Nowadays the unstoppable and continuously increasing energy demand to satisfy current and future needs has promoted research on the field of clean energy production and storage towards zero-carbon emission technologies that enable to mitigate the effects of global warming and climate change. In this new scenario, batteries play a key role as the most significant energy storage technology, given their high energy density, simplicity and long life.
In the framework of the next generation of more sustainable and reliable energy storage devices, sodium metal batteries emerge as the ideal candidates to replace lithium ones. This mainly responds to their high theoretical capacity (1166 mAh g-1), which results in expected energy densities in the order of 1605 Whg-1 and 1275 Whg-1 for Na-air and Na-S batteries, respectively, both superior when compared with conventional lithium-ion batteries (387 Whg-1)[1]. Moreover, in view of overcoming drawbacks associated to liquid electrolytes (low thermal and electrochemical stability, high flammability and dendrite growth) that lead to safety issues[2], batteries based on the use of all-solid-state electrolytes have been proposed[3],[4]. Solid-state electrolytes not only prevent flammability but also suppress dendrite growth during cycling, acting as ionic conductors and separators at the time[5],[6]. Moreover, they also present enhanced electrochemical and thermal stability, providing a wider potential window and higher working temperature range[7].
In this work, we propose a new concept in rigid hybrid all-solid-state electrolytes based on porous NASICON ceramic layers with formula Na3.16Zr1.84Y0.16Si2PO12, obtained by combining tape-casting and low-temperature hot pressing, infiltrated with highly conductive cross-linked polymer electrolytes based on amorphous polymer policondensates and different sodium salts. The hybrid electrolytes are investigated in terms of microstructure, mechanical properties and electrochemical behavior. The highest discharge capacity obtained at 80ºC is 145mAh/g (C/20) in half-cell configuration (Na/Hybrid electrolyte/FePO4), which corresponds to 78% of the theoretical capacity value of FePO4.

[1] Zheng, Y.; Pan, O.; Clites, M.; Byles, B.W.; Pomerantseva, E.; Li, C.Y. Adv. Energy Mater. 8, 2018, 801885.
[2] Croce, F.; Appetecchi, G.; Persi, L.; Scrosati, B. Nature 394, 1998, 456.
[3] Zhang, Z.; Zhang, Q.; Shi, J.; Chu, Y.S.; Yu, X.; Xu. K.; Hu, Y.S. Adv. Energy Mater. 7, 2017, 1601196.
[4] Hou, M.; Liang, F.; Chen, K.; Dai, Y.; Xue, D. Nanotechnology 31, 2020, 132003.
[5] Kim, J. J.; Yoon, K.; Park, I.; Kang, K. Small Methods 1, 2017, 1700219.
[6] Fan, L.; Wei, S. Y.; Li, S. Y.; Li, Q.; Lu, Y. Y. Adv. Energy Mater. 8, 2018, 1702657
[7] Liu,W.; Lee, S.W.; Lin, D.; Shi, F.; Wang, S.; Sendek, A.D.; Cui, Y. Nat. Energy 2, 2017, 17035.