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Rechargeable aluminum batteries (RABs) are extensively developed due to their cost‐effectiveness, eco‐friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture‐sensitive and corrosive. To address these problems, a 4‐ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4‐ethylpyridine molar ratio on the electrode charge–discharge properties are systematically examined. A maximum graphite capacity of 95 mAh g−1 is obtained at 25 mA g−1. After 1000 charge–discharge cycles, ≈85% of the initial capacity can be retained. In situ synchrotron X‐ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon‐fiber paper electrodes are confirmed in the 4‐ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N2‐filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications. [ABSTRACT FROM AUTHOR]

Highlights • High energy density 0.3Li 2 MnO 3 –0.7LiMn 1.5 Ni 0.5 O 4 (0.3LMO–0.7LMNO) composite cathodes are synthesized using auto-combustion. • At 60 °C, Li/Li+ - PMP-TFSI/0.3LMO - 0.7LMNO half-cell yield ∼316 mAh/g in 2.5–4.8 V range. • As compared to organic electrolyte, composite cathode yield superior electrochemical properties in ionic liquid (IL) at elevated temperature. • IL has higher thermal stability and thus ideal for high-safety applications. Abstract In this work, we have compared the electrochemical characteristics of auto combustion synthesized 0.3Li 2 MnO 3 –0.7LiMn 1.5 Ni 0.5 O 4 composite cathode using conventional organic electrolyte and Li+/PMP-TFSI (N-propyl-N-methyl pyrrolidinium-bis(trifluoromethanesulfonyl) imide) ionic liquid (IL) at 25 °C and 60 °C. At 60 °C, IL electrolyte yields superior specific discharge capacity, cycleability, rate performance and voltage fading characteristics of the composite cathode. We have argued that the superiority of IL electrolyte is related to its relatively higher decomposition temperature. The effect of ILs on the cycle induced layered to nickel free spinel phase transformation in the composite cathode is also investigated by post cycling XRD. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ionic‐liquid (IL) electrolytes, characterized by large potential windows, intrinsic ionic conductivity, low environmental hazard, and high safety, are used for micropore‐ and mesopore‐rich activated‐carbon (ACmicro and ACmeso) supercapacitors. IL electrolytes consisting of various cations [1‐ethyl‐3‐methylimidazolium (EMI+), N‐propyl‐N‐methylpyrrolidinium (PMP+), and N‐butyl‐N‐methylpyrrolidinium (BMP+)] and various anions [bis(trifluoromethylsulfonyl)imide (TFSI−), BF4−, and bis(fluorosulfonyl)imide (FSI−)] are investigated. The electrolyte conductivity, viscosity, and ion transport properties at the ACmicro and ACmeso electrodes are studied. In addition, the capacitance, rate capability, and cycling stability of the two types of AC electrodes are systematically examined and post‐mortem material analyses are conducted. The effects of IL composition on the charge–discharge capacitances of the ACmicro electrodes are more pronounced than those for the ACmeso electrodes. The FSI‐based IL electrolytes, for which electrochemical properties are cation dependent, are found to be promising. Incorporating EMI+ with FSI− results in a low electrolyte viscosity and a fast ion transport, giving rise to optimized electrode capacitance and rate capability. Replacing EMI+ with PMP+ increases the cell voltage (to 3.5 V) and maximum energy density (to 42 Wh kg−1) of the ACmicro cell at the cost of cycling stability. A puzzle of pores and ions: A suitable combination of activated carbon pore size and ionic‐liquid (IL) composition can achieve desirable electric double‐layer capacitor performance. A bis(fluorosulfonyl)imide (FSI)‐based IL is more promising than the bis(trifluoromethylsulfonyl)imide (TFSI)‐ and BF4‐based IL counterparts. Replacing 1‐ethyl‐3‐methylimidazolium with N‐propyl‐N‐methylpyrrolidinium increases the cell voltage to 3.5 V, improving the energy density of the supercapacitor. [ABSTRACT FROM AUTHOR]

