Why Lithium Batteries Need Secondary Protection？

Reason:

Due to their inherent safety risks and the uncertainties of their operating environments, lithium-ion batteries require secondary protection. The primary reasons are:

Potential Failure of Protection ICs and FETs:

Lithium-ion battery packs typically rely on a primary protection system involving Protection ICs (Integrated Circuits) and FETs (Field-Effect Transistors) to prevent overcharge, over-discharge, and overcurrent. However, these components can fail due to environmental factors (e.g., high temperature, vibration) or improper use (e.g., short circuit, overload), leading to the failure of the primary protection.

Overcharge Leading to Thermal Runaway:

Overcharging can cause electrolyte decomposition, gas generation, or a rapid temperature increase within the lithium battery, subsequently triggering thermal runaway, and even leading to fire or explosion. When primary protection fails, secondary protection becomes a critical barrier to prevent such accidents.

Mandatory Regulatory Standards:

Safety standards such as UL 1973, IEC 62619, and GB 43854-2024 explicitly mandate that lithium battery systems must incorporate multi-level protection mechanisms to effectively reduce safety risks in abnormal conditions.

Based on the aforementioned reasons, secondary protection for lithium batteries is required.

SETsafe | SETfuse Solutions & Products:

A common secondary protection measure is to connect a product in series within the battery charge / discharge circuit: the [Heat CutOff (HCO) (Three-Terminal Fuse)], which provides:

Overcurrent Protection:

When the current abnormally increases (e.g., due to a short circuit), the Heat CutOff (Three-Terminal Fuse) heats up and rapidly melts, interrupting the circuit and preventing battery overheating or damage.

Overcharge Protection:

The Heat CutOff (Three-Terminal Fuse) can sense overvoltage or abnormal charging conditions through its built-in mechanism, triggering its internal heater to actuate, thereby preventing the further development of overcharge.

Risk Reduction:

By promptly disconnecting the charge/discharge circuit, the Heat CutOff (Three-Terminal Fuse) effectively reduces the possibility of thermal runaway, fire, or explosion.

Heat CutOff (HCO) (Three-Terminal Fuse): Learn more

For lithium battery secondary protection, SETsafe | SETfuse also offers a broader range of products and diverse protection methods. For detailed information, please refer to the attached PDF document.

SETsafe | SETfuse provides professional solutions to ensure optimal performance for your product applications.

Summary

Secondary protection is a vital complement to the lithium battery safety system. It provides an additional layer of safety in case of primary protection failure, meeting stringent regulatory requirements and mitigating accident risks. This multi-level protection mechanism is particularly crucial in complex application scenarios.

Rechargeable Battery Safety Protection

SETsafe & SETfuse Multi-Product Solutions & Products

Rechargeable Battery Safety Protection SETsafe & SETfuse Solution_V1.3_May 8,2025.pdf

Contents of the Document: 

8 Category of Products to Solve Battery Overcharge, Over Discharge, Over Temperature and Over Voltage.

Heat CutOff (HCO) (Three-Terminal Fuse) Application Areas:

Smartphones / Tablets / Laptops.

Power Tools.

Electric Scooters.

Electric Bicycles.

Electric Motorcycles.

Portable Power Banks / Portable Chargers.

Home Energy Storage Systems.

Rechargeable Battery Packs / Storage Batteries.