Concentration shift experiment with an electrode of active material for precise electrochemical analysis

Abstract

To precisely evaluate the electrochemical properties of a battery of active material, we proposed a “concentration shift experiment” using single-particle electrochemical measurement (SPEM) and a diluted electrode sheet (DES). SPEM can be used for information, such as the charge–discharge and resistance properties of only the active material (extremely dilute condition: ≈0). DES consists of concentrations varying from 1% to 100% of the active material (LiCoO₂) and inactive material (α-Al₂O₃), electrically conductive additive and binder polymer onto an Al current collector. The resistance components derived from the LiCoO₂ single particles were measured and calculated. Their apparent activation energy (E_a) was 27 kJ mol⁻¹, which is relatively low compared with the applied-type sheet electrode (30–60 kJ mol⁻¹). Simple electric/ionic conductive route was analyzed using SPEM cell, and the fundamental LiCoO₂ originated E_a could be calculated. Resistance components attributed to LiCoO₂ were also measured and extracted by alternating current impedance measurements using DES. The resistance non-linearly decreased with LiCoO₂ concentration, and the percolation and inhomogeneity of LiCoO₂ particles were suspected. The planful isolation of an active material particle should be critical for the overall information on an electrode particle.