Synergistic protective effect of a BN-carbon separator for highly stable lithium sulfur batteries

Lithium sulfur (Li-S) batteries have drawn much attention as next-generation batteries because of their high theoretical capacity (1672 mAh g−1), environmental friendliness and low cost. However, several critical issues, which are mainly associated with the polysulfide shuttling effect, result in their poor electrochemical performance. Carbon-modified separators have been introduced to attempt to address these systemic challenges. However, this approach focused only on the suppression of dissolved polysulfides on the cathodic side without considering the further entrapment of polysulfides on the anodic side. In this study, we first designed a multifunctional trilayer membrane comprising a carbon layer and a boron nitride (BN) layer to facilitate the electrochemical performance of Li-S batteries and protect the Li anode from unexpected side reactions. When a BN-carbon separator was employed, the sulfur cathode delivered stable capacity retention over 250 cycles and an excellent specific capacity (702 mAh g−1) at a high current density (4 C). The BN-carbon separator also facilitated the uniform plating/striping of Li and, thus, suppressed the severe growth of dendritic Li on the electrode; this led to the stable operation of the Li anode with a high Coulombic efficiency and improved cycling performance. A membrane that enhances the performance of high-capacity lithium–sulfur batteries has been developed by a team in Korea and the USA. Adding sulfur to lithium-ion batteries is predicted to improve their storage capacity, but in practice the number of times a battery can be charged and discharged is limited by the formation of compounds called polysulfides, which corrode the lithium anode. Now, Ungyu Paik from Hanyang University and co-workers have shown that using a three-layer membrane made of carbon, a polymer and boron nitride can limit this problem. Unlike previous carbon-modified separators, the trilayer membrane both suppresses dissolution of polysulfides on the cathode side and protects the anode from unwanted side reactions. The separator enabled the sulfur cathode to maintain a stable capacity over 250 cycles. The BN-carbon separator was first demonstrated as a multifunctional trilayer membrane to facilitate the better electrochemical performances of Li-S batteries and protect a Li anode from unexpected side reactions. Unlike the previous approach to block the polysulfides only within the cathodic side, the concept of placing a BN interlayer on anodic side showed promising results in achieving high electrochemical performances of Li-S batteries and stable operations of lithium metal at a high current density.