Full technical analysis of the reasons for the continuous explosion of lithium battery news

　　The application of lithium batteries in life has suddenly expanded, mainly due to the widespread use of smart phones, wearable devices, electric bicycles and new energy vehicles. Often contains a lot of misleading information.

　　The application of lithium batteries in life has suddenly expanded, mainly due to the widespread use of smart phones, wearable devices, electric bicycles and new energy vehicles. Often contains a lot of misleading information. In this article, we start from the simple application of lithium battery to the complex application one by one.　　 Measure the battery performance, there are several important indicators: 　　 One, charge and discharge rate: the higher the better　　"C" is a special symbol to describe the size of the battery charge and discharge current. 1C discharge means the amount of current required to discharge the battery from full to empty within 1 hour. iPhone6 battery capacity is 1810mAH, then the 1C discharge current of this battery is 1.81 amps; each battery used in BYD e6 electric car has a capacity of 200 AH, then the 1C discharge current of this battery is 200 amps. If a battery is discharged at a high rate, it usually emits less energy than a low rate. Full technical analysis: why the explosion news of lithium batteries continuously discharges electricity under different discharge rates. From the test results of the above figure, it can be seen that the energy released by this power battery using 10C discharge is 85% of that under 1C discharge, and the energy released by 20C discharge is only 1C discharge. 70% below.　　 Second, the number of charge and discharge cycles: The more the better, 500 times is a common value for lithium batteries. The number of charge and discharge cycles for lithium batteries made of different materials ranges from 300 to 3000 times. The specific meaning of this value may be slightly different for each factory. It can be roughly understood as: According to the charge and discharge rate specified by the manufacturer (such as 1C discharge, 0.3C charge; each time from 0% to 100%, the cycle is repeated) , After 500 cycles, the battery capacity is still 80% of the original. The relationship between the number of charge and discharge and usage habits is too great, let's give a few examples. 1. The influence of the charge and discharge intensity on the number of cycles is marked by the factory: each time charge and discharge from 0% to 100%, 1C discharge, 0.3C charge, the capacity decays to 80% after 500 times. This is the most stringent test cycle. It doesn’t need to be so strict. Look at the following. If the power cycle is 25%-75%, 1C discharge, 0.3C charge, after 2000 times, the capacity decays to 80%. 　　 If the power cycle is 50%-100%, 1C discharge, 0.3 charge, capacity decays to 80% after 1800 times. 2. The impact of shallow charge on life. Factory mark: each time from 0% to 100%, 1C discharge, 0.3C charge, capacity attenuation after 500 times 80% is the most stringent test cycle. It can also be less stringent. See below, the power cycle is 25%-75%, 1C discharge, 0.3C charge. After 2000 times, the capacity decays to 80% 　　 every time The power cycle is 50%-100%, 1C discharge, 0.3 charge, after 1800 times, the capacity decays to 80%　　. The above two examples show that the smaller the charge and discharge rate, the more conducive to the life extension; shallow charge and shallow discharge are also Conducive to life extension.　　3. Internal resistance: The smaller the better. This parameter changes with the load, temperature and other factors. As the battery life decreases, the internal resistance gradually increases. The lower the internal resistance of the battery, the more high-rate charging and discharging is possible. The internal resistance of an ordinary 18650 battery is about 50mΩ, and that of a power-type 18650 battery is about 15mΩ. If you want to know how big the internal resistance is, you need to use a special device to measure it, not a normal multimeter.　　Technical full analysis: why the explosion of lithium batteries continues to 　　 a tool for measuring battery internal resistance 　　four, battery consistency 　　The battery produced with the same material and the same process has the higher the consistency of the capacity, internal resistance, and charge-discharge curve, the better. Whether batteries can be assembled into battery packs on a large scale is very important. The larger the battery pack size, the higher the requirements for consistency. In the following pages, we will follow the difficulty of the application: 　　 1. Lithium batteries in mobile phones, tablets, wearable devices 2. Lithium batteries in laptops and mobile power sources 3. Lithium batteries in electric bicycles 4. Lithium batteries in electric vehicles The battery introduces some knowledge separately, so that the paging is sorted according to the battery size from small to large.　　I. Lithium batteries in mobile phones, tablets, and wearable devices　　Why is this field the simplest? Because there is only one lithium battery in these devices, and they are basically ternary lithium batteries. Ternary means three elements: nickel, cobalt, manganese, and Li (NiCoMn) O2, the cathode material of this lithium battery, are not exactly the same. The ratio of the three elements will be adjusted according to the requirements of use.　　Technical full analysis: Why do lithium batteries explode continuously 　　One, the charge-discharge rate　　Batteries used in digital devices usually have very low requirements for this. It is difficult for you to use a fully charged cell phone to automatically shut down within an hour, right? No one would design a digital device with a battery life of only 1 hour. It can last for at least 3 hours, so the discharge rate of the battery is about 0.3C to meet the demand, and the charging requirements are often very low. Generally, digital devices that are fully charged in 3-4 hours are acceptable to everyone, so the requirements on the battery are required for charging It is also around 0.3C.　　