Simultaneously Enhance Humidity Tolerance and Ionic Conductivity of Halide Electrolytes by Cation-Anion Co-Doping

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Halide solid-state electrolytes (SSEs) are crucial for all-solid-state batteries (ASSBs) due to their high ionic conductivity and oxidation stability.
• Practical application of halide SSEs is hindered by poor humidity tolerance and reduced ionic conductivity.
• Developing stable and conductive SSEs is key for advancing ASSB technology.

Purpose of the Study:

• To synthesize and characterize novel halide SSEs for high-performance ASSBs.
• To investigate the effect of cation-anion co-doping on ionic conductivity and stability.
• To evaluate the electrochemical performance of ASSBs utilizing the developed SSEs.

Main Methods:

• Synthesis of Li3/3-xIn1-xMxCl5.6F0.4 (M = Hf, Zr, Fe, Y) via co-doping of Li3InCl6 with M and F ions.
• Ionic conductivity measurements at room temperature.
• Humidity tolerance testing by monitoring conductivity retention over 24 hours.
• Experimental analysis combined with Born–von Karman boundary conditions (BVSE) and Ab initio Molecular Dynamics (AIMD) simulations.
• Fabrication and electrochemical testing of ASSBs using Li2.98In0.98Hf0.02Cl5.6F0.4 as the SSE.

Main Results:

• Li2.98In0.98Hf0.02Cl5.6F0.4 exhibited the highest ionic conductivity of 1.04 mS cm-1 at room temperature.
• The material demonstrated good humidity tolerance, retaining 87.96% of its conductivity after 24 hours of exposure.
• AIMD and BVSE simulations revealed that Cl- doping with F- enhances structural rigidity and water stability, while Hf4+ doping increases Li+ vacancy concentration for improved conduction.
• An ASSB assembled with this SSE showed a high discharge capacity of 83.6 mAh g-1 and 78.6% capacity retention after 100 cycles.

Conclusions:

• Cation-anion co-doping is an effective strategy for designing advanced halide SSEs.
• The developed Li2.98In0.98Hf0.02Cl5.6F0.4 offers a promising solution for high-performance and stable ASSBs.
• This research provides a pathway for the commercialization of halide-based ASSBs.