Framework Materials and Polymer Electrolytes for Next Generation Lithium- and Sodium-based Batteries

The growing global energy demand, coupled with the increasing reliance on renewable sources, and the urgent need to cut carbon emissions, has intensified the search for safer, more efficient, and sustainable energy-storage solutions. Lithium-ion batteries (LIBs) currently dominate the market, yet concerns over resource scarcity, cost, and electrolyte safety motivate the exploration of complementary technologies such as sodium-ion batteries (SIBs), which offer greater elemental abundance and attractive sustainability prospects. This thesis investigates key framework materials and design strategies aimed at advancing next-generation LIBs and SIBs, with particular focus on understanding and overcoming the critical limitations that currently constrain their performance and durability. Chapter 1 presents a general overview of the principles and challenges associated with energy production and storage. In Chapter 2, polymer electrolyte systems are explored as feasible and safer alternatives to conventional liquid electrolytes in LIBs. Their performance is enhanced through two complementary strategies: the incorporation of inorganic fillers, which boosts ionic conductivity and mechanical stability, and the blending of distinct polymer matrices, which combines the strengths of each component to overcome the inherent limitations of single-polymer systems. Chapter 3 shifts the focus to Prussian blue analogues (PBAs) as cathode materials for sodium-ion batteries, addressing three critical challenges: (i) structural defects such as Fe(CN)6 vacancies and coordinated water, which hinder Na storage and transport; (ii) irreversible phase transitions and lattice distortions that drive structural collapse and capacity fading; and (iii) interfacial side reactions with the electrolyte that deteriorate mechanical and chemical stability. Through targeted optimization strategies, including metal doping, these degradation mechanisms are effectively mitigated. In Chapter 4, alternative electrolyte architectures for SIBs are examined, spanning from a gel polymer electrolyte based on a PEO PVDF blend to a fully fluorine-free cell configuration employing a quasi-solid single-ion conducting polymer electrolyte. Both systems are evaluated in terms of ion transport, stability, and their compatibility with PBA for practical full-cell configurations. Finally, Chapter 5 investigates anode-less sodium batteries as a pathway toward high-energy, lightweight storage systems. Three classes of framework materials—coordination polymers (CPs), metal–organic frameworks (MOFs), and covalent organic frameworks (COFs)—are evaluated as nucleation substrates to direct uniform Na deposition. Particular attention is given to how their structural and chemical features, including metal-centre identity, porosity, and ligand environment, govern plating behaviour and overall electrochemical stability. Overall, the aim of this thesis is to provide fundamental insights and practical strategies for improving cell safety through the replacement of flammable liquid electrolytes, and designing advanced framework materials that function either as highly stable sodium-battery cathodes or as efficient nucleation substrates enabling uniform sodium metal deposition in anode-less architectures. Collectively, these results address key limitations of both LIBs and SIBs, enhancing the achievable energy density, cell safety, and helping to narrow the performance gap between sodium- and lithium-based technologies.