Electrode Anode Testing for Electric Vehicle Batteries
There are multiple ways in which batteries can fail. One of the most common modes of failure is caused by the electrode coating material cracking or delaminating from the current collector. This cracking or delaminating is typically caused by the constant charging and discharging of the battery as well as by mechanical loading of the battery in use. It is critical to understand the adhesion strength and longevity of electrodes to ensure that a battery does not fail before the end of its predicted life cycle.
As battery manufacturers work to understand the adhesive properties of their cathode and anode materials, many are also introducing new electrode makeups in an effort to increase the safety and energy density of batteries. Most of these changes are to the anode material with additions such as silicone, which requires further testing and analysis. It is critical to understand how electrode adhesion is influenced by different binders and elements. The three types of testing most commonly used to characterize the adhesive properties and monitor production material for electrodes are 90° peel tests, 180° peel tests, and tack tests.
180° Peel Test
The most commonly performed peel tests are 90° and 180° peel tests. 180° testing has an advantage over 90° testing in simplicity of setup and ease of alignment. This testing can be done using low force grips and load cells along with a substrate that helps the flexible material maintain proper alignment during testing. It is best to consider pneumatic grips and a metal substrate to ensure high throughput and a proper 180° peel throughout each test.
90° Peel Test
90° peel testing is commonly seen as an alternative to 180° degree peel testing. The 90° peel test generally involves slightly higher loads than the 180° peel test and can be set up more quickly because it often does not require a substrate. Instron’s most common solutions for this testing are a standard 90° peel fixture or a pneumatic peel fixture designed specifically to test the adhesion of electrodes. The pneumatic 90° peel fixture was developed specifically for electrode adhesion testing and provides improved repeatability and throughput while also aiding the operator in consistent specimen placement and alignment at 90°. For the upper fixture, a pneumatic grip optimizes throughput and repeatability and is recommended for testing delicate materials.
A tack test is an electrode adhesion test that has been backed by researchers as an additional way to test the adhesion of electrodes to a battery's current collector. Instead of slowly peeling electrodes from the current collector, a tack test focuses on the adhesion strength of an entire predetermined area of electrodes, allowing for quicker evaluation of electrode adhesion over a large area. Instron’s tack testing fixture is designed for ease of specimen preparation as well as high throughput and repeatability. It features predetermined contact areas in addition to a spherically seated and lockable upper fixture, which ensures parallelism between both fixtures. Due to the fast speeds of this testing, a testing system with a very high data rate collection will ensure the best possible results and throughput.