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.

Solid-state sodium-ion batteries with sodium metal anodes possess high safety and reliability, which are considered as a promising candidate for the next generation of energy storage technology. However, poor electronic and ionic conductivities at the interface between electrodes and solid-state electrolytes restrict its practical application. Herein, we demonstrate a β″-Al₂O₃ electrolyte with a vertically porous-dense bilayer structure to solve this problem. The carbon-coated vertically porous layer serves as a high mass-loading host for Na₃V₂(PO₄)₃ cathode and provides fast electronically and ionically conductive pathways. In addition, the dense layer is produced to prevent sodium dendrite growth and improve mechanical strength of β″-Al₂O₃ electrolyte. Experimental results show that the cathode loading in vertically porous layer can reach to 8 mg cm⁻², and the porous-dense bilayer β″-Al₂O₃ electrolyte-based battery exhibits a reversible specific capacity of 87 mAh g⁻¹ and a capacity retention of 95.5% over 100 cycles at a current density of 0.1 C, which is superior to that of the traditional dense β″-Al₂O₃ electrolyte-based battery. This work based on electrolyte structure design represents an efficient strategy for the development of solid-state sodium-ion batteries with high mass-loading cathode.

Cubic Li-Garnet Li₇La₃Zr₂O₁₂ (c-LLZO) is one of the promising solid-state electrolyte candidates for the next generation high safety solid-state batteries. However, preparing the electrolyte has many challenges. Li-loss during high temperature sintering is one of them. Mother powder with the same component of green garnet pellets is often used to co-fire with the pellets to compensate the Li-loss. Due to the high weight ratio of rare earth element La and non-recyclability of mother powder, it is worthy to explore low-cost mother powders to replace them. In this paper, low cost compounds such as Li₅AlO₄, Li₂TiO₃, Li₂SiO₃, Li₄SiO₄ and (Li₂O)_x-(ZrO₂)_1-x (x = 0.6–0.8) are investigated for substitution of the mother powder for compensating Li-loss during the sintering of LLZO. Dense Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) samples have been prepared by sintering with (Li₂O)_0.733(ZrO₂)_0.267 powder at 1150 ℃ for 5 h with the relative density of 95% and conductivity of 5.7 × 10⁻⁴ S cm⁻¹ at 25 ℃, which show same performance with LLZTO ceramics sintered with LLZO mother powder.