Abstract
Solid electrolyte is the key component in all-solid-state batteries (ASBs). It is required in electrodes to enhance Li-conductivity and can be directly used as a separator. With its high Li-conductivity and chemical stability towards metallic lithium, lithium-stuffed garnet material Li7La3Zr2O12 (LLZO) is considered one of the most promising solid electrolyte materials for high-energy ceramic ASBs. However, in order to obtain high conductivities, rare-earth elements such as tantalum or niobium are used to stabilize the highly conductive cubic phase. This stabilization can also be obtained via high levels of aluminum, reducing the cost of LLZO but also reducing processability and the Li-conductivity. To find the sweet spot for a potential market introduction of garnet-based solid-state batteries, scalable and industrially usable syntheses of LLZO with high processability and good conductivity are indispensable. In this study, four different synthesis methods (solid-state reaction (SSR), solution-assisted solid-state reaction (SASSR), co-precipitation (CP), and spray-drying (SD)) were used and compared for the synthesis of aluminum-substituted LLZO (Al:LLZO, Li6.4Al0.2La3Zr2O12), focusing on electrochemical performance on the one hand and scalability and environmental footprint on the other hand. The synthesis was successful via all four methods, resulting in a Li-ion conductivity of 2.0–3.3 × 10−4 S/cm. By using wet-chemical synthesis methods, the calcination time could be reduced from two calcination steps for 20 h at 850 °C and 1000 °C to only 1 h at 1000 °C for the spray-drying method. We were able to scale the synthesis up to a kg-scale and show the potential of the different synthesis methods for mass production.
Highlights
Due to their high energy density and cycle stability, lithium-ion batteries (LIB) are one of the most common battery types in mobile and stationary applications today [1,2].after almost 30 years of development and optimization since their market launch, LIBs are about to reach their physicochemical limit [3]
To a classical solid-state reaction (SSR) as a dry synthesis route, three different wet-chemical routes based on an aqueous solution were used: spraydrying (SD), co-precipitation (CP), and a solution-assisted solid-state reaction (SASSR)
The solution-assisted solid-state reaction method was first used by Ma et al for the synthesis of NASICON Na-ion solid electrolyte [29]
Summary
Due to their high energy density and cycle stability, lithium-ion batteries (LIB) are one of the most common battery types in mobile and stationary applications today [1,2].after almost 30 years of development and optimization since their market launch, LIBs are about to reach their physicochemical limit [3]. Due to their high energy density and cycle stability, lithium-ion batteries (LIB) are one of the most common battery types in mobile and stationary applications today [1,2]. Advanced battery concepts such as all-solid-state batteries (ASB) are considered as one of the most promising candidates for future energy storage technologies They offer several advantages over conventional LIBs with regard to stability, safety, and energy density [4,5]. Due to its high Li-ion conductivity (up to 1 × 10−3 S/cm), garnet-based Li7 Zr3 La2 O12 compounds are considered the most promising for oxide-based ceramic electrolyte ASSB. To stabilize the high lithium-ion conducting cubic garnet phase at room temperature, substitution of Li7 Zr3 La2 O12 is necessary. As the required substitution levels and their prices are rather high, they make the material more expensive
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