Non-nucleophilic Electrolytes Research Articles

Electrolyte Engineering with Carboranes for Next-Generation Mg Batteries.

To realize an energy storage transition beyond Li-ion competitive technologies, earth-abundant elements, such as Mg, are needed. Carborane anions are particularly well-suited to realizing magnesium-ion batteries (MIBs), as their inert and weakly coordinating properties beget excellent electrolyte performance. However, utilizing these materials in actual electrochemical cells has been hampered by the reliance on the Mg2+ salts of the commercially available [HCB11H11]- anion, which is not soluble in more weakly binding solvents apart from the higher glymes. Herein, we demonstrate it is possible to iteratively engineer the [HCB11H11]- anion surface synthetically to address previous solubility issues and yield a highly conductive (up to 7.33 mS cm-1) and electrochemically stable (up to +4.2 V vs Mg2+/0) magnesium electrolyte that surpasses the state of the art. This novel non-nucleophilic electrolyte exhibits highly dissociative behavior regardless of concentration and is tolerant of prolonged periods of cycling in symmetric cells at high current densities (up to 2.0 mA cm-2, 400 h). The hydrocarbon functionalized carborane electrolyte presented here demonstrates >96% Coulombic efficiency when paired with a Mo6S8 cathode. This approach realizes a needed candidate to discover next-generation cathode materials that can enable the design of practical and commercially viable Mg batteries.

Toward High-Performance Mg/S Batteries with M4-Assisted Mg(AlCl4 )2 /PYR14TFSI/DME Electrolyte and MoS2 @CMK/S Cathode.

Rechargeable magnesium batteries (RMBs) are considered as one of the most promising candidates for next-generation batteries. However, the popularization of RMBs is seriously plagued due to the lack of suitable non-nucleophilic electrolytes and the passivation of Mg anode. Herein, a novel non-nucleophilic electrolyte is developed by introducing (s)-1-methoxy-2-propylamine (M4) into themagnesium aluminum chloride complex (MACC)-like electrolyte. The as-synthesizes Mg(AlCl4 )2 -IL-DME-M4 electrolyte enables robust reversible cycling of Mg plating/stripping with low overpotential, high anodic stability, and ionic conductivity (8.56mScm-1 ). These features should be mainly attributed to the in situ formation of an MgF2 containing Mg2+ -conducting interphase, which dramatically suppresses the passivation and parasitic reaction of Mg anode with electrolyte. Remarkably, the Mg/S batteries assemble with as-synthesize electrolyte and a new type MoS2 @CMK/S cathode deliver unprecedented electrochemical performance. Specifically, the Mg/S battery exhibited the highest reversible capacity up to 1210mAhg-1 at 0.1C, excellent rate capability and satisfactory long-term cycling stability with a reversible capacity of 370mAhg-1 (coulombic efficiency of ≈100%) at 1.0C for 600 cycles. The study findings provide a novel strategy and inspiration for designing efficient non-nucleophilic Mg electrolyte and suitable sulfur-host materials for practical Mg/S battery applications.

Non-Nucleophilic Electrolytes with Non-Fluorinated Hybrid Solvents for Long-Life Magnesium Metal Batteries

Growing energy demands and the widespread of renewable power sources call for high-energy storage systems beyond lithium-ion batteries (LIBs). Rechargeable magnesium batteries (RMBs) are high-energy, safer, and more cost-effective alternatives to LIBs and lithium metal batteries (LMBs) thanks to Mg’s high volumetric capacity (3832 mAh cm-3)1, low theoretical potential (-2.37 V vs SHE)2 and earth-abundance3. Non-nucleophilic and non-fluorinated compounds are the most important class of materials to enable sustainable rechargeable magnesium (Mg) batteries, however, they suffer from poor stability due to the formation of unstable solid-electrolyte-interphase (SEI).4 Here, we design a hybrid-solvent electrolyte by dispersing a non-nucleophilic solution in a non-fluorinated weakly-coordinating solvent to prevent parasitic reactions and form stable SEI. This strategy significantly improved the cycle life of the Mg anode from 24 to 4000 hours (in Mg-Mg symmetric cells) and realized a stable cycle life of Mg-Mo6S8 full cells for more than 2300 hours with an average CE of 99.96%. The non-fluorinated weakly-coordinating solvent suppressed uneven Mg growth and contributed to the formation of polymeric SEI, which filled the cracks of pristine SEI, preventing side reactions and passivation. This strategy revealed the critical role of weakly-coordinating solvents in stabilizing Mg anode for reversible Mg batteries.

