Measurement of three-dimensional microstructure in a LiCoO₂ positive electrode

In this work we elucidate the 3D microstructure of the LiCoO₂ phase in a fresh commercial Li-ion battery positive electrode using a focused ion beam-scanning electron microscope. The particles have a highly irregular shape that includes significant internal cracking. These cracks provide a higher surface area for Li charge transfer, and they provide alternate pathways for Li transport within particles. In addition, the cracks would substantially alter the stress distributions within particles during Li-insertion and make the particles more susceptible to fracture. The particles were typically made up of multiple grains whose boundaries may also affect intraparticle Li-ion transport and fracture strength. While the particles do contact each other, the cross-sectional area of contact is quite small, emphasizing the importance of binder and conductive carbon for providing structural integrity to the electrode.