High Performance Pure Sulfur Honeycomb-like Architectures Synthesized By Cooperative Self-Assembly Strategy for the Lithium/Sulfur Battery

In this study, pure sulfur particles with honeycomb morphology were prepared via a cooperative self-assembly process, in which sodium dodecyl benzene sulphonate (SDBS) was used as a soft template to form the porous structure. To the best of the authors’ knowledge, there has been no report on using the cooperative self-assembly method to prepare honeycomb-like sulfur particles. Moreover, the method proposed in this paper is simple, easily scaled up, and has low energy consumption. As shown in Figure 1a, the structure of SDBS in aqueous solution can easily take on different forms, responding to the concentration of SDBS (C_SDBS) and the concentration of salt (C_salt) in the solution¹. The mechanism of the pore formation is shown in Figure 1b and c. First, after dropping H₂C₂O₄ solution into Na₂S₂O₃ and SDBS solution, the SDBS lamellar micelles are transformed to spherical micelles as the concentrations of SDBS and salt decrease. At the same time, the sulfur starts to precipitate. Thus, cooperative self-assembly occurs between the sulfur and the SDBS spherical micelles. Then, many more sulfur particles are produced, resulting in further condensation. Secondly, after adding a large amount of H₂O into the above solution, the SDBS spherical micelles break, and the SDBS is removed. The sulfur particles with porous honeycomb-like structure are then finally obtained, which is shown in Figure 1e. We believe that this method can provide useful information to a broad audience of readers working on the synthesis of porous sulfur for various applications, such as in chemical fertilizers, the pharmaceutical industry, the rubber and fibre industries, bioleaching processes, anti-microbial agents, insecticides, fumigants, etc. It will also be of interest to researchers working on Li/Sulfur batteries, which are now considered as an environmentally friendly and competitive alternative to classical Li-ion batteries. Due to their porous structure, the Li/S batteries fabricated from the as-prepared honeycomb-like sulfur cathode without any extra adsorption additives show significantly improved electrochemical performance compared with the batteries using commercial sulfur powder. As shown in Figure 1f, the cells with the honeycomb-like sulfur electrode retained a reversible discharge capacity higher than 650 mAh g⁻¹ for 50 cycles, while the discharge capacity of the commercial sulfur (FESEM image in Figure 1d) is about 200 mAh g^-1. And the honeycomb structure also gave much better rate capability than that of the commercial sulfur electrode.

Figure captions:

Figure 1. (a) Different types of SDBS structure in aqueous solution; (b) details of the synthesis; (c) mechanism of the synthesis of the honeycomb like sulfur particles; (d) FESEM image of commercial sulfur; (e) FESEM image of honeycomb-like sulfur; (f) cycling performance of honeycomb-like sulfur electrode and commercial sulfur electrode in lithium/sulfur batteries.

Reference:

1. N. Pal and A. Bhaumik, Adv.Colloid and Interface Sci., 2013, 189, 21-41