Tuning a Solvation Structure of Lithium Ions Coordinated with Nitrate Anions through Ionic Liquid‐Based Solvent for Highly Stable Lithium Metal Batteries

Abstract

Rational design of promising electrolyte is considered as an effective strategy to improve the cycling stability of lithium metal batteries (LMBs). Here, an elaborately designed ionic liquid-based electrolyte is proposed that is composed of lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, 1-ethyl-3-methylimidazolium nitrate ionic liquid ([EMIm][NO 3 ] IL) and fluoroethylene carbonate (FEC) as the functional solvents, and 1,2-dimethoxyethane (DME) as the diluent solvent. Using [EMIm][NO 3 ] IL as the solvent component facilitates a special Li + -coordinated NO 3 − solvation structure, which enables the continues electrochemical reduction of solvated NO 3 − and the formation of remarkably stable and conductive solid electrolyte interface. With FEC as another functional solvent and DME as the diluent solvent, the formulated electrolyte delivers high oxidative stability and ionic conductivity, and endows improved electrochemical reaction kinetics. Therefore, the formulated electrolyte demonstrates exceedingly reversible and stable Li stripping/plating behavior with high average Coulombic efficiency (98.8%) and ultralong cycling stability (3500 h). Notably, the high-voltage Li|LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell with IL-based electrolyte exhibits enhanced cyclability with a capacity retention of 65% after 200 cycles under harsh conditions of low negative/positive ratio (3.1) and lean electrolyte (2.5 µL mg −1 ). This study creates the first NO 3 − -based ionic liquid electrolyte and evokes the avenue for practical high-voltage LMBs.

Constructing an inorganic-rich solid electrolyte interphase by adjusting electrolyte additives for stable Li metal anodes

“…Preferential reduction of additives was further demonstrated by cyclic voltammetry (CV) tests in a voltage range of 0–2.5 V. As can be observed in Fig. 1b and S2,† the distinct peak around 1.4 V could be assigned to the reduction of DFP − , 40 and the typical potential peak ranging from around 1.6 V originated from the reduction of NO 3− , which enables the generation of SEI containing LiF and Li 3 N. 41…”

“…Preferential reduction of additives was further demonstrated by cyclic voltammetry (CV) tests in a voltage range of 0-2.5 V. As can be observed in Fig. 1b and S2, † the distinct peak around 1.4 V could be assigned to the reduction of DFP − , 40 and the typical potential peak ranging from around 1.6 V originated from the reduction of NO 3− , which enables the generation of SEI containing LiF and Li 3 N. 41 Subsequently, the ion transport behavior was investigated by detailed electrochemical measurements, mainly including Li + transference numbers (t Li +) and ionic conductivity. The t Li + were measured according to the classical Bruce-Vincent method by assembling Li‖Li symmetric cells.…”

From Inorganic to Organic Iodine: Stabilization of I+ Enabling High-Energy Lithium–Iodine Battery

“…The low peak intensity of I + is due to the loss of active materials upon washing during the sample preparation for the XPS measurement, and the existence of I – and I 0 in the XPS spectra is because of the incomplete conversion upon charge. Interestingly, the N 1s XPS spectra (Figure S6) reveal the changes in the peak at ∼408 eV, which corresponds to the NO 3 – species . During the redox processes, the peak associated with NO 3 – undergoes significant changes, indicating alterations in the surrounding environment.…”

“…Interestingly, the N 1s XPS spectra (Figure S6) reveal the changes in the peak at ∼408 eV, which corresponds to the NO 3 − species. 47 During the redox processes, the peak associated with NO 3 − undergoes significant changes, indicating alterations in the surrounding environment. At a fully discharged voltage of 2.0 V, the NO 3 − peak is not prominent.…”

Electrolyte Engineering via Fluorinated Siloxane Solvent for Achieving High-Performance Lithium-Metal Batteries

“…4−6 Such an ideal candidate offers an option to achieve the desperate demand of energy density up to 400 Wh kg −1 when paired with high-voltage nickel-rich cathodes. 7,8 However, the practical employments of LMA are induced by the uncontrollable side reactions between the highly reactive lithium and electrolytes. These parasitic reactions induce the unstable and mechanically fragile solid-state electrolyte interface (SEI) layer, finally incurring sharp dendrite growth, low Coulombic efficiency (CE), poor lifespan, and even safety issues of cells.…”