Carbon Nitride Phosphorus as an Effective Lithium Polysulfide Adsorbent for Lithium–Sulfur Batteries

Abstract

Lithium–sulfur (Li–S) batteries are attracting substantial attention because of their high-energy densities and potential applications in portable electronics. However, an intrinsic property of Li–S systems, that is, the solubility of lithium polysulfides (LiPSs), hinders the commercialization of Li–S batteries. Herein, a new material, that is, carbon nitride phosphorus (CNP), is designed and synthesized as a superior LiPS adsorbent to overcome the issues of Li–S batteries. Both the experimental results and the density functional theory (DFT) calculations confirm that CNP possesses the highest binding energy with LiPS at a P concentration of ∼22% (CNP22). The DFT calculations explain the simultaneous existence of Li–N bonding and P–S coordination in the sulfur cathode when CNP22 interacts with LiPS. By introducing CNP22 into the Li–S systems, a sufficient charging capacity at a low cutoff voltage, that is, 2.45 V, is effectively implemented, to minimize the side reactions, and therefore, to prolong the cycling life of Li–S systems. After 700 cycles, a Li–S cell with CNP22 gives a high discharge capacity of 850 mA h g–1 and a cycling stability with a decay rate of 0.041% cycle–1. The incorporation of CNP22 can achieve high performance in Li–S batteries without concerns regarding the LiPS shuttling phenomenon.