Lithium batteries can be broadly categorized into two types: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain lithium in its metallic state and are rechargeable.

The Tesla electric car we know is using 18650 lithium-ion batteries through the series-parallel connection of the battery plate. With the increasing popularity of new energy vehicles, the power battery industry has also become hot!

Here we will learn to understand the manufacturing process of lithium batteries through the form of illustrations.

Below is a graphic explanation of the 21 production processes of lithium batteries:

Step 1: Negative electrode homogenization

Negative electrode homogenization is an important part of the battery manufacturing process, which involves mixing the negative electrode active material, conductive agent and binder together, and making them evenly dispersed and forming a stable paste through kneading.

 

After mixing, the paste needs to be treated to remove air bubbles and impurities and improve the quality of the paste.

Processing methods include ultrasonic degassing, vacuum degassing, etc. These methods are highly effective in removing air bubbles to improve paste filling, while removing minute gases and moisture to improve paste stability and processability.

 

Step 2 Anode homogenization

Anode homogenization is a key step in the lithium battery manufacturing process, which involves mixing the anode active material, conductive agent, binder and other additives into a uniform slurry for subsequent coating, pressing and other process steps.

 

Advantages of the positive electrode homogenization process:

The advantage of the positive electrode homogenization process is that it can ensure that the positive electrode material is fully mixed with the conductive agent, binder and other raw materials, thus improving the performance and stability of the battery. In addition, by precisely controlling the proportion of slurry and process parameters, stable and reliable cathode materials can be prepared, which provides a strong guarantee for the overall performance of the battery.

 

Step 3 Coating

Coating technology refers to the coating of adhesives and other fluids on the substrate through the coating equipment, and then through the conveyor winding system will be coated with the fluid coating through the oven drying or curing way to make the substrate to add a layer of film with special functions. This technology has a wide range of applications in industrial manufacturing, especially in industry, people’s livelihood, electronics and optoelectronics, communications, new energy, construction and dozens of other industries.

 

 

Coating technology has the following advantages:

High efficiency: the coating machine is able to realize high-speed, continuous coating operation and improve production efficiency.

Uniformity: Through precise control system and coating system, uniformity of coating thickness can be realized to ensure product quality.

Flexibility: Coating technology is applicable to a wide range of substrates and coating materials, with wide applicability.

Environmental protection: modern coating technology focuses on environmental protection and energy saving, adopting low-pollution and low-energy equipment and processes.

 

Step 4 Laminating

The laminator breaks down the bonded anode and cathode materials into smaller particles by means of the high-speed rotating shaft and laminating rollers, or firmly fixes multiple sheets together to form a more compact positive and negative electrode structure. The laminator generally consists of a spindle, laminating wheel, feeding device, transmission system and control system. The laminator delivers the raw lithium battery material to the machine’s feed opening, and then the laminating wheel begins to rotate under the action of the main shaft. The laminator clamps the material between the two laminating wheels, and then compresses the material with force to compress it into the desired shape and size.

Technical Characteristics

High efficiency: the laminator can realize high-speed and continuous operation and improve the production efficiency.

Uniformity: Through precise control system and rolling equipment, uniformity of coating or compaction layer can be realized to ensure product quality.

Flexibility: The laminator is suitable for a wide range of materials and scenarios, and can be adjusted and optimized according to the needs of different production processes.

Environmental protection: modern mills focus on environmental protection and energy saving, adopting low-pollution and low-energy equipment and processes.

 

Step 5 Slitting

Slitting is an important part of the battery manufacturing process, the main function is to longitudinally slit the coated and completed larger width film sheet, divide it into many, and wind it into a certain width specification of the upper and lower single rolls. The slit poles will be used in the subsequent battery assembly process.

 

 

Step 6: Baking

The main purpose of baking is to remove moisture and volatile organic compounds from the pole piece to improve the stability and reliability of the pole piece. The baking process ensures better performance of the wafers in the subsequent cell assembly process.

 

 

Baking Process

Preparation stage: Before baking, the baking equipment needs to be checked and preheated to ensure that the equipment operates normally and reaches the set baking temperature. At the same time, it is also necessary to pre-treat the pole piece, such as cleaning, drying, and so on.

