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18650 lithium battery separator

Time:2021-01-11 Views:292

  18650 lithium battery separator


  For consumable lithium-ion batteries (batteries used in mobile phones, notebook computers, and digital cameras), 25-micron separators are gradually becoming the standard. However, due to the increasing use of portable products, thinner diaphragms, such as 20 micrometers, 18 micrometers, 16 micrometers, and even thinner diaphragms, have begun to be widely used.

18650 lithium battery separator(图1)

  For power batteries, due to the mechanical requirements of the assembly process, thicker diaphragms are often required. Of course, safety is also very important for large power batteries, and thicker diaphragms often mean better safety at the same time. /HEV uses a diaphragm with a thickness of about 40 microns.

  ②Air permeability

  MacMullin number: The ratio between the resistivity of the diaphragm containing the electrolyte and the resistivity of the electrolyte itself. The smaller the value, the better, the value of the expendable 18650 lithium ion battery is close to 8.

  Gurley number: The time required for a certain volume of gas to pass through a certain area of a diaphragm under certain pressure conditions. It is proportional to the internal resistance of the battery assembled with the diaphragm, that is, the larger the value, the greater the internal resistance.

  It is meaningless to simply compare the Gurley numbers of two different diaphragms, because the microstructures of the two types of diaphragms may be completely different; but the Gurley number of the same type of diaphragm can well reflect the size of the internal resistance, because the same type of diaphragm Relatively speaking, the microstructure is the same or comparable.

  ③Infiltration degree

  In order to ensure that the internal resistance of the battery is not too large, the diaphragm is required to be completely wetted by the electrolyte used in the battery, which is related to the diaphragm material itself and the surface and internal microstructure of the diaphragm.

  Rough judgment: take a typical electrolyte (such as EC:DMC=1:1, 1M LiPF) and drop it on the surface of the diaphragm to see if the droplets will disappear quickly and be absorbed by the diaphragm.

  Accurate judgment: use an ultra-high time-resolution camera to record the process from the droplet contacting the diaphragm to the disappearance of the droplet, calculate the time, and compare the infiltration degree of the two diaphragms by the length of time.

  ④The chemical stability of 18650 lithium battery separator

  The diaphragm is required to be inert in the electrochemical reaction, inactive to strong reduction and strong oxidation, not to attenuate the mechanical strength, and not to produce impurities. It is generally believed that the current PE or PP materials for diaphragms can meet the chemical inertness requirements.

  ⑤The aperture of the 18650 lithium battery diaphragm

  To prevent electrode particles from directly passing through the diaphragm, the diaphragm diameter is required to be 0.01-

  0.1um, when less than 0.01um, the lithium ion penetration capacity is too small, greater than

  At 0.1um, the battery is easy to short-circuit when dendrites are formed inside the battery.

  The electrode particles currently used are generally on the order of 10 microns, while the conductive additives used are on the order of 10 nanometers. Fortunately, carbon black particles tend to agglomerate to form large particles. Generally speaking, the sub-micron pore size membrane is sufficient to prevent the direct passage of electrode particles. Of course, some problems such as micro short circuit caused by poor surface treatment of some electrodes and more dust are not excluded.

  ⑥ Piercing strength of 18650 lithium battery separator

  Puncture strength: at a certain speed (3-5 meters per minute), a needle with a diameter of 1 mm without sharp edges is pierced into the annular fixed septum, which is the maximum force applied to the needle to penetrate the septum.

  Because the method used in the test is very different from the actual battery situation, it is not particularly reasonable to directly compare the puncture strength of the two types of separators. However, when the microstructure is certain, the puncture strength is relatively high. Low defect rate. However, the pure pursuit of high puncture strength will inevitably lead to the degradation of other properties of the diaphragm. ⑦ Thermal stability

  The separator needs to be thermally stable within the battery temperature range (-20℃~60℃). Generally speaking, PE or PP materials currently used in diaphragms can meet the above requirements.

  Generally, under vacuum conditions, at a constant temperature of 90°C for 60 minutes, the transverse and longitudinal shrinkage of the diaphragm should be less than 5%.

  ③The thermal shutdown temperature of the 18650 lithium battery diaphragm

  Thermal shutdown temperature: The temperature when the internal resistance is increased by three orders of magnitude when the simulated battery (with a separator between two flat electrodes and the electrolyte for general lithium-ion batteries is used) is heated.

  Closed cell temperature: The temperature at which the diaphragm pores are blocked by the heat generated when an external short circuit or abnormal large current passes.

  Melting rupture temperature: heating the diaphragm, the temperature when the temperature exceeds the melting point of the sample to cause the sample to rupture.

  ④Porosity of 18650 lithium battery separator

  The porosity of most lithium ion battery separators is between 30%-50%. The size of the porosity has a certain relationship with the internal resistance, but the absolute value of the porosity between different kinds of diaphragms cannot be directly compared.

  What are the parameter requirements for solar polymer batteries?

  The equivalent circuit diagram and current-voltage characteristic curve of the solar polymer battery are shown in the figure:

  For organic solar polymer batteries, the main evaluation parameters are as follows:

  (1) Open circuit voltage (Voc): refers to the terminal voltage of the solar polymer battery when the current is zero when the current is zero, and it is also the maximum voltage generated by the solar battery, usually in V. The open circuit voltage of the solar polymer battery is related to the light intensity, temperature and acceptor material, and mainly depends on the energy level difference between the HOMO energy of the donor and the LUMO energy of the acceptor:

  Solar polymer battery parameters

  (2) Short-circuit current (Jsc): The short-circuit current is the current that passes when the voltage and resistance are both zero, that is, the current of the device without an external electric field bias. It is the maximum output current of the solar cell, in mA. cm.

  The main influencing factors of the magnitude of the short-circuit current are: the absorption of sunlight by the active layer, the quantum efficiency of charge separation, the transmission of carriers in the material, and the loss during the transmission.

  (3) Fill factor (FF): It is defined as the ratio of the maximum power of the solar polymer battery to the product of the open circuit voltage and the short-circuit current. It illustrates the ability of the solar polymer battery to provide the maximum output power. Its definition is

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