Why are lithium batteries mostly small?

Power lithium battery has always been the leading power source for electric vehicles. Long life, high energy density, great potential for improvement. The safety function is sufficient to change, and the energy density can continue to rise. In the foreseeable future (rumored around 2020), it will be possible to catch up with the endurance and cost-effectiveness of gasoline-powered vehicles, and enter the first stage of maturity of electric vehicles. But lithium batteries also have their problems. ➤1: Why are most of the lithium batteries very small? The lithium batteries, cylindrical batteries, soft-pack batteries, and square batteries that we have seen look generally beautiful. We can't find the big guys like traditional lead-acid batteries at all. Why is this? Energy? With high density, lithium batteries are often afraid to plan for large capacity. The energy density of lead-acid batteries is about 40Wh/kg, while the energy density of lithium batteries has exceeded 150Wh/kg. The higher the energy convergence, the higher the safety requirements. First of all, a single lithium battery with too high energy will cause an accident, resulting in thermal runaway, and the battery reacts violently. In a short time, too much energy will not be released, which is very dangerous. The capacity of each battery should be limited, especially when safety technology and control capabilities have not been fully developed. Secondly, the energy is wrapped by the lithium battery shell. Once an accident occurs, the firefighters and the extinguishing agent cannot touch and cannot do anything. Only in the event of an accident can they cut off the scene, and the accident battery will react until the energy is exhausted. Of course, for safety reasons, there were many safety measures for lithium batteries at that time. Put the cylindrical battery. Safety valve. When the internal reaction of the battery exceeds the normal scale, the temperature rises. With the appearance of the secondary reaction gas, the pressure reaches the planned value, and the safety valve is actively opened to release the pressure. As soon as the safety valve was opened, the battery was completely broken. Thermistor. Some batteries are equipped with a thermistor. Once the resistance reaches a certain temperature, the resistance will increase and the current in the circuit will decrease, preventing further temperature rise. The core equipment of the fuse has the function of an overcurrent fuse. Once the overcurrent danger occurs, the circuit is disconnected to prevent the occurrence of vicious accidents. ➤2: Common problems of lithium batteries Lithium batteries cannot be made into a large battery, so we have to organize a lot of small batteries, we go to the same place, sincerely cooperate, and we can also fly by electric car. At this time, the demand faces a problem, commonality. Our daily experience is that two dry batteries, the positive electrode and the negative electrode are connected, and the flashlight can emit light. Who cares if it is an ordinary job. Large-scale deployment of lithium batteries is not easy. The difference in lithium battery parameters mainly refers to the difference in capacity, internal resistance and open circuit voltage. The following problems can be found when applying different cell strings. The capacity of the worst battery determines the capacity of the entire battery pack. In order to prevent the battery from overcharging and discharging, the logic settings of the battery management system are as follows: during discharge, when the lowest single voltage reaches the discharge cut-off voltage, the entire battery pack stops discharging; during charging, when the highest single voltage reaches the charge cut-off voltage, the charging stops. Connect the two batteries in series. One battery has a capacity of 1C and the other has a capacity of 0.9c. In series, the two batteries pass the same amount of current. When charging, a small-capacity battery must be fully charged before it reaches the charging cut-off state before the system continues to charge. When discharging, a small-capacity battery must first release all available energy, and the system immediately stops discharging. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Analysis of the advantages and defects of lithium batteries