Many people simply equate lithium battery packs with "battery assembly." However, this process is actually a highly integrated system engineering process that combines electrochemistry, mechanical design, electronics, and thermal management. Every step is crucial to the performance, safety, and lifespan of the battery system.
1. Cell Selection: The "Foundation" of the Packing Process, Consistency is Key
Building a reliable battery system begins with cell selection. Core requirements include performance consistency screening and on-demand selection. Voltage, internal resistance, and capacity are the three core parameters of a cell, and rigorous screening is required to ensure that each cell's parameters are perfectly matched. If a cell's capacity is 10% lower than others, it will charge and discharge first during long-term charge-discharge cycles, accelerating aging and potentially causing uneven charging and discharging across the entire battery pack, potentially posing a safety risk.
2. Structural Design: Balancing Safety and Practicality in Space
Battery packs must adapt to the end product and withstand the rigors of complex environments. Structural design requires finding the optimal balance between space, weight, and strength. For example, battery packs for new energy vehicles must be designed to closely fit the vehicle's spatial layout while also possessing a high-strength structure to withstand vibrations, bumps, and even collisions during driving, protecting the battery cells from crushing. Energy storage battery packs must also consider cabinet installation dimensions and ensure stacking stability. To reduce energy consumption, especially for automotive applications, battery packs utilize lightweight materials such as aluminum alloy and carbon fiber. However, lightweighting does not mean cutting corners. Engineers utilize topological optimization to strengthen the structure at key stress points, reducing weight while increasing rigidity and protecting the battery cells from damage due to vibration and impact.
3. Electrical Connection: A Precise Path for Current and Signals. Even a single error is essential. After the battery cells are assembled, reliable electrical connections are crucial for powering the battery pack and are also a high-risk area for safety hazards. The busbar shape has been optimized to further reduce heat generation. The high-voltage wiring harness in the battery pack, responsible for transmitting high currents, must be thickened and kept away from heat sources. Low-voltage signal lines, responsible for transmitting data, must be routed away from the high-voltage harness to prevent EMI from causing erroneous data and misinterpretation by the BMS. All connections are insulated to prevent electrical creepage and breakdown. The entire battery pack must also meet IP ratings to ensure safety in rainy, submerged, and other environments.
4.Thermal Management: The Battery's "Thermostat," Temperature Determines Lifespan
Excessively high lithium battery temperatures accelerate aging and may even cause thermal runaway. Excessively low temperatures lead to a sudden drop in capacity and slower charging. The thermal management system acts as the battery pack's "thermostat," maintaining an optimal temperature range of 25-40°C. Regarding heat dissipation, new energy vehicle battery packs often use liquid cooling. Liquid cooling plates embedded within the battery pack circulate coolant to remove heat, ensuring more uniform temperature control. Air cooling is cost-effective and simple, making it suitable for applications like energy storage batteries, where heat generation is relatively low. In winter, the battery pack activates its heating function, preheating the battery cells using PTC heating plates or electric heating films to prevent reduced battery life in winter.
5. BMS: The "Brain" of the Battery Pack, the Core of Intelligence
If the battery cell is the "heart" of the battery pack, then the BMS is the "brain," responsible for monitoring, protecting, and optimizing battery performance. The BMS uses sensors to collect real-time data on each cell's voltage and temperature, as well as the current flowing through the entire battery pack. It then uses algorithms to estimate the SOC and SOH, providing the user and the vehicle's control system with constant visibility into the battery's condition. Even if the cell parameters initially match, variations can develop over time. The BMS uses passive balancing (using resistors to discharge high-voltage cells to level the voltage) or active balancing (using energy transfer for greater efficiency and power savings) to prevent overcharging and discharging of individual cells, thereby extending the life of the entire battery pack. The BMS also has a series of preset "safety red lines." If any of these parameters, such as voltage, temperature, and current, are exceeded, the circuit will be immediately disconnected to prevent further damage. This serves as the battery pack's "last line of defense."
In addition to the BMS, battery packs must also incorporate multiple safety features from other perspectives, such as electrical and mechanical safety. Before leaving the factory, battery packs must undergo three major tests: electrical performance, safety, and environmental adaptability. This ensures they can function properly in diverse environments and regions.
