In the lithium battery industry chain, the conductive agent is one of the important auxiliary materials for the positive and negative electrode materials of lithium batteries, accounting for about 5% of the cost of lithium battery materials. There are currently three types of mainstream conductive agents, including conductive carbon black, carbon nanotubes and graphene.
Classification of conductive agents
The conductive agent is an auxiliary material for lithium batteries, which is mixed with positive electrode materials and negative electrode materials to produce electrode sheets. Positive electrode: The positive electrode materials of lithium batteries mainly include lithium iron phosphate, ternary materials, lithium cobalt oxide, etc., which provide lithium sources for lithium batteries. However, these positive electrode materials have poor conductivity and are difficult to meet the performance requirements of lithium batteries.
Therefore, a certain amount of conductive agent will be added when making the positive electrode sheet, so that the conductive material fills the gap between the active materials of the positive electrode material, which is used to increase the conductivity of electrons and lithium ions, and accelerate the process by forming a conductive network on the surface of the active material. Electron transport rate, while absorbing and retaining electrolyte, provides more electrolyte interfaces for lithium ions, thereby improving battery charging efficiency and extending lithium ion battery life.
The negative electrode of a lithium battery is usually composed of graphite, etc., which has good electrical conductivity. However, during the repeated charging and discharging of graphite, the intercalation and detachment of lithium ions will cause the expansion and contraction of the graphite particle volume. As the number of times increases, the gap between the graphite particles increases, the electrical conductivity decreases, and some even fall off the electrodes, no longer participate in the electrochemical reaction, and reduce the capacity of the lithium battery.
Therefore, adding a certain proportion of conductive agent in the negative electrode material helps to maintain the conductivity of the negative electrode material. There are three types of current mainstream conductive agents, including conductive carbon black, carbon nanotubes and graphene. Spherical conductive carbon black has a small contact area and its conductivity is weaker than the other two types; tubular carbon nanotubes have excellent conductivity but are expensive; flake graphene will hinder the forward flow of current due to its shape.
Conductive carbon black presents a point-contact conductive network in the electrode material, that is, it forms a point-contact conductive network between active materials. The amount of carbon black conductive agent added to the positive electrode material is usually about 3%.
Factors for choosing conductive agent
When selecting a conductive agent, conductivity, dosage and cost should be considered. Compared with traditional carbon black, the new conductive agent:
- Performance advantages
The lower the impedance, the better the conductivity. According to the prospectus of Tiannai Technology, the impedance of carbon nanotubes is only about 1/2 of carbon black. Low impedance can improve polarization at the same time, and the cycle performance is better.
- Small addition amount
the addition amount of traditional carbon black conductive agent is about 3% of the weight of the positive electrode material, while the addition amount of new conductive agents such as carbon nanotubes and graphene is reduced to 0.8%-1.5%. The material saves space and thus increases energy density.
- Higher unit price
The price of adding carbon nanotubes per unit lithium battery is 2.0-4.0 times the price of conductive carbon black SP.
Overview of conductive carbon black
Carbon black (Carbon black) is a kind of amorphous carbon, which is a kind of light, loose and extremely fine black powder. Products obtained by incomplete combustion or thermal decomposition. The microstructure is composed of spherical nano-scale particles agglomerated into clusters and fibrous aggregates. According to the use of carbon black, it can be divided into carbon black for rubber and carbon black for non-rubber.
Non-rubber conductive carbon black has the characteristics of high specific surface area, high structure, high purity and excellent conductivity, which makes it have a wider application field than ordinary carbon black, and can be widely used in batteries, electromagnetic wave shielding materials, and power cable shielding wires, oil pipelines and anti-static electronic components packaging materials and other fields. Conductive carbon black belongs to non-rubber carbon black, which is divided into conductive furnace black, low-end acetylene black, mid-range Super P, high-end Ketjen black, etc.
Physical properties of conductive carbon black
The structure of carbon black: X-ray diffraction research on the internal structure of carbon black particles proves that the carbon atoms in carbon black particles are arranged in a network of hexagonal planes forming a second-degree ordered formation plane (basal plane). The atomic spacing of the hexagonal arrangement is exactly the spacing of graphite (1.42ù), and such a layer plane is arranged into 3~5 layers (the acetylene carbon black is between 6~7 layers).
The average interlayer spacing is larger than that of graphite, graphite is 3.35ù, carbon black is usually between 3.48~3.56ù, depending on the type of carbon black. These layer planes are approximately parallel and equidistant, but due to the twist and translation between the layers, they do not present the ABABAB... three-degree ordered stacking order like graphite. There are three main types of common conductive carbon black: low-end acetylene black, mid-range Super P, and high-end Ketjen black.
Acetylene black has the smallest oil absorption value, the worst conductivity, and the specific surface area is larger than SP, so it is more difficult to disperse. SP is in the form of ball chains, has good oil absorption value and the smallest specific surface area, and is the conductive carbon black with the best conductivity and dispersibility among the three types. Ketjen black has a unique branched chain shape. There are many conductive contact points of the conductor, and the branched chains form more conductive paths.
Therefore, only a small amount of addition can achieve extremely high conductivity. It is the most cutting-edge superconductor at present. Carbon black, but its large specific surface area makes it difficult to disperse, and domestically produced products are expensive to import without breakthroughs. Currently, they are only used in high-end lithium batteries. The market space is expected to gradually open up after the problems of dispersion and import substitution are resolved.
Preparation process of conductive carbon black
Conductive carbon black is generally produced using the oil furnace method. Add high-temperature coal tar, coke oven gas, auxiliary additives, etc. to the carbon black reaction furnace according to the procedure to generate initial carbon black, add quenching water to the quenching kettle to produce carbon black flue gas, and the carbon black flue gas enters the main bag filter, and the collected The carbon black enters the air conveying system through the airtight valve of the main bag filter respectively.
After passing through the particle pulverizer, it is collected into the powder carbon black storage tank and then sent to the wet granulator for granulation. It is then dried, screened to remove off-spec carbon black and processed. Usually, the wet granulation and the previous heavy oil cracking process are called the front process, and the subsequent drying, screening, purification, demagnetization, packaging and other processes are called the post process.
Upstream and downstream situation of conductive carbon black
The upstream of conductive carbon black includes the cost of SP carbon black mainly comes from purchasing coal tar and electricity. Coal tar accounts for 60%-80% of the cost. The downstream includes The downstream of SP carbon black is mainly lithium battery manufacturers CATL, ATL, etc. Lithium battery manufacturers dope SP carbon black with carbon nanotubes, graphene, etc. according to their own needs, and then coat the positive and negative electrodes. The downstream application scenarios of lithium batteries are mainly new energy vehicles, energy storage, consumer electronics, two-wheeled vehicles, etc.
Market situation of conductive carbon black
Since conductive carbon black accounts for a small proportion of the cost of lithium batteries, the current market for conductive carbon black is small, mainly depending on the future market growth. Before 2022, China has long relied on the import of conductive carbon black for lithium, and now the main suppliers are foreign-funded enterprises Imerys, Japan Lion, NEC and foreign-funded enterprises that produce and operate in China.
These companies have invested a lot of resources in the development of conductive carbon black for a long time, leading the products and blocking the technology. Among them, the French Imerys family accounted for 70% of the market share. Conductive carbon black is one of the important auxiliary materials for lithium batteries. Before 2020, due to the limited market space for conductive carbon black under the constraints of the overall scale of the lithium battery industry, the technical barriers to superimposing conductive carbon black are high.