Due to the successful commercialization of lithium-ion batteries (LIBs), there is a growing interest in developing new battery materials with improved properties. The uneven distribution of natural resources, the low abundance of battery materials in the Earth’s crust, and the growing geopolitical concerns should also be considered and addressed. In this context, alternative battery technologies, such as sodium-ion batteries (SIBs) and lithium metal batteries (LMBs), are getting attention by researchers, due to the low cost of readily available sodium resources and the very high capacity of a lithium metal anode, etc. Conventional electrolytes of any battery technology are today heavily based on fluorinated salts and volatile organic solvents, posing serious safety issues all the way from synthesis to application and recycling. Additionally, the increasing concerns of per- and polyfluoroalkyl substances (PFAS) highlight the urgent demand to explore performant fluorine-free electrolytes, ideally also non-flammable.

In this study, novel fluorine-free ionic materials and electrolytes have been designed and their physical and electrochemical properties thoroughly investigated. In the first part (Paper I), fluorine-free “solvent-in-salt” (SIS) sodium electrolytes based on sodium bis(2-(2-ethoxyethoxy)ethyl) phosphate (NaDEEP) salt and tris(2-(2-ethoxyethoxy)ethyl) phosphate (TEOP) solvent are presented. The addition of TEOP increased the electrochemical oxidation stability of the SIS electrolytes and an unusual ionic conductivity behavior is observed – the ionic conductivities of the electrolytes increase with increasing salt concentration. In the second paper (Paper II), a series of new orthoborate-based ionic materials, containing the bis(glycolato)borate (BGB) anion and phosphonium/ammonium cations are prepared and compared with the popular bis(oxalato)borate (BOB) salts. Some of these ionic materials are room temperature ionic liquids (RTILs), while others are organic ionic plastic crystals (OIPCs). The tetrabutylphosphonium bis(glycolato)borate ([P₄₄₄₄][BGB]) OIPC displays much higher decomposition temperature than the structural analogous [P₄₄₄₄][BOB] IL, and multinuclear solid-state NMR spectroscopy indicated weaker cation-anion interactions in phosphonium-based salts than the ammonium-based ones.

Given the excellent moisture and thermal stabilities brought by the BGB anion, a family of BGB-based alkali and alkaline metal salts were synthesized and characterized (Paper III). The LiBGB-based electrolytes using dimethyl sulfoxide (DMSO), triethyl phosphate (TEP) and trimethyl phosphate (TMP) have excellent moisture stability, optimal ionic conductivity, better aluminum (Al) passivation and long-term Li plating-stripping performance. Sequentially, the next study (Paper IV) is focused on investigating the effect of additives on the performance of these electrolytes, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc. Finally, in the fifth paper (Paper V), two- and three-component eutectic electrolytes based on pyrrolidinium saccharinate [Pyrr][Sac], lithium saccharinate Li[Sac] and/or [P₄₄₄₄][BGB] salts were created. The physicochemical properties of these salts as well as the Li compatibility and cell performance are thoroughly investigated. Overall, these studies identified several new fluorine-free salts and electrolytes with beneficial properties that can potentially be used in next-generation batteries.

Wood has been a crucial material for construction throughout history. However, due to poor natural durability of wood, it is difficult to use outdoors without any additional treatment. Conventionally, wood has been fully or partially impregnated with preservatives. However, some substances are harmful to mankind and environment, hence, regulated strictly. Therefore, methods for achieving sustainable protection of wood have been required and one method that has been investigated for achieving this has been through chemical modification. 

This doctoral thesis aims to develop a new modification system for solid wood in use class 3. The objective was to develop a wood modification system based on maleic anhydride (MA) and sodium hypophosphite (SHP) that enables exterior use without leaching by weathering. To meet this requirement, the modification should involve formation of stable cross-linking, altering the interaction between moisture and wood, consequently enhancing dimensional stability and biological resistance. 

To test the possibility of using MA and SHP, Scots pine sapwood (Pinus sylvestris L.) was treated with various ratio of chemical reagents, curing temperatures and durations. The treated wood was subjected to repetitive wet-dry cycle to assess its dimensional stability and leachability of chemical reagents. The result indicated formation of a stable cross-linking between wood constituents. 

To further investigate the formation of cross-link, solid-state 13C cross-polarization magic-angle-spinning (CP-MAS) nuclear magnetic resonance (NMR), 31P MAS NMR and X-ray photoelectron spectroscopy (XPS) were employed. The findings indicated that the cross-linking was likely to involve phosphonate (C-P-O) bonds. These results provided a deeper fundamental understanding of the reaction mechanisms between wood, MA and SHP, providing further scope for improved treatment systems in the future.

