Synergetic effects of Fe-N-C and LiFePO4 in modified separator on improved adsorption and catalytic conversion reaction of soluble LiPSs for Lithium-sulfur batteries

"Shuttle effect" is a serious obstacle in the development of high-performance lithium-sulfur batteries and modified separator is considered an effective strategy to prevent the shuttle effect of soluble polysulfides (LiPSs). Herein, we demonstrate a modified polypropylene (PP) separator composed of nitrogen-doped carbon coated LiFePO4 (NC-LFP), Ketjen black carbon (KB) and polyvinylidene fluoride (PVDF) (NC-LFP interlayer), which can improve adsorption and catalytic conversion toward LiPSs. The analysis shows that NC-LFP interlayer could effectively adsorb LiPSs and therefore suppress its shuttle effects due to the Fe-N-C functional groups in the nitrogen-doped carbon coated on LFP polar particles. The DFT analysis and the electrochemical performance test demonstrate the Fe-N-C functional groups in NC-LFP interlayer provide lower activation barrier for catalytic conversion reaction of LiPSs to Li2S and vice versa. The coin cells with NC-LFP modified separator exhibit an initial discharge specific capacity of 907 mAh/g at 1C. After 500 cycles, the specific capacity is 702 mAh/g with a retention rate of 79.5 %. Moreover, at 8C rate, the discharge-specific capacity of 667.5 mAh/g is achieved. The use of NC-LFP interlayer modified separators realizes lithium-sulfur batteries with long-cycle life and high-rate performance, providing an emerging strategy for high-performance Li-S batteries.