Temperature-assisted densification methods are typically
used in
oxide-based solid-state batteries to suppress resistive interfaces.
However, chemical reactivity among the different cathode components
(which include a catholyte, the conducting additive, and the electroactive
material) still represents a major challenge and processing parameters
need thus to be carefully selected. In this study, we evaluate the
impact of temperature and heating atmosphere in the LiNi0.6Mn0.2Co0.2O2 (NMC), Li1+x
Al
x
Ti2–x
P3O12 (LATP), and Ketjenblack
(KB) system. A rationale of the chemical reactions between components
is proposed from the combination of bulk and surface techniques and
overall involves a cation redistribution in the NMC cathode material
that is accompanied by the loss of lithium and oxygen from the lattice
enhanced by LATP and KB, which act as lithium and oxygen sinks. The
final result is the formation of several degradation products, starting
at the surface, that lead to a rapid capacity decay above 400 °C.
Both the reaction mechanism and threshold temperature depend on the
heating atmosphere, with the air atmosphere being more favorable compared
to oxygen or any other inert gases.
One of the main technological challenges oxide-based solid-state batteries face today is the densification of their components to reach good interfacial contact. The most common approach requires co-sintering of the different components (electroactive material, catholyte and conducting additive) at high temperatures, which often results in the inter-diffusion of elements that deteriorate the overall cathode performance. In this work, the impact of different carbon grades in the thermal response of LATP-NMC622-Carbon electrodes is evaluated and shown to significantly influence the chemical compatibility between components. By means of a combination of bulk and surface characterization techniques including gas adsorption, X ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis, it is shown that carbons with low surface area are more adequate as result in higher oxidation temperatures and hence are less reactive.
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