【作者】 王艳宜；

【导师】 易国斌；

【作者基本信息】 广东工业大学 ， 应用化学， 2012， 硕士

【摘要】 锂离子电池负极材料作为提高锂离子二次电池能量及循环寿命的重要因素,在世界范围内得到了广泛的研究。与商业化的碳极相比,合金负极材料具有理论容量高、快速充放电能力等优点,因而是一类非常有发展前景的高比能锂离子电池负极材料。其中SnSb中的Sn和Sb都具有储锂活性,比SnCu SnNi等活性/惰性体系具有更高的理论比容量,得到了更广泛的研究。但由于合成的合金负极材料的粒径大,分布不均,合金粉末存在团聚现象严重,导致电池循环寿命差。通过化学还原法得到了由纳米SnSb合金和微米级Ag组成的复合负极材料。充放电前后FE-SEM形貌分析及交流阻抗分析表明,微米级Ag的存在使复合材料表面和内部逐渐形成了不规则的层状结构和大小不一的空隙,大大减小了锂离子的扩散距离,减少了滞留在活性物质中的锂,增加了体积膨胀时所需的空间,有效的防止复合负极材料在多次体积膨胀过程中的粉化脱落,大大提高了SnSb-Ag复合合金负极材料的循环稳定性。通过优化Ag的含量及充放电电压区间,SnSbAgo.2复合材料的循环性能最好,在0.1-0.5V电压区间进行充放电时,循环性能最好,50次循环后其比容量仍达到518mAh/g,与第二次放电容量相比,其容量保持率高达82.04%。研究表明,将Sn-基合金或者纳米粒子与碳纳米管复合可以有效提高负极材料的电化学性能。在SnSb-Ag/CNT复合材料的制备过程中,选择管径为60-100nm的碳纳米管,且在制备过程中将CNTs分散在NaBH4溶液中,电化学性能较好,50次循环后其容量仍高达573.8mAh/g。通过比较SnSb-Ag和SnSb-Ag/CNT充放电前后的微观形貌变化,以及充放电曲线和循环伏安曲线发现Ag和CNTs对SnSb-Ag/CNT复合材料的电化学性能的提高有很大的作用：CNTs由于管径大,阻止了合金粒子间的团聚,增大了合金粒子间的缓冲空间,减小了锂离子的扩散距离和锂在活性物质中的滞留；同时能有效缓冲合金粒子体积膨胀时中产生的巨大应力,减弱了粒子之间的作用力,降低了粒子的粉化速率。而Ag的存在使整个充放电过程处在复杂的多步的反应过程中,有效地缓解了反应过程中新析出的纳米粒子的团聚,促进反应的充分进行,从而提高了循环性能。通过优化复合材料中Ag和CNTs的比例,以及控制充放电区间,SnSbAg0.1/6%CNT在0.05-1.5V时电化学性能更为优越,50次循环以后,放电比容量仍达到639.6mAh/g,且能适应高低温环境中。更多还原

【Abstract】 Improving the energy capacity and cycle life of lithium-ion batteries is an important target, and as such, research on lithium-ion battery anode materials has generated much interest. Compared with graphite anodes, alloy anode materials have a high theoretical capacity and a fast charge/discharge rate, making alloys a class of very promising high-specific energy Li-ion battery anode materials. Both Sn and Sb in SnSb alloy anode materials have the capacity to store lithium, resulting in a higher theoretical specific capacity than other active/inert systems, such as SnCu and SnNi materials, and have been widely studied. Alloy anode materials undergo severe structural and volume changes during the charge/discharge cycle process across large sizes, resulting in uneven ion distribution, serious agglomeration and poor cycle stability.Nano-SnSb and micro-sized Ag alloy composite anode materials were synthesized using chemical reduction method. The addition of Ag made SnSb-Ag composite alloy anode materials, which formed a laminated structure with irregular gap sizes on the surface and interior of the structure after several cycles of insertion-extraction of lithium ions. This approach greatly shortened the lithium ion diffusion distance, reduced the trapping of lithium in the active materials, and increased the space available for volume expansion. As a result, powder drop off during the volume expansions was prevented, resulting in greatly improved cycle stability for the SnSb-Ag composite alloy anode materials.The SnSbAgo.2composite alloy anode material showed excellent electrochemical performance with a50-cycle capacity of518mAh/g, with a reversible capacity retention rate of82.04%between0.1V and1.5V.Recent research has demonstrated that the electrochemical performance of some Sn-based metals and nanoparticles can be significantly improved using CNTs (carbon nanotubes) as compounds. The SnSb-Ag/CNT composites, using L60-100nm CNTs and dispersing CNTs in NaBH4aqueous solution, will get good cycle performance with a50-cycle capacity of573.8mAh/g.Ag and CNTs play an important part in electrochemical properties by comparing the micro structures before and afer cycling, the CV curves, charge and discharge profiles. Silver was used to promote the entire charge-discharge process in the complex multi-step reaction process and, to some extent, alleviate the reunion of the nanoparticles in the reaction process, fully promote the reaction and improve the cycling performance. During the Li intercalation process, CNTs, with a large space volume and formed a network structure, prevented particle aggregation and increased the buffer space between the alloy particles, which greatly reduced the diffusion distance of lithium ions and the occurrence of lithium trapping in the active electrode materials. CNTs also have excellent mechanical properties and toughness, they effectively buffer enormous stresses during the volume expansion of alloy particles, weakening the forces between the particles and reducing the rate of formation of powder particles, resulting in good electrochemical performance. The SnSbAg0.1/6%CNT composite anode exhibited excellent cycle life by controlling the lithiation of the anode material. The reversible capacity for the50th cycle was639.6mAh/g between0.05and1.5V.更多还原