Cation-Ordering-Driven Design of Superionic Lithium Halospinels.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Materials Science

Background:

• All-solid-state batteries (ASSBs) require cost-effective inorganic solid electrolytes (SEs) for next-generation energy storage.
• The promising halospinel Li₂Sc_2/3Cl₄ SE has high ionic conductivity but is limited by the high cost of scandium (Sc).
• Developing lower-cost alternatives is crucial for the practical application of ASSBs.

Purpose of the Study:

• To screen and synthesize lower-cost cation-substituted halospinel compositions for solid electrolytes.
• To investigate the impact of cation substitution on ionic conductivity and stability.
• To establish a methodology for predicting and discovering novel solid electrolyte materials.

Main Methods:

• Combined M3GNET universal machine learning interatomic potential (UMLIP) and density functional theory (DFT) for efficient material screening.
• Experimentally synthesized predicted Mg²⁺-, Al³⁺-, and Zr⁴⁺-substituted Li₂Sc_2/3Cl₄ spinels.
• Employed molecular dynamics (MD) simulations with moment tensor potentials (MTPs) to analyze ion transport mechanisms.

Main Results:

• Synthesized Mg²⁺-, Al³⁺-, and Zr⁴⁺-substituted halospinels with substitution fractions of 20.9%–37.5%, achieving ionic conductivities up to 1.85 mS cm^-1.
• Achieved Fe³⁺ substitution, although with a minor Fe²⁺ impurity.
• MD simulations revealed that Li⁺/Sc³⁺/Mⁿ⁺ ordering significantly influences conductivity in disordered substituted compositions.
• Demonstrated ASSBs with Li_1.75Sc_0.416Zr_0.25Cl₄ operating at high current densities (2 mA cm^-2) with good capacity retention (80% of low-rate performance).

Conclusions:

• Cost-effective cation substitution is a viable strategy to mitigate the material cost of Sc-based halospinel solid electrolytes.
• The developed computational methodology accelerates the discovery of novel disordered lithium solid electrolytes.
• This work provides a foundation for designing high-performance ASSBs through rational material design.