1. The purpose of adding a conductive agent to a lithium battery In the lithium battery charge and discharge cycles, there are positive and negative current through the pole piece, there will be a net reaction occurs, the electrodes show lost its balance, the deviation from the equilibrium potential of the electrode potential, it is often said polarization produced . Lithium battery polarization can be divided into ohmic polarization, electrochemical polarization and concentration polarization. The polarization voltage is an important parameter for reacting the internal electrochemical reaction of a lithium ion battery . If the polarization voltage is unreasonable for a long time, the precipitation of the lithium metal of the negative electrode will be accelerated, and in severe cases, the diaphragm will pierce the short circuit. According to the initial experimental data of lithium batteries, the conductivity of the living material alone is insufficient to meet the requirements of the electron migration rate. In order to enable the electrons to move quickly, the addition of the conductive agent occurs. The primary role of the conductive agent is to increase the electronic conductivity. The conductive agent plays a role of collecting microcurrent between the active material and the active material and the current collector to reduce the contact resistance of the electrode, increase the migration rate of electrons in the lithium battery, and reduce the polarization of the battery. In addition, the conductive agent can also improve the processability of the pole piece, promote the infiltration of the electrolyte to the pole piece, thereby improving the service life of the lithium battery. Second, commonly used lithium battery conductive agent Commonly used lithium battery conductive agents can be divided into traditional conductive agents (such as carbon black, conductive graphite, carbon fiber, etc.) and new conductive agents (such as carbon nanotubes, graphene and their mixed conductive paste, etc.). Commercially available conductive agents are SPUER Li, S-O, KS-6, KS-15, SFG-6, SFG-15, 350G, acetylene black (AB), Ketjen black (KB), and vapor grown carbon fiber (VGCF). ), carbon nanotubes (CNT), and the like. (1) Carbon black Carbon black is chain or grape-like under scanning electron microscopy, and a single carbon black particle has a very large specific surface area (700 m 2 /g). The high specific surface area and close packing of the carbon black particles facilitate the close contact between the particles and constitute a conductive network in the electrode. The process problem caused by the larger surface area is difficult to disperse and has strong oil absorption. This requires improving the dispersibility by improving the mixing process of the active material and the conductive agent, and controlling the amount of carbon black within a certain range. (usually 1.5% or less), the carbon black form and its mixed state in the living material are shown in Fig. 1. (2) Conductive graphite Conductive graphite also has good conductivity, its own particles are closer to the particle size of the active material, and the particles are in point contact with the particles, which can form a conductive network structure of a certain scale, and improve the conduction rate while being used for the negative electrode. It can also increase the capacity of the negative electrode. (3) Carbon fiber (VGCF) The conductive carbon fiber has a linear structure, and a good conductive network is easily formed in the electrode, which exhibits good electrical conductivity, thereby reducing electrode polarization, reducing internal resistance of the battery, and improving battery performance. In the battery with carbon fiber as the conductive agent, the contact form of the living material and the conductive agent is point-line contact, which is not only beneficial to improving the conductivity of the electrode but also reducing the amount of the conductive agent, compared with the point contact form of the conductive carbon black and the conductive graphite. Increase battery capacity. The dispersion of VGCF and conductive carbon black in living materials is shown in Figure 2: (4) Carbon nanotubes (CNT) CNTs can be classified into single-walled CNTs and multi-walled CNTs. The one-dimensional structure of carbon nanotubes is similar to fibers in the form of long columns and hollow inside. The use of carbon nanotubes as a conductive agent can better lay out a perfect conductive network, which is also in the form of point-line contact with active materials, for improving battery capacity (increasing the compaction density of the pole piece), rate performance, battery cycle life and reduction Battery interface impedance has a great effect. At present, some products of BYD and AVIC lithium batteries use CNT as a conductive agent, and the reaction has a good effect. Carbon nanotubes can be divided into two types of growth states: entangled type and array type. No matter which form is used in lithium batteries, there is a problem that it is dispersed. At present, high-speed shearing, dispersing agent can be added to make a dispersion slurry. , ultra-fine grinding beads electrostatic dispersion and other processes to solve. (5) Graphene As a new type of conductive agent, graphene has a unique sheet-like structure (two-dimensional structure), and the contact with the active material is a point-to-surface contact rather than a conventional point contact form, so that the function of the conductive agent can be maximized and the effect can be reduced. The amount of the conductive agent can be used to increase the capacity of the lithium battery. However, due to its high cost, the difficulty of dispersion and the hindrance of lithium ion transmission have not been fully industrialized. (6) Binary and ternary conductive paste In the latest research progress, the conductive agent selected for some lithium batteries is a mixed slurry of two or three of CNT, graphene, and conductive carbon black. The composite of the conductive agent into a conductive paste is a requirement for industrial applications, and is also a result of synergy and excitation between the conductive agents. Whether it is carbon black, graphene or CNT, it is very difficult to disperse when it is used alone. If you want to mix it with the active material, you need to spread it without stirring the electrode slurry. Then put it into use. The ternary slurry is used for the stirring state of the positive active material as shown in Figure 3: Third, the future of conductive agents The form and type of the conductive agent are different, and the microstructure is an important factor affecting the electrical conductivity. From the granularity of carbon black to the one-dimensional structure of carbon fiber and CNT to the current two-dimensional sheet structure of graphene, this is a process of continuous improvement. In practical applications, carbon black has been widely used as a conductive agent, and the process is very mature. CNT has been used as a conductive agent in power batteries and has been tested and applied by many manufacturers, and has achieved good results. However, graphene has not been widely used in the conductive agent industry due to its cost and process problems. Each of the conductive agents has its own advantages, and the long and short complementary, multi-mixed conductive paste will be the mainstream development direction of the future conductive agent. Pv Inverter Energy Meter,Iot Wireless Energy Meter,Ev Charging Meter,Prepaid Energy Meter Jiangsu Acrel Electrical Manufacturing Co., LTD. , https://www.acrel.com.pk