copper foil in tensile testing machine

Foil Testing for Electric Vehicle Batteries

ev battery icon  

The electric vehicle battery industry is constantly improving the energy density and safety of their products. A significant focus is on the aluminum and copper foils used in each cell as current collectors. Thinner foil helps to reduce battery weight (contributing to energy density), and longer/wider foil increases production efficiency (contributing to cost reduction). However, as innovation drives foil materials to become thinner, it becomes even more critical to accurately capture their material properties and ensure that adequate quality control measures are in place.

Many companies in the industry are currently working on producing copper foil between 4 and 12 microns thick. However, as copper foil becomes thinner, longer, and wider, improved technology is required to address wrinkling and tearing concerns during production. Given that batteries need to be able to withstand the mechanical loading under normal use, as well as expansion and contraction when charging and discharging over time, the current collector foil must also be able to withstand these factors without yielding. Ensuring that these newer foils are able to withstand the loads required of it during both use and production, increased mechanical testing is needed.

Relevant standards for this application include ASTM E345, EN 546-2, and DIN 50154, which can be used as guidance for testing EV battery foils.

A standard tensile test is the most appropriate way to determine the mechanical properties of aluminum and copper foil specimens. Typically, elongation at break and maximum load are the key material properties that are calculated in mechanical testing, as these properties help ensure the quality of the foil; whether or not it will be able to withstand the mechanical loading and expansion/contraction in use.

While some standards may call out gripping options, such as wedge action grips, Instron has found that pneumatic side action grips are the optimal solution for foil under 20 microns thick. Pneumatic side action grips offer the ability to fine tune the clamping pressure and they will always provide constant pressure throughout each test. The use of pneumatic grips also improves throughput for these high-volume materials, as quality control labs can test hundreds of specimens per day. An additional factor that must be considered is the type of clamping surface, such as the jaw faces used. The optimal jaw faces to pair with pneumatic side action grips are rubber-coated faces. The soft and pliable rubber is able to adequately hold foil material throughout the duration of a test, while minimizing the stress concentration added by clamping the specimens.

foil testing in universal testing machine


Two of the biggest challenges that come from testing foil material are the preparation and alignment of the specimen. Specimen preparation is extremely critical for such fragile specimens. The better the quality of the cut, the better the quality of the edges will be for each specimen. Poorly cut edges increase the chances of the material breaking prematurely. Premature failure reduces the quality of the test results, and can lead to the need for re-testing.

Specimen alignment is also critical for repeatability and protection of the specimen, as thin foils can be noticeably affected by minor misalignment within the grips. Additionally, having to adjust foils within the grips multiple times can sometimes lead to premature breaks due to the damage caused by clamping and unclamping. We highly recommend using Instron’s Precision Specimen Loader to reduce variability in test results while improving ergonomics and safety.

Automation systems from Instron introduce a new level of productivity for foil testing. As battery production volumes continue to increase, throughput and efficiency are critical to keep up with demand. Utilizing an automation system with the recommended equipment for each application can free up operators and maximize throughput, while maintaining optimal results.

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Precision Specimen Loader

The Precision Specimen Loader for Thin Films provides a safer, more ergonomic, accurate, and more convenient way to load thin film and foil specimens into Instron 2712-052 grips.

The Importance of Specimen Alignment when Tensile Testing Thin Films and Foils

Tensile testing of thin films and foils presents more challenges than that of rigid specimens, particularly in regards to specimen alignment. Good specimen alignment produces more consistent results with higher mean strain values and higher force at break values.

6800 Series Premier Testing Systems Brochure

Instron 6800 Series Universal Testing Systems provide unparalleled accuracy and reliability. Built on a patent-pending Operator Protect system architecture with an all-new Smart-Close Air Kit and Collision Mitigation features, the 6800 Series makes materials testing simpler, smarter, and safer than ever before.

3400 Series - Affordable Testing Solutions

Instron 3400 Series Universal Testing Systems for Tensile, Compression, Bend, and other material property tests.

Bluehill Universal Brochure

Bluehill Universal Software is built from the ground-up for touch interaction and an intuitive user experience. Discover simpler and smarter testing with features such as pre-loaded test methods, QuickTest in seconds, enhanced data exporting: and Instron Connect – a new feature that provides a direct communication link to Service. Users of previous versions of software such as Bluehill 2 and Bluehill 3 can easily upgrade to the newest version of Bluehill.

2712-04X Series Pneumatic Side-Action Grips

Pneumatic side-action grips offer a versatile gripping solution for a wide range of materials. Rated capacities between 1 and 10 kN.

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