The
garnet-type Li7La3Zr2O12 (LLZO) ceramic solid electrolyte combines high Li-ion conductivity
at room temperature with high chemical stability. Several all-solid-state
Li batteries featuring the LLZO electrolyte and the LiCoO2 (LCO) or LiCoO2–LLZO composite cathode were demonstrated.
However, all batteries exhibit rapid capacity fading during cycling,
which is often attributed to the formation of cracks due to volume
expansion and the contraction of LCO. Excluding the possibility of
mechanical failure due to crack formation between the LiCoO2/LLZO interface, a detailed investigation of the LiCoO2/LLZO interface before and after cycling clearly demonstrated cation
diffusion between LiCoO2 and the LLZO. This electrochemically
driven cation diffusion during cycling causes the formation of an
amorphous secondary phase interlayer with high impedance, leading
to the observed capacity fading. Furthermore, thermodynamic analysis
using density functional theory confirms the possibility of low- or
non-conducting secondary phases forming during cycling and offers
an additional explanation for the observed capacity fading. Understanding
the presented degradation paves the way to increase the cycling stability
of garnet-based all-solid-state Li batteries.
Highly efficient energy conversion and storage technologies such as high‐temperature solid oxide fuel and electrolysis cells, all‐solid‐state batteries, gas separation membranes, and thermal barrier coatings for advanced turbine systems depend on advanced materials. In all cases, processing of ceramics and metals starting from powders plays a key role and is often a challenging task. Depending on their composition, such powder materials often require high sintering temperatures and show an inherent risk of abnormal grain growth, evaporation, chemical reaction, or decomposition, especially in the case of long dwelling times. Electric current‐assisted sintering (ECAS) techniques are promising to overcome these restrictions, but a lot of fundamental and practical challenges must be solved properly to take full advantage of these techniques. A broad and long‐term expertise in the field of ECAS techniques and comprehensive facilities including conventional field‐assisted sintering technology/spark plasma sintering (FAST/SPS), hybrid FAST/SPS (with additional heater), sinter forging, and flash sintering (FS) devices are available at the Institute of Energy and Climate Research: Materials Synthesis and Processing (IEK‐1). Herein, main advantages and challenges of these techniques are discussed and the concept to overcome current limitations is introduced on selected examples.
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