What are the advantages and disadvantages of conductive paste for lithium-ion batteries?

The lithium ion battery conductive paste is mainly a carbon-based conductive paste, and includes conductive carbon black, conductive graphite, carbon nanotubes, graphene and mixed slurry thereof. Generally, carbon black and graphite are referred to as conventional conductive pastes, and carbon nanotubes, graphenes and mixed pastes thereof are referred to as novel conductive pastes.

Conductive carbon black

Conductive carbon black is currently the most widely used conductive paste for lithium ion batteries. Carbon black is an amorphous carbon. It is chain or grape-like under scanning electron microscope. It is light and loose, with small particle size (D50=40Na), large specific surface area, poor dispersion in slurry. It is easy to agglomerate and has strong oil absorption. Since the conductive carbon black cannot form a good conductive network, the conductivity is relatively poor, and the resistance is high and it is easy to be polarized. Therefore, when a pole piece is produced using conductive carbon black, it is often used in combination with materials such as graphite, carbon nanotubes and graphene.

At present, the conductive carbon blacks sold in the market mainly include SuperP, SuperS, 350G, acetylene black, Ketjen black (CarbonECP, CarbonECP600JD) and the like.

Conductive graphite

Graphite is a crystal with a hexagonal layered structure, relatively coarse (D50=3-6um), slightly less conductive than conductive carbon black, but with better compressibility and dispersibility. Therefore, the conductive graphite is generally used in combination with the conductive carbon black, which not only improves the dispersibility of the conductive agent, reduces the polarization of the pole piece, but also improves the redox ability of the electrode and the charge and discharge performance of the battery.

At present, the conductive graphites on the market mainly include KS-6, KS-15, SFG-6, SFG-15 and the like.

Carbon nanotube

Carbon nanotubes (CNTs) can be classified into single-walled carbon nanotubes and multi-walled carbon nanotubes, and are newly developed conductive materials in recent years. Carbon nanotubes and living materials are in point-line contact form, which not only acts as a "lead" in the conductive network, but also has an electric double layer effect, which enhances electrolyte absorption, improves battery capacity, rate performance, battery cycle life and reduces Battery polarization has a positive effect and is an ideal conductive material, but the disadvantage of carbon nanotube materials is that they are not easily dispersed. Therefore, carbon nanotubes are generally added to carbon black for use in combination.

At present, Tiannai Company is a leading enterprise in the R&D and production of carbon nanotubes in China.

Graphene

Graphene has a sheet-like structure and is in surface contact with the active material, and has excellent electrical conductivity. When used as a conductive agent, the amount of the conductive agent can be reduced. However, the sheet-like structure of graphene also hinders the diffusion of lithium ions, resulting in a decrease in battery rate performance. Due to its high cost, the disadvantages of dispersion and the hindrance of lithium ion diffusion have not been fully industrialized. Therefore, graphene is currently generally added to carbon black for use.

At present, Qingdao Haoxin, Shenzhen Nanoport, Shandong Yuhuang, Xiamen Kaina and many other companies are producing graphene conductive paste.

Mixed conductive paste

Mixed conductive paste is the paste formed by mixing carbon nanotubes, graphene and conductive carbon black. The purpose of using a mixed conductive paste is to exert synergy, complementarity, and excitation between the conductive agents. Of course, the problem of dispersion of the mixed slurry will be more prominent.

The advantages and disadvantages of several conductive pastes coexist, and specific choices need to be considered comprehensively. In practical applications, carbon black is still the most widely used conductive material in lithium ion batteries due to the cost and process maturity. Carbon nanotubes and graphenes are the darlings of the new era, representing new hopes. With the joint efforts of scientific research, enterprises and financial institutions, they have achieved good results in scientific research and practical applications. However, the combined use cost of carbon nanotubes and graphene hinders industrial batch use. In the end, who will lead the mainstream of lithium ion battery conductive paste in the future, we will wait and see.

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