Dec 31, 2019 Pageview：263
Li-polymer, also known as polymer lithium battery, is a new kind of battery with high energy density, miniaturization, ultra-thin, lightweight, high safety and low cost. In terms of shape, lithium polymer batteries have the characteristics of ultra-thin, which can meet the needs of a variety of products, and be made into any shape and capacity. The minimum thickness of the battery can be 0.5mm.
Compared with lithium ion batteries, lithium polymer batteries have the following characteristics:
There is no battery leakage issue. The battery does not contain liquid electrolyte, and uses colloidal solid.
It can be made into thin battery: As for 3.6V 400mAh capacity, its thickness can be as thin as 0.5mm.
The battery can be designed in many shapes.
Flexible deformation of the battery: the maximum bending of the polymer battery is about 90°.
It can be made into a single high voltage cell: the battery with liquid electrolyte can only achieve high voltage by several batteries in series, while the polymer battery can be made into a multi-layer combination in a single battery to achieve high voltage due to the lack of liquid.
It will have twice the capacity of a lithium-ion battery with the same size.
Because polymer cells are affected by safety issues and restricted in size, it is difficult to break through the capacity of single cells. We need to increase the energy density and capacity. There are few high-capacity polymer lithium cells circulating in the market. The following are some high capacity polymer lithium cells:
Energy Density is the amount of energy stored in a unit of space or mass. The energy density of a battery is the amount of energy released per unit volume or mass in the battery. The energy density of battery is generally divided into two dimensions: weight energy density and volume energy density.
Battery weight energy density = battery capacity × discharge platform/weight, fundamental unit is Wh/kg(watt-hour /kg)
Battery volume energy density = battery capacity × discharge platform/volume, fundamental unit is Wh/L(watt-hour/liter)
The higher the energy density of the battery, the more energy is stored per unit volume, or weight.
As solid electrolyte take the place of liquid electrolyte, compared with liquid lithium ion battery, polymer lithium ion battery has the advantages of thin thickness, arbitrary area and shape, etc. Therefore, the battery shell can be made with aluminum-plastic composite film, so as to improve the specific capacity of the whole battery. Polymer lithium-ion batteries can also use polymers as anode materials, which will increase the energy density of current liquid lithium-ion batteries by more than 20 percent.
The capacity of lithium-polymer batteries is related to the size of the battery, depending on the thickness, width and length of the battery. It also has to do with the material and size of the battery.
However, due to the non-standard shape of lithium polymer battery, the actual calculation formula of lithium polymer battery capacity is very complicated, which is not linear with the volume. Many factors need to be taken into account, such as different materials, which have a great impact on the actual capacity. The larger the size, the larger the capacity/volume ratio is.
As a rule of thumb, we can quickly estimate the capacity of polymer batteries. Commonly used estimation formulas (estimation only) :
Capacity = thickness × width × length ×K (the unit of K is mAh/mm3)
The range of K value is (0.07~0.11), and the value of K depends on the size of the capacity. The larger the capacity, the larger the value of K; the smaller the capacity, the smaller the value of K (it can be regarded that the larger the size, the larger the value of K).
The estimated results can only be used as a reference. We can also use professional capacity testers to measure the capacity of lithium polymer batteries.
Methods to improve the capacity of lithium polymer batteries
By using silicon anode material, the capacity of lithium polymer battery can be effectively increased. Under the condition of completely embedded lithium, the specific capacity of pure Si can reach 4200mAh/g(Li4.4Si), but it is accompanied by volume expansion of up to 300%, which will lead to particle breakage and differentiation of pure silicon materials in the process of embedded lithium. Cathode material dropping results in a very serious decline of the capacity in the process of material recycling.
Use materials with smaller thickness rebound: after the circulation of polymer lithium ion battery, the thickness will have a certain rebound; The design needs to reserve the rebound thickness after the cycle; When the material with smaller thickness rebound is used, the reserved space for the thickness rebound can be transferred to the design thickness of the cell, thus increasing the design capacity of the cell.
Increase the capacity of lithium polymer battery by connecting batteries in parallel. That is to say, by connecting the anode of the battery with the cathode of other batteries, and the cathode with the cathode of other batteries, the battery can be made into a battery pack, and the battery capacity can be increased without changing the output voltage of the battery.
Battery capacity is the most important indicator of battery performance, which is directly related to the battery working time.
To test the capacity of lithium polymer battery, the battery needs to be fully charged and discharged to the final voltage under certain conditions. The capacity released during discharge is the actual capacity of the battery. This method takes a long time, but it is the most accurate and only way to test battery capacity. There is no other efficient way.
The lithium polymer battery capacity tester is an instrument that tests how much power a lithium polymer battery can store. Due to the limited life for lithium polymer batteries, it is necessary for us to carry out capacity testing of lithium polymer batteries in the process of production, so as to meet our needs.
This battery capacity tester can test the capacity of lithium ion battery, polymer battery, nickel-metal hydride battery, nickel-cadmium battery, lithium iron phosphate battery and other types of rechargeable battery and cell;
The instrument can also test voltage and internal resistance. It can also detect the overcharge protection voltage and over-discharge protection voltage when testing the charge and discharge values;
The battery capacity detector can be directly operated by LCD screen and keyboard, and the battery capacity can be tested without connecting to a computer.
It can also be connected to the computer and operate directly by the computer software. The test process can be recorded by computer software at any time (the recording frequency can be set) and the graph can be generated automatically.
For lithium polymer batteries, the most common concern is the life, safety and battery life of lithium polymer batteries. In fact, as for whether the traditional battery, or the rapid developing lithium polymer batteries, battery life and durability play an important role on consumer choice.
So what factors are associated with lithium polymer battery life?
The life of lithium polymer batteries is related to the number of charging times, not directly related to the number of charging times. After each charge cycle, the capacity will reduced a bit. Under the international standard, the average lithium polymer battery life is between 500 and 800 times, and A-grade polymer battery will have up to 800 times.
If a lithium-polymer battery is used in a high temperature environment at above 35 ° c, the battery will continue to store less power, so the battery will not last as long as it does in a normal temperature environment. When used and recharged in such a high temperature environment, the battery will be damaged to a great extent, thus affecting its service life. Even charging in a hot environment can cause varying degrees of damage to the battery, so try to avoid charging in a high temperature environment. If charge a battery at a low temperature, such as less than 40 ° c, it may damage the battery.
If the battery is often damp, or the user doesn’t use the original charger to charge the battery, then the battery will be damaged greatly. In addition, do not charge the battery several times a day. Charging and discharging will also affect the battery life.
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