A non-nucleophilic electrolyte based on all-inorganic salts with conditioning-free characteristic for rechargeable magnesium batteries

Conditioning-free electrolytes with high reversibility of Mg plating/stripping are of vital importance for the commercialization of the superior rechargeable magnesium batteries (RMBs). In the present work, a non-nucleophilic electrolyte (denoted as MLCH) based on all-inorganic salts of MgCl2, LiCl and CrCl3 for RMBs is prepared by a straightforward one-step reaction. As a result, the MLCH electrolyte shows the noticeable performance of high ionic conductivity (3.40 mS cm−1), low overpotential (∼46 mV vs Mg/Mg2+), high Coulombic efficiency (∼93%), high anodic stability (SS, ∼2.56 V vs Mg/Mg2+) and long-term (more than 500 h) cycling stability, especially the conditioning-free characteristic. The main equilibrium species in the MLCH electrolyte are confirmed to be the tetracoordinated anions of [LiCl2(THF)2]− and solvated dimers of [Mg2(µ-Cl)3(THF)6]+. The addition of LiCl can assist the dissolution of MgCl2 and activation of the electrode/electrolyte interface, resulting in a superior Mg plating/stripping efficiency. The synergistic effect of LiCl, CrCl3, a small amount of HpMS and the absence of polymerization THF enable the conditioning-free characteristic of the MLCH electrolyte. Moreover, the MLCH electrolyte exhibits decent compatibility with the cathodic materials of CuS. The Mg/CuS full cell using the MLCH electrolyte presents a discharge specific capacity of 215 mAh g−1 at 0.1 C and the capacity can retain ∼72% after 40 cycles. Notably, the MLCH electrolyte has other superiorities such as the broad sources of materials, low-cost and easy-preparation, leading to the potential prospect of commercial application.

Organic Non-Nucleophilic Electrolyte Resists Carbonation during Selective CO2 Electroreduction

The spontaneous reaction of CO2 with water and hydroxide to form (bi)carbonates in alkaline aqueous electrolytes compromises the energy and carbon efficiency of CO2 electrolyzers. We hypothesized that electrolyte carbonation could be mitigated by operating the reaction in an aprotic solvent with low water content, while also employing an exogenous non-nucleophilic acid as the proton donor to prevent parasitic capture of CO2 by its conjugate base. However, it is unclear whether such an electrolyte design could simultaneously engender high CO2 reduction selectivity and low electrolyte carbonation. We herein report selective CO2 electroreduction with low carbonate formation on a polycrystalline Au catalyst using dimethyl sulfoxide as the solvent and acetic acid/acetate as the proton-donating medium. CO2 is reduced to CO with over 90% faradaic efficiency at potentials relative to the reversible hydrogen electrode that are comparable to those in neutral aqueous electrolytes. 1H and 13C NMR studies demonstrate that only millimolar concentrations of bicarbonates are reversibly formed, that the proton activity of the medium is largely unaffected by exposure to CO2, and that low carbonation is maintained upon addition of 1 M water. This work demonstrates that electrolyte carbonation can be attenuated and decoupled from efficient CO2 reduction in an aprotic solvent, offering new electrolyte design principles for low-temperature CO2 electroreduction systems.

Advances in Cathodes for High-Performance Magnesium-Sulfur Batteries: A Critical Review

Large-scale energy storage with high performance and at a reasonable cost are prerequisites for promoting clean energy utilization. With a high theoretical energy density of 1722 Wh·kg−2, high element abundance (e.g., Mg of 23,000 ppm, S of 950 ppm on earth), and low theoretical cost, Mg-S batteries offer considerable potential as candidates for electrical energy storage. However, due to the intrinsic complex reaction chemistry of sulfur cathodes and metal anodes, such as slow diffusion of the divalent ion, the shuttle of soluble polysulfide, and irreversible deposition of Mg ions on metal electrodes, Mg-S batteries still need further optimization to meet requirements for practical applications. In addition to stabilizing metal anodes, developing a suitable sulfur cathode is desperately needed. This review summarizes recent research progress in sulfur cathodes, interlayers, and non-nucleophilic electrolytes, highlighting the main challenges and corresponding strategies for electrode material designs. Notably, we emphasize a fundamental understanding of the structure-composition relationship. Furthermore, state-of-the-art characterization techniques are described that help reveal the pertinent electrochemical mechanisms whereby Mg-S cells function. Finally, possible research directions are discussed.

Bifunctional non-nucleophilic electrolyte enables long-life magnesium batteries via elimination of passive film on Mg anode

Magnesium batteries are one of the ideal candidates for next-generation battery systems with high energy density and safety. However, the development of compatible non-nucleophilic electrolytes and the passivation of the Mg anode are the primary obstacles that impede their development. Here, a non-nucleophilic electrolyte is proposed through in-situ reactions between AlCl3 + InCl3/TEG (AI-E) electrolyte and Mg anode, which kills two birds with one stone that magnesium salts with the structures of [MgCl·TEG]+ and [MgCl·2TEG]+ are generated and the passive film on Mg anode is converted into solid electrolyte interphase (SEI). Compared with the Mg(TFSI)2 electrolyte, the polarization of the Mg anode in the AI-E electrolyte decreases from 2.0 V to 0.08 V for 400 cycles, and the Mg/S battery with the AI-E electrolyte reaches an improved discharge voltage plateau of 1.12 V for 50 cycles. This work expects to provide a one-step method for magnesium salt synthesis and Mg anode passivation.

