Juliane Hüttl

Different classes of solid electrolytes for all-solid-state batteries (ASSB) are currently being investigated, with each of them suitable for a different ASSB concept. Their combination in hybrid battery cells enables the use of their individual benefits while mitigating their disadvantages. The cubic stuffed garnet Li₇La₃Zr₂O₁₂ (LLZO), for example, is stable in contact with metallic lithium but has only moderate ionic conductivity, whereas the thiophosphate Li₁₀SnP₂S₁₂ (LSPS) is processable using conventional battery manufacturing technologies and has an excellent lithium-ion conductivity but an inferior electrochemical stability. In this work, we, therefore, present a layered hybrid all-solid-state full-cell concept that accommodates a lithium metal anode, a LiNi_0.8Co_0.1Mn_0.1O₂-based composite cathode with an LSPS catholyte (LSPS/NCM811) and a sintered monolithic LLZO separator. The electrochemical stability of LLZO and LSPS at cathodic potentials (up to 4.2 V) was investigated via cyclic voltammetry in test cells, as well as by cycling half cells with LSPS or a mixed LSPS/LLZO catholyte. Furthermore, the pressure-dependency of the galvanostatic cycling of a Li | LLZO | LSPS/NCM811 full cell was investigated, as well as the according effect of the Li | LLZO interface in symmetric test cells. An operation pressure of 12.5 MPa was identified as the optimal value, which assures both sufficient inter-layer contact and impeded lithium penetration through the separator and cell short-circuiting.

New sodium-based battery concepts require solid electrolytes as ion conducting separators. Besides NaSICON and β-Al₂O₃ in the Na₂O-R₂O₃-SiO₂ system (R = rare earth), a rarely noticed glass-ceramic solid electrolyte with the composition Na₅RSi₄O₁₂ (N5-type) exists. The present study addresses the investigation of the ionic conductivity of Na₅RSi₄O₁₂ solid electrolytes sintered from pre-crystallized glass-ceramic powders. The sintering behavior (optical dilatometry), the microstructure (SEM/EDX), and phase composition (XRD), as well as electrochemical properties (impedance spectroscopy), were investigated. To evaluate the effect of the ionic radii, Y, Sm and Gd rare elements were chosen. All compositions were successfully synthesized to fully densified compacts having the corresponding conducting N5-type phase as the main component. The densification behavior was in agreement with the melting point, which decreased with increasing ionic radii and specific cell volume. Alternatively, the ionic conductivities of N5-phases decreased from Y to Gd and Sm containing samples. The highest ionic conductivity of 1.82 × 10⁻³ S cm⁻¹ at 20 °C was obtained for Na₅YSi₄O₁₂ composition. The impact of grain boundaries and bulk conductivity on measured values is discussed. A powder-based synthesis method of this glass-ceramic solid electrolyte using different rare earth elements opens possibilities for optimizing ionic conductivity and scalable technological processing by tape casting.

The development of rechargeable batteries with high‐energy density is critical for future decarbonization of transportation. Anode‐free Li‐ion batteries, using a bare current collector at the anode side without any excess of Li, provide the highest volumetric energy density (>1500 Wh L⁻¹) among all possible cell configurations. Furthermore, elimination of the anode material coating reduces material consumption and greatly simplifies cell production, which in turn lowers costs. Although significant progress has been made recently by the application of modified current collectors, optimized cycling parameters and improved liquid electrolytes, insufficient efficiencies, and dendritic growth during lithium plating lead to poor cycle life of typically less than 100 cycles as well as safety issues. Alternatively, very recent studies have demonstrated anode‐free solid‐state batteries that combine the benefits of high energy anode‐free cell configuration and solid‐state systems with high safety, exceeding 1000 cycles. This review provides an overview of recent developments toward anode‐free solid‐state batteries and highlights the current issues and challenges in this nascent field. It is concluded that, although major challenges remain at the present, the lessons learned in the fields of liquid electrolytes and solid‐state lithium metal batteries can accelerate the development of anode‐free solid‐state batteries of practical relevance.