Li₂O Solid Electrolyte Interphase: Probing Transport Properties at the Chemical Potential of Lithium

Abstract

Lithium (Li) anodes suffer numerous challenges arising from the chemically inhomogeneous nature of the native solid electrolyte interphase (SEI), which impedes smooth plating and leads to dendrite growth. In spite of much attention paid to engineering Li interfaces of late, there is still limited understanding of the desired chemical composition of an improved Li SEI. One major challenge has been a lack of empirical data on the structure-property-performance relations in individual SEI phases, and specifically those present at a metallic Li interface, where the chemical potential imposed by Li will yield different material properties than the bulk analogues typically invoked to understand SEI behavior. Herein, we report preparation of single-component SEIs of lithium oxide (Li2O) grown ex situ onto Li foils by controlled metal-gas reactions, generating 'deconstructed' model interfaces with nanoscale thickness (20-100 nm) similar to the native, yet more complex multiphasic SEI. The model Li|Li2O electrodes serve as a platform for further chemical and electrochemical characterization. In particular, electrochemical impedance spectroscopy, combined with interface modeling, is used to extract transport properties (ionic conductivity, diffusivity, charge carrier concentration and activation energy barriers) of Li|Li2O in symmetric cells with EC/DEC electrolyte. The Li2O SEI is further studied as a function of synthesis condition, revealing microstructural sensitivities that can be tuned to modulate transport behaviors. Finally, results are compared with single-phase Li|LiF interfaces synthesized herein and with the native SEI to isolate chemistry-and structure-specific differences.

Poor Stability of Li2CO3 in the Solid Electrolyte Interphase of a Lithium‐Metal Anode Revealed by Cryo‐Electron Microscopy

“…[34] The amorphous inorganic components consist of both ceramic-like Inorg Amor , and metallic Li Amor . [35] plus interfacial diffusion along the grain boundaries and phase boundaries, should be further investigated. Reports showed that the space charge effect along the interfaces of these nanocrystalline inorganic phases can sometime generate a higher ionic carrier concentration and improves the ionic conductivity.…”

“…Reports showed that the space charge effect along the interfaces of these nanocrystalline inorganic phases can sometime generate a higher ionic carrier concentration and improves the ionic conductivity. [35,36] The success of the DTD additive is attributed to the formation of stable SEI with a gradient distribution of the organic and inorganic components that have high mechanical and chemical stability. In particular, a gradient amorphous matrix (polymeric → inorganic → metallic) with nanocrystalline embedded phases of Li 2 SO 4 , Li 2 CO 3 , Li 2 O appear to be a quite general structural model.…”

“…The optimal SEI should have Li 2 O, LiF, and overlithiated Li 2 SO 4 to separate the Li 2 CO 3 components from directly touching Li metal. The ionic conductivity of Li + in the nanocrystalline Li 2 O, Li 2 SO 4 , Li 2 CO 3 , and percolating amorphous phases that make up the SEI, [ 35 ] plus interfacial diffusion along the grain boundaries and phase boundaries, should be further investigated. Reports showed that the space charge effect along the interfaces of these nanocrystalline inorganic phases can sometime generate a higher ionic carrier concentration and improves the ionic conductivity.…”

Recent Progress in Understanding Solid Electrolyte Interphase on Lithium Metal Anodes

“…successfully created an artificial SEI that is consisted of pure Li 2 O. [ 37 ] After the systematic investigations on the Li 2 O SEI, it was discovered that the ionic conductivity of Li 2 O on SEI is ≈10 −9 S cm −1 at room temperature. Intriguingly, the ionic conductivity of Li 2 O SEI is three magnitudes higher than that of a sintered Li 2 O pellet (10 −12 S cm −1 ).…”

Constructing nitrided interfaces for stabilizing Li metal electrodes in liquid electrolytes

“…It was proved that LiF, Li 2 O, and Li 2 CO 3 in native SEI diffuse Li + via grain boundaries, as their intrinsic ionic conductivity is relatively low (up to ~ 10 −9 S cm −1 ). 25, [49][50][51] Nitrides such as lithium nitride (Li 3 N) and LiN x O y have much higher ionic conductivity (up to ~ 10 −3 S cm −1 ), [52][53][54] and they can provide faster Li + migration channels in the SEI. Therefore, nitrided SEI can facilitate Li + diffusion and improve the kinetics of the Li plating process.…”