Unlocking New Heights of Lithium Batteries Performance

In the manufacturing process of lithium batteries, the coating process is like a crucial bridge, directly determining the performance and quality of the battery. And coating uniformity is the cornerstone of this bridge, whose importance is self-evident.

I. Definition and Measurement Indicators of Coating Uniformity

Coating uniformity refers to the consistency of the coating thickness or glue amount distribution within the coating area. It can be measured by the deviation or deviation percentage of the coating thickness or glue amount at each point within a certain area relative to the average coating thickness or glue amount in that area, or by the difference between the maximum and minimum coating thickness or glue amount within a certain area. The coating thickness is expressed in µm, and the glue amount is expressed in g/㎡.
II. Manifestations and Impacts of Coating Uniformity Problems
(I) Problem Manifestations

1. Thickness differences occur on the surface of the electrode sheet, and the active material distribution is uneven. This is mainly due to insufficient precision of the coating equipment, improper control of process parameters, or quality problems of raw materials. This unevenness will lead to inconsistent electrochemical performance inside the battery and affect the overall performance.
2. There are areas with locally too thick or too thin coating. Locally too thick coating will reduce the energy density, increase the internal resistance, and affect the charging and discharging performance; locally too thin coating may lead to safety problems such as insufficient capacity and even short circuit.
(II) Impacts on Lithium Batteries

1. Inconsistent battery capacity affects the overall performance stability. Due to the different contents of active materials, the area with smaller capacity will reach the charging and discharging limit first, thereby affecting the overall performance of the battery.
2. Reduces the battery energy density and limits the energy storage capacity. Uneven coating will reduce the space utilization rate, and the locally too thick area will also increase the weight, further reducing the energy density.
3. Shortens the battery cycle life and reduces the reliability of use. Inconsistent electrochemical performance will cause local overcharging or overdischarging during the charging and discharging process, accelerating battery aging.
III. Solutions
(I) Optimizing Substrate Selection

Select substrates with high surface flatness, uniform thickness, and suitable material characteristics to directly improve the coating quality.
(II) Controlling the Properties of Adhesives
Precisely adjust the working viscosity of adhesives to enhance their affinity for the substrate surface and ensure coating uniformity and stability.
(III) Precision Machining of Coating Rolls

Strictly control the geometric tolerances of the coating rolls, improve their rigidity, ensure the quality of dynamic and static balance, optimize the surface quality, and ensure temperature uniformity to reduce coating deviations.
(IV) Precise Control of the Design and Operating Speed of the Coating Machine
A stable coating machine can improve the overall stability, enhance the precision and sensitivity of the combined pressure mechanism of the coating steel roll and rubber roll, and achieve precise coating.
(V) Optimizing Process Parameters** Precisely control parameters such as coating speed, thickness, and temperature to achieve uniform material distribution and consistent thickness and ensure coating quality.
(VI) Introducing Automated Operations** Advanced automated control systems can achieve precise setting and real-time adjustment of process parameters, reduce the interference of human factors, and improve product consistency and stability.
IV. Comparison of Coating between Lithium Iron Phosphate and Ternary Lithium Batteries

In the coating process of lithium batteries, lithium iron phosphate is more prone to coating problems compared to ternary lithium batteries. The slurry of lithium iron phosphate has a large surface area and strong adhesion, and is prone to the phenomenon of "getting thinner and thinner" during coating, and has higher requirements for equipment and processes, such as precise control of coating temperature and speed.Therefore, special attention needs to be paid to the optimization and control of the coating process of lithium iron phosphate batteries.
For the uneven coating problem of lithium iron phosphate batteries, improvements can be made in the following aspects:

1. Select "linear" conductive agents, such as VGCF (vapor-grown carbon fiber), CNTs (carbon nanotubes), and metal nanowires. In the electrode sheets composed of them and active materials, the conductive channels are more unobstructed, which can improve the bonding effect, reduce the amount of conductive agents and binders, improve polarization and cycle performance, and enhance heat dissipation and absorption performance, but they have high costs and the problem of dispersion needs to be solved.
2. Improve the dispersion effect. Improve the stability of the slurry by improving the formulation and batching steps and using methods such as ultrasonic dispersion to reduce the probability of particle contact agglomeration.
3. Improve the slurry handling process. Increase the stirring speed during slurry storage, shorten the handling time of the turnover barrel or switch to pipeline transportation to avoid slurry viscosity.
4. Adopt extrusion coating (spray coating). Although it can improve the surface texture and thickness unevenness of knife coating, the equipment price is high and the requirement for slurry stability is high.
V. Innovative Thinking on Improving the Coating Uniformity of Ternary Lithium Batteries

For the improvement of the coating uniformity of ternary lithium batteries, exploration can be carried out from the following aspects:
1. Customized Substrate Development: Cooperate with suppliers to develop coating substrates specifically for ternary lithium batteries to further improve the surface flatness and thickness uniformity, and optimize the material characteristics to better match the ternary materials.
2. Intelligent Adhesive System: Develop an intelligent adhesive system that can monitor and automatically adjust the viscosity in real time, and precisely control the performance of the adhesive according to different production conditions and material characteristics to ensure coating uniformity and stability.
3. Advanced Coating Roll Technology: Introduce new materials and manufacturing processes to improve the wear resistance, corrosion resistance, and thermal stability of the coating rolls, and reduce the coating unevenness caused by roll surface wear and temperature changes. At the same time, use big data analysis and artificial intelligence technology to monitor the operating status of the coating rolls in real time and carry out predictive maintenance to ensure that they are always in the best working condition.
4. High-Precision Coating Machine Upgrade: Continuously improve the design and manufacturing technology of the coating machine to improve the stability and precision control ability of the operating speed. Adopt advanced sensors and control systems to achieve real-time monitoring and precise adjustment of the coating process, and timely detect and correct any factors that may affect uniformity. For example, use laser measurement technology to monitor the coating thickness in real time and automatically adjust the coating parameters through the feedback control system to ensure thickness uniformity.
5. Process Parameter Optimization Algorithm: Develop a process parameter optimization algorithm based on machine learning and big data analysis, find the best combination of coating speed, thickness, and temperature parameters through the analysis of a large amount of production data, and maximize the coating uniformity. At the same time, use real-time monitoring data to continuously optimize and adjust the algorithm to adapt to different production conditions and material changes.
6. Full-process Automation Integration: Build a full-process automated production line from raw material preparation to coating completion to reduce the impact of human factors on coating uniformity. Through the integration of automated equipment and systems, achieve seamless connection and collaborative work of each link to improve production efficiency and product quality. For example, adopt an automated slurry preparation system, precise conveying equipment, and an intelligent coating machine control system to ensure the stability and consistency of the entire production process.

Coating process uniformity is a key challenge in lithium battery manufacturing. Through continuous innovation and optimization, we can open up new paths for the performance improvement and industrial development of lithium batteries. Whether it is lithium iron phosphate or ternary lithium batteries, we need to continuously explore and improve the coating technology to meet the growing market demand and higher performance requirements.