All solid-state battery systems are of great interest because of potential benefits in gravimetric and volumetric energy density, operable temperature range, and safety in comparison to traditional liquid electrolyte based systems. One of the most promising solid electrolytes to realize such battery systems are Li7La3Zr2O12 garnets and variants (LLZO). Those show very high ionic conductivities coupled with Li+ transfer numbers approaching 1, as well as good chemical and electrochemical stabilities in a wide potential window. Recently, however, it has been recognized that interfacial electrochemical stability represents a major drawback hindering long-term operation of all solid-state batteries (ASSBs). Thus, identifying the origins of the underlying electrochemical limitations occurring at the LLZO|electrode interface is of utmost importance for development of durable systems with inherently safe ceramic electrolytes.
By applying model solid-state battery structures, this study aims at a deep understanding of the interfacial processes and improvement strategies crucial to boost the electrochemical performance of ASSB with regard to a practical battery application (see Figure 4). Within a FWF stand-alone project I use a large LLZO single crystals (several inches) as a platform that enables a systematic investigation of the factors leading to high interfacial resistances as well as to evaluate approaches (e.g., coating, additives, interlayers) to overcome this limitation. Furthermore, microelectrodes on polycrystalline LLZO will be used to study the impact of inhomogeneities in ASSBs, which is proposed to be one of the major causes for battery failure in liquid electrolyte based batteries. Electrodes will be prepared on LLZO by RF magnetron sputtering and various other coating techniques, and will be electrochemically tested by impedance spectroscopy during and after cycling.
The interfaces will be characterized by a broad spectrum of advanced analytical techniques, such as aberration corrected scanning transmission electron microscopy in combination with electron energy-loss spectroscopy and correlative scanning electron microscopy and Raman spectroscopy. For monitoring the local charging state, spatially resolved laser ablation inductively coupled plasma – mass spectrometry (LA-ICP-MS) will be used. This combination of high quality samples and the use of a broad spectrum of sophisticated analytical techniques can reveal the underlying processes at the interface to provide guidelines for a systematic improvement to final enable future ASSB technologies.