Ribbon product for lithium ion battery pack protection overview

Ribbon product for lithium ion battery pack protection overview

First, the question is raised:

Compared with NiMH or NiCd batteries, lithium-ion batteries have high current density and are widely used in various portable devices. Lithium-ion batteries are often very sensitive to overcharging. When charging to the voltage across the battery is too high, it will increase the risk of battery leakage, smoke, burning, bursting (such dangers are often quite severe). Overcharging can be caused by loss of charge, incorrect electrodes, or incorrect charger usage. When the charge and discharge current is too large or externally short-circuited, the internal heating may damage the battery or burn other components, which will seriously shorten the cycle life of the battery.

The task of the protection circuit is to monitor the parameters of the battery charge and discharge status against various faults that may occur in the battery to ensure battery life and performance, and to protect the battery and external devices (such as mobile phones, PDAs, laptops, etc.) from damage.

Mobile phone batteries typically use a primary protection circuit consisting of a battery-integrated integrated IC and a metal oxide FET. The protection IC controls the turn-on or turn-off of the FET by monitoring the voltage across the battery and the discharge current to prevent overcharging, short-circuiting, over-discharge, and the like.

Although a single protection is generally considered reliable, the protection IC or MOS-FET may be damaged when the ESD voltage is too high or too warm, and the IC will oscillate when shorted, while most IC+MOS-FET circuits are charged. The detection of discharge overcurrent is indirect and does not guarantee overcurrent protection in all operating states of the battery, and the reliability of protection is also reduced. After adding the special PTC for battery protection in the protection circuit, even if the protection circuit fails or the temperature rise is high, the PTC can protect against overcharge, overcurrent, short circuit, over temperature and other faults to ensure that the battery is misused. In the case of abuse or abuse, security issues do not occur.

Second, the solution:

Early batteries used fuses or bimetals as secondary protection devices for overcurrent, short circuit, and overtemperature. However, failures such as battery overcurrent are often temporary, and do not mean permanent damage to the battery. The defect that the fuse cannot be recovered causes the battery manufacturer's quality assurance cost to increase; while the bimetal can recover itself, but it will not Stopping the action/recovery will result in early fatigue wear and contact of the contacts and thus loss of protection. In addition, the bimetal has a large volume and weight for the demanding requirements of the portable device for the volume and weight of the battery. Polymer PTCs have advantages in providing secondary protection for batteries with self-healing, low resistance, and no additional volume requirements.

1. Overcharge protection:

According to GB/T18287-2000 requirements for over-charge protection of lithium-ion batteries, we have over-charged tests with batteries with a nominal capacity of 720 mAh and no PTC protection for battery protection. Voltage and surface temperature. (The charging power supply is set to constant current 2C A charging, the constant voltage value is 2 times the nominal voltage)

From the above test results, it can be observed that the surface temperature of the battery without PTC protection can reach 120 °C when overcharged, and eventually it will leak or ignite or explode; and it is equipped with Kete KT16-1750DL polymer PTC. The surface temperature of the battery does not exceed 80 °C.

2. Short circuit protection:

When the battery is short-circuited externally, the current can reach more than 15A. Under normal circumstances, the limit operating parameters of the power FET will be easily exceeded; in addition, the working state of the protection IC cannot be stabilized when short-circuited. All of the above problems lead to inadequate battery short-circuit protection. The polymer PTC provides protection before the MOS tube is broken down, ensuring the cycle life of the battery and reducing the manufacturer's quality assurance costs.

The polymer protection PTC thermistor for battery protection of Shanghai Kete Polymer Materials Co., Ltd. is a strip-shaped, nickel-plated copper lead, which is suitable for use in high current density lithium ion batteries for portable equipment.