Tuning the Solvent Alkyl Chain to Tailor Electrolyte Solvation for Stable Li-Metal Batteries

Abstract

1,2-Dimethoxyethane (DME) has been considered as the most promising electrolyte solvent for Li-metal batteries (LMBs). However, challenges arise from insufficient Li Coulombic efficiency (CE) and poor anodic stability associated with DME-based electrolytes. Here, we proposed a rational molecular design methodology to tailor electrolyte solvation for stable LMBs, where shortening the middle alkyl chain of the solvent could reduce the chelation ability, while increasing the terminal alkyl chain of the solvent could increase the steric hindrance, affording a diethoxymethane (DEM) solvent with ultra-weak solvation ability. When serving as a single solvent for electrolyte, a peculiar solvation structure dominated by contact ion pairs (CIPs) and aggregates (AGGs) was achieved even at a regular salt concentration of 1 m, which gives rise to anion-derived interfacial chemistry. This illustrates an unprecedentedly high Li||Cu CE of 99.1% for a single-salt single-solvent (non-fluorinated) electrolyte at ∼1 m. Moreover, this 1 m DEM-based electrolyte also remarkably suppresses the anodic dissolution of Al current collectors and significantly improves the cycling performance of high-voltage cathodes. This work opens up new frontiers in engineering electrolytes toward stable LMBs with high energy densities.

An Amphiphilic Molecule‐Regulated Core‐Shell‐Solvation Electrolyte for Li‐Metal Batteries at Ultra‐Low Temperature

“…Even holding at higher potential up to 5.0 V, there is no obvious leakage current observed for both TFMP/DME and TTE/DME electrolytes (Figure S22). The excellent Al corrosion prevention is originated from the weak solvation ability of the electrolytes that are unable to dissolve the Al 3+ complexes, thereby accumulating a passivation layer of Al 3+ complexes to suppress the Al corrosion [27, 28] …”

“…As shown in Figure 1a, for conventional 1 m LiFSI‐DME electrolyte, the Li + is strongly solvated with DME solvent, which leads to the solvent‐derived organic‐rich SEI. The SEI with organic‐rich components normally has high porosity, and is high fragile and resistive, which causes low Li plating/stripping CE and fast battery failure [27, 28] . Furthermore, inferior oxidative stability of DME solvent as well as serious Al corrosion associated with diluted LiFSI‐based electrolyte has prevented its application towards high‐voltage cathodes.…”

“…The excellent Al corrosion prevention is originated from the weak solvation ability of the electrolytes that are unable to dissolve the Al 3 + complexes, thereby accumulating a passivation layer of Al 3 + complexes to suppress the Al corrosion. [27,28] Given that the TFMP/DME electrolyte with peculiar core-shell-solvation endows excellent compatibility with Li metal anode as well as excellent anodic stability, it was explored as a promising electrolyte for high voltage Li j j NMC811 cells. As shown in Figure 6a, at room temperature, the Li j j NMC811 cell using 1 m LiFSI-TFMP/DME electrolyte exhibits much better rate capability from 0.1 C to 20 C compared to that of using 1 m LiFSI-TTE/DME LHCE, which is attributed to its higher ionic conductivity, lower desolvation energy, and lower SEI resistance that effectively accelerates the electrochemical kinetic (Figure 4a).…”

“…The SEI with organic-rich components normally has high porosity, and is high fragile and resistive, which causes low Li plating/stripping CE and fast battery failure. [27,28] Furthermore, inferior oxidative stability of DME solvent as well as serious Al corrosion associated with diluted LiFSI-based electrolyte has prevented its application towards highvoltage cathodes. Besides, the DME solvent with strong solvating ability is tend to bind strongly with Li + , resulting in high desolvation energy that leads to poor electrochemical kinetic, especially at low temperature.…”

Adhesion of Bis-Salphen-Based Coordination Polymers to Graphene: Insights from Free Energy Perturbation Study

“…Both covalent and van der Waals interactions were described by OPLS-AA force field [ 50 , 51 ], with the exception for the atoms of the imine group (-C=N-), explicit parametrization of which was introduced in OPLS_2005 force field [ 52 ] and is essential for accurate description of salphen compounds. While many improvements were introduced over the years with more recent parametrizations [ 53 , 54 , 55 , 56 ], such as more precise torsions for DNA backbone chain and better description of nucleic acid interaction, the OPLS-AA force field is still widely used for molecular simulations in liquid state, such as including recent studies of SARS-CoV-2 inhibitors [ 57 ], chromophores [ 58 ] and electrolytes for novel batteries [ 59 ]. It is also implemented in many open source toolkits for building input files for molecular dynamics simulations, such as Moltemplate [ 60 ], used in this work.…”