Evaluation of Ga0.2Li6.4Nd3Zr2O12 garnets: exploiting dopant instability to create a mixed conductive interface to reduce interfacial resistance for all solid state batteries

Accelerating the Development of LLZO in Solid-State Batteries Toward Commercialization: A Comprehensive Review

Solid-state batteries (SSBs) are under development as high-priority technologies for safe and energy-dense next-generation electrochemical energy storage systems operating over a wide temperature range. Solid-state electrolytes (SSEs) exhibit high thermal stability and, in some cases, the ability to prevent dendrite growth through a physical barrier, and compatibility with the "holy grail" metallic lithium. These unique advantages of SSEs have spurred significant research interests during the last decade. Garnet-type SSEs, that is, Li7La3Zr2O12 (LLZO), are intensively investigated due to their high Li-ion conductivity and exceptional chemical and electrochemical stability against lithium metal anodes. However, poor interfacial contact with cathode materials, undesirable lithium plating along grain boundaries, and moisture-induced chemical degradation greatly hinder the practical implementation of LLZO-based SSEs for SSBs. In this review, the recent advances in synthesis methods, modification strategies, corresponding mechanisms, and applications of garnet-based SSEs in SSBs are critically summarized. Furthermore, a comprehensive evaluation of the challenges and development trends of LLZO-based electrolytes in practical applications is presented to accelerate their development for high-performance SSBs.

Excellent Stability of Ga-Doped Garnet Electrolyte against Li Metal Anode via Eliminating LiGaO2 Precipitates for Advanced All-Solid-State Batteries

Ga-doped garnet-type Li₇La₃Zr₂O₁₂ (Ga-LLZO) ceramics have long been recognized as ideal electrolyte candidates for all-solid-state lithium batteries (ASSLBs). However, in this study, it is shown that Ga-LLZO easily and promptly cracks in contact with molten lithium during the ASSLB assembly. This can be mainly ascribed to two aspects: (i) lithium captures O atoms and reduces Ga ions of the Ga-LLZO matrix, leading to a band-gap closure from >5 to <2 eV and a structural collapse from cubic to tetrahedral; and (ii) the in situ-formed LiGaO₂ impurity phase has severe side reactions with lithium, resulting in huge stress release along the grain boundaries. It is also revealed that, while the former process consumes hours to take effect, the latter one is immediate and accounts for the crack propagation of Ga-LLZO electrolytes. A minute SiO₂ is preadded during the synthesis of Ga-LLZO and found effective in eliminating the LiGaO₂ impurity phase. The SiO₂-modified Ga-LLZO solid electrolytes display excellent thermomechanical and electrochemical stabilities against lithium metals and well-reserved ionic conductivities, which was further confirmed by half-cells and full batteries. This study contributes to the understanding of the stability of garnet electrolytes and promotes their potential commercial applications in ASSLBs.