锂离子电池三维中空锡合金/高分子膜核壳纳米线阵列电极的构建和稳定化研究

Three-dimensional (3D) Sn alloy nanowire array is of great significance for the development of high-capacity and high-power lithium-ion battery. However, the application is limited by the poor stability of 3D nanostructure and large volume change caused by the alloying process of Sn and Li. Accordingly, in the present research, polymer nanomembrance/hollow Sn alloy nanowrie core-shell nanostructure array is developed to improve the stability. Hollow nanostructure and polymer are used to relieve the volume change during the charging and discharging process, and polymer nanomembrance can be also used to prevent the deformation caused by the interconnection among nanowries. The effects of the composition, structure and modulus of the polymer nanomembrance/hollow Sn alloy nanowrie core-shell array materials on the volume change, stability and electrochemical performance are studied, and the mechanism is explored. Based on this, the composite electrode of the hollow Sn nanowrie/polymer electrolyte membrane core-shell nanostructure array is proposed to consult the stable interface between the anode and electrolyte. The interface compatility between polymer electrolyte and metal nanowires electrode interface and a series of complex processes such as mass transfer, surface reaction and charge tranfer are further studied. Based on this, the ion transport mechanism of electrolyte is proposed.

三维锡基纳米线阵列电极对发展高容量和大功率锂离子电池有重要的价值，但三维结构稳定性差和锡锂合金化过程中体积膨胀造成的充放电循环寿命低限制了其应用。本项目从三维锡基纳米线阵列负极的稳定化出发，设计了高分子纳米膜包覆的中空锡合金纳米线核壳结构，利用中空结构和高分子壳的柔性，缓解锡在充放电过程中体积变化，同时利用高分子膜阻止三维纳米线阵列电极由于形变导致的破坏。揭示中空锡合金/高分子膜三维核壳结构纳米线阵列负极组成、结构，核和壳材料的模量与充放电过程中电极体积变化、稳定性以及电化学性能之间的内在关系，探讨其作用机制。在此基础上，构建高分子电解质膜与三维锡纳米线阵列一体化相结合的复合电极，以构筑稳定的电极与电解质界面，进一步探讨高分子电解质与金属纳米线电极界面相容性，传质以及电荷传递等一系列复杂过程，揭示电解质膜的离子传输机理。

针对新型锡基锂离子电池负极嵌脱锂过程中体积膨胀造成结构破坏，SEI膜不稳定，容量快速衰减等问题，本项目从解决三维锡基纳米线阵列负极的稳定性这一科学问题出发，构建了高分子纳米薄膜包覆的三维中空锡合金纳米管阵列核壳电极。首先，利用电流置换法得到中空Sn-Cu、Sn-Ni、Sn-Co纳米颗粒和纳米线，并分别用聚吡咯、聚苯胺及导电聚合物凝胶、聚环氧乙烷固体电解质等包覆。结果表明，中空Sn-Cu颗粒100次循环后，比容量能维持在650 mAhg-1，另两种中空纳米颗粒也保持在600 mAhg-1，而且聚合物包覆后的中空锡合金纳米材料循环性能更加稳定，而锡纳米颗粒循环50次后，比容量仅为63 mAhg-1。研究证实了利用中空结构和高分子纳米膜能有效缓解锡负极充放电过程中体积膨胀对结构的破坏，改善电子传输和界面稳定性，从而提高新型锡负极的循环稳定性。在此基础上构建了高分子纳米薄膜包覆的三维纳米管阵列电极，PEO包覆Sn-Ni纳米管阵列负极在200次循环后比容量仍然高达625 mAhg-1。三维阵列结构提高了电极与集流体之间的电子传输速度和倍率性能。通过研究获得了三维阵列结构电极高分子的包覆技术并较好地解决了避免锡阵列负极从集流体上脱落的难题。研究发现，锡负极循环稳定性改善机理是中空结构为锡负极体积膨胀提供了自由空间，避免了因局部应力集中造成电极结构的破坏，合金相有效减低锡颗粒嵌脱锂时发生团聚和粉化；高分子纳米薄膜抑制电极纳米结构的破坏，结合模拟结果证明高分子包覆层对纳米管的局部应力有很好的分散作用，并且防止了SEI膜的持续增厚，改善了负极与电解液间的界面稳定性，极大地提高了锡基负极的循环稳定性和倍率性能。本项目这一成果不但可用于缓解锡基负极材料的体积膨胀，对同样受体积膨胀影响的金属氧化物、硅等新型大容量锂离子电池负极材料也具有理论和应用价值。近来通过类似方法改善新型负极循环稳定性在国际上得到广泛认同和采纳。本项目瞄准未来生产需求在电流置换方法基础上进一步研发了新的易于产业化、便捷的中空制备和高分子包覆工艺，制备出多壳层中空结构，既能缓解体积膨胀，又有效提高了中空负极的体积能量密度。在高分子包覆的基础上发展了导电聚合物凝胶，既有更好的包覆效果又可作为负极材料的粘合剂和导电剂，组装的全电池性能显著提高。项目进行过程中共发表SCI收录论文24篇，申请中国专利12项，已获得授权1项。