Analyze the design specifications of lithium batteries

Since there are hundreds of millions of mobile phones in the world, the failure rate of security protection must be less than one in 100 million to be safe. Because the failure rate of circuit boards is generally much higher than one in 100 million. Therefore, the design of the battery system must have more than two safety lines. A common design error is to use the charger (adapter) directly to recharge the battery pack. This makes the overcharge protection completely on the protection board of the battery pack. Although the failure rate of the protective plate is not high, even if the failure rate is as low as one in a million, the probability of an explosion accident occurs every day in the world. If the battery system can provide overcharge, overdischarge and overcurrent two kinds of safety protection, the failure rate of each protection is one in ten thousand, through two kinds of protection, the failure rate can be reduced to one hundred million. The general block diagram of the battery charging system is shown in the figure below, including the charger and the battery pack. The charger consists of two parts: an adapter and a charging controller. The adapter converts ac to dc, and the charge controller limits the maximum current and voltage of dc. The battery pack contains a protection board and a battery, and a PTC to limit the maximum current. The AC and DC functions of the adapter: the current limit and voltage limit of the electrical controller. Charger function: protection board overcharge, overdischarge, overcurrent protection. Battery pack function: current limiter. Take the mobile phone battery system as an example. The overcharge protection system uses the charger's output voltage to be set at about 4.2v to achieve the first layer of protection, so that even if the protection board on the battery fails, the battery will not be overcharged and dangerous. The second type of protection is the overcharge protection function on the protection board, which is generally set at 4.3v. In this way, the protection board is usually not responsible for cutting off the charging current, and only works when the charger voltage is abnormally high. The overcurrent protection is composed of a protection board and a current limiter. It is also two shields to prevent overcurrent and external short circuits. Because over-discharge will only occur during the use of electronic products. Therefore, the general design is that the circuit board of this electronic product provides the first protection, and the protection board on the battery pack provides the second protection. When the electronic product detects that the power supply voltage is lower than 3.0v, it should automatically shut down. If this function is not considered during product design, the protection board will close the discharge circuit when the voltage drops to 2.4v. Overview: The battery system design must have two electronic protection functions: overcharge, overdischarge, and overcurrent. Remove the protective cover and charge. If the battery explodes, this is a bad design. Although the above methods provide two kinds of protection, because consumers often buy non-original chargers to charge after the charger is broken, the charger often removes the charge controller in order to reduce the cost. As a result, bad money drives out good money, and there are many bad chargers on the market. This eliminates the first and most important line of defense, preventing it from overcharging. Overcharging is the most important factor leading to battery explosion, so inferior chargers can be said to be the culprit of battery explosion. Of course, not all battery systems use the above approach. In some cases, the battery pack also has a charge controller design. For example, many laptop computers have a charge controller on the battery stick. This is because notebook computers usually have a built-in charging controller, and consumers can only use one adapter. Therefore, the external battery pack of the notebook computer must have a charge controller to ensure that the external battery pack is safe when the adapter is used for charging. In addition, charging products used in car cigarette lighters are sometimes made into battery packs in charge controllers. The last line of defense: If the electronic defense fails, the last line of defense is supplied by the cell. The safety level of the battery can be roughly divided according to whether the battery can be isolated by external short circuit and overcharge. This is because if lithium atoms accumulate on the surface of the battery before the explosion, the energy of the battery will be greater. In addition, overcharge protection is often due to consumers using inferior chargers and there is only one line of defense. Therefore, the ability to resist overcharge is more important than the ability to resist external short circuits. Compared with steel shells, aluminum shells have higher safety performance. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Which is better, lithium battery or lead-acid battery?