With the rapid development of science and technology, the imminent depletion of fossil fuels and the increasingly serious environmental pollution caused by the improvement of living standards, all countries attach great importance to the development of renewable and sustainable clean energy from the sun and wind. However, for these intermittent renewable clean energy sources, good energy storage systems and devices are very important. Based on mass production and environmental protection and green concepts, the new generation of energy storage devices must meet the requirements of low-cost manufacturing process, low-polluting and recyclable materials, safe device operation, and long service life.
Supercapacitors, also known as electrochemical capacitors, are an important and promising energy storage device because they can be charged and discharged faster than most batteries, have a longer lifespan, and have a longer lifespan than conventional capacitors. Therefore, supercapacitors have received great attention in the past decade. According to the different energy storage mechanisms, super capacitors can be divided into three categories: electric double layer capacitors, pseudocapacitors and hybrid supercapacitor batteries or super batteries.
The pseudocapacitor utilizes the redox electrochemical reaction of the electrode active material in the electrolyte to store energy. Because the Faraday charge transfer of the whole active material is involved, the capacitance value per electrode area is much higher than that of the electric double layer capacitor, and the electrode active material must undergo a large number of, fast, continuous and reversible electrochemical reactions within a certain operating potential range. Therefore, having a variety of switchable chemical states or valences is a basic requirement for electrode materials.
Super battery is a relatively new energy storage device, which combines the Faraday charge transfer of part of the pseudo-capacitor characteristics as an energy source, and the Coulomb electrostatic force of part of the characteristics of an electric double layer capacitor as a power source.
The application range of supercapacitors is quite extensive, including forming a composite power system with batteries on electric vehicles to make up for the shortcomings of insufficient battery power; as a high-power power supply system for 3C or medical products; as a backup power storage system; As a memory protection device; as a wearable electronic device, etc.
Transition metal oxide electrode materials such as manganese oxide, copper oxide, vanadium oxide, nickel oxide, etc., not only can be applied to lithium-ion battery electrode materials and have excellent energy storage properties, but also can be extended to capacitor electrode materials, not only making capacitors are cheaper, their performance is greatly improved, and more importantly, they are more environmentally friendly.
In 2009, the global supercapacitor market has exceeded 275 million US dollars, and it has continued to increase with an average annual growth rate of 21.4% in recent years. In recent years, in order to meet people's demand for portable or wearable electronic products, the application of supercapacitors has grown rapidly, such as in mobile phones, wearable electronic devices, and flexible displays.
New Breakthrough in Super Battery
The research team of Professor Cary Pint of Vanderbilt University in the United States recently designed a new hybrid material that combines the advantages of capacitors and batteries, which is very suitable for making 3C products such as mobile phones or the casing of mobile devices, and is also a super battery (hybrid type capacitor battery). It behaves like a capacitor, can maintain an ultra-long charge and discharge life cycle, and can store and provide energy equivalent to current lithium-ion batteries. Although the energy density is still lower than that of lithium-ion batteries, designing a larger casing is enough to make up for the lack of energy. More importantly, this design can also save the space occupied by traditional batteries, which is conducive to thinning products.
In addition, Professor Pinter expects this super battery material to be used in various types of building structures, such as the exterior and side (interior) walls of houses, and the chassis of aircraft and automobiles. By turning this battery material into a structural material, an energy storage device with the same load-bearing durability as traditional structural materials, the service life of this energy storage system is also longer than that of traditional building materials. The main purpose of studying this technology is to develop energy storage materials that can be integrated in houses, thereby improving the economic value of rooftop solar cells and realizing distributed grid systems.
Although the super batteries developed by Professor Cary Pint's research team can currently store only about 1/10 of the energy of lithium-ion batteries, the number and size of them can be used as structural materials to make up for it, and more importantly, their lifespan ratio. The battery is 1,000 times longer, making it ideal for mobile devices, cars, airplanes, and housing structures.
While stored energy should be the most important metric, 10 times less stored energy and 1,000 times more uses mean 100 times more energy can be stored over the life of the system. Therefore, these super cells are more suitable for structural applications. If the energy storage material fails and needs to be replaced every few years, there is no point in developing the material to build houses, cars or planes.
The research team of Stanford University professors also combined supercapacitor and lithium battery technology to develop clothing batteries and paper batteries. Clothes have become a lightweight new energy storage medium, which can be charged or combined with solar energy technology to store electricity. Just like wearing a power storage device on the body, the emergence of paper batteries is expected to become a thin, high-efficiency energy storage device. Professors at Stanford University in the United States said that the research team has been designing how to apply nanotechnology to life, and clothing batteries and paper batteries are simple life applications of nanotechnology.
