【作者】 郎野；

【导师】 孙克宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 硕士

【摘要】 近年来,由于能源、环境危机的日益加剧以及电子信息行业的高速发展,锂离子电池受到前所未有的关注。但相对于负极材料和电解质来说,锂离子电池正极材料依旧是制约其发展和应用的关键因素。具有尖晶石结构的5V正极材料LiNi_0.5Mn_1.5O₄由于其结构稳定、放电电压高等优点,成为锂离子电池正极材料的研究热点之一,但循环容量衰减的弊端制约了其商业化。本文采用溶胶凝胶法合成尖晶石型LiNi_0.5Mn_1.5O₄,并分别采用双掺杂和表面包覆改性的方法提升材料的循环性能。首先,采用Cr³⁺和F-双掺杂的方法提高LiNi_0.5Mn_1.5O₄正极材料的循环稳定性,考察了Cr³⁺取代不同过渡金属元素以及Cr³⁺含量的影响。研究发现Cr³⁺和F-双掺杂未改变材料的结构,可显著提升材料的循环稳定性以及倍率性能。综合比较,LiNi_0.5Mn_1.4Cr_0.1O_3.95F_0.05性能最佳,其具有较高的4.7 V平台容量,循环100次后,容量保持率为93.8%。提出引入阳离子空位的方法提高双掺杂材料的倍率性能,合成了LiNi0.325Mn1.5Cr0.1O3.95F0.05,该材料具有十分优越的倍率和循环性能。在5C和10C倍率下的放电容量分别为123.89 mAh g-1、104.44 mAh g^-1;0.2C倍率下循环50次,容量保持率为97.5%。CV和EIS测试表明倍率性能提升的原因在于空位的存在减少锂离子脱嵌阻力,提高固相扩散系数和电化学活性。其次,分别在LiNi_0.5Mn_1.5O₄的表面包覆AlF₃和TiO₂,并考察AlF₃与TiO₂包覆量对循环性能的影响。发现AlF₃包覆层能有效的抑制电解液对正极材料的腐蚀以及活性物质的溶解,随着包覆量的增加效果更加显著。当AlF₃的包覆量为3 mol%时,LiNi_0.5Mn_1.5O₄/AlF₃的循环性能最佳,室温下循环50次后,容量为119.23 mAh·g^-1,容量保持率为94.5%;55℃时放电容量为116.29 mAh·g^-1,循环50次后,容量保持率为84.0%。包覆的TiO₂起到了HF收集体的作用,当包覆量为3 mol%时,循环性能最佳,室温下循环100次后,容量保持率为92.5%;55℃下循环50次后,容量保持率为77.9%。更多还原

【Abstract】 ]In recent years, due to the increasing crisis of energy and environment and the rapid development of electronic information industry, more and more attentions have been paid to the lithium-ion batteries. Comparision with the anode and electrolyte, the cathode materials of lithium ion batteries have been crucial factors that restrict their development and application. 5V cathode material spinel LiNi_0.5Mn_1.5O₄ is proved to be one of the studying hotspots of lithium ion cathode materials since its stable structure and high discharge voltage. However, the disadvantage of capacity fade limits its commodification. In this paper, spinel LiNi_0.5Mn_1.5O₄ was synthesized by sol-gel method, and co-doping and surface coating modifications have been adopted to enhance the cycling performance, respectively.Firstly, the method of Cr³⁺ and F- co-doping was used to improve the cycling stability of LiNi_0.5Mn_1.5O₄ cathode material, and the effects of substitution of different transition metal elements by Cr³⁺and Cr3 + content were investigated. The studies showed that Cr³⁺ and F- co-doping did not change the structure of material, and significantly improved the cycling stability and rate capability. By the comprehensive comparison, LiNi_0.5Mn_1.4Cr_0.1O_3.95F_0.05 showed the best performance. It expressed higher capacity at 4.7 V platform, and the capacity retention was 93.8% after 100 cycles.Cation vacancy was introduced into the co-doping materials to enhance the rate capacity. The prepared LiNi0.325Mn1.5Cr0.1O3.95F0.05 showed the excellent rate capability and stable cycle performance. Its discharge capacities were 123.89 mAh·g^-1 and 104.44 mAh·g^-1 at 5C and 10C discharge rate, respectively, and the capacity retention was 97.5% after 50 cycles at 0.2C charge-discharge current. CV and EIS measurements showed that the enhancement of rate performance was due to the existence of vacancies, which reduced the resistance of lithium ion deintercalation and improved solid diffusion coefficient and the electrochemical activity.Secondly, AlF₃ and TiO₂ were coated on the surface of LiNi_0.5Mn_1.5O₄, and the influence on the cycling performance caused by the coating content of AlF₃ and TiO₂ was researched. It was found that the coating AlF₃ can effectively restrict the corrosion of the cathode materials and the dissolution of active substances, and the effect was getting more outstanding with the increase of coating amounts. The electrochemical performance of LiNi_0.5Mn_1.5O₄ with 3 mol% coating AlF₃ was the best, the capacity was 119.23 mAh·g^-1 with capacity retention of 94.5% mAh·g^-1 at room temperature after 50 cycles, while it was 116.29 mAh·g^-1 with capacity retention of 84.0% after 50 cycles at 55℃. The coating TiO₂ played a role of HF collectors. When the coating amount was 3 mol%, it showed the best cycling performance. The capacity retention was 92.5% after 100 cycles at room temperature, and 77.9% after 50 cycles at 55℃.更多还原