Pole manufacturing process is mainly coating and rolling process, of which the rolling process is very critical. Pole rolling process mainly to solve the following key issues:
Reduce the elongation and widening rate of the pole piece in the rolling process and reduce the damage rate of the pole piece coating material pore structure;
(2) Increase the thickness uniformity of the pole piece coating to improve the cross-sectional shape of the pole piece.
(3) improve the compaction density consistency of electrode material after pole piece rolling;
(4) Reduce the rebound of the surface electrode material after pole piece rolling;
The compaction density of the electrode surface coating material has a very important relationship with the electrochemical performance of the battery. A reasonable compaction density can effectively increase the electrochemical performance of the battery, reduce the contact resistance and the AC impedance of the electrode, and increase the participation in the electrochemical reaction Of the active material area, thereby significantly improving the electrochemical performance of the pole piece coating material.Li-ion battery pole piece manufacturing belongs to the field of high precision manufacturing, pole piece rolling is distinguished from the strip strip rolling, strip strip rolling is a metal Material longitudinal extension and lateral width of the process, the material density during rolling does not change the battery electrode surface of the electrode material is a pore structure, the positive and negative electrode during rolling electrode material is compacted, the density changes Pole rolling is a pore structure is filled, the coating particles gradually dense process.
Pole rolling the purpose of the following points:
1) to ensure smooth and smooth pole piece surface to prevent the burr on the coating surface piercing the diaphragm caused by short circuit;
2) the pole piece coating material compaction, reducing the volume of the pole piece to improve the energy density of the battery;
3) the active material, conductive particles closer contact to improve electronic conductivity;
4) to enhance the bonding strength of the coating material and the current collector to reduce the battery pole piece in the cycle of powder falling out of the situation, improve battery cycle life and safety performance.
Previously, the lithium battery pole piece rolling process basic analysis (click to read) The article shared the basic knowledge of rolling, some people asked the roller temperature and the battery pole piece and battery performance impact, this share a copy of the information, extract some of them Roller temperature of the lithium battery pole piece impact.Polar roll into two ways of cold rolling and hot rolling, the current foreign methods have been widely used hot rolling, while the domestic or use more cold-rolled way. Compared with cold-rolled, hot-rolled mainly has the following advantages:
1) can reduce about 50% of the pole piece rebound;
2) the thickness of the pole piece can be reduced to the thickness of the process requirement by using the smaller rolling force, and the rolling force can be reduced by 62% at the maximum;
3) to enhance the binding force of the coating material and the current collector to reduce the occurrence of powder discharge during the charge-discharge cycle and improve the cycle life of the battery.
Liu Binbin and other use of LiFePO4 as the cathode material, lithium as a negative electrode material, made of button lithium ion batteries to surface density, compaction density and thickness consistency of the three parameters as an indicator to examine the positive electrode sheet rolling temperature of the battery pole Film and the electrochemical performance of the battery.
Figure 1 different rolling temperature of the pole piece thickness
Fig. 1 shows the thickness curves of the 100μm-coated pole pieces at different rolling temperatures. As shown in the figure, as the rolling temperature increased from 20 ° C to 90 ° C and then increased to 160 ° C, 1.9μm reduced to ± 1.3μm and then reduced to ± 0.8μm, the uniformity of the thickness of the pole piece gradually increased, this is because as the rolling temperature increases, the pole piece coating deformation resistance decreases, the plastic becomes better, making the pole piece surface Thicker more uniform.
Fig.2 SEM image of the surface of the pole piece coating material at different rolling temperatures
Figure 2 shows the surface SEM images of the electrodeposited coating materials under different rolling temperatures. As shown in the figure, when the rolling temperature is 20 ° C, the particles in the surface part of the pole piece coating are more closely bonded and part of the area is not yet close enough, And there is a small amount of micropores. When the rolling temperature is 90 ℃, the degree of close bonding of the particles on the surface of the pole piece increases, the number of the micropores decreases and the number of micropores decreases. When the rolling temperature is 160 ℃, The degree of close bonding further increases, the area of close bonding further increases, and the number of micropores is further reduced. The different rolling temperature changes the deformation resistance of the coating so that the surface of the pole piece coating material has different densities.
Figure 3 Coulomb efficiency of each sample cell
Figure 3 is the Coulomb efficiency of each sample cell, 9 #, 8 #, 3 # were 20 ℃, 90 ℃, 160 ℃ under the conditions of the roller pressed piece of battery production can be seen from Figure 3, when the rolling temperature from 20 ℃ The coulombic efficiency of the samples also increased when the temperature was raised to 90 ° C. and then increased to 160 ° C. The coulombic efficiency is the ratio of the specific discharge capacity to the specific charge capacity during the same charge and discharge cycle and decreases as the thickness uniformity of the electrode plate increases , Coulomb efficiency will be increased accordingly.
Figure 4 Cyclic voltammetry performance of each sample cell
Figure 4 is the cyclic voltammetry performance curve of each sample, 9 #, 8 #, 3 # were 20 ℃, 90 ℃, 160 ℃ under the conditions of the roller electrode plate produced from the figure shows the experimental sample when the rolling temperature When the temperature is 160 ℃, the upward oxidation peak and the downward reduction peak have better symmetry, the peak position difference is the smallest, and the reversibility of charge and discharge is also the best, which proves that the coulombic efficiency must be high.
