Effect of Processing Route and Dopant on Capacity/Fading of Layered Oxide Cathode

Abstract

Although several crystal structures have been demonstrated and shown reversible capabilities during lithiation/delithiation processes in cathode of Li ion batteries; oxides with layered structure still remain the ones that provide higher capacities. However, higher charging capacity means the creation of more ionic/electronic defects in both cation and/or anion sublattices of layered structure. Higher defect concentration in either cation or anion sublattices tend to destabilize its crystal structure. As a result, the phase change is frequently observed in repeatedly cycled cathode. Furthermore, the phase-changing layered cathode tends to show the capacity fading after cycling tests. Based on defect consideration, the stability of highly defective materials may be enhanced by using dopant and/or better processing control. In this study, the electrical/electrochemical/structural properties of NMC 811 and LiNi0.8Co0.15Al0.05 will be investigated. Since Ni content 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 NMC 811 and LiNi0.8Co0.15Al0.05 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 analyzing results will be illustrated based on the chemical characteristics of doping ions and the accompanying defects created.