1. Cell Sorting
This is the first critical step to ensure the consistency of the battery PACK. Each individual cell undergoes rigorous testing for multiple key indicators, including:
Capacity: Measured using professional equipment to ensure the energy storage capacity of each cell meets the production requirements.
Voltage: Detected to screen out cells with abnormal voltage (too high or too low) that may affect the overall performance of the battery pack.
Internal Resistance: Tested to avoid cells with excessively high internal resistance, which could cause uneven current distribution and heat accumulation during charging and discharging.
Appearance: Checked manually or by machine vision for defects such as scratches, bulges, leakage or deformation on the cell surface.
Consistency: Cells are classified and grouped based on the above indicators. Only cells with highly consistent parameters are selected for subsequent assembly to prevent performance degradation or safety risks of the battery pack due to large differences between cells.
2. Module Assembly
After cell sorting, qualified cells are assembled into battery modules according to the design requirements of voltage and capacity. The main operations include:
Series-Parallel Connection: Cells are connected in series (to increase voltage) or parallel (to increase capacity) in a preset arrangement (such as square matrix, cylindrical array) to form the basic structure of the module.
Cell Fixation: Use fixtures, brackets or bonding materials to fix the cells in the module frame, preventing cell displacement caused by vibration or impact during use.
Separator Installation: Insulating separators (usually made of materials like PP or PE) are placed between adjacent cells to avoid short circuits caused by contact between cells.
Connecting Plate & BMS Integration: Install metal connecting plates (such as copper or aluminum) to realize current transmission between cells; at the same time, connect the Cell Monitoring Unit (CMU) of the Battery Management System (BMS) to the cells to prepare for subsequent parameter monitoring.
3. Welding & Connection
This link directly affects the electrical conductivity and structural stability of the battery module. Common welding processes and requirements are as follows:
Welding Processes: Select appropriate processes according to cell types and connecting plate materials:
Spot Welding: Widely used for cylindrical cells, with the advantages of fast speed and low cost, but requires strict control of welding current and pressure to avoid damaging the cell shell.
Laser Welding: Suitable for square and soft-pack cells, featuring high welding precision, strong joint strength and low contact resistance, which can effectively reduce energy loss during current transmission.
Ultrasonic Welding: Mainly used for connecting soft-pack cell tabs, using high-frequency vibration to realize solid-state welding of metals, without high temperature, thus protecting the cell electrolyte.
Quality Requirements: After welding, check the joint for defects such as false welding, cold welding or cracks; measure the contact resistance of the joint to ensure it is within the design range (usually less than 5mΩ) to prevent local overheating caused by excessive resistance.
4. Enclosure Encapsulation
The enclosure provides mechanical protection, environmental sealing and heat dissipation channels for the battery module, and the key operations include:
Enclosure Selection: Choose enclosures made of materials such as aluminum alloy, stainless steel or engineering plastics (like ABS, PC) according to application scenarios (e.g., automotive, energy storage). Aluminum alloy enclosures are preferred for their lightweight and good heat dissipation performance.
Sealing & Shock Absorption: Install waterproof rubber gaskets or foam gaskets at the joint of the enclosure to achieve IP67 or IP68 waterproof and dustproof levels; paste shock-absorbing materials (such as EVA foam) between the module and the enclosure to reduce the impact of external vibration on the cells.
Heat Dissipation Structure Installation: If the battery PACK adopts active heat management (such as liquid cooling or air cooling), install heat dissipation pipelines, fans or heat sinks in the enclosure, and ensure the tight fit between the heat dissipation components and the module to improve heat transfer efficiency.
5. Testing & Quality Inspection
This is a comprehensive evaluation of the assembled battery PACK to eliminate defective products. The main test items include:
Functional Testing:
BMS Function Test: Verify whether the BMS can normally monitor parameters such as cell voltage, current and temperature; test protection functions (overcharge, over-discharge, over-current, over-temperature) to ensure timely cutoff when abnormal conditions occur.
High-Voltage Insulation Test: Use an insulation resistance tester to detect the insulation performance between the high-voltage circuit of the PACK and the enclosure, requiring the insulation resistance to be greater than 100MΩ under a certain test voltage (usually 500V or 1000V).
Aging Testing: Place the battery PACK in a constant temperature and humidity chamber, perform 5-10 charge-discharge cycles (simulating actual use conditions), and monitor the capacity attenuation rate and voltage stability to screen out products with poor early cycle performance.
Capacity Testing: Charge the PACK to full capacity at a specified current (usually 0.2C), then discharge it to the cut-off voltage at the same current, and calculate the actual capacity. Only products whose actual capacity reaches 95% or more of the rated capacity are considered qualified.
Environmental Adaptability Testing: For special application scenarios, conduct tests such as high-temperature (60-85℃), low-temperature (-20--40℃) performance test, vibration test and impact test to verify the stability of the PACK in harsh environments.
6. Aging & Capacity Verification (Supplementary Testing)
Different from the preliminary aging test in the "Testing & Quality Inspection" link, this step focuses on long-term stability verification:
Long-Term Aging: Place qualified PACKs in a standard environment (25±2℃) for 30-90 days of standing or cyclic aging (50-100 cycles), and regularly detect parameters such as capacity, internal resistance and self-discharge rate to evaluate the long-term storage and cycle life of the product.
Capacity Consistency Recheck: After aging, re-test the capacity of each PACK to ensure that the capacity difference between different batches of products is within 3%, avoiding large performance differences in subsequent applications.
7. Final Packaging & Shipping
After all tests are passed, the battery PACK enters the final logistics preparation stage:
Labeling: Paste product nameplates on the enclosure, including information such as rated voltage, rated capacity, UN number (for dangerous goods transportation), production date and batch number.
Protective Packaging: Use cartons, pallets or shock-absorbing boxes for packaging; fill buffer materials (such as bubble film, corrugated paper) between PACKs to prevent collision damage during transportation. For export products, packaging must comply with the requirements of the International Air Transport Association (IATA) or International Maritime Dangerous Goods Code (IMDG Code).
Barcode Recording: Attach a unique barcode or QR code to each PACK, which is linked to the production data (such as cell batch, test results, aging records) in the MES system to realize full-life cycle traceability.
Storage & Shipping: Store qualified products in a dry, ventilated and temperature-controlled warehouse (0-40℃, relative humidity ≤65%); arrange transportation according to customer requirements, and provide documents such as dangerous goods transportation certificate (if applicable) and test report to ensure smooth customs clearance and delivery.
