Preparation of nanosized red phosphorus and its application in sodium-ion batteries

Sodium-ion batteries (SIBs) are highly desirable energy storage devices because of their low cost, high safety, and environmental compatibility. Therefore, SIBs have wide application prospects in the fields of large-scale energy storage and electric vehicles. SIBs have a similar energy storage mechanism as that of lithium-ion batteries (LIBs) and can be fabricated using existing LIB production equipment. Thus, SIBs are the most promising alternative to LIBs. However, the radius of Na⁺ is ~34% larger than that of Li⁺; therefore, many electrode materials developed for LIBs are unsuitable for SIBs. The exploration of novel electrode materials for SIBs has garnered significant interest in recent years. Among various candidate anode materials for SIBs, red phosphorus is a promising material owing to its ultrahigh theoretical specific capacity (2596 mA·h·g^–1), suitable oxidation–reduction potential (0.4 V vs Na/Na⁺), and abundance. However, the capacity utilization, long-term cycle stability, and rate performance of red phosphorous are limited due to its low intrinsic conductivity and a large volume effect upon sodium storage. At present, an effective approach for the modification of red phosphorus anodes is to prepare nanosized red phosphorus (NRP). Miniaturizing red phosphorus prevents structural damage via large volume changes during charge/discharge processes and also shortens Na⁺ transmission distances, which enables high electrochemical activity and long-term cycling stability. Herein, recent studies on NRP preparation for advanced SIBs are extensively reviewed. NRP preparation methods typically include ball milling, vaporization condensation, and chemical deposition. Other novel approaches such as thermal reduction, vapor growth, and solvothermal synthesis have also been reported. Ball milling is straightforward and scalable; however, strict guidelines are required to prevent the red phosphorus from burning and exploding, and slight oxidation and particle aggregation are unavoidable. Vaporization-condensation strategies are suitable for the uniform deposition of NRP onto a matrix but are limited by low phosphorus loading and residual white phosphorus. Chemical deposition methods are promising due to their simplicity, control over particle size, and scalability. There are two main chemical deposition strategies, i.e., the reduction of phosphorus-containing compounds and the dissolution and deposition of phosphorus amines. The former method is facile and compatible with ambient temperatures, while the latter method is safe, cost effective, and has high yields. Further studies should focus on morphology design, increasing phosphorus loading, and developing novel chemical reduction methods. We hope that this review promotes the development of red phosphorous anodes for application in SIBs.