Lychee seed-derived microporous carbon for high-performance sodium-sulfur batteries

Sodium-sulfur (Na–S) batteries are regarded as one of the promising next-generation energy storage systems; while being more cost-effective than lithium-sulfur batteries, Na–S batteries also suffer from the shuttle effect. Different strategies to tackle the long-chain polysulfide product shuttling issue have been proposed, mainly focusing on sulfur product confinement with costly materials and complex methods. Seeking high-performance and low-cost electrode material precursors is of great importance to promoting Na–S battery applications. We present a high specific surface area microporous carbon framework synthesized from degradable biowaste, namely lychee seeds, with a facile room-temperature etching process. Unlike the traditional dissolution-precipitation mechanism, a quasi-solid-state route takes place with the help of micropore (0.48 nm) confinement, preventing the formation of long-chain polysulfides for excellent electrochemical performance. The obtained Na–S battery exhibits an outstanding initial reversible discharge specific capacity of 1395 mAh g−1 at 0.2C and still maintains a high capacity of 518 mAh g−1 after 500 cycles at 1.0C. The lychee seed-derived microporous carbon provides insights into sustainable and scalable host fabrication for high-performance sulfur-based batteries.