All solid-state batteries offer the possibility of increased safety at potentially higher energy densities compared to conventional lithium-ion batteries. In an all-ceramic oxide battery, the composite cathode consists of at least one ion-conducting solid electrolyte and an active material, which are typically densified by sintering. In this study, the reaction of the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) and the active material LiNi0.6Co0.2Mn0.2O2 (NCM622) is investigated by cosintering at temperatures between 550 and 650 °C. The characterization of the composites and the reaction layer is performed by optical dilatometry, X-ray diffractometry, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, as well as scanning transmission electron microscopy (STEM). Even at low sintering temperatures, elemental diffusion occurs between the two phases, which leads to the formation of secondary phases and decomposition reactions of the active material and the solid electrolyte. As a result, the densification of the composite is prevented and ion-conducting paths between individual particles cannot be formed. Based on the experimental results, a mechanism of the reactions in cosintered LATP and NCM622 oxide composite cathodes is suggested.

Li-ion all-solid-state batteries (ASSBs) employing solid electrolytes (SEs) can address the energy density and safety issues that plague the current state-of-the-art Li-ion battery (LIB) architecture. To that end, intimate physical and chemical bonding has to be established between high-performance cathodes and high-voltage stable SEs to facilitate high Li + transfer. The production of intimate interfaces in oxide cathode−solid electrolyte composites requires high-temperature (>1000 °C) processing, which results in a range of degradation products. Here, we report the morphological, structural, and chemical changes that occur in commercial Ni-rich layered LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode in contact with oxide SE Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) when cosintered between 550 °C and 650 °C. The structural evolution of pristine NCM622 heat-treated at a temperature of 650 °C is contrasted with the NCM622 from the composites using aberration-corrected scanning transmission electron microscopy (AC-STEM). At high spatial resolutions, the degradation of NCM particles in the composites proceeds via phase transitions from R3̅ m (layered) to Fd3̅ m (spinel) to Fm3̅ m (rocksalt) to amorphous at the grain boundaries and via pit formations and intragranular crack nucleation and propagation in the bulk. Automated crystal orientation mapping (ACOM) in combination with low-dose TEM was used to investigate the beam-sensitive cathode−solid electrolyte interfaces. To provide statistical relevance to the investigations undertaken, ACOM-TEM was used in combination with time-of-flight secondary ion mass spectroscopy (ToF-SIMS). By combining these techniques, we show that the phase transitions of the NCM particles are correlated with simultaneous lithium transfer from NCM regions to LATP regions with evolving temperature.

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