Q&A: How to do hermeticity test and burst test for cylindrical lithium batteries? A clear article

In the context of the power battery and energy storage industry into the era of high safety, the cylindrical lithium battery "Seal Reliability" has become a key indicator in determining battery life, performance and safety.

Whether it's a 14500, 18650, 21700, or a longer cylinder of a larger size, the production line must perform two core tests:

• Air tightness test: Determine if there is a risk of air leakage from battery seals
• bursting test: Verification of the pressure limit and safety against explosion of the housing

These two tests ensure that the batteries are "in good condition".High pressure charging and discharging, electrolyte volatilization, mechanical compression, high temperature expansionIt can maintain stable sealing under working conditions such as "Cold", avoiding safety accidents such as bulging, liquid leakage, fire and so on.

Ⅰ. The structural fate of cylindrical cells: the inevitability of destructive testing

The structural design of lithium cylindrical batteries determines that their detection becomes a difficult problem.The top cap of the cylindrical cell is laser-welded to the steel shell housing to form a seal, and this welded area is the only location where leakage is possible.But it is precisely this location that cannot be tested non-destructively from the outside.

Traditional water immersion test? The cell casing is completely sealed and water cannot enter the interior to verify soldering quality.
Externally pressurized test? Pressure cannot be transferred to the weld interface and test results are meaningless.

The only solution: Punch holes in the bottom of the battery and apply pressure from the inside to verify the sealing of the top weld.

This is the first dilemma facing the industry:To test the seal, the seal must first be broken.

Ⅱ. What is done to test the air tightness of lithium cylindrical batteries?

Since punching holes is inevitable, let's make this 'damage' precise, manageable, and worthwhile.

Precision Industrial Technology Customized Cylindrical Lithium Battery for CustomersAirtightness Tester

Step 1: Minimally invasive perforation technique

A microscopic hole is made in the bottom of the battery (near the negative cap), usually between 0.5 and 2mm in diameter. The location and size of this hole is precisely calculated:

Location Selection Logic::

• Away from welding areas without affecting structural strength
• Close proximity to the inner chamber for quick pressure build-up
• Standardized positioning to ensure detection consistency

Dimensional control requirements::

• Small enough not to significantly affect mechanical strength
• Large enough for fast gas flow
• Highly repeatable to avoid testing errors

Step 2: Specialized Fixture Systems

Cylindrical batteries come in a variety of sizes, from 18650 to 21700 to the larger 32650, each requiring customized fixtures.

The Triple Function of Fixture Design::

functional hierarchy	technical requirement	Realization of value
physical location	Precise fixation of battery position	Ensure testing consistency
sealing fit	Seamless alignment with punch locations	Preventing gas leakage
Fast switching	modular design	multi-functional

Precision Engineering's Workplace SolutionsAdopting the upper and lower mold structure, it can be adapted to different battery specifications through simple mold replacement, and this design makes the return on investment of the testing equipment increase dramatically.

Step 3: Pressure application and monitoring

Fill the internal cavity of the battery with test gas, the pressure is usually set at1000~1500 kPaBetween.

The monitoring methodology is mainly based onpressure dropThe

Detection Principle: Close the gas line after inflation to a set pressure and monitor the pressure drop over a certain period of time. If there are micro leaks in the weld, the pressure will continue to drop.

Typical Test Parameters::

• Inflation time: 15~20 seconds
• Balancing time: 15~20 seconds
• Detection time: 15~20 seconds
• Judgment standard: pressure drop ≤ 1000 Pa

The accuracy of this method can be1 Pa levelIt is capable of detecting tiny leaks that are completely undetectable to the naked eye.

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1. Placement of customized test fixtures

Different sizes of batteries need to correspond to different "¢".Upper mold + lower mold" compression structure to ensure:

• Sealing surface reproducibility
• No leakage of test pressure
• Uniform force on the core axis

Precision Engineering'sAir tightness testing equipmentMultiple cores of different sizes can be covered by replacing the upper and lower molds to maximize the reuse rate of the device.

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2. Apply set pressure (e.g. 1000 kPa)

JC-B015 Airtightness Burst TesterFill the inside of the cell with air and raise it to the set pressure.

