Nonpolar Cosolvent Driving LUMO Energy Evolution of Methyl Acetate Electrolyte to Afford Lithium‐Ion Batteries Operating at −60 °C

Abstract

The operation of lithium‐ion batteries (LIBs) at low temperatures (<−20 °C) is hindered by the low conductivity and high viscosity of conventional carbonate electrolytes. Methyl acetate (MA) has proven to be a competitive low‐temperature electrolyte solvent with low viscosity and low freezing point, but its interfacial stability is poor and remains elusive until now. Here, it is revealed thaat the reductive stability of MA‐based electrolytes is fundamentally governed by the anion‐prevailed solvation structure. Based on this framework, fluorobenzene is employed in the electrolyte to promote the entry of anions into the solvation shell via dipole‐dipole interactions and the generation of free MA, thus enhancing the lowest unoccupied molecular orbital energy of MA. The designed electrolyte enables LiCoO2 (LCO)/graphite cells to exhibit excellent cycling performance at −20 °C (90% retention after 1000 cycles at 1 C) and to remain 91% of their room‐temperature capacity at a super‐low temperature of −60 °C at 0.05 C. Thanks to the plentiful free MA, this electrolyte has a high conductivity (2.61 mS cm−1) at −60 °C and allows LCO/graphite cell to charge at −60 °C. This study offers the possibility of practical applications for those solvents with poor reductive stability and provides new approaches to designing advanced electrolytes for low‐temperature applications.

Engineering a well-connected ion-conduction network and interface chemistry for high-performance PVDF-based polymer-in-salt electrolytes

“…19 It is worth noting that the introduction of HFA additive into SSEs brings in a new peak at 752 cm −1 in the Raman spectra, which is attributed to the characteristic peak of nanometric aggregates (n-AGGs). 33 The n-AGGs are formed via the interconnection of the scattered and localized AGGs, and then they can create a continuous pathway for fast Li To explore the role of HFA additive in inducing the formation of n-AGGs, the density functional theory (DFT) calculations were performed. As depicted in Fig.…”

Challenges and Advances in Rechargeable Batteries for Extreme‐Condition Applications

“…When used in commercial LiCoO 2 ||graphite cells, the capacity retention increased from 10% to 91% after 50 cycles at −60 °C at 0.05C (Figure 6e). [135] Besides the use of low melting-point cosolvents, tuning the interactions between electrolyte salts and solvents is also an effective approach to decrease the electrolyte freezing point at extremely low temperatures. Although DOL has a low melting point (−95 °C), it tends to undergo ring-opening polymerization in the presence of Lewis acidic salts at low temperatures, resulting in a drastic decrease of electrolyte ionic conductivity and hence battery failure.…”

“…Reproduced with permission. [135] Copyright 2023, Wiley. f) Chemical structures of EC, FEC, ethyl propyl ether (EPE), fluorinated cyclic carbonate (F-AEC), fluorinated linear carbonate (F-EMC), and fluorinated ether (F-EPE); g) comparison of cycling performances of LiNi 0.5 Mn 1.5 O 4 ||graphite cells with different fluorinated electrolytes at 45 °C.…”

Electrolyte Design for Lithium‐Ion Batteries for Extreme Temperature Applications

“…[49] For example, fluorobenzene has reportedly been used to stabilize methyl acetate-based electrolyte for LIBs to operate at −60 °C. [50]…”