Understand the small amount of lithium battery materials
How to act as a connection
Only when graphite and carbon black particles are uniformly dispersed in the slurry and electrode can lithium-ion batteries show better performance. Because graphite and carbon black particles are hydrophobic and non-polar, they aggregate in water without additives and cannot be dispersed.
When the graphite anode and carbon black are dispersed, the anionic dispersant is the main one, supplemented by the nonionic dispersant, which can obtain a stable dispersion system. Generally, the manufacturers uses SBR and CMC as binders, CMC is called a thickener, and SBR is called a binder. Take a look at the technology used by top 10 lithium battery anode material factories in this process.
● Reasons for choosing synergy as a binder
Although the adhesion is very strong, it cannot be stirred at high speed for a long time. In addition, the dispersion effect is not good, and too much SBR will produce greater swelling, so it is not used alone as a binder.
The thickener can play a good role in the dispersion of cathode graphite. It is brittle if the binder is only equipped with graphite slurry with CMC. In the post-production process, the graphite will collapse during rolling, and serious powder loss will occur during slitting.
The reasonable proportion of CMC and SBR mixing in the homogenization process can make up for each other’s defects, so the cathode slurry has good coating performance. Among them, the binder mainly plays the role of bonding, and CMC plays the role of thickening.
Different graphite and carbon blocks need to be optimized to obtain the best melting properties. From the composition of the battery cathode, the specific surface area is the smallest, and the binder film covers the surface of the graphite particles.
As well as the presence of the middle with the graphite particles, the formation of a connection network between them acts as a bridge. At the same time, the particles have no binding force, and they are combined in the slurry to form a film, so that the binding force can be formed to bind the particles.
Effect on graphite dispersion
When only the low content of thickener in the slurry has a binder, the graphite particles are agglomerated in the homogenization process and cannot be dispersed well.
When the ratio of CMC to graphite is moderate, SBR is added to the slurry to disperse graphite particles and the viscosity and modulus of the slurry will be reduced.
Graphite plays a leading role in the dispersion of slurry, and is preferentially adsorbed to the surface of graphite. When the amount of addition is very low, the binder will be adsorbed on it, which has a certain effect on the dispersion of graphite.
With the increase of the amount of addition, the adsorption of the surface also increases, and the binder cannot be adsorbed on the surface, which in turn does not play a role in the dispersion of graphite.
When a certain amount is reached, the excess CMC binding that cannot be adsorbed on the graphite causes the gravitational force to be greater than the repulsive force, which will cause agglomeration between particles. Therefore, CMC plays a key role in the dispersion of slurry.
Effect of lithium battery drying temperature
Lithium-ion batteries strictly control moisture during the production process, and increasing the drying temperature of the battery cell is the main way to reduce moisture.
During the cell drying process, the binder will be heated at a high temperature, and a binder with different properties may affect electrode performance. Therefore, it is also very important to study the effect of cell drying on battery maintenance and binder performance.
The thermal properties of water-based binders were analyzed, and crosslinking occurs in LA132 when the temperature is too high. As a result, the adhesion of the active material to the current collector is damaged, and the battery cycle performance deteriorates. With another pole piece, the performance is almost unaffected by the drying temperature, and crosslinking does not occur when heated.
Effect on low temperature performance
Reduce the growth of RCT cells under low temperature conditions, and the application of SBR can effectively improve the low temperature characteristics of batteries.
During charging. Its membrane covers a specific surface, and the most effective way to embed graphite in the lithium ion transmission process is to bypass the SBR film to reach the surface.
The electrolyte is the mobile carrier of lithium ion transport of lithium batteries, and the better the wetting performance of the two, the more conducive to the conduction of lithium ions between interfaces. Different SBRs behave differently with the same electrolyte.
Low temperature battery discharge data using different SBRs showed that wetting performance was improved by 4%. At 0 °C, the battery is 15% lower. As can be seen here, the impact on lithium ion battery storage is significantly improved.
Effect on anode expansion
Graphite anode often encounter problems such as material loss and large thickness rebound. The expansion of the anode pieces has an important impact on the cycle performance and internal resistance of the battery, so we need to understand the effect of the binder on the expansion of the cathode piece.
CMC mainly plays a thickening role in sludge. SBR plays a strong bonding role, and it is precisely because of the high elasticity of SBR that the cathode sheet will have a large degree of thickness rebound after the rolling process.
- The higher the elasticity and strength, the lower the expansion rate of the cathode.
- The expansion of the cathode is related to the pressure experienced during rolling and the elasticity and strength of the binder.
- The content is the same, the pressure is the same when rolling, and the higher the elastic modulus and strength of SBR, the lower the expansion rate of the cathode.
- The smaller the content, the smaller the pressure during rolling, and the smaller the expansion rate.
Anode expansion causes the core deformation of the battery, affecting the lithium ion transport channel, which in turn has a serious impact on the battery cycle performance. Elasticity affects the rebound of the electrode, and the larger the modulus of elasticity, the smaller the rebound of the electrode thickness.
In the selection of battery materials, priority should be given to selecting binders with high elasticity, and the material ratio adjustment process should be reduced as much as possible, which can improve the cycle life of the battery.
In summary, the slurry process in the manufacturing process of lithium ion batteries improves the microstructure and increases the amount of energy storage film under specific conditions through the optimized design of the binder.
Improve the low temperature performance of the battery by improving the wettability of the electrolyte. Although small, it plays a key role in overall performance. In the lithium battery manufacturing process, people pay more attention to and explore a reasonable ratio and process with CMC in order to fully play a role in battery performance.