Mainly due to potential cost advantages sodium-ion batteries (NIBs) have the potential to become an alternative to lithium-ion batteries. Layered sodium manganese oxide is a material class seen as suitable candidate for future NIB cathodes, owing to a good compromise between operating voltage and capacity, so as for the low cost and high abundance of manganese. However, cycling stability still remains a problem.[1,2]
The scope of this work was to investigate different approaches to address the low cycling stability of the base material of this structural class, i.e. P2-NaxMnO(2+z) (x ≈ 0.7, z = 0.05 – 0.25) and to identify levers for improvements. Two successful strategies are presented in this work. One approach is the incorporation of a relatively small amount of cobalt (~10%) into the host structure leading to significant performance improvement; the other is an optimisation of the morphology. A combination of both strategies leads to a material with comparably best discharge capacity and cycling stability.
The underlying mechanism were investigated in comparison studies by applying various techniques.[3–5] By utilising operando X-ray diffraction we were able to related Co-doping and morphology to structural changes and battery performance. These results were correlated with electrochemical studies. Preliminary results employing X-ray absorption spectroscopy and high resolution X-ray spectro-microscopy to further understand how the chemical and structural changes occurring across the entire electrode and spatially resolved within individual hollow spheres impact cycling performance are in preparation.
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