18650 rechargeable battery lithium 3.7v 3500mah

　　High-speed CT technology restores the truth about thermal runaway of LG 18650 battery!

　　Once thermal runaway occurs in lithium-ion batteries, it will seriously threaten the life and property safety of users. Therefore, how to prevent thermal runaway is the ultimate goal of all lithium-ion battery designers. However, in order to prevent the occurrence of thermal runaway from the design, it is necessary to thoroughly understand the root causes of lithium-ion batteries in the process of thermal runaway.

　　Once thermal runaway occurs in lithium-ion batteries, it will seriously threaten the life and property safety of users. Therefore, how to prevent thermal runaway is the ultimate goal of all lithium-ion battery designers. However, in order to prevent thermal runaway from the design, it is necessary to thoroughly understand the internal reaction process of the lithium-ion battery during the thermal runaway process. However, the thermal runaway reaction speed of lithium-ion batteries is fast, the temperature is high, and at the same time limited by the sealed structure of lithium-ion batteries, it is difficult for us to observe the reaction process of thermal runaway of lithium-ion batteries intuitively and accurately.

　　X-rays have very strong penetrating ability and can pass through the shell of lithium-ion batteries to observe the internal structure of lithium-ion batteries. In particular, tomography technology allows us to directly generate three-dimensional images of lithium-ion batteries, but usually X-ray imaging It is relatively slow, and it is impossible to track the structural changes inside the lithium-ion battery during the thermal runaway process of the lithium-ion battery. The emergence of synchrotron radiation technology has greatly increased the energy of X-rays, thereby effectively reducing the time required for exposure, thus greatly improving the imaging speed. DonalP.Finegan (first author) of London City College and others used synchrotron radiation technology to greatly increase the speed of CT scanning, and conducted in-depth understanding and research on the structural changes inside the 818650 battery during the thermal runaway process.

　　In the experiment, DonalP.Finegan used two types of 18650 batteries from LG as the research objects (with capacities of 2.2Ah and 2.6Ah respectively). Through the application of the synchrotron radiation light source of the European Synchrotron Radiation Center, DonalP.Finegan increased the adoption speed of CT to 1.25Hz And 2.5Hz, while the ordinary two-dimensional shooting speed reaches 1250Hz, which also allows us to "see" for the first time the impact of thermal runaway gas production and high temperature on the structure of lithium-ion batteries.

　　In the experiment, DonalP.Finegan used the high temperature method to trigger thermal runaway of two LG 18650 batteries respectively (as shown in the figure above). Among them, the core bone was added in the middle of the 2.6Ah battery cell, which can serve as a support and is conducive to improving the lithium-ion battery. The safety, while the 2.2Ah battery does not have a core bone. The author used a thermal imager to track the temperature change of the battery during the thermal runaway process (2.6Ah battery is video 1, 2.2Ah battery is video 2). From the video, we can see that when the heating starts, the temperature of the 2.6Ah battery shows a slow rising trend. At 168s, the temperature of the battery casing rises to 230°C, and then the temperature of the battery begins to rise rapidly to exceed 260°C (the temperature of the thermal imager The highest observed temperature is 260°C), and then within a very short period of time, due to the increase of gas pressure inside the battery, the gas and electrode decomposition products inside the battery are ejected from the position of the battery cover, and the battery thermal runaway occurs. The thermal runaway time of the 2.2Ah battery was 217s after the heating started.

　　In order to analyze the changes in the internal structure of LG batteries during thermal runaway, DonalP.Finegan also used high-speed CT technology to analyze the internal three-dimensional structures of 2.6Ah batteries (Video 3) and 2.2Ah batteries (Video 4) during thermal runaway triggering. Scan and rebuild. Because the 2.6Ah battery has a core bone inside the battery, it can theoretically support the battery and prevent the battery from collapsing during the thermal runaway process. The CT image of the 2.6Ah battery immediately before the thermal runaway can It can be seen that the position of most of the cells is still intact, but the cell structure is obviously deformed at the center of the cell near the core bone, which may be caused by the separation of positive and negative electrodes caused by local side reaction gas production.

