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.

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.

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.

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.