As the commercialization of lithium batteries becomes more and more extensive, the charging and discharging process of lithium batteries on the surface of the positive electrode material is that when the battery is discharged, the lithium ions in the pores enter the positive active material, and if the current increases, the polarization increases. , it is difficult to discharge, so the conductivity between electrons is poor, and the conductivity of the active material alone is far from enough. In order to ensure that the electrode has good charge and discharge performance, a certain amount of conductive agent is usually added during the production of the pole piece. , between the active materials and the current collector to collect the microcurrent.
Conventional conductive agents SUPER-P, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, etc. are mainly used as conductive materials for lithium-ion batteries. These conductive agents have their own advantages and disadvantages.
Application of Conductive Agent
1. SP
At present, the domestic lithium-ion battery conductive agent is still dominated by the conventional conductive agent SP. Carbon black has better ionic and electronic conductivity, because carbon black has a larger specific surface area, so it is beneficial to the adsorption of electrolyte and improve ionic conductivity. In addition, the carbon primary 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 artificial graphite as the negative electrode material, the artificial graphite as a conductive agent has a smaller particle size, which is beneficial to the compaction of the pole piece particles and the improvement of the ionic and electronic conductivity.
3. CNT conductive agent
The application ratio in the field of high-end digital batteries is as high as more than 50%, and the application ratio in the field of power batteries is relatively low. However, in recent years, with the gradual improvement of power battery performance requirements such as energy density, rate performance, and cycle life, the application ratio 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 among conductive carbon blacks and has long been in a leading position in the market. Compared to other conductive carbon blacks for batteries, Ketjen Black has a unique branched-like morphology. The advantage of this form is that the conductor has many conductive contact points, and the branches form more conductive paths, so a very high conductivity can be achieved with only a small amount of addition (other carbon blacks are mostly spherical or flake-like, 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, and the top 10 lithium batteries are basically in use or tested. Among them, EC-300J is mainly used for nickel-metal hydride and nickel-cadmium batteries; ECP and ECP-600JD are mainly used for lithium batteries with high rate, large capacity and current density, among which ECP-600JD is particularly prominent. The industry generally believes that its superior electrical conductivity, high purity and unique branched structure will emerge in the era of iron and lithium as the cathode material.
There are two types of Ketjen Black products used in batteries: Carbon ECP, Carbon ECP600JD, and CP300JD.
The content of conductive agent
a) The role of the conductive agent in the electrode is to provide a channel for electron movement, and the conductive agent contains
Appropriate amount can obtain higher discharge capacity and better cycle performance. If the content is too low, there will be few electronic conduction channels, which is not conducive to high current charge and discharge;
b) The presence of the conductive agent can affect the distribution of the electrolyte in the battery system. Due to the space limitation of the lithium-ion battery, the amount of electrolyte injected is limited, generally in a state of poor liquid, and the electrolyte is used as the internal connection of the battery system. The distribution of positive and negative ions has a crucial impact on the migration and diffusion of lithium ions in the liquid phase. When the content of the conductive agent in one electrode is too high, the electrolyte is concentrated in this electrode and the lithium ion transfer process of the other electrode is slow, the polarization degree is high, and it is easy to fail after repeated cycles, thus 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 reduce the capacity, while too little will lead to low utilization of active materials in the electrode, and high-rate discharge performance will decline.
At present, carbon nanotubes and graphene can be made into conductive paste, and the price is much more expensive than ordinary carbon black SP. Carbon black is a very mature conductive agent, and the price is relatively stable. With the increase of the scale effect of CNT and graphene in the future, the price of CNT and graphene has relatively large room for decline, and the future application prospects are objective.
Lithium-ion battery is a kind of secondary battery that uses lithium-containing compound as positive electrode. The interior of a lithium-ion battery is mainly composed of a positive electrode, a negative electrode, an electrolyte and a separator.
Lithium-ion batteries work primarily by the movement of lithium ions between the positive and negative electrodes. During the charging and discharging process, Li+ intercalates and deintercalates back and forth between the two electrodes: during charging, Li+ is deintercalated from the positive electrode, intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharge, the opposite is true.
Lithium-ion batteries have many notable features, and their advantages are mainly as follows:
1. High voltage: the working voltage of the single battery is as high as 3.7-3.8V (the lithium iron phosphate is 3.2V, which is 3 times that of the Ni-Cd and Ni-MH batteries.
2. Large specific energy: the actual specific energy that can be achieved is about 555Wh/kg, that is, the material can reach a specific capacity of more than 150mAh/g (3-4 times that of Ni-Cd, 2-3 times that of Ni-MH, close to about 88% of its theoretical value.
3. Long cycle life: generally it can reach more than 500 times, even more than 1000 times, and lithium iron phosphate can reach 8000 times. For electrical appliances with low current discharge, the service life of the battery will double the competitiveness of the electrical appliances.
4. Good safety performance: no pollution, no memory effect. As the predecessor of Li-ion, the lithium battery is prone to short-circuit due to the formation of dendrites, which reduces its application field: Li-ion does not contain cadmium, lead, mercury and other elements that pollute the environment; some processes (such as sintering A major drawback of the Ni-Cd battery of , is the “memory effect”, which seriously restricts the use of the battery, but Li-ion does not have this problem at all.
5. Small self-discharge: The self-discharge rate of fully charged Li-ion stored at room temperature for 1 month is about 2%, which is much lower than 25-30% of Ni-Cd and 30-35% of Ni-MH.
6. Fast charging: 1C charging for 30 minutes can reach more than 80% of the nominal capacity, and phosphorus iron batteries can reach 90% of the nominal capacity in 10 minutes.
7. Working temperature: The working temperature is -25~45°C. With the improvement of electrolyte and positive electrode, it is expected to expand to -40~70°C.
Lithium-ion batteries also have some shortcomings, mainly in the following aspects:
1. Aging: Unlike other rechargeable batteries, the capacity of lithium-ion batteries will slowly decline, which is related to the number of uses and temperature. This phenomenon of decay can be expressed as a decrease in capacity or an increase in internal resistance. Because it is related to temperature, it is easier to reflect in electronic products with high operating current. Replacing graphite with lithium titanate appears to increase life.
2. Recovery rate: About 1% of new products from the factory need to be recycled for various reasons.
3. Intolerant of overcharge: When overcharged, the excessively embedded lithium ions will be permanently fixed in the lattice and cannot be released, which can lead to short battery life.
4. Intolerant of over-discharge: During over-discharge, the electrode deintercalates too much lithium ions, which can cause the lattice to collapse, thereby shortening the life.
In recent years, the application range of lithium-ion batteries has become more and more extensive. Lithium batteries are widely used in energy storage power systems such as water, fire, wind and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. At present, lithium batteries have gradually expanded to electric bicycles, electric vehicles and other fields.
