The secret to next-gen batteries? It could be in the binder, says ORNL

A recent study focused on polymer binders could point to future breakthroughs in solid-state batteries, enabling safer, more powerful, and longer-lasting energy storage. Researchers at Oak Ridge National Laboratory have discovered that the molecular weight of these often-overlooked components plays a crucial role in the performance and durability of sulfide solid-state electrolytes (SSEs), a key element of next-generation battery technology.

Toward solid-state batteries

Solid-state batteries offer several advantages over conventional lithium-ion designs. They provide higher energy density, potentially enabling longer ranges in electric vehicles and more compact batteries in portable devices, including smartphones and laptops. Additionally, solid-state batteries boast a superior safety profile, eliminating the risk of fires associated with liquid electrolytes in traditional lithium-ion batteries. Yet the practical implementation of solid-state batteries has faced hurdles. One major challenge is achieving high ionic conductivity while maintaining mechanical stability in the solid-state electrolyte. Ionic conductivity is crucial for efficient battery operation, while mechanical stability ensures the battery’s structural integrity over numerous charge-discharge cycles. In research published in ACS Energy Letters, the scientists describe why the choice of polymer binders, essential for creating robust, freestanding SSE films, and how that can help overcome the challenges.

The role of molecular weight

Under the guidance of Guang Yang, Ph.D., the researchers explored the role of polymer binder entanglement in developing flexible, sheet-type sulfide solid-state electrolytes (SSEs) for all-solid-state batteries. Their study revealed that the molecular weight of polymer binders has a dual impact on SSE films. First, the higher molecular weight binders improve the film’s robustness but increase electrical resistance. Second, the lower molecular weight binders enhance uniformity but lack structural strength. This delicate balance between molecular weight and performance is crucial for optimizing SSE films. Most notably, the team’s research suggests the potential to double energy storage capacity to 500 watt-hours per kilogram.

What’s next

Looking ahead, the research team plans to build a prototype device integrating their thin film into next-generation negative and positive electrodes. This will allow them to test the SSE under practical battery conditions, evaluating its performance, durability, and scalability. To support this research, the team is upgrading their laboratory facilities. They plan on establishing 7,000 square feet of specialized lab space with controlled low-humidity environments. They also will need to improve safeguards when working with sulfide materials, which are prone to contamination. “To address this, we need dedicated glove boxes in our chemistry lab,” Yang explained. “It can be challenging in many settings to allocate resources for such specialized equipment. At ORNL, we have eight glove boxes specifically for this work.”