As lithium batteries become more widely commercialized, the charging and discharging process of lithium batteries on the surface of the positive electrode material involves lithium ions entering the positive electrode active material when the battery discharges. If the current increases, polarization increases, making discharge difficult and resulting in poor conductivity between electrons. The conductivity of the active material itself is far from sufficient. In order to ensure that the electrode has good charging and discharging performance, a certain amount of conductive agent is usually added during the electrode manufacturing process. This agent serves to collect micro-currents between the active materials and the current collector.
As lithium batteries become more widely commercialized, the charging and discharging process of lithium batteries on the surface of the positive electrode material involves lithium ions entering the positive electrode active material when the battery discharges. If the current increases, polarization increases, making discharge difficult and resulting in poor conductivity between electrons. The conductivity of the active material itself is far from sufficient. In order to ensure that the electrode has good charging and discharging performance, a certain amount of conductive agent is usually added during the electrode manufacturing process. This agent serves to collect micro-currents between the active materials and the current collector.
Review of conductive agents
Important conductive agents used in lithium batteries include conventional conductive agents such as SUPER-P, KS-6, conductive graphite, carbon nanotubes, graphene, and carbon fiber VGCF, each with its own advantages and disadvantages. Specifically:
Application of conductive agents
01:SP
Currently, conventional conductive agents (SP) are still the main conductive agents used in domestic lithium batteries. Carbon black has better ionic and electronic conductivity because it has a larger specific surface area, which is beneficial for electrolyte adsorption and thus improves ionic conductivity. In addition, the primary particle agglomeration of carbon forms a branched structure, which can form a chain conductive structure with the active material, helping to improve the electronic conductivity of the material.
02: Graphite conductive agent
It is primarily made of artificial graphite. Compared to artificial graphite used as a negative electrode material, artificial graphite, as a conductive agent, has a smaller particle size, which is beneficial for the compaction of electrode particles and for improving ionic and electronic conductivity.
03: CNT conductive agent
While CNT conductive agents have a high application rate of over 50% in high-end digital batteries, their application rate in power lithium batteries is relatively low. However, in recent years, as the requirements for energy density, rate performance, and cycle life of power lithium batteries have gradually increased, the application rate of CNT conductive agents in this field is gradually rising.
04: Kochen Black
Ketjenblack achieves high conductivity with extremely low addition amounts, making it a top-quality conductive carbon black and maintaining a leading market position for a long time. Compared to other conductive carbon blacks used in batteries, Ketjenblack has a unique branched morphology. The advantage of this morphology is that it provides numerous conductive contact points, with the branches forming many conductive pathways. Therefore, only a small amount is needed to achieve extremely high conductivity (other carbon blacks are mostly spherical or flake-shaped, requiring much higher addition amounts to achieve the desired electrical properties).
Ketjen Black is a cutting-edge super-conductive carbon black, currently used or tested by almost all of the top 10 lithium battery manufacturers. EC-300J is primarily used in nickel-metal hydride and nickel-cadmium batteries; ECP and ECP-600JD are mainly used in high-rate, high-capacity, and high-current-density lithium batteries, with ECP-600JD showing particularly outstanding performance. The industry generally believes that its superior conductivity, high purity, and unique branched structure will make it stand out in the era of lithium iron phosphate (LFP) cathode materials.
There are two products using Ketjen Black in batteries: CarbonECP and CarbonECP600JD, CP300JD.
The content of conductive agent
a) The purpose of conductive agents in electrodes is to provide channels for electron movement. Appropriate conductive agent content can achieve higher discharge capacity and better cycle performance. If the content is too low, there will be fewer electron conduction channels, which is not conducive to high current charging and discharging. If the content is too high, it will reduce the relative content of active materials and reduce the battery capacity.
(b) The presence of conductive agents can affect the distribution of electrolyte within the battery system. Due to space limitations in lithium batteries, the amount of electrolyte injected is limited, generally resulting in a lean electrolyte state. As the ion medium connecting the positive and negative electrodes within the battery system, the distribution of the electrolyte has a crucial impact on the migration and diffusion of lithium ions in the liquid phase. When the conductive agent content in one electrode is too high, the electrolyte accumulates at that electrode, slowing down the lithium ion transport process at the other electrode, resulting in higher polarization and making it prone to failure after repeated cycles, thus affecting the overall performance of the battery.
C) The content of the conductive agent should reach a turning point. Too much will only reduce the electrode density and decrease the capacity, while too little will result in low utilization of the active material in the electrode and a decrease in high-rate discharge performance.
Outlook for conductive agents
Analysis suggests that both carbon nanotubes (CNTs) and graphene can currently be made into conductive pastes, but they are significantly more expensive than ordinary carbon black (SP). Carbon black is a well-established conductive agent with relatively stable prices. With increased economies of scale, the prices of CNTs and graphene have considerable potential for reduction, indicating promising future applications.
