The structural stability and capacity increase of a phosphorus-doped hard carbon produced by zinc oxide templating used in sodium-ion batteries:

Abstract

Sodium (Na)-ion batteries (NIBs) are attracting increasing attention as next-generation energy storage systems because they do not rely on rare metals. Hard carbon (HC) is considered their most promising anode material. By tailoring the pore structure by templating methods, HC materials with a high energy density have been developed for NIBs. However, further improvements are required to achieve the desired properties without compromising the excellent characteristics already achieved. This study aims to further increase the battery capacity of zinc oxide (ZnO)–templated HC using a simple phosphorus (P)-doping method. We investigated the effects of soaking in phosphoric acid and subsequent heat treatment on the carbon morphology and electrochemical properties. The results showed that P doping increased the battery capacity without altering the ZnO–templated HC morphology. Both the sloping and plateau regions of the capacity increased, suggesting that P doping promotes Na adsorption on the carbon surface and Na storage between the layers and in the pores. Furthermore, the types of P functional groups depended on the synthesis conditions and influence the battery performance. These findings show that surface modification with specific P functional groups can effectively increase the Na storage capability of HCs.