New progress in lithium-sulfur battery technology

　　Guide: According to the latest news, American scientists have recently overcome the main obstacle facing lithium-sulfur batteries-electrolyte dissolution, and solved the problem of rapid failure of lithium-sulfur batteries. This technological breakthrough is expected to greatly enhance the competitiveness of lithium-sulfur batteries in the market. At present, the main international chemical energy storage technologies include sodium-sulfur batteries, lithium batteries, flow batteries, lead-acid batteries, and lithium iron phosphate batteries.

　　 OFweek lithium grid comprehensive report: At present, the main international chemical energy storage technologies include sodium-sulfur batteries, lithium batteries, flow batteries, lead-acid batteries, lithium iron phosphate batteries, etc. A researcher at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences said that with the development of the renewable energy industry and the electric vehicle industry, energy storage technology and industry are highly valued by various countries, and the research and development of various new electrochemical energy storage battery technologies continue to make progress. Among them, the more representative ones are flow batteries, lithium-sulfur batteries and lithium-air batteries, but their technological development is facing some practical challenges.　　Flow battery energy storage technology 　　Flow battery is generally an electrochemical energy storage device that realizes the mutual conversion of electric energy and chemical energy through the oxidation-reduction reaction of liquid active materials, so as to realize the storage and release of electric energy. It has become one of the best choices in the field of energy storage due to its outstanding advantages such as independent power and capacity, deep charge and discharge, and good safety. Since the flow battery was invented in the 1970s, it has undergone various projects from laboratory to enterprise, from prototype to standard product, from demonstration application to commercial promotion, from small to large, and from single to integrated functions. More than 100 items, with a cumulative installed capacity of approximately 40 MW.　　 The all-vanadium flow battery has an installed capacity of 35 MW, which is currently the most widely used flow battery. Dalian Rongke Energy Storage Technology Development Co., Ltd. (hereinafter referred to as Rongke Energy Storage), supported by the Dalian Institute of Chemical Physics, cooperated with Dalian Institute of Chemical Physics to realize the localization and large-scale production of key materials for all-vanadium redox flow batteries . Among them, electrolyte products have been exported to Japan, South Korea, the United States, Germany and the United Kingdom in large quantities. The developed high-selectivity, high-durability, low-cost non-fluorine ion conductive membrane has better performance than perfluorosulfonic acid ion exchange membrane, and the price is only 10% of the latter, which truly breaks the cost bottleneck of the vanadium redox flow battery. ". Through structural optimization and application of new materials, the rated working current density of the all-vanadium redox flow battery stack has been increased from the original 80mA/c㎡ to 120mA/c㎡ while maintaining the same performance. The cost of the stack has been drastically reduced by nearly 30%. The body stack specification reaches 32 kilowatts and has been exported to the United States and Germany. In May 2013, the world's largest 5 MW/10 MWh all-vanadium redox flow battery energy storage system designed and constructed was successfully connected to the grid in the 50 MW Wuniushi Wind Farm of Guodian Longyuan. Since then, the 3MW/6MWh energy storage project for grid-connected wind power in Jinzhou and the 2MW/4MWh energy storage project of Guodian Hefeng, which are successively implemented in Jinzhou, are also important examples of China's exploration of energy storage business models.　　 Another leading company in the field of vanadium flow batteries is Sumitomo Electric of Japan. The company restarted the flow battery business in 2010, and will build a 15 MW/60 MWh all-vanadium flow battery power station in 2015 to solve the peak shaving and power generation caused by the grid connection of large-scale solar power stations in a local area of Hokkaido Under the pressure of quality, the successful implementation of this project will be another milestone in the field of all-vanadium flow batteries. In 2014, UniEnergy Technologies, LLC (UET) of the United States established a 3MW/10MWh all-vanadium flow battery energy storage system with the support of the US Department of Energy and the Washington Clean Fund. In this project, UET will apply its mixed acid electrolyte technology for the first time to increase the energy density by about 40%, broaden the use temperature window and voltage range of all vanadium flow batteries, and reduce thermal management energy consumption.　　 At present, improving the energy efficiency of the flow battery, the reliability of the system, and reducing its cost are important issues for the large-scale popularization and application of flow batteries. The development of high-performance battery materials, optimization of battery structure design, and reduction of battery internal resistance are the key technologies. Recently, Zhang Huamin and his research team used battery material innovation and structural innovation to increase the charging and discharging energy efficiency of the all-vanadium redox flow battery cell at a working current density of 80mA//c㎡ from 81% a few years ago to 93. %, which fully proves that it has broad development space and prospects.　　