Effect of Electrode Adhesion Strength on Lithium-ion Battery Performance
“Introduction/Background
Lithium ion batteries (LIBs) have many applications ranging from small electronic devices to big battery packs used in electric vehicles. Good adhesion properties at the interface of electrode and substrate is crucial for achieving the desired battery performance. Improper adhesion is caused due to various reasons including generation of internal stress, mismatch of surface energies, etc. Particularly in thick electrodes, which are desirable for high energy density, adhesion strength outweighs other limiting factors for performance. Although a few groups have explored the adhesion properties of LIB electrodes, their effect on the performance and the parameters effecting the adhesion have not been studied. The conventional 180° mechanical peel test is a well-known technique to measure adhesion strength by peeling away the electrode from the current collector. Impact of various parameters such as thickness of electrode, binder material, viscosity of slurry, and different current collectors on the adhesion strength of the electrode are studied and corresponding change in battery performance is observed.
Methodology
Experimental design is done to carefully measure the effect of each parameter. The peel test is done on a 13.5-mm-wide and 30-mm-long electrode sandwiched between two 3 M adhesion tapes and the adhesion strength is measured using micromechanical test system (MTS Tensile Strength Machine). The adhesive tape was removed by peeling at an angle of 180° on the system with a load cell of 10 lbf at the rate of 0.025 in/sec. The electrodes were fabricated keeping the same composition (85% active material, 7.5 wt % conductive carbon, 7.5 % binder mixture).
Results & Conclusion
The electrochemical performance of Li-ions cells fabricated using aqueous-based tape-casting is evaluated, and the results are correlated with the adhesion strength. The results indicate that good adhesion is essential to realize maximum battery performance, particularly at high C-rates. We also noted that for increasing thickness, surface roughened current collectors, high viscosity of slurry, and using composite binders improved the adhesion strength thereby performance.”