Technical full analysis: Why does the news of lithium battery explode continuously 　　 Regardless of domestically produced or imported lithium batteries such as Panasonic or Samsung, 1C discharge is the minimum specification, and the requirements for battery discharge in digital devices are far lower than the general standards of the battery industry. The charging rate is roughly the same as the basic indicators that the battery industry can currently achieve. If there is no special design, there is generally no need to worry. Full technical analysis: why the explosion of lithium battery news keeps OPPO’s battery flash charging characteristics, and higher requirements for charging. Recently, there have been special cases in the mobile phone industry. OPPO has proposed the characteristics of fast charging, which actually proposes special features for battery manufacturers. need. For OPPO’s latest N3, VOOC flash charge promises to charge 75% of the battery in 30 minutes. This is calculated as a charging current of 1.5C, which is 10 times the charging rate of ordinary mobile phone batteries. N3 is also reasonable at 3999 yuan. At least this battery will be one or two times more expensive than ordinary batteries.　　2. Number of charge and discharge cycles　　 Among digital devices, mobile phones are considered the most intensely used product. We charge it once a day. If the number of cycles is 500 times, the life span is 500 days. Is that correct? In fact, it is out of the conditions of use, so it is wrong. A cycle of 500 times refers to 1C discharge, and a continuous cycle of 500 times under 0.3C charge, the battery capacity is still 80% of the original. However, the discharge rate of our mobile phones is much less than 1C, often between 0.01C-0.5C. Therefore, after 700 cycles, 80% of the battery is usually left. This has been 2 years and the mobile phone is almost out of date. Apple is very smart in this regard. It deliberately does not use high-power batteries. Not only can it gain the advantages of thinness and lightness, but also because you will inevitably change to the next-generation iPhone in 2 years, why have to spend more on the battery? ? As for some people, it is obvious that the battery life is less in one year, and there is a reason for this, and we will analyze it later. Technical analysis: Why is it not good for lithium battery to keep 100% power at all times? Other digital devices, such as tablet computers, have longer battery charging and discharging cycles, but sometimes it is found that the battery life is significantly reduced in less than 2 years. This reason is also explained, and you will know it by reading the complete article.　　3. Battery internal resistance 　　 There is no special explanation.　　Four, battery consistency 　　 there is no special explanation.　　II. Lithium batteries in laptops and mobile power sources　　 What do the common 4-cell, 6-cell and 8-cell specifications of notebook batteries mean? This refers to the number of 18650 batteries. Taking 8 cores as an example, there are 2 combinations, one is 2 series and 4 parallel, and the other is 4 series and 2 parallel. Which one is used depends on the voltage conversion circuit of the notebook manufacturer Design, and battery compartment shape.　　Technical full analysis: Why does the news of lithium battery explode continuously 　　4-cell notebook battery　　This statement can also be described as a mobile power supply. The commercially available decent brand mobile power supply with a capacity of 10400mAh is made up of 4 2600mAh 18650 battery cells in parallel. In order to seize the Chinese market, Samsung SDK adopts low prices for large orders, and even loses the cost of selling 1 US dollars per unit, so many big-brand mobile power manufacturers like to use this cheap and high-quality battery cell, also because the single capacity is 2600, so the capacity of mobile power is often a multiple of 2600mAh: 5200mAh, 7800mAh, 10400mAh. 1. Charge and discharge rate New laptop batteries can discharge light in less than 1 hour, so the discharge rate of 1C is sufficient for them, and the charging requirements are not high. For example, the laptop battery can be fully charged within 3-4 hours. accept. For mobile power sources, the requirements for battery charge and discharge rates are even lower, almost the lowest among all digital devices. Full technical analysis: why the news of the explosion of lithium batteries continues. The internal structure of the Xiaomi 10400 mobile power bank. For the current 10400mAh (3.7V) mobile power supply in the market, the maximum output current is 2A (5V), which means it takes 3.7 hours to use the maximum current. In order to discharge light, the discharge rate is sufficient as long as 0.3C is satisfied. In terms of charging, the usual specification is 10400mAh with a 1.0A input port. This charging rate is only 0.13C. This is the reason why there are so many low-quality mobile power products: even regular manufacturers can buy the lowest performance in the battery market (note that low performance and poor quality are not exactly the same, but they are still highly related). In addition, it can also meet the requirements of use specifications. 2. The number of charge and discharge cycles The frequency of use of laptops and mobile power supplies is significantly lower than that of mobile phones. Mobile phones can be charged once every three days at most. However, on average, mobile power supplies and laptops may not be able to charge and discharge once a week. The life span of 50 cycles of charging and discharging can last one year. For mature lithium batteries, the worst and worst can provide 300 cycles of cycle life, which is enough for people who use laptops and mobile power supplies for 6 years of normal use.