Anion‐Regulated Sulfur Conversion in High‐Content Carbon Layer Confined Sulfur Cathode Maximizes Voltage and Rate Capability of K–S Batteries
Zuobei Jiang, Na Li, Lingyi Li, Feiming Tan, Junxi Huang, Shaoming Huang
Abstract
Abstract Potassium–sulfur (K–S) batteries have attracted attention in large‐scale energy storage systems. Small‐molecule/covalent sulfur (SMCS) can help to avoid the shuttle effect of polysulfide ions via solid–solid sulfur conversion. However, the content of SMCS is relatively low (≤40%), and solid–solid reactions cause sluggish kinetics and low discharge potentials. Herein, SMCS is confined in turbo carbon layers with a content of ≈74.1 wt% via a C/S co‐deposition process. In the K–S battery assembled by using as‐fabricated SMCS@C as cathode and KFSI‐EC/DEC as an electrolyte, anion‐regulated two‐plateau solid‐state S conversion chemistry and a novel high discharge potential plateau at 2.5–2.0 V with a remarkable reversible capacity of 384 mAh g −1 at 3 A g −1 after 1000 cycles are found. The SMCS@C||K full cell showed energy and power density of 72.8 Wh kg −1 and 873.2 W kg −1 , respectively, at 3 A g −1 . Mechanism studies reveal that the enlarged carbon layer space enables the diffusion of K + ‐FSI‐ ion pairs, and the coulombic attraction between them accelerates their diffusion in SMCS@C. In addition, FSI − regulates sulfur conversion in situ inside the carbon layers along a two‐plateau solid‐state reaction pathway, which lowers the free energy and weakens the S─S bond of intermediates, leading to faster and more efficient S conversion.