导 师: 贾殿赠
学科专业: 070304
授予学位: 硕士
作 者: ;
机构地区: 新疆大学
摘 要: LiFePO/_4结构稳定、资源丰富,安全性能好、无毒、环境友好,而且随着温度升高,材料容量增大,适合于比较苛刻的条件下使用。系列研究表明LiFePO/_4已经成为最有前途的锂离子电池正极材料之一。目前合成橄榄石型LiFePO/_4多采用高温固相法或溶液法与高温固相法相结合的方式合成,需要多个步骤且周期长。本文从降低锂离子电池的生产成本和提高材料的电化学性能出发,主要研究了水热法和微波法合成橄榄石型LiFePO/_4的工艺,以及掺杂改性来提高电池材料的容量和稳定性等问题。得以下几方面的研究结果。 /(1/)采用水热法合成LiFePO/_4材料。研究了反应时间对产物结构和电化学性能的影响,当反应时间较短时产物形貌为棒状,反应时间为16 h时为球形粒子,随时间增长产物的形貌趋向无规则的块状。其中球形粒子电化学性能最好,C//2放电制度下,首次放电容量为50 mAh//g,经50圈循环后保持在49 mAh//g。 /(2/)通过正交实验优化微波法合成LiFePO/_4的工艺条件。得到的最佳合成条件是反应时间为15min,掺杂柠檬酸的量为5 mmol,微波功率为750w。该条件下,合成的LiFePO/_4在C//2放电制度下,最大放电容量达到了125 mAh//g。 /(3/)针对LiFePO/_4导电性差等问题,对其进行掺杂改性研究。通过在前驱体中掺入活性碳、乙炔黑、微米银、多壁碳纳米管等作为导电剂,微波反应制备了LiFePO/_4材料。电化学测试表明掺入微米银和多壁碳纳米管的样品效果较好。通过研究微米银不同的质量分数以及多壁碳纳米管的不同管径对LiFePO/_4电化学性能的影响,得出银的最佳掺杂量为3/%,所得样品首次放电容量为143 mAh//g,循环50圈后容量为93 mAh//g,多壁碳纳米管的最佳管径为10-20 nm,所得样品首次放电容量为157 mAh//g,循环50圈后容量为97 mAh//g。 /(4/)在前驱体中掺入蔗糖、柠檬酸、� With the advantages of good stability, rich resources, high safety, non-toxicity, and increasing capacity with rising temperature, LiFePO/_4 meets the requirements of harsh conditions. Prolific research has proved that LiFePO/_4 is one of the most promising lithium-ion battery cathode materials. At present, LiFePO/_4 is mainly synthesized by high temperature solid-state reaction or the combination of solution method and high temperature solid-state reaction, which require complex steps and long period. To reduce the cost of lithium-ion batteries and improve the electrochemical capacity of cathode materials, the present thesis focuses on synthesizing LiFePO/_4 by hydrothermal method and microwave heating as well as improving the capacity and stability of the battery materials with doping. Results of the present study are as follows: /(1/) Hydrothermal method is employed to synthesize LiFePO/_4 cathode materials. The effect of reaction time on the structure and electrochemical performance of the product is researched. When the reaction time is short, the product is rod-like. When the reaction time is 16 h, the particles of LiFePO/_4 are spherical. The shape of the product tends to become irregular with increasing time. Spherical particles have the highest capacity. The initial capacity reaches 50 mAh//g, which maintains at 49 mAh//g after 50 charge-discharge cycles at C//2 rate. /(2/) The synthesized conditions of LiFePO/_4 by microwave heating are optimized by orthogonal experiment. The optimum synthesized condition is 15 min, 5 mmol citric acid and 750 w. Under this condition, the highest capacity of synthesized LiFePO/_4 reaches 125 mAh//g at C//2 rate. /(3/) Doping of different materials is conducted to improve the poor conductivity of LiFePO/_4. LiFePO/_4 is prepared by microwave heating with doping of activated carbon, carbon black, Ag and MWCNTs as conductive materials. Electrochemical testing has shown that doping of Ag and MWCNTs can achieve better effect. After analyzing the eff
领 域: [电气工程]