Adhesion of coatings in Li-ion battery electrodes by scratch test

Adhesion of electrode coatings is a crucial factor in production of lithium-ion batteries. Poor adhesion leads to low capacity, short cycle time and eventually to thermal runaway. However, peel test, currently used for adhesion tests, is often difficult to implement. This work shows the application of the scratch test for adhesion testing of lithium-ion battery electrodes.

Production of lithium-ion batteries includes several important steps that involve mechanical loading of the coating on the electrodes. The electrode foils pass over several drums where the dried coating is subject to mechanical load which can cause its delamination from the metallic foil. Delaminated coating creates a defect that not only decreases the capacity of the battery but it can easily lead to thermal runaway (fire). Sufficient adhesion of the electrode coating is therefore one of key factors that must be controlled both during the development of new deposition process and during series production of batteries. Design of lithium-ion batteries is also partially dictated by a trade-off between the capacity and mechanical strength: while high binder content in the electrode coating is needed for better adhesion of the electrode layer, the same high binder content leads to decreased capacity of the battery. The determination of the adhesion of the active layers on electrodes is therefore important for the development of new, high capacity batteries.
Cathode coatings in today’s batteries are mostly based on lithium iron phosphate (LiFePO4), lithium ion manganese oxide (LiMn2O4, LMO), lithium nickel manganese cobalt oxide (LiNiMnCoO2, NMC) or LiNiO2 (LNO). The typical thickness range of these coatings, deposited from semi-liquid slurry, is 30 μm to 60 μm. Anode coatings are based on carbon black or, recently, on Si, with various binders and additives preventing volumetric changes and mechanical (including reduced adhesion) failure associated with charge-discharge cycles of the battery.

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