Novel Synthetic Method And Its Properties Of Lithium-ion Battery Cathode Material LiFePO₄/C

Lithium-ion batteries has many advantages such as high voltage stable, small size, light weight, high power, long cycle life, low self-discharge rate, no pollution, no leaks, no memory effect and can use of a long time, so it is the best energy in 21century. Currently, the bottleneck in the development of lithium-ion battery is the cathode material, lithium-ion battery cathode material is not only required to have a high specific capacity and good charge-discharge performance and cycle performance, and price is also an important factor can not be ignored. Iron-based compound is cheap and China has much raw material, the biggest advantage is non-toxic, these have all contributed to the battery industry set off a series of iron-depth study of cathode materials. Series of iron phosphate compounds, LiFePO₄ has the highest theoretical capacity (170 mAh/g) and energy density(550 Wh/kg), and high discharge voltage (3.5 V), so it is a very promising new green energy. In this thesis, We use rheological phase method which on the basis of electrochemical method to prepare lithium-ion battery cathode material LiFePO₄/C, study of various factors on the preparation of LiFePO₄/C's performance, optimize the synthesis of LiFePO₄/C of the process conditions. The main contents and results are as follows:1. Lithium-ion battery cathode material LiFePO₄/C was obtained by electrochemical synthesis and rheological phase method, spray drying and granulation, sintered at 700℃. The morphology and structure of the product was characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observation. The capacity and cycle performance of LiFePO₄/C composite materials was characterized by charge and discharge test. The results showed that the LiFePO₄ particles are uniform, have better electrochemical performance, at room temperature and 0.1 C current density charge or discharge, the discharge capacity can reach 145.9 mAh/g, and after cycle 40 times, there is little capacity fading about 2%.2. LiFePO₄/C composite cathode materials were synthesized by vegetable proteins soya bean milk assisted rheological phase method. XRD and SEM observations show that the LiFePO₄/C composite materials have good crystallinity, ultrafine sphere-like particles of 200 nm size and in situ carbon. The electrochemical performance of the LiFePO₄ by galvanostatic cycling studies demonstrates excellent cycle stability. The Li/LiFePO₄ cell displays a high initial discharge capacity of more than 156 mAh/g and the first columbic efficiency was 98.7%, and maintains 149 mAh/g after 40 cycles at 0.1 C and capacity retention of more than 95%, indicating high electrochemical capacity and excellent cycling stability, have potential value for industrial applications.