The principle of the clothes battery is to soak the cloth (fiber) of clothes in ink containing carbon nanotubes, and the carbon nanotubes will be attached to the fibers of the clothes, and it has the ability to store electric charge. This technology can also be applied to other cotton or polymer fiber clothes, giving clothes the ability to store electrical charges. At the same time, the application of this design can be very diverse, for example, electronic displays can be installed on clothes or the clothes can be used to charge electronic products such as mobile phones. This clothing battery performs about the same as traditional batteries in terms of energy storage and charging life.
The research team of Stanford University professors is also developing clothing batteries with solar charging function. It is believed that because the application technology of clothing batteries is not difficult, and the materials and costs are not too high, it should be commercialized within a few years.
Are there any pollution or safety issues when wearing clothing batteries on the body? Research team said that the clothing battery will have a special combination packaging, which will not be dangerous to the user's body.
As for the paper battery, it is a rechargeable secondary battery, which is different from the current paper batteries introduced by Israel and Finland, which are primary batteries. The professors at Stanford University in the United States said that the paper battery developed by the team can not only be used in mobile electronic devices and wearable electronic devices, but also can be used in various electrical devices that require instant high-capacity power. According to the research team's test, this paper battery can be repeatedly charged and discharged up to 40,000 times, which is 10 times that of traditional lithium-ion batteries.
The principle of the paper battery is to apply a special ink solution containing carbon nanotubes and silver nanowires as a coating on the paper. The coating will form a one-dimensional structure of the film and adhere to the surface of the fibrous paper. It will become a highly conductive power storage element, and the conductive paper can be used as a current collector and an electrode, respectively, and assembled into a low-cost, light and high-efficiency paper battery.
There is a great need for low-cost, high-efficiency energy storage devices such as existing batteries and capacitors. However, there have been significant hurdles in developing the market for electric vehicles and electric trucks due to the heavy weight and short lifespan of batteries. Now that thin paper batteries are available, they can not only be used in electric vehicles or hybrid vehicles, but also make electronic products lighter and have a longer service life. In the future, paper electronic products can be further developed. Because paper batteries are very low cost, they are also well suited for grid energy storage.
In recent years, paper-based printed products have been losing ground due to the advent of online electronic media such as e-mails and e-books, and are almost on the verge of disappearing. Now the invention of paper batteries has the opportunity to supply power to various electronic devices.
Application of Synchrotron Radiation Technology
With the increasing attention of energy issues, various energy storage battery materials have been continuously researched and developed. The research focus is generally on the design and improvement of its nanostructure, and there is a lack of discussion on the energy storage mechanism involved between the battery electrode and the electrolyte during the real charge and discharge process. Especially in the super battery, there are only a few manganese oxides at present. Discussion on materials related to copper oxide in electrolytes such as aqueous and non-aqueous solutions. Only by fully understanding the energy storage mechanism in the charging and discharging process can we find the most suitable combination of energy storage electrodes and electrolyte materials to achieve the best performance of the battery.
To explore the energy storage reaction and mechanism of the charging and discharging process, it is often necessary to do on-site tests with electrolytes. Several research equipment of the National Synchrotron Radiation Research Center meet this condition. The penetrating X-ray microscope can be used to instantly observe whether the energy storage electrode material has obvious expansion reaction during the charging and discharging process. Excessive expansion during the charging and discharging process can easily cause the brittleness and detachment of the energy storage material, which affects the performance and service life of the battery. X-ray diffraction can be used to understand the crystal phase changes of materials during charging and discharging, and help to understand whether these materials are reversible.
In addition, the use of synchrotron radiation X-ray absorption spectroscopy technology with a self-built experimental module can be used to instantly observe the charge transfer and valence state changes of energy storage electrode materials during charging and discharging. It can be found from the experimental process that when the valence state change or charge transfer of the material is more obvious, the better the energy storage performance of the material is. This discovery can help to select the most suitable oxide valence states and metal oxides as energy storage materials, and can deduce a reasonable energy storage (charge transfer) mechanism. At the same time, this module can be used to understand the stability of materials, and even establish a set of programs that can predict the service life of batteries, which can be used to calculate the service life of various materials under continuous charging and discharging, and effectively eliminate defective products.
In the case of global energy depletion, the development of high-efficiency energy storage batteries is one of the solutions. With the rapid development of materials engineering and technology, perhaps in the next few years, all kinds of cloth batteries and paper batteries can become super batteries that can be seen everywhere in daily life.