User Benefits
- A thermostatic chamber makes it possible to measure the adhesion force of cathode materials in actual temperature
environments. - A copper foil peeling test device enables to conduct peel tests while maintaining a 90° angle in a thermostatic chamber.
- By using a load cell with a wider accuracy guarantee range than a conventional one, it is possible to conduct high-
accuracy tests even with small test forces.
Introduction
Lithium-ion batteries play an important role in various electronic devices due to their high energy density and excellent charging efficiency. To improve battery performance, materials and processing methods are actively being developed, and strength measurement is one of the essential evaluation methods. This Application News focuses on the adhesion strength of the electrode sheets used as battery electrodes. Fig. 1 shows the structure of an electrode sheet. An electrode sheet consists of an electrode material that adheres to a current collector, through which electrons move. The electrode material is composed of a cathode active material such as lithium iron phosphate and an insulating material known as a binder. When the adhesion between the electrode material and the current collector is weak, the electrode material may delaminate from the current collector, preventing electrons from moving in the electrode sheet and increasing the electrical resistance. Therefore, evaluating the adhesion strength is important for improving battery performance. In this application, test equipment, test conditions, and results of the peel test for battery cathode materials are described. The temperature dependence of the adhesion strength of the electrode materials is also described.
Apparatus
Fig. 2 and Table 1 show the test apparatus, and Fig. 3 shows the specimen structure. The tests were conducted using a Precision Universal Testing Machine AGS -V, with 1 kN screw-type flat grips and a copper foil peeling test device mounted on it. The specimens consisted of rectangular metal plates covered with double-sided tape, which were then coated with cathode active materials. The specimens were set in the copper foil peeling test device and the aluminum foil was gripped by the screw-type flat grip. The foil was always peeled off in a 90° direction relative to the specimen, ensuring that the center of the load coincides with the center of AGS-V.
Test Conditions
Table 2 shows test conditions. In this test, the force and its
temperature dependence were evaluated. The temperature
conditions included room temperature, 50 °C, and 70 °C.
Test Results
Fig. 4 shows the force-displacement curve. The dash-dotted curve is at room temperature, dotted curve is at 50 °C, and real curve is at 70 °C. The tests were conducted three times at each temperature whereas the shown curve is one representative specimen of the three. The average values of adhesion force are shown in Table 3. Adhesion forces were calculated from the average force between 20 mm and 80 mm of the displacement. These results show that when the temperature gets higher, adhesion force becomes larger.
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