The notorious “shuttle effect” of lithium polysulfides (LiPSs) has suppressed the large‐scale commercial application of lithium‐sulfur batteries (LSBs). Also, the intrinsic advantages including inhibiting the shuttling‐circulation and promoting the conversion of LiPSs, on the separator are deemed as stimulating blocks on the exploitation of LSBs. Herein, guided by theoretical calculations, we have designed doping‐heteroatoms boron (B) and phosphorus (P) on graphitic carbon nitride (g‐C3N4), to suppress the “shuttle effect” of LiPSs and improve the battery cycling performance. Theoretical calculations show strong chemical bonding between Li atom and N substance of g‐C3N4, and corroborates synergistic mechanism of electron transfer and van der Waals interaction. The high adsorption energies with doping B/P atoms enable LiPSs adsorption on the separators inhibiting shuttle loss. As expected, the experiment data also demonstrate that superior electrochemical performance are achieved by utilizing B‐doped g‐C3N4 (BCN) separator. Incorporating the B‐doped g–C3N4 (BCN) separator in LSBs delivered an initial specific capacity of 1050 mAh g−1 at 1 C and 920 mAh g−1 at 2 C. Notably, it achieved a decay rate of 0.08% and 0.1% at 1 and 2 C, respectively, after 500 cycles. This study furthers our understanding of B/P doping separator enhancement and restraining LiPSs shuttling loss for an improved LSBs performance.

It is a concern that cells with lithium (Li) metal anodes and LiNi0.8Co0.1Mn0.1O2 (NCM 811) cathodes exhibit high energy density. However, the chemical and electrochemical properties of an original solid electrolyte interphase (SEI) film formed by the Li metal reaction are unstable, resulting in uneven plating and rapid growth of Li dendrites. Due to the high nickel content of NCM 811, Ni4+ dissolved at the electrode interface leads to side reactions and irreversible rock salt structure, forming an unstable cathodic electrolyte interphase (CEI) film. Ion liquid (IL) electrolytes provide a strategy for forming stable SEI/CEI and keeping NCM 811 structural stability, but their high viscosity has limited their electrochemical performance. Functionalize pyrrolidine with ether and cyano groups is introduced, the high flexibility of the ether group can reduce the viscosity of the IL-based electrolyte, and the oxygen atom can provide Li+ coordination sites to accelerate Li+ transport. The strong electron absorption ability of the cyano group shows the strong coordination ability with transition metal ions to inhibit the erosion of CEI by side reactions. Under the dual function of cyano and ether groups, more TFSI− participate in the formation of the SEI film, which leads to the increase in beneficial components with high ionic conductivity, further inhibiting dendrite growth and promoting uniform plating. Thus, LiǁLi cells, with 0.5 wt. % 1-cyanopropyl-1-diethyl ether pyrrolidine bisfluoromethanesulfonimide salt [PYR1(4CN)(2O2)TFSI], revealed excellent plating voltage stability for more than 450 h. After 200 cycles, the discharge specific capacity of LiǁNCM 811 cells was 123 mAh g−1 and an excellent capacity retention of 62.1% at 1 C. This work shows a strategy of improving SEI/CEI from the electrolyte with cyano and ether groups and provides a feasible horizon in the long-term cycle performance of lithium metal batteries.