Effective incorporation of nitrogen and boron in worm-like carbon foam for confining polysulfides

Flexible electrode materials toward rational design and low-cost fabrication are crucial to energy storage applications. Herein, a three-dimensional (3D) flexible N, B co-doped carbon foam (NBC) is developed, enabling efficient polysulfides confinement. N, B co-doping is employed to overcome the conflict between heteroatom doping and stability of carbon lattice, because one B and one N atoms are isoelectronic to two C atoms. B atoms in such a carbon structure possess positive charge which can interact with S_n²⁻ anions in forming S_n^{2− …} B while N atoms form negative charge which construct a strong-couple interaction with Li⁺ cations in forming N⋯Li₂S_n. Moreover, the fabrication approach of corresponding flexible 3D carbon form is extremely facile derived from the self-gelation of agar. When used as the host for S, such a 3D carbon foam provides a continuous conductive structure, accommodates the volume change during long-term cycling and serves as a barrier for polysulfides dissolution. As a result, cycling performance of high sulfur loading (5.8 mg cm⁻²) NBC-S electrode exhibits high areal capacity of 5.6 mA h cm⁻² (965 mA h g⁻¹) with a very small capacity decay of 0.03% per cycle over 350 cycles at 0.2 C. © 2019 Elsevier Ltd