Liquid flow, lithium sulfur, metal air energy storage battery technology competition

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. Zhang Huamin, a researcher at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, said that with the development of the renewable energy industry and the electric vehicle industry, energy storage technologies and industries are highly valued by countries, and research and development of various new types of electrochemical energy storage battery technologies are progressing. . Among them, there are representative flow batteries, lithium-sulfur batteries and lithium-air batteries, but their technical development faces some practical challenges.

Flow battery energy storage technology

A liquid flow battery is generally an electrochemical energy storage device that realizes the mutual conversion of electrical energy and chemical energy by a redox reaction of a liquid active material, thereby realizing energy storage and release. Because of its independent power, capacity, deep charge and discharge, and good safety, it has become one of the choices in the field of energy storage.

Since the invention of the flow battery in the 1970s, it has gone through everything from laboratories to enterprises, from prototypes to standard products, from demonstration applications to commercial promotion, from small to large scales, from single to comprehensive functions. More than 100 items, the cumulative installed capacity is about 40 MW.

With an installed capacity of 35 MW, the all-vanadium flow battery is 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 of the Chinese Academy of Sciences, cooperated with Dalian Chemical Physics Institute 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, Korea, the United States, Germany and the United Kingdom. Developed high-selectivity, high-durability, low-cost non-fluorine ion-conducting membrane performance superior to perfluorosulfonic acid ion exchange membrane, the price is only 10% of the latter, truly breaking the "cost bottleneck of all vanadium redox flow battery" ".

Through structural optimization and new material applications, the rated operating current density of the all-vanadium redox flow battery stack has been increased from the original 80 mA/cm2 to 120 mA/cm2 while maintaining the same performance, and the cost of the stack has dropped by nearly 30%. The body stack has a specification of 32 kW and has been exported to the US and Germany. In May 2013, the designed and built global ** 5 MW/10 MWh all-vanadium flow battery energy storage system was successfully connected to the grid at Guodian Longyuan Wo Niu Shi 50 MW wind farm. Since then, the 3 MW/6 MWh energy storage project and the Guodian and Feng 2 MW/4 MWh energy storage projects for wind power integration in Jinzhou have been implemented, which is also an important case for China to explore the energy storage business model.

Another leading company in the field of all-vanadium flow batteries is Sumitomo Electric. 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 peaking and power generation brought by the grid connection of large-scale solar power stations in parts of Hokkaido. Quality pressure, the successful implementation of the project will be another milestone in the field of all vanadium flow batteries. In 2014, US UniEnergy Technologies, LLC (UET), with the support of the US Department of Energy and the Washington Clean Fund, established a 3 MW/10 MW all-vanadium flow battery energy storage system. In this project, UET will use its mixed acid electrolyte technology for the first time to increase the energy density by about 40%, and broaden the temperature window and voltage range of the all-vanadium flow battery to reduce thermal management energy consumption.

At present, improving the energy efficiency of the flow battery and the reliability of the system and reducing its cost are important issues for the large-scale popularization and application of the flow battery. Developing high-performance battery materials, optimizing battery structure design, and reducing battery internal resistance are key technologies. Recently, Zhang Huamin and his research team have improved the charge and discharge energy efficiency of all vanadium redox flow battery cells at an operating current density of 80 mA/cm2 through battery material innovation and structural innovation from 81% to 93 years ago. %, fully proved that it has broad development space and prospects.

Lithium-sulfur battery technology

In recent years, the traditional lithium-ion battery technology has been continuously improved, but the specific energy of the battery still cannot meet the requirements of the application. The battery technology is still the bottleneck of the development of portable electronic equipment and electric vehicles. In order to achieve innovative breakthroughs in high-energy battery technology, researchers have chosen to make breakthroughs in the selection of lithium-sulfur batteries with higher energy density and metal-air batteries such as lithium air, and have made some progress. Some new battery technologies have seen the dawn of practical applications.

Lithium-sulfur battery is a kind of battery with sulfur element as positive electrode and metallic lithium as negative electrode. Its theoretical specific energy density can reach 2600Wh/kg, and the actual energy density can reach 450Wh/kg. At the same time, the elemental sulfur is low in price, abundant in output and environmentally friendly. It is the most high-energy battery technology closest to industrialization.

Internationally, representative R&D companies for lithium-sulfur batteries include Sion Power, Polyplus, Moltech, Oxis and Samsung in the United States. Among them, Sion Power's results are the most representative. In 2010, Sion Power applied lithium-sulfur batteries to drones, charging them with solar cells during the day and powering them at night, creating a record of 14 days of continuous flight of drones. It is a successful application example of lithium-sulfur batteries. In China, research on lithium-sulfur batteries is mainly concentrated in the research institutes of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Beijing Institute of Technology, etc., and has achieved rapid development in recent years. At present, lithium-sulfur batteries developed in China are already in the world's leading position in energy density (>450Wh/kg), but after dozens of normal charge and discharge, the energy density is greatly attenuated, and its cycle life needs to be improved.

Lithium-sulfur batteries are the cutting-edge technologies that the world is competing to develop, and their industrialization prospects are generally optimistic. How to greatly improve the charge and discharge cycle life and safety of the battery will become the key to the industrialization of lithium-sulfur batteries.

Metal air battery technology

Currently, metal-air batteries, especially lithium-air batteries, have attracted a lot of attention and made many significant advances.

The lithium-air battery uses lithium metal as the negative electrode, and the oxygen in the air is the positive electrode active material, and the mutual conversion of electric energy and chemical energy is realized by the electrochemical reaction between lithium and oxygen. The theoretical energy density of the battery can reach about 3500Wh/kg, which is 10 times that of a lithium ion battery, which is close to gasoline. Focusing on the potential application prospects of lithium-air batteries, countries around the world have carried out related research work. IBM has been working on the "Battery 500" project, which is expected to achieve the goal of 500-mile battery life on a single charge; and the addition of companies such as Asahi Kasei in Japan will drive research on diaphragms and electrolytes.

Lithium-air batteries are not a new concept, first proposed by Lockheed researchers in 1976. In 1996, Abraham et al. proposed an organic electrolyte system, which opened up a new situation in lithium-air battery research. At present, lithium-air battery research mainly focuses on the positive electrode, which directly determines the performance indicators of the battery. In terms of energy density, the most representative one is graphene. Researchers at the Pacific Northwest National Laboratory have prepared a layered graphene material with a bubble structure that achieves a discharge specific capacity of about 15,000 mAh/g, far exceeding existing lithium-ion batteries.

However, the oxygen-containing intermediate product formed during the charging and discharging of the lithium-air battery will chemically react with the carbon material, the electrolyte, etc., resulting in the formation of a large amount of by-products (such as lithium carbonate), which greatly affects the cycle of the battery. Is a bottleneck that restricts its development. Bruce et al. used porous gold and titanium carbide for the positive electrode to effectively suppress side reactions, and the capacity retention rate of 100 cycles was greater than 95%.

High energy density is a major advantage of lithium-air batteries, and cycle stability is a key and facing challenge to its technological development. On the other hand, the purification of metallic lithium and the dendrite inhibition during lithium negative protection and charge and discharge, the development of high-activity positive catalytic components and selective oxygen permeable membranes, and the design and integration of battery structures are all practical processes. Effectively solved the problem.