【作者】 王妍；

【导师】 王淑兰；

【作者基本信息】 东北大学 ， 物理化学， 2013， 硕士

【摘要】 金属锡具有理论比容量(990 mAh/g)高、适合大电流放电等优点,是发展前景广阔的新型锂离子电池负极材料之一。然而充放电过程中金属锡剧烈的体积变化导致活性材料变形脱落,降低了电池的使用寿命。将材料纳米化及掺杂“惰性”金属制成合金,利用纳米材料巨大的比表面积及对锂非活性的“惰性”金属框架可以有效缓冲锡的体积变化,提高锡基负极材料的循环稳定性。本文以不锈钢为基底,采用脉冲电沉积方法,通过在镀液中添加十二烷基硫酸钠后制备了具有晶须结构的锡膜负极。通过X射线衍射分析、扫描电镜、线性扫描伏安法和红外光谱法分析其组成、结构及形貌。十二烷基硫酸钠在电极表面的吸附使镀层压应力增大,产生晶须。研究了不同电沉积温度、时间和电流密度得到的锡负极,采用恒流充放电、循环伏安和交流阻抗方法研究了锡电极的充放电性能和循环性能,分析并比较了材料结构、形貌与性能之间的区别与联系。实验证明,25℃时电流密度为0.4 mA/dm2,沉积900 s得到的金属锡薄膜材料颗粒大小均匀、排列紧密,具有较好的电化学性能,首次放电容量为1037.1 mAh/g,15个循环时衰减为149.5 mAh/g,在随后的循环中,由于SEI膜的保护作用和多孔电极的缓冲作用,比容量衰减缓慢,充放电50个循环,放电容量仍保持在90 mAh/g以上,具有一定的电化学稳定性,另外锡须对锡镀层的变形剥落存在一定的缓冲作用。本文在不同条件下对锡薄膜进行热处理,研究了氧化物及锡铁合金的生成对锡电极电化学性能的影响。结果表明,锡合金电极中掺杂“惰性”的氧元素和铁元素可以有效减缓金属锡的体积效应、改善锡电极的循环性能,提高首次循环库伦效率。在氩气保护下,200℃对锡膜负极进行热处理24 h,得到Sn-Fe合金电极,其最大放电其比容量为650.6 mAh/g,在随后的15个循环中比容量仍高于500mAh/g。在氩气氛围中,温度为240℃热处理24 h,由于合金化反应的充分进行,晶须数量急剧减少,首次库伦效率为87.2%,Sn-Fe合金电极的最大放电比容量为724.1 mAh/g,30次时,减少至240 mAh/g;在200℃空气中氧化24 h,部分Sn被氧化为SnO,对合金电极的循环性能及电极反应过程均有一定影响,首次放电容量为496.4 mAh/g,第二次循环时,放电容量达到最大值594.9 mAh/g,10～25次循环时,比容量保持在300 mAh/g左右,具有良好的循环稳定性,随后逐渐降至164.6 mAh/g。更多还原

【Abstract】 Tin-based anode material is popular for high theoretical specific capacity (990 mAh/g), strong adaptability for high current charge-discharge. However, tin’s volume changes so large in charging and discharging that causes active materials collapse and inactivation, lastly reduces the service life of battery. Prepare nano-powders and tin-based alloys can improve the cycle life of tin effectively. Large specific surface area of nano-powders and inert element as framework can buffer the volume expansion and improve the cyclic life.This work had prepared tin film with whiskers on the stainless steel substrate by adding sodium dodecyl sulfate(SDS) in bath by pulse electrodeposition, whose compositon, structure and morphology was analyzed by X-ray diffraction(XRD), Scanning electron microscope(SEM), Linear sweep voltammetry(LSV) and Infrared spectroscopy(IR). The sorption of SDS on electrode led to compressive stress in coating increasing, then whiskers formed on the surface. Tin anodes were got by changing temperature, time and current density in electrodeposition, of which charge-discharge performance and cycle performance had been studied by charge/discharge, cyclic voltammetry(CV)and AC impedance. Results:when the current density was 0.4 mA/dm2 and plating 900 s, tin film with uniform grain size got better electrochemical performance. The first-discharging specific capacity was 1037.1 mAh/g. Until the 15th cycle, the discharge capacity decreased to 149.5 mAh/g, and then decayed slowly in the subsequent cycles by SEI and porous electrode, showing the tin electrode had some electrochemical stability, keeping at 90 mAh/g after 50 cycles; in addition, whiskers on the surface could buffer the pulverization and exfoliation.This research had studied the electrochemical properties of oxide and Sn-Fe alloy after heat treatment of tin anode. It was showed that inert O and Fe doping in tin-based electrode could availably reduce the volume effect, improve the cycle stability and initial coulomb efficiency. Sn-Fe alloy anode was got at 200 ℃ in argon for 24 h, whose most-discharge specific capacity was 650.6 mAh/g, and remaining higher than 500 mAh/g in the subsequent 15 cycles. Due to the alloying reaction carried out fully at 240 ℃ in argon for 24 h, tin whisker has reduced sharply; the coulomb efficiency increased to 87.2%. The maximum discharge capacity of Sn-Fe alloy anode was 724.1 mAh/g, decreasing to 240 mAh/g in 30th cycle. Tin film treated at 200 ℃ in air make part of Sn oxidized to SnO, which had a certain impact on cyclic performance and electrode reaction of anode. The first discharge capacity was 496.4 mAh/g, rising to 594.9 mAh/g till the 2nd cycle; the specific capacity maintain about 300 mAh/g in 10～25 cycles, showing good cycling stability, decreasing to 164.6 mAh/g gradually.更多还原