What Are The Characteristics Of Lithium-sulfur Batteries? Why Is It Said To Have Great Development Prospects?

- Dec 21, 2019-

Lithium-sulfur batteries are considered to be a promising next-generation battery system, and have become a leading research hotspot in the field of high specific energy energy storage devices. With the rapid development of mobile electronic equipment, electric vehicles and smart grids in recent years, the demand for high-energy-density battery systems has continued to increase. Lithium-sulfur batteries use elemental sulfur or sulfur-containing compounds as the positive electrode and metallic lithium as the negative electrode. Energy storage is achieved based on the multi-electron conversion reaction between sulfur and lithium. Graphite batteries have more than 6 times the theoretical energy density (387Whkg-1). At the same time, sulfur is rich in natural resources, low in price and environmentally friendly. It is expected to further reduce battery costs and meet the requirements for batteries in electric vehicles and large-scale energy storage. Therefore, lithium-sulfur batteries are considered to be a promising next-generation battery system, and have become a leading research hotspot in the field of high specific energy energy storage devices. Due to the low conductivity of sulfur, the polysulfide of the intermediate product during charge and discharge is easily soluble in the electrolyte, and the volume change during charge and discharge is large, lithium-sulfur battery cathodes usually face problems such as low utilization of active materials, poor cycle stability, and low coulomb efficiency. , Severely restricted its large-scale commercial application. How to improve the conductivity of the sulfur positive electrode, how to effectively improve the conductivity of the sulfur positive electrode, 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 their practical application. Li Feng, a researcher at the Institute of Metal Research of the Chinese Academy of Sciences, introduced to the China Science News that because carbon materials have the advantages of high electrical conductivity, large surface area, rich pore structure, and diverse structures, they can build efficient and stable conductive networks for sulfur electrodes. It has a good adsorption and anchoring effect on polysulfides, and at the same time provides a buffer space for the volume expansion of sulfur, thereby effectively improving the utilization of active materials, the kinetics of electrochemical reactions, and the stability of electrode cycling. To this end, they are based on carbonaceous materials and focus on the key problems of sulfur cathodes. Starting from the construction of carbon material's conductive / limited network, interface control, and integrated electrode structure design, they optimize the design of 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 the charge and discharge process, providing a scientific basis for the design of high energy density and long cycle life lithium-sulfur batteries.
In addition to advances in the design of integrated electrode structures and cathode materials, recent studies have shown that structural design and improvement of lithium-sulfur batteries can also effectively suppress or eliminate the shuttle effect. Since the battery structure is mainly composed of a positive electrode, a negative electrode, and a separator, the design of adding an interlayer between the positive electrode and the negative electrode and the modification of the separator can effectively suppress the diffusion of polysulfides and the growth of the lithium dendrite of the negative electrode, thereby improving the utilization of the active material. And increase battery cycle life. A high-pore-capacity graphene was used as a sulfur carrier, a part of graphene oxide was used as a spacer layer, and a highly conductive graphene was used as a current collector. An all-graphene-based anode structure design was proposed. High pore volume graphene achieves a sulfur content of 80 wt% of the electrode material and a sulfur load of 5 mgcm-2 of the electrode. The appropriate amount of oxygen-containing groups on the surface of partially graphene oxide can effectively adsorb polysulfides and improve the cycle performance of the electrode. The highly conductive graphene current collector can improve the adhesion between the electrode active material and the current collector. At the same time, its light weight helps to improve the overall energy density of the battery. Through the synergistic effect of the three kinds of graphene, the all-graphene sulfur cathode can achieve up to 90% utilization of active materials and excellent cycle stability. We will use in-situ or ex-situ characterization techniques to observe the structural changes of different sulfur content and sulfur-loading electrodes during charging and discharging, and their impact on metal lithium anodes, and explore the capacity of high-sulfur-loading electrodes under long-term cycling. The mechanism of attenuation and reduction of Coulomb efficiency, and the overall improvement of the battery from aspects such as electrolyte optimization and lithium negative electrode protection, etc., provide guidance for further improving the stability and reversibility of the high sulfur load electrode. Li Feng said that in the future, they will assemble lithium-sulfur full cells and test their electrochemical performance based on the design idea of carbon-based integrated electrodes, and explore practical applications.
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