Abstract:
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.
References:[1] V. Palomares, P. Serras, I. Villaluenga, K.B. Hueso, J. Carretero-Gonzalez, T. Rojo, Energy Environ. Sci. 5 (2012) 5884-5901.
[2] V. Palomares, M. Casas-Cabanas, E. Castillo-Martínez, M.H. Han, T. Rojo, Energy Environ. Sci. 6 (2013) 2312-2337.
[3] M.H. Han, E. Gonzalo, G. Singh, T. Rojo, Energy Environ. Sci. 8 (2015) 81-102.
[4] C. Delmas, C. Fouassier, P. Hagenmuller, Phys. B+C. 99 (1980) 81-85.
[5] N. Ortiz-Vitoriano, N.E. Drewett, E. Gonzalo, T. Rojo, Energy Environ. Sci. 10 (2017) 1051-1074.
[6] J. Billaud, G. Singh, A.R. Armstrong, E. Gonzalo, V. Roddatis, M. Armand, T. Rojo, P.G. Bruce, Energy Environ. Sci. 7 (2014) 1387-1391.
[7] E. Gonzalo, N. Ortiz-Vitoriano, N.E. Drewett, B. Acebedo, J.M. Lopez del Amo, F.J. Bonilla, T. Rojo, J. Power Sources. 401 (2018) 117-125.
[8] M. Bianchini, E. Gonzalo, N.E. Drewett, N. Ortiz-Vitoriano, J.M. Lopez Del Amo, F.J. Bonilla, B. Acebedo, T. Rojo, J. Mater. Chem. A. 6 (2018).
[9] E. Gonzalo, M.H. Han, J.M. Lopez del Amo, B. Acebedo, M. Casas-Cabanas, T. Rojo, J. Mater. Chem. A. 2 (2014) 18523-18530.
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