Specification For Design Of Lithium Batteries

As there are hundreds of millions of mobile phones worldwide, to achieve security, the failure rate of security protection must be less than one in 100 million. As a result, the failure rate of circuit boards is generally much higher than 1 in 100 million. Therefore, when designing a battery system, there must be more than two safety lines of defense. A common misconception is to use the charger directly to charge the battery. This places the burden of overcharge protection entirely on the protective plate on the battery pack. Although the failure rate of the protection board is not high, even if the failure rate is as low as one in a million, the probability of explosion accidents occurring worldwide is still daily. If the battery system can provide two separate safety protections for overcharge, over discharge, and over current, if the failure rate of each protection is 1/10000, the two protections can reduce the failure rate to 1/100 million.
Common battery charging systems include chargers and battery packs The charger includes an adapter and a charging controller. The adapter converts AC power to DC power, and the charging controller limits the maximum current and voltage of DC power The battery pack contains two major parts, a protective plate and a battery cell, as well as a PTC to limit the maximum current. Adapter AC to DC function: electrical controller current and voltage limiting. Charger function: protection board against overcharge, over discharge, over current, etc.
Battery pack function: current limiting plate. Taking the mobile phone battery system as an example, the overcharge protection system uses the charger output voltage to be set at around 4.2V to achieve the first layer of protection, so that even if the protective plate on the battery pack fails, the battery will not be overcharged and cause danger. The second protection is the overcharge protection function on the protection board, which is generally set to 4.3V. In this way, the protection board usually does not have to be responsible for cutting off the charging current, and only needs to be activated when the charger voltage is abnormally high. Overcurrent protection is handled by a protective plate and current limiter, which are also two layers of protection to prevent overcurrent and external short circuits. Due to over discharge, it only occurs during the use of electronic products. Therefore, the general design is to provide the first layer of protection by the circuit board of the electronic product, while the protective board on the battery pack provides the second layer of protection. When the electronic product detects that the power supply voltage is below 3.0V, it should automatically shut down. If this feature is not designed during the design of the product, the protection board will close the discharge circuit when the voltage drops to 2.4V.
Summary: When designing a battery system, it is necessary to provide two separate layers of electronic protection against overcharge, over discharge, and over current. Remove the protective plate and charge it. If the battery explodes, it indicates poor design. Although the above method provides two layers of protection, consumers often purchase non original chargers to charge after the charger breaks down. Charger manufacturers, based on cost considerations, often remove the charging controller to reduce costs. As a result, bad money drives out good money, and many inferior chargers appear on the market. This makes overcharge protection lose its first and most important line of defense. Overcharging is the most important factor that causes battery explosions, so poor quality chargers can be called the prime culprit in battery explosions. Of course, not all battery systems use the above scheme. In some cases, there will also be a design of a charging controller within the battery pack.
The last line of defense: If electronic protective measures fail, the last line of defense will be provided by the battery. The safety level of a cell can be roughly differentiated based on whether the cell can withstand external short circuits and overcharges. Before the battery explodes, if lithium atoms accumulate inside the material surface, the explosion power will be greater. Moreover, the protection against overcharge is often left with only one line of defense due to consumers using inferior chargers. Therefore, the ability of the cell to withstand overcharge is more important than the ability to withstand external short circuits. Compared to the safety of steel shell cores, aluminum shell cores have a high safety advantage.