Electrochemical Properties of Low Co-Containing Layered Oxide Cathodes Viewing from Structural, Defect and Processing Variations

Abstract

Layered oxides containing transition metal ions are known to exhibit higher capacities than ones with spinel or olivine structures. However, higher charging capacity means the creation of more ionic/electronic defects in both cation and/or anion sublattices of layered structure. As a result, their structural and electrochemical properties are strongly affected by the formation and/or elimination of these defects. Moreover, the existing defects in layered oxides are typically determined by the condition of fabrication processes, for instance the oxygen partial pressure. The capacity fading observed in layered oxides is typically caused by the phase transformation of cycled layered oxides. In addition, the structural instability of layered oxides may be due to repeated formation/elimination of large amount of defects. Doping of aliovalent ions has been widely used for control of defects through charge compensation mechanism. Thus, the main objective of this work to investigate (i)the structural/electrochemical properties, (ii) charging/discharging/cycling behaviour (ii) effect of aliovalent doping on high Ni/low Co-containing layered oxides. In this study, the electrical/electrochemical/structural properties of layered oxide containing 80% Ni in transition metal layer are investigated. Layered oxides are fabricated using either solid state reaction or co-precipitation techniques. Ni content in is fixed at 80% in the transition metal ion layers in these cathode materials, the variation in electrochemical properties will be caused by the minor elements/dopants such as Mn and Al. First, the electrical measurement of layered oxides are conducted using sintered disc. Assembled cells using above-mentioned cathode and Li anode with desired liquid electrolyte will be tested and cycled. XPS, SEM and XRD analyses will be conducted on as-assembled as well as cycled cells. The analysed results will be illustrated based on the chemical characteristics of doping ions and the accompanying defects created.