Defence of doctoral thesis: Hugo Françon – Utilizing Cellulose Nanofibrils in the Assembly of Sustainable and Scalable Energy Storage Materials
Supervisor: Professor Lars Wågberg, KTH
Opponent: Professor Jodie Lutkenhaus, Texas A&M University
Energy storage is a key technology sector that can be improved to lower carbon emissions, replace fossil fuel energy supplies and thus contribute to creating a more sustainable future. Current methods of large-scale energy storage device production have raised concern regarding their cost, carbon footprint and sustainability. The mining of raw materials is particularly problematic, being notorious for its high environmental cost. For this reason, there is an urgent need to develop more sustainable materials that can be used in energy storage devices. Cellulose, a biopolymer commonly extracted from plants, is an abundant and versatile material, known for its large-scale use in pulping and papermaking. Owing to its chemical versatility, it can be assembled into a variety of materials, some of which have attracted interest in the preparation of more sustainable energy storage devices. A particularly interesting example is cellulose nanofibrils (CNFs), a bio-based nanomaterial combining great mechanical properties with chemical functionality. CNFs have been used in the preparation of materials showing a wide array of sizes (from nano- to macro-scale), structures and physicochemical properties.
This thesis investigates the use of CNFs in the preparation of more sustainable energy storage materials, focusing on processes compatible with upscaling. First, this work aims to improve the preparation of low-density materials (aerogels), to be used as electrodes for pseudocapacitors and batteries. To this end, CNF aerogels were prepared through a novel freeze-linking method (Article I), that was then further improved with the use of complexing biopolymers (Article II) and functionalized into energy storage materials using conjugated polymers (Articles I and II). Next, CNFs were used in the preparation of anode materials for Li-ion batteries. Their use as bio-based binders in the preparation of electrochemically and mechanically superior electrodes (Article III) was investigated, further enabling the preparation of free-standing and recyclable graphite anodes (Article IV).