In this article, we investigate the electrochemical performance of the amorphous sodium iron carbonophosphate upon transitioning from organic electrolytes (lithium hexafluorophosphate (LiPF 6) –ethylene carbonate (EC): diethyl carbonate (DEC) based) to ionic-liquid (N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide; PMP-FSI) based electrolytes. The amorphous sodium iron carbonophosphate is synthesized using microwave-assisted hydrothermal process to obtain the desired phase and microstructure. The nanoparticle morphology, along with the amorphous structure, results in excellent electrochemical properties when tested as cathode for lithium-ion and sodium-ion batteries with organic and ionic-liquid based electrolytes. It is observed that the room-temperature and high-temperature (∼60 °C) cycling performance is superior when ionic-liquids are used instead of organic electrolytes, resulting in nearly fade-free electrochemical cells. Specific capacity retention of ∼97% is reported after 500 cycles with 3 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/PMP-FSI ionic-liquid at a specific current density of 400 mAg−1 (room temperature), in comparison to ∼70% after 500 cycles for 1 M LiPF 6 in EC: DEC = 1:1. At high temperatures (∼60 °C), ionic-liquids outperform the conventional organic electrolytes in terms of capacity retention and rate capability. Post-mortem analysis of the electrodes indicates that a dense and ionically conductive protective film, composed of anion-reduced moieties, is responsible for the superior high-temperature performance of amorphous sodium iron carbonophosphate with the ionic-liquids. [Display omitted] • Electrochemical evaluation of amorphous Na 2 FePO 4 CO 3 with ionic-liquid electrolytes. • Thermodynamic model based on polarization work proposed for mechanism of operation. • Measurements of electrochemical properties at room temperature and 60 °C. • Nearly fade-free cycling characteristics established at room temperature and 60 °C. • Excellent rate-capability upto charge-discharge rate of ∼20C established. [ABSTRACT FROM AUTHOR]

Highly concentrated lithium bis(fluorosulfonyl)imide (LiFSI) salt dissolved in carbonate solvent is employed as a high-performance and robust organic electrolyte for Li-ion batteries. The influences of Li salt type, concentration, and solvent type (such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylene carbonate (EC)) on the electrochemical properties of Li metal and graphite anodes are systematically assessed. A superior electrolyte composition of 5.5 M LiFSI-DMC/EC is achieved, enhancing the anti-flammability, coulombic efficiency, and high rate capability. The optimal efficiency values of Li electrodeposition/stripping utilizing 5.5 M LiFSI-DMC/EC are 97.0% and 94.5% at 0.4 and 6 mA cm−2, respectively. Such an enhanced performance is due to the formation of a three-dimensional ion network, composed of contact ion pairs (CIPs) and ion aggregates (AGGs) in the highly concentrated LiFSI electrolyte, which effectively decreases the number of free solvent molecules and inhibits the formation of undesired dendritic Li structures. Raman spectroscopy is employed to confirm the formation of CIP and AGG compounds within the electrolyte. The electrochemical data of the 5.5 M LiFSI-DMC/EC electrolyte cell demonstrates a remarkable improvement in the specific capacity and rate capability of a graphite anode. Image 1 • An electrolyte containing LiFSI salt and carbonate was used for Li-ion batteries. • Influence of Li salt, concentration, solvent, and composition was investigated. • An optimal composition, 5.5 M LiFSI-DMC/EC and 5.5 M LiFSI-DEC/EC, was determined. • Raman spectroscopy was used to confirm the formation of ICP and AGG compounds. • Specific capacity and high-rate capability of Li and graphite anodes were improved. [ABSTRACT FROM AUTHOR]

Electrolyte recipes and Li metal anode host materials are developed for lithium-metal batteries. 1,2-dimethoxyethane/ethylene carbonate mixed solvent with 1 M lithium bis(fluorosulfonyl)imide and 1 wt% LiNO 3 is shown to form a robust solid electrolyte interphase and improve Coulombic efficiency and cyclability during Li metal plating/stripping. This electrolyte can withstand high potential, allowing the operation of a LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC-811) cathode. One-dimensional carbon nanotubes, two-dimensional graphene nanosheets, and three-dimensional ordered mesoporous carbon CMK-8 are used as the host materials for the accommodation of Li metal. The strong and continuous conducting network of CMK-8 with interpenetrating open channels is found to be a promising scaffold for Li metal. With the proposed electrolyte, the CMK-8 electrode enables uniform Li plating/stripping with a high Coulombic efficiency of 99.2% under a practical current density of 1 mA cm−2. Moreover, a long life of >550 charge-discharge cycles is achieved. The high structural stability of CMK-8 upon cycling is confirmed using electron microscopy and Raman spectroscopy. Finally, we use a Li-free CMK-8 electrode, an NMC-811 cathode, and the proposed electrolyte to construct a full cell. The electrochemical properties are evaluated. [Display omitted] • Electrolyte and anode host materials are developed for lithium-metal batteries. • The proposed electrolyte induces a robust SEI and withstands high potential. • 1-D CNT, 2-D graphene, and 3-D CMK-8 carbon host materials are examined. • CMK-8 structure can minimize the dead Li amount and suppress Li dendrite formation. • Superior CE of 99.2% and great stability of up to 550 cycles are found for CMK-8. [ABSTRACT FROM AUTHOR]

