Biobased cellulose nanofibrils (CNFs) constitute important building blocks for biomimetic, nanostructured materials, and considerable potential exists in their hybridization with tailorable polymeric nanoparticles. CNFs naturally assemble into oriented, fibrillar structures in their cross-section. This work shows that polymeric nanoparticle additives have the potential to increase or decrease orientation of these cellulose structures, which allows the control of bulk mechanical properties. Small amounts of these additives (<1 wt%) are shown to promote the alignment of CNFs, and the particle size is found to determine a tailorable maximum feature size which can be modified. Herein, X-ray scattering allows for the quantification of orientation at different length scales. This newly developed method of measuring cross-sectional orientation allows for understanding the influence of nanoparticle characteristics on the CNF network structure at different length scales in hybrid cellulose-nanoparticle materials, where previously quantitative description has been lacking. It thus constitutes an important foundation for further development and understanding of nanocellulose materials on the level of their nanoscale building blocks and their interactions, which in turn are decisive for their macroscopic properties.

The electrolyte plays a key role in the performance of novel lithium-ion battery concepts. Hybrid polymer-liquid electrolytes (HEs) are suitable candidates for novel concepts of lithium-ion batteries (LIBs) and lithium-metal batteries (LMBs), where high ionic conductivity coupled with mechanical integrity are required at the same time. HEs are produced through polymerization-induced phase separation (PIPS) of a monomer/electrolyte mixture which allows for the formation of a two-phase system where the domains create a bicontinuous structure. Electrochemical performance and thermomechanical behavior can be tailored through several variables e.g., monomer and solvent chemistries, solvent concentration, and curing conditions. The present study is focused on the chemical structure of the monomer where methacrylate and acrylate monomers are compared as homopolymers or copolymers in HEs. The number of ethylene oxide (EO) units in the backbone of the monomers are furthermore analyzed as a structural parameter. The results show that the monomer structure not only affects the electrochemical and thermomechanical properties, but also defines the morphology of the HEs obtained, which can be in the form of a bicontinuous structure, a gel, or a mixture of the two, according to the kinetic and thermodynamic variables affecting the phase separation and the ultimate Tg of the polymer.

An increasing demand for alternative electrolyte systems is emerging to address limitations associated with traditional liquid electrolytes in lithium-ion batteries (LIBs). Hybrid polymer-liquid electrolytes (HEs) combine the merits of solid polymers and liquid electrolytes in a heterogeneous phase-separated system where the polymer phase encapsulates the liquid ion-conducting phase. These electrolytes are synthesized through polymerization-induced phase separation (PIPS), resulting in the formation of a porous three-dimensional polymer network. Carbon black (CB) serves as conductive additive in LIBs electrodes, enhancing electric conductivity and thereby improving the battery performance and lifespan. How CB, already present in conventional electrodes, affects the PIPS process during the formation of HEs for LIBs, focusing on the material interactions and the formed microstructure properties, has been investigated. Addition of CB does not negatively affect the result of PIPS process, and it permits high conversion rate and compatibility with HE at all CB concentrations investigated. Morphological analysis in combination with nuclear magnetic resonance (NMR) and electrochemical impedance spectroscopy (EIS) reveals consistent macroporous and mesoporous structures, indicating the robustness of HEs to CB content variation. Understanding the interaction between CB and HEs during the manufacturing process and the impact of CB on the structural integrity and compatibility of the HE system, aids the integration of HEs with existing electrode materials in practical battery configurations.

The global shift towards renewable energy sources and the electrification of transportation necessitates advanced energy storage solutions, with lithium-ion batteries (LIBs) at the forefront. However, conventional batteries with liquid electrolytes in LIBs pose several limitations such as flammability, poor chemical stability, leakage risks, overall safety concerns, and limited processability. This thesis investigates hybrid polymer-liquid electrolytes (HEs) as an alternative to address these issues in LIBs as well as a way to obtain additional functionalities e.g. improved structural integrity.

The research is organized into four main studies. Paper I focuses on the three-dimensional (3D) reconstruction and analysis of HE structures. Using focused ion beam-scanning electron microscopy (FIB-SEM), the study reveals the complex, interconnected pore networks within HEs that are critical for ionic conductivity and mechanical stability.

Paper II explores the impact of porosity on the ionic and molecular mobility within HEs. By varying the liquid electrolyte content, the study demonstrates how increased porosity enhances ion mobility, directly correlating with improved electrochemical performance. Nuclear magnetic resonance (NMR) diffusion experiments further elucidate the transport mechanisms within the polymer matrix, showing a significant increase in ion diffusion rates with higher electrolyte content.