The impact of the modification on wood-water interactions was analyzed using low-field nuclear magnetic resonance (LFNMR) to study water in the wood at a saturated state. Additionally, the hydrophilicity of cell walls was studied via infrared spectroscopy after deuteration using liquid D2O. The results indicated that the modification reduced the affinity of the wood cell wall to water without altering the number of accessible hydroxyl groups.  

Finally, the modified wood was evaluated for fungal decay resistance, mechanical strength test (bending), and thermal stability. The modification significantly reduced mass loss caused by wood-decaying fungi by limiting the moisture uptake in wood and altering the chemical structure of wood. On the other hand, the modification did not improve resistance to fungal growth on the wood surface, suggesting that nutrient accessibility on surface was not influenced by the modification. A bending test showed that while the modulus of elasticity (MOE) was not affected, modulus of rupture (MOR) decreased to half that of untreated wood. Thermal resistance was improved due to the presence of phosphonate, which can promote the formation of a protective char layer and radical moieties. 

This study demonstrated the potential of modifying wood with MA and SHP to enhance durability, dimensional stability, and fire resistance. The modification formed stable cross-link within the wood components, reducing water interaction and improving resistance to biological degradation. However, the reduction in MOR limits its suitability for load-bearing applications. Despite this, the results suggest that the modified wood could be a viable alternative for non-load bearing exterior applications.

Future research should focus on optimising the modification process by reducing temperature, duration, and solvent use while maintaining performance. Investigating catalysts for the reaction may help address these challenges. Additionally, long-term field testing under real environmental conditions is needed to evaluate the durability and stability of the modified wood. Environmental impact assessments and life cycle analysis will also be crucial for ensuring commercial feasibility and sustainability.

Electric power transmission systems transfer large amounts of power (typically hundreds of MW) over long distances (typically hundreds of kilometres) at high voltage (typically hundreds of kilovolts). The operational security of the transmission system has always been high top priority for the transmission system operator (TSO); because of this supply interruptions originating in the transmission grid are very rare. 

To maintain the high reliability of a transmission grid, TSOs deploy the N-1 operational security criterion. The predominant shortcoming of this criterion is that all contingency cases are treated as equal; no differential is made concerning probability and impact of individual contingency cases. 

Operational risk assessment complements the N-1 security assessment method, by incorporating the probability of contingency cases and their impact, the latter in terms of severity factors.  Important elements of operational risk assessment are lead time, instantaneous component outage model, contingency definition, contingency list and filtering, probability of contingency cases, and severity factor. The existing literature on operational risk assessment concentrates on contingency filtration and ranking. Only a limited amount of literature exists on definition of severity factors. 

The main purpose of this thesis is to identify and summarise different existing and required research trends on the fundamental elements of operational risk assessment.  The contributions of the thesis include:

•   Identifying the fundamental elements of operational risk assessment and highlighting potential barriers against the practical implementation of operational risk assessment into the transmission system. Currently, TSOs are not deploying operational risk assessment, among others due to the absence of proper guidance and because of the high reliability resulting from the (N-1) criterion. Potential barriers against implementation of operational risk assessment, that were identified in the work, include absence of acceptable operational risk criteria, lack of a common and standardized set of severity factors, lack of sufficient knowledge on interpretation of operational risk results, and improper guidance on when and which types of measures are required to reduce the operational risk. 
• Introducing multi-state component models, including hidden failures, to operational risk assessment. In the power grid, major blackouts occur due to contingency cases involving protection failures. Including protection and protection failures in operational risk assessment results in several practical and mathematical challenges. Practical challenges include obtaining transition rate data; mathematical challenges include computing the time-dependent state probability of a large Markov model. This thesis addresses these mathematical challenges and provides a way to resolve them.  
• Clarifying the role of severity factor in operational risk assessment and proposing different deterministic and stochastic severity factors. The definition of the severity factor has a big impact on the way in which the results from operational risk assessment should be interpreted. A common set of severity factors is important for the interpretation of operational risk results and for the exchange of information and experience.

An important finding from this work is that operational risk assessment provides additional dimensions to the operational security planning, next to deterministic security criteria. However, several research gaps remain that need to be filled before implementation of operational risk assessment to existing transmission systems is possible.