The lithium-ion batteries we see, cylindrical batteries, soft pack batteries, and square batteries, are generally handsome in appearance and cannot be found as large as traditional lead-acid batteries. Why is this?

Due to its high energy density, lithium batteries often dare not be designed with large capacity. The energy density of lead-acid batteries is around 40Wh/kg, while lithium batteries have exceeded 150Wh/kg. The increase in energy concentration increases the demand for safety.

Firstly, a single lithium battery with excessive energy can experience accidents, causing heat loss and rapid internal reactions. In a short period of time, excessive energy can be released nowhere, making it very dangerous. Especially when the development of security technology and control capabilities is not sufficient, the capacity of each battery should be restrained.

Secondly, the energy wrapped in the lithium battery shell is beyond the reach of firefighters and fire extinguishing agents in the event of an accident, and can only be isolated from the scene during the accident, allowing the accident battery to react on its own until the energy is exhausted.

Of course, for safety reasons, current lithium batteries have been designed with multiple safety measures. Take cylindrical batteries as an example.

Safety valve: When the internal reaction of the battery exceeds the normal range, the temperature rises, and side reaction gas is generated, and the pressure reaches the design value, the safety valve automatically opens to release the pressure. At the moment the safety valve is opened, the battery completely fails.

Thermistors, some cells are equipped with thermistors. Once overcurrent occurs, the resistance increases sharply after reaching a certain temperature, and the current in the circuit decreases, preventing further temperature rise.