With the rapid development of electric vehicles, clean energy storage, and portable electronic products, the development of matched high-energy, high-power, long-life electrochemical energy storage devices has become an urgent need. Supercapacitors, also known as electrochemical capacitors, are one of the most important electrical energy storage devices. Their rapid charge and discharge in seconds, tens of thousands of cycles, 100% charge and discharge efficiency, and high safety are the lithium ion battery. Secondary battery can not be compared. However, the low energy density limits the further application of supercapacitors in consumer electronics, electric vehicles, smart grids, and clean energy. How to increase the energy density of a supercapacitor on the premise of maintaining its high power and long life is an urgent problem to be solved. By studying the variation of the potential of electrode materials in various carbon-based supercapacitors with the charge-discharge process, scientists from the Advanced Carbon Materials Research Department of the National (United) Laboratory of Materials Science at the Institute of Metal Research, Chinese Academy of Sciences have found that the ultra-capacitors have low energy density. One of the root causes is that the positive and negative electrodes cannot be operated under the optimal potential window after assembly into a device, so the energy density is very low. In order to solve this problem, they proposed the use of electrochemical charge injection (ECI) to change the surface electrochemical structure of the electrode material, thereby regulating the electrochemical potential of the positive and negative electrode materials to the optimal initial potential, as shown in Figure 1a. Show. The assembled positive and negative electrodes are assembled into a supercapacitor, as shown in FIG. 1b, c, the positive and negative electrodes reach the upper and lower limits of the available potential of the electrolyte at the same time during the charging process, which greatly improves the working voltage and specific capacity of the supercapacitor. . Since the energy stored in the supercapacitor is proportional to the operating voltage and the capacity of the active material, its energy density is greatly increased, as shown in Figure 1d. This method is universal and it has been validated on many types of carbon-based supercapacitors. In particular, the graphene lithium ion supercapacitor with graphene as active material not only maintains the high power characteristics of the supercapacitor, but also has an energy density that exceeds that of the nickel-metal hydride battery and is close to that of the lithium ion battery. . Related research results were published in "Angewandte Chemie International Edition, 2013, 52, 3722-3726" and were selected as "Hot Paper" by the magazine. However, for graphene lithium-ion supercapacitors, along with the dramatic increase in energy density, there is a concomitant decrease in their cycle life (25% attenuation in 1000 cycles). By monitoring and analyzing the working ranges of the positive and negative electrodes, it was found that the continuous reaction of the positive electrode and the electrolyte in the range of 1.5V-1.0V (vs. Li/Li+) resulted in a low cycle life. In order to solve this problem, an electrochemical precoating method (PEC) is used to preliminarily coat the positive electrode surface with a layer of nanometer-scale protective layer through the decomposition of lithium difluorooxalatoborate (LiODFB), as shown in FIG. 2a. The protective layer has the characteristics of electronic insulation and ion conduction, thus not only can prevent the direct contact and decomposition of the active material and the electrolyte, but also can ensure high ion diffusion and transmission in the electrode. FIG. 2 b is a schematic assembly diagram of a general graphene lithium ion super capacitor and a lithium ion super capacitor using PEC to treat the graphene anode. Lithium-ion supercapacitors that use PEC to handle the positive electrode of graphene not only exhibit excellent energy density and high power characteristics (Fig. 2c), but also have better cycle stability than a typical graphene-lithium ion supercapacitor (per cycle The attenuation is only 0.011%, as shown in Figure 2d. The relevant results were received and published by Advanced Energy Materials (2015, DOI: 10.1002/aenm.201502064). At the same time, how to design a practical cell structure to achieve the above lithium ion super capacitor technology is equally important. To this end, a design idea for a smart cell of a lithium ion super capacitor was proposed. Along with the assembly of lithium-ion supercapacitors, a series of intelligent functions were developed based on this design, as shown in Figure 3. Compared to a traditional supercapacitor cell (Figure 3a), the smart cell introduces a lithium electrode and two voltage sensors (Figure 3b). The schematic diagram of its intelligent function is shown in Fig. 3c. (1) Raising the energy density: The lithium electrode can be used as a voltage regulator to effectively realize potential control in the cell and obtain high energy density, as shown in Fig. 3d. (2) Safety monitoring: The built-in voltage sensors V1 and V2 monitor the working state of the positive and negative electrodes in real time, which can improve the safety of the batteries. As shown in Figure 3e, when the working potential of the positive electrode exceeds the safety interval of the electrolyte, V2 is automatically Alarm, device service termination, which can effectively prevent the occurrence of security risks. (3) Capacity self-recovery: For batteries with potential safety hazards, self-repair can be effectively achieved through a lithium electrode voltage regulator. As shown in Figure 3f, the self-repaired cell (SLIC-R) can work normally and use. Therefore, the technology avoids the resource and environmental problems caused by the disposal of used batteries. The relevant results were published in "Energy Storage Materials, 2015, 1, 146-151". In recent years, the Advanced Carbon Materials Research Department has carried out a series of work on the design of carbon materials and devices for high-energy density supercapacitors. In particular, it has been invited to write a vision for the development of this field for "Energy Storage Materials" (Energy Storage Materials). Papers, related results have been concerned by domestic and foreign counterparts. The above work has received strong support from the National Nanoscale Research Program, the National Natural Science Foundation of China, and the Strategic Pilot Project of the Chinese Academy of Sciences. Freight Elevator,Cargo Elevator,Freight Lift,Freight Lift Elevator Homefriend&FUJI Elevator Co.,Ltd , https://www.jfujilift.com
Research Progress of High Energy Density Lithium Ion Supercapacitors for Metals