Establish an Advanced Electrolyte/Graphite Interphase by an Ionic Liquid-Based Localized Highly Concentrated Electrolyte for Low-Temperature and Rapid-Charging Li-Ion Batteries

Abstract

Ionic liquid electrolytes (ILEs) possess nonflammability, low volatility, good thermal stability, and high electrochemical stability, but poor compatibility with graphite (Gr) because of the irreversible cointercalation of the organic cations into the Gr interlayers, which severely limits their application in Gr anodes. Herein, a facile strategy is reported to solve the compatibility between ILEs and Gr by using a kind of ionic liquid-based localized highly concentrated electrolyte (LHCE) to establish a thin and robust solid electrolyte interphase (SEI) to inhibit the cointercalation of cations into the Gr anode. Simultaneously, the anion-derived inorganic SEI layer possesses lower interphase impedance than the solvent-derived organic SEI layer formed by a commercial carbonate electrolyte, hence the Gr/ Li cells manifest a fast-charging capability with superior rate capability, good cycling stability, and impressive low-temperature charge/discharge performance at −30 °C. This work offers a new design strategy for advanced electrolytes for next-generation LIBs with high safety, fast-charging ability, and low-temperature applications.

Locally Concentrated Ionic Liquid Electrolytes for Lithium‐Metal Batteries

“…The organic cations with purely alkyl side chains, e.g., Pyr 13 + , Pip 13 + , Pyr 14 + , and Emim + (Table 1, Figure 1), do not coordinate to Li + , and the first solvation sheath of Li + in the LCILEs is governed by the negatively charged anions [29–31, 41, 44, 46, 48, 57, 61] …”

“…[32][33][34][35][36][37][38][39][40] The strong electron-withdrawing effect of the fluorinated groups weakens the solvating ability of the co-solvents towards Li + , and the consequent nonsolvating feature allows the dilution of CILEs with the local Li + coordination and elevated Li + transference number preserved. [29][30][31][41][42][43][44] The non-solvating co-solvents could promote the formation of more protective SEIs kinetically enhancing the stability of LMAs against the electrolytes. [30,31,41,45,46] As a result, the Li + transport and fluidity of CILEs are promoted without compromising the CE of Li stripping/plating.…”

“…Recently, non‐solvating fluorinated ethers and aromatic molecules have been employed as new co‐solvents to resolve the aforementioned issues, [30, 31] which is inspired by a similar approach for concentrated electrolytes based on conventional organic solvents [32–40] . The strong electron‐withdrawing effect of the fluorinated groups weakens the solvating ability of the co‐solvents towards Li + , and the consequent non‐solvating feature allows the dilution of CILEs with the local Li + coordination and elevated Li + transference number preserved [29–31, 41–44] . The non‐solvating co‐solvents could promote the formation of more protective SEIs kinetically enhancing the stability of LMAs against the electrolytes [30, 31, 41, 45, 46] .…”

Co-Intercalation-Free Ether-Based Weakly Solvating Electrolytes Enable Fast-Charging and Wide-Temperature Lithium-Ion Batteries

“…Lithium-ion batteries (LIBs) based on a graphite (Gr) anode have been widely applied in our daily life for portable electronics, electric vehicles, and large-scale grid storage because of their long lifespan, high energy density, low self-discharge characteristic, and reasonable costs. , However, their fast-charging and low-temperature performance is not satisfying, − which is significantly affected by Li + transport kinetics and the applicable temperature range of the electrolytes, as well as desolvation ability of Li + ions before they are intercalated into Gr interlayers. − Unfortunately, in extensively used commercial carbonate electrolytes, the strong Li + –solvent coordinating interaction makes solvent molecules unable to be quickly separated from Li + at a high current density or low temperature. For example, propylene carbonate (PC)-based electrolyte fails to support a reversible Li + (de)­intercalation in a Gr anode, leading to a severe co-intercalation and subsequent decomposition of the [Li-PC] + complex ions and causing the exfoliation of the Gr structure. − Simultaneously, the high melting point of other traditional carbonate solvents (e.g., ethylene carbonate (EC): 36.4 °C; dimethyl carbonate (DMC): 4.6 °C) leads to easy solidification of the electrolyte at low temperature, which blocks the Li + transport and severely deteriorates the low-temperature performance of LIBs. , …”

“…9−11 Simultaneously, the high melting point of other traditional carbonate solvents (e.g., ethylene carbonate (EC): 36.4 °C; dimethyl carbonate (DMC): 4.6 °C) leads to easy solidification of the electrolyte at low temperature, which blocks the Li + transport and severely deteriorates the lowtemperature performance of LIBs. 12,13 Compared to conventional carbonate solvents, ether solvents reveal better application potential in fast-charging and low-temperature batteries owing to their low melting point and low viscosity. 14,15 However, the ether-based electrolytes, especially linear ether solvents such as 1,2-dimethoxyethane (DME), are incompatible with a Gr anode-like PC solvent.…”