【作者】 汤展峰；

【导师】 杨文胜；

【作者基本信息】 北京化工大学 ， 化学， 2010， 硕士

【摘要】 锂离子电池具有工作电压高、循环性能好、比能量大、环境友好等优点,已经成为21世纪绿色电池的首选。锂离子电池的关键材料之一是正极材料。尖晶石LiMn2O4原材料丰富、低毒性、低成本及容易制备而被视为最有应用前途的锂离子电池正极材料之一。但是LiMn2O4循环稳定性尤其高温循环稳定性差,制约了其发展,其容量衰减的主要原因是锰的溶解、Jahn-Teller效应以及HF对正极材料的腐蚀。目前商品化锂离子电池的正极材料主要是具有α-NaFeO2型层状结构的LiCoO2,但LiCoO2价格昂贵,实际比容量偏低,仅为140 mAh·g-1左右,仅为其理论比容量274mAh·g-1的50%,且抗过充性能差,这主要是由于在充电过程中随锂离子的脱出,LiCoO2晶体结构发生不可逆相变所致。针对这些问题,本论文采用表面包覆改性的方法提高LiMn2O4的高温循环性能、LiCoO2的抗过充电性能和循环稳定性。具体研究内容如下：(1)采用钴铝水滑石(CoAl-LDH)为包覆材料前驱体制备CoAl-LDH包覆尖晶石LiMn2O4,再焙烧得到钴铝复合金属氧化物(CoAl-MMO)包覆尖晶石LiMn2O4正极材料,并分别对恒pH值法、成核晶化隔离法和复合共沉淀法(恒pH值法+成核晶化隔离法)合成LDH包覆LiMn2O4进行比较,考察前驱体合成方法对CoAl-MMO包覆LiMn2O4材料结构、形貌和电化学循环性能的影响,发现复合共沉淀法在LiMn2O4表面包覆效果最好,制备出来的CoAl-MMO包覆LiMn2O4电化学循环性能最佳。采用复合共沉淀法合成不同CoAl-MMO包覆量的LiMn2O4正极材料,并考察了CoAl-MMO包覆量对LiMn2O4材料结构、形貌和电化学性能的影响。(2)采用共沉淀法制备CoAl-LDH包覆在层状LiCoO2表面,再焙烧得到CoAl-MMO包覆LiCoO2正极材料。CoAl-MMO包覆稳定了LiCoO2的晶体结构,改善了材料的抗过充性能和循环稳定性。以中间相碳微球(MCMB)为负极,以CoAl-MMO包覆LiCoO2为正极组装成AA电池。在充放电电压范围分别为2.75-4.2V和2.75-4.4V,1C充放电倍率条件下,CoAl-MMO包覆的LiCoO2材料的首次放电比容量分别为141 mAh·g-1和160 mAh·g-1,400次循环的容量保持率分别为93.8%和91.3%,分别优于LiCoO2的87.5%和69.2%的容量保持率。更多还原

【Abstract】 Lithium ion battery is the primary choice of the green battery in the 21th century due to its advantages such as high operating voltage, brilliant cycle stability, high theoretical capacity and environmental friendly. Spinel lithium manganese oxide (LiMn2O4) with the merits of abundant manganese resources, low cost, low toxicity and ease of preparation, is a most promising candidate material for lithium ion battery. However, its cyclic stability is poor in nonaqueous electrolytes, especially at a higher temperature above 55℃. The capacity fading is mainly due to dissolution of Mn2+, Jahn-Teller effect and corrosion of HF. At present, layered LiCoO2 is the major cathode material of commercial lithium ion battery. However, the main problems of LiCoO2 cathode material are its expensive cost, low practical capacity, poor overcharge tolerance. The main reason is that the crystal structure of LiCoO2 materials undergoes irreversible phase transformation as the lithium ions deintercalate during the charging process. In order to improve cycling property of LiMn2O4 at high temperature and overcharge tolerance of LiCoO2, this paper mainly involves two aspects with surface treatment:(1) LiMn2O4 coated with Co-Al layered double hydroxide (CoAl-LDH) precursor is calcined to obtain Co-Al mixed metal oxide (CoAl-MMO) coated LiMn2O4. The CoAl-LDH coated LiMn2O4 precursor is prepared by constant value of pH titrate method, the separate nucleation and aging steps (SNAS) method and the complex coprecipitation method(constant value of pH titrate method and the SNAS method). The effects of different mehods of preparation of CoAl-LDH coated LiMn2O4 precursor on the structure, morphology and electrochemical performance of CoAl-MMO coated LiMn2O4 have been studied, the complex coprecipitation method is best. Then we study the effect of coating amounts on the structure, morphology and electrochemical cycling performance of CoAl-MMO coated LiMn2O4 prepared by the complex coprecipitation method.(2) LiCoO2 coated with CoAl-LDH precursor prepared by coprecipitation method is calcined to obtain CoAl-MMO coated LiCo02. The CoAl-MMO coating stabilizes the crystal structure, and improves the overcharge tolerance and cycling performance of LiCoO2. When the voltage range is 2.75-4.2 V and 2.75-4.4 V, and the discharge rate is 1C, the initial discharge capacity of CoAl-MMO (1.0wt.%Co,0.17wt.%Al) coated LiCoO2 is 141 mAh-g-1 and 160 mAh·g-1, and the 400th capacity retention is 93.8%and 91.3%, which is better than 87.5% and 69.2% of pristine LiCoO2 respectively.更多还原