Combustion-synthesized sodium manganese (cobalt) oxides as cathodes for sodium ion batteries |
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Authors: | Nicolas Bucher Steffen Hartung Irina Gocheva Yan L. Cheah Madhavi Srinivasan Harry E. Hoster |
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Affiliation: | 1. TUM CREATE, Singapore, 138602, Singapore 2. Technische Universit?t München, 85748, Garching, Germany 3. School of Materials Science and Engineering, Nanyang Technological University, Singapore, 639798, Singapore
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Abstract: | We report on the electrochemical properties of layered manganese oxides, with and without cobalt substituents, as cathodes in sodium ion batteries. We fabricated sub-micrometre-sized particles of Na0.7MnO2?+?z and Na0.7Co0.11Mn0.89O2?+?z via combustion synthesis. X-ray diffraction revealed the same layered hexagonal P2-type bronze structure with high crystallinity for both materials. Potentiostatic and galvanostatic charge/discharge cycles in the range 1.5–3.8 V vs. Na | Na+ were performed to identify potential-dependent phase transitions, capacity, and capacity retention. After charging to 3.8 V, both materials had an initial discharge capacity of 138 mA?h?g?1 at a rate of 0.3 C. For the 20th cycle, those values reduced to 75 and 92 mA?h?g?1 for Co-free and Co-doped samples, respectively. Our findings indicate that earlier works probably underestimated the potential of (doped) P2-type Na0.7MnO2?+?z as cathode material for sodium ion batteries in terms of capacity and cycle stability. Apart from doping, a simple optimization parameter seems to be the particle size of the active material. |
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