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

Abstract

Garnet-type Li7La3Zr2O12 (LLZO) solid electrolytes (SE) demonstrates appealing ionic conductivity properties for all-solid-state lithium metal battery applications. However, LLZO (electro)chemical stability in contact with the lithium metal electrode is not satisfactory for developing practical batteries. To circumvent this issue, we report the preparation of various doped cubic-phase LLZO SEs without vacancy formation (i.e., Li=7.0 such as Li7La3Zr0.5Hf0.5Sc0.5Nb0.5O12 and Li7La3Zr0.4Hf0.4Sn0.4Sc0.4Ta0.4O12). The entropy-driven synthetic approach allows access to hidden chemical space in cubic-phase garnet and enables lower solid-state synthesis temperature as the cubic-phase nucleation decreases from 750 to 400 degrees C. We demonstrate that the SEs with Li = 7.0 show better reduction stability against lithium metal compared to SE with low lithium contents and identical atomic species (i.e., Li=6.6 such as Li6.6La3Zr0.4Hf0.4Sn0.4Sc0.2Ta0.6O12). Moreover, when a Li7La3Zr0.4Hf0.4Sn0.4Sc0.4Ta0.4O12 pellet is tested at 60 degrees C in coin cell configuration with a Li metal negative electrode, a LiNi1/3Co1/3Mn1/3O2-based positive electrode and an ionic liquid-based electrolyte at the cathode|SE interface, discharge capacity retention of about 92% is delivered after 700 cycles at 0.8mA/cm(2) and 60 degrees C. Conventional compositions of garnet solid electrolytes have limited access to the cubic phase for a high Li content of 7.0, which is beneficial for stability against Li metals. Here, the authors unlock the hidden chemical space via a high entropy strategy, enabling stable long-term battery cycling.