Influence of Processing Route and Chemical Composition on Electrochemical Properties of High-Capacity Layered Oxide Cathodes

Abstract

To obtain high-capacity Li ion batteries; oxide cathodes with layered structure still remain the ones that provide high enough capacities. It is known that electrons and Li+ ions are being extracted simultaneously in the charging process. During high-voltage charging, more ionic/electronic defects formed in layered oxides will be created. Thus, their electrochemical and structural properties are strongly affected by the formation and/or elimination of these defects. Higher defect concentration, like Li vacancies, VLi’, tends to destabilize its crystal structure. As a result, the phase transformation may occur in the cycled cathode. Accordingly, the capacity fading was frequently observed in cycled layered cathode due to the phase-changing process. Moreover, the existing defects in layered oxides are typically determined by the condition of fabrication processes, for instance the dopants and oxygen partial pressure.In this study, two well-known layered oxides with fixed 80% Ni in the transition metal ion layer, namely NMC 811 and LiNi0.8Co0.15Al0.05O2 (NCA), were investigated. Their minor elements/dopants Mn and Al may play an important role on affecting their defect chemistry as well as electrochemical properties. Thus, their electrical/electrochemical/structural properties are examined as a function of the minor dopants, Mn and Al. First, the electrical measurement of NMC 811 and LiNi0.8Co0.15Al0.05O2 are conducted. Assembled cells using above-mentioned cathode and Li anode with desired liquid electrolyte were tested and cycled. SEM and XRD analyses were conducted on assembled and cycled cells. The analysis and results are illustrated based on the chemical characteristics of doping ions and the electronic/ionic defects induced.