Baking stage: Put the pre-treated pole piece into the oven and bake it according to the set baking time and temperature. During the baking process, the temperature, humidity and other parameters in the oven need to be monitored to ensure the stability and safety of the baking process.

Cooling phase: After baking, the pole pieces need to be taken out of the oven and cooled. The cooling process not only helps to protect the wafers from thermal damage, but also helps to stabilize the performance of the wafers.

 

 

 

Step 7 Winding

The main purpose of winding is to tightly wind the positive electrode, negative electrode and diaphragm components together to form a cell with a certain capacity. This process has a significant impact on the performance, capacity and safety of the battery. Through precise winding control, it can ensure that the material inside the battery is evenly distributed, improving the efficiency and safety of the battery.

 

 

In the battery winding process, some key parameters such as winding speed, tension and alignment will have an impact on the performance and quality of the battery. Specifically:

Winding speed: too fast or too slow winding speed may have an impact on the quality of the cell. Too fast a speed may lead to uneven distribution of material inside the cell, while too slow a speed may affect production efficiency.

Tension: The amount of tension directly affects the tightness and capacity of the cell. Appropriate tension can make the internal materials of the core fit closely together, improving the capacity and efficiency of the core; however, too much tension may lead to deformation or rupture of the core, affecting the safety and life of the core.

Alignment: Alignment refers to the degree of alignment of the positive pole piece, diaphragm and negative pole piece in the winding process. Good alignment ensures even distribution of materials inside the battery cell, improving the performance and safety of the battery cell.

 

Step 8 Casing

The casing process is a key part of the battery production process, which involves placing the cells into the battery casing to protect the cells and ensure the safety and performance stability of the battery.

 

Casing process flow:

Cell Assembly: The cells are removed from the production line and placed on the assembly equipment through automated or manual operation.

Battery case assembly: The battery case is removed from the production line, cleaned and placed on the assembly equipment.

Sealant application: Sealant is applied at specific locations on the battery case to ensure the sealing performance of the battery. The sealant should be applied evenly and in the right amount to avoid too much or too little.

Placement of battery cells: Remove the assembled battery cells from the assembly equipment and place them precisely in the battery case. There should be a tight fit between the battery cell and the battery shell without any gap.

Battery case closure: Dock the battery case of the assembled battery cell with the other half of the battery case and make it completely closed by automated or manual operation. The closed battery shell should be flat, no deformation, no liquid leakage.

Welding fixation: Use the welding process to fix the two halves of the battery shell to ensure that the structure of the battery is solid. Welding temperature, time and pressure should be controlled to avoid damage to the battery.

Step 9 Spot Welding

Battery spot welding process is a technology to weld the electrode material and wire strips on the battery assembly together. It utilizes the principle of resistance heating to instantaneously heat the electrodes and wires at a high temperature, causing the welding materials to melt at high temperatures and form a welded joint connection. This process is widely used in electric vehicles, energy storage devices and other fields.

 

Spot welding process flow

Preparation:

Clean the surface of the electrode and wire to ensure that there is no dust and oil.

Check whether the welder and power supply are working properly.

Set welding parameters:

Determine the appropriate welding current, time and pressure according to the battery type and material. The setting of these parameters is critical to the quality of the weld and needs to be precisely controlled.

Install the battery assembly:

Assemble electrodes and wires to the welding fixture to ensure accurate and stable position.

Perform welding:

Place the welding fixture on the welding machine and press the start button to begin welding. During the welding process, the welding machine heats and pressurizes the electrodes and wires according to the preset parameters, causing them to melt and form a welded joint.

Inspect the quality of the weld:

Check the appearance of the welded joints for uniformity, smoothness and absence of defects such as cracks and porosity.

Use quality inspection tools to test the resistance, strength and other indicators of the welded joints to ensure that the weld quality meets the requirements.

Repair welding or trimming:

If any welded joint is not qualified, it can be processed by patch welding or trimming until it meets the quality requirements.

Spot welding process optimization and development

Automation: Introduce robot welding technology to improve production efficiency.

