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Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is a promising inorganic solid electrolyte due to its high Li + conductivity and electrochemical stability for all-solid-state batteries. Mechanical characterization of LLZTO is limited by the synthesis of the condensed phase. Here we systematically measure the elastic modules, hardness, and fracture toughness of LLZTO polycrystalline pellets of different densities using the customized environmental nanoindentation. The LLZTO samples are sintered using the hot-pressing method with different amounts of Li 2 CO 3 additives, resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of 13.21 ± 5.22 μm. The mechanical properties show a monotonic increase as the sintered sample densifies, elastic modulus and hardness reach 158.47 ± 10.10 GPa and 11.27 ± 1.38 GPa, respectively, for LLZTO of 98% density. Similarly, fracture toughness increases from 0.44 to 1.51 MPa⋅m 1/2 , showing a transition from the intergranular to transgranular fracture behavior as the pellet density increases. The ionic conductivity reaches 4.54 × 10 −4 S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 cycles. This study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries. 

Abstract The interface between cathode and electrolyte is a significant source of large interfacial resistance in solid‐state batteries (SSBs). Spark plasma sintering (SPS) allows densifying electrolyte and electrodes in one step, which can improve the interfacial contact in SSBs and significantly shorten the processing time. In this work, we proposed a two‐step joining process to prepare cathode (LiCoO₂, LCO)/electrolyte (Li_0.33La_0.57TiO₃, LLTO) half cells via SPS. Interdiffusion between Ti^4+/Co³⁺was observed at the interface by SEM/STEM, resulting in the formation of the Li−Ti−La−Co−O and Li−Ti−Co−O phases in LLTO and the Li−Co−Ti−O phase in LCO. Computational modeling was performed to verify that the Li−Ti−Co−O phase has a LiTi₂O₄host lattice. In a study of interfacial electrical properties, the resistance of this interdiffusion layer was found to be 10⁵ Ω, which is 40 times higher than the resistance of the individual LLTO phase. The formation of an interdiffusion layer is identified as the origin of the high interface resistance in the LLTO/LCO half‐cell. 

In this study, fabrication processes of solid electrolyte/cathode interfaces for their use in next‐generation all‐solid‐state lithium‐ion battery (LIB) applications are described. Standard lithium–aluminum–titanium–phosphate (LATP) solid electrolyte and lithium–manganese oxide (LMO) spinel cathode ceramic half cells are assembled using two all‐solid‐state methods: a) co‐sintering the cathode and electrolyte materials via field‐assisted sintering and b) field‐assisted high‐temperature bonding. The morphology and composition of the interfaces are analyzed by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). This study reveals that the formation of interphases can be significantly decreased by separately performing the densification and joining procedures. Electrochemical impedance spectroscopy (EIS) is applied to understand and determine the effect of the manufactured interfaces on the system conductivity. Based on the results, it is concluded that the high‐temperature bonding technique appears to be a suitable technique for future production of all‐solid‐state LIBs.