【作者】 李静；

【导师】 黄玉代； 马育新；

【作者基本信息】 新疆大学 ， 化学， 2017， 硕士

【摘要】 聚丙烯隔膜（PP）作为锂离子电池的重要组成部分之一,主要起分隔正负极和传输Li+的作用。但PP隔膜表面具有较高的表面能,表现出较强的憎水性,这不仅不利于电解液的浸润,还不利于电解液的保持。而且当温度达到PP的熔融温度时（165℃）,会导致隔膜的微孔闭合以致隔膜失效。因此,提高PP隔膜的亲水性和热稳定性一直是研究的重点。当PP隔膜应用到锂硫电池时,又增加了一个新问题,即:聚硫化物的穿梭效应。因此如何改性隔膜,使之能有效减缓穿梭效应,就成为了PP隔膜改性研究的又一难点。本文针对这三个问题,对隔膜进行改性研究,并将其应用于锂硫电池,取得了良好的效果。（1）通过涂覆的方法,成功制备了具有Al₂O₃和CNT双涂层的改性隔膜（CAF）。因高熔点的Al₂O₃存在,使得隔膜的热稳定性增加,而且涂层的疏松表面能增加隔膜对电解液的润湿性,加速Li+的传输。将该改性隔膜应用于锂硫电池发现,涂层不仅能通过位阻效应,还能通过Al₂O₃与聚硫化物间的化学作用力,减缓聚硫化物的穿梭效应。CNT具有优异的导电性,可作为第二电极,进一步提高活性物质的利用率。因此采用CAF隔膜的锂硫电池,其放电容量和倍率性能得到大幅提升,在0.2 C下其首次放电容量为1096 mAh g^-1,循环100圈后为760.4 mAh g^-1,容量保持率为69.3%。（2）利用表面活性剂（吐温、曲拉通和聚乙二醇）的两性,使其疏水端紧密地粘附在隔膜上,亲水端上的-OH与生成的SiO₂粒子上的-OH结合,从而将SiO₂固定在隔膜表面。该改性隔膜使用寿命长,其润湿性和热稳定性也得到大幅提高。将其应用于锂硫电池时,SiO₂和聚硫化物间较强的化学作用力,能有效缓解聚硫化物的穿梭效应。在0.2 C下的首次放电容量达937 mAh g^-1,循环200圈后容量仍为603.5 mAh g^-1,每圈的衰减率仅为0.05%。（3）通过苯胺自聚合沉积在隔膜上,成功制备了聚苯胺（PANI）改性的隔膜。PANI沉积层的疏松结构和高熔点（>350℃）,使得该改性隔膜的润湿性和热稳定性有所增加。将其应用于锂硫电池时,导电PANI能提供更多的反应位点,有效缓解聚硫化物的穿梭效应,提高电池的循环性能和倍率性能。在0.2 C下其首次放电容量达925.4 mAh g^-1,循环100圈后剩余429.9 mAh g^-1。（4）利用多巴胺（PD）共聚沉积聚乙烯亚胺（PEI）至PP隔膜表面,从而制备PD和PEI共聚改性的隔膜。研究发现:改性隔膜表面的极性官能团（羟基和氨基）能降低隔膜的表面能,增加隔膜对电解液的润湿性。将改性隔膜应用于锂硫电池发现,改性隔膜上的阳离子聚合物PEI,能通过静电作用力将聚硫化物束缚,有效缓解穿梭效应,提升锂硫电池的电化学性能。在0.2 C下A1P3的循环性能最佳,首次放电容量达1033.4 mAh g^-1,循环200圈后为411.1 mAh g^-1。更多还原

【Abstract】 The polypropylene separator（PP）is one of the important component in lithium-ion batteries,which can transfer lithium-ion,separate the cathode and anode,and avoid short circuit.But the PP separator shows strong hydrophobic nature owing to its high surface energy.It is not only unfavorable to absorb the electrolyte,but also not conducive to maintain the electrolyte.Moreover,the micropores on the PP separator will be closed when temperature rises to 165 ℃.Many researches focus on how to enhance the hydrophilia and thermostability of the PP separator.When the PP separator is assembled to the Li-S batteries,there is a new problem called shuttle effect.So it becomes difficult to modify the separator and alleviate the shuttle effect.To deal with these problems,we have done some researches on modification of the PP separator in this paper.When the modified PP separators are applied to Li-S batteries,the electrochemical performance are improved.（1）The PP separator coated with Al₂O₃ and CNT has been successfully prepared（CAF）.The thermal stability and the wettability of the modified separator are obviously improved due to the inorganic Al₂O₃ and porous structure of the coating layer.The coating could alleviate the shuttle effect by steric effect and chemical interaction between Al₂O₃ and polysulfides.What’s more,the CNT coating layer acts as the second electrode,provides more reaction points and improves the utilization of active material due to the superior conductivity.The discharge capacity and the rate capacity of Li-S batteries assembled with CAF separator are greatly improved.The first discharge capacity is 1096 mAh g^-1,and the dstill remains 760.4 mAh g^-1 at 0.2 C after 200 cycles.（2）The hydrophobic groups of surfactant（Tween,Triton X and PEG）are strongly attached to the surface of the PP separator.It may be because the hydrophilic groups react with hydroxyl of the cross-linked silica networks.So the SiO₂ nanoparticles are decorated on the PP separator tightly with assistance of surfactant.The thermal stability and wettability of the modified separator are also improved.The first discharge capacity of the battery using the modified separator is 937 mAh g^-1.And the specific capacity still performs 603.5 mAh g^-1 with the decay rate of only 0.05% per cycle at 0.2 C after 200 cycles.（3）The polyaniline decorated PP separator has been successfully prepared by the polymerization and deposition of aniline.The wettability and the thermal stability of the modified separator are obviously improved owing to the inorganic polyaniline layer and its loose structure.The electrochemical performance of the Li-S battery with the modified separator is also improved.It is ascribed to that the polyaniline layer with conductivity could provide more reaction points and alleviate the shuttle effect.The first discharge capacity is 925.4 mAh g^-1,and remains 429.9 mAh g^-1 at 0.2 C after 200 cycles.（4）The modified separator is prepared by the copolymerization and deposition of dopamine（PD）and poly（ethylene imine）（PEI）.The surface of the modified separator contains many polar functional groups（-COOH and-NH2）,which reduce the surface energy and improve the wettability of the separator.Moreover,the electrostatic interactions between PEI and polysulfides could alleviate the shuttle effect and enhance the electrochemical performance of the Li-S battery.The first discharge capacity of the Li-S batteries with the modified separator is 1033.4 mAh g^-1,and remains 411.1 mAh g^-1 at 0.2 C after 200 cycles.更多还原