Paper III examines the role of nanosized carbon black (CB) particles in the polymerization-induced phase separation (PIPS) process used to synthesize HEs. The addition of CB improves the conductivity of HEs without compromising their morphological integrity. The study finds that even small amounts of CB can substantially enhance the overall conductivity, making CB-rich HEs potential candidates for multifunctional roles within battery electrodes, such as conductive binders.

Paper IV evaluates the practical application of HEs by integrating them into commercial LIB electrodes. The HE-infused electrodes maintain their structural and electrochemical properties even after multiple charge-discharge cycles, proving their potential for use in commercial applications.

This thesis contributes to the development of multifunctional electrolytes that not only address the safety issues associated with liquid electrolytes but also advance multifunctionality in LIBs. The methodologies and findings presented provide a foundation for future research in high-performance, safer, and more sustainable battery technologies.

Den globala förändringen mot förnybara energikällor och elektrifieringen av transporter kräver avancerade energilagringslösningar, med litiumjonbatterier (LIB) i framkant. Konventionella batterier med flytande elektrolyter i LIB har dock flera begränsningar såsom brandfarlighet, kemisk instabilitet, risk för läckage, begränsade bearbetbarhet och säkerhetproblem. Denna avhandling undersöker ”hybrid polymer-liquid electrolytes” (HEs) som ett alternativ för att ta itu med dessa problem i LIBs samt ett sätt att erhålla ytterligare funktionaliteter t.ex. förbättrad strukturell integritet.

Forskningen är organiserad i fyra huvudstudier. Artikel I fokuserar på tredimensionell (3D) rekonstruktion och analys av HE-strukturer. Med hjälp av ”focused ion beam-scanning electron microscopy” (FIB-SEM) visar studien de komplexa, sammankopplade pornätverken inom HEs som är avgörande för jonkonduktivitet och mekanisk stabilitet.

Artikel II utforskar inverkan av porositet på jonisk och molekylär rörlighet inom HEs. Genom att variera innehållet av flytande elektrolyt visar studien hur ökad porositet förbättrar jonmobiliteten, vilket direkt korrelerar med förbättrad elektrokemisk prestanda. ”Nuclear magnetic resonance” (NMR) diffusionsexperiment belyser transportmekanismerna inom polymermatrisen ytterligare och visar en signifikant ökning av jondiffusionshastigheter med högre elektrolythalt.

Artikel III undersöker rollen av kimrökspartiklar (CB) i nanostorlek i den polymerisationsinducerade fasseparationsprocessen (PIPS) som används för att syntetisera HE. Tillsatsen av CB förbättrar konduktiviteten hos HE utan att kompromissa med deras morfologiska integritet. Studien visar att även små mängder CB avsevärt kan förbättra den totala konduktiviteten, vilket gör CB-rika HEs potentiella kandidater för multifunktionella roller inom batterielektroder, såsom ledande bindemedel.

Artikel IV utvärderar den praktiska tillämpningen av HE:er genom att integrera dem i kommersiella LIB-elektroder. De HE-innehållande elektroderna bibehåller sina strukturella och elektrokemiska egenskaper även efter flera laddnings-urladdningscykler, vilket bevisar deras potential för användning i kommersiella tillämpningar.

Denna avhandling bidrar till utvecklingen av multifunktionella elektrolyter som inte bara tar upp säkerhetsfrågorna förknippade med flytande elektrolyter utan också främjar multifunktionaliteten i LIB. Metoderna och resultaten som presenteras ger en grund för framtida forskning inom högpresterande, säkrare och mer hållbar batteriteknologi.

Alternative electrolyte systems such as hybrid electrolytes are much sought after to overcome safety issues related to liquid electrolytes in lithium ion batteries (LIBs). Hybrid solid-liquid electrolytes (HEs) like the heterogeneous structural battery electrolyte (SBE) consist of two discrete co-existing phases prepared by polymerization-induced phase separation: one solid polymer phase providing mechanical integrity and the other one a percolating liquid ion-conducting phase. The present work investigates the ion and the solvent mobility in a series of HEs using morphological, electrochemical impedance and NMR spectroscopic methods. All the dried HEs exhibit a porous structure with a broad pore size distribution stretching down to <10 nm diameter. Penetration of the individual components of the solution, that is the ions and the solvent, in the solid polymer phase is demonstrated. Yet, it is the pores that are the main ion conduction channels in the liquid-saturated HEs and, in general, translational mobility is strongly dependent on the volume fraction and size of the pores and, thereby, on the initial liquid electrolyte content. We also observe that the translational mobility of solvent and the ions vary differently with the pore volume fraction. This finding is explained by the presence of small mesopores where the mobility strongly depends on the specific interactions of the molecular constituent with the pore wall. These interactions are inferred to be stronger for the EC/PC solvent than for the ions. This study shows how the morphology and the chemical composition of HEs affect the ionic and molecular transport in the system.

