Particle Size-Graded Bilayer Electrodes for Enhanced Transport in Layered Transition Metal Oxide Cathodes

Thick electrodes are a promising route to increase battery energy density by increasing the fraction of active material relative to inactive components. However, at high cycling rates, greater mass transport limitations in thick electrodes can lead to poor capacity utilisation and reduced power density. Although advanced electrode structuring strategies have been explored, many require expensive manufacturing changes or complex post-processing. An alternative approach uses standard battery manufacturing methods to sequentially coat active materials with different particle sizes or compositions. In this work, polycrystalline LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) particles of two sizes were used to fabricate particle size-graded bilayer electrodes. An impedance-based finite element model was developed to evaluate transport properties in the graded structures and was validated using electrochemical impedance spectroscopy (EIS) and rate tests. Operando synchrotron diffraction revealed a more homogeneous state of charge when smaller particles were positioned near the separator and larger particles near the current collector. Together, the modelling and experimental results show that simple particle size grading improves ion transport and reaction uniformity, enhancing capacity utilisation. This approach offers a practical pathway to improve the power performance of next-generation battery electrodes.