Solid-state lithium-sulfur batteries are gradually becoming a research hotspot in the field of new energy due to their excellent performance and great potential. This kind of battery not only significantly improves the stability and safety of lithium-sulfur batteries, but also enhances their mechanical modulus by using a solid-state electrolyte instead of the traditional liquid organic electrolyte. Lithium-sulfur batteries are widely used, but the practicality of lithium-sulfur batteries is low due to limitations in technology and materials. Recently, a team led by engineers at the University of California, San Diego, developed a new cathode material for solid-state lithium-sulfur batteries that is highly conductive and repairable, overcoming the limitations of lithium-sulfur battery imprinting. Solid-state lithium-sulfur batteries are rechargeable batteries consisting of a solid electrolyte, an anode made of lithium metal, and a cathode made of sulfur. Solid-state lithium-sulfur batteries are likely to become a high-quality alternative to current lithium-sulfur ion batteries in the future due to their higher density energy and lower cost, and they store twice as much energy per kilogram as traditional lithium-ion batteries. In addition, solid-state lithium-sulfur batteries use materials that are less expensive and more environmentally friendly than traditional lithium-ion batteries. However, lithium-sulfur solid-state batteries have been facing challenges in their development due to the properties of the sulfur cathode itself. First, sulfur does not perform well as an electron conductor, which limits its electron transfer efficiency in batteries. Second, sulfur cathode undergoes significant volume expansion and contraction during battery charge/discharge cycles, and this volume change leads to damage to the cathode structure and reduces its contact area with the solid electrolyte. These two issues interact with each other and together reduce the cathode's charge transfer capability, which in turn affects the overall performance and lifetime of the solid-state battery. To address these issues, the team developed a new cathode material: a crystal composed of sulfur and iodine. By inserting iodine molecules into the crystalline sulfur structure, the researchers dramatically increased the electrical conductivity of the polar cathode material by 11 orders of magnitude, making it 100 billion times more conductive than crystals made of sulfur alone. In addition, the new crystalline material has a low melting point of 65°C (149°F), a value lower than the temperature of a hot cup of coffee. This property means that after a battery has been charged, its polar cathode material can be re-melted relatively easily. This is critical for repairing interfacial damage that may occur during charge/discharge cycling, and in this way, damage during the charge/discharge process of solid-state batteries can be effectively addressed. Industry insiders commented on this, "This sulfur iodide cathode presents a unique concept that could address some of the major barriers to the commercialization of lithium-sulfur batteries."
To verify the effectiveness of the new cathode material, the researchers subjected a test battery to repeated charging and discharging cycles, which remained stable for more than 400 cycles while retaining 87 percent of its capacity. This discovery has the potential to significantly improve the lifespan of solid-state lithium-sulfur batteries, thereby addressing one of the major challenges facing such batteries. He mentioned that the battery is able to self-heal through a simple temperature boost, an ability that will greatly extend the overall life cycle of the battery.
In other words, through this self-healing mechanism, solid-state batteries are able to maintain longer-lasting performance after repeated charging and discharging processes. This characteristic opens the way for solid-state batteries to move towards practical applications, making battery technology a major step forward. This innovative self-repair capability not only improves the reliability and efficiency of batteries, but also lays a solid foundation for the commercialization and widespread application of solid-state batteries.
