Design of atomic cobalt selenide-doped sulfurized polyacrylonitrile cathode with enhanced electrochemical kinetics for high performance lithium-SPAN batteries

• A cobalt selenide doped sulfide polyacrylonitrile (CoSe 2 @SPAN) is designed as a cathode for Li-SPAN batteries. • Matched-degree of HOMO level of the nucleophilic reagent S 2– and LUMO level of the electrophilic reagent Li + is significantly improved. • The narrowed energy gap between LUMO and HOMO of CoSe 2 -10@SPAN contributes to the fast reaction kinetics. • Larger Gibbs free energy variation before and after lithiation process promotes the electrochemical reaction . In this work, sulfurized polyacrylonitrile (SPAN) cathodes with atomically dispersed Co and Se active site, namely cobalt selenide doped-sulfide polyacrylonitrile (CoSe 2 - x @SPAN, x = 6, 10, 15) with different CoSe 2 doping concentrations of 6, 10, and 15 wt%, were fabricated by co-heating approach to strengthen the charge conductivity and catalytic activity of SPAN cathode. Atomic scale CoSe 2 were doped into the SPAN skeleton to expediating the redox kinetics of lithium storage process, and the catalytic mechanism was made clear by a viewing angle of frontier molecular orbital theory. The DFT calculation results show that CoSe 2 @SPAN has a more uniform electrostatic potential distribution with a smaller LUMO-HOMO band gap, which is more conducive to electron transport. The Co/Se loaded SPAN polymer constructed by N-Co-S chemical coordination improves the matching degree between the highest occupied molecular orbital (HOMO) of the nucleophile S 2− and the lowest unoccupied molecular orbital (LUMO) of the electrophile Li + during the discharge process, and effectively reduces the bonding orbital σ level of the deposited product Li 2 S, thereby promoting the lithium storage kinetics of CoSe 2 @SPAN cathode material and avoiding the shuttle effect. Meanwhile, the larger Gibbs free energy variation during the lithiation process indicates the enhanced reaction kinetics of the CoSe 2 @SPAN cathode. Ultimately, The Li-SPAN battery with CoSe 2 -10@SPAN cathode delivers high reversible capacity of 1475 mAh g −1 at 0.2 A/g, superior rate capability and long-term capacity retention of 71.1% after 500 cycles at 1.0 A/g. Accordingly, this study offers insights into the utilization of frontier molecular orbital theory (FMO) to improve the redox kinetics and sulfur utilization of Li-SPAN batteries.