Unlocking the hidden chemical space in cubic-phase garnet solid electrolyte for efficient quasi-all-solid-state...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Garnet-type Li7La3Zr2O12 (LLZO) solid electrolytes (SEs) offer high ionic conductivity for all-solid-state lithium metal batteries.
• The electrochemical stability of LLZO with lithium metal electrodes remains a critical challenge for practical battery development.

Purpose of the Study:

• To synthesize and characterize novel doped cubic-phase LLZO SEs with a stoichiometric Li content (Li=7.0) to enhance electrochemical stability.
• To investigate the effect of doping on the synthesis temperature and phase stability of LLZO.
• To evaluate the performance of the developed LLZO SEs in a solid-state lithium metal battery configuration.

Main Methods:

• Entropy-driven synthesis of various doped cubic-phase LLZO SEs with Li=7.0, including Li7La3Zr0.5Hf0.5Sc0.5Nb0.5O12 and Li7La3Zr0.4Hf0.4Sn0.4Sc0.4Ta0.4O12.
• Lowering solid-state synthesis temperatures through controlled cubic-phase nucleation.
• Electrochemical stability testing against lithium metal.
• Coin cell testing of Li7La3Zr0.4Hf0.4Sn0.4Sc0.4Ta0.4O12 at 60°C with LiNi1/3Co1/3Mn1/3O2 cathode and ionic liquid interface.

Main Results:

• Successfully synthesized cubic-phase LLZO SEs with Li=7.0 without vacancy formation, achieving lower synthesis temperatures (down to 400°C).
• Demonstrated improved reduction stability of Li=7.0 LLZO SEs against lithium metal compared to Li=6.6 counterparts.
• Achieved 92% discharge capacity retention after 700 cycles at 0.8 mA/cm² and 60°C in a full solid-state battery configuration.

Conclusions:

• The entropy-driven synthesis approach enables access to new compositions and lowers synthesis temperatures for LLZO SEs.
• LLZO SEs with stoichiometric lithium content (Li=7.0) exhibit superior electrochemical stability, crucial for lithium metal battery applications.
• The developed Li7La3Zr0.4Hf0.4Sn0.4Sc0.4Ta0.4O12 SE shows promising long-term cycling performance, paving the way for practical all-solid-state batteries.