Effective Carbon Pores to Improve the Electrochemical Performance of Phosphorus as an Anode for Sodium Ion Batteries

We propose here that carbon pores provide key reaction sites for stable electrochemical reactions in phosphorus sodium ion batteries (SIBs). Phosphorus showing a high theoretical capacity (2596 mA h/g) due to a three-electron reaction with sodium ions is a remarkable negative material for SIBs. However, both low electrical conductivity of phosphorus and the capacity fading due to a large volume change during the charge–discharge process lead to a low reaction efficiency. The phosphorus introduced into relatively large mesoporous or macroporous carbons showed a high capacity of 2445 mA h/g at the first charge process, whereas capacities are no more than 1100 mA h/g in microporous or small mesoporous carbons in which the cyclability is also poor. This result clearly indicates that the carbon pores with a pore size close to or above 50 nm are effective reaction spaces for stabilization of the alloying–dealloying reaction of phosphorus with sodium ions.