Square battery
Square lithium-ion batteries typically refer to aluminum-cased or steel-cased square batteries. Square batteries are widely used in China. With the rise of lithium-ion batteries for automotive power in recent years, the contradiction between vehicle range and battery capacity has become increasingly prominent. Domestic power lithium battery manufacturers mostly use aluminum-cased square batteries with higher energy density because their structure is simpler. Unlike cylindrical batteries, which use high-strength stainless steel for the casing and have explosion-proof safety valves and other accessories, square batteries are lighter overall and have a relatively higher energy density. Square batteries are manufactured using two different processes: winding and stacking.
Cylindrical battery
Cylindrical batteries are primarily steel-cased cylindrical lithium iron phosphate batteries. These batteries are characterized by high capacity, high output voltage, good charge-discharge cycle performance, stable output voltage, high-current discharge capability, stable electrochemical performance, safe use, wide operating temperature range, and environmental friendliness. They are widely used in solar lighting, lawn lighting, backup power, power tools, and toy models.
A typical cylindrical battery structure includes: positive electrode cap, safety valve, PTC element, current cut-off mechanism, gasket, positive electrode, negative electrode, separator, and casing.
pouch battery
Pouch batteries are liquid lithium-ion batteries encased in a polymer shell. Their biggest difference from other batteries lies in the flexible packaging material (aluminum-plastic composite film), which is also the most critical and technically challenging material in pouch lithium-ion batteries. The packaging material and structure of pouch batteries give them many advantages.
Differences in technical characteristics between square, cylindrical and flexible packaging
1. Battery shape: Square lithium-ion batteries can be any size, while pouch batteries can be made thinner, which is something cylindrical batteries cannot do.
2. Rate characteristics: Due to the limitations of the process of welding multiple tabs to cylindrical lithium-ion batteries, the rate characteristics are slightly worse than those of the square multi-tab method.
3. Discharge platform: Since the same positive electrode material, negative electrode material and electrolyte are used, the discharge platform is theoretically the same. However, the internal resistance of square batteries is slightly higher, so the discharge platform is slightly higher.
4. Product quality: Cylindrical lithium-ion battery technology is very mature, and the probability of secondary cutting defects in the electrode sheets is low. Moreover, the winding process is more mature and automated than the stacking process. The stacking process is still using a semi-manual method, which has an adverse effect on the quality of the battery.
5. Electrode welding: The electrodes of cylindrical lithium-ion batteries are easier to weld than those of square lithium-ion batteries. Square batteries are prone to poor welding, which affects battery quality.
6. Packing: Round batteries are easier to use, so the packing method is simple and the heat dissipation is good. When packing square batteries, the heat dissipation problem must be solved.
