Advanced Functional Materials for Lithium-Sulfur Batteries

The increasing demand for sustainable and high-energy storage systems is one of the biggest challenges of modern society. While lithium-ion batteries have dominated the market, their energy density is reaching fundamental limits, raising concerns about their sufficiency for future applications like electric mobility. Furthermore, the dependence on rare transition metals like cobalt and nickel leads to economic, geopolitical, and environmental issues which requires new sustainable alternative electrochemical storage systems. Lithium-sulfur (Li-S) batteries are one of the promising candidates to surpass lithium ion batteries due to their high energy density (2600 Wh kg−1) and specific capacity (1675 mAh g−1). Sulfur is abundant, low-cost and environmental friendly making them an attractive sustainable alternative. Besides these advantages, Li-S batteries face several major challenges hindering their commercialization. The most critical is the polysulfide shuttle effect leading to severe capacity fading and poor cycle life. Additionally, the low conductivity of sulfur causes sluggish redox kinetics and the volume changes during cycling damages the integrity of the sulfur electrode. To overcome these challenges advanced functional materials are needed which can simultaneously immobilize lithium polysulfides, accelerate their redox conversion, and buffer volume expansions. Herein, three classes of advanced functional materials are introduced to tackle the above mentioned challenges. First, recycled anode graphite from lithium-ion batteries is modified and functionalized by two different acid treatments. Afterwards, these materials are applied as host material and their influence on the battery performance is analyzed. As a result, the procedure shows an improvement by enhancing sulfur confinement and electronic transport, while it also offers a closed-loop approach for the transition from lithium-ion to Li-S batteries. Second, a comparative study of three different metal nitrides as separator coatings for Li-S batteries is presented. Besides the electrochemical performance, also a post-mortem analysis by applying SEM and XPS is performed to get insides into the mechanisms of metal nitride-based catalyst materials in Li-S batteries. Third, the influence of single-atom Cr incorporation into nitrogen-doped graphene (Cr@NG) is investigated with support from first-principles calculations and experimental characterization methods. The incorporation offers substantial advantages in electron transport and catalytic activity, making Cr@NG a promising multifunctional separator coating. This work investigates the structure-property-performance relationships of advanced functional materials in Li-S batteries. Utilizing advanced characterization techniques, electrochemical testing, and first-principles calculations, it explores their mechanisms to mitigate the shuttle effect, contributing to the development of practical, high-energy-density, and sustainable storage solutions.