What is the Battery Module, Cell, and Pack?
When discussing battery modules, it is essential to distinguish them from two other terms: battery cell and battery pack. All three are forms of batteries but differ based on their application stages. Here's a breakdown:
- Battery Cell: The smallest unit of a battery. A single cell generates a certain amount of energy, and its performance directly affects the overall system.
- Battery Module: A mid-sized unit, comprising several battery cells connected in series or parallel, housed in a common structure. The module ensures that the cells are supported, fixed, and protected, contributing to temperature control and overall structural integrity.
- Battery Pack: The largest unit, consisting of multiple modules combined with a Battery Management System (BMS) and other management components. The battery pack serves as the final energy source, such as those used in electric vehicles.
What is a Battery Module?
The battery module is an intermediate unit between the battery cell and the battery pack. It consists of a combination of battery cells housed together and connected externally. Its primary function is to protect and fix the position of the cells, ensuring their performance is not damaged by deformations or overheating.
Most lithium battery modules available on the market are used for electric vehicles. Manufacturers often offer standard modules with fixed parameters, and if these do not meet customer needs, customized modules can be created.
Comparison: Battery Module vs Cell
Battery cells are the foundation of the module and directly impact its performance. Selecting the right type of cells is the first critical step. The cells are connected either by bolting or welding, with laser welding being the more common method for electric vehicle modules due to its durability in handling vibrations and shocks.
Li-ion battery cells can be divided into soft packs, cylindrical cells and square cells： depending on their structure.
| Soft pack | cylindrical | square | |
| Advantages |
The external structure has small effect on the cell, the material used for the packaging has a low mass and the energy density of the battery is high. |
High process maturity, mature shell structure, low process manufacturing cost. |
High protection for the cell, can ensure the explicit conduction of internal heat by reducing the thickness of the single cell, and the safety performance of the cell is greatly improved. High capacity of single cells, less cells required for battery pack. |
| Disadvantages |
The sealing process of large capacity batteries is more difficult and relatively unreliable, and the mechanical strength of the aluminium-plastic composite film used is low, and the life of the aluminium-plastic composite film limits the life of the battery. |
Uneven distribution of current density on the collector, resulting in an uneven reaction of the individual internal parts. The heat generated in the battery cell is difficult to dissipate quickly and the accumulation poses a safety risk to the battery. |
Complex internal structure, high demands on the production process. The energy density of the cells was low in the early days, and in recent years there has been a major breakthrough in this area. |
Comparison: Battery Module vs Pack
A battery pack consists of several battery modules and a BMS. For smaller battery packs, cells can be used directly without the need for a module, reducing weight and size. However, in applications like electric vehicles, where high voltage, energy density, and safety are key factors, battery modules offer distinct advantages.
Modules allow for improved heat dissipation, structural strength, and maintenance ease. They are also easier to replace individually, as opposed to dealing with issues at the cell level, making modules an essential component in large-scale battery systems like those used in EVs.
| bolt-on | weld-on | |
| Advantages |
1. Simple and easy connection, low cost 2. Easy to assemble and disassemble, convenient for maintenance |
1. Good consistency and low contact resistance. 2. The contact resistance is stable because the contact surface is closed and not easily oxidized. |
| Disadvantages |
1. Surface is prone to corrosion. 2. Influenced by preload force, surface quality, unstable contact resistance |
High equipment cost and high initial investment. |
Conclusion
Battery modules play a crucial role in providing a balance between capacity, safety, and durability. They offer structural integrity, modularity, and standardized production, making them ideal for demanding applications such as electric vehicles, where energy efficiency and ease of maintenance are paramount
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