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

Wednesday, 6 March 2019
Areas Adjacent to the Forum (Scripps Seaside Forum)
K. Z. Fung (Hierarchical Green-Energy Materials Research Ctr, NCKU), K. Fung (Department of Greenergy, National University of Tainan), H. J. Yang (Dept of Materials Science, National Cheng Kung University), C. C. Chang (Lithium ion battery R&D Center, Department of Greenergy, National University of Tainan), and S. Y. Tsai (Hierarchical Green-Energy Materials Research Ctr, NCKU)
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.