Advanced Ultralow‐Concentration Electrolyte for Wide‐Temperature and High‐Voltage Li‐Metal Batteries

Abstract

High‐voltage Li‐metal batteries (LMBs) are regarded as next‐generation high‐energy‐density storage devices to apply to extensive fields such as electric vehicles, space explorations, subsea operations, and grid‐scale storages. Unfortunately, their practical applications are restricted by some defects of commercial carbonate electrolytes including flammability, low oxidation stability, narrow temperature operation window, and Li dendrites growth. Herein, a novel ultralow‐concentration electrolyte (ULCE, 0.1 m) is fabricated by dissolving lithium difluoro(oxalato)borate in N‐methyl‐N‐methoxyethyl‐pyrrolidinium bis(trifluoromethylsulfonyl)imide ([MEMP][TFSI]) ionic liquid and 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropylether. This advanced ULCE exhibits impressive merits including low cost, non‐flammability, wide operation temperature (−100 to +70 °C), and high electrochemical window (5.75 V). Meanwhile, it helps to suppress Li dendrite growth due to the combined effect of the cation shielding by MEMP+ cations and robust solid electrolyte interphase formed by the preferential decomposition of DFOB− and TFSI− anions. The LiNi0.6Co0.2Mn0.2O2 (NCM622)/Li cell with ULCE shows outstanding performance under a high voltage of 4.5 V and a wide temperature range from −60 to 70 °C. This work provides a distinctive sight to design advanced electrolyte for lower cost, safe, and wide‐temperature high‐energy‐density LMBs.

Ion Transport Kinetics in Low‐Temperature Lithium Metal Batteries

“…[ 23,40 ] In addition, the ionic mobility of electrolyte is related to salt concentration. [ 41 ] The results show that the electrolyte with high concentrated salt significantly promotes Li + mobility to provide sufficient ion flux. [ 42 ] However, numerous anions with high volume hamper cation mobility and Li + diffusion coefficient due to their high viscosity at low temperature.…”

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

“…12,13 Pure ionic liquid electrolytes (ILEs), which only contain anions and cations and the Li + ions only coordinate with anions, have been extensively confirmed that they prefer to form anion-derived SEI layer to restrain the growth of Li dendrite and show satisfying cycling stability in Li-metal batteries (LMBs). 14,15 More importantly, they possess intrinsic nonflammability, low volatility, good thermal stability, and high electrochemical stability and are being regarded as great options for safe electrolyte solvents. 16,17 Unfortunately, ILEs exhibit poor compatibility with a graphite anode because the organic cations, such as imidazolium, piperidinium, and pyrrolidinium, can be irreversibly electrochemically reduced or intercalated into the graphene interlayers.…”

“…Pure ionic liquid electrolytes (ILEs), which only contain anions and cations and the Li + ions only coordinate with anions, have been extensively confirmed that they prefer to form anion-derived SEI layer to restrain the growth of Li dendrite and show satisfying cycling stability in Li-metal batteries (LMBs). , More importantly, they possess intrinsic nonflammability, low volatility, good thermal stability, and high electrochemical stability and are being regarded as great options for safe electrolyte solvents. , Unfortunately, ILEs exhibit poor compatibility with a graphite anode because the organic cations, such as imidazolium, piperidinium, and pyrrolidinium, can be irreversibly electrochemically reduced or intercalated into the graphene interlayers. − Meanwhile, the drawbacks of ILE, including low ionic conductivity, high viscosity, poor wettability to an electrode and diaphragm, and high melting point, severely restrict their further application in fast-charging and low-temperature LIBs . It is very significant for promoting the application of ILEs in LIBs to solve the compatibility between ILEs and graphite anode, reduce the electrolyte viscosity, and advance the wettability between ILEs and electrode/diaphragm.…”

Understanding the role of additive in the solvation structure and interfacial reactions on lithium metal anode

“…There are many recent reports on lithium metal anode additives, such as tris(hexauoroisopropyl)phosphate (THFP), 31 AgNO 3 , 32 lithium disuorobis(oxalato)phosphate (LiDFBOP) [32][33][34] and LiNO 3 , 32,[35][36][37][38] CaCO 3 , 39 lithium cyano tris(2,2,2-triuoroethyl) borate (LCTFEB), 40 LiBF 4 , 41 acrylonitrile (AN), 42 tris(penta-uorophenyl)borane(TPFPB) (or tris(pentauorophenyl)phosphine; TPFPP) 43 and lithium diuoro(oxalato)borate (LiDFOB). 44 LiDFBOP is seldom reported in LSBs but LiDFBOP can reinforce the solid electrolyte interface in LSBs, 33 and shows signicant improvements in cycling performance 30 in 1,2dimethoxyethane/1,3-dioxolane (DME/DOL) electrolyte. Elucidating the microscopic mechanism is important for subsequent study of such additives, in order to increase the accuracy of additive exploration in LSBs.…”