【作者】 王淼；

【导师】 郭瑞松；

【作者基本信息】 天津大学 ， 材料学， 2008， 硕士

【摘要】 当今能源和环境问题日渐突出,同时随着科技的迅猛发展对电池的性能提出了更高的要求。LiFePO4作为新一代的锂离子电池正极材料,因其结构稳定、来源广泛、价格低廉、安全性能好、对环境无污染、理论容量高等优点而成为目前各国的研究热点。电子电导率低和锂离子扩散速率慢是影响LiFePO4性能的主要因素,本文采取新的碳源和高价金属阳离子掺杂等手段对LiFePO4进行了微波合成与改性,得到了具有优异电化学性能的LiFePO4复合正极材料。利用XRD、SEM和TEM等测试方法对正极材料的相组成和微观形貌进行了分析,组装扣式电池后,采用恒流充放电技术测试其电化学性能。以柠檬酸为碳源合成的LiFePO4/C正极材料,当添加10wt%柠檬酸时材料的电化学性能最好,在0.1C倍率下首次放电比容量最高,达到141.63mAh·g-1,10次循环后比容量保持在134.33 mAh·g-1,仅损失5.16%;在0.3C和1C倍率下的首次放电比容量分别为116.54mAh·g-1和87.21mAh·g-1,循环性能较好。以PAM为碳源合成的LiFePO4/C正极材料,当添加5wt%PAM时在0.1C倍率下的首次放电比容量最高,为150.22mAh·g-1,循环10次后放电比容量为104.71mAh·g-1,容量衰减较多。在0.3C和1C倍率下的首次放电比容量分别为95.15mAh·g-1和57.21mAh·g-1,其高倍率放电容量和循环性能都不是很好。以TiO2为金属离子添加物合成了LiFePO4/Ti4+正极材料,当掺杂1%Ti4+时样品的性能最佳,在0.1C倍率下的首次放电比容量为123.08 mAh·g-1,第10次循环的放电比容量为116.63mAh·g-1;在0.3C和1C倍率下的首次放电比容量分别为97.92mAh·g-1和59.38mAh·g-1,循环性能良好。合成了LiFePO4/(C+Ti4+)复合正极材料,以添加5%柠檬酸和掺杂1%Ti4+的样品的电化学性能最好,在0.1C下的首次放电比容量为138.52 mAh·g-1,循环10次后放电比容量为129.42mAh·g-1;在0.3C和1C倍率下的首次放电比容量分别为114.95mAh·g-1和102.39mAh·g-1,循环性能稳定。更多还原

【Abstract】 Higherandhigherrequirements forlithium ionbatteries areput forwardwiththequick developments of science and technology and due to the serious problems ofenergyand environment. LiFePO4 is becoming the hot issue as a cathode material forlithium ion batteries because of its stabilization, abundance, cheapness, security,environmental friendlyness and high theoretical capacity. However, its low electronconductivity and low lithium ion diffusion rate are the major obstacles affecting thepropertiesofLiFePO4.Theaimsofthepresentworkaretoincorporatethenewsourceof carbon and to dope with higher valence of ion to improve the electrochemicalproperties of LiFePO4. LiFePO4/C, LiFePO4/Ti4+ and LiFePO4/(C+Ti4+) compositecathode materials were synthesized using microwave heating. The microstructure andmorphologies of these composites were investigated by XRD, SEM and TEM. Thelithium ion batteries were assembled in an Ar-filled glove box. The electrochemicalperformanceswereevaluatedbygalvanostaticcharge-discharge.Carbon-coated LiFePO4 composite was synthesized using citric acid as carbonsource. The material with 10wt% carbon exhibited the best electrochemicalperformance. Its initial charge specific capacity is 141.63 mAh·g-1 at 0.1C. Thecapacitymaintained to be 134.33 mAh·g-1 after 10 cycles, with the capacityloss ratiobeing 5.16%. The initial charge specific capacity is 116.54 mAh·g-1 and 87.21mAh·g-1 at 0.3C and 1C, respectively. And the cycling behavior of the material isgoodundertheseconditions.LiFePO4/C composite using PAM as carbon source delivered a high initialspecific discharge capacityof 150.22 mAh·g-1 with 5wt% PAM at 0.1C. The capacitymaintained to be 104.71mAh·g-1 after 10 cycles. The capacityloss ratio is larger thanthat with citric acid as carbon source. The initial charge specific capacity is 95.15mAh·g-1 and 57.21 mAh·g-1 at 0.3C and 1C, and the cycling behavior of the materialisnotsogood.LiFePO4/Ti4+ composite showed a high initial specific discharge capacity of123.08 mAh·g-1 with 1mol% Ti4+ at 0.1C. The capacity maintained to be 116.63mAh·g-1 after 10 cycles. The initial charge specific capacity is 97.92 mAh·g-1 and59.38 mAh·g-1 at 0.3C and 1C, respectively, and the cycling behavior of the material isquitepoor.LiFePO4/(C+Ti4+) composite using citric acid and TiO2 delivered a high initialspecific discharge capacity of 138.52 mAh·g-1 with 5wt% citric acid and 1mol% Ti4+at 0.1C. The capacity maintained to be 129.42 mAh·g-1 after 10 cycles. The initialcharge specific capacity is 114.95 mAh·g-1 and 102.39 mAh·g-1 at 0.3C and 1C, andthecyclingbehaviorofthematerialisverygood.更多还原