Physicochemical Concepts of the Lithium Metal Anode in Solid-State Batteries

Abstract

Developing reversible lithium metal anodes with high rate capability is one of the central aims of current battery research. Lithium metal anodes are not only required for the development of innovative cell concepts such as lithium–air or lithium–sulfur batteries, they can also increase the energy density of batteries with intercalation-type cathodes. The use of solid electrolyte separators is especially promising to develop well-performing lithium metal anodes, because they can act as a mechanical barrier to avoid unwanted dendritic growth of lithium through the cell. However, inhomogeneous electrodeposition and contact loss often hinder the application of a lithium metal anode in solid-state batteries. In this review, we assess the physicochemical concepts that describe the fundamental mechanisms governing lithium metal anode performance in combination with inorganic solid electrolytes. In particular, our discussion of kinetic rate limitations and morphological stability intends to stimulate further progress in the field of lithium metal anodes.

The Devil is in the Defects: Electronic Conductivity in Solid Electrolytes

“…These are: (i) the formation of highly reactive interfaces between the electrodes and the SE, 26,[32][33][34][35][36][37][38][39] (ii) the loss of physical contact between the electrode and SE over multiple cycles, 26,40 and (iii) the suppression of dendrites -branched filaments of metallic Li. 13,[37][38][39][41][42][43][44][45] R.T. electronic conductivity σ e (S/cm) The nucleation-growth of Li dendrites in solid-state batteries drives cell failure. 33,45 Dendrites in SEs and their decomposition products at the interface with electrodes have been linked to an increase in the values of electronic conductivity (s e ) of solid electrolytes.…”

“…13,[37][38][39][41][42][43][44][45] R.T. electronic conductivity σ e (S/cm) The nucleation-growth of Li dendrites in solid-state batteries drives cell failure. 33,45 Dendrites in SEs and their decomposition products at the interface with electrodes have been linked to an increase in the values of electronic conductivity (s e ) of solid electrolytes. 13,26,27 Indeed, the electronic conductivity of specific SEs coupled with their facile Li + -ion transport may eventually promote the swift recombination of electrons and Li + ions into metallic Li, resulting in local nucleation of dendrites.…”

“…13,26,27 Indeed, the electronic conductivity of specific SEs coupled with their facile Li + -ion transport may eventually promote the swift recombination of electrons and Li + ions into metallic Li, resulting in local nucleation of dendrites. 13,18,37,41,[43][44][45] The electron leakage in SEs can also lead to subtle and prolonged processes of battery self-discharge. It has been demonstrated that electrolyte decomposition products at both high and low voltages (vs. Li/Li + ) may display intrinsic electronic conductivity, 32,33,38,46 whose magnitudes remain elusive.…”

“…It has been demonstrated that electrolyte decomposition products at both high and low voltages (vs. Li/Li + ) may display intrinsic electronic conductivity, 32,33,38,46 whose magnitudes remain elusive. 13,14,45 While s e values are typically reported for completeness, the focus of many reports (e.g., references in Figure 1) shifts entirely to the high intrinsic Li + -ionic conductivity of novel SE chemistries. Solid electrolytes that are oxides, sulfides, or selenides, and even phosphates and silicates, 25 typically display band gaps >4 eV as seen in Figure 1.…”

How Does External Pressure Shape Li Dendrites in Li Metal Batteries?

“…There is remarkable progress on material advancement (including interface optimization, [ 6 ] functional frameworks, [ 7 ] as well as liquid and solid electrolyte innovation [ 8 ] ) to suppress Li dendrites and enhance the performance of Li metal anodes. For instance, Zhang et al proposed a strategy of sustainable solid electrolyte interphase (SEI), successfully realizing a long cycle life of over 150 cycles (80% capacity retains) while only four cycles with pristine SEI in Li metal coin cells under practical conditions.…”