What are the problems facing lithium-sulfur batteries?

Lithium-sulfur batteries use elemental sulfur or sulfur-containing compounds as the positive electrode, and metal lithium as the negative electrode. The energy storage is based on the multi-electron conversion reaction between sulfur and lithium. Its theoretical energy density is as high as 2600Whkg-1, which is currently commercial lithium cobalt oxide The theoretical energy density of graphite batteries is more than 6 times (387Whkg-1). At the same time, sulfur is rich in natural resources, low in price and environmentally friendly, which is expected to further reduce battery costs and meet the requirements for batteries in the field of electric vehicles and large-scale energy storage. Therefore, the lithium-sulfur battery is considered to be a promising next-generation battery system, and has become a frontier research hotspot in the field of high-specific energy storage devices. Due to the low conductivity of sulfur, the polysulfide, which is the intermediate product of charge and discharge, is easily soluble in the electrolyte, and the volume changes greatly during charge and discharge, lithium-sulfur battery cathodes usually face low active material utilization, poor cycle stability, and low coulombic efficiency. The problem has severely restricted its large-scale commercial application. Improving the conductivity of the sulfur anode How to effectively improve the conductivity of the sulfur anode, inhibit the dissolution of polysulfides and buffer the volume change of the active material, is one of the keys to the development of high-performance lithium-sulfur batteries and ultimately their practical applications. Li Feng, a researcher at the Institute of Metal Research of the Chinese Academy of Sciences, explained to the my country Science Journal: Because carbon materials have the advantages of high conductivity, large surface area, rich pore structure, and diversified structures, they can build an efficient and stable conductive network for sulfur electrodes, and It plays a good role in adsorption and anchoring of polysulfides, and at the same time provides buffer space for the volume expansion of sulfur, thereby effectively improving the utilization rate of active materials, electrochemical reaction kinetics and electrode cycle stability. To this end, based on carbon materials, they focused on the key problems of sulfur cathodes, and proceeded from the construction of carbon material conduction/restriction network, interface regulation and integrated electrode structure design, and optimized the sulfur cathode structure to improve sulfur. Its electrochemical activity inhibits the dissolution and diffusion of polysulfide ions in the electrolyte, and buffers the volume change of sulfur during charging and discharging, providing scientific basis for the design of high energy density and long cycle life lithium-sulfur batteries. We found that compared with large-diameter carbon nanotubes, the use of carbon nanotubes with a smaller diameter has higher electron conduction efficiency, and can ensure the electron/ion diffusion path under the condition of achieving higher sulfur content, thereby improving sulfur utilization rate. Dr. Fang Ruopian from the Institute of Metals of the Chinese Academy of Sciences explained that based on this understanding, they realized a sulfur/single-walled carbon nanotube network structure composite electrode with a sulfur content of up to 95wt% by using a single-walled carbon nanotube film with an interconnected conductive network structure. It is uniformly distributed in nanometers in the composite electrode. Through a simple stacking method, an areal capacity of 8.63mAhcm-2 can be achieved, which improves the practical value of the electrode. The research team obtained a three-dimensional interconnected hollow carbon fiber foam after high-temperature carbonization of cotton, which was used as a three-dimensional current collector, combined with carbon nanotubes and carbon black nanoparticles, to construct a multi-level conductive network with both short and long ranges for the sulfur electrode. The design of a composite sulfur electrode with a sulfur load per unit area of u200bu200bup to 21.2 mgcm-2 was developed. The three-dimensional current collector can ensure good conductive contact with the active material on the three-dimensional scale, thereby improving the utilization rate of the active material at high sulfur loading, and achieving an areal capacity of up to 23.32mAhcm-2 and good cycle stability. Based on the high adsorption capacity of the three-dimensional current collector for the electrolyte, we propose a new mechanism of confined polysulfide: while the electrode adsorbs the electrolyte, it also adsorbs the polysulfide dissolved in the electrolyte on the positive electrode area, thus effectively The diffusion of polysulfides is inhibited, and the good cycle stability of the electrode is ensured. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What is the principle of a battery?