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Investigation of Water-Washing Effect on Electrochemical Properties of Ni-Rich NCA Cathode Material for Lithium-Ion Batteries

This study was conducted to understand the effect of well-known water-washing process on Ni-rich LiNi0.885Co0.100Al0.015O2 (NCA) cathode material, which reduces the amount of residual lithium compounds in NCA to improve lithium-ion batteries (LIBs) characteristics. X-ray absorption fine structure (XAFS) analysis revealed that the oxidation state of the surface nickel in washed NCA particles was reduced. The fact was consistent with the increase in charge transfer resistance (Rct) measured by the electrochemical impedance spectroscopy (EIS) method. From X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses, it was found that the residual lithium compounds were washed away not only from the surface of NCA particles but also from grain boundaries or voids in between primary particles of NCA, by water-washing process. Differential scanning calorimetry (DSC) measurements suggested that an increase in specific surface area of NCA particles by water-washing was attributed a rapid heat release from the charged cathode material during heating to. On the other hand, cross-sectional scanning electron microscope (SEM) images showed that the crack formation inside washed NCA particles were suppressed after charge/discharge cycling. As a result, the capacity retention of washed NCA electrode at 60 °C cycling was improved.