Lithium battery soft short circuit

　　Soft short circuit (Soft Short is the main cause of some battery unevenness. Similar flaws during battery production may cause short -circuit resistance of the battery by 40kq or more. The self -release rate caused by this high impedance can reach 0.1mA or monthly monthly 3%. Some qualified batteries that are out of factory may also cause soft short circuit problems, but most of the batteries will not occur, so the capacity can be maintained for several years. Strictly speaking, soft short circuit is a kind of mechanical and electrical change. It is composed of a single battery, so this battery can be charged repeatedly without capacity loss. However, a soft and short -circuit battery will lose 3%per month in the series of battery packs, while other batteries have no loss.

　　When the SOC of the battery in the battery pack is different, the total capacity will be reduced. Before the corresponding capacity is reduced, the battery package needs to be adjusted once when used, and it is often adjusted from time to time after being stored, so that the initial capacity loss can be restored. At the same time, only a simpler balance is required in each charging process to avoid re -mating. These continuous adjustments are usually unacceptable at all. After the first use, the future discharge process will no longer need to be balanced. For example, assuming that there are two series of battery C1 and C2 in a battery packet, C1 discharge 3%per month, and the SOC value drops from 40%to 31%after three months. C2 does not have a soft short circuit, so SOC remains 40%. When charging, the SOC of C2 returns to 100%, while C1 can only return to 91%. During the discharge, the C2 is still 9%when the SOC of C1 reaches 0%. Therefore, the battery packet generates 9%loss. If a differential current applies to C1 is balanced, the two batteries and the entire battery bag will restore a full capacity. The loss of C1 does not reduce the capacity of the battery pack, as shown in Figure 1A and 1b. The degradation of battery capacity degeneration is reduced due to the differences in production or process, and the possibility of this situation is usually very small in the production process. In addition, the battery performance produced in the same batch is usually the same, so the battery in most battery packs does not have an uneven problem. However, the battery may accidentally occur in small defects. If the temperature of the battery pack work changes greatly in this case, then some batteries will reduce the performance of other batteries faster than other batteries. For example, the area of battery packs used in the computer is very large, so a part of the battery pack will be close to the power or CPU, which is more heated in this battery than other batteries. Such problems can be made up by battery balance. This equilibrium treatment must be implemented during the charging and discharge process. This process is called maximum capacity/energy. However, this is difficult to achieve in practical applications, and it is not intuitive enough. The problem of maximization of capacity/energy needs to be further studied. Keep the battery balancing monitoring battery voltage and temperature tracking the battery voltage change. When the battery voltage changes more than 10mV, the circuit starts the balanced processing to match different battery voltage in the battery pack. This equilibrium is achieved by "diversion" battery (the highest voltage battery) current. Generally, after connecting a power transistor and a current -limiting resistance, it is parallel to each battery in the battery pack to control the balance process. During the charging process, the power transistors are partially diverted to the current of the battery, so that its charging speed is slower than other batteries. During the discharge process, the power transistor can be used to increase the effective load of the battery, so that its discharge speed is faster than other batteries, and the battery is balanced in the charging/discharge mode. The power consumption of the external transistor must pay attention to the selection of power transistors and current limit resistance in the design of the power consumption circuit to keep the current within a reasonable range. If the equilibrium current is too high, the power consumption will be very large, causing the battery pack to rise or increase the burden of component; on the contrary, if the balanced current is too low, it will take a longer time or multiple cycles to play a balanced role, thereby reducing the battery equilibrium efficiency efficiency , Even lost meaning.

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