Multi-scale characterization of submicronic NASICON-type solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 degraded by spark plasma sintering

One of the most promising and developed disruptive technology of energy storage for the future is all solid-state batteries. The NASICON phase LATP (Li1.3Al0.3Ti1.7(PO4)3) is widely studied especially thanks to its high ionic conductivity and mechanical strength. However, high temperature densification is required to obtain a dense and conductive material. Here we explore the fast sintering by Spark Plasma Sintering (SPS) of submicronic LATP particles, and the impact of the heating rate on the physico-chemical and transport properties of the pristine powder. High-speed rate for the sintering process induces particles’ growth, avoiding any reduction of titanium. The impurity AlPO4 plays a major role on the conductivity, depending on its content but also on its distribution within the composite, either as a coating (surface modification) or as crystalline particles within the grain boundaries. An intimate understanding of the ceramic composites was achieved using combination of advanced characterization techniques to get a multi-scale description of the material, from the pristine to the sintered states, from the surface to the bulk, and from the atomic long range to the local scales. Sharing these fundamental results is essential, with among other motivations, the spreading of our interpretation of complex spectroscopic results (Electronic Spin Resonance (ESR) spectroscopy, solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS)), key for characterization of reactivities at interfaces in this work and in others. •The understanding of complex sintering processes and reactivity requires to combine multiscale advanced characterizations (here XRD NMR, ESR and XPS), from the long range to the local scales and from the bulk to the surface of the particles. Only this powerful scrutinization allows understanding why the apparently optimized (purest and most densified) material shows unexpected degraded properties.•Sintering by spark plasma sintering (SPS) allows to reach, at lower temperature and in few minutes only, higher densification than conventional method for submicronic LATP NASICON-type solid state electrolytes.•SPS sintering conditions have major impacts on the crystallinity, microstructure, composition and thus conductivity of submicronic LATP NASICON-type solid state electrolytes.•Despite partial reduction of Ti4+ into Ti3+ and a colour change from white to blue, higher densification and similar transport pro