The composition, method and parameter analysis of lithium energy storage battery system PACK!
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The lithium-ion battery PACK technology is an essential component in the energy storage industry. Let’s explore some fundamental knowledge about battery PACK together.
The lithium-ion battery PACK, also known as a battery module, refers to the manufacturing process of lithium-ion batteries, involving packaging, encapsulation, and assembly. It involves connecting multiple lithium-ion individual cells in a series-parallel configuration while considering factors such as mechanical strength, thermal management, and BMS compatibility. Its important technical aspects include overall structural design, welding and processing control, protection level, and active thermal management systems. For example, when two batteries are connected in series or parallel and assembled into a specific shape according to customer requirements, it is referred to as a PACK.
2. Composition of battery PACK
The composition of a battery PACK primarily includes several important components: individual cell modules, electrical systems, thermal management systems, enclosures, and BMS (Battery Management System).
▶Battery module:If we compare a battery PACK to a human body, then the module can be considered as the “heart,” responsible for storing and releasing electrical energy.
▶Electrical system:It mainly consists of components such as connecting copper busbars, high-voltage harnesses, low-voltage harnesses, and electrical protection devices. The high-voltage harness can be seen as the “major arterial blood vessels” of the battery PACK, continuously delivering battery energy to the end load. The low-voltage harness can be seen as the “neural network” of the battery PACK, transmitting real-time monitoring signals and control signals.
▶Thermal management system:The thermal management system mainly includes 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 can be likened to installing an air conditioning system for the battery PACK.
Batteries generate heat during discharge mode. To ensure that the batteries operate within a reasonable temperature range and to enhance their cycle life, it is generally required to maintain a temperature difference within the system of ≤5°C.
▶Cabinet：The enclosure of the battery PACK is mainly composed of components such as the casing, casing cover, metal bracket, panels, and fixing screws. It can be seen as the “skeleton” of the battery PACK, providing support and protection against mechanical impacts, vibrations, and environmental hazards.
▶BMS：Battery management system The Battery Management System (BMS) can be considered as the “brain” of the battery. It is primarily responsible for measuring parameters such as battery voltage, current, and temperature. It also includes functionalities such as cell balancing. The BMS can transmit data to a Manufacturing Execution System (MES) for further analysis and monitoring.
3. Features of battery PACK
- A lithium-ion battery PACK requires a high level of consistency in terms of capacity, internal resistance, voltage, discharge curve, and lifespan.
- The cycle life of a battery PACK is generally lower than that of an individual battery due to inherent differences among the batteries in the PACK, leading to faster degradation of certain batteries during use.
- The battery PACK needs to be used under specific conditions, including charging and discharging currents, charging methods, and temperature. This is to ensure the safety and stable performance of the battery.
- After the formation of the lithium-ion battery PACK, there is a significant increase in battery voltage and capacity. Therefore, it requires protection measures such as charge balancing, temperature monitoring, voltage monitoring, and overcurrent monitoring.
- The battery PACK must meet the required voltage and capacity specifications as per the design requirements.
4. PACK methods
Series and parallel connection：A battery module is formed by connecting individual cells in series and parallel. Parallel connection increases the capacity while keeping the voltage constant, while series connection doubles the voltage while keeping the capacity constant. For example, if 15 cells with a voltage of 3.2V are connected in series, the total voltage would be 48V, which is a series voltage boost. Similarly, if two cells with a capacity of 50Ah are connected in parallel, the total capacity would be 100Ah, which is a parallel capacity expansion.
Battery core requirements：According to the design requirements, it is necessary to select battery cells for parallel and series connections that are consistent in type and model. The differences in capacity, internal resistance, and voltage values should not exceed 2%. Whether it is pouch cells or cylindrical cells, they both require multiple series and parallel combinations.
PACK’s craftsmanship：Battery PACKs are typically assembled using two methods: laser welding, ultrasonic welding, or pulse welding. These are commonly used welding techniques known for their reliability, although they may not be easily replaceable.
Energy storage battery laser welding equipment
The second method involves using elastic metal contacts. The advantage of this method is that it eliminates the need for welding, making battery replacement easier. However, it may also lead to poor contact reliability.
Taking into account production yield, efficiency, and the internal resistance of the connection points, laser welding is currently the preferred choice for many battery manufacturers.
5. How to understand the technical parameters of battery PACK
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- Combination method：1P24S
In the context provided, “S” represents the series connection of battery cells, while “P” represents the parallel connection of battery cells. Therefore, “1P24S” indicates a configuration of 24 cells connected in series and 1 cell connected in parallel. When cells are connected in series, the voltage is multiplied. In this case, the rated voltage would be 3.2V multiplied by 24, resulting in a total voltage of 76.8V.
- Rated Capacity:280Ah
The rated capacity of a battery refers to the capacity at which the battery can operate continuously under rated working conditions. The rated capacity of a battery, denoted as C and measured in ampere-hours (Ah), is the product of the discharge current in amperes (A) and the discharge time in hours (h). Therefore, a rating of 280Ah means that the battery can be discharged continuously for 2 hours at a maximum discharge rate of 0.5C.
- Rated energy:21.504kWh
The rated energy (Wh) of a battery is calculated by multiplying the nominal capacity (Ah) by the nominal voltage (V). Therefore, the total energy that a battery can deliver is determined by both its capacity and voltage.