Researchers discover new electrode material that could improve solid-state battery performance

According to foreign media reports, a Japanese research team recently developed a new electrode material by combining lithium sulfate and lithium ruthenate to improve the performance of all-solid-state batteries (ASSBs). Lithium-ion batteries need to have high safety and high energy density to achieve large-scale application, and all-solid-state lithium batteries using inorganic solid electrolytes are no exception. The energy density can be further improved by using high-capacity lithium excess electrode materials. However, this method has never been applied to all-solid-state batteries.

The difficulty of using high-capacity lithium-excess electrode materials in all-solid-state batteries lies in the electrode-electrolyte interface structure. The researchers used Li2SO4 to amorphize the lithium-excess model material Li2RuO3, and for the first time demonstrated the existence of reversible oxygen redox reactions in all-solid-state batteries. The amorphous nature of the Li2RuO3-Li2SO4 matrix enables it to contain active materials with high conductivity and ductility, thereby providing a good interface with charge transfer capabilities and achieving stable operation of all-solid-state batteries.

(Image source: Science Advances)

The invention of commercial lithium-ion batteries (LIBs) in the 1990s marked a turning point in the technological revolution. Today, lightweight rechargeable batteries are used in a wide range of electronic devices, from pacemakers to electric cars . However, the growing popularity of lithium-ion batteries has also raised two major issues: safety issues: batteries may fail if they are not manufactured to the highest standards; and insufficient reserves: lithium is present in small quantities in the earth's crust, while modern technology requires a large amount of lithium.

Therefore, scientists are looking for various alternatives to make batteries safer and more sustainable. Associate Professor Atsushi Sakuda, Dr. Kenji Nagao and their colleagues in the Department of Applied Chemistry at Osaka Prefecture University in Japan have been working on all-solid-state batteries (ASSBs). 

The main difference between ASSBs and conventional LIBs is that the former use solid rather than liquid electrolytes. Liquid electrolytes in LIBs are highly flammable, have low conductivity, and are prone to leakage, making them dangerous. Solid electrolytes are stable and non-flammable, making ASSBs highly safe and high-performance. ASSBs can also be "miniaturized" because they do not require diaphragms or cooling systems. However, the difficulty in achieving effective contact between the electrolyte and the electrode active materials leads to reduced battery energy density and battery performance.

Dr. Sakuda said: "Therefore, finding new and efficient electrode materials is the key to making high energy density ASSBs." To solve the above problems, the researchers studied the electrode composition. The main decisive factor in the battery is the active material in the electrode: it loses or gains electrons through redox reactions, thereby realizing the charge transfer between the electrode and the electrolyte. The more reactions, the more charge is stored in the battery, and the higher its energy density.

Therefore, researchers developed a cathode material by combining two lithium compounds: lithium sulfate (Li2SO4) and lithium ruthenate (Li2RuO3). This material provides more space for ion flow, thereby achieving rapid charge transfer. Adding Li2SO4 can also make the overall structure more ductile and amorphous, achieving reversible redox reactions while further compressing the material, thereby greatly improving electronic and ionic conductivity and enhancing battery stability.

The new battery has a reversible capacity of 270 mAh/g, outperforming most ASSBs. The researchers hope to further advance the development of new solid-state batteries by replacing the expensive ruthenium (Ru) element in the electrode with a similar but cheaper metal, and believe that their research method provides a solid foundation for manufacturing next-generation batteries. By demonstrating that ASSBs can be safely used in electric vehicles, the researchers hope that ASSBs will become a leading candidate for next-generation batteries.