Electrolytes for high-voltage lithium batteries

Weak Solvent–Solvent Interaction Enables High Stability of Battery Electrolyte

“…The electrolyte is one of the most important components in metal ion batteries (e.g., lithium-ion batteries, LIBs), which plays the role in transporting metal ions (M + , e.g., Li + ) and even determining the battery performance. − In principle, the current most commonly used nonaqueous electrolyte is mainly prepared by dissolving the metal salt (e.g., LiPF 6 ) and additives into the organic solvent (e.g., carbonate solvent) according to the stoichiometric ratio. − Besides satisfying the basic physicochemical properties of electrolyte (e.g., ionic conductivity, wetting capability, cation transfer number, etc.) that enables the transportation of ions, , pursuing high electrochemical stability of electrolyte is crucial to mitigate the electrolyte decomposition for a long lifespan, particularly at the high voltage operating conditions. , As a result, sieving an organic solvent that has a wide voltage window (e.g., methyl 2,2,2-trifluoroethylcarbonate (FEMC), 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), ethyl methanesulfonate electrolyte (EMS), glutaronitrile (GLN)) and/or adding additives (e.g., 3-cyano-5-fluorophenylboronic acid (CFBA), ethoxy­(pentafluoro)­cyclotriphosphazene (PFPN), tris­(trimethylsilyl) phosphite (TMSP), lithium difluorophosphate (LIDFP)) that can form a robust solid electrolyte interphase (SEI) layer on the electrode has become the most common strategies to design a stable electrolyte and electrode interface. , …”

“…10,11 As a result, sieving an organic solvent that has a wide voltage window (e.g., methyl 2,2,2-trifluoroethylcarbonate (FEMC), 12 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), 13 ethyl methanesulfonate electrolyte (EMS), 14 glutaronitrile (GLN) 15 ) and/or adding additives (e.g., 3-cyano-5-fluorophenylboronic acid (CFBA), 16 ethoxy-(pentafluoro)cyclotriphosphazene (PFPN), 1 7 tris-(trimethylsilyl) phosphite (TMSP), 18 lithium difluorophosphate (LIDFP) 19 ) that can form a robust solid electrolyte interphase (SEI) layer on the electrode has become the most common strategies to design a stable electrolyte and electrode interface. 20,21 In this way, the redox properties of the electrolyte components, including solvent, additive, and anion during the polarization, 22−25 as well as the recently proposed M + − solvent−anion complex formed during the desolvation process on the electrode surface, 26−28 have been widely studied to evaluate the electrolyte, 5 since they can be highly influenced by the widely existing electrostatic interactions between M + , anions, and solvent molecules with uneven charge distribution. Then, varying the interactions of M + −solvent, M + −anion pair, and anion−solvent by changing the type and quantity of solvents, anions, additives, etc., have received significant attention recently to tune the electrolyte properties.…”

A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High‐Concentration Electrolytes over Electrochemical Performance of Lithium‐Ion Batteries

“…The capacity decay rates of Gr||NMC811 cells operated at high voltages can be determined by the following factors: (1) the structural degradation of NMC811 (inter/intra‐microcracking, phase change from layered structure (space group R3 m) to a rock‐salt structure (space group: Fm $${\bar{3}}$$ m ), (2) the thickening of SEI and cathode electrolyte interphase (CEI) due to cathodic and anodic decomposition of electrolyte, and (3) cross‐talks between positive and negative materials (e.g. transition metal migration) [8] . Among these factors, an electrolyte influences the rate of capacity decay mainly by participating in interfacial and interphasial activities.…”

“…[14a] It is recently discovered that the concomitant decompositions of LiPF 6 and EC in conventional electrolyte facilitate the detrimental phase change of high-Ni NMC materials. [8] Because LHCEs employ LiFSI as the conducting salt, being chemically more stable than LiPF 6 , the detrimental effect of LiPF 6 on cathode degradation can be successfully circumvented in LHCEs. Even though FEC causes aggravated structural degradation in DME and TMP a -based LHCEs, the severity of the degradation still does not compare to that caused by conventional electrolytes.…”

“…[7] However, aging processes such as positive electrode cracking, structural degradation of positive electrode material, anodic decomposition of LiPF 6 and ethylene carbonate (EC) in conventional electrolytes, transition metal dissolution, solid electrolyte interphase (SEI) poisoning by transition metal cations, are significantly accelerated after adopting these two measures. [8] Several aging processed are directly caused by the conventional lithium hexafluorophosphate (LiPF 6 )-organocarbonate-based electrolytes. Because the conventional electrolytes fail to reconcile with the high energy density battery chemistries, [8,9] energetically dense LIBs suffer from significantly shortened battery life when conventional electrolytes are used.…”