基于联吡啶共价有机框架材料纳米片的插层结构设计及其在锂硫电池中的应用

Interlayer Structure Design Based on Bipyridine Covalent Organic Framework Nanosheets and Its Application in Lithium-Sulfur Batteries

摘要:

以单质硫为正极材料的锂硫电池（LSBs），因其高的理论比容量和能量密度，在储能领域中受到广泛地关注。然而，LSBs在充放电过程中会产生可溶性多硫化物（LiPSs），LiPSs在电极之间的穿梭效应会导致电池容量快速衰减，从而阻碍LSBs的实际应用。为了有效地抑制LiPSs在LSBs中的穿梭效应，设计合成了一种基于联吡啶共价有机框架（COFs）材料的纳米片（Tp-Bpy），并将其用作LSBs的多功能插层。Tp-Bpy纳米片得益于联吡啶中均匀分散的氮位点的强吸附和催化活性，以及其纳米结构可提供更多活性位点等特性，能够很好地吸附LiPSs，并对LiPSs进行催化转化，从而抑制LiPSs的穿梭效应。Tp-Bpy纳米片插层在LiPSs氧化还原反应过程中具有更快的转化动力学，以及降低液固转化过程的电化学极化特性。相较于未修饰的传统聚丙烯（PP）隔膜，Tp-Bpy纳米片插层所组装的LSBs倍率性能和循环稳定性得到明显提升。实验结果表明，以Tp-Bpy纳米片插层所组装的LSBs，在0.1 C下的放电初始容量可达1 223 mAh?g^-1，在1 C下循环500次后的放电比容量仍有452 mAh?g^-1，单圈衰减率低至0.093%。Tp-Bpy纳米片插层材料已成为解决LSBs中LiPSs穿梭效应的主要研究方向之一，本研究为开发新的多功能插层提供了理论支撑。

Abstract:

Lithium-sulfur batteries （LSBs） with elemental sulfur as cathode have received extensive attention in the field of energy storage due to their high theoretical specific capacity and energy density. However， the shuttle effect of soluble lithium polysulfides （LiPSs） during charge and discharge will lead to rapid capacity decay， which impedes the practical application of LSBs. In order to effectively inhibit the shuttle effect of LiPSs in LSBs ， a bipyridine COF nanosheet （Tp-Bpy） was designed and used as a multifunctional interlayer for LSBs in this study. Benefiting from the strong adsorption and catalytic activity of the uniformly dispersed nitrogen sites in bipyridine linkers， as well as the nanosheet structure can provide more active sites. LiPSs can be well adsorbed and catalyzed by Tp-Bpy nanosheets， thus inhibiting its shuttle effect. Tp-Bpy nanosheet interlayer has faster transformation kinetics during LiPSs redox reaction， and reduces electrochemical polarization during liquid-solid transformation. Compared with the unmodified traditional polypropylene （PP） separator， the rate performance and cycle stability of the LSBs assembled with Tp-Bpy nanosheet interlayers have been significantly improved. Experiments have shown that the LSBs assembled with Tp-Bpy nanosheet interlayers exhibited an initial discharge capacity of 1 223 mAh?g^-1 at 0.1 C. In addition， the specific capacity was maintained at 452 mAh?g^-1 at 1 C after 500 cycles with a decay rate of 0.093% per cycle. Tp-Bpy nanosheets interlayers have emerged as a prominent research avenue in combating the shuttle effect of LiPSs in LSBs. This study contributes valuable theoretical underpinnings to the advancement of novel multifunctional interlayer.