Charge Transport in Single NCM Cathode Active Material Particles for Lithium-Ion Batteries Studied under Well-Defined Contact Conditions

We present a technique for systematically investigating electronic and ionic charge transport in single Li(Ni1/3Co1/3Mn1/3)O2 (NCM 111) secondary particles as a function of size. We perform electrochemical impedance spectroscopy employing ion-blocking electrodes. Micrometer-sized spherical particles are arranged in cylindrical particle traps on a patterned substrate. A specially designed electrochemical cell is used to contact and measure individual immobilized particles in a defined contact geometry. The obtained electronic and ionic resistances of the particles as a function of size are compared with model calculations based on a homogeneous sphere with finite contact areas. The modeling reveals that electronic transport mainly occurs in the bulk of the NCM 111 particles, whereas ionic transport takes place along the particle surface. The extracted material parameters are in good agreement with literature values, showing the reliability of our measurement technique and its potential for systematic studies on the single-particle level.