Unveiling and Alleviating Chemical "Crosstalk" of Succinonitrile Molecules in Hierarchical Electrolyte for High-Voltage Solid-State Lithium Metal Batteries

Succinonitrile-based plastic crystal electrolytes have emerged for high-energy-density Li metal batteries in terms of their superior ambient ionic conductivity, low flammability, and benign compatibility with high voltage cathode, but are hampered by inherent instabilities toward Li anodes. Constructing hierarchical solid electrolytes structure is a fundamental approach to protect Li anode from succinonitrile attacks, with succinonitrile-based oxidation-resistance layer facing high voltage cathode and reduction-tolerant layer contacting Li anode. However, free succinonitrile molecules in succinonitrile-based electrolyte layer can diffuse across the electrolyte/electrolyte interface and further reach Li anode surface during the battery cycle. This chemical "crosstalk" cause reduction-tolerant electrolyte layer to fail to protect the Li anode from the attacks of free succinonitrile molecules. Nano Li6.4La3Zr1.4Ta0.6O12 is introduced creatively into succinonitrile-based electrolyte layer. By taking advantage of the complexation between La atoms in Li6.4La3Zr1.4Ta0.6O12 and N atoms in succinonitrile, the free succinonitrile molecules are successfully immobilized in succinonitrile-based electrolyte layer. The resulting low resistance and highly durable solid electrolyte interphase and cathode electrolyte interphase endow NCM622||Li batteries with remarkable cycle stability. Our research provides a new idea for the real application of plastic crystal electrolytes in high voltage solid-state lithium metal batteries.