| Lithium ion batteries have become one of the most important batteries in 21th century because of its high volume and mass energy density, high working voltage, long life and little self discharge. As one of the cathode materials for lithium ion batteries, spinel LiMn2O4 attracts great attention due to its low cost, abundant Mn resource, low toxicity and environmental friendly nature. The principle of charge & discharge for lithium ion batteries, its structure and the research progress on cathode materials was presented in this paper. Two new methods were developed to synthesize LiMn2O4. In order to overcome the severe capacity fading which limits the commercial application of lithium ion batteries, Fe was adopted to partially substitute of Mn and Al2O3 was used for the surface modification.The super-fine powders of spinel LiFexMn2-xO4 (x=0, 0.05) were synthesized using EDTA- citric acid (EDTA-CA) sol-gel method with manganese acetate, lithium nitrate as raw materials. The precursor and synthesized powders of LiMn2O4 were characterized by TG-DSC, XRD, CV and galvanostatic charge and discharge. It is found that the optimal sintering temperature is 600 oC. At room temperature, the initial discharge capacity of the half cell with LiMn2O4 cathode material is 120.2 mAh·g-1 at the current density of 0.5 C and the capacity can remain 70% of initial capacity after 50 cycles. By Fe doping, the initial discharge capacity decreased to 113.6 mAh·g-1, however, the LiFe0.05Mn1.95O4 material performed improved cycle ability, maintaining 83% of initial capacity after 50 cycles. An improved solid state reaction method was also developed, in which low toxicity acetone was used as a dispersant making the Li2CO3 and MnO2 to mix homogeneously.Furthermore, we adopted two-step calcinations to achieve a high crystalline spinel LiMn2O4 which played an important role in the electrochemical property. The electrochemical characterizations indicated that the spinel LiMn2O4 prepared by the improved solid state reaction method shows a higher capacity, and better cycle stability. It has an initial capacity of 117 mAh·g-1 at a current density of 0.2 C between 3.3 - 4.5 V and good cycle stability, maintaining 94% of its initial capacity after 40 cycles. Moreover, the LiMn2O4 prepared by the improved method shows better discharge ability at high rates than that prepared by the conventional method. This method has a great potential for the commercial preparation of LiMn2O4 because it can produce the LiMn2O4 with enhanced capacity and cycle life by a simple way with low cost of raw materials.In order to improve the cycle performance of material at high temperature, the LiMn2O4 was modified by coating its surface with a thin layer of amorphous A12O3. In buffer solution, Al(OH)3 can be heterogeneous nucleation, therefore after heat treatment, a thin layer of A12O3 could form on the surface of the spinel. Obviously, coating the surface of LiMn2O4 with A12O3 can modify the properties of its surface, which is exposed to the electrolyte solution and avoid the parasite reactions. A12O3 can also capture the HF from electrolyte, which reacts with the LiMn2O4 and accelerate the dissolution of Mn, then the cycle stability of the spinel material was improved.
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