Aug 13, 2019 Pageview：23
The inconsistency in the performance of the core is formed during the production process and deepened during the use process. The core in the same battery pack is weak and becomes weaker at an accelerated rate. The degree of dispersion of parameters between the single core increases with the degree of aging.
Lithium battery power has firmly occupied the position of the power of electric vehicles. It has long service life, high energy density, and great potential for improvement. Security can be changed and energy density can continue to rise. In the foreseeable time(it is said around 2020), it will be possible to catch up with the fuel car's endurance and cost-effectiveness and enter the first stage of maturity of electric cars. However, lithium batteries also have lithium battery troubles.
1: Why are most lithium batteries small
The lithium batteries we see, the cylindrical batteries, the soft-pack batteries, the square batteries, are generally beautiful and can not find the size of a traditional lead-acid battery. Why is this?
The energy density is high, and lithium batteries often do not dare to design large capacity. The energy density of lead-acid batteries is about 40 Wh / kg, while lithium batteries have exceeded 150 Wh / kg. The energy concentration is increased, and the requirements for safety are raised.
First of all, a single high-energy lithium battery that encounters an accident, causes thermal runaway, rapid internal reaction of the battery, and in a short period of time, excess energy is not released. It is very dangerous. The capacity of each battery should be restrained, especially when safety technologies and regulatory capabilities are not sufficiently developed.
Second, the energy wrapped up by the lithium battery shell, once there is an accident, firefighters and fire extinguishers can not be touched and can not do anything. They can only isolate the scene when an accident occurs, and the accidental battery reacts on its own and the energy burns out.
Of course, for safety reasons, the current lithium battery has designed multiple safety measures. Take a cylindrical battery as an example.
Safety valve, when the internal reaction of the battery exceeds the normal range, the temperature rises, and with the generation of side reaction gas, the pressure reaches the design value, the safety valve automatically opens, and the pressure is released. When the relief valve opens, the battery is completely disabled.
Thermistors, some cores are equipped with thermistors. Once there is a flow, the resistance value increases steeply after reaching a certain temperature, and the current in the loop decreases to prevent further temperature increase.
The fuse is equipped with a fuse that has the function of overflow melting. Once there is a risk of Overflow, the circuit is disconnected to avoid vicious accidents.
2: Lithium battery consistency
Lithium batteries can not be made into a large one, had to organize a large number of small power core, everyone to one place, sincere cooperation, can also fly with electric vehicles. At this point, there is a problem with consistency.
Our daily experience is that two dry batteries, the positive and the negative poles are connected, and the flashlight can emit light. Who cares if it is inconsistent? But the large-scale use of lithium batteries is not so simple.
The inconsistency of lithium battery parameters mainly refers to the inconsistency of capacity, internal resistance, and open circuit voltage. Inconsistent core strings are used together and the following problems occur.
Capacity loss, core monomer constitutes a battery pack, capacity conforms to the "barrel principle", the capacity of the worst core determines the capacity of the entire battery pack.
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