Design principles for self-forming interfaces enabling stable lithium-metal anodes

Abstract

The path toward Li-ion batteries with higher energy densities will likely involve use of thin lithium (Li)-metal anode (<50 µm thickness), whose cyclability today remains limited by dendrite formation and low coulombic efficiency (CE). Previous studies have shown that the solid–electrolyte interface (SEI) of the Li metal plays a crucial role in Li-electrodeposition and -stripping behavior. However, design rules for optimal SEIs are not well established. Here, using integrated experimental and modeling studies on a series of structurally similar SEI-modifying model compounds, we reveal the relationship between SEI compositions, Li deposition morphology, and CE and identify two key descriptors for the fraction of ionic compounds and compactness, leading to high-performance SEIs. We further demonstrate one of the longest cycle lives to date (350 cycles for 80% capacity retention) for a high specific-energy Li||LiCoO2 full cell (projected >350 watt hours [Wh]/kg) at practical current densities. Our results provide guidance for rational design of the SEI to further improve Li-metal anodes.

Design rules for liquid crystalline electrolytes for enabling dendrite-free lithium metal batteries

“…A 20 µm-thick Li electrode with perfectly flat interface is used as the initial configuration for the anode upon which Li is electrodeposited. The low initial thickness ensures that the cell has a high energy density due to the high fraction of Li passed per cycle (85,86). The simulation parameters and the details of the initial and boundary conditions are provided in SI Appendix.…”

Comparative performance of ex situ artificial solid electrolyte interphases for Li metal batteries with liquid electrolytes

“…When using thick electrodes, eventual “soft shorts” (i.e. stable electronic connection between the electrodes) cannot be easily detected, and long-term stable cycling is seemingly observed ( Albertus et al., 2018 ; Xiao et al., 2020 ; Zhu et al., 2020 ). Electrochemical impedance spectroscopy measurements are sometimes reported to exclude the occurrence of soft shorts.…”

“…This can facilitate the manufacturing of the ASEI, as Cu foils can be handled in open air. Upon pre-deposition of a certain amount of Li in a dedicated cell, the device is disassembled and the ASEI-protected thin Li electrode is coupled to another Li foil or to a cathode material for further tests ( Zhu et al., 2020 ). Alternatively, the ASEI-coated Cu current collector can be directly used in Cu|Li cells or as negative electrode in “anode-free” full cells ( Nanda et al., 2020 ).…”

Leveraging Cation Identity to Engineer Solid Electrolyte Interphases for Rechargeable Lithium Metal Anodes

“…This is further extended by exploring the charge transfer from the Li surface to the electrolyte and salt molecules using Bader analysis, which has previously been used to demonstrate correlations between charge transfer and chemical reactivity at the electrode-electrolyte interface. 40,52 The top row in Figure 4 shows the molecular structures of the electrolyte in the simulated systems. The second and third rows represent the final optimized atomic geometries from the DFT simulation, showing a top view (second row) and a side view (third row).…”

“…When examined with energy dispersive X-ray spectroscopy (EDS) and atomic absorption spectroscopy (AAS), we find that K + does not participate in electrochemical reaction. Rather, density functional theory (DFT) calculations, which are widely applied to study electrode/electrolyte interfacial chemistry, 29,40 suggest that differences in ion-solvent coordination between K + and Li + are responsible for the observed changes in SEI composition and thickness, and may ultimately lead to the observed alterations in Li deposition morphology. Our findings suggest that tuning cation identity in the electrolyte salt may be a new route to optimize electrolyte formulations for rechargeable Li metal anodes.…”