N‐alkyl‐N‐alkyl pyrrolidinium‐based ionic liquids (ILs) are promising candidates as non‐flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)‐based solid polymer ...electrolytes (SPEs), but they present limitations in terms of lithium‐ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium‐ion transport than alkyl‐substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium‐metal polymer batteries.
Ionic liquids (ILs) allow improvement of the ionic conductivity of ternary PEO‐based solid polymer electrolytes. However, the lack of Li‐ion coordination of these plasticizers and the addition of extra ions results in a low Li‐ion conductivity. An oligo(ethylene oxide)‐based IL was synthesized to overcome these limitations and enable additional transport modes, resulting in a high Li‐ion conductivity.
•Ionic liquid cations with oligo(ethylene oxide) side chains have been prepared.•The effect of the side chain length on Li+ solvation was studied.•The effect of the ionic liquids as solid polymer ...electrolyte plasticizers is reported.•The increased solvation of the longer side chains leads to improved performance.
Ternary solid polymer electrolytes (TSPEs) with ionic liquids (ILs) including alkyl-based ammonium cations and low coordinating anions suffer from the lack of Li+ ion coordination by the ILs compared to the immobile polymer backbone, in terms of Li+ ion transport. Thus, solvating ionic liquids (SILs) with an oligo(ethylene oxide) side chain attached onto the cation were prepared to improve the interaction between Li+ and the IL and accelerate Li+ transport in TSPEs. A variety of methods, such as pulsed field gradient nuclear magnetic resonance spectroscopy, Li metal plating/stripping and measurements of Sand's times were used to show that Li+ ion transference numbers increase with the oligo(ethylene oxide) side chain length in SIL-based TSPEs, which results in faster Li+ ion transport and translates into much slower lithium depletion at a given current, thereby delaying the onset of fast dendrite growth of lithium metal.
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A durable lithium metal polymer battery with extended cycle-life is designed by exploiting cross-linked poly(trimethylene carbonate) (PTMC) electrolytes and LiNi0.6Mn0.2Co0.2O2 (NMC622) with ...well-defined protective coating (0.5 wt% of LiNbO3 on the surface layer, <5 nm thickness). The presented materials demonstrate feasibility of faster cycling at rates of 1C and 2C at temperatures of 40 and 60 °C, exhibiting prominent capacity retention of 91% and 80% SOH (state of health) after 500 cycles. At higher cross-linking densities, the introduced quasi-solid polymer electrolytes afford good cycling performance and sufficient suppression of high surface area lithium depositions as well as improved ability of solvent entrapment, hence reflecting a considerable step forward towards achieving all solid-state polymer-based cells.
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•Side-chain modified grafted macrocycles as versatile class of electrolytes.•Optimized cross-linking density for quasi-solid carbonate-based polymers.•High performance and capacity retention in NMC622||Li cells at rapid cycling.•Extended cell longevity due to well-defined LiNbO3 cathode coatings.
Gel polymer electrolytes (GPEs) based on poly (vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) containing propylene carbonate (PC), isobutyronitrile (IBN) and trimethyl acetonitrile (TMAN) ...solvent blend electrolytes were developed to enhance high temperature electrochemical performance and to improve safety of LiNi3/5Mn1/5Co1/5O2 (NMC622)‖graphite lithium ion battery (LIB) cells. These liquid electrolytes (LE) consist of lithium bis(trifluoro-methane)sulfonimide (LiTFSI) as conducting lithium salt and PC/nitrile (1:1, v/v) solvent blends. Ethylene sulfite (ES) and vinylene carbonate (VC) were used as solid electrolyte interphase (SEI) forming additives and contributing to an excellent cycling stability of electrolytes comprising nitrile solvents in NMC622‖graphite cells. Electrochemical impedance spectroscopy (EIS), pulsed field gradient nuclear magnetic resonance spectroscopy (PFG NMR) and relative permittivity determination reveal remarkable ion conducting properties of IBN and TMAN solvents. Since their electrolytes are incompatible with lithium metal electrodes, their electrochemical stability window (ESW) was determined using lithiated lithium titanate (Li7Ti5O12) (LTO) as counter and reference electrodes and the obtained values were confirmed by quantum mechanical computation. Differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) confirmed significantly improved safety of IBN and TMAN containing electrolytes. Therefore, PVdF-HFP-based GPEs containing PC/nitrile solvent blends are a promising alternative to SOTA electrolyte for battery cycling at elevated temperature (60 °C) in NMC622‖graphite cells.
