Bulk-type SSLB based on LLZ:Ta achieves high specific areal capacity and operational current densities.

The development of high-capacity, high-performance all-solidstate batteries requires the specific design and optimization of its components, especially on the positive electrode side. For the first time, we were able to produce a completely inorganic mixed positive electrode consisting only of LiCoO 2 and Ta-substituted Li 7 La 3 Zr 2 O 12 (LLZ:Ta) without the use of additional sintering aids or conducting additives, which has a high theoretical capacity density of 1 mAh/cm 2 . A true all-solid-state cell composed of a Li metal negative electrode, a LLZ:Ta garnet electrolyte, and a 25 μm thick LLZ:Ta + LiCoO 2 mixed positive electrode was manufactured and characterized. The cell shows 81% utilization of theoretical capacity upon discharging at elevated temperatures and rather high discharge rates of 0.1 mA (0.1 C). However, even though the room temperature performance is also among the highest reported so far for similar cells, it still falls far short of the theoretical values. Therefore, a 3D reconstruction of the manufactured mixed positive electrode was used for the first time as input for microstructure-resolved continuum simulations. The simulations are able to reproduce the electrochemical behavior at elevated temperature favorably, however fail completely to predict the performance loss at room temperature. Extensive parameter studies were performed to identify the limiting processes, and as a result, interface phenomena occurring at the cathode active material/solid−electrolyte interface were found to be the most probable cause for the low performance at room temperature. Furthermore, the simulations are used for a sound estimation of the optimization potential that can be realized with this type of cell, which provides important guidelines for future oxide based all-solid-state battery research and fabrication.

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Thin film batteries based on solid electrolytes having a garnet-structure like Li 7 La 3 Zr 2 O 12 (LLZ) are considered as one option for safer batteries with increased power density. In this work we show the deposition of Ta-and Al-substituted LLZ thin films on stainless steel substrates by r.f. magnetron sputtering. The thin films were characterized by XRD, SEM and time-of-flight-secondary ion mass spectrometry (ToF-SIMS) to determine crystal structure, morphology and element distribution. The substrate temperature was identified to be one important parameter for the formation of cubic garnet-structured LLZ thin films. LLZ formation starts at around 650°C. Single phase cubic thin films were obtained at substrate temperatures of 700°C and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF-SIMS and XRD indicated that this layer consists of γ-LiAlO 2. The combined total ionic conductivity of the γ-LiAlO 2 interlayer and the LLZ thin film (perpendicular to the plane) was determined to be 2.0x10-9 S cm-1 for the sample deposited at 700°C. In-plane measurements showed a room temperature conductivity of 1.2x10-4 S cm-1 with an activation energy of 0.47 eV for the LLZ thin film.

Solid-state lithium batteries comprising a ceramic electrolyte instead of a liquid one enable safer highenergy batteries. Their manufacturing usually requires a high temperature heat treatment to interconnect electrolyte, electrodes, and if applicable, further components like current collectors. Tantalum-substituted Li 7 La 3 Zr 2 O 12 as electrolyte and LiCoO 2 as active material on the cathode side were chosen because of their high ionic conductivity and energy density, respectively. However, both materials react severely with each other at temperatures around 1085 °C thus leading to detrimental secondary phases. Thin-film technologies open a pathway for manufacturing compounds of electrolyte and active material at lower processing temperatures. Two of them are addressed in this work to manufacture thin electrolyte layers of the aforementioned materials at low temperatures: physical vapor deposition and coating technologies with liquid precursors. They are especially applicable for electrolyte layers since electrolytes require a high density while at the same time their thickness can be as thin as possible, provided that the separation of the electrodes is still guaranteed.

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The garnet‐type phase Li7La3Zr2O12 (LLZO) attracts significant attention as an oxide solid electrolyte to enable safe and robust solid‐state batteries (SSBs) with potentially high energy density. However, while significant progress has been made in demonstrating compatibility with Li metal, integrating LLZO into composite cathodes remains a challenge. The current perspective focuses on the critical issues that need to be addressed to achieve the ultimate goal of an all‐solid‐state LLZO‐based battery that delivers safety, durability, and pack‐level performance characteristics that are unobtainable with state‐of‐the‐art Li‐ion batteries. This perspective complements existing reviews of solid/solid interfaces with more emphasis on understanding numerous homo‐ and heteroionic interfaces in a pure oxide‐based SSB and the various phenomena that accompany the evolution of the chemical, electrochemical, structural, morphological, and mechanical properties of those interfaces during processing and operation. Finally, the insights gained from a comprehensive literature survey of LLZO–cathode interfaces are used to guide efforts for the development of LLZO‐based SSBs.