Lithium battery conductive additive is the key auxiliary material of lithium battery, which is used to improve the conductivity of positive and negative electrodes. Conductive additive is a key auxiliary material for lithium-ion batteries, which plays an important role in improving battery conductivity, battery capacity, rate performance, and cycle performance.
The role of lithium electrical conductive additive
Since most of the active materials of positive electrode materials have poor conductivity and large internal resistance, conductive additive is needed to form a conductive network to improve the conductivity between the active materials of electrode materials and the current collector.
At present, conductive additive is mainly used on positive electrode sheets. In the future, as The silicon-based negative electrode accelerates the penetration, and the application of the conductive additive on the negative electrode sheet will speed up.
In addition, the conductive additive can also improve the processability of the pole piece, promote the infiltration of the electrolyte on the pole piece, effectively increase the migration rate of lithium ions in the electrode material, and reduce polarization, thereby improving the charge and discharge efficiency and service life of the electrode.
Distribution of conductive additive on positive and negative electrodes
Positive electrode
It mainly improves the electrical conductivity of the positive electrode material. Lithium-ion cathode materials have poor conductivity. It is necessary to add a certain proportion of conductive additive to ensure that the conductive material fills the gaps between the active materials of the cathode material to form a good conductive network to improve the conductivity of the cathode material.
Negative electrode
Conductive additive mainly weakens the expansion of the negative electrode material and improves the cycle life. Although the electrical conductivity of the negative electrode material is good, the continuous embedding and shedding of lithium electrons will cause the expansion and contraction of the graphite particle volume during the multiple charge and discharge processes, resulting in an increasing gap between the graphite particles.
It can also reduce the electrical conductivity, and some even detached from the electrode and the capacity of lithium-ion batteries. Adding a conductive additive can improve the surface performance of the negative electrode and maintain the conductivity of the battery.
Conductive additive accounts for about 1% of battery cost, with low cost sensitivity and high downstream acceptance. Since the conductive additive does not account for a high proportion of the cost of lithium batteries, the price sensitivity is weak.
Therefore, although the cost of the new conductive additive is higher than that of the traditional conductive additive, the new conductive additive can significantly improve the energy density and performance of fast charging lithium ion battery. So lithium battery manufacturers have a higher degree of acceptance, and the cost may not be not the primary consideration.
Comparison of old and new conductive additiv
New conductive additive vs traditional conductive additive
Comprehensive comparison in multiple dimensions currently commonly used conductive additives for lithium batteries mainly include carbon, conductive graphite, VGCF (vapour-grown carbon fiber), carbon nanotubes, and graphene. Among them, carbon, conductive graphite and VGCF are traditional conductive additive. Carbon nanotubes and graphene are new conductive materials.
Conductive carbon black
chain or grape shape, with a high specific surface area. Carbon can form point-to-point contact with active materials, which is beneficial to the adsorption of electrolytes and improve ionic conductivity. The addition amount is about 3%, which is a cost-effective conductive material, but its conductivity is relatively general and it depends on imports.
Currently, the main conductive carbon is Divided into conductive carbon black, superconducting carbon black, special conductive carbon black.
Carbon nanotubes
They can be divided into single-walled tubes and multi-walled tubes. The one-dimensional carbon nanotubes are cylindrical, hollow inside, and have good electronic conductivity. The fiber structure can be in point-to-line contact with the active material, forming a continuous conductive network in the electrode active material, acting as a “wire”, which is beneficial to improve battery capacity, rate performance, battery cycle life, and reduce battery impedance.
Graphene
It has a two-dimensional flake structure and forms a point-to-face contact with the active material, which can maximize the role of the conductive additive and reduce the amount of the conductive additive, thereby increasing the proportion of the active material and increasing the capacity of the lithium battery. In the case of a small amount of addition, graphene can better form a conductive network, and the effect is much better than that of conductive carbon.
Conductive graphite
Graphite conductive additive is artificial graphite with smaller particle size, more developed pores and specific surface area, which can form point-to-point contact with active materials, which is beneficial to improve the compaction density of pole piece particles and improve ion and electronic conductivity. In the negative electrode can increase the capacity of the negative electrode.
Industrial chain of conductive carbon black
The overall supply of conductive carbon industry is in short supply. Conductive carbon is used in middle and high-end special carbon in the field of conductive additive. The main component of carbon black is carbon, and its basic particle size is between 10-100nm. Therefore, it has excellent rubber reinforcement, coloring, conductivity or antistatic and ultraviolet absorption functions.
It is the earliest nano-scale material developed and applied by humans. Carbon black is produced by incomplete combustion or pyrolysis of hydrocarbon compounds (liquid or gaseous), mainly composed of carbon elements, and exists in the form of colloidal particles similar to spheres and aggregates with colloidal size. The appearance of carbon black is black powder.
