Confined phosphorus in carbon nanotube-backboned mesoporous carbon as superior anode material for sodium/potassium-ion batteries

Sodium and potassium ion batteries (SIBs and PIBs) hold promise as potential low-cost and large-scale energy storage devices due to the earth abundance of sodium and potassium. Among all proposed anode materials, red phosphorus (P) has been recognized as a promising candidate owing to its high theoretical capacities for use in both SIBs and PIBs (2596 mA h g(-1) for Na3P and 843 mA h g(-1) for KP); however, its intrinsic insulating property and large volume change during cycling lead to poor cycling and rate performance. To overcome these issues, we have designed and synthesized a carbon nanotube-backboned mesoporous carbon (TBMC) material for the impregnation of red P. The TBMC was synthesized by a synchronic growth of resorcinol-formaldehyde resin/SiO2 on carbon nanotubes, followed by carbonation of the resin and removal of the SiO2. The resulting TBMC was then infiltered with red P at elevated temperatures, forming a P@TBMC composite. In this unique composite, multi-walled carbon nanotubes facilitate the electron transfer due to the high content of sp(2) carbon, while the mesoporous carbon layers offer voids to load appropriate amounts of P but leave enough space to alleviate the huge volume change of the P upon sodiation/potassiation. Therefore, the P@TBMC composite exhibits excellent cycling performance and rate capability as the anode for both SIBs and PIBs. For example, the P@TBMC composite shows a high reversible desodiation capacity (similar to 1000 mA h g(-1) at 0.05 A g(-1)), superior rate performance (similar to 430 mA h g(-1) retained at 8 A g(-1)), and excellent cycle life (no capacity decay for 800 cycles at 2.5 A g(-1)). More impressively, the P@TBMC, as an anode of PIBs, exhibits electrochemical performance superior to all the reported anodes for PIBs, namely, delivering a reversible capacity of similar to 500 mA h g(-1) 0.05 A g(-1) and a stable capacity of 244 mA h g(-1) at 0.5 A g(-1) for 200 cycles. The design based on confining active materials into hybrid carbon nanostructures integrated with highly conductive sp(2) carbon and porous carbon is expected to shed light on the development of high-performance electrode materials for metal-ion batteries and other energy storage systems.