The Property Research Of LiFePO₄ New Lithiun Ion Battery Cathode Materials

LiFePO₄ is a new kind of lithium ion battery anode materials, it has larger theoretical capacity (170 mAh/g), charging and discharging voltage moderate (3.4V), abundant resources, environment friendly, the process of charging and discharging little volume change (6.8%), stable structure, good thermal stability, therefore it is regarded as the most potential positive materials replacement of acid lithium cobalt materials.This paper firstly outlines the component, the principle and the advantages and disadvantages of lithium-ion secondary battery, introduces the research progress of the lithium ion battery anode materials and the LiFePO₄ materials, LiFePO₄ structure, common synthesis method, the market situation and the main factors of influencing the material electrochemical performance: a, low electronic conductivity (about 10-9S/cm2), leading to its poorer high rate discharge properties; b, lower Li⁺ diffusion coefficients on solid phase, leading to a slower solid reaction kinetics; c, lower vibration real density. Then, selecting proper carbon sources and optimizing the synthesis process to get smaller, particle size uniform, distributed spherical particle, to improve the conductivity, shorten Li⁺ diffusion time on solid phase of material, synthesis more optimal performance LiFePO₄ materials. According to the problems we study, its main content as follows:1. For the commercial samples testing and analysising, giving a reasonable performance evaluation, locking experimental goal.2. In order to improve the inherent electronic conductivity and diffusion coefficient of material, this paper using glucose for carbon sources, adopting different lithium source and changing heat treatment condition to synthesis LiFePO₄/C battery anode materials, optimize the performance with best lithium source, discuss low temperature condition synthesis LiFePO₄/C battery anode material and characteristic the structures, morphology and electric performance of LiFePO₄/C material.3. In order to further reduce the cost of material, this paper adopts a cheap trivalent iron as iron source, Li₂CO₃ as lithium source, through adding different carbon source one step carbon reduction method synthesis high-density spherical LiFePO₄ positive material, through one step carbon reduction method with different carbon source mixed to synthesis high-density spherical LiFePO₄/C, characterize the morphology of the material and electrical properties, then continuously optimize the synthesis process to improve the discharge capacity significantly.4. To continuously improve the electrochemical properties of materials and obtain high-energy LiFePO₄/C compound materials, this paper uses polyvinyl alcohol (PVA) granulation template as auxiliary by a new two-step reduction method method to synthetize LiFePO₄/C positive materials, and its morphology and electrochemical properties were also investigated.5. Try to synthetize LiFePO₄/C nanoscale compound materials by precipitation control crystallization method and carbon reduction method coupled, to further improve the electrochemical performance.