Materials design of ionic conductors for solid state batteries

Abstract

A rapidly approaching theoretical limit of Li-ion batteries pushes the desire for next-generation energy storage devices [1]. One of the promising candidates is the all-solid-state battery with inorganic solid ion conductors. By replacing the currently employed liquid electrolyte, this battery architecture is thought to pave the way for a significant enhancement in the energy density with a Li-metal anode, as well as increase the battery safety [1][2][3][4]. The superior thermal stability of solid electrolytes enables operation without cooling, leading to a further gain in energy density when it comes to the device integration. Utilization of Na-ions may even enhance environmental friendliness. The solid ionic conductor performs the function of the separator, as well as the electrolyte in the electrode composites. Therefore, when replacing the liquid-solid interfacial contact that already proves cumbersome in today's lithium-ion batteries, solid-solid interfaces will show different degradation kinetics [5,6]. Although the diffusion kinetics in electrode materials matters in practice [7], as only one type of charge carrier is available effectively leading to cation transference numbers of unity, fast-charging seems possible due to minute cell polarization at high currents [8]. However, instability of the ionic conductors towards the electrodes makes protection concepts necessary [9][10][11][12]. While the interfacial stability and battery architecture are still open questions in the field, high ionic conductivity is paramount for all-solid-state battery operation [2,13]. Conductivities at room temperature above 1 mS cm −1 are typically considered to be sufficient for building research-based devices, whereas likely higher conductivities >10 mS cm −1 will be needed for high energy densities with thick electrode configurations and fast charging/discharging [14].The process of ionic conduction in solids has received attention over decades due to the possible application of oxide ion conductors in sensors and fuel cells and cation conductors in batteries, for instance as electrode materials [15][16][17][18][19][20]. The understanding of lithium and sodium solid-state ionic conductors grew when Na β″alumina, the NASICON (Na SuperIonic CONductor), and LISICON (Li SuperIonic CONductor) structures were found [21][22][23]. However, grain boundaries and mechanical brittleness of these materials have limited the

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Challenges of today for Na-based batteries of the future: From materials to cell metrics

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Exploring the Influence of Substitution on the Structure and Transport Properties in the Sodium Superionic Conductor Na11+xSn2+x(Sb1−yPy)1−xS12

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