Dynamic lithium-compensation mechanism for densification of garnet-type Li₇La₃Zr₂O₁₂ electrolyte by Li₂O atmosphere buffer pair

Solid-state lithium metal batteries are one of the most promising options for next-generation batteries pursuing high-energy density and high-safety. However, the inevitable volatilization of lithium compounds during sintering leads to low relative density and low ionic conductivity of solid-state electrolytes. Herein, the dynamic lithium-compensation mechanism is proposed to facilitate the densification of Ta-substituted garnet-type electrolyte (Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT)) through the reversible manipulating of Li₂O atmosphere. Li₂ZrO₃ is used as mother powder additive, which reacts with Li₂O in sintering atmosphere and forms Li₆Zr₂O₇. Li₂ZrO₃/Li₆Zr₂O₇ buffer pair manipulates the sintering Li₂O atmosphere, which is vital for LLZT, within the Li₂O partial pressure range corresponding to Li₂ZrO₃ and Li₆Zr₂O₇. Furthermore, the reversibility mechanism of buffer pair for Li₂O absorption and release is revealed. The obtained LLZT exhibits a relative density of over 96% and an ionic conductivity exceeding 7 × 10⁻⁴ S·cm⁻¹ with no abnormal grain growth. The symmetric cell demonstrates an excellent lithium dendrite suppressing ability (stable cycling at a current density of 0.3 mA·cm⁻² for over 1000 h). Such dynamic lithium-compensation strategy has been successfully applied in atmosphere manipulation of LLZT sintering process, which reduces the dependence of LLZT on the Li₂O atmosphere, making it conducive to large-scale preparation of electrolyte ceramics.