Professional Custom Lithium-Ion Battery Manufacturer
Lithium Battery Production Process
1、Production of Positive and Negative Electrodes(Pole piece production)
In the production of lithium battery electrodes, positive electrode materials, negative electrode materials, conductive agents, and binders are prepared. These are then mixed (typically using two methods: dry mixing and wet mixing; our factory uses wet mixing), coated (applying the mixed slurry onto copper and aluminum foil), dried in high-temperature ovens, and compressed using rolling equipment to produce electrodes. It’s crucial to note that mixing is fundamental for high-quality lithium batteries, as the processing quality of the positive and negative electrode slurries directly determines the electrode quality, thereby affecting the battery’s charge-discharge and storage performance. Thus, the first step to a good lithium-ion battery is producing high-quality slurry.
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
1.1 Slurry Preparation(mixing)
Slurry preparation involves adding the materials required for the positive and negative electrodes into an automatic mixer tank in the order specified by the SOP. The mixing process is carried out following the SOP requirements for mixing time, power, and environmental temperature and humidity. The positive and negative electrode slurries need to be filtered for iron removal using iron removal equipment.After mixing, the slurry’s viscosity, solid content, and fineness must be tested to ensure they meet SOP standards before proceeding to the next step.
- Positive Electrode Materials:Positive active material (e.g., lithium cobalt oxide, ternary materials, lithium iron phosphate, lithium manganese oxide), conductive agent, binder, NMP.
- Negative Electrode Materials:Negative active material (e.g., graphite), conductive agent, binder, deionized water.
- Key Control Points:Workshop temperature and humidity, material feeding sequence, NMP purity, deionized water conductivity, mixing time, power, slurry viscosity, solid content, and fineness.
1.2 Coating
Coating is the process of uniformly applying the qualified slurry onto metal foil and drying it to produce positive and negative electrodes. Positive electrodes are created by coating aluminum foil with positive slurry, while negative electrodes involve coating copper foil with negative slurry. It is essential to strictly control the single- and double-sided coating surface density and dimensions, ensuring single-sided density fluctuations are within ±2g/㎡. The coating dimensions directly affect the battery size (mainly thickness and width). Additionally, the appearance of coated electrodes is critical—there should be no pits, scratches, or exposed foil on the surfaces of positive or negative electrodes.There are three coating methods: transfer coating, extrusion coating, and roll coating. Each method has its own advantages and disadvantages. Our company uses the transfer coating method.
- Key Control Points:Workshop temperature and humidity, electrode surface density, dimensions, and appearance.
1.3 Rolling
Rolling compresses the coated electrodes to the designed compact density and thickness using rolling machines, ensuring smooth surfaces and tighter material integration. This process increases the electrode’s volumetric energy density. Positive electrodes generally require one pass due to minimal rebound, while negative electrodes, which rebound more significantly, typically require two passes. The rolling process must strictly control electrode thickness consistency, as this impacts the battery’s charge-discharge performance, safety, and overall thickness.
- Key Control Points:Workshop temperature and humidity, post-rolling electrode thickness.
1.4 Slitting
Slitting involves cutting the wide, rolled electrode sheets into narrower strips of the designed width. It is critical to monitor the service life of the slitting blades, as worn blades can cause burrs on the electrode edges, which are a major cause of internal short circuits, voltage drops, and even fires. Additionally, the slitting speed of the automatic slitting machine must be strictly controlled, as the long rolled electrodes and narrow cut strips are prone to breakage during the process. Electrodes must be inspected every two hours for edge burrs.
- Key Control Points:Workshop temperature and humidity, electrode width after slitting, and edge burrs after slitting.
1.5 Electrode Making
Electrode Making involves welding tabs (aluminum for the positive electrode and nickel or nickel-plated copper for the negative electrode) to the slit electrode strips using automatic tab welding machines, attaching insulating tape to the tabs, and cutting the electrode strips to the design length. Key attention points include ensuring no tab welding defects (as tab welding defects lead to high internal resistance in the cell) and monitoring burrs from tab cutting and electrode cutting. Maintenance and replacement of tab and electrode cutting blades should be performed regularly based on their service life.
- Key Control Points:Workshop temperature and humidity, tab welding quality, tab cutting burrs, electrode cutting burrs, and total electrode length.
2、Battery Cell Production
After producing the positive and negative electrodes, they are wound together with a separator to form the battery cell. The cell undergoes a short-circuit test, is sealed in an aluminum-plastic composite film, dried in a vacuum oven, filled with electrolyte, and subjected to high-temperature aging to ensure the electrolyte penetrates fully into the cell.
