Lithium batteries are divided into polymer lithium batteries and liquid lithium batteries, how to distinguish it? What are the differences and advantages of polymer lithium batteries and liquid lithium batteries?

　　In fact, there are some simpler methods that can be distinguished directly from the appearance. Generally, polymer lithium batteries are not protected by iron-made shells and have a certain degree of softness. Liquid lithium batteries are generally protected by a hard case, such as the 18650 lithium batteries on the market.

　　One thing everyone should pay attention to: 18650 refers to a cylindrical battery with a diameter of 18mm and a length of 65mm. Although most of the 18650 on the market are liquid lithium batteries, any statement that "polymer lithium batteries are safer than 18650 XX" is wrong.

　　The working principle of the two is the same. Both charge and discharge are realized through the process of lithium ion insertion and extraction. The insertion of lithium ions into the negative electrode is charging, and the extraction of lithium ions from the negative electrode is discharge.

　　Lithium batteries contain three basic elements: positive electrode, negative electrode, and electrolyte (materials filled between the two levels). Of course, there is a separator that prevents direct contact between the positive and negative electrodes (of course, lithium ions can pass smoothly, but the separator does not It will cause an explosion due to a short circuit); The main difference between liquid lithium ion batteries and polymer lithium ion batteries is:

　　1. Differences in materials: In polymer lithium batteries, at least one of the above three basic elements must be made of polymer materials, for example, the electrolyte solution is replaced by polyacrylic acid, polymethacrylic acid, etc.

　　2. The difference in electrolyte morphology: liquid lithium-ion batteries mostly use liquid organic solvents + conductive salts, while polymer lithium batteries replace these electrolytes with gels/solids (see battery model for specific components).

　　Simple comparison between polymer lithium battery and liquid lithium battery:

　　The energy density of liquid lithium batteries (Wh/L)>300~280 can be customized (shape) flexible and difficult, and heavy (metal protective shell is required). The energy density of the polymer lithium battery is customized to be higher, the shape design is more flexible, it can be of any shape, and the weight is lighter.

　　1. Energy density: The greater the energy density, the more capacity a unit volume can have. The energy density of the polymer lithium battery has now reached 600Wh/L+ through the improvement of the material/thickness of the negative electrode (anode) and separator.

　　2. Degree of customization: The polymer lithium battery is easier to be thinner in shape, and there is no need to use a metal protective shell to wrap it, so it is easier to customize into various shapes.

　　3. Weight: liquid lithium battery is heavier, polymer lithium battery is lighter, the same volume.

　　4. Safety: Under extreme conditions (for example, overcharge/high temperature), a violent chemical reaction will occur inside the lithium battery, generating a lot of gas. At this time, the liquid lithium battery is wrapped by a metal shell, so when the internal pressure is quite large, the shell will A rupture explosion occurs, and because the polymer lithium battery is only wrapped with packaging aluminum film (or plastic shell), as long as the internal pressure is slightly higher, it will expand or rupture, and will not cause an explosion. But it should be noted that both liquid lithium batteries and polymer lithium batteries can burn under extreme conditions.

　　5. Cost: In addition to the higher material cost of polymer lithium batteries than liquid lithium batteries, because polymer lithium batteries can be customized to a higher degree, more costs will be incurred in the design and manufacturing process, such as various customized Tooling fixtures, test equipment, etc., cause the cost of polymer lithium batteries to be higher than that of liquid lithium batteries with standard/regular shapes.