Parameter optimization: Improve welding quality and stability by studying battery materials and welding parameters.

Development trend: With the rapid development of electric vehicles, energy storage equipment and other fields, the battery spot welding process will continue to play an important role and develop in the direction of more efficient, more stable and more reliable.

 

Step 10 Baking

The main purpose of the battery baking process is to remove moisture from both the inside and outside of the battery to improve the stability and reliability of the battery. Additionally, baking aids in solder circulation, ensuring the quality and reliability of the solder joints, as well as simulating the aging process of the battery, accelerating the aging of the battery to validate the performance and life of the battery.

The specific process of battery baking process includes the following steps:

Temperature setting: Set the appropriate baking temperature according to the type and requirements of the battery. Different battery materials and structures may require different baking temperatures.

Heating preheating: Place the battery cells or battery packs into the baking equipment for heating preheating, so that the internal temperature of the battery rises gradually. The preheating process helps the water inside the battery to evaporate gradually.

Stable baking: After the internal temperature of the battery reaches the set temperature, it is kept for a certain period of time to allow the evaporation of water inside the battery and complete welding circulation. This time depends on the type of battery and requirements and usually takes anywhere from a few hours to tens of hours.

Cooling Shutdown: The heating is stopped and the cell or battery pack is removed and cooled so that its temperature is gradually reduced. The cooling process not only helps to protect the battery from thermal damage, but also helps to stabilize the battery’s performance.

Inspection and Verification: Baked batteries are inspected for appearance, electrical performance tests, etc. to verify the baking effect. These tests can ensure that the battery meets the quality requirements and has good performance.

 

Step 11 Liquid injection

Battery manufacturing liquid injection refers to the process of controlling the amount of liquid electrolyte and the injection time, so that the liquid electrolyte is injected into the battery from the liquid injection port. Its main purpose is to form ion channels to ensure that the battery in the charging and discharging process there are enough lithium ions in the positive and negative electrode sheet migration, to achieve reversible cycle.

 

Battery liquid injection process usually includes the following steps:

Pre-treatment:

Prepare the battery and liquid injection materials, select the appropriate volume and ratio.

Clean the battery to ensure that there are no impurities and residual electrolyte inside the battery.

Charge the battery to a certain level of charge.

Liquid injection:

Clean the liquid injection tool and prepare the liquid injection material.

Control the amount and speed of liquid injection to avoid too much or too little. Pay attention to avoid air bubbles during liquid injection, you can place the liquid injection material for a period of time in advance to let it remove air bubbles naturally.

At the end of the liquid injection, pay special attention to the cleaning of the mud plug to avoid blocking the liquid injection hole.

Placement:

Leave the battery for a period of time after liquid injection to allow the liquid injection to fully penetrate into the battery. Depending on the type of battery and the amount of liquid injection, usually between 2 and 4 hours.

Control the temperature and environment during the placement period to avoid too high or too low temperature.

Testing:

Test the battery at the end of the placement to ensure that the quality of the liquid injection is good. The test mainly includes battery charge, battery voltage, battery temperature and other parameters.

If you find that there is a problem with the quality of the liquid injection, you need to re-inject the liquid.

 

Step 12 Weld caps

Welding the caps refers to the process of fixing the battery caps (also known as battery protection caps) on the battery by welding. The main purpose of this step is to protect the inside of the battery from external environmental damage, such as dust, moisture, corrosion, etc., and to ensure safe isolation between the positive and negative electrodes of the battery to prevent short circuits.

 

Process optimization and development

With the continuous development of battery technology and the expansion of application areas, the battery manufacturing welding cap cap process is also continuously optimized and developed. For example, the use of advanced welding equipment and technology, such as laser welding, ultrasonic welding, etc., can improve the quality and efficiency of welding; at the same time, through the optimization of welding parameters and process flow, can reduce production costs and improve product performance.

 

 

Step 13 Cleaning

Battery manufacturing cleaning is an indispensable part of the battery production process, the purpose of which is to remove the dirt, impurities and residues on the surface of the battery to ensure the cleanliness of the battery components, thereby improving the performance and life of the battery.

