Doping of Sodium Chromium Oxide Cathode Materials to Enhance Electrochemical Performance for Sodium-Ion Batteries

• Main Author: Wang, Ziyong
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Chemistry; Materials science; Nanotechnology
• ISBN: 9781392867273; 1392867274

In this project, we investigated the effects of doping several types of metals to NaCrO2 on its electrochemical performance. The doping method is aiming to stabilize the O3-type structure by partial substituting some of Cr with other metals during intercalation/deintercalation by suppressing Cr6+ migration to alkaline slab, and thus facilitate long-term cycle performance and reversible capacity. All doped NaCrO2 powders were hereby denoted to NaMe0.1Cr0.9O2 (Me=Al, Co, Ni, Mn). To achieve metal-doped NaCrO2 powders, sodium, chromium and dopant sources were mixed with various metal oxides and then subjected to 6-hour high energy ball milling, followed by heating in flow-Ar tube at 900℃ for 1 hour. Pristine NaCrO2 powder synthesized in the same process was to make comparisons with doped ones. To understand the mechanism of doping, field emission scanning microscopy (FESM) and energy Disperse Spectroscopy (EDS), as well as X-ray diffractometer (XRD), were employed to analyze the morphology and composition of final products. Benefiting from Ni doping, NaNi0.1Cr0.9O2 cell exhibited a high reversible capacity of 132 mAh g-1 at the initial cycle in a potential region between 2.0 and 3.6 V vs. Na/Na+, and 78 % of capacity retention over 70 cycles. For NaMn0.1Cr0.9O2, reversible capacity at first discharge is about 30 mAh g-1, lower than that of Ni-doped and pristine NaCrO2, while the cycle retention stays at nearly 100% after 100 cycles. The opposite charge/discharge behaviors from Ni- and Mn-doped NaCrO2 provide us a potential method for the optimization of cathode materials with the best electrochemical performance in the future.