Hierarchical structure of lead acid batteries

The individual cells, modules, and systems of a battery constitute the three levels of the battery energy storage system
1. Battery cell
definition:
The battery cell is the smallest unit for electrochemical energy conversion, consisting of core components such as positive electrode, negative electrode, electrolyte, separator, and outer shell. The nominal voltage is usually open circuit voltage (such as 2V for lead-acid battery cells and 3.2-3.7V for lithium-ion battery cells)
Function and Features:
Directly participate in chemical reactions to achieve the mutual conversion of electrical energy and chemical energy.
Performance directly affects the capacity, lifespan, and safety of the overall system.
Common types include cylindrical, soft pack (polymer), and square aluminum shell.
Example:
In new energy vehicles, lithium iron phosphate or ternary lithium batteries are typical single-cell batteries.
2. Battery module
definition:
The module is composed of multiple individual batteries combined in series or parallel, and integrates protection circuits, heat dissipation structures, and casings, which can directly provide electrical energy output
Function and Features:
Enhance capacity or voltage: Increase capacity in parallel and voltage in series.
Structural protection: The design of the shell and frame ensures physical stability between individual units, preventing damage from vibration or impact.
Fundamentals of Thermal Management: Some modules have built-in temperature sensors or heat dissipation channels to provide support for subsequent system level management.
Example:
Multiple lithium battery cells are welded in parallel and packaged into modules to form standardized energy storage units.
3. Pack/System battery system
definition:
The battery system is further composed of multiple modules, and integrates a battery management system (BMS), thermal management system, electrical connections, and safety protection devices to form a complete power supply or energy storage system.
Function and Features:
Energy output: meets the application requirements of high voltage and large capacity (such as electric vehicles and energy storage power stations).
Intelligent management: BMS monitors real-time parameters such as voltage, temperature, and current to ensure safe operation and optimize charging and discharging efficiency.
Safety protection: including safety devices, fire isolation layers, and emergency power-off mechanisms to prevent risks such as thermal runaway.
Example:
The battery pack of new energy vehicles usually consists of dozens of modules connected in series, supplemented by BMS and liquid cooling system, forming a complete power battery system.
example:
The structure of lead-acid battery systems is relatively simple (such as a 12V system consisting of six 2V cells connected in series), while lithium battery systems are more complex and require multiple layers of protection and management.