Cleaning method:

●Soak method: Soak the battery components in the cleaning agent for a period of time, and then rinse them off with deionized water.

●Spray method: Spray the cleaning agent with a sprayer, and then rinse it off with deionized water.

●Ultrasonic cleaning method: Put the battery components into the cleaning agent and clean them in an ultrasonic cleaner to effectively remove the dirt.

 

 

Step 14 Dry Storage

Dry storage is an important part of the battery manufacturing process to ensure that the internal environment of the battery is dry and free of moisture. Moisture will have a negative impact on the battery, such as reacting with lithium ions, resulting in reduced battery performance, shortening the life of the battery, and may even cause safety accidents. Therefore, dry storage is an indispensable step in the battery manufacturing process.

 

 

Environmental requirements for dry storage
Temperature control: The temperature of the battery preparation and drying room should be controlled between 20~30℃ to ensure that the battery is stored in a suitable temperature range. This temperature range helps maintain the internal stability of the battery and prevents the battery from overheating or overcooling.

Humidity Control: Humidity is the most critical factor in dry storage. In general, the humidity in a battery preparation dry room should be maintained between 30 and 50%. Too dry environment may lead to water loss in the battery, affecting the battery performance; while too humid environment is likely to lead to oxidation, corrosion and other problems in the battery support structure.

Air Quality Requirements: The air quality in the battery preparation dry room also needs to be controlled. The concentration of particulate matter in the air must not be higher than 100,000 / cubic meter, and a certain degree of filtration. This is because particulate matter is easy to adhere to the surface of the electrode sheet, affecting battery performance.

Dry storage technology and methods
In the battery manufacturing process, dry storage is generally used in two ways: vacuum drying and oven drying. Vacuum drying is achieved by reducing the ambient pressure so that the water evaporates at a lower temperature, thus achieving the purpose of drying. Oven drying is the use of hot air circulation, the battery is placed in the oven, through the heating of water evaporation, to achieve the drying effect.

 

 

Step 15 Detecting Alignment

The alignment of the battery mainly refers to the accuracy of the relative position and angle between the internal components of the battery (such as electrodes, poles, etc.). This alignment not only relates to the physical structure of the battery, but also directly affects the electrochemical performance and safety of the battery.

 

Alignment Inspection Process

Preparation stage: Select appropriate testing equipment and set up suitable testing conditions (e.g. light source brightness, contrast and focal length, etc.).

Position the battery to be tested: Place the battery to be tested on the testing equipment and ensure that the internal components of the battery are smooth and unobstructed.

Capture images: Use the inspection equipment to capture images of the internal components of the battery, and capture images at different angles and positions as required.

Image Processing: Import the captured image into the image processing software for image enhancement, filtering and smoothing to reduce noise and improve image quality.

Edge Detection: Use the edge detection algorithm to find the boundaries of the components inside the cell and calculate their positions and angles.

Calculate Alignment: Calculate the alignment of a component based on its boundary position and angle. This usually involves geometric criteria or statistical methods such as parallelism, concentricity or offset.

Determine alignment: Based on the pre-set alignment criteria, determine if the cell to be tested is qualified. If it fails, the cause of the problem needs to be further analyzed and appropriate corrective measures taken.

Record the results: Record the alignment test results, including the identification of the battery to be tested, testing time and alignment values.

Alignment requirements and standards
For different types of batteries and different application scenarios, the alignment requirements and standards may vary. However, in general, the alignment of a battery should be controlled within a small range to ensure its performance and safety. For example, the double-sided alignment of lithium batteries is usually required to be within 0.02mm.

 

Sixteenth step: Shell coding

Shell coding is used to label the battery shell with variable information such as product lot number, barcode, 2D code, etc. to ensure product traceability and identification.

 

 

Coding requirements

Printing code content: need to label the product lot number, bar code, two-dimensional code and other variable information, to ensure that the bar code and two-dimensional code recognizable rate.

Spraying position: The spraying position should be precise and should not exceed the product outline to ensure the clarity and aesthetics of the spraying information. The specific spraying position may vary depending on the type, size and process requirements of the battery.