•Excellent ionic conductivity of isobutyronitrile.•Suppressed anodic Al dissolution in presence of considered nitrile co-solvents.•High oxidative stability of considered nitrile-based liquid electrolytes.•High thermal stability of resulting PVdF-HFP-based gel polymer electrolytes.
The water‐in‐salt concept has significantly improved the electrochemical stability of aqueous electrolytes, and the hybridization with organic solvents or ionic liquids has further enhanced their ...reductive stability, enabling cell chemistries with up to 150 Wh kg−1 of active material. Here, a large design space is opened by introducing succinonitrile as a cosolvent in water/ionic liquid/succinonitrile hybrid electrolytes (WISHEs). By means of succinonitrile addition, the solubility limits can be fully circumvented, and the properties of the electrolytes can be optimized for various metrics such as highest electrochemical stability, maximum conductivity, or lowest cost. While excessive nitrile fractions render the mixtures flammable, careful selection of component ratios yields highly performant, nonflammable electrolytes that enable stable cycling of Li4Ti5O12–LiNi0.8Mn0.1Co0.1O2 full cells over a wide temperature range with strong rate performance, facilitated by the fast conformational dynamics of succinonitrile. The WISHEs allow stable cycling with a maximum energy density of ≈140 Wh kg−1 of active material, Coulombic efficiencies of close to 99.5% at 1C, and a capacity retention of 53% at 10C relative to 1C.
Solubility limits of suitable salts hinder the development of water‐in‐salt electrolytes. By introducing cosolvents, these limitations are circumvented and a large design space is opened for non‐flammable, water‐based hybrid electrolytes. Here, succinonitrile is introduced as an electrolyte component, and its fast conformational dynamics is exploited to afford energy‐dense batteries based on Li4Ti5O12 and LiNi0.8Mn0.1Co0.1O2 with a strong rate performance over a wide temperature range.
Solid polymer electrolytes (SPEs) have attracted considerable attention for high energy solid‐state lithium metal batteries (LMBs). In this work, potentially ecofriendly, solid‐state ...poly(ε‐caprolactone) (PCL)‐based star polymer electrolytes with cross‐linked structures (xBt‐PCL) are introduced that robustly cycle against LiNi0.6Mn0.2Co0.2O2 (NMC622) composite cathodes, affording long‐term stability even at higher current densities. Their superior features allow for sufficient suppression of dendritic lithium deposits, as monitored by 7Li solid‐state NMR. Advantageous electrolyte|electrode interfacial properties derived from cathode impregnation with 1.5 wt% PCL enable decent cell performance until up to 500 cycles at rates of 1C (60 °C), illustrating the high potential of PCL‐based SPEs for application in high‐voltage LMBs.
A potentially ecofriendly, solid‐state poly(ε‐caprolactone)‐based star polymer electrolyte with cross‐linked structures is introduced that robustly cycles against LiNi0.6Mn0.2Co0.2O2 (NMC622) composite cathodes, affording long‐term stability even at higher current densities. Its superior features allow for sufficient suppression of dendritic lithium deposits, as monitored by 7Li solid‐state NMR.
N‐alkyl‐N‐alkyl pyrrolidinium‐based ionic liquids (ILs) are promising candidates as non‐flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)‐based solid polymer ...electrolytes (SPEs), but they present limitations in terms of lithium‐ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium‐ion transport than alkyl‐substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium‐metal polymer batteries.
Ionic liquids (ILs) allow improvement of the ionic conductivity of ternary PEO‐based solid polymer electrolytes. However, the lack of Li‐ion coordination of these plasticizers and the addition of extra ions results in a low Li‐ion conductivity. An oligo(ethylene oxide)‐based IL was synthesized to overcome these limitations and enable additional transport modes, resulting in a high Li‐ion conductivity.
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