What is the difference between 18650 lithium battery and polymer lithium battery?


  1.  

18650 is the originator of lithium-ion batteries-a standard lithium-ion battery model set by Japan's SONY company in order to save costs, where 18 represents a diameter of 18mm, 65 represents a length of 65mm, and 0 represents a reduced battery. SONY has always aimed to treat lithium-ion batteries as alkaline batteries. There are certain industry standards, just like No. 5 batteries and No. 7 batteries, basically the same in the world. However, since one of the major advantages of lithium-ion batteries is that they can be designed according to customer needs, it is impossible to have a unified standard, so until now the lithium-ion battery industry is basically only 18650 this type.

typical 18650 battery cell

2. the polymer battery refers to a lithium-ion battery that uses an aluminum-plastic packaging film as an outer package, also known as a soft-pack battery. This packaging film is composed of three layers, namely a PP layer, an Al layer and a nylon layer. Since PP and nylon are polymers, this cell is called a polymer battery.

typical polymer lithium battery

3. The shape of the 18650 battery is cylindrical and there is liquid inside. Because of the characteristics of the battery design and raw materials, the power type 18650 battery is suitable for high current discharge. Therefore, almost all high-power products on the market use 18650 lithium batteries, but ultra-thin notebooks, especially It is a tablet computer, etc., because it requires a thin appearance, so instead of using 18650 batteries, polymer lithium batteries are used, but high-power digital cameras are different. Because the flash charge and discharge require a large voltage and instantaneous large current, so only The use of 18650 power lithium battery or other types of power batteries is only slightly smaller. For example, 18500 power lithium batteries are commonly used in digital camera products; and with the advantages of high energy density and high current discharge of 18650 power lithium batteries, so Now the so-called polymer lithium battery refers to a lithium ion battery that uses a polymer as an electrolyte. Specifically, it is divided into two types: "half polymer" and "full polymer". "Semi-polymer" refers to coating a layer of polymer (generally PVDF) on the separator to make the cell's adhesion stronger, the battery can be made harder, and its electrolyte is still a liquid electrolyte. "All polymer" refers to the use of a polymer to form a gel network inside the cell, and then the electrolyte is injected to form the electrolyte. Although "all polymer" batteries still use liquid electrolyte, the amount is much less, which greatly improves the safety performance of lithium ion batteries.

4. 18650 is relatively cheaper, while polymer lithium batteryis more expensive.

18650 international price is about 1USD / pcs, if calculated according to 2Ah, it is about 3RMB / Ah. The price of polymer lithium battery is 4RMB / Ah at the low-end cottage factory, 5 ~ 7RMB / Ah at the mid-end, and above 7RMB / Ah at the high-end. Such as ATL, Lishen, etc., can generally be sold for about 10RMB / Ah, and your order may not be accepted if it’s not big order.

5. 18650 battery has poor security than polymer lithium battery

We know that under extreme conditions (such as overcharge, high temperature, etc.), lithium-ion batteries will undergo violent chemical reactions inside, producing a large amount of gas. The 18650 battery uses a metal shell with a certain strength. When the internal air pressure reaches a certain level, the steel shell will burst and explode, resulting in a terrible security accident.

This is why the room where the 18650 battery is tested must generally be protected by layers, and must not be entered during the test. Polymer batteries do not have this problem. Even in extreme cases, due to the low strength of the packaging film, as long as the air pressure is slightly higher, it will rupture and will not produce an explosion. The worst case is combustion. So in terms of safety, polymer batteries are better than 18650 batteries.

6.18650 battery has Lower energy density

The general 18650 battery capacity can be about 2200mAh, so the energy density is calculated to be about 500Wh / L, and the energy density of polymer batteries is currently close to 600Wh / L.

7. Polymer batteries also have some disadvantages. The main reason is that the cost is relatively high. Because it can be designed according to customer needs, the research and development costs in it must be included. In addition, the shape and variety are varied, which leads to the fact that various tooling fixtures are non-standard parts in the manufacturing process, which also increases the cost accordingly. The versatility of the polymer battery itself is poor, which is also brought by the flexible design. Often for the difference of 1mm, it is necessary to design a new one for the customer.

Generally speaking, there is wide choice in market, just pick up the most fit one for yourself.

 

 


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