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LiPO VS Li-ion: Which One is Better?

Lithium battery refers to lithium-ion secondary rechargeable batteries. From the appearance point of view, there are three types of cylindrical steel shell, square aluminum shell and soft pack. Among them, soft pack is the polymer we are going to discuss today. It can be seen that the polymer battery is actually a lipo battery, which is a kind of lithium battery. In this context, lithium ion  batteries specifically refer to cylindrical lithium batteries. Therefore, which is better for lipo and Li-ion batteries, the actual discussion is which is better for polymer and cylindrical lithium batteries.

Let’s compare one by one from the following aspects to try to find out the answer.

Lithium Polymer VS Lithium ion Battery

Materials: ROOT CAUSE

Li-ion batteries use liquid electrolytes, while lipo batteries use gel electrolytes and solid electrolytes inside. Lithium Polymer batteries refer to the use of polymer materials in at least one of the three components of the positive electrode, negative electrode or electrolyte. Macromolecules mean large molecular weights, and the corresponding concept is small molecules. Macromolecules have high strength, high toughness and high elasticity. The polymer materials currently developed for polymer batteries are mainly used for positive electrodes and electrolytes.

①The cathode material of polymer batteries, in addition to the inorganic compounds of lithium batteries, can also use conductive polymer polymers;

②. The electrolytes of polymer batteries have polymer electrolytes (solid or colloidal) and organic electrolytes, and lithium batteries use electrolytes (liquid or colloidal).

In fact, domestic polymers cannot really be called polymers, and they cannot be truly solid. It is more accurate to call them liquids without flow-ability.

Packaging Method and Appearance

Lipo battery is encapsulated with aluminum-plastic film, and the shape can be customized at will, which can be thick or thin, large or small. Lipo batteries can be thin, any area, and any shape, because their electrolytes can be solid or colloidal rather than liquid. The Li-ion battery uses electrolyte, so the lithium battery needs a sturdy shell as a secondary packaging to accommodate the electrolyte. Therefore, this also makes the lithium battery increase part of its weight. Li-ion batteries are packaged in steel shells, with the most cylindrical shapes. The most common is 18650, which refers to a diameter of 18mm and a height of 65mm. The shape is fixed. So 18650 lithium battery cannot be changed at will. Because lipo batteries do not have a metal shell, the advantage can be highlighted that they are thin and light. However, the disadvantage is that there is no metal shell protection, which is easily damaged by external forces. Surely, lipo battery is of safety.

SAFETY

There is no flowing liquid inside the lipo battery so it has no liquid leakage risk. When the internal temperature is very high, the aluminum-plastic film shell is just flatulence or bulging, and it will not explode. The safety is higher than that of Li-ion batteries. Of course, this is not absolute. If the instantaneous current of the lipo battery is large enough to cause a short circuit, the battery will spontaneously ignite or explode. However, the probability of this happening is extremely low. Although Li-ion batteries encapsulated in metal shells will also have a pressure relief port design, the risk of explosion and fire will be higher when the pressure or temperature is too high. Therefore, the occurrence of mobile phone and tablet computer security accidents is mostly caused by this situation.

ENERGY DENSITY

The capacity of a 18650 lithium battery with a general energy density can be about 2200mAh. In this way, the energy density is about 500Wh/L, while the energy density of lipo batteries can be close to 600Wh/L in mass production at this stage.

CELL VOLTAGE

Because lipo batteries use polymer materials, they can be combined into multiple layers in the cell to achieve high voltage, while the nominal capacity of Li-ion cells is 3. 6V. In order to achieve high voltage in actual use, multiple cells need to be connected in series to form an ideal high-voltage working platform.

ELECTRICAL CONDUCTIVITY

The ion conductivity of the solid electrolyte of lipo batteries is low. At present, some additives are mainly added to make it a gel electrolyte to improve the conductivity. This only increases the ion conductivity, unlike Li-ion batteries, which maintain a stable value without being affected by the quality of auxiliary materials.

PRODUCTION PROCESS

For lipo battery, the thinner, the better the production.  Since the outer packaging of the lipo battery uses a thinner aluminum film, which is thinner than steel and aluminum shells, and the production method is different from liquid Li-ion batteries, the thinner the lipo battery, the better the production. In theory, batteries with a thickness of less than 0.5mm can be produced.

For Li-ion battery, the thicker, the better the production. Li-ion batteries are the opposite. The thicker the better the production. Batteries with a thickness of less than 4mm are difficult to produce. Even if they are produced, the capacity is obviously not as good as polymer lithium batteries, and the cost has no advantage.Therefore, the thinner the battery, the lower the production cost of the polymer and the higher the production cost of the liquid.

It can be seen that which one is better for lipo and Li-ion battery, it seems that polymer has the advantage. But what exists is reasonable, and they must have irreplaceable aspects of each other in different ways. Let’s look at the last item:

PRICE

The price is generally more expensive for lipo batteries with the same energy than Li-ion batteries. But it cannot be said that this is the disadvantage of thelipo battery. At present, in the field of consumer electronics, such as notebooks, mobile power supplies, etc. , more and more lipo battery is used instead of Li-ion batteries. In a small battery compartment, to achieve the maximum energy density in a limited space, a lipo battery is still used. Because of the fixed shape of the Li-ion battery, it cannot be customized according to the customer’s design. However, there is no uniform standard size for lipo batteries, which in turn has become a disadvantage in some aspects. The battery used in Tesla Motors is composed of more than 7,000 18650 batteries in series and parallel, plus a power supply control system.

It is difficult to say absolutely which polymer batteries and lithium batteries are good. They have their own merits. If you have to draw a conclusion, polymer batteries are more in small-scale applications, while lithium batteries are more promising in large-scale applications. If polymer batteries can break through the limitations of price and design, it may represent the development trend of batteries, because their environmental protection and safety are more in line with the trend.

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