Coding quality: The printer needs to be based on the speed of the production line, and at the same time to ensure that the coding speed and coding quality. The code should be clear and accurate, without misplacement, deformation, blurring and other phenomena.

Ink adhesion and drying time: the ink adhesion and drying time need to be ensured.

Step 17 Formation

Formation, also known as activation, is an important process in the battery manufacturing process. Its main purpose is to activate the electrochemically active substances inside the battery through certain charging and discharging means after the battery production is completed, especially the formation of a stable solid electrolyte interface membrane (SEI membrane), in order to prevent the irreversible depletion of the electrolyte and lithium ions, so as to ensure the high performance and safe operation of the battery.

 

Chemical formation is a complex process that usually includes the following steps:

Initial charging: During the initial charging process, a reduction reaction occurs at the negative electrode to form a stable SEI film. This process is critical to the performance of the battery as it directly affects storage performance, cycle life, multiplier performance and safety.

Stepped current charging: In order to form a good SEI film and improve productivity, charging is generally done by stepping the current from small to large. This charging method helps to gradually activate the active substances inside the battery and ensures the uniformity and stability of the SEI film.

Discharge and Recharge: After completing the initial charge, the battery undergoes a process of discharge and recharge. This cycle helps to further activate the battery and verify its performance.

 

Step 18 OCV Measurement

OCV is the potential difference between the positive and negative terminals of a battery in an open circuit state, i.e. without an external load connected. It directly reflects the electrochemical state inside the battery and is closely related to the state of charge (SOC), capacity and health of the battery. Therefore, OCV measurement is important for evaluating battery performance, predicting battery life, and detecting battery failures.

 

Principle and method of OCV measurement

Measurement principle: OCV measurement is done by disconnecting the battery from the external load, waiting for a period of time so that the internal chemical reaction of the battery reaches equilibrium, and then measuring the open-circuit voltage of the battery. During this process, the lithium ions inside the battery migrate in the electrolyte and eventually reach equilibrium, at which time the measured voltage is the OCV.

Measurement method:

Static test method: the battery is placed in a discharged state, after a period of time to measure the OCV. this method is simple and easy to implement, but the test time is longer.

Rapid test method: use the battery separator and other equipment to quickly discharge the battery, and then measure the OCV, this method can shorten the test time, but may have a certain impact on the battery performance.

Charge-discharge cycle test method: Record the change of OCV of the battery through multiple charge-discharge cycles. This method can evaluate the performance and stability of the battery more comprehensively.

 

Step 19 Normal Temperature Storage

Normal temperature storage is an important part of ensuring stable battery performance and quality.

 

Temperature range:

Short-term storage (e.g., less than 6 months): Batteries should be stored at temperatures between -20°C and 35°C, with humidity within the range of 65±20% RH. This temperature range ensures that the battery’s performance will not be affected by excessive high or low temperatures during storage.

Long-term storage (e.g., more than 6 months): It is recommended that batteries be stored in a dry environment between 10°C and 25°C with a humidity of 65±20% RH. In addition, batteries for long-term storage should be charged to 50% to 70% and a complete charge/discharge should be performed periodically (every 3 months) to prevent irreversible loss of capacity due to self-discharge resulting in too low a charge.

Environmental Requirements:

The battery should be stored in a dry, non-corrosive gas, well-ventilated environment, away from water, fire and high temperature.

The storage environment should be kept clean to avoid sharp objects causing damage to the battery.

 

Step 20 Compacting

Battery compartmentalization is simply understood as capacity sorting and performance screening for the battery. By charging and discharging each piece of lithium battery, the computer records the data of each test point, so as to get the capacity and internal resistance of each piece of battery, and determine the quality level of lithium battery.

 

Purpose of Capacity Separation

For different types of batteries and different application scenarios, the alignment requirements and standards may vary.

However, in general, the alignment of a battery should be controlled within a small range to ensure its performance and safety.

For example, the double-sided alignment of lithium batteries is usually required to be within 0.02mm.

Sixteenth step: Shell coding

Shell coding is used to label the battery shell with variable information such as product lot number, barcode, 2D code, etc. to ensure product traceability and identification.