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How Pressure Relief Valves Work in Cylindrical Lithium Cells | Safety Mechanism Explained by Huawen New Power

How Pressure Relief Valves Work in Cylindrical Cells

Pressure relief valves are critical safety components integrated into cylindrical lithium battery cells. They serve as the last line of defense against overpressure conditions that could otherwise lead to rupture, fire, or explosion.

Cylindrical Cell Pressure Relief Valve Diagram

1. What Is a Pressure Relief Valve?

A pressure relief valve (also known as a vent or safety valve) is a small metal disc located at the cell’s top cap. It is designed to open when the internal gas pressure inside the cell exceeds a safe threshold, allowing gases to escape safely.

Key Function: Prevent the cell casing from bursting by releasing excessive internal pressure caused by overcharging, overheating, or internal short-circuiting.

2. How It Works: Step-by-Step Process

Pressure Relief Valve Working Mechanism
  1. Normal Operation: The internal pressure remains stable under 0.1–0.3 MPa.
  2. Abnormal Condition: Due to heat, gas builds up and increases internal pressure.
  3. Activation: Once pressure reaches 1.0–1.5 MPa (depending on cell type), the valve ruptures at a pre-weakened seam.
  4. Pressure Release: Gas is vented through the top, preventing cell rupture or explosion.
  5. Deactivation: The valve remains permanently open, rendering the cell inoperative but safe.

3. Common Causes of Pressure Buildup

Cause Description Result
Overcharging Excessive voltage leads to gas generation and internal heat. Valve activates to vent gases.
Internal Short Circuit Defects or mechanical damage cause local heating. Rapid pressure increase.
Thermal Runaway Heat chain reaction causes uncontrolled temperature rise. Critical safety event — valve must function properly.

4. Visual Representation: Pressure vs. Time

Pressure vs. Time Graph for Cylindrical Cells

As shown above, under normal conditions, pressure remains flat. During overcharge or overheating, pressure spikes until the safety valve activates, releasing gas and stabilizing the cell.

5. Material and Design Variations

  • Material: Usually aluminum or nickel-plated steel.
  • Activation pressure: Calibrated between 1.0–1.5 MPa for standard 18650/21700 cells.
  • Design: Radial vent, burst disk, or scored cap types are common.

6. Importance for Battery Pack Safety

Warning: When designing lithium battery packs, ensure all cells are equipped with functional pressure relief valves and adequate venting channels in the pack casing to allow safe gas release.

Huawen New Power ensures all cylindrical cells used in our battery packs undergo strict safety validation, including valve integrity testing and overpressure simulations, to deliver reliable and safe lithium power solutions.

7. Summary Table

Aspect Function Safety Impact
Pressure Relief Valve Releases gas at high pressure Prevents explosion or casing rupture
PTC/Current Interrupt Device Interrupts current flow during overcurrent Prevents further heating
Vent Channel Guides gas out of battery pack Prevents secondary ignition

Author: Huawen New Power Battery Engineering Team
Learn more: www.huawennewpower.com

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