Multifunctional Positive Electrodes for Structural Batteries

Abstract

The rising demand for energy, coupled with the environmental consequences of CO2 emissions primarily stemming from the combustion of fossil fuels, has prompted the exploration of sustainable solutions for energy generation and storage. Specifically, the automotive industry is transitioning to electric-powered and lightweight vehicles equipped with batteries for generating and storing electric energy. The conventional lithium-ion batteries (LIB) offer high efficiency and energy density, however the presence of mono-functional material with no mechanical performance, liquid electrolyte, and hard protecting casing with poor load-bearing capability marks the battery dependent on inert structural components, which makes the battery bulky and limits its capacity.Structural battery composites, based on carbon fibre (CF), serve a dual purpose by not only storing energy but also acting as integral structural components, potentially replacing inert structural elements [1]. The integration of structural batteries into vehicles and aircraft offers additional power while significantly reducing weight, leading to a substantial enhancement in the overall energy efficiency of the vehicle [2,3].Nevertheless, there exist several challenges in realizing these structural battery composites. For instance, CF-based cathode composites face issues like low energy capacity and weak interfacial strength due to the inadequate adhesion of active materials to the CF surface. Additionally, the current manufacturing methods, such as blade or spray coating, rely on harmful organic solvents.To overcome these limitations, the concept of all-fibre structural batteries is introduced in the present work. In this approach, carbon fibre tows are utilized directly as the negative electrode, like graphite, while electrochemically active functional carbon fibres serve as positive electrodes and a two-phase solid-liquid electrolyte functions as the structural battery electrolyte (SBE). This essentially offers massless energy storage. The electrodes are manufactured using economically friendly, abundant, cheap, and non-toxic iron-based materials like olivine LiFePO4. Graphene, renowned for its high surface area and electrical conductivity, is incorporated to enhance the ion transport mechanism. Furthermore, a vacuum-infused solid-liquid electrolyte is cured to bolster the mechanical strength of the carbon fibres (CFs) and provide a medium for lithium-ion migration. Electrophoretic deposition is selected as a green process to manufacture the structural cathodes with homogeneous mass loading and pouch cells are employed to test the electrochemical performance of LiFePO4-based structural cathodes.