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Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
2.1 Winding
Winding involves rolling the positive electrode, negative electrode, and separator into a battery cell of the designed dimensions, with the separator placed between the electrodes. The winding equipment typically includes prismatic winding machines (for prismatic and irregular lithium-ion batteries) and cylindrical winding machines (for cylindrical lithium-ion batteries).
Dust control is critical during this process, requiring hourly vacuuming, as dust directly affects battery performance. The tension of the winding machine also needs strict control, as excessive tension can deform the battery during capacity grading. Regular inspections of the battery cell’s thickness and width are essential, especially for cells with tight dimensional tolerances.
- Key Control Points:Workshop temperature and humidity, dust control, winding tension, battery cell dimensions.
2.2 Battery Cell Short-Circuit Testing
This step uses an insulation short-circuit tester to measure the internal resistance between the positive and negative tabs of the battery cell, identifying and removing short-circuited cells to prevent defects from progressing to the next stage. The tester parameters must be adjusted according to each battery’s design specifications to avoid false positives or negatives.
- Key Control Points:Workshop temperature and humidity, tester parameters.
2.3 Aluminum-Plastic Composite Film Forming(ALP Pouch Foming)
The aluminum-plastic composite film, a lightweight material used to seal the battery cell, is formed by punching the film roll into shells of the required dimensions. This step must ensure zero defects such as cracks or pinholes, as these issues can cause electrolyte leakage or corrosion downstream. The shell’s pit depth must also match the battery cell dimensions to ensure proper sealing and appearance.
- Key Control Points:Workshop temperature and humidity, shell pit depth, and shell appearance (no cracks or pinholes).
2.4 Inserting Can And Sealing
The winding-completed cell is placed into a qualified aluminum-plastic composite film shell. A top-side sealing machine seals the shell’s top and sides. It is crucial to control the sealing thickness and flatness to prevent leaks. Over-sealing at the tab-end can cause the aluminum layer of the composite film to contact the tab, potentially forming a galvanic cell that corrodes the aluminum and leads to leaks or swelling. Most sealing machines are equipped with instruments to detect short circuits between the cell and the aluminum layer, which automatically rejects defective cells.
- Key Control Points:Workshop temperature and humidity, sealing equipment temperature, pressure, sealing thickness, and short-circuit detection.
2.5 Protective Film Application
A protective film is applied to safeguard the battery cell’s exterior. Since the outer nylon layer of the aluminum-plastic composite film is prone to scratches, a protective film slightly wider than the cell (0.5–1.0 mm) is applied to prevent imprints during subsequent processing. The film’s adhesive strength must also be controlled to balance adhesion and ease of removal.
- Key Control Points:Workshop temperature and humidity, protective film width, and adhesive strength.
2.6 Nozzle Expansion
The unsealed side of the cell’s airbag is expanded using a Teflon rod, facilitating subsequent electrolyte injection. A small airbag opening can cause electrolyte spillage during filling, leading to contamination. Care must be taken to avoid damaging the cell body during this process.
- Key Control Points:Workshop temperature and humidity, nozzle expansion quality.
2.7 Vacuum Baking
Cells with expanded nozzles are placed in high-temperature vacuum ovens for pulsed vacuum baking, reducing moisture to ≤100 ppm. Moisture and dust are critical factors affecting battery performance. Given that electrodes and cells can absorb moisture during handling, this step is vital to maintain low moisture levels before electrolyte injection. The dew point of the oven and transition areas must be controlled, typically ≤-20°C.
- Key Control Points:Dew point in ovens and transition rooms, cell moisture content after baking, baking parameters.
2.8 Electrolyte Injection
This step involves injecting electrolyte into the baked cells with moisture levels ≤100 ppm. Cells are pre-weighed, filled with a specified amount of electrolyte, and weighed again to confirm the electrolyte volume is within the design range. Insufficient electrolyte can impair charge-discharge, cycle, and safety performance, while excessive electrolyte can cause external defects.
- Key Control Points:Dew point in the injection chamber, electrolyte volume, and electrolyte type.
2.9 Primary Sealing
After electrolyte injection, cells are placed in vacuum ovens for 3–4 cycles to ensure complete electrolyte penetration into the core, fully wetting the electrodes and separator. The airbag edge is then heat-sealed. The sealing machine’s parallel alignment must be verified to ensure uniform sealing without weak spots.
- Key Control Points:Sealing equipment parameters (pressure, temperature).