Typical test pressure:

• 300~500 kPa: conventional consumer batteries
• 1000~1500 kPa: Automotive grade high security cylindrical cell
• ≥1500 kPa: high-strength specialty cores (e.g., energy storage, power blade support cores)

Precision Engineering is currently availableAirtightness testers available with test ranges up to 3 MPaThe

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3. Voltage stabilization and detection

After a set stabilization time, theJC-B015 Airtightness Blasting TesterStart reading the leak:

• Pressure drop ΔP
• Leak rate Q
• Maximum Leakage Threshold Limit

Video case in point:
The customer requested that "leakage pressure ≤1000 Pa is considered acceptable", and the test value of "223 Pa" is in the fully acceptable range.

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4. Outcome: pass/fail

The air tightness meter automatically judges and outputs:

• OK (seal pass)
• NG (leakage exceedance)

It also supports MES traceability, curve mode, core code recording, and production line beat synchronization.

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5. Precision EngineeringAir tightness testercharacteristics

• No damage to the product (for laboratory sampling or mass production full inspection)
• Detects small leaks
• Controlled and fast testing process
• Can cover multiple cell types

Ⅲ. How is the lithium cylindrical battery burst test done?

If the air tightness test is to verify that "theSeal pass or fail"Then the blast test is to monitor.How reliable is the strength".

The Core Value of Blast Testing::

Batteries may be encountered in actual use:

• Transient high voltage due to internal short circuit
• Gas precipitation due to overfilling
• Elevated internal pressure at high ambient temperatures

These abnormal operating conditions must provide sufficient strength margins for the battery case to neither burst easily (safety risk) nor be overly robust (interfering with proper safety valve operation).

Methods of performing burst tests

continuous uplift strategy

Unlike the rapid inflation of airtightness testing, burst testing utilizes theSlow and even pressure rise::

Typical Burst Pressure Range: 1~3.5 MPa, depending on the value:

• Housing material (steel vs. aluminum)
• Wall thickness design
• Welding process
• Battery Specifications

Rupture pattern analysis

Normally, the battery should occur at the top cover or cap soldering locationcontrolled rupture. If the following abnormalities occur:

• Shell sidewall cracking: Weld too strong, shell too weak
• Bottom rupture: Structural design flaws
• irregular tear: Uneven weld quality

These anomaly patterns need to be fed back into the design and process for improvement.

Ⅳ. Precision Industrial Technology: Cylindrical lithium battery hermeticity + burst test industry solutions

As an industry leader in the field of airtightness testing for more than ten years, Precision Engineering has the following practical advantages in the new energy field:

● One machine with multi-mode, supporting different cell sizes

By changing the upper and lower molds, cylindrical cells of different diameters and lengths can be tested, saving tooling costs and increasing capacity utilization.

:: Integrated airtight + blasting program

One device does it all:

• airtightness testing
• Pressure resistance test
• burst test

More suitable for R&D and mass production of automotive grade and power storage cells.

:: High pressure capability (≥1 MPa)

Meet the structural pressure verification requirements for power batteries.

:: Accurate and stable results

Micro-leakage level testing is realized by high-precision sensors with a combination of algorithms such as differential pressure method and direct pressure method.

Served more than 3600+ well-known customers, including leading power battery factories

It is also CE certified and validated for international markets, making it suitable for global customer introduction.

V. Recommended Parameters for Airtight + Burst Testing of Cylindrical Cores

Test items	Typical Pressure	goal
Air tightness test	1000~1500 kPa	Detecting seal microleakage
Pressure resistance test	1.0~1.5 MPa	Verification of structural strength margins
bursting test	2.0~4.0 MPa (depending on model)	Acquire extreme stress capacity

Precision Engineering can provide pressure backcalculation services according to different core structures to make the limit value more scientific, consult us at any time to get free cases and programs.

Summarize

In the safety system of cylindrical lithium batteries, the hermeticity test ensures "no leakage in normal use" and the burst test ensures "no rupture under extreme working conditions".

The detection logic is summarized below:

• Air tightness testing = screening for conformity
• Burst Test = Product Design Verification

Precision Industrial Technology's comprehensive airtight + burst test program is especially suitable for new energy and energy storage companies to establish a complete quality system.

If you are looking for inspection solutions for cylindrical lithium batteries.Precision EngineeringWe provide complete support from equipment to service and help you establish a scientific quality management system.

Original Statement:this paper was written byShenzhen Jingchenggongke Technology Co., Ltd.Written by the technical team, reproduced with attribution.Data sources:Precision Engineering internal test data and customer cases.