Mechanical properties of Li-ion electrodes with Zn addition measured by nanoindentation

Mechanical properties of electrode coatings seem to attract less attention in regard to their adhesive properties which are crucial for production of high-quality batteries. However, elastic modulus and ability to withstand plastic deformation play an important role in development of new electrode coatings and new production processes. For example, if the coating is not heat dried sufficiently, it will not hold enough electric charge and the capacity of the battery will be low. Insufficient drying clearly affects the elastic modulus and elastic modulus can therefore be an indicator of the quality of the drying process. Another example of modification of the electrode coating and its mechanical properties is addition of precursors, namely of Zn or Cu based, to the electrode coating’s binder, which can circumvent large volume changes associated with lithiation. The effects of Zn precursors are reflected not only in the electrochemistry of the electrode but also in changes of elastic modulus. Similarly, homogeneity of electrode coatings, important for stability and prevention of lithium dendrites formation, is reflected by homogeneous mechanical properties of the electrode coating. Characterization of mechanical properties can therefore be very useful in several phases of electrode coating development. While it is possible to obtain mechanical properties of electrode coatings by tensile tests, the easier method for their assessment is nanoindentation. Nanoindentation has been developed to characterize thin coatings and it is therefore an ideal tool for mechanical characterization of electrode coatings. It also allows to generate depth profiles of elastic modulus and hardness, which show the gradient of stiffness from the surface to the current collector. Finally, nanoindentation can also be employed for crushing of particles in the slurry that is deposited on the current collector. Indeed, the strength of the particles determines from a great part the mechanical resistance of the electrode coating which shall be high enough to successfully pass all production phases.