| Low cost and high energy density are two unremitting pursue goals of lithium ion batteries. Up to now, the high price and low capacity of the widely used cathode materials are the ’bottleneck’ in the developing and applying of high energy density lithium ion batteries. Therefore, the research and development of new cathode materials with low cost and high capacity, as well as the optimization of synthesis processes to lower the cost, is the key issue in this area. In this case, we carried out the investigation of several low cost, high capacity Mn/Fe-based cathode materials. The main contents and conclusions are as follows:1. Electrochemically inactive Li2MnO3derived from solid state reaction is activated by reducing the average valance of Mn through the pyro lysis of chemically absorbed stearic acid. A series of Mn-based cathode materials with different Mn average valances and crystal phases are obtained by altering the pyro lysis temperature. The material derived from340℃maintains the layered structure of Li2MnO3, and has a reversible capacity of255mAh g-1. This method provides a way for the developing and using of Li2MnO3as cathode materials for lithium ion batteries.2. Co, Ni free Mn-based layered Li-rich cathode material xLi2MnO3·(1-x)LiMnO2is successfully synthesized for the first time by the pyro lysis of chemically absorbed steraic acid, using solid state synthsized Li2MnO3nanoparticles as raw material. Materials withx=0.74,0.57,0.48,0.39, can be obtained by altering the amount of absorbed stearic acid. All of these obtained materials have a reversible capacity>210mAh g-1, and the capacity is increased as decreasing the value of x. When x=0.57, this material has a reversible capacity approaching to250mAh g-1, and shows well cyclic and rate performances. These Co, Ni free materials are abundance in raw sources, therefore, they are a new kind of low cost, high capacity cathode materials for lithium ion batteries, and have high potential in commercialization.3. Single crystal xLi2MnO3·(1-x)LiMnO2nanoplates with diameter of-200nm and thickness of～60nm are successfully synthesized using single crystal Li2MnO3nanoplates by the pyro lysis of chemically absorbed stearic acid. Li2MnO3nanoplates are prepared through solid state reaction using the hydrothermal synthesized MnO2nanoplates. Since the transition metal layers parallelize to the radical direction in xLi2MnO3·(1-x)LiMnO2nanoplates, the reversible capacity is lower than that of nanoparticles with irregular morphology. However, the cyclic performance is obviously improved, leading to the material with x=0.44performs a reversible capacity as high as270mAh g-1with a well cyclic performance. These results prove that the cyclic performance of xLi2MnO3·(1-x)LiMnO2can be enhanced by tailoring the morphology of material particles, and it is an important guidance in the research of improving the electrochemistry performances of such material.4. Carbon coated LiFePO4nanocomposite is successfully synthesized by a pyrolysis process of in situ formed lithiuim stearate at400℃, using FePO4·xH2O amorphous nanoparticles precipitated from solution at room temperature and LiOH·H2O as raw materials. Such material with an average particle size～80nm and a well coated carbon layer on the particle surface, performs a discharge capacity of160mAh g-1at1C and100mAh g-1at IOC, and can retent96%capacity after200cycles at1C, showing excellent electrochemical performances. The present simple method can prepare carbon coated LiFePO4with good electrochemical performances at a comparatively low temperature, which is beneficial for lowering the energy consumption and cost, and for promising its large scale commercial production. |
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