Designer solid electrolytes for no-liquid lithium metal batteries

Author: EIS Release Date: Jul 18, 2023

Tokyo Institute of Technology has created a strategy to produce high ionic conductivity solid electrolytes for all-solid-state batteries with lithium metal electrodes.

 

TokyoTech solid ionic conductor

Such solid batteries could offer better battery safety – lithium metal (as opposed to lithium-ion) liquid electrolyte batteries have a poor safety record – but inferior ion conductivity is hampering their development.

 

Inferior conductivity can be intrinsic to the electrolyte, or due to, for example, poor wetting of the cathode resulting in ionic resistance across the interface – poor wetting prevents the electrolyte ‘reaching into’ thick cathodes.

 

 

“Many studies have shown that inorganic ionic conductors tend to show better ion conductivity after multi-element substitution, probably because of the flattened potential barrier of Li-ion migration, which is essential for better ion conductivity,” said project leader Professor Ryoji Kanno.

 

 

 

The team set out to establish design rule for synthesising high-entropy crystals of lithium ion conductors using element substitution.

 

It took inspiration from the chemical compositions of two existing Li-based solid electrolytes: argyrodite (Li6PS5Cl) and LGPS (Li10GeP2S12) crystals.

 

By substituting elements in the LGPS-type material Li9.54Si1.74P1.44S11.7Cl0.3, the researchers created crystals with composition Li9.54[Si1−δMδ]1.74P1.44S11.1Br0.3O0.6, where M is either germanium or tin, and δ can be different values between 0 and 1.

 

With germanium and δ=0.4, the new material was used as a catholyte in a solid-state lithium battery with 1mm or 0.8mm thick cathodes

 

Discharge capacity was 26.4mAh/cm2 at 25°C for 1mm cathodes and 17.3 mAh/cm2 at -10°C for 0.8 mm, “with the area-specific capacity 1.8 and 5.3 times larger than those reported for previous state-of the-art all solid-state lithium batteries, according to the university. “Theoretical calculations suggested that the enhanced conductivity of the solid electrolyte could be a result of the flattening of the energy barrier for ion migration, caused by a small degree of chemical substitution in the crystal.”

 

“In effect, the proposed design rule lays a solid groundwork for exploring new super-ionic conductors with superior charge-discharge performance, even at room temperature,” said Kanno.