Rationally Design a Sulfur Cathode with Solid‐Phase Conversion Mechanism for High Cycle‐Stable Li–S Batteries

Abstract

Solid–solid reactions are very effective for solving the main challenges of lithium–sulfur (Li–S) batteries, such as the shuttle effect of polysulfides and the high dependence of electrolyte consumption. However, the low sulfur content and sluggish redox kinetics of such cathodes dramatically limit the practical energy density of Li–S batteries. Here a rationally designed hierarchical cathode to simultaneously solve above‐mentioned challenges is reported. With nanoscale sulfur as the core, selenium‐doped sulfurized polyacrylonitrile (PAN/S7Se) as the shell and micron‐scale secondary particle morphology, the proposed cathode realizes excellent solid–solid reaction kinetics in a commercial carbonate electrolyte under high active species loading and a relatively low electrolyte/sulfur ratio. Such an approach provides a promising solution toward practical lithium sulfur batteries.

Progress and Perspectives of Organosulfur for Lithium–Sulfur Batteries

“…Though many models have been proposed to explain the electrochemical properties of SPAN from different aspects, many of them are debatable. [58,59] In some reports, the bonds between the terminal S atoms and carbon atoms break and reform during the charge and discharge process while others not. And the formation of N-S bonds is only reported by some recent articles.…”

“…A specific capacity of 430 mA h g −1 could be achieved based on the total mass of both Li anode and S@ pPAN cathode. He et al [68] designed and synthesized a novel S@PAN/S 7 Se composite as the cathode material. The sulfur particles were wrapped by Se-doped sulfurized poly acrylonitrile (PAN/S 7 Se), which acted as an in situ block layer so that electrolyte could not penetrate.…”

Synergistic improvement of the overall performance of lithium-sulfur batteries

“…(b) Rate performance of the Se 0.06 SPAN measured at various current densities in ether-based electrolyte and carbonatebased electrolyte [79] . Schematic of the S@PAN/S 7 Se cathode: (c) 3D view and (d) simplified 2D cross-section view of the hieratical structured composite cathode before and after electrochemical cycling [78] . (e) Rate capability of S@PAN/S 7 Se electrode at different current densities [78] .…”

“…Schematic of the S@PAN/S 7 Se cathode: (c) 3D view and (d) simplified 2D cross-section view of the hieratical structured composite cathode before and after electrochemical cycling [78] . (e) Rate capability of S@PAN/S 7 Se electrode at different current densities [78] . (f) Cycling performances of the S@PAN/S 7 Se cathode at 60°C [78] 此外，采用 S 的同族元素 Te 作为共熔添加剂，还成功将准固的反应机制由锂硫 电池体系拓展到钠离子电池中，并取得了很好的效果 [80,81] 。硒掺杂反应原理以及电化 学性能如图 4 所示。 1.1.3 稳定正极电解质界面的构筑 除了以上微孔限域和结构设计的策略，我们还通过界面改性使电池在首周放电时 形成了正极电解质界面 CEI，从而实现了"固-固"反应。这种机制因为消除了 LiPSs 的 生成，理论上可以降低电解液的用量。 索鎏敏等人 [58] 设计了一种高盐浓度电解液，通过电解液组分的调控降低了电解液 的用量。由于电解液中游离的自由溶剂分子极少，锂盐将优先于溶剂分子发生反应， 在电极表面形成致密稳定的 CEI，从而抑制了 LiPSs 的溶解穿梭，提升了电池的循环稳 定性。 本课题组 [82] 通过调控电解液组分，设计了一种由双三氟甲磺酰亚胺锂(LiTFSI: SEI 从而实现"固-固"机制的示意图 [82] 。(b) CMK-3/S@SEI 正极的循环性能和库仑效率 图 [82] 。CMK-3/S 正极在醚类(c1)和 HFE 基电解液(c2)中经过化成反应后的透射电子显 微镜(TEM)图像 [83] 。(d) 不同电解质的燃烧实验 [83] 。(e) 经过化成反应后的 CMK-3/S 正 极在 0.5 C 时的循环性能和库仑效率图 [83] Figure 5 Solid-solid conversion realized by constructing stable CEI.…”

“…(c) A scheme of the S 8 /mesoC-S 2-4 /microC core-shell structure and the proposed (de)lithiation process inside the MMCS carbon structure [74] . (d) A typical discharge profile and the corresponding A c c e p t e d https://engine.scichina.com/doi/10.1360/TB-2021-1123 electrochemical reactions of the S/MMCS electrode [74] 1.1.2 结构设计 正极材料的选择和结构的设计优化对锂硫电池的性能提升有显著作用，近年来， 人们在构筑复合正极材料方面做了许多工作，旨在实现电子传导能力强、导电剂与活 性物质硫高效接触、具有良好的 LiPSs 捕获能力和稳固电极结构的新型复合正极。 通过构筑"固-固"反应硫正极材料，有效避免了可溶性 LiPSs 的形成。王久林等人 [75] 于 2002 年设计了硫化聚丙烯腈(S@pPAN)新型正极材料，该正极材料在放电过程中 不会产生长链的 LiPSs，有效抑制了穿梭效应，但该材料较低的硫含量(＜50%)限制了 电池的能量密度 [76,77] 。为了提高硫化聚丙烯腈 S@pPAN 体系中较低的硫含量(＜50%)， 本课题组 [78] 具有醚相容性和优越的性能 [79] 。(b) 硒掺杂后的电化学性能：Se 0.06 SPAN 在醚类和酯类 电解液中不同电流密度下的倍率性能 [79] 。电化学循环前后 S@PAN/S 7 Se 结构的(c)三维 示意图和 d)简化的二维横截面示意图 [78] 。(e) S@PAN/S 7 Se 正极在不同电流密度下的倍 率性能图 [78] 。(f) S@PAN/S 7 Se 正极在 60 ℃下的电化学循环性能图 [78] Figure 4 Reaction process principle and electrochemical performance of Se-doping S@pPAN.…”