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Efficient and low-cost anode materials for the sodium-ion battery are highly desired to enable more economic energy storage. Effects on an ultrathin carbon nitride film deposited on a copper metal electrode are presented. The combination of effects show an unusually high capacity to store sodium metal. The g-C3N4 film is as thin as 10 nm and can be fabricated by an efficient, facile, and general chemical-vapor deposition method. A high reversible capacity of formally up to 51 Ah g(-1) indicates that the Na is not only stored in the carbon nitride as such, but that carbon nitride activates also the metal for reversible Na-deposition, while forming at the same time an solid electrolyte interface layer avoiding direct contact of the metallic phase with the liquid electrolyte.
Despite intensive research on porous carbon materials as hosts for sulfur in lithium-sulfur battery cathodes, it remains a problem to restrain the soluble lithium polysulfide intermediates for a long-term cycling stability without the use of metallic or metal-containing species. Here, we report the synthesis of nitrogen-doped carbon materials with hierarchical pore architecture and a core-shell-type particle design including an ordered mesoporous carbon core and a polar microporous carbon shell. The initial discharge capacity with a sulfur loading up to 72 wt% reaches over 900 mA h g(sulf)(ur)(-1) at a rate of C/2. Cycling performance measured at C/2 indicates similar to 90% capacity retention over 250 cycles. In comparison to other carbon hosts, this architecture not only provides sufficient space for a high sulfur loading induced by the high-pore-volume particle core, but also enables a dual effect of physical and chemical confinement of the polysulfides to stabilize the cycle life by adsorbing the soluble intermediates in the polar microporous shell. This work elucidates a design principle for carbonaceous hosts that is capable to provide simultaneous physical-chemical confinement. This is necessary to overcome the shuttle effect towards stable lithium-sulfur battery cathodes, in the absence of additional membranes or inactive metal-based anchoring materials.