Sequential phosphorization and carbonization with modulated d-p orbital interactions in cobalt phosphides for enhanced polysulfide redox kinetics
Chenshan Lv, Zhi Zheng, Liangtao Yang, Hailiang Cao, Peng Li, Yanqin Miao, Wei Deng, Yuan Chen
Abstract
Cobalt phosphides are potential catalysts to assist the conversion of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. However, existing synthesis methods have difficulty precisely tuning their band valences, which is crucial to balancing intermediate products' adsorption and conversion abilities in Li-S batteries. Moreover, studies on the relationship between their band structures and electrochemical performance are limited. Herein, we report cobalt phosphides (Co x P) with a heterogeneous interface of CoP/Co 2 P embedded in hollow carbon nanofibers (denoted as Co x P@HCNF) via a one-step sequential phosphorization and carbonization strategy, which is applied as an effective interlayer for Li-S batteries. The Co band valence in Co x P was adjusted to regulate the d-p band gap. Theoretical calculations predict that Co x P with a narrowed d-p band center can optimize the electron transfer kinetics and the adsorption affinity with LiPSs. Li-S full cells with a Co x P@HCNF interlayer demonstrated a high specific capacity of 1265 mA h g −1 at 0.2C and excellent cycle stability of 788 mA h g −1 over 400 cycles at 2.0C. A cell with a lean electrolyte (6.0 μL mg −1 ) and a high sulfur loading (6.2 mg cm −2 ) delivered a high areal capacity of 4.5 mA h cm −2 at 0.5C. This study demonstrates that bimetallic coupling-induced electronic-state modulation effectively balances the chemical adsorption and catalytic capability for developing high-performance Li-S batteries.