Non-nucleophilic electrolyte with non-fluorinated hybrid solvents for long-life magnesium metal batteries

Non-nucleophilic and non-fluorinated compounds are the most important class of solvents to enable sustainable rechargeable magnesium batteries but suffer from poor stability due to the formation of an unstable solid–electrolyte-interphase.

Boosting the cycling stability of rechargeable magnesium batteries by regulating the compatibility between nanostructural metal sulfide cathodes and non-nucleophilic electrolytes

Boosting the cycling stability of rechargeable magnesium batteries by regulating the compatibility between nanostructural metal sulfide cathodes and non-nucleophilic electrolytes

Facile and Economic Synthesis of Robust Non-Nucleophilic Electrolyte for High-Performance Rechargeable Magnesium Batteries.

A cost-effective and highly efficient electrolyte with a wide electrochemical window, high reversibility of Mg plating/stripping, non-/low-corrosivity, good compatibility with cathode materials, and tolerance of trace water and impurity is crucial for the commercialization of rechargeable magnesium batteries. In this work, a novel boron-centered non-nucleophilic electrolyte that meets all the above requirements is prepared via a facile and economic approach from the raw materials B(TFE)3/MgCl2/CrCl3/Mg (BMCM). The as-prepared BMCM electrolyte is mainly composed of tetracoordinated anions [B(TFE)4]- and solvated cations [Mg2(μ-Cl)2(DME)4]2+. The BMCM electrolyte demonstrates attractive electrochemical performance, with a low overpotential (∼139 mV), a high Coulombic efficiency (∼97%), a high anodic stability (∼3.5 V vs Mg/Mg2+), and a long-term (more than 500 h) cycling stability. Moreover, BMCM shows good compatibility with the CuS cathode material. The CuS|BMCM|Mg full cell delivers a discharge specific capacity of 231 mAh g-1 (at 56 mA g-1), which can retain ∼88% even after 100 cycles. Importantly, the BMCM electrolyte is cost-effective and tolerant of trace impurity and water, which has great potential to be commercialized. This work is expected to promote the development of practical rechargeable magnesium batteries.

Anti-Heterogeneous catalysis revealed by the amidomagnesium halide chemistry in lithium sulfur batteries

The simultaneous engineering of sulfur cathode and Li anode is critical for electrolyte-starved high-energy–density Li-S batteries. Herein, we challenge the conventional wisdom of heterogeneous and homogeneous catalyses in Li-S batteries, the concept of anti-heterogeneous catalysis is proposed to synchronously realize effective LiPS trapping/conversion and protection of Li anode through employing a small amount of non-nucleophilic electrolyte additive of an amidomagnesium halide, hexamethyldisilazide magnesium chloride (HMC). Regulated by the amidomagnesium halide chemistry, over 1000 h of cycling is realized in Li/Li symmetric cells, revealing superb compatibility of the HMC-incorporated electrolyte with lithium metal. Meanwhile, via elevating the dissociation free-energy barrier of Li+ in LiPS, the liquid HMC catalysts significantly decrease the solubility of lithium ploysulfides and promote the multistep conversion of sulfur electrochemistry, which enable a quasi-solid-state reaction and minimal shuttle effect. Practically, a high energy density of 423 Wh kg−1 with decent cycling stability is achieved in electrolyte-starved pouch cells.

Non-passivating Anion Adsorption Enables Reversible Magnesium Redox in Simple Non-nucleophilic Electrolytes

Non-passivating Anion Adsorption Enables Reversible Magnesium Redox in Simple Non-nucleophilic Electrolytes

Sulfurized-Pyrolyzed Polyacrylonitrile Cathode for Magnesium-Sulfur Batteries Containing Mg2+/Li+ Hybrid Electrolytes

Magnesium-sulfur (Mg-S) batteries are an alternative electrochemical energy-storage system with higher safety as well as large theoretical volumetric energy density than lithium-sulfur (Li-S) batteries. Herein, we further research sulfurized-pyrolyzed polyacrylonitrile (S@pPAN) composite containing 47.3 wt% sulfur as cathode of Mg-S batteries with nucleophilic (PhMgCl)2-AlCl3 + LiCl/THF electrolyte. Except a significant restraint of the reaction between the nucleophilic electrolyte and the electrophilic sulfur, polysulfide dissolution and shuttle are effectively suppressed. Electrochemical performance is further