Revealing the mechanical behaviour and material micro-structure of graphite electrode coatings in lithium-ion batteries during lithiation.

Understanding the mechanical behaviour of graphite electrode coatings during lithiation is crucial for optimizing high-performance lithium-ion batteries. The first experiment reveals the elastoplastic response of liquid electrolyte-immersed graphite active particles bonded with sodium carboxymethyl cellulose and styrene butadiene rubber (CMC/SBR) across various states of charge (SOCs). Simultaneously, we have developed a phenomenological model to simulate the mechanical response of graphite-CMC/SBR composites during lithiation by tracking the evolution of mechanical properties within graphite particles and the composite's porosity. The results uncover that the graphite electrode coatings undergo significant elastic-plastic mechanical deformation and are strengthened and brittle due to active particle hardening and decreasing porosity in the lithiation process. Upon completion of lithiation, the graphite electrode coatings exhibit a twofold increase in ultimate stress and elastic modulus while microhardness quadruples. However, fracture elongation decreases by 60%. Furthermore, the lithiation process enhances the adhesion properties of the electrode coating. Importantly, our proposed model shows excellent agreement between the predicted tensile stress-strain curves and experimental data. Finally, we unveiled the influence of graphite electrode coating's plastic behaviour and liquid electrolyte on the mechanical integrity of the cylindrical battery structure.