Schematic illustration showing the interfaces in different high-Ni cathodes.
Schematic illustration showing the interfaces in different high-Ni cathodes.

All-solid-state batteries are a promising next-generation energy storage system because of their high energy density and safety. The long-term stability of all-solid-state batteries depends to a large degree on the stability of the electrode-electrolyte interfaces. Now researchers from The University of Texas at Austin report that adding Ti2O3 particles to the high-Ni cathode LiNi0.8Co0.1-Mn0.1O2 (or NCM811) of solid sulfide electrolyte batteries boosts performance and cyclability [Fang et al., Materials Today (2023), ].

Typically, all-solid-state batteries rely on cathodes comprising active material, solid electrolyte, and an electronic conductor such as carbon black, carbon nanotubes or carbon fibers. However, using high-Ni oxide material with carbon leads to decomposition of the sulfide electrolyte. Sulfide electrolytes without carbon would, therefore, be highly attractive for all-solid-state batteries.

“In all-solid-state batteries, the cathodes are often mixed with a solid electrolyte to provide good ionic transport within the cathode, but the solid electrolyte is an electronic insulator,” explains Arumugam Manthiram, who led the work with John B. Goodenough.

Sulfide solid electrolytes are attracting interest because of their superior ionic conductivities compared with organic liquid electrolytes and better formability than oxide-based solid electrolytes, together with their potential to deliver a high energy density. However, the cathode/sulfide electrolyte interface produces large resistances as a result of a passivating interface layer, which leads to capacity degradation and poor performance.

“In order to achieve both good ionic and electronic transport, we incorporated Ti2O3, which has high electronic conductivity,” says Manthiram. “The incorporation of electrically conductive Ti2O3 into the cathode-electrolyte composite enhances the charge-discharge rates and capacity retention during cycling.”

The conductive Ti2O3 not only provides a fast conduction path for electrons in the cathode-electrolyte composite but could also absorb any oxygen released from the high-Ni NCM811 cathode during cycling, stabilizing the interface and suppressing oxidation of the electrolyte. The cathode modified with Ti2O3 demonstrates a good capacity retention of 86.5% after 140 cycles of charging and discharging.

The researchers believe that these results could broaden the approach to exploring materials for solid-state batteries and ultimately help all-solid-state batteries achieve better performance.

“The findings will help the battery community to recognize the importance of good electronic and ionic transport within the cathode in all-solid-state batteries and find possible ways to keep a better cathode-electrolyte interface by absorbing any oxygen released from the cathode during cycling,” suggests Manthiram.