The structure of an EV battery pack includes cells for energy storage, a Battery Management System (BMS) for monitoring and protection, a thermal management system for temperature control, a protection board to prevent short circuits, an enclosure for physical protection, and connecting components for electrical connections. The assembly process starts with cell inspection and sorting to ensure consistency. Insulation treatment and precise welding follow to ensure safety and reliability. Modules are assembled from cells, integrated with the BMS, and placed into the enclosure for final assembly. Testing covers electrical performance, safety features, thermal management efficiency, and cycle life to ensure high quality and durability. Production line equipment such as sorting machines, labeling machines, welding devices, and comprehensive testing systems support efficient manufacturing and stringent quality control.

I. Structure of the Battery Pack

The EV battery pack mainly consists of the following components:

1. Cells: The core components of the battery pack, responsible for storing and releasing electrical energy. Common cell types include cylindrical, prismatic, and pouch cells.

2. Battery Management System (BMS): Monitors parameters such as voltage, current, and temperature of the battery, and achieves dynamic balancing, protection, and communication management.

3. Thermal Management System: Includes heating methods such as heating films, PTC heaters, and liquid heating, as well as cooling methods like natural cooling, forced air cooling, and liquid cooling.

4. Protection Board: Prevents short circuits and overcharging of the cells, ensuring the safety of the battery pack.

5. Enclosure: Typically made of plastic or metal materials, providing physical protection.

6. Connecting Components: Including busbars and flexible connectors, used for the electrical connections between cells.

II. Assembly Process

1. Cell Inspection: Testing parameters such as capacity, rate, and cycle life of the cells to ensure they meet usage requirements.

2. Sorting and Grouping: Selecting and pairing cells based on parameters like internal resistance and voltage to ensure consistency.

3. Insulation Treatment: Applying insulating paper to the positive terminals of the cells to prevent short circuits.

4. Welding Process: Using technologies such as laser welding and ultrasonic welding to connect cells with connecting components, ensuring a secure connection.

5. Module Assembly: Assembling cells into modules according to the design plan, either in series or parallel.

6. BMS Integration: Integrating the BMS into the module to ensure it can properly monitor the battery's condition.

7. PACK Final Assembly: Placing the modules into the enclosure and installing components such as the BMS and connectors.

III. Testing Process

1. Initial Inspection: Checking the integrity of the enclosure and the condition of the connectors, and identifying any obvious physical damage or defects.

2. Electrical Performance Testing:

   • Voltage Testing: Measuring the open-circuit voltage and working voltage of the battery module.

   • Current Testing: Measuring the current magnitude and variation trends of the battery module under different charging and discharging conditions.

   • Capacity Testing: Testing the available capacity and energy density of the battery module through charge-discharge cycles.

   • Internal Resistance Testing: Measuring the direct current resistance (DCR) of the PACK to identify any poor welding.

3. Safety Testing:

   • Short Circuit Detection: Ensuring the PACK has no short-circuit risks.

   • Relay Function Testing: Verifying the correct installation of relays and the normal operation of low-voltage drive.

   • High-Voltage Interlock Testing: Checking the high-voltage interlock loop of the high-voltage connectors.

   • Overcharge, Overdischarge, Short Circuit, and Overcurrent Testing: Evaluating the protection functions of the battery pack under abnormal conditions.

4. Thermal Management System Testing: Testing the impedance of heating films or the inlet and outlet temperatures of liquid cooling pipes to ensure the thermal management system works properly.

5. Cycle Life Testing: Assessing the performance and lifespan of the battery pack through charge-discharge cycles.

IV. Production Line Equipment

1. Sorting Machine: Used for sorting and grouping cells, such as the CAC-FX10D cylindrical battery sorting machine.

2. Labeling Machine: For automatically applying insulating paper.

3. Welding Equipment: Such as lithium battery spot welders, used for welding cells with connecting components.

4. Testing Equipment: Including comprehensive testing equipment for finished batteries and aging testing equipment.

5. Automation Equipment: Such as six-axis robots and vision recognition systems, used for high-precision assembly of modules.

6. Safety Protection System: Including a three-level protection system for safety during the testing process.

Through the detailed explanations of the structure, assembly process, testing process, and production line equipment, a comprehensive understanding of the production process of an EV battery pack can be obtained.

The production environment for a lithium battery PACK assembly line has strict requirements, which mainly include the following aspects:

1. Temperature and Humidity Control: The temperature and humidity of the production environment must be strictly controlled to prevent variations in material properties and ensure the high energy density and long cycle life of the cells. For example, some process steps require a dew point temperature of no more than -30℃.

2. Air Quality and Cleanliness: Air purification equipment should be installed to ensure the air quality of the production environment and avoid contamination of the battery assembly process by dust and other impurities, which could affect battery performance and quality.

3. Electrostatic Protection: The production process should have electrostatic protection capabilities to prevent damage to battery components from static electricity.

4. Noise Control: Major noise-emitting equipment, such as crushers, pumps, and fans, should be equipped with vibration reduction, noise elimination, and sound insulation measures. The boundary noise of the factory should comply with relevant standards.

5. Safety and Fire Prevention: The fire protection design of the building should comply with regulations, with a fire resistance rating of no less than Grade II. Formation areas, aging areas, and finished battery warehouses should be independent fire compartments, separated from other areas by firewalls and fire-resistant floors.

6. Environmental Monitoring and Assessment: Companies should establish a monitoring system to assess pollutant emissions and their impact on the surrounding environment, and keep records.

These requirements ensure the stability of the lithium battery PACK assembly process and the reliability of product quality, while also safeguarding the safety and sustainability of the production environment.