What kinds of lithium battery conductive agent have?

First, the purpose of adding the conductive agent into the lithium battery

Lithium the battery in the charge and discharge cycle, is current through the anode plate, there will be a net reaction occurs, shows that the electrode lost the original equilibrium state and electrode potential will deviate from the equilibrium potential, the result is often said that the polarization. Lithium battery polarization can be divided into ohm polarization, electrochemical polarization and concentration polarization. Polarization voltage is reaction lithium ion batteries internal electrochemical reaction of the important parameters, if long-term unreasonable polarization voltage, leads to negative lithium metal precipitation is accelerated, severe cases can Pierce the diaphragm lead to short circuit. According to experimental data, the early lithium-ion batteries rely on the living quality electrical conductivity is insufficient to meet the requirements of the electron transfer rate, in order to make the electronic can fast moving position, the conductive agent to join.

The primary role is to improve the electronic conductivity of conductive agent. Conductive material between active materials, and active materials have the effect of collecting micro electric current to reduce the contact resistance of electrode, improve the migration velocity of the electrons in the lithium battery, reducing the battery polarization. In addition, the conductive agent can also improve the pole piece workability, promote the electrolyte infiltration of pole piece, so as to improve the service life of lithium-ion batteries.

Second, the commonly used lithium batteries conductive agent

Commonly used lithium batteries conductive agent can be divided into the traditional conductive agent (such as carbon black, conductive graphite, carbon fiber, etc.) and the new type of conductive agent (such as carbon nanotubes, graphene and its blending conductive paste, etc.).Number of conductive formulations on the market are SPUERLi, S - O, KS - 6, KS - 15, SFG, SFG to 15, 350 g, acetylene black (AB), jean (KB), the growth of the gas phase carbon fiber (VGCF), carbon nanotube (CNT) and so on.

(1) Carbon black

Black carbon chains or grape shaped under the scanning electron microscopy (sem), a single carbon black particles is very large specific surface area (700 m2 / g).High specific surface area, bulk carbon black particles are closely to close contact between particles, composition of the conductive network in the electrode. Larger than the surface dispersion is difficult technology problem, has strong oil absorption, this needs by improving living material, mixing process of conductive agent to improve its dispersion, and control the amount of carbon black in a certain range (usually 1.Less than 5%), carbon black and its mixed in living material status is shown in figure 1.

(2) Conductive graphite

Conductive graphite also has good electrical conductivity, its particles are close to living material particle size, particle and particle in the form of point contact between, can form a certain scale of conductive network structure, improve the conductive rate at the same time for more when the cathode anode capacity can be improved.

(3) Carbon fiber (VGCF)

Conductive carbon fiber with linear structure, easy to form good conductive network in the electrode, show the good electrical conductivity, and thus reduce the electrode polarization, reduce the battery internal resistance and improve battery performance.In carbon fiber inside the battery as conductive agent, live material and conductive agent contact form for point, line, compared to the conductive carbon black and conductive graphite little contact form, and is not only beneficial to improve the electrode conductivity, can reduce the conductive agent, increase the battery capacity. VGCF and conductive carbon black dispersed state in the live material comparison is shown in figure 2:

(4) The carbon nanotube (CNT)

CNT can be divided into single-walled CNT and multi-walled CNT, one dimensional structure of carbon nanotubes and fibers similar to show long cylindrical in shape and hollow inside. Using carbon nanotubes as a conductive agent can better cloth up perfect conductive network with the live material in the form of point line contact, to increase the battery capacity (improve sheet compaction density), performance, battery cycle life and reduce the battery impedance interface has a great effect. At present, byd, catic lithium electric parts products using CNT as conductive agent, the reaction has good effect. Carbon nanotubes can be divided into the badger type and array type two kinds of growth condition, whatever the form of its application in the lithium battery has a problem that, at present can by high-speed shear, adding dispersant, dispersed slurry, superfine grinding beads to solve electrostatic dispersion process.

(5) Graphene

Graphene as a new type of conductive agent, because of its unique lamellar structure (2 d) structure, for point of contact with the active substances - surface contact instead of conventional little contact form, and so can maximize play a role of conductive agent, reducing the amount of conductive agent, and can use more active substances, improve lithium battery capacity. But due to its high cost, dispersing difficulties and has the disadvantages such as obstacles to lithium ion transport has not yet been fully industrialized application.

(6) Binary, ternary conductive paste

In the latest research progress of lithium battery using conductive agent is between CNT, graphene, conductive carbon black mixed pulp of two or three. Conductive paste of composite conductive agent make it is the demand of the industrial application, is also the result of the synergy between the conductive agents, excitation function. Carbon black, graphene and CNT, when used alone has its three great difficulty, if you want to live with the material mixing, may need to be done on an electrode paste mixing before it spread out and then put into use. Three yuan slurry used in the anode material mixing state as shown in figure 3:

Third, the future of the conductive agent

Morphology, different kinds of conductive agent, and its microstructure is the important factors influencing the electrical conductivity. From the carbon black particle to the carbon fiber, the one dimensional structure of CNT now graphene two-dimensional lamellar structure, it is a process of continuous improvement. In practice, has been very widely used carbon black as conductive agent, process is also very mature. CNT as a conductive agent applied to power battery test and application have been more manufacturers, has obtained the good effect. But graphene due to its cost, process problem has not been applied widespread in conductive agent industry. Each conductive agent each have their advantages and complement each other, the conductive paste mix will be conductive agent in the mainstream of development direction in the future.

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