Synthesis and characterisation of novel layered electrode materials for sodium-ion batteries

Canhoto Cardoso, Joel and Tapia Ruiz, Nuria (2025) Synthesis and characterisation of novel layered electrode materials for sodium-ion batteries. PhD thesis, Lancaster University.

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Abstract

This thesis explores the development of new materials for sodium-ion battery (NIBs) electrodes. The transfer of some energy storage capacity from lithium-ion batteries (LIBs) to alternative technologies is crucial to address the growing demand for lithium, which is not adequately supported by known reserves. By mitigating some of the forecasted supply constraints, NIBs offer a viable and cost-effective alternative, especially as the demand for high energy and power density in electrical energy storage applications continues to rise. However, the lack of high capacity and high cycle life electrode materials for NIBs is still limiting the implementation of this technology. In this thesis, we attempt to tackle these limitations by exploring novel approaches to enhance both cathode and anode materials for NIBs: In Chapter 3 (i), the effects of calcium pillaring and dual calcium pillaring combined with fluorination on O3-type sodium and iron oxides as cathodes are studied. With this aim, -NaFeO2 was doped at 2, 3 and 5 % with calcium. For the dual calcium and fluorine-doping, -NaFeO2, doping corresponded to 2, 3 and 5 % calcium-doping and 4, 6 and 10 % fluorine-doping. The structure and electrochemical performance of these materials were characterised. Chapter 4 (ii) investigates the impact of transition metal substitution on P2-type sodium, manganese, and nickel oxides as cathodes. In this chapter, the structure, electrochemical performance and stability of Na0.67Mn0.8Ni0.15Ti0.05O2, Na0.67Mn0.8Ni0.15Fe0.05O2 and, Na0.67Mn0.8Ni0.15Cu0.05O2 was characterised. Finally, Chapter 5 (iii) focuses on titanate, lanthanum titanate, and yttrium-based perovskite oxides as anodes. With this aim, NaLaTiO4 and NaYTiO4 were synthesised, structurally and electrochemically characterised. To confirm the general structures of the materials, this thesis employs X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), 23Na nuclear magnetic resonance (NMR), and diffuse reflectance spectroscopy. The electrochemical response is then studied using galvanostatic cycling, cyclic voltammetry, the galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. Finally, operando XRD techniques are applied to unravel the sodium insertion and desorption mechanisms when possible, and ex-situ XRD is used where operando methods are not feasible. In Chapter 3, the synthesis of pristine, calcium-doped and dual calcium and fluorine-doped -NaFeO2 was achieved with a small amount of impurity. The addition of Ca2+ to the structure causes the unit cell to contract due to the increased electrostatic forces of Ca2+ and O2-, compared with Na+ and O2-. Dual doping with calcium and fluorine causes an expansion of the unit cell due to the decrease of electrostatic forces between the alkali metals and F-. The calcium-doping at 5 % has resulted in an increase of capacity retention from 41 % to 77 % after 100 cycles, however, with 68 % of the initial capacity of the pristine material. With dual calcium and fluorine doping with 5 and 10 %, respectively, the capacity retention was 79 % after 100 cycles, with 84 % of the initial capacity of the pristine material. In Chapter 4, Na0.67Mn0.8Ni0.15Ti0.05O2, Na0.67Mn0.8Ni0.15Fe0.05O2 and, Na0.67Mn0.8Ni0.15Cu0.05O2 showed negligible changes in the size of the unit cell, due to the similar ionic radii of nickel, titanium, iron and copper in the structure. All materials except Na0.67Mn0.8Ni0.15Ti0.05O2 showed good air and water stability. The initial capacity of Na0.67Mn0.8Ni0.15Ti0.05O2, Na0.67Mn0.8Ni0.15Fe0.05O2 and, Na0.67Mn0.8Ni0.15Cu0.05O2 was 102, 111 and 136 mA h g-1, respectively. Capacity retention was 44, 89 and 88 % after 200 cycles. In Chapter 5, NaLaTiO4 and NaYTiO4 showed little to no activity as anodes for NIB, contrary to when these materials are used in anodes for LIB. This is likely due to the large Na+ volume, compared to Li+.