Powder aerosol deposition (PAD) to produce thin ion-conductive NaSICON films in the µm range for high-performance all solid-state sodium batteries

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With compact solid-state batteries higher energy densities can be achieved compared to cells with liquid electrolytes and they are also safer. Compared to lithium batteries, sodium cells also use more environmentally friendly and abundant raw materials. By producing thin but dense solid electrolyte layers at room temperature, high-performance, low-cost, and low-energy powder aerosol deposition, or PAD, has the potential to significantly simplify the construction of planar cells. The dense but only a few µm-thin membranes should have sufficient ionic conductivities to allow an all solid-state sodium battery to operate at room temperature. The objective of this research project is therefore to demonstrate whether PAD is suitable for producing µm-thin yet dense sufficiently ionic conductive NaSICON membranes for high-performance solid-state sodium batteries and to develop suitable process parameters by comparative characterization of the resulting electrolyte membranes. Specifically, three known NaSICON compositions are to be used to show how dense, sodium ion-conducting NaSICON membranes can be prepared via PAD, what ionic conductivities at room temperature compared to bulk ceramics can be achieved, and how the ionic conductivities are affected by the layer morphology. In a second step, it is to be clarified to what extent moderate annealing far below the sintering temperature can reduce the lattice deformations and thus increase the ionic conductivity. In addition, interfacial resistances could be reduced as a result. For this purpose, the conductivity-limiting processes are analyzed by impedance spectroscopy and correlated with the PAD-related layer morphology and the lattice deformations of the electrolyte membrane. From this, the ion conductivity promoting process parameters of PAD and thermal post-treatment can be derived for the three NaSICON compositions. The transport of sodium ions through the manufactured solid electrolyte layers and thus the proof of dense and stable PAD-NaSICON membranes is demonstrated by galvanostatic cycling of built-up and thermally post-treated half-cells. Based on this, a simple full cell is finally built by PAD of cathode active material and the most promising NaSICON material. This will provide a proof of principle of the functionality of planar PAD-NaSICON cells for future solid sodium batteries with low operating temperatures with a first estimation of possible current densities. Positive project results could be the starting point for further research work on the potential of innovative PAD functional layers in solid-state batteries, which could ultimately also generate industrial interest thanks to the industrial scalability of PAD.