【作者】 潘思仲；

【导师】 陈猛；

【作者基本信息】 哈尔滨工程大学 ， 应用化学， 2007， 硕士

【摘要】 正极材料对锂离子电池的性能影响很大。近年来锂离子电池正极材料研究较多的主要有LiCoO₂、LiMn₂O₄、LiNiO₂等化合物。目前商品化的锂离子电池一般都是采用LiCoO₂作为正极材料，但钴资源有限，价格昂贵，且对环境污染较大，而锂锰氧的循环性能较差，容量相对较低。本论文以LiNiO₂为研究对象，采用溶胶—凝胶法对其进行一元和二元掺杂，合成了α-NaFeO₂型层状结构的LiNi_1-xCo_xO₂和LiNi_0．8-xCo_0．2Al_xO₂，采用沉淀法在LiNi_0．8Co_0．2O₂表面上包覆一层Al₂O₃膜。详细研究了掺杂元素的不同比例和包覆量的比例等条件对合成该种正极材料的结构和电化学性能的影响。在合成的LiNi_1-xCo_xO₂体系锂离子电池正极材料中，经电化学性能测试表明，经过Co元素的掺入，材料的循环性能得到显著提高，当掺杂量x为0．2时，即化学组成为LiNi_0．8Co_0．2O₂的综合性能最佳，首次放电比容量为170．40 mAh·g^-1，循环30次后放电比容量为149．86 mAh·g^-1，容量保持率为89．95％。采用溶胶—凝胶法进行二元掺杂，在这一部分内容中，通过在LiNi_0．8Co_0．2O₂正极材料中用Al取代部分Ni进行改性，合成出具有良好层状结构的LiNi_0．8-xCo_0．2Al_xO₂正极材料。对其电化学性能研究发现，LiNi_0．77Co_0．2Al_0．03O₂材料第50次循环时的放电容量达149．51 mAh·g_-1，是首次放电容量的90．66％。通过XRD结构测定、循环伏安扫描测试和电化学阻抗测试表明对LiNi_0．8Co_0．2O₂进行Al掺杂，增强了材料层状结构的稳定性，有效抑制了锂离子嵌入脱出过程中材料的相转变，其循环稳定性得到了明显改善。采用沉淀法在LiNi_0．8Co_0．2O₂表面包覆一层Al₂O₃膜，经包覆后材料的首次放电容量有所降低，但有效的抑制了电解液对LiNi_0．8Co_0．2O₂正极材料的侵蚀，改善了材料的循环性能。当Al₂O₃的包覆量为0．7％（质量分数）时，材料的综合性能最优，初始放电容量为164．84 mAh·g^-1，经过30次循环后放电容量为155．63 mAh·g_-1，容量保持率为94．41％。更多还原

【Abstract】 The cathode materials have a strong influence over the properties of the lithium-ion battery. Compounds such as LiCoO₂, LiMn₂O₄ and LiNiO₂ are attractive cathode materials for lithium-ion battery. Now the commercialized lithium-ion battery mostly uses LiCoO₂ as cathode material, but cobalt suffers the disadvantage of limited resource, high price and heavy pollution to environment. Though LiMn₂O₄ enjoys the advantage of low-price, easy preparation and non-toxicity to environment, yet its cycleability not good and specific capacity low. In this paper, both LiNi_1-xCo_xO₂ and LiNi_0.8-xCo_0.2Al_xO₂ materials synthesized by sol-gel method and LiNi_0.8Co_0.2O₂ coated Al₂O₃ by precipitation method have the same layered structure （α-NaFeO₂） with LiNiO₂. The ratio of doping element and coating amount and the relation between the ratio and the electrochemical performance are studied detailed.In the LiNi_1-xCo_xO₂ system, the research of electrochemical performance tests shows that LiNi_0.8Co_0.2O₂ have the best electrochemical properties, which had an initial discharge specific capacity of 170.40 mAh·g^-1 and retaining about 89.95% after 30 cycles.In the second part, the electrochemical performance of the LiNi_0.8Co_0.2O₂ cathode is modified by multiple substitutions with Al element by sol-gel method. Single-phase solid solution of LiNi_0.8-xCo_0.2Al_xO₂ has been synthesized and characterized by X-ray diffraction （XRD） and examined by charge-discharge cycling. The LiNi_0.77Co_0.2Al_0.03O₂ compounds show a discharge capacity of 149.51 mAh·g^-1 after 50 cycles that corresponds to 90.66% capacity retention. The results of XRD, cyclic voltammograms （CV）, and electrochemical impedance spectrum （EIS） show that co-doping with Al stabilizes the layered structure, the phase transitions that occur during extraction or intercalation of Li⁺ ions are significantly suppressed, and the cyclic capability is improved.LiNi_0.8Co_0.2O₂ coated with Al₂O₃ was synthesized by precipitation method. The initial discharge specific capacity reduce somewhat, but the cycle performance had been improved. The initial discharge specific capacity is 164.84 mAh·g^-1 and retaining about 94.41% (155.63 mAh·g^-1) after 30 cycles, while the coating amount is 0.7%.更多还原