Internal Structure & Series/Parallel Combination Principles of Lithium Battery Cells
Lithium battery cells are mainly manufactured in two mainstream forms: cylindrical cells and prismatic square cells. Most cells adopt a spiral winding internal design. A thin, high-permeability polyethylene separator film is placed between positive and negative electrode layers to avoid direct contact and internal short circuits.
For the positive electrode system: active materials cover multiple mainstream formulas, including lithium cobalt oxide, NCM nickel-cobalt-manganese ternary material, lithium manganese oxide and lithium iron phosphate (LFP). These cathode powders are coated onto aluminum foil that serves as the conductive current collector.
The negative electrode uses graphitized carbon as active material, evenly coated on copper foil to form the anode current collector. The entire winding core is immersed in organic liquid electrolyte to support ion movement during charge and discharge cycles.
For safety protection, standard lithium cells are fitted with safety relief valves. Most cylindrical cell models also add built-in PTC thermal cut-off components. When overheating, overcharging or external short-circuit failures occur, these safety parts cut off current flow and release internal pressure, effectively preventing cell swelling, leakage or fire risks.
Each single lithium cell has a nominal voltage of 3.7V for ternary/lithium cobalt/lithium manganese systems. Cells built with LFP cathode material deliver a stable nominal voltage of 3.2V. Single cells have fixed limited capacity and cannot satisfy high voltage or large power demand alone.
Manufacturers connect multiple cells via series or parallel assembly to build complete battery packs:
1.Series connection: Raise total output voltage, fit high-power equipment like electric motorcycles and household energy storage;
2.Parallel connection: Expand total capacity, extend continuous running time for e-bikes and portable power tools.
Mixed series-parallel layouts are widely used in customized lithium packs. By matching different cell combinations, we tailor finished battery solutions to meet voltage, capacity and power standards of consumer electronics, electric two-wheelers, industrial backup power and residential ESS systems.
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