Influence of Cathode Calendering Density on the Cycling Stability of Li-Ion Batteries Using NMC811 Single or Poly Crystalline Particles

Abstract

Calendering of battery electrodes is a commonly used manufacturing process that enhances electrode packing density and therefore improves the volumetric energy density. While calendering is standard industrial practice, it is known to crack cathode particles, thereby increasing the electrode surface area. The latter is particularly problematic for new Ni-rich layered transition metal oxide cathodes, such as NMC811, which are known to have substantial surface-driven degradation processes. To establish appropriate calendering practices for these new cathode materials, we conducted a comparative analysis of uncalendered electrodes with electrodes that have a 35% porosity (industrial standard), and 25% porosity (highly calendered) for both single crystal (SC) and polycrystalline (PC) NMC811. PC cathodes show clear signs of cracking and decrease in rate capability when calendered to 25% porosity, whereas SC NMC811 cathodes, achieve better cycling stability and no penalty in rate performance at these high packing densities. These findings suggest that SC NMC811 cathodes should be calendered more densely, and we provide a comprehensive overview of both electrochemical and material characterisation methods that corroborate why PC and SC electrodes show such different degradation behaviour. Overall, this work is important because it shows how new single-crystal cathode materials can offer additional advantages both in terms of rate performance and cycling stability by calendaring them more densely.