The increasing market of electric vehicles and the growing importance of renewable energy sources calls for next-generation high-efficiency batteries. Li-ion batteries, which dominate the current market, are limited by capacity due to the use of graphite as electrodes and expensive metal oxide cathodes. Alternatively, Lithium-sulfur batteries (Li-S) are found to be promising next-generation substitutes for lightweight energy storage systems thanks to their high theoretical capacity, which is about five times more than lithium-ion batteries. However, there are critical challenges in the current Li-S batteries, including i) poor electronic conductivity of elemental sulfur, ii) large volume expansion of cathode during the charge/discharge process, and iii) polysulfide shuttling, causing active material loss and shuttle effects. These phenomena result in rapid capacity decay of the Li-S battery.
The MOGLiS (MOF@rGO-based cathodes for Li-S Batteries) project employs nanotechnology and thin film fabrication techniques to address the current challenge of Li-S batteries. Flexible cathodes for Li-S batteries have been designed based on the developed nanomaterials containing Metal-Organic Frameworks (MOFs) anchored on the basal planes of the reduced Graphene Oxide (rGO), named MOF@rGO, to improve Li-S batteries’ overall performance, e.g., ultra-long cyclic life and high-rate capability with minimum capacity decay. Fabrication protocols using the innovative MOF@rGO materials to make flexible, lightweight cathodes, including sulfur impregnation procedures, were also optimized, evolving from the original design to the notably improved 2nd generation MOF@rGO materials. The fabricated MOF@rGO cathodes have been tested in the coin cells. Compared with the traditional method of simply mixing MOF with rGO, the novel MOF@rGO approach offers significantly higher cyclic life with a lower capacity decay. The MOF@rGO cathode also exhibited outstanding rate capability, even at a very high charging-discharging rate. The exceptional electrochemical performances place the developed MOF@rGO-based cathode as one of the best cathodes for polysulfide adsorption and conversions reported to date.
In addition, during the MOF screen process, we found that bimetallic MOF materials could be used to coat commercial separators to prevent polysulfide shuttling and further increase Li-S batteries’ cyclic life and stability. Therefore, novel MOF-modified separators were fabricated and tested, exhibiting dramatically improved performance. The developed separator can also prevent lithium dendrite formation due to the uniform pore size and hence the even Li+ transport and deposition. A high cycle life at a high initial capacity was obtained, and promising specific capacity was also documented even under a high sulfur loading and a low electrolyte-to-sulfur ratio.
NTNU and SINTEF are the project partners, and the Warsaw University of Technology (WUT) is the international collaborator. The implementation of the MOGLiS project has been successful, and most of the planned research activities have been performed following the schedule and reached the milestones. The resources at NTNU and SINTEF have been fully exploited through effective collaboration and joint publications. The project outcomes demonstrate the potential of the developed cathode material and separators for flexible and foldable batteries with very high capacity and advantages over existing batteries in terms of size, safety, and efficiency. Two patents were generated on the developed new cathode material for Li-S batteries and the novel separator design, respectively, in collaboration with the Technology Transfer Office (TTO) at NTNU. Three journal papers were prepared and submitted to high-level journals.
The research outcomes of the MOGLiS project from the Norwegian partners mainly include the following aspects :
(1) Invention of novel functional materials to manufacture high-performance Li-battery cathodes.
- Two patents have been filed through the Technology Transfer Office (TTO).
- After the patents were filed, three papers have been prepared and are expected to be soon submitted to high-impact journals.
(2) Establishment of design principles of the functional material configuration for enhanced cathode performance.
- The fabrication procedure has been updated from generation zero to the 1st and 2nd generation materials.
(3) A new separator concept for Li-S battery using the developed nanomaterials.
- The separator concept discovered during the project has been tested with excellent results.
- The concept and results were used to establish new projects, including a project funded by the Research Council of Norway in 2023 (the 3S Battery project).
Overall, the MOGLiS project results are expected to enhance the innovation potential in the Li-S battery technology by facilitating progress in Li-S batteries' durability and longevity, a crucial aspect for the next generation Li-S batteries, thus supporting Norwegian and the EU’s policies for green energy transition and mitigating carbon emissions.
Lithium-sulfur (Li-S) batteries are attractive next generation energy storage devices in sectors like transportation due to their higher theoretical capacity and energy density. The lack of high-performance cathodes that can overcome the decay in cell capacity with cycling hinders the current market realization of Li-S batteries. The MOGLiS project aims at fabricating high performance cathode materials using novel MOF@rGO architectures. These new nanostructures will be synthesized and upscaled by the Norwegian partners in this project with the aim of engineering high performance cathodes sourced from carefully crafted chemistry and tailored nano-architectures. The resulting cathodes will be characterized with superior electrical and mechanical properties with efficient immobilization of sulfur compared to state-of-the-art Li-S cathodes. Upscaling of the developed functional materials using novel flow reactor technology in the view of securing commercialization interests is also planned in MoGLiS. These next generation flexible Li-S cathodes will be designed and demonstrated at TRL 4 for a high initial capacity >1300 mAh.g-1 and a reversible capacity, after 20 cycles, superior to 1200 mAh.g-1, but also a high cyclability with demonstrations >100 cycles with a capacity loss of less than 0.010% per cycle, for a sulfur loading in the cathode superior to 75%.