Does charging speed have an impact on the degradation of CR2016 battery?

　　Lithium-ion batteries increase in charge and discharge times during use, and their capacity gradually decreases. The so-called decline refers to the intuitive feeling of gradually running out of power. Like our mobile phones, it can last a whole day on a single charge when you first buy it, but it can only last half a day when fully charged. This is why lithium-ion batteries lose capacity with use. This kind of product with fast replacement speed is also better solved. We may have replaced the phone with a new one before the battery capacity ran out, but this long-lasting durability of an electric car doesn't quite cut it. Generally speaking, the service life of a car may be about 10 years, during which it may need to be charged 1,000 to 2,000 times (assuming charging every other day). In order to meet the needs of electric vehicles, the lithium-ion battery of electric vehicles must be Put forward certain requirements for its service life.

　　There are many factors that affect the life of lithium-ion batteries. Operating temperature, charging and discharging current, charging and discharging blocking voltage, etc. will all affect the degradation rate of lithium-ion batteries. The mechanisms of lithium-ion battery capacity decline can be divided into three categories: increase in internal resistance and polarization, loss of anode and cathode active materials, and loss of Li. External factors also have different effects on these three types. For example, lifepo4 material batteries usually have very good cycle performance, but research by derekkn.wong and others from the University of Texas Allenton University in the United States has shown that if the lifepo4 battery of model 266650 is subjected to 15c pulse discharge and 15c continuous discharge under the usage conditions, the lifepo4 battery's The impact will be completely different. A lithium iron phosphate battery with 15c pulse discharge cannot discharge 15c after its capacity drops 40 times, but the 1c discharge is reduced by 6%/20 times. The capacity of 15c continuous discharge battery decreases slowly, and 15c can be discharged after 60 times, but the decay rate of 1c ratio is 14%/20% faster than that of 15c pulse discharge. Mechanism research shows that the battery with 15c pulse discharge contains more LiF in the cathode SEI film, and LiF interferes more with lithium ion diffusion. The Li diffusion resistance and charge exchange resistance of the battery increase rapidly, so during the charging and discharging process, The polarization voltage is too large, causing the high current discharge capacity of lifepo4 to decrease rapidly.

　　The discharge system of lithium-ion batteries relies heavily on users, and a good discharge system may not be suitable for all users. However, since the charging agent is mainly controlled by the designer, the study of the impact of the charging agent on the reduction of battery life can better guide the design of lithium-ion batteries. Yanggo from Beijing Jiaotong University and others studied the impact of various charging systems on the decline in lithium-ion battery life, studied their mechanism of action, and proposed a model for the decline in lithium-ion battery life. Yanggau research shows that if the charging current and blocking voltage exceed a certain number, the deceleration of the lithium-ion battery may be greatly accelerated. In order to reduce the degradation rate of the lithium-ion battery, the charging and discharging current and blocking voltage must be selected to suit multiple systems.

　　 In this test, Xiangyang used commercial 18650 batteries, used licoo2 as the cathode material, and graphite as the cathode material. The impact of other charging currents on the battery decay rate was tested, as shown in the figure below. As shown in Figure a below, the charging current has a great influence on the decay rate of lithium-ion batteries. According to the 0.5c charging ratio, the degradation rate of the battery in the first 150 cycles is 0.020%/loop, 150-800 times is 0.0156%/loop, and after 800 times it is 0.0214%/loop and is stable. According to the 0.8c charging ratio, the battery's degradation rate is 0.0243%/cycle for the first 150 times, -0.175%/cycle for 150-800 times, and 0.0209%/cycle after 800 times. For 1c ratio filling, the decay rate for the first 150 times is 0.032%/cycle, the decay rate from 150 to 600 times is 0.0188%/cycle, and the decay rate after 600 times is 0.0271%/cycle. 1.2c charging causes the decay rate for the first 100 times to be 0.0472%/cycle, the attenuation source rate for 100 to 400 times to be 0.0226%/cycle, and the decay rate after 400 times to be 0.0356%/cycle. Charging with a ratio of 1.5c is very different from charging batteries with a different ratio, and the average rate of degradation is much faster than using a 0.078%/loop charge than batteries with other ratios. Judging from the data mentioned earlier, as the charging ratio increases, the decay rate of lithium-ion batteries also increases rapidly. Judging from the slope of the curve, the decay rate of the battery has three different stages. The decay rate in the previous period is slower. fast (first stage), a stable stage with slower decay speed in the middle (second stage), and a later stage with accelerated decay speed (third stage). According to research on the decay mechanism of three-stage batteries, the first stage may decay faster because the growth of the battery SEI film consumes some Li. In the second stage, the structure of the SEI film is stable and the interior is relatively stable, so the decay rate is slow. In the third stage, the battery ages, the loss of active materials begins to occur, the electrode active interface decreases, and the battery is very sensitive to current response. Figure c is an experiment on the impact of different cut-off voltages on the battery decline rate. The test results show that increasing the cut-off voltage to 4.3v will cause a sharp decline in battery cycle performance, and reducing the cut-off voltage will effectively improve the battery cycle performance.

　　 If the charging current is less than 1c, the dynamic internal resistance of the battery will change almost the same as the battery cycle, but if the charging current exceeds 1c, the dynamic internal resistance of the battery will increase rapidly as the charging speed increases. The test results in Figure b show that when the charging blocking voltage is 4.3v, the dynamic internal resistance of the battery increases very quickly, which indicates that the high blocking voltage aggravates the dynamic condition of the battery, while when the blocking voltage is 4.1v and 4.2v, the battery dynamic Internal resistance increases more slowly.

　　As mentioned above, no matter what the charging current or brownout voltage is, as long as the charging current or voltage exceeds this value, the battery will degrade faster; for the above battery, if the charging current and blocking voltage exceed this value, the battery will degrade faster ;If it is less than this value, even if the charging current and blocking voltage are increased, the battery's degradation rate will not be significantly increased. Research on the mechanism of the impact of charging current and cut-off voltage on the battery decay rate shows that when the charging current is lower than 1c, the main impact is the loss of anode and cathode active materials. If the cut-off voltage is lower than 4.2v, the main impact is the loss of Li. If the charging If the current and cut-off voltage are higher than this value, the loss of anode and cathode active materials and Li loss will be greatly accelerated.

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