Synergistic Effects on Lithium Metal Batteries by Preferential Ionic Interactions in Concentrated Bisalt Electrolytes

Abstract

Lithium metal batteries (LMBs) have the potential to deliver a greater specific capacity than any commercially used lithium battery. However, excessive dendrite growth and low Coulombic efficiencies (CEs) are major hurdles preventing the commercialization of LMBs. In this study, two different salts, lithium difluorophosphate (LiDFP) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), are chosen for use in concentrated electrolytic systems. By mixing salts with vastly different cation–anion interaction energies, the ion solvation structures in the electrolyte can be modulated to enhance the physical/electrochemical properties and suppress Li dendrite growth in LMBs. Among the investigated electrolyte systems, 2.2 m LiDFP + 1.23 m LiTFSI in 1,2‐dimethoxyethane is proposed as a highly promising electrolyte system because of its high conductivity (6.57 mS cm−1), CE (98.3%), and the formation of an extremely stable solid–electrolyte interface layer. The bisalt electrolyte presented herein, as well as the associated concepts, provide a new avenue toward commercial LMBs.

Simultaneous Stabilization of the Solid/Cathode Electrolyte Interface in Lithium Metal Batteries by a New Weakly Solvating Electrolyte

“…[1,3] To deal with the aforementioned issues, a variety of solutions have been investigated. Considerable efforts have been devoted to the formation of a sound SEI layer on the Li anode and these include but are not limited to adding additives into conventional electrolytes, [7][8][9][10] using highly concentrated electrolytes including localized high concentration electrolytes, [4,[11][12][13][14][15][16] and employing different organic solvents. [17][18][19][20][21] Recently, highly concentrated electrolytes have attracted great attention.…”

Confronting the Challenges in Lithium Anodes for Lithium Metal Batteries

“…[ 21 , 22 , 23 ] Compared with the concentrated mono‐salt, the concentrated dual‐salt effectively improves the ion conductivity of the high‐concentration electrolyte (HCE) system. [ 24 ] Although the problem of lithium anode has been alleviated to some extent, to our knowledge, there is still a gap between the performances of present lithium metal batteries and practical application. Calculation and simulation, such as, molecular dynamic simulation and phase field model, are used to propose new directions for the improvement of host materials, electrolyte formulations, etc.…”

Energetics of Li+ Coordination with Asymmetric Anions in Ionic Liquids by Density Functional Theory

“…The structure of Li + solvates in concentrated electrolytes has a significant impact on Li + transport and is influential in the rate capability of rechargeable lithium ion batteries (LIBs) (Borodin et al, 2018;Yamada et al, 2019;Krachkovskiy et al, 2020;Pham et al, 2021). ILs present an extreme case of a concentrated electrolyte where the electrolyte is made entirely of discrete ions and lacks neutral solvent molecules.…”

“…These properties are desirable for lithium battery systems and thus are of great interest for safe, high-density energy storage devices (Galinski et al, 2006;Bae et al, 2013;Navarra, 2013;Eftekhari et al, 2016). However, Li + transport in ILs is complex and hindered by the high viscosity, mainly due to Coulombic interactions and specific Li + -anion interactions, which leads to the formation of clusters that decrease the mobility of Li + in the bulk liquid (Lesch et al, 2014;Pham et al, 2021). Li + transport in ILs has been studied mostly by Raman spectroscopy, nuclear magnetic resonance spectroscopy, transference measurements, density functional theory (DFT), and classical molecular dynamic (MD) simulations (Borodin et al, 2006;Umebayashi et al, 2007;Duluard et al, 2008;Lassègues et al, 2009;Umebayashi et al, 2010;Castiglione et al, 2011;Fujii et al, 2013;Haskins et al, 2014;Borodin et al, 2018).…”