Which kind of conductive agent is better for lithium battery?
conductive agent has two main functions in the entire lithium battery pack: conducting electrons and absorbing electrolyte; so after adding conductive agent, it can improve the rate, cycle, reduce internal resistance and increase battery capacity of lithium battery pack; The conductive agent can not be added more or less, too much will not only affect the energy density, but also affect the performance of the positive electrode gram capacity.
According to the material, the conductive agent of lithium battery pack is divided into: metal conductive agent and carbon material conductive agent; currently the main conductive agent of carbon material is used, mainly: Super- P, acetylene carbon black, graphite, VGCF, CNT, etc.
In terms of resistivity, CNT has the smallest resistivity, followed by VGCF, and Super-P has the largest resistivity; however, the problems faced by VGCF and CNT are dispersion and price issues;
Some domestic manufacturers are studying well-dispersed conductive liquids, but the effect is not very good, and the cost performance is not cost-effective. Therefore, the most commonly used conductive agents are Super-P and conductive graphite.
In addition, acetylene carbon black is also effective, mainly nano-superconducting acetylene carbon black. Adding a small amount can greatly improve the conductivity.
At present, most lithium battery manufacturers use composite conductive agents, which is a mixture of several conductive agents:
The commonly used combination is SP+KS series; or SP+VGCF, etc.; even some manufacturers use It is a 3-component conductive agent.
The role of the conductive agent:
a) The role of the conductive agent in the electrode is to provide a channel for electrons to move, and the appropriate content of the conductive agent can achieve higher discharge capacity and better Cycle performance. Too low content will result in fewer electronic conductive channels, which is not conducive to high-current charging and discharging; too high a content will reduce the relative content of active materials and reduce battery capacity.
b) The presence of conductive agent can affect the distribution of electrolyte in the battery system. Due to the space limitation of lithium-ion batteries, the amount of electrolyte injected is limited, and it is generally in a state of lean. The electrolyte is the ionic body that connects the positive and negative electrodes in the battery system, and its distribution has a vital influence on the migration and diffusion of lithium ions in the liquid phase. When the content of conductive agent in one electrode is too high, the electrolyte is concentrated in this electrode and the lithium ion transmission process of the other electrode is slow, the polarization degree is high, and it is prone to failure after repeated cycles, thereby affecting the overall performance of the battery .
C) When the content of the conductive agent reaches 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 high rate discharge performance decline.
1. SP conductive agent
Currently, the domestic lithium-ion battery conductive agent is still dominated by conventional conductive agent SP. Carbon black has better ionic and electronic conductivity. Because carbon black has a larger specific surface area, it is beneficial to the adsorption of electrolytes and improves ion conductivity. In addition, the primary carbon particles agglomerate to form a branched structure, which can form a chain conductive structure with the active material, which helps to improve the electronic conductivity of the material.
2. Graphite conductive agent
It is basically artificial graphite. Compared with the negative electrode material artificial graphite, the artificial graphite as the conductive agent has a smaller particle size, which is beneficial to the pole piece particles. The compaction and improvement of ionic and electronic conductivity.
3. CNT conductive agent
The application proportion in the field of high-end digital batteries is as high as over 50%, and the application proportion in the field of power batteries is relatively low. However, in recent years, as power batteries have gradually increased performance requirements such as energy density, rate performance, and cycle life, the proportion of CNT conductive agents in this field is gradually increasing.
4. Ketjen Black
Ketjen Black only needs a very low addition amount to achieve high conductivity, so Ketjen Black has always been the best of conductive carbon blacks. It has been in a leading position in the market since. Compared with other conductive carbon blacks used in batteries, Ketjen Black has a unique branched morphology. The advantage of this form is that the conductor has many conductive contact points and the branched chain forms more conductive paths. Therefore, a very high conductivity can be achieved with a small amount of addition (other carbon blacks are mostly spherical or flakes, Therefore, a high amount of addition is required to achieve the required electrical properties).
Ketjen Black is currently a relatively cutting-edge super conductive carbon black. At present, the top 10 lithium batteries are basically in use or testing. Among them, EC-300J is mainly used for nickel-metal hydride and nickel-cadmium batteries; ECP and ECP-600JD are mainly used for high-rate, large-capacity and current density lithium batteries, among which ECP-600JD is particularly prominent. The industry generally believes that its superior electrical conductivity, high purity and unique branched chain structure will emerge in the era when iron-lithium is used as a cathode material.
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