[Display omitted] • A FSI-based IL electrolyte for high-voltage LiNi 0.5 Mn 1.5 O 4 cathode is proposed. • Three electrolyte design strategies are implemented to improve FSI-based IL. • The Li+, FSI−, and TFSI− fractions in IL electrolyte are modulated and optimized. • Our electrolyte design takes into account the graphite anode compatibility. • 5-V graphite//LiNi 0.5 Mn 1.5 O 4 full cell with great performance is demonstrated. Ionic liquids (ILs), with wide electrochemical stability window, high thermal stability, and nonvolatility, are promising electrolytes for lithium-ion batteries. Among ILs with various types of anion, bis(fluorosulfonyl)imide (FSI−)-based ILs are particularly appealing owing to their high ionic conductivity, low viscosity, and great anode compatibility. However, strong corrosivity of FSI− toward the Al current collector at high potential restricts their practical utilization. In this study, three strategies are implemented to overcome this limitation. Li+ fraction modulation, FSI−/bis(trifluoromethyl)sulfonylimide (TFSI−) molar ratio optimization, and their synergistic combination are used to achieve optimal charge–discharge of a high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode with an Al substrate. The effects of the IL composition on the electrochemical properties of a graphite anode are also investigated. The proposed IL electrolyte, which lacks any organic solvents, has an optimal Li+/FSI−/TFSI− molar ratio and thus can effectively suppress the Al corrosion, allowing a 5-V graphite//LNMO full cell to be realized. A reversible capacity of ~ 135 mAh g−1 (based on LNMO) and a capacity retention of ~ 85% after 200 cycles are found for the full cell. This study opens a new route for FSI−-based IL electrolytes in the field of high-voltage and high-safety lithium-ion battery applications. [ABSTRACT FROM AUTHOR]

This study adopts high-concentration ether electrolytes to improve high-rate capability, cycling stability, and Coulombic efficiency (CE) for lithium ion batteries with lithium anode. A series of ether-based electrolytes including lithium bis(fluorosulfonyl)imide (LiFSI)-glyme/ethylene carbonate (EC), LiFSI-glyme/EC, LiFSI-diglyme/EC, LiFSI-triglyme/EC, LiFSI-tetraglyme (G4)/EC, and LiFSI-1,3-dioxolane (DOL)/EC, along with commonly used LiPF 6 -DEC/EC were prepared to delineate the influences of concentration, chain length, molecular structure (linear or ring ether), and EC additive on the electrochemical performance of Li anodes. An optimum composition for ether-based electrolyte was determined resulting in significant improvement in anti-flammability as well as CE at both low and high rates. At ultra-high current density operation (e.g. 6 mA cm−2), the CE was 95.5 and 97.1% with 3 M LiFSI-G4/EC and 3 M LiFSI-DOL/EC, respectively. Using 1 M LiPF 6 carbonate-based electrolyte tend to grow a needle-like dendritic structure when depositing lithium metal on Cu foils, whereas high-concentration ether electrolyte promotes a knot-like and rounded Li metal microstructure. High concentration EC-based electrolytes, are capable of facilitating Li+ almost in tandem with solvent molecules, thereby reducing the number of free molecules, reducing the chance of side reaction with Li metal, and subsequently inhibiting the formation of dendritic Li structures. Image 1 • Ether electrolytes are used to improve Coulombic efficiency for Li-ion batteries. • This study reveals two key factors: chain length and molecular structure in ether. • An optimal composition for ether electrolyte is beneficial anti-flammability. • The Coulombic efficiency reaches 95.5% at high current using 3 M LiFSI-G4/EC. • High-concentration ether electrolyte promotes a knot-like Li metal microstructure. [ABSTRACT FROM AUTHOR]

Cubic-phase Li 7 La 3 Zr 2 O 12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al- and Ga-doped LLZO can transform to a cubic-phase garnet at 900 °C. After 1200 °C sintering, a Li 2 ZrO 3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900–1200 °C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO 4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications. Image 1 • Electrolyte architecture designs are developed using Ga-doped LLZO (LGLZO). • Electrolyte & interfacial resistances vary with PEO/LiTFSI/LGLZO ratio. • Optimal conductivity of PEO-LiTFSI-LGLZO is ∼3.3 × 10−4 S cm−1 at 65 °C. • All-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell shows promising redox performance. [ABSTRACT FROM AUTHOR]