Nowadays, commercially available lithium batteries are based on liquid electrolytes, due to their high ionic conductivity at room temperature. But the search for new battery technologies that can substitute the existing ones has become very important in the last decades, mainly due to issues related to safety, durability and manufacturing complexity. Hence, all-solid-state lithium-metal batteries (employing solid electrolytes) have gained attention because of their higher energy density, while being safer, and more chemically and thermally stable than conventional lithium-ion batteries [1,2]. When it comes to solid electrolytes, ceramics offer higher chemical and thermal stability, better mechanical properties and wider electrochemical window. However, their low performances and interfacial detrimental interactions with the electrodes still need to be improved for their implementation  into final devices.

A possible strategy to address these drawbacks and improve battery performance involves the employment of innovative manufacturing processes, as 3D printing and ultra-fast high temperature sintering (UHS). Both techniques are explored in this work for NASICON-type ceramic electrolytes and Co-free cathodes.

Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolytes were printed by stereolithography (SLA) in complex geometries generally impossible to produce with conventional ceramic manufacturing techniques. Up to date, only a few studies have reported the production of full ceramic electrolytes by 3D printing [5-7].  Here we present the development of LAGP full-ceramic electrolytes by SLA, exploring different complex geometries to improve the electrolytes behaviour (i.e. area specific resistance, critical current density, available capacity in a full battery). Crack-free dense (>80% of theoretical density) LAGP electrolytes were succesfully prepared, showing conductivities in good agreement with LAGP manufactured by conventional techniques (10⁻⁴ S cm⁻¹), without detrimental reactions or degradation due to the debinding step. Additionally, plating/stripping galvanostatic tests were carried out on symmetrical cells Li/3DPrinted-LAGP/Li up to 200h.

In parallel to the development of electrolytes, Co-free composite cathodes have also been studied. LiFePO₄ (LFP) was chosen as active material to be combined with LAGP in the composites. The cathodes were attached by an optimized conventional thermal treatment (650 ºC, 4h, N₂ atmosphere) onto LAGP sintered pellets. The compatibility of the involved materials was investigated showing no degradation phenomena or unwanted reactions. Finally, a full cell Li/LAGP/LFP-LAGP(50:50) was mounted, tested by EIS and cycled at constant currents. Despite the limited capacity detected, these first results represent a promising step forward towards full ceramic batteries based on these combination of materials.

UHS was also developed for both electrolytes and cathodes. This technique was presented in 2020 as a sintering technique capable of densifying ceramics in seconds, to reduce both the manufacturing times and energy consumption respect to conventional thermal processes, while avoiding degradation phenomena [8-10]. In the case of materials containing lithium, UHS can also be helpful to minimize lithium losses [8-10]. UHS evaluation on sintering of electrolytes and cathodes will be presented. LAGP was sintered by UHS in less than 2 minutes reaching very high densification (88%) and ionic conductivities comparable with the ones obtained by conventional sintering. Furthermore, LFP-LAGP composite cathodes were successfully attached on LAGP electrolytes by UHS avoiding detrimental interfacial interactions. As last step UHS was successfully applied for debinding and sintering of 3D printed LAGP electrolytes, lowering the times needed for these processes from days to minutes.

Finally, advanced characterization techniques as Grazing-Incidence Wide-Angle X-ray Scattering using Synchrotron radiation (GIWAXS) and Glow Discharge Emission Spectrometry (GDOES) were employed to study possible side reactions between these materials, and lithium content differences comparing conventional thermal treatments and UHS.