Joachim Maier1

1, Max Planck Institute for Solid State Research, Stuttgart, , Germany

The contribution addresses advantages and disadvantages of solid electrolytes for batteries [1]. Much of the enthusiasm for solid electrolytes is due to the prejudice that they are thermodynamically more stable than liquids. With very few exceptions, however, this is not the case and passivation layers have to be invoked. In fact, in particular the superionic conductors experience an internal conflict, as the same reason that leads to the superionic property is typically detrimental to thermodynamic stability. This is discussed especially for the recently found superconductor in the Li-Sn-S system [2]. The most severe difference between solids and liquids naturally lies in the mechanical behavior. The pros (form stability and better suppression of dendrite growth) have to be contrasted with the major disadvantage, in particular the difficulty of forming well-behaved contacts.
Two points which reveal characteristic differences in the transport behavior are treated in greater detail: Single ion conductivity in superionic conductors and interfacial effects. Two alternative approaches are discussed that have the potential to combine advantages of the solid matter with advantages of the liquid state [3,4].
Finally, the applicability of solid electrolytes is considered in conjunction with ionic and electronic conductivities of the electrode phases under concern [5].

[1] B. Lotsch and J. Maier, J. Electroceramics, published online 2017, DOI 10.1007/s10832-017-0091-0.
[2] T. Holzmann, L. M. Schoop, M. N. Ali, I. Moudrakovski, G. Gregori, J. Maier, R. J. Cava, B. V. Lotsch, Energy Environ. Sci., 2016, 9, 2578-2585.
[3] C. Pfaffenhuber, M. Göbel, J. Popovic, and J. Maier, Phys. Chem. Chem. Phys. 2013, 15, 18318-18335.
[4] K.-D. Kreuer, A. Wohlfarth, C. C. de Araujo, A. Fuchs, and J. Maier, ChemPhysChem, 2011, 12 2558-2560.
[5] C. Zhu, R. Usiskin, Y. Yu, and J. Maier, Science, 2017, accepted.