　　We can get the answer from the two pictures below about the stable use of the core bone on the cell structure. In the picture a below, we can see that because there is a core bone in the middle of the cell, the structure of the cell does not occur after the battery is depressurized. Obvious damage, but in Figure b below, we can see that the structure of the battery cell has been significantly damaged after the battery pressure release occurs due to the absence of the support of the core bone. This is mainly because a lot of gas has accumulated between the positive and negative electrodes before the battery pressure release occurs, so after the battery explosion-proof valve is opened, the gas will be discharged along the position of least resistance, resulting in no The supporting battery core has undergone significant deformation, and the deformation of the battery core has also greatly increased the risk of short circuit of the battery.

　　What voltage should be used to charge a 3.7v lithium battery

　　2018-06-01 81530 views

　　Generally, a 3.7v lithium battery needs a "protection board" for overcharge and overdischarge. If the battery does not have a protection board, it can only use a charging voltage of about 4.2v, because the ideal full charge voltage of a lithium battery is 4.2v, and the voltage exceeds 4.2v. Damage to the battery, while charging in this way, it is necessary to monitor the condition of the battery at all times.

　　5v can be used if there is a protective board (4.8 to 5.2 can be used), the USB5v of the computer or the 5v charger of the mobile phone can be used.

　　For a 3.7V battery, the charge cut-off voltage is 4.2V, and the discharge cut-off voltage is 3.0V. Therefore, when the open circuit voltage of the battery is lower than 3.6V, it should be able to charge. It is best to use the 4.2V constant voltage charging mode, so you don't need to pay attention to the charging time. Charging with 5V is prone to danger of overcharging.

　　1. Float charge. Refers to charging while working online. This method is often used in backup power supply occasions. If it is lower than 12 volts, it cannot be charged, and if it is too high, it will affect the operation of the circuit. Therefore, when the floating charge works, the voltage is 13.8 volts.

　　2. Cycle charging. Refers to fully charging the battery to restore the capacity. When fully charged, the charger is not disconnected for measurement. Generally, it is around 14.5 volts, and the maximum does not exceed 14.9 volts. After disconnecting the charger for 24 hours, it is generally around 13 volts to 13.5 volts. About 12.8 to 12.9 volts after a week. The specific voltage value of different batteries is different.

　　The usual lithium battery cell is 3.7v, the voltage is 4.2v when fully charged, the nominal voltage after series connection is only 7.4v, 11.1v, 14.8v... the corresponding full voltage (that is, the no-load output voltage of the charger) is 8.4v, 12.6v, 16.8v... cannot be 12v integers, just like the interval of lead-acid storage battery is 2v, full is 2.4v, correspondingly only the nominal 6v, 12v, 24v... full voltage (The same is the output voltage of the charger) respectively 7.2v, 14.4v, 28.8v... I don't know what kind of lithium battery you are?

　　The output of the charger is generally 5V, and 4.9 volts is also a non-standard. If you want to use this charger to charge the battery directly, it will definitely not work, but as long as it is charged by a mobile phone or a dock, it has a control circuit inside. It will be limited within the allowable range of the lithium battery, unless the circuit is damaged, don't worry about this

　　The usual lithium battery cell is 3.7v, the voltage is 4.2v when fully charged, the nominal voltage after series connection is only 7.4v, 11.1v, 14.8v... the corresponding full voltage (that is, the no-load output voltage of the charger) is 8.4v, 12.6v, 16.8v... cannot be 12v integers, just like the interval of lead-acid storage battery is 2v, full is 2.4v, correspondingly only the nominal 6v, 12v, 24v... full voltage (The same is the output voltage of the charger) respectively 7.2v, 14.4v, 28.8v... I don't know what kind of lithium battery you are?

　　18500 batteries are widely used in cylindrical lithium batteries, and can be used in electronic fields such as electronic cigarettes, toys, security, and vehicles.

　　Enterprises with mature cell technology include BAK, Tiansheng, Huayuebao and other manufacturers, with stable performance. The definition rule of its model is: such as 18650 type, which refers to the battery with a diameter of 18mm and a length of 65mm, and a 18500 battery with a diameter of 18mm and a length of 50mm, which is a cylindrical battery.

　　Voltage: 3.6V (conventional universal battery, used for electronic products and low-power electrical equipment with a maximum discharge of 1C. Discharge conditions can be changed according to the situation)