Review on the Experimental Characterization of Fracture in Active Material for Lithium-Ion Batteries

Nowadays, lithium-ion batteries are one of the most widespread energy storage systems, being extensively employed in a large variety of applications. A significant effort has been made to develop advanced materials and manufacturing processes with the aim of increasing batteries performance and preserving nominal properties with cycling. Nevertheless, mechanical degradation is still a significant damaging mechanism and the main cause of capacity fade and power loss. Lithium ions are inserted and extracted into the lattice structure of active materials during battery operation, causing the deformation of the crystalline lattice itself. Strain mismatches within the different areas of the active material caused by the inhomogeneous lithium-ions concentration induce mechanical stresses, leading ultimately to fracture, fatigue issues, and performance decay. Therefore, a deep understanding of the fracture mechanics in active materials is needed to meet the rapidly growing demand for next-generation batteries with long-term stability, high safety, excellent performance, and long life cycle. This review aims to analyze the fracture mechanics in the active material microstructure of electrodes due to battery operations from an experimental point of view. The main fracture mechanisms occurring in the common cathode and anode active materials are described, as well as the factors triggering and enhancing fracture. At first, the results obtained by performing microscopy and diffraction analysis in different materials are discussed to provides visual evidence of cracks and their relation with lattice structure. Then, fatigue phenomena due to crack growth as a function of the number of cycles are evaluated to assess the evolution of damage during the life cycle, and the effects of fracture on the battery performance are described. Finally, the literature gaps in the characterization of the fracture behavior of electrode active materials are highlighted to enhance the development of next-generation lithium-ion batteries.