasted with the first discharge capacity. The results show that the solution process has some superior characteristics to solid-state reaction.(2) The LiMn2O4 ultrafine powder with higher purity and superior electrochemical properties can be synthesized by complexing with citric acid and metal ions. On theother hand, the product synthesized by acetic acid have some impurity and poor electrochemical properties. And the proportion of reagent has important effects to the product. When manganese ion excess, the product would be impurity. However, when lithium ion excess, the products show poor electrochemical properties. Therefore, synthesized LiMn2O4 ultrafine powder with higher purity and superior electrochemical properties should be controlled the proportion of reagent (Li : Mn=1 : 2).(3) The results show that LiMn2O4 spinel with higher degree of crystallinity and superior electrochemical properties could be synthesized with higher calcined temperature and longer calcined time. When the proportion of reagent is 1 : 2, and complexing with citric acid, the precursor was quickly heated at 800 C for 20 hours in air, the purity LiMn2O4 ultrafine powder with higher degree of crystallinity and superior electrochemical properties was prepared. The precursor synthesized by the same condition was heated at 450C for 1 hours and subsequently heat-treated at 750 C for 15 hours in air. The powder of LiMn2O4 spinel with prefect crystal structure also shows high specific capacity and stable cycle property.(4) The doped spinel phase lithium manganese oxides with prefect crystal structure could be synthesized by solution process. The lattice parameters of doped LiMn2O4 decreased, reflecting the lattice shrinkage of spinel LiMn2O4 phase. The results of charge/discharge cycle show that the lithium manganese oxides doped cobalt and nickel have better cycle properties and lower discharge capacity than the undoped LiMn2O4. However, the lithium manganese oxide doped aluminium has lower discharge capacity and poor cycle property.