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High‐capacity cathodes (LiNi0.8Mn0.1Co0.1O2, NMC811) are promising for vehicle electrification because of their high gravimetric energy density. However, their electrochemical performance still relies upon the stability of the cathode electrolyte interphase (CEI). A highly reactive cathode interface leads to parasitic side reactions with electrolytes, resulting in accelerated capacity fading. Well‐developed LiF and LiF‐like inorganic compounds are believed to be good CEI components for stabilizing such reactive electrode interfaces. However, it is challenging to form an optimal surface sub‐nanolayer of LiF on the cathode surfaces because of the complexity of the electrochemical reaction during battery cycling. Herein, the formation of a conformal LiF layer on the NMC811 electrode surface via an in situ ion‐exchange metathesis process is reported, demonstrating a promising electrochemical performance because of a LiF‐stabilized CEI. In situ generated LiF‐coated NMC811 electrodes exhibit ≈97% capacity retention up to 100 cycles at a 0.3 C rate with average coulombic efficiency of ≈99.9% and ≈80% capacity retention up to 200 cycles at a 1 C rate with average coulombic efficiency of >99.6%. This finding may pave the way for reengineering the CEI to enhance the electrochemical performances and cycling stability of the high‐capacity cathodes. [ABSTRACT FROM AUTHOR]

The formation of the solid electrolyte interphase (SEI) in an ionic liquid electrolyte of 0.5 m lithium bis(fluorosulfonyl)imide (LiFSI) in 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide at high cell voltages (1.7–1.9 V) is investigated in ordered mesoporous carbon (OMC) based Li metal cells using an operando small‐angle neutron scattering (SANS) technique coupled with electrochemical impedance spectroscopy and ex situ X‐ray photoelectron spectroscopy (XPS). It is demonstrated that discharging the OMC Li metal cells to ≈2 V and holding the cell voltage constant induces a rapid current increase with time, confirming extensive reduction and SEI formation. XPS analysis reveals that LiF is formed at open cell voltage (OCV), which is attributed to the carbenes generated at the lithium negative electrode because of its reaction with EMIm cation diffusing to and initiating the reaction with FSI− anions at the carbon positive electrode. It is confirmed that the chemical reaction at OCV and electrochemical reduction at high cell voltage of the FSI− anion plays a protective role against EMIm cation co‐intercalation into the carbon positive electrode during the initial discharge. Operando SANS studies also suggest that slight differences occur in the surface composition and reaction mechanism as a function of cell voltage. [ABSTRACT FROM AUTHOR]

Solid Electrolyte Interphases: Insight into the Solid Electrolyte Interphase Formation in Bis(fluorosulfonyl)Imide Based Ionic Liquid Electrolytes (Adv. Funct. 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, ionic liquids, lithium bis(fluorosulfonyl)imide, neutron scattering, operando characterization, solid electrolyte interphase Keywords: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide; ionic liquids; lithium bis(fluorosulfonyl)imide; neutron scattering; operando characterization; solid electrolyte interphase EN 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ionic liquids lithium bis(fluorosulfonyl)imide neutron scattering operando characterization solid electrolyte interphase 1 1 1 06/07/21 20210615 NES 210615 In article number 2008708, Charl J. Jafta, Xiao-Guang Sun, Craig Bridges, and co-workers use high surface area mesoporous hard carbons to demonstrate that surface passivation for the bis(fluorosulfonyl)imide anion (FSI SP - sp ) occurs via chemical reactions at the open cell voltage, and through electrochemical reactions at cell voltages near 2 V. The research provides insight into the design of anions for stable inorganic salt passivation of electrode interfaces in next generation batteries. [Extracted from the article]

Abstract Three trimethylsilyl based malonate esters, bis(trimethylsilyl) 2-methyl-2-fluoromalonate (BTMSMFM), bis(trimethylsilyl) 2-ethyl-2-fluoromalonate (BTMSEFM) and bis(trimethylsilyl) 2-propyl-2-fluoromalonate (BTMSPFM), have been used as additives in 1.0 M LiPF 6 /ethylene carbonate (EC)-dimethyl carbonate (DMC)-diethyl carbonate (DEC) (1-1-1, by v) baseline electrolyte for LiNi 0.80 Co 0.15 Al 0.05 O 2 (NCA) based high voltage lithium ion batteries. The NCA half-cells with 5 wt% BTMSMFM exhibit higher capacity retention than that in the baseline electrolyte at different upper cut off voltages, that is, 4.2, 4.3, 4.4 and 4.5 V vs. Li/Li+. Scanning electron microscope (SEM) show that the additive successfully prevents the formation of thick solid electrolyte interphase (SEI) films on the surface of the NCA electrodes. X-ray diffraction (XRD) further reveals that the crystal structure of NCA is also maintained in the electrolyte with 5 wt% BTMSMFM at high cut off voltages. Besides beneficial to NCA cathode, the BTMSMFM additive also ensures better cycling performance of the graphite based half-cells and NCA/graphite full-cells, and thus is a promising additive for application in rechargeable lithium ion batteries. Highlights • BTMSMFM additive significantly improves long cycling stability of NCA half-cells up to 4.5 V. • BTMSMFM additive prevents the formation of thick SEI films in conventional carbonate electrolytes. • BTMSMFM additive preserves structural stability of NCA material at different upper cut off voltages. • Electrolyte decomposition and parasitic side reactions are suppressed effectively. [ABSTRACT FROM AUTHOR]