In the field of automotive power battery applications, where are the advantages and disadvantages of 18650 lithium battery and soft battery?
 
The difference in electrolyte form is the key
 
As two mainstream power batteries on the market, 18650 batteries and lithium polymer soft pack batteries are distinguished by the package material of the casing. The 18650 battery is generally a steel casing package (18 indicates a diameter of 18 mm, 65 indicates a length of 65 mm, and 0 indicates a cylindrical battery), and the structure of the inner electrode sheet and the diaphragm is a wound type. The lithium polymer soft pack battery is made of aluminum plastic film, and the inner electrode sheet and the diaphragm are stacked (stacked layer by layer).
 
Although the shape and internal structure are different, the principles of the two batteries are basically the same. Both batteries have a positive electrode, a negative electrode and an electrolyte. The positive electrode material is generally lithium cobaltate, lithium nickel cobalt manganese oxide (ternary material), lithium iron phosphate or lithium manganate, and the negative electrode material is generally graphite, and the electrolyte is Lithium hexafluorophosphate solution.
 
The main difference between the two is that the electrolyte is different in one of the internal materials of the battery: the electrolyte inside the lithium polymer soft pack battery is a polymer, generally a gel or a solid, and the electrolyte inside the 18650 battery is generally liquid.
 
Each has its own advantages and disadvantages
 
18650 lithium battery and lithium polymer soft pack battery have their own advantages and disadvantages. At present, 18650 battery production has a high degree of automation, battery consistency and safety have reached a high level, and the battery itself is small in size and light in weight, which makes it unique in the modularization and standardization of system development. Many people believe that the use of 18650 battery as the source of power for new energy electric vehicles is the best choice at this stage.
 
However, the 18650 battery also has the disadvantage of being unavoidable, that is, the monomer capacity is low (generally around 2~4Ah). This makes the 18650 battery require a large number of batteries in the application, and the battery management system that maintains cell consistency and battery cooling is more complicated.
 
Compared with the 18650 battery, the lithium polymer soft pack battery has a high capacity, and has the advantages of being thinner, arbitrarily aread, and arbitrarily shaped (it is possible to produce ultra-thin batteries of 0.33 mm, 0.50 mm, etc.) The main disadvantages are poor consistency and poor mechanical strength. Based on the characteristics of lithium polymer soft pack batteries, lithium polymer soft pack batteries are increasingly being used in mobile phones, notebook computers, mobile power supplies and other fields. However, due to the poor conductivity of the colloidal (or solid) electrolyte and the large internal resistance, 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 batteries are Nissan Leaf's cascading soft pack batteries?
 
In fact, although lithium polymer soft pack batteries are generally referred to as soft pack batteries, soft pack batteries are not all lithium polymer batteries because they can also use liquid electrolyte. Nissan Leaf's battery is a soft pack battery with liquid electrolyte.
 
Whether it is a lithium polymer soft pack battery or a soft pack battery whose internal material is a liquid electrolyte, the soft pack battery is generally packaged in an aluminum plastic film. The thickness of the aluminum plastic film is thin and the mechanical strength is poor. In the extreme case of collision of the automobile, the aluminum plastic film is prone to breakage and cause accidents, which is the main defect of the soft pack battery used in the new energy vehicle.
 
It is reported that in order to ensure safety, Nissan Leaf has added an aluminum shell to the outside of the four battery modules. Even so, battery leakage is still a fatal flaw in the Nissan Leaf battery. Nissan Leaf battery has the title of “Leaking King” among the riders and is often criticized by people.