Bio-degradable Li-ion battery anodes

Biobatt is a project that has focused on development of a new anode material for Li-ion batteries. This is a material based on diatoms from algae, which are harvested from the ocean. For fabrication of battery anodes, sodium alginate binders are used, that are extracted from brown algae. Both of these are renewable resources, thus providing a sustainable process for development of improved Li-ion battery electrodes. Both these materials are produced in Norway. It should also be added that the alginates are soluble in water, which allows for replacement of the current toxic solvents used in the battery production process, by water. Using these naturally occurring and renewable elements combined with low toxicity solvents, makes this new technology considerably more environmentally friendly than existing technology. Within the framework of the project we have worked both with silica from algae, as well as synthetic silica. New methods for simple processing of the material from diatom frustules, which is harvested directly from the sea, has been developed. These consist of a simple cleaning procedure, as well as procedures for crushing the materials in order to obtain an optimized particle size distribution with respect to application as electrode material in Li-ion batteries. These materials are close to pure silica, with a very interesting microstructure, which most probably is beneficial for the reaction with lithium. Due to the low conductivity of the materials, particles are coated with a carbon coating, and a thorough optimization of this procedure has been undertaken, with respect to precursor (glucose, starch, sucrose), amount of carbon, and heat treatment. The diatom frustules have been characterized by means of TEM in order to identify secondary phases, and both types of frustules have been characterized by FTIR, XPS and Raman in order to identify differences in surface chemistry and structure. TEM has also provided valuable information on the structure and thickness of the carbon coating. It has been demonstrated that the electrodes can cycle with high stability at a capacity of up to 750 mAh/g, which is far above the conventional graphite, which has a theoretical capacity of 372 mAh/g. The electrodes have been cycled both in half cells and in full cells. Special procedures have been developed for pre-activation (electrochemical) of the electrodes, which again leads to more stable cycling. Stable cycling in full cells has been demonstrated after this pre-activation. In addition, it has been shown that chemical pre-lithiation is as efficient as electrochemical pre-activation, and more convenient to implement. In spite of the stable cycling and the high capacities demonstrated, there are still challenges related to irreversible voltage losses in the electrodes, which again limits the energy density. This needs to be solved by improved pre-processing routes, or improved procedures for the pre-lithiation. In the last phase of the project, focus has been put on fundamental characterization with high-energy X-rays, and a measurements campaign has been conducted at the Petra III synchrotron in Hamburg. The measurements were performed both on the materials, as well as on in-house designed cells for in-situ measurements during cycling. The data provides information on the lithiation of the materials, and the compounds formed during cycling. The data are currently under evaluation, and will be presented in a publication during 2021. Within the framework of this project there is also an activity focusing specifically on RRI «Responsible Research and Innovation». This activity has a particular focus on transfer of knowledge between academia and industry in the area of batteries. An extensive series of interviews with relevant stakeholders (total of 25) in industry and academia has been conducted, in order to better understand interactions between research and innovation. A scenario-analysis has been conducted in collaboration with the advisory board (three members from industry and international research) relevant for the research activity in the project. The social scientist has spent much time together with the experimental scientists in order to get an understanding of the technical research activities. In general, the project activities were found to represent responsible research in terms of ethics and sustainability. This work has been summarized in a publication which will be sent within 2021. In summary, the research activities have been conducted as planned, and the results have been summarized in several publications 3 papers have already been accepted, 1 in currently in the review process, and another 3 papers are in the pipeline. 3 Post Docs and 5 master students have been affiliated to the project. Even is the research has not yet resulted in a commercially viable process, Norwegian companies have confirmed their interest in the work.

I prosjektet er det gjennomført forskning for bedre å forstå, og kunne utnytte silika som anodemateriale i Li-ion batteri, med en spesiell fokus på silika fra alger. Det er utviklet prosedyrer for rensing, knusing, påføring av karbonbelegg, og materialene er karakterisert i små-skala battericeller. Det er vist at denne typen silika har høy kapasitet i forhold til lagring av litium, men at elektrodene har relativt høye spenningstap. For at materialene skal være kommersielt interessante for en batteriproduksjon, må det utvikles bedre metoder for pre-prosessering (reduksjon) av materialet.

Bio-Batt aims to develop a Li-ion battery (LIB) solution where SiO2 can be used as anode material combined with water soluble alginate binders. Nanostructures of silica have shown stable cycling capacity of up to 800 mAh/g without suffering from similar performance issues as Si. One of the most recent publications concerns the use of diatoms in combination with red algae as anode material in LIBs. Half cells were tested with a capacity of 500 mAh/g after 80 cycles. The two main issues encountered in silica anodes are the poor conductivity and high volume expansion during cycling. Morphology and composition of the silica anode will therefore be key parameters to achieve high and stable electrochemical performance. Here, diatoms which are naturally 3D nanostructured silica based materials will be investigated, in addition to microsilica from Elkem. Various pre-treatmens and conductive coatings will be investigated in order to provide higher conductivity for improved capacity and cycling rates. New water soluble binder materials will also be investigated for the electrode production. Recent investigations have shown that various alginates may be used as binder materials in LIBs. These alginate binders will be investigated with respect to chemical compatibility with the active material, electrochemical stability in the given potential window, and performance in combination with various silica materials. The project also has a goal to work towards commercialization, and thus third party verification will be performed at ETH in Zurich. The project will be executed in collaboration with the Department of Interdisciplinary Studies of Culture, which will make sure that the RRI perspective is implemented throughout the project. Common meetings and workshops will be held to ensure that RRI becomes a fully integrated part of the project.