18650 lithium battery compared to polymer battery.

18650 lithium battery compared to polymer battery.

The so-called polymer lithium battery refers to lithium-ion batteries that use polymers as electrolytes, which can be further divided into two types: "semi polymer" and "fully polymer". Semi polymer "refers to coating a layer of polymer (usually PVDF) on the isolation membrane to enhance the adhesion of the battery cell, making the battery harder and the electrolyte still in liquid form. The "all polymer" refers to the use of polymer to form a gel network inside the cell, and then inject electrolyte to form an electrolyte. Although "all polymer" batteries still require the use of liquid electrolytes, the amount used is much less, which greatly improves the safety performance of lithium-ion batteries. To the best of my knowledge, only SONY is currently mass producing "all polymer" lithium-ion batteries.

On the other hand, polymer batteries refer to lithium-ion batteries that use aluminum-plastic packaging film as the outer packaging, commonly known as soft pack batteries. This packaging film consists of three layers, namely PP layer, Al layer, and nylon layer. As PP and nylon are polymers, this type of battery cell is called a polymer battery.

1. Lower price
The international price of 18650 is approximately 1USD/pcs, which is about 3RMB/Ah if calculated based on 2Ah. The price of polymer lithium batteries is 4 RMB/Ah for low-end counterfeit factories, 5~7 RMB/Ah for mid-range factories, and above 7 RMB/Ah for mid to high end factories.

2. Not customizable

SONY has always wanted to make lithium-ion batteries like alkaline batteries, with certain industrial standards, just like the 5th and 7th batteries, which are basically the same all over the world. However, due to one of the major advantages of lithium-ion batteries being the ability to design their appearance according to customer needs, there cannot be a unified standard.

3. Poor safety
We know that in extreme situations such as overcharging and high temperatures, lithium-ion batteries undergo violent chemical reactions internally, 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 rupture and explode, causing a terrifying safety accident.

4. Low energy density
A typical 18650 battery can achieve a capacity of around 2200mAh, resulting in an energy density of approximately 500Wh/L, while the energy density of polymer batteries can currently approach 600Wh/L in mass production.

But polymer batteries also have their own drawbacks. The main reason is that the cost is relatively high, and since it can be designed according to customer needs, the research and development costs need to be included. Moreover, due to the varied shapes and diverse types, various fixtures and jigs used in the manufacturing process are non-standard components, which correspondingly increases costs. Polymer batteries themselves have poor universality, which is also due to flexible design. Often, in order to achieve such a 1mm difference, a new one needs to be designed for customers.