Reduced floating of Li-ion battery binders -Lithium - Ion Battery Equipment
The occurrence of binder floating is mainly due to drying conditions. The drying conditions mainly include drying method (electric heating, infrared heating or steam heating), drying temperature (temperature selection), oven setting (several sections of oven), temperature gradient, etc.
Liu Ping of China Electronics Technology Group Co., Ltd. studied the drying method of a certain cathode slurry. The effect of drying temperature and oven setting on the peel strength of the pole piece is shown in the figure:(Lithium - Ion Battery Equipment)
Comparison chart of peeling strength of positive pole pieces in different temperature ranges
In the figure, the Z axis is the peel strength value, the X axis is the distribution of the temperature interval, and the Y axis is the temperature setting of the interval. Here, 2/2 in the X-axis represents that the drying section consists of four sections of ovens, where the oven temperature settings are the same for every two sections.
Similarly, 3/1 means that the temperature settings of the three ovens are the same, and the oven temperature settings of the other section are different. It can be clearly seen from the figure that no matter which interval is distributed, the peel strength curve shows the same trend distribution. The peel strength in the temperature interval containing 150°C is relatively high, and the peel strength in the 2-2 interval setting is significantly higher than 1-3 and 3-1 intervals.
Under the same oven temperature range setting, such as 2-2, it can be seen that the peel strength of the pole piece is the largest under the temperature setting of 90°C-150°C, and the peel strength is the lowest under the temperature range setting of 120°C-150°C, which means that at 120°C At the drying temperature of ℃, the migration of the binder has a great influence on the cohesiveness of the binder.
The above example illustrates a method for selecting the temperature of the drying section and setting the temperature zone in the coating process for your reference. With the improvement of the requirements for coating efficiency, the coating speed has increased from the initial ten meters per second to seventy or eighty meters per second, and the selection of temperature and the control of temperature zone are becoming more and more important.
In order to prevent the floating problem of the binder during the drying process, the control of the temperature zone will select a three-stage or four-stage or even a multi-stage temperature gradient distribution. Generally, the low temperature is used to prevent the sprayed pole piece from entering the high temperature zone. The defect caused by the quick, interruption is the high temperature range. In this range, the crystallinity of PVDF is high, and it has good adhesion, which has a positive effect on the internal resistance and cycle performance of the fabricated battery.
In the third stage, the temperature is lowered to a lower temperature to prevent shrinkage and coating defects after the excessively high temperature is suddenly cooled. Due to the different active materials and PVDF materials used by each company, it is necessary to conduct individual experiments to determine the optimal drying temperature and temperature zone setting conditions.
The selection of conditions needs to meet the performance and production efficiency of lithium-ion batteries at the same time. In order to improve efficiency, battery quality cannot be ignored, nor can production efficiency be reduced by blindly pursuing perfect performance to increase production costs. The drying method with multi-gradient temperature settings can effectively Reduce the degree of uneven distribution of the binder caused by the floating of the PVDF binder, and also ensure the production efficiency of the pole piece.
Liu Ping of China Electronics Technology Group Co., Ltd. studied the drying method of a certain cathode slurry. The effect of drying temperature and oven setting on the peel strength of the pole piece is shown in the figure:(Lithium - Ion Battery Equipment)
Comparison chart of peeling strength of positive pole pieces in different temperature ranges
In the figure, the Z axis is the peel strength value, the X axis is the distribution of the temperature interval, and the Y axis is the temperature setting of the interval. Here, 2/2 in the X-axis represents that the drying section consists of four sections of ovens, where the oven temperature settings are the same for every two sections.
Similarly, 3/1 means that the temperature settings of the three ovens are the same, and the oven temperature settings of the other section are different. It can be clearly seen from the figure that no matter which interval is distributed, the peel strength curve shows the same trend distribution. The peel strength in the temperature interval containing 150°C is relatively high, and the peel strength in the 2-2 interval setting is significantly higher than 1-3 and 3-1 intervals.
Under the same oven temperature range setting, such as 2-2, it can be seen that the peel strength of the pole piece is the largest under the temperature setting of 90°C-150°C, and the peel strength is the lowest under the temperature range setting of 120°C-150°C, which means that at 120°C At the drying temperature of ℃, the migration of the binder has a great influence on the cohesiveness of the binder.
The above example illustrates a method for selecting the temperature of the drying section and setting the temperature zone in the coating process for your reference. With the improvement of the requirements for coating efficiency, the coating speed has increased from the initial ten meters per second to seventy or eighty meters per second, and the selection of temperature and the control of temperature zone are becoming more and more important.
In order to prevent the floating problem of the binder during the drying process, the control of the temperature zone will select a three-stage or four-stage or even a multi-stage temperature gradient distribution. Generally, the low temperature is used to prevent the sprayed pole piece from entering the high temperature zone. The defect caused by the quick, interruption is the high temperature range. In this range, the crystallinity of PVDF is high, and it has good adhesion, which has a positive effect on the internal resistance and cycle performance of the fabricated battery.
In the third stage, the temperature is lowered to a lower temperature to prevent shrinkage and coating defects after the excessively high temperature is suddenly cooled. Due to the different active materials and PVDF materials used by each company, it is necessary to conduct individual experiments to determine the optimal drying temperature and temperature zone setting conditions.
The selection of conditions needs to meet the performance and production efficiency of lithium-ion batteries at the same time. In order to improve efficiency, battery quality cannot be ignored, nor can production efficiency be reduced by blindly pursuing perfect performance to increase production costs. The drying method with multi-gradient temperature settings can effectively Reduce the degree of uneven distribution of the binder caused by the floating of the PVDF binder, and also ensure the production efficiency of the pole piece.
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