Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage
Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage
复制标题
DOI：
10.1002/adma.201304962
复制
发表时间：
2014-05-01
影响因子：
29.4
通讯作者：
Liu, Jun
中科院分区：
文献类型：
--
作者：
Ji, Liwen;Gu, Meng;Liu, Jun
钠（Na）离子电池（NIB）作为锂离子电池（LIB）的替代品最近引起了广泛关注，[1]特别是用于大规模储能应用。[1a B，h]已经做出了显著的努力来改善阴极和阳极两者的Na离子储存性质。对于阴极，各种氧化物化合物[2]和聚阴离子化合物[1c，d，f，h，3]已被深入研究。对于阳极，研究了硬碳、[1 e]有机材料[4]和Na离子插层化合物。[1c最近，各种过渡金属及其合金，如锡（Sn）、[6]锑（Sb）、[7]锗（Ge）、[5a]和SnSb合金[8]也被研究作为可再充电NIB的阳极。然而，对于这些阳极材料，由于大的体积膨胀和收缩[7a，8a]，在电化学循环期间严重的结构退化导致电极内电接触的减少或损失，然后导致相当大的性能衰减。[7a为了克服与这种机械降解相关的不利影响，已经提出了由碳基质支撑的纳米结构颗粒的复合材料。[6b即使如此，Na离子插入/脱嵌的高可逆容量和延长的循环稳定性仍然难以实现。[6b可再充电电池的电化学性质在很大程度上取决于电极材料的结构以及电解质与电极之间的界面反应，特别是在电极表面上形成的固体电解质界面（SEI）层。[3b在LIB中，已经发现石墨和Si阳极上的SEI层可以显著影响循环稳定性和倍率性能。[10]进一步的研究表明，由于电解质的分解以及电解质与电极之间的反应，SEI膜中含有多种产物，如LiOCH 3、R-CH 2 OCO 2 Li和R-CH 2 OLi。[10]发现一些添加剂如氟代碳酸亚乙酯（FEC）在操纵SEI形成中起关键作用，这导致改善的钝化和抑制电解质中的副反应，从而改善电极和电池的整体电化学性质。[10]由于Na和Na +-插层阳极材料的高化学反应性，SEI膜对于NIB甚至更关键。[5e然而，对于用于Na+存储材料的SEI层的形成，存在有限的基本探索。[1e在本文中，我们研究了多孔碳纳米管（CNF）支撑的SnSb纳米复合材料作为可充电NIB的阳极，使用静电纺丝和随后的热处理工艺。[13]研究了在电解液中添加和不添加FEC添加剂的电极的SEI形成及其与电化学性能的相关性。在不含FEC的电解液中，该多孔CNF-SnSb基NIB体系的电解液分解严重。电解质分解导致形成各种富氧产物，如碳酸钠、烷基碳酸钠、醇钠和聚碳酸钠。FEC的存在可以使电解质的还原分解最小化，改变循环的电极表面钝化层的形态/结构变化和化学组成，并最终导致形成薄的、化学/机械稳定的和结构致密的SEI膜。这种稳定的SEI膜稳定了电极，改善了Na离子的迁移动力学，并实现了高可逆容量（约350 mAh g− 1），优异的容量保持率为99.4%，
Sodium (Na)-ion batteries (NIBs) have recently attracted wide attention as an alternative to Li-ion batteries (LIBs),[1] in particular for large-scale energy storage applications.[1a, b, h] Significant efforts have been made to improve the Na-ion storage properties of both cathodes and anodes. For the cathodes, various kinds of oxide compounds [2] and polyanion compounds [1c, d, f, h, 3] have been intensively investigated. For the anodes, hard carbon,[1e] organic materials,[4] and Na ion intercalation compounds have been investigated.[1c, d, f, 5] Recently, a variety of transition metals and their alloys, such as tin (Sn),[6] antimony (Sb),[7] germanium (Ge),[5a] and SnSb alloys,[8] have also been studied as anodes for rechargeable NIBs. However, for these anode materials, severe structural degradation during electrochemical cycling due to large volume expansion and contraction [7a, 8a] leads to reduction or loss of electric contact within the electrodes and then considerable performance fading.[7a, 8a] To overcome the adverse effects associated with such mechanical degradation, composites of nanostructured particles supported by carbon matrices have been proposed.[6b, c, 7a, 8b] Even so, high reversible capacity and prolonged cycling stability for Na-ion insertion/de-insertion are still difficult to achieve.[6b, 8b] The electrochemical properties of rechargeable batteries depend greatly on the architecture of electrode materials and the interfacial reactions between electrolyte and electrodes, in particular the solid electrolyte interphase (SEI) layers formed on the electrode surfaces.[3b, 5e, 9] In LIBs, it has been found that the SEI layers on graphite and Si anodes could significantly influence the cycling stability and rate capability.[10] Further investigation indicates that the SEI films contain a wide range of products, such as LiOCH 3, R–CH 2OCO 2Li and R–CH 2OLi, due to the decomposition of electrolyte and the reactions between electrolyte and the electrode.[10] Some additives such as fluoroethylene carbonate (FEC) are found to play a critical role in manipulating the SEI formation which leads to the improved passivation and the suppression of side reactions in electrolytes and thus improves the overall electrochemical properties of the electrodes and the batteries.[10] The SEI film is even more critical for NIBs due to the high chemical reactivity of Na and theNa+-intercalated anode materials.[5e, 7b, 11] However, there have been limited fundamental explorations on the formation of the SEI layer for Na+ storage materials.[1e, 7a, 12] In this paper, we studied porous carbon nanofiber (CNF)-supported SnSb nanocomposites as anodes for rechargeable NIBs using electrospinning and a subsequent thermal treatment processes.[13] The SEI formation and its correlation with the electrochemical properties of the electrode with and without FEC additive in the electrolytes were investigated. In the FEC-free electrolyte, the electrolyte decomposition is serious in this porous CNF-SnSb-based NIB systems. The electrolyte decomposition leads to the formation of various kinds of oxygenrich products, such as Na carbonate, Na alkyl carbonates, Na alkoxide and Na polycarbonates. The presence of FEC can minimize the reductive decomposition of the electrolyte, modify the morphological/structural change and chemical composition of the cycled electrode surface passivation layer, and finally lead to the formation of a thin, chemically/mechanically stable and structurally compact SEI film. This stable SEI film stabilizes the electrodes, improves the migration kinetics of Na ions, and enables a high reversible capacity (∼ 350 mAh g− 1), excellent capacity retention of 99.4% for …