What are the advantages and disadvantages of
18650 lithium batteries and soft pack batteries in the field of automotive power battery applications?
The key lies in the different forms of electrolytes
As the two mainstream power batteries in the current market, 18650 batteries and lithium polymer soft pack batteries are distinguished by the packaging material of the outer shell. 18650 batteries are generally enclosed in a steel shell (18 represents a diameter of 18mm, 65 represents a length of 65mm, 0 represents a cylindrical battery), and the structure of the internal electrode plates and separators is wound. The outer packaging of lithium polymer soft pack batteries uses aluminum-plastic film, and the internal electrode sheets and separators are stacked layer by layer.
Although the appearance and internal structure are different, the principles of these two types of batteries are basically the same. Both types of batteries have a positive electrode, a negative electrode, and an electrolyte. The positive electrode material is generally lithium cobalt oxide, lithium nickel cobalt manganese oxide (ternary material), lithium iron phosphate, or lithium manganese oxide, while the negative electrode material is generally graphite. The electrolyte is lithium hexafluorophosphate solution.
The main difference between the two lies in one of the internal materials of the battery - the shape of the electrolyte is different: the electrolyte inside the lithium polymer flexible battery is polymer, generally gel or solid, while the electrolyte inside the 18650 battery is generally liquid.
Each has its own advantages and disadvantages, with different application fields
18650 lithium batteries and lithium polymer soft pack batteries each have their own advantages and disadvantages. At present, the automation level of 18650 battery production is high, and the consistency and safety of the battery have reached a high level. In addition, the small size and light weight of the battery itself make it unique in terms of modularity and standardization in system development. Many people believe that using 18650 batteries as the power source for new energy electric vehicles is the optimal choice at this stage.
However, 18650 batteries also have an unavoidable drawback, which is their low individual capacity (generally around 2-4 Ah). This requires a very large number of batteries for the 18650 battery in application, making the battery management system that maintains cell consistency and battery heat dissipation even more complex.
Compared with 18650 batteries, lithium polymer soft pack batteries have higher single cell capacity and advantages such as thinning, arbitrary area, and arbitrary shape (ultra-thin batteries such as 0.33mm and 0.50mm can be produced). Their main disadvantages are poor consistency and mechanical strength. Based on the characteristics of lithium polymer pouch batteries, lithium polymer pouch batteries are increasingly being used in fields such as mobile phones, laptops, and power banks. However, due to the poor conductivity and high internal resistance of colloidal (or solid) electrolytes, lithium polymer soft pack batteries are rarely used in electric vehicles.
Soft pack batteries are not all lithium polymer batteries
Since lithium polymer soft pack batteries are rarely used in electric vehicles, what type of battery is Nissan Leaf's stacked soft pack battery?
In fact, although lithium polymer pouch batteries are generally referred to as pouch batteries, not all pouch batteries are lithium polymer batteries because pouch batteries can also use liquid electrolytes. The battery of Nissan Lingfeng is a soft pack battery that uses liquid electrolyte.
Whether it is lithium polymer pouch batteries or pouch batteries with liquid electrolyte as the internal material, pouch batteries are generally encapsulated with aluminum-plastic film. The thickness of aluminum-plastic film is thin, and its mechanical strength is poor. In extreme situations such as car collisions, aluminum-plastic film is easily damaged, leading to accidents. This is the main drawback of using soft pack batteries in new energy vehicles.
It is reported that in order to ensure safety, Nissan Lingfeng has added an aluminum shell outside the battery module composed of four individual units to ensure safety. Nevertheless, battery leakage remains the fatal flaw of Nissan Leaf batteries, which are often criticized as the "leakage king" among car enthusiasts.