Lithium-sulfur battery technology　　In recent years, traditional lithium-ion battery technology has continued to advance, but the specific energy of the battery still cannot meet the application requirements, and battery technology is still the biggest bottleneck for the development of portable electronic devices and electric vehicles. In order to achieve an innovative breakthrough in high specific energy battery technology, researchers have chosen the direction of the breakthrough to be higher energy density lithium-sulfur batteries and metal-air batteries such as lithium-air, and certain progress has been made. Some new battery technologies have seen the dawn of practical applications.　　According to the latest news, American scientists have recently overcome the main obstacle facing lithium-sulfur batteries-electrolyte dissolution, and solved the problem of rapid failure of lithium-sulfur batteries. This technological breakthrough is expected to greatly enhance the competitiveness of lithium-sulfur batteries in the market. In a paper published in the journal Nanoscale of the Royal Society of Chemistry, researchers at the Burns School of Engineering at the University of California, Riverside announced that they have recently successfully developed a nanoscale sulfur particle that is combined with silica. The formed cathode material can prevent the dissolution of the lithium-sulfur battery electrolyte and significantly improve the battery performance.　　 Lithium-sulfur battery is a battery with sulfur as the positive electrode and metallic lithium as the negative electrode. Its theoretical specific energy density can reach 2600Wh/kg, and the actual energy density can reach 450Wh/kg. At the same time, elemental sulfur is cheap, rich in output, and environmentally friendly. It is currently the closest industrialized high-energy battery technology.　　 Internationally, representative R&D manufacturers of lithium-sulfur batteries include SionPower, Polyplus, Moltech in the United States, Oxis in the United Kingdom and Samsung in South Korea. Among them, the results of SionPower are the most representative. In 2010, SionPower applied lithium-sulfur batteries to drones. They were charged by solar cells during the day and discharged at night to provide power. This created a record of continuous flight of the drone for 14 days. It is a more successful application example of lithium-sulfur batteries. In China, research on lithium-sulfur batteries is mainly concentrated in scientific research units such as Dalian Institute of Chemical Technology, China National Defense Chemical Research Institute, Beijing Institute of Technology, etc., and has achieved rapid development in recent years. At present, the domestically developed lithium-sulfur battery has a world-leading energy density (>450Wh/kg), but after dozens of normal charging and discharging times, the energy density is greatly reduced, and its cycle life needs to be improved urgently.　　 Lithium-sulfur battery is a cutting-edge technology developed by countries all over the world, and its industrialization prospects are generally optimistic. How to greatly improve the battery's charge-discharge cycle life and use safety will become the key to the industrial development of lithium-sulfur batteries.　　Metal-air battery technology　　At present, metal-air batteries, especially lithium-air batteries, have attracted people's attention and have made many significant progress.　　 Lithium-air batteries use metallic lithium as the negative electrode and oxygen in the air as the positive electrode active material. Through the electrochemical reaction between lithium and oxygen, the mutual conversion of electrical energy and chemical energy is realized. The battery's theoretical energy density can reach about 3500Wh/kg, which is 10 times that of lithium-ion batteries and close to gasoline. Focusing on the potential application prospects of lithium-air batteries, countries around the world have carried out relevant research work. IBM has been committed to the "Battery 500" project, hoping to achieve the goal of 500 miles for electric vehicles on a single charge; and the participation of companies such as Asahi Kasei in Japan will promote the research of diaphragms and electrolytes.　　 Lithium-air battery is not a new concept. It was first proposed by Lockheed researchers in 1976. In 1996, Abraham and others proposed an organic electrolyte system, which created a new situation in the research of lithium-air batteries. At present, research on lithium-air batteries is mainly focused on the positive electrode, which directly determines the performance indicators of the battery. In terms of energy density, graphene-based materials are the most representative. Researchers at the Pacific Northwest National Laboratory in the United States have prepared a layered graphene material with a bubble-like structure, achieving a specific discharge capacity of about 15000mAh/g, far exceeding the existing lithium-ion batteries. However, the oxygen-containing intermediate products generated during the charging and discharging process of lithium-air batteries will chemically react with carbon materials, electrolytes, etc., resulting in the formation of a large number of by-products (such as lithium carbonate, etc.), which greatly affects the battery cycle process , Is the bottleneck problem restricting its development. Bruce et al. used porous gold and titanium carbide for the positive electrode, which can effectively inhibit side reactions, and the capacity retention rate of 100 cycles is greater than 95%.　　 High energy density is the main advantage of lithium-air batteries, and cycle stability is the key and difficult problem faced by its technological development. On the other hand, the purification of lithium metal, the protection of lithium negative electrodes and the suppression of dendrites during charging and discharging, the development of highly active cathode catalyst components and selective oxygen permeation membranes, and battery structure design integration technologies are all required for its practical process. Effectively solve the problem.