Characteristics of three energy storage technologies: supercapacitors, fuel cells and metal-air batteries

Characteristics of three energy storage technologies: supercapacitors, fuel cells and metal-air batteries

Super capacitor

Super capacitor is an energy storage product between electrostatic capacitor and secondary battery. From the perspective of electrode materials and energy storage principles, supercapacitors can be divided into three categories, including electric double-layer supercapacitors, mass-capacitance supercapacitors, and hybrid supercapacitors.

Electric double-layer supercapacitors, in which the electric charge is electrostatically stored on the electric double-layer interface between the electrode and the electrolyte, no chemical reaction occurs during the entire charge and discharge process, so the product has a long cycle life and a fast charge and discharge speed. Supercapacitors mainly use carbon materials with high specific surface area as electrodes, and use aqueous or organic solutions as electrolytes. Since the introduction of industrialized products by Japanese companies such as NEC and Panasonic in the 1880s, supercapacitors have been widely used in electronic products, electric toys and other fields. In recent years, with the further reduction of product costs and the increase of product energy density, manufacturers represented by Russia’s Econd and American Maxwell have begun to expand their products to some high-power applications, and actively expand the market in the fields of electric vehicles, rail transit energy recovery systems, small new energy power generation systems, and military weapons. Many Chinese supercapacitor manufacturers, including Jishengxingtai and Aowei Technology, are also stepping up their efforts to expand the supercapacitor product market.

Waist-capacitance supercapacitors, electrode materials undergo a highly reversible oxidation-reduction reaction during the charging and discharging process, resulting in a capacitance related to the electrode charging potential. Since the electrochemical change process of Faraday charge transfer in this type of capacitor not only occurs on the surface of the electrode, but also can penetrate deep into the electrode, theoretically, a higher capacitance and energy density can be obtained than an electric double layer capacitor. At present, such capacitor electrode materials are mainly metal oxides and conductive polymers. Among metal oxide electrode materials, oxide nails are the most in-depth research in the world. However, because the material is too expensive, it is only used in small-scale applications in military and other fields. The use of conductive polymers as capacitor electrode materials is a new research field developed in recent years, but due to the short life of the electrode materials, there is no commercial application for the time being.

The hybrid supercapacitor is a hybrid product of the above two types of capacitors, and its characteristics are also between the two, with a higher energy density (up to 30Wh/L, which is 3 times that of electric double layer supercapacitors), and a long cycle life. At present, the most mature research is lithium-ion capacitor products, and manufacturers mainly include Japanese companies such as Hitachi, Zhaoei Electronics, and ACT. Although these manufacturers have introduced industrialized lithium-ion capacitor products, because the current product cost is more than 50% higher than that of electric double-layer supercapacitors, there are still certain obstacles in market application.

Read more: Development trend of supercapacitor technology

The fuel cell

The fuel cell was invented by the British Grove in 1839. It is a device that directly converts the chemical energy stored in the fuel and oxidizer into electrical energy. When the fuel cell is continuously supplied with fuel and oxidant from the outside, it can continuously generate electricity.

According to the different media that conduct electrons and protons, they can be divided into proton exchange membrane fuel cells (PEMFC), alkaline fuel cells (AFC), direct methanol fuel cells (DMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), and solid oxide fuel cells (SOFC).

Proton exchange membrane fuel cells are currently the most concerned fuel cell by R&D institutions and commercial applications, ranging from portable power sources for mobile phones and other electronic devices to power for cruise ships, cars and buses, and cogeneration systems for power stations. Has a wide range of applications. The main manufacturers of PEMFC include Ballard Power Systems in Canada and Plug Power in the United States. Companies such as Shanghai Shenli and Beijing Fuyuan have also been able to provide commercial fuel cell products, and many research institutions such as the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences and Tsinghua University are also studying battery materials and battery systems in depth.

Phosphoric acid fuel cells are the first fuel cells to be built for large-capacity applications. Complete sets of 2MW, 4.5MW, and 11MW fuel cell power generation equipment and demonstration power stations have been built, and they have entered commercial operation. Since its operating temperature is around 200°C, most of the heat can be recovered in the form of hot water. At present, its core technology is centrally mastered by Japan’s Fuji Electric Corporation, Toshiba Corporation and other companies.

Metal-air battery

Metal is used as the negative electrode active material, oxygen in the air or pure oxygen is used as the positive electrode active material, and the electrolyte is an alkaline or neutral battery. The negative electrode active material can be metallic zinc, aluminum, lithium, etc., which are respectively called zinc-air battery, aluminum-air battery, lithium-air battery, etc. This site mainly discusses zinc-air batteries.

Zinc-air battery is a battery in which metallic zinc is used as the negative electrode active material, oxygen or pure oxygen in the air is used as the positive electrode active material, and the electrolyte is alkaline or neutral. It has the advantages of low self-discharge rate, high energy density, battery capacity not affected by discharge intensity and temperature, high safety, low raw material cost, and environmental protection. At the current level of technology, zinc-air batteries can be used for low discharge rates (such as navigation lights, hearing aids) or occasions that do not require recycling (such as power supply for individual equipment in the field of troops or silent driving power for submarines).

Some companies around the world have devoted themselves to the application of zinc-air batteries in the field of electric vehicles. For example, the zinc-air battery used in electric postal vehicles developed by Electric Fuel Co., Ltd. in Israel, and the zinc-air battery used in buses and trucks with a total weight of 9t developed by Dreisback Electromotive of the United States. China’s Beijing Changli, Xi’an Zincba and other companies are also developing such batteries.

Read more: Development trend of fuel cell technology and metal-air battery technology