2.10 High-Temperature Aging
The sealed cells are placed in a 45°C aging chamber for 24 hours to ensure complete electrolyte penetration into the raw materials.
- Key Control Points:Aging chamber temperature and duration.
3、Battery Cell Activation Process
By this stage, the physical structure of the battery cell has been completed. The following processes focus on activating the cell, converting its internal chemical energy, and conducting basic tests.
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Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
3.1 Formation
Formation is the first activation process for lithium-ion battery cells, where they are charged at a low constant current. During this process, reactions occur at the solid-liquid phase interface between the electrode material and electrolyte, forming a passivation layer called the Solid Electrolyte Interface (SEI) film on the electrode surface. The SEI film allows only lithium ions to pass through, preventing solvent molecules from co-intercalating and damaging the electrode material. This significantly improves cycle performance and battery lifespan. After formation, all cells undergo a low-voltage test to eliminate defective cells before moving to the next process. At this point, the cell has a voltage and officially becomes a functional battery. The formation temperature plays a critical role, as low temperatures hinder SEI film formation. For prismatic batteries, high-temperature pressure formation is used, while cylindrical batteries require a room temperature of at least 25°C.
- Key Control Points:Charging current, charging time, formation temperature.
3.2 Room Temperature Aging
After formation, the cells are rested at room temperature to allow stabilization and equilibrium of their internal electrochemical system.
- Key Control Points:Aging temperature, Aging time.
3.3 Secondary Sealing
Secondary sealing involves using automated equipment to vacuum out excess air from the cell and sealing it at high temperatures, cutting off the excess airbag. This step removes residual air and impurities to ensure the cell’s structural integrity. Inadequate vacuuming may cause soft prismatic cell bodies or micro gas pockets on cylindrical cells. Effective vacuuming requires a high-performance vacuum pump and precise vacuum control. As the final sealing process, any weak or excessive sealing can lead to electrolyte leakage or corrosion.
- Key Control Points:Vacuum level of sealing equipment, sealing time, sealing pressure, sealing temperature.
3.4 Capacity Testing
Capacity testing evaluates whether the battery meets its design expectations. Each cell undergoes a charge-discharge test using capacity testing equipment. The cells are charged at constant current and voltage and then discharged at constant current to measure discharge capacity. Charging voltage limits vary by nominal voltage:
- 7V nominal voltage: 4.2V charge limit.
- 8V nominal voltage: 4.35V charge limit.
- 85V nominal voltage: 4.4V charge limit.
For multi-series or multi-parallel battery assemblies, cells are grouped by capacity in 10mAh or 20mAh increments. Testing should be conducted at an ambient temperature of 25–35°C to ensure consistent results.
- Key Control Points:Testing environment temperature, charging/discharging parameters (current, time, voltage limits).
3.5 Full Dimension Inspection
Cells with protective films are individually placed into fixtures of specified thickness and width to ensure each cell’s dimensions meet design requirements.
- Key Control Points:Fixture dimensions.
3.6 OCV1 Testing
Open-circuit voltage (OCV) testing measures the voltage difference between the positive and negative electrodes without any load after the cell has reached chemical equilibrium. OCV1 is the first such test conducted at T1 time after sufficient resting to eliminate internal polarization effects. Voltage and internal resistance are measured.
- Key Control Points:Workshop temperature and humidity, stability of testing equipment.
3.7 High-Temperature Aging
After OCV1 testing, the cells are placed in a 45°C aging chamber for 48 hours. This step observes the internal electrochemical stability and balance, while also accelerating secondary reactions within the cells.
- Key Control Points:Aging chamber temperature, resting duration.
3.8 OCV2 Testing
OCV2 testing is conducted after high-temperature resting (T2 time) to remeasure voltage and internal resistance. This allows for calculating the self-discharge rate (K-value) to assess cell consistency and detect internal defects.
Self-discharge rate (K-value) = (OCV1 – OCV2) / Aging Time
Cells with micro short circuits, abnormal side reactions, or uneven active material will exhibit abnormal self-discharge rates, aiding in the early detection of defective products.
- Key Control Points:Workshop temperature and humidity, testing equipment stability, self-discharge rate standards.
4、Battery PACK Process
Battery PACK refers to the process of assembling multiple cells into a final battery product according to customer requirements and specifications, including attaching a protection circuit board (PCB/PCM).
