Abstract
Expanding energy crises and environmental issues are attracting attention. Efficient and effective energy storage systems and decarbonization strategies are urgently demanded. For energy storage, Li-ion batteries are dominating the market, however, they are reaching their theoretical limits and are usually not considered green energy storage systems. On the other hand, traditional decarbonization strategies are struggling to address the current challenge of more severe carbon emissions. Studying and developing green, sustainable next-generation energy storage and decarbonization technologies are necessary. Upcycling waste from human activity into advanced materials for energy storage and decarbonization is able to not only ease the energy issues but also help with carbon neutrality, which is considered a promising route to overcoming the challenges. Among all recyclable materials, carbon materials have attracted intensive attention as they are abundant and readily upcycled into high value-added carbon materials. Although the high-end materials, especially biomass carbon polymer and carbon nanomaterials, are not yet commercially viable in the market, it is predicted that they may hold the key to a new era of high-capacity energy storage and high-efficiency decarbonization. This dissertation aims to convert carbon-based waste into high value-added carbon materials via green, sustainable methods, find applications in energy storage and decarbonization, and study the conversion and function mechanisms. In this dissertation, paper waste and end-of-life Li-ion battery anodes were chosen to be the waste feedstocks to prepare advanced carbon materials for energy storage and decarbonization.
Specifically, in Chapter 2, cellulose fibers were extracted from paper waste through a simple process and coated onto commercial separators in Li-S batteries to improve their performance. The performance of the batteries with or without cellulose fibers was tested and the working mechanisms of the cellulose fibers were experimentally explored. The Li-S batteries with cellulose fibers exhibited a longer lifespan and better stability than the batteries without cellulose fibers. In Chapter 3, a more thorough mechanism study of the cellulose fibers was conducted using computational tools. Battery working conditions were set up in molecular dynamics simulations, which showed that the cellulose fiber was capable of blocking more polysulfides and randomizing more Li-ions. Functional groups on the cellulose fibers were built in density functional theory models, which revealed that the groups could repel polysulfides and attract and redirect Li-ions. In Chapter 4, the possibility of employing the cellulose fibers as an adsorber of CO2 was explored using computational methods. Compared with one of the most commonly seen CO2 adsorbers, activated carbon, cellulose fibers were predicted to possess much better CO2/N2 selectivity while remaining comparable capacity. In Chapter 5, Li-ion battery anodes were recycled by an innovative approach to maximizing the capability of being exfoliated into graphene afterward. In sequence, carbon nanotubes (CNTs) were greenly and seamlessly grown on the upcycled graphene, and the obtained hybrid carbon material was exploited as a sulfur substrate to assemble Li-S batteries. Thanks to the large space for sulfur loading and volume expansion as well as excellent electrical conductivity, the battery with the graphene/CNT hybrid achieved much better longevity and stability compared with the battery using commercial graphite.
The findings bring new insights into deriving valuable and sustainable carbon materials from low-cost and environmentally friendly sources to enrich energy storage and decarbonization, paving the way towards a waste-to-wealth, circular society.
