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.