Briefly describe the protection of lithium-ion batteries

Since the birth of lithium-ion batteries, safety issues have been accompanied. With the popularity of portable electronic devices such as mobile phones and tablet computers, the requirements for battery capacity are getting higher and higher, and at the same time, the battery is required to be smaller and smaller. The energy density of the battery core is required to be high, and the danger is also greater. Therefore, the protection of lithium-ion batteries is indispensable. Different manufacturers have proposed different protection schemes for different types of lithium-ion batteries.

Battery type and its protection

Lithium-ion batteries are available in a variety of categories. They can be divided into cylindrical and square shapes according to their shape. They can be divided into lithium-ion and lithium-polymer batteries according to the state of the electrolyte. At present, most of the batteries used in mobile power supplies are cylindrical 18650 cells. (18mm diameter, length 65mm) and square lithium polymer battery core.

The safety is analyzed below from the battery structure.

1. Cylindrical Lithium Ion Battery (18650)

The battery core has a PPTC (Recoverable Safety Device) for over temperature and over current protection. When the battery core temperature is too high or the current is too high, the PPTC will become a high-resistance state, thereby blocking the battery core charging and discharging current, and avoiding the battery fire and explosion.

2. Square lithium battery

The design of MHP-TA and PPTC close to the battery core enables the MHP-TA and PPTC to better sense the battery temperature. When the battery temperature rises abnormally, it can exhibit high resistance, hinder the charge and discharge current of the battery, and ensure the safe use of the battery. .


The protection circuit can be divided into two parts:
Active component protection (protection IC and Mosfet), also known as primary protection, passive component protection (MHP, PTC, Fuse), also known as secondary protection. The primary protection circuit is mainly for the overcharge, over discharge, overload and short circuit of the battery. The IC detects the battery voltage and the charge and discharge current to control the Mosfet to turn on or off to ensure the lithium battery works in a safe state.