Synthesis and characterisation of novel layered electrode materials for sodium-ion batteries
Creators: name: Canhoto Cardoso, Joel
Publisher: name: Lancaster University
Year: 2025

description: 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+.