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
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Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
4.1 Battery Cell Testing
Before the PACK process, the cells are tested for voltage and internal resistance to ensure all cells meet quality standards. For multi-series and parallel battery packs, cells are grouped based on SOP requirements for voltage, capacity, internal resistance, and self-discharge rate (K-value) to ensure consistency within each group. Additionally, each batch undergoes comprehensive testing after capacity grading, including initial performance, electrical performance, safety, mechanical properties, environmental resilience, and storage performance.
4.2 Tab Cutting
During lithium-ion battery design, the standard exposed length of positive and negative tabs is typically 10–12mm. Before PACK assembly, tabs are trimmed to specific lengths based on the pack design to ensure assembly efficiency and quality.
- Key Control Points:Post-cutting tab length.
4.3 Welding of PCB/PCM
Welding the PCB/PCM to lithium-ion batteries serves as a critical step to ensure battery safety and provide functional support. The PCB/PCM integrates several functions, such as overcharge and over-discharge protection, temperature monitoring, and stable current output. It also protects the battery from overload damage while enabling its connection to external devices.
Welding Methods
1、Laser Welding(Description: A non-contact welding method using a laser beam to heat and melt the metal surfaces for connection.)
Advantages:
① Fast and precise, no additional filler materials required.
② Suitable for electrodes of various shapes and sizes.
Disadvantages:
① High equipment cost and operational complexity.
② Requires skilled operators and a higher technical threshold.
2、Ultrasonic Welding(Description: High-frequency vibrations generate heat to fuse metal components.)
Advantages:
① No preheating required, eliminating thermal treatment steps.
② Fast and precise, environmentally friendly (no waste gases or residues).
③ Applicable to various electrode shapes and sizes.
Disadvantages:
① Welding interface must be clean to ensure quality.
② Limited depth for thicker materials.
③ May produce noise and vibration during operation.
3、Soldering(Description: Utilizes heating equipment (e.g., soldering iron) to melt solder wire and bond it to metal surfaces.)
Advantages:
① Simple and cost-effective for small-scale production.
② Easy to repair and rework.
Disadvantages:
① High thermal impact may damage internal structures (e.g., separators and electrolytes), posing safety risks.
② Low mechanical strength, unsuitable for high mechanical stress.
③ Lower efficiency compared to automated methods.
4、Dual-Needle Spot Welding (Description: Two electrode needles contact the surface of the welding materials, releasing a high-current pulse to rapidly heat and weld the contact points.)(used by our company)
Advantages:
① High efficiency with welding times in milliseconds, ideal for large-scale production.
② Stable and consistent welding quality with automated control.
③ Broad applicability for different metal thicknesses, such as copper, aluminum, and stainless steel.
④ Lower equipment cost compared to laser welding, with simpler operation and maintenance.
Disadvantages:
① Limited to thinner materials (e.g., ≤1mm) due to equipment power constraints.
② Welding strength is lower than that of laser welding.
③ Clean surfaces are essential to prevent weak bonds or high contact resistance.
Regardless of the welding method, static protection measures must be in place to prevent damage to electronic components on the PCB/PCM.
Among the various welding methods, our company has adopted dual-needle spot welding as the primary method for connecting PCB/PCM to lithium-ion batteries. This choice is based on its efficiency, consistent quality, and cost-effectiveness for large-scale production.
Key Notes:
Regardless of the welding method used, strict electrostatic protection measures are essential to prevent damage to the electronic components on the PCB/PCM due to electrostatic discharge (ESD).
- Process Control Points: Welding Quality,Ensure there are no weak welds, over-welds, or reversed polarity connections between the positive and negative terminals.
4.4 Insulation Taping
After tab welding, high-temperature insulating tape is applied to the PCB/PCM to prevent short circuits between electronic components and the battery’s positive/negative tabs or the aluminum layer of the aluminum-plastic film.
- Key Control Points:Tape adhesion and insulation effectiveness.
4.5 Fixing of PCB/PCM
The PCB/PCM is secured to the battery using high-temperature tape or insulating adhesive to stabilize the battery pack structure and ensure consistent dimensions.
- Key Control Points:Adhesive strength and final product dimensions.
4.6 Comprehensive Testing
After completing the PACK process, every battery undergoes comprehensive testing for voltage, internal resistance, overcurrent protection, and other parameters to ensure it meets customer requirements.
- Key Control Points:Testing parameters strictly follow SOP requirements.
5、Shipping
The batteries are packaged according to customer specifications, including a shipping inspection report. Each box is labeled with clear identifiers such as battery model, batch number, and shipping date. Finally, the logistics company is arranged to deliver the products to the customer.
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Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
Mixing
Automatic feeding and vacuum mixing
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