Functional Carbon Surfaces for Stable Passivation of Sodium-Ion Battery Electrodes

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Non-technical DescriptionIntermittent renewable energy sources like wind and solar require large-scale, cost-effective methods for energy storage. There is currently no technology that could provide this amount of energy storage with acceptable safety, lifetime, and cost. Rechargeable sodium-ion batteries are more promising than lithium-ion batteries for large-scale storage based on their earth-abundant resources and lower raw material cost. However, the lifetime of current sodium-ion technology is limited by inefficient interfaces between solid and liquid materials inside the battery. With the support of the Solid State and Materials Chemistry program, this project will develop better understanding of this interfacial chemistry. The results will allow researchers to design materials that last longer and to predict the lifetime of those materials much faster than traditional methods. The educational benefits of the project include graduate and undergraduate researcher training in electroanalytical chemistry, battery science, microfabrication, and reactor design. The PI has also partnered with a local high school's chapter of Girls Who Code to introduce high school students to electronics and engineering design.Technical DescriptionInsufficient passivation from the Solid Electrolyte Interphase (SEI), a surface film at the electrode/electrolyte interface, limits the lifetime of sodium-ion batteries. Even basic understanding of how the SEI forms, grows, and transports charges is severely lacking. This work will apply an innovative combination of microfluidic reactors, electrochemical generator-collector experiments, and redox mediator studies in order to develop methods for critical insight into the form and function of the SEI. Reducing reactor volume mimics the surface:volume ratio of a real battery while the well-defined convection field is still amenable to transport and kinetic analysis. This unconventional approach controls the residence time of the electrolyte degradation reactions and can be used to map passivation efficiency to the concentration and chain-length of solubilized oligomers. The microflow reactor also permits electrochemical generator-collector experiments to amperometrically detect reaction products. Such four-electrode measurements are not possible in a normal battery and will permit the amperometric detection of soluble degradation products and mediator studies of charge transport and reaction in the SEI. Patterned carbonaceous electrodes in model geometries will be synthesized by controlled oxidation of pyrolyzed photoresist. These electrodes will be characterized spectroscopically and microscopically in order to relate their electrochemical performance to the nature of the carbon surface. The results of the study will impact both existing and emerging materials for sodium-ion batteries by determining how carbon surface chemistry can be used to control both the catalysis of desirable SEI products and their effective precipitation into stable films.