Practical Guide! Detailed Explanation of Lithium-ion Battery Packs

1. 1. Concept and Definition of Energy Storage PACK
2. An energy storage PACK, or battery pack, is the core power unit of an energy storage system. It combines numerous individual batteries through scientific series and parallel connections, and integrates a battery management system, thermal management system, structural components, electrical components, etc., to form a complete energy storage unit. In an energy storage system, the PACK is like the "heart," directly determining energy storage capacity, power output characteristics, etc. Its working principle is based on the movement of lithium ions between the positive and negative electrodes; during charging, lithium ions move from the positive electrode to the negative electrode, and vice versa during discharging. By integrating various components, the PACK can efficiently store and release electrical energy, providing stable power support for wind farms, photovoltaic power plants, etc., and is a key device for realizing energy storage and conversion.

2. Composition of Battery PACK

The important components of a battery PACK include four parts: individual battery modules, electrical system, thermal management system, enclosure, and BMS.

▷ Battery Module: If a battery PACK is likened to a human body, then the module is the "heart," responsible for the storage and release of electrical energy.

▷ Electrical System: Primarily composed of connecting copper busbars, high-voltage wiring harnesses, low-voltage wiring harnesses, and electrical protection devices. The high-voltage wiring harness can be considered the "main arteries" of the battery pack, continuously delivering battery power to the end load, while the low-voltage wiring harness can be seen as the "neural network" of the battery pack, transmitting detection and control signals in real time.

▷ Thermal Management System: Thermal management systems mainly employ two methods: air cooling and liquid cooling. Liquid cooling can be further divided into cold plate liquid cooling and immersion liquid cooling. The thermal management system is essentially like installing an air conditioner for the battery pack. Batteries generate heat during discharge; to ensure the battery operates within a reasonable ambient temperature and improve cycle life, the system temperature difference is generally required to be ≤5℃.

▷ Housing: Primarily composed of the housing, housing cover, metal bracket, panel, and fixing screws, it can be considered the "skeleton" of the battery pack, providing support, resistance to mechanical shock and vibration, and environmental protection.

▷ BMS: Short for "Battery Management System," it can be likened to the "brain" of the battery. It is primarily responsible for measuring battery parameters such as voltage, current, and temperature, and also has functions such as equalization. It can transmit data to the MES (Manufacturing Execution System).

3. Characteristics of Battery Packs

▷ Lithium-ion battery packs require high consistency in battery characteristics (capacity, internal resistance, voltage, discharge curve, lifespan);

▷ The cycle life of a battery pack is shorter than that of a single cell;

▷ It must be used under specific conditions (including charging and discharging current, charging method, temperature, etc.);

▷ After a lithium-ion battery pack is assembled, the battery voltage and capacity are significantly increased, requiring protection through charging equalization, temperature, voltage, and overcurrent monitoring;

▷ The battery pack must meet the designed voltage and capacity requirements.

4. Packing Methods

▷ Series-Parallel Composition: Battery modules are composed of individual battery cells connected in parallel and series. Parallel connection increases capacity without changing the voltage, while series connection doubles the voltage without changing the capacity. For example, 15 3.2V cells connected in series produce 48V (series boost); two 50Ah cells connected in parallel produce 100Ah (parallel capacity expansion).

▷ Cell Requirements: Select cells according to your design requirements. Parallel and series-connected cells must be of the same type and model, with differences in capacity, internal resistance, and voltage not exceeding 2%. Both soft-pack and cylindrical batteries require multiple series connections.

▷ Pack Manufacturing Process: Battery packing is achieved in two ways: First, through laser welding, ultrasonic welding, or pulse welding, commonly used methods with good reliability but difficult replacement. Second, through flexible metal contact, eliminating the need for welding and facilitating battery replacement, but potentially leading to poor contact.

Considering production yield, efficiency, and connection point internal resistance, laser welding is currently the preferred method for many battery manufacturers.

5. What constitutes a complete pack production line?

A lithium battery pack production line refers to a systematic collection of equipment and processes required to produce lithium battery packs.

It typically includes six core stages: cell manufacturing, cell testing, cell grading, cell assembly, packaging, and quality inspection. Among these, cell manufacturing and cell assembly are the most critical, directly impacting the performance and quality of the lithium battery pack.

▷ Cell Manufacturing: This is the first step in the production line and can be divided into the preparation of positive and negative electrode materials, cell forming, cell electrolyte injection, and cell maturation.

Cell forming is the most critical step, using methods such as winding, lamination, and stamping. It determines the shape and size of the cell, directly affecting its performance and lifespan.

Different forming methods are suitable for different lithium battery products, and the specific method depends on the situation.

▷ Cell Testing: This process mainly filters out substandard cells, ensuring the smooth operation of subsequent production stages. It mainly includes cell capacity testing, cell internal resistance testing, and cell temperature testing. These tests help manufacturers understand cell performance, identify problems in a timely manner, and make adjustments and optimizations.

6. Future Prospects of Lithium Battery Packs

With the continuous expansion of the energy storage battery market, PACK production lines are constantly being improved and refined to enhance battery pack performance and quality.

When automation becomes widespread, the pack process will shift from labor-intensive to technology-driven, focusing on parameter matching and battery pack design, while the rest will be handled by machines. In the future, the technological direction of lithium battery pack production lines will mainly include the following aspects: 1. Intelligentization: By introducing technologies such as artificial intelligence and the Internet of Things, the production line will be automated, intelligentized, and information-based, improving production efficiency and product quality.

2. Greening: Through the adoption of environmentally friendly materials and energy-saving and emission-reduction measures, the production process will be made green and sustainable.

3. Personalization: Customized production lines and services will be provided according to the needs and requirements of different customers, improving customer satisfaction and loyalty.

4. Safety: By strengthening safety management and risk control, the safety and stability of the production process will be ensured.