Dual-confinement engineering and enhanced polysulfide affinity in a porphyrin-derived hierarchical Co9S8/CNT composite for superior potassium-ion storage

The development of high-performance anode materials is crucial for advancing potassium-ion batteries (PIBs). Among various prospective anode candidates for PIBs, Co 9 S 8 -type cobalt sulfides have attracted extensive research interest benefiting from their high theoretical specific capacity and cost-effective raw material sources. However, cobalt sulfide anodes like Co 9 S 8 suffer from severe volume expansion and the polysulfide shuttle effect, which greatly limited its practical application. Herein, a hierarchical Co 9 S 8 composite integrated with carbon nanotubes (CNTs) is synthesized via the in-situ sulfurization of cobalt tetraphenylporphyrin (CoTPP) and CNTs. The resulting Co 9 S 8 /TPP/CNTs composite features a unique 3D flower-like architecture of interwoven, porphyrin-derived N, S-codoped carbon nanosheets and a conductive CNT network. This structure confines ultrafine Co 9 S 8 nanoparticles (∼10 nm), prevents nanosheet stacking, and establishes a robust conductive framework. Benefiting from dual-confinement and enhanced polysulfide affinity, the optimized electrode delivers superior potassium storage performance: a high reversible capacity of 499.6 mAh g −1 after 700 cycles at 100 mA/g, and 381.5 mAh g −1 after 5000 cycles at 1 A g −1 . It also shows remarkable rate capability (493.2 and 312.0 mAh g −1 at 50 and 2000 mA/g, respectively). Ex situ characterization and DFT calculations reveal that the structure alleviates volume strain, anchors polysulfides, and facilitates capacitive-dominated kinetics. A full cell paired with a PTCDA cathode demonstrates satisfactory cycling stability, highlighting the composite's practical potential as a high-performance anode for PIBs.