Molten salt synthesis and characterization of fast ion conductor Li6.75La3Zr1.75Ta0.25O12

Processing and Properties of Garnet-Type Li7 La3 Zr2 O12 Ceramic Electrolytes

Garnet-type solid electrolyte Li₇ La₃ Zr₂ O₁₂ (LLZO) is widely considered as one of the most promising candidates for solid state batteries (SSBs) owing to its high ionic conductivity and good electrochemical stability. Since its discovery in 2007, great progress has been made in terms of crystal chemistry, chemical and electrochemical properties, and battery application. Nonetheless, reliable and controllable preparation of LLZO ceramics with desirable properties still remains as big challenges. Herein, this review summarizes various synthetic routes of LLZO ceramics and examines the influence of various key processing parameters on the chemical and electrochemical properties. Focusing on correlation of processing parameters and properties, this review aims to provide new insights on a reliable and controllable production of high-quality LLZO ceramic electrolytes for SSB application.

Highly Conductive Garnet-Type Electrolytes: Access to Li6.5La3Zr1.5Ta0.5O12 Prepared by Molten Salt and Solid-State Methods

Tantalum-doped garnet (Li_6.5La₃Zr_1.5Ta_0.5O₁₂, LLZTO) is a promising candidate to act as a solid electrolyte in all-solid-state batteries owing to both its high Li⁺ conductivity and its relatively high robustness against the Li metal. Synthesizing LLZTO using conventional solid-state reaction (SSR) requires, however, high calcination temperature (>1000 °C) and long milling steps, thereby increasing the processing time. Here, we report on a facile synthesis route to prepare LLZTO using a molten salt method (MSS) at lower reaction temperatures and shorter durations (900 °C, 5 h). Additionally, a thorough analysis on the properties, i.e., morphology, phase purity, and particle size distribution of the LLZTO powders, is presented. LLZTO pellets, either prepared by the MSS or the SSR method, that were sintered in a Pt crucible showed Li⁺ ion conductivities of up to 0.6 and 0.5 mS cm^-1, respectively. The corresponding activation energy values are 0.37 and 0.38 eV, respectively. The relative densities of the samples reached values of approximately 96%. For comparison, LLZTO pellets sintered in alumina crucibles or with γ-Al₂O₃ as sintering aid revealed lower ionic conductivities and relative densities with abnormal grain growth. We attribute these observations to the formation of Al-rich phases near the grain boundary regions and to a lower Li content in the final garnet phase. The MSS method seems to be a highly attractive and an alternative synthetic approach to SSR route for the preparation of highly conducting LLZTO-type ceramics.

Sulfide and Oxide Inorganic Solid Electrolytes for All-Solid-State Li Batteries: A Review

Energy storage materials are finding increasing applications in our daily lives, for devices such as mobile phones and electric vehicles. Current commercial batteries use flammable liquid electrolytes, which are unsafe, toxic, and environmentally unfriendly with low chemical stability. Recently, solid electrolytes have been extensively studied as alternative electrolytes to address these shortcomings. Herein, we report the early history, synthesis and characterization, mechanical properties, and Li+ ion transport mechanisms of inorganic sulfide and oxide electrolytes. Furthermore, we highlight the importance of the fabrication technology and experimental conditions, such as the effects of pressure and operating parameters, on the electrochemical performance of all-solid-state Li batteries. In particular, we emphasize promising electrolyte systems based on sulfides and argyrodites, such as LiPS5Cl and β-Li3PS4, oxide electrolytes, bare and doped Li7La3Zr2O12 garnet, NASICON-type structures, and perovskite electrolyte materials. Moreover, we discuss the present and future challenges that all-solid-state batteries face for large-scale industrial applications.

Combined Modification of Dual-Phase Li4Ti5O12-TiO2 by Lithium Zirconates to Optimize Rate Capabilities and Cyclability

The low electrical conductivity and ordinary lithium-ion transfer capability of Li₄Ti₅O₁₂ restrict its application to some degree. In this work, dual-phase Li₄Ti₅O₁₂-TiO₂ (LTOT) was modified by composite zirconates of Li₂ZrO₃, Li₆Zr₂O₇ (LZO) to boost the rate capabilities and cyclability. When the homogeneous mixture of LiNO₃, Zr(NO₃)₄·5H₂O and LTOT was roasted at 700 °C for 5 h, the obtained composite achieved a superior reversible capacity of 183.2 mAh g^-1 to the pure Li₄Ti₅O₁₂ after cycling at 100 mA g^-1 for 100 times due to the existence of a scrap of TiO₂. Meanwhile, when the composite was cycled by consecutively doubling the current density between 100 and 1600 mA g^-1, the corresponding reversible capacities are 183.2, 179.1, 176.5, 173.3, and 169.3 mAh g^-1, signifying the prominent rate capabilities. Even undergoing 1400 charge/discharge cycles at 500 mA g^-1, a reversible capacity of 144.7 mAh g^-1 was still attained, denoting splendid cyclability. From a series of comparative experiments and systematic characterizations, the formation of LZO meliorated both the Li⁺ migration kinetics and electrical conductivity on account of the concomitant superficial Zr⁴⁺ doping, responsible for the comprehensive elevation of the electrochemical performance.