Editors: | F. Kongoli, M.A. Alario Franco, J. Etourneau, S. Kalogirou, F.D.S. Marquis, R. Martins, K. Poeppelmeier, B. Raveau, Y. Shimakawa, M. Takano |
Publisher: | Flogen Star OUTREACH |
Publication Year: | 2019 |
Pages: | 130 pages |
ISBN: | 978-1-989820-08-7 |
ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
Sodium ion Batteries (SIBs) offer a strong alternative to existing battery technologies, particularly in the field of stationary storage due to their potentially low cost, and natural abundant precursors.[1,2] One key component of an SIB is the cathode, the nature of which is critical to its performance. Sodium layered oxides (SLOs), with the stoichiometry NaTMO2 (TM = one or more transition metals, e.g. Mn, Fe, Co, Ni, etc.), are a promising family of cathode materials due to their excellent electrochemical properties, structural simplicity, and tuneable stoichiometries.[3] SLOs, consisting of repeating sheets of TMO6 layers with Na ions located between, are classified by a letter and number (e.g. O3-, P2-, etc.) where the letter indicates the Na is located (O: octahedral, P: prismatic) and the number indicates the number of interlayers that are surrounding.[4]
Performance of these materials is frequently governed by their structure, and in this work we will highlight the importance of taking this into consideration. For example, while Manganese-rich layered oxides are particularly attractive due to their combination of low cost and low toxicity, their performances are often hindered by the effect of Jahn-Teller distortion (resulting from the presence of Mn3+).[5] We will not only discuss this in detail, but also highlight mitigation strategies, such as doping with electrochemically active (e.g. Fe) and inactive (e.g. Mg, Ti) elements, or synergetic P2/O3 combination effects.[5-8]
We will also examine the importance of Na-ion conductivity, determined through the use of combined electrochemical techniques and solid-state NMR spectroscopy, and show how the mobility of Na ions is related to the different local environments of Na ions (i.e. O- or P- phase) and diffusion pathways.[9] This way, we will not only show a thorough knowledge where SLO structure is key to understanding their behaviour, but also how to link this to the key descriptors for the cathode material's electrochemical performance.