Carbon black has a wide range of downstream applications, and conductive carbon, that is, it is used in the field of conductive additive. Carbon black is a rubber reinforcing filler and the second rubber raw material after raw rubber.
Carbon black is also used as a colorant, ultraviolet shielding agent, antistatic agent or conductive additive, and is widely used in many industrial products such as plastics, chemical fibers, inks, coatings, electronic components, leather chemicals, and dry batteries.
Carbon black can also be used in metallurgy and carbon industries as high-purity carbon materials. It can be divided into two categories according to the application, namely rubber carbon and special carbon, and conductive carbon, is used in the field of conductive additive.
The cost of raw materials such as coal tar accounts for 80%. From the perspective of cost structure, the cost of raw materials such as conductive carbon coal tar in China will account for 80.5% in 2022.
The reason is that the international situation will be tense in 2021. China’s reduction in coal imports and the low operating rate under the dual-control policy of domestic coking plants will lead to tight supply and demand of tar, and the price of coal tar will rise by 61.46% throughout the year.
The downstream application market is rich, and there are differences in upstream raw materials at home and abroad. From the perspective of upstream raw materials, the upstream of Chinese carbon is dominated by coal tar, and the upstream of other countries’ carbon is dominated by naphtha. From the perspective of downstream application markets, carbon is a reinforcing filler for rubber, second only to raw rubber.
Two-bit rubber raw materials, while carbon can be used as colorant, UV shielding agent, antistatic agent or conductive additive, widely used in many industries such as plastics, chemical fibers, inks, coatings, electronic components, leather chemicals and dry batteries, carbon black as a high-purity carbon material, it can also be used in metallurgy and carbon material industries.
Production of carbon black
The carbon black production process is the cracking of hydrocarbons under high temperature to generate carbon and hydrogen. At present, the commonly used it preparation methods include furnace method, bath method, thermal cracking method and acetylene method.
Among them, the most commonly used conductive carbon black SUPER P Li (SP for short) is mainly prepared by furnace method, and the mainstream production process of conductive carbon is mainly for the furnace process and acetylene cracking method.
Furnace carbon black
Fuel additives and hot air are transported to the combustion section of the reaction furnace for combustion to form a combustion gas flame with extremely high temperature. When the high-temperature combustion gas flame passes through the throat section of the reaction furnace, the atomized hot raw material oil is introduced into the gas flow.
The atomized raw oil is mixed with the high-temperature combustion gas flame and passed into the reaction section of the reaction furnace, where it is pyrolyzed to generate carbon black.
Acetylene carbon black
Using acetylene as raw material, it is isolated from air in a cracking furnace and cracked to generate acetylene carbon and hydrogen. It is mainly used to manufacture conductive polymers and batteries.
Conductive carbon black for lithium batteries
Conductive carbon products for lithium batteries are significantly differentiated, and the performance gap is large. Low specific surface area, high oil absorption value, and low metal ion content are the core technical indicators for the successful application of conductive carbon.
Particle size and specific surface area
Carbon black particle size means the primary particle size of carbon black, and specific surface area refers to the sum of the surface areas of its particles per unit mass or unit volume. The particle size is small, the specific surface area is large, and it has better ion and electron conductivity, which is conducive to the adsorption of electrolytes and improves ion conductivity.
Branched chain structure
The branched chain structure can form a chain conductive structure with active materials, increase the conductive contact points, and help to improve the electronic conductivity of the material.
DBP absorption
The structure of carbon black can be measured with the DBP (dibutyl phthalate) absorption value.
Surface functional groups
The amount of surface functional groups determines the difficulty of carbon black dispersion. The more functional groups are, the easier it is to disperse, but too many will weaken the electrical conductivity.
Metal ion content
Excessive metal ion content will cause battery self-discharge and affect safety performance. Generally, the metal ion content of conductive carbon for lithium batteries is relatively high, generally less than 10ppm.
At present, the conductive additive for lithium-ion batteries in China is still dominated by traditional conductive additive conductive carbon, of which SP products are the mainstream in the market.
SP conductive carbon black
It belongs to small particle conductive carbon black, which is cheap and practical. It has no lithium storage function and only conducts electricity.
Ketjen black
Only a very low amount of addition is required to achieve high conductivity. Compared with other conductive carbon used in batteries, Ketjen black has a unique branched chain shape, with many conductive contact points of the conductor, and branched chains form more conductive paths, so only a small amount of addition can achieve high conductivity.
Acetylene carbon black
It is a carbon black obtained by continuous pyrolysis of acetylene with a purity of more than 99% obtained by decomposing and refining the by-product gas during pyrolysis of calcium carbide.
After raising the temperature inside the reaction furnace to the starting temperature of acetylene decomposition above 800°C, introduce acetylene to start thermal decomposition. The reaction temperature should be kept around 1800°C.
