Lithium-ion batteries refer to lithium-ion secondary rechargeable batteries, from the outside, there are three types of cylindrical steel case, square aluminum case and soft pack, where the soft pack is the polymer in the title, thus, the polymer is actually a lithium polymer battery. Put in this context, lithium batteries refers specifically to the cylindrical lithium battery. Therefore polymer and lithium batteries which is better, the actual discussion is polymer and cylindrical lithium batteries which is better.

Let’s try to find out the answer by comparing each of the following areas.

1. Materials
Lithium batteries use a liquid electrolyte, while polymer batteries use gel electrolytes and solid electrolytes inside. In fact, domestic polymers can not really be called polymers, can not do a true solid state, it is more accurate to call there is no flowable liquid. This is beside the point, so I won’t go into it here.

2.  Packaging and appearance
Polymer using aluminum plastic film package, the shape can be customized, can be thick or thin, can be large or small.
Lithium batteries use steel encapsulation, the shape of the most cylindrical, the most common is 18650, refers to the diameter of 18mm, height 65mm. shape is fixed. The shape is fixed and cannot be changed at will.

3.  Safety
There is no flowing liquid inside the polymer and no leakage. When the internal temperature is very high, the aluminum plastic film shell also just swells or bulges, and will not explode. It is safer than lithium batteries. Of course this is not absolute, if the polymer battery instant current is high enough to short-circuit, battery spontaneous combustion or explosion can also occur. A few years ago the Samsung mobile phone battery explosion, as well as this year’s Lenovo laptop recalled due to battery defects, are the same problem.

4. Energy Density
The general 18650 battery capacity can do about 2200mAh, which calculates the energy density of about 500Wh/L, and polymer battery energy density at this stage of mass production can be close to 600Wh/L.

5.  cell voltage
Polymer batteries use polymer materials, can be made into a multi-layer combination of cells to achieve high voltage, while the nominal capacity of lithium battery cells is 3.6V, in order to achieve high voltage in practical use, you need to connect multiple cells in series to form an ideal high-voltage operating platform.

Which is better, polymers or lithium batteries?
Thus, it seems that polymer and lithium-ion battery which is better dominates. But what exists is reasonable, and they definitely have aspects of each other that are irreplaceable in different ways.
Let’s look at the last item:

6. Price.
Usually polymers of the same energy are more expensive than lithium batteries. But it cannot be said that this is a disadvantage of polymers.
Nowadays, in the field of consumer electronics, such as laptops and mobile power supplies, more and more polymers are being used instead of lithium batteries.
In a small battery compartment, to achieve the maximum energy density in a limited space, it is still necessary to use polymers. Because of the fixed shape of lithium batteries, it is not possible to customize them with the customer’s design.
But polymer batteries do not have a uniform standard size, which in turn is a disadvantage in some respects. Tesla car, the battery is used by more than 7000 18650 after series and parallel connection, plus the power control system and composition.

It seems that the polymer or lithium-ion battery which is better, which is better or worse, still depends on the circumstances, can not give a single conclusion.