21ENGBIO Engineering biomineralized carbon-sulfur composites for clean energy technologies

Electrical energy storage is a vital issue in our attempt to transition from an economy based on fossil fuels to the widespread use of decarbonized energy sources. Lithium-sulfur (Li-S) batteries are a promising successor to the commercial Li-ion batteries that are powering today's electronic devices and electric vehicles, holding a theoretical capacity an order of magnitude higher. However, the commercial utilization of Li-S batteries is delayed due to several issues related to the properties the sulfur materials composing their cathode and their poor stability during charge-discharge cycles. These problems can be mitigated by embedding sulfur within conductive carbon materials and organic polymers. However, the production of such carbon-sulfur (C-S) composites is currently a complex and energy-intensive chemical process. Here, we propose to harness the potential of some bacteria to naturally form C-S composites, through a process called biomineralization. We will work with the bacterium Sulfuricurvum kujiense, which produces sulfur minerals with organic envelopes. The bacteria grow at room temperature using only CO2, hydrogen sulfide and nitrate as substrates. Battery materials may thus be produced through a clean and energy-efficient biological process, while recycling three harmful waste products of human activity.

In this project, we aim at gaining a better understanding of the biological and chemical parameters controlling the properties of the C-S composites produced by Sulfuricurvum kujiense, and demonstrate that these composites are efficient battery materials and that they can be produced at large scale. If successful, this project will prepare future approaches aimed at genetically engineering Sulfuricurvum kujiense to optimize C-S composite production and properties for Li-S battery applications. With this research, we will contribute to the design of more sustainable battery materials for the storage of energy from renewable sources, and thus participate in achieving decarbonization, one of the pressing challenges of the 21st century and a prerequisite to the achievement of our global climate goals.

This reject will investigate the formation of composites of elemental sulfur and organic carbon by biomineralizing bacteria, as potential cathode materials for Lithium-sulfur (Li-S) batteries. Li-S batteries are potential successors to current Li-ion batteries, holding a theoretical capacity an order of magnitude higher. However, several issues are delaying their commercialization, principally due to poor cycling stability of the sulfur cathode. Much of recent R&D efforts have focused on overcoming these drawbacks by developing cathodes where sulfur is embedded within conductive carbon materials and/or organic polymers. The fabrication of such carbon-sulfur (C-S) composites is currently a complex and energy-intensive process. We propose to move towards a biological approach using the S-oxidizing bacterium Sulfuricurvum kujiense, which forms extracellular S biominerals encapsulated within polymeric organic envelopes. S. kujiense grows autotrophically using nitrate, hydrogen sulfide, and carbon dioxide as substrates, offering the potential to produce desirable cathode materials in a process that is significantly simpler, greener, and more energy efficient than existing synthesis protocols, while recycling environmentally harmful products of human activity. We will lay the foundations for the future deployment of engineering biology strategies for optimized C-S production by S. kujiense by gaining a fuller understanding of the biological and chemical controls on C-S composite biomineralization, testing the electrochemical properties of the C-S biocomposites in battery settings, and demonstrating upscalability in bioreactor cultures. This project will seed the development of a novel engineering biology system for the design of green materials for next-generation energy storage technologies. It will directly contribute to efforts to unlock the fundamental potential of biology to create more sustainable production processes and achieve decarbonization.