Understanding Behavior of Cathode Active Materials with Different Particle Sizes in Mixed Electrode through Current Distribution Measurement

The performance of a lithium-ion battery can be improved by mixing two or more kinds of cathode active materials in one electrode. In particular, energy density can be increased by mixing active materials having different particle sizes because the electrode can be filled with more active materials. As the performance of a battery is determined by the combination of the properties of the material itself and the electrode design conditions, it is most important to understand the characteristics of the material and the electrode independently. However, since the potential in a mixed electrode is measured as the mixed potential of each active material, it is not easy to identify how each active material behaves electrochemically under the current load condition. In this experiment, we attempted to separate only the effects of active materials while minimizing the influence of the electrode density, which affects the mass transfer in the porous electrode. For this purpose, two electrodes consisting of small and large particles are placed in one pouch cell and connected in parallel with Li metal as a counter electrode. By measuring the current flowing through each electrode individually, we observed how small and large particles work in mixed electrode. Since the influence of mass transfer inside the electrode was minimized, it was assumed that the mass transfer did not affect the currents divided into each electrode. Thus, current flowing to each electrode is determined by the relative contributions of charge transfer and solid diffusion kinetics. Large particles have smaller charge transfer resistance and slower solid diffusion than small particles. If rate-liming step is charge transfer, more currents flow to large particles by small charge transfer resistance. If rate-limiting step is solid diffusion, more currents flow to small particles due to the fast diffusion in active materials. Through this experiment, we could analyze the behavior of active materials having different particle sizes in mixed electrode by detecting the current respectively.