Structural batteries are multifunctional composite materials that can carry mechanical load and store electrical energy. Their multifunctionality requires an ionically conductive and stiff electrolyte matrix material. For this purpose, a bi-continuous polymer electrolyte is used where a porous solid phase holds the structural integrity of the system, and a liquid phase, which occupies the pores, conducts lithium ions. To assess the porous structure, three-dimensional topology information is needed. Here we study the three-dimensional structure of the porous battery electrolyte material using combined focused ion beam and scanning electron microscopy and transfer into finite element models. Numerical analyses provide predictions of elastic modulus and ionic conductivity of the bi-continuous electrolyte material. Characterization of the three-dimensional structure also provides information on the diameter and volume distributions of the polymer and pores, as well as geodesic tortuosity. Structural battery composites contain a porous solid phase that holds the structural integrity of the system with a liquid phase in the pores. Here, the porous structure is studied using combined focused ion beam and scanning electron microscopy and transferred into finite element models.

Hybrid polymer-liquid electrolytes (HEs) are suitable candidates for novel concepts of lithium-ion batteries (LIBs) and lithium-metal batteries (LMBs), where high ionic conductivity coupled with mechanical performance are required at the same time, thus giving such batteries the definition of multifunctional materials. HEs are produced through polymerization-induced phase separation (PIPS) of a monomer / liquid electrolyte mixture having suitable solubility parameters. This process allows for the formation of a two-phase system, where the domains develop a bicontinuous structure. Electrochemical performance and thermomechanical behavior can be tailored through several variables e.g., monomer and solvent chemistries, solvent concentration and curing conditions. The present study is focused on the chemical structure of the monomer where methacrylate and acrylate monomers are compared as homopolymers or copolymers. The number of ethylene oxide (EO) units in the backbone of the monomers are furthermore analyzed as a structural parameter. The results show that the monomer structure not only affects the electrochemical and thermomechanical properties, but also defines the morphology of the HE obtained, which can be in the form of a bicontinuous structure, a gel, or a mixture of the two, according to the kinetic and thermodynamic variables affecting the phase separation and the ultimate Tg of the polymer.

To address the increasing demand for efficient, safe, and sustainable energy storage solutions in the transition towards renewable energy and electrified society, this study explores hybrid polymer-liquid electrolytes (HEs) as a novel solution to overcome challenges in traditional liquid electrolytes used in lithium-ion batteries (LIBs). Particularly, the research is focused on polymerization-induced phase separation (PIPS) synthesized HEs with distinct phase-separated systems, where an ion-conducting liquid phase percolates the macropores and mesopores within the formed thermoset solid phase. This study investigates the feasibility of using HEs with commercial cathodes and highlights their respective merits and challenges. The feasibility of infusing cathode (i.e. the positive electrode) with HEs synthetized via PIPS within both micron-sized and nano-sized confined spaces is proved. By incorporating these HE-infused electrodes into half-cell configurations, the study proves that the HEs are compatible with high voltage electrodes, and they exhibit energy density comparable with traditional systems. A significant focus is placed on assessing the morphological and electrochemical stability of HEs after cycling.

An increasing demand for alternative electrolyte systems is emerging to address limitations associated with traditional liquid electrolytes in lithium-ion batteries (LIBs). Hybrid polymer-liquid electrolytes (HEs) combine the merits of solid polymers and liquid electrolytes in a heterogeneous phase separated system where the polymer phase encapsulates the liquid ion-conducting phase. These electrolytes are synthesized through polymerization-induced phase separation (PIPS), resulting in the formation of a porous three-dimensional polymer network. Carbon black (CB) serves as conductive additive in LIBs electrodes, enhancing electric conductivity and thereby improving the battery performance and lifespan. The study investigates how CB, already present in conventional electrodes, affects the PIPS process during the formation of HEs for LIBs, focusing on the material interactions and the formed microstructure properties. Addition of CB does not negatively affect the result of PIPS process, and it permits high conversion rate and compatibility with HE at all CB concentrations investigated. Morphological analysis in combination with nuclear magnetic resonance (NMR) and electrochemical impedance spectroscopy (EIS) reveals consistent macroporous and mesoporous structures, indicating the robustness of HEs to CB content variation. By shedding  light on the interaction between CB and HEs during the manufacturing process and the impact of CB on the structural integrity and compatibility of the HE system, we aid the integration of HEs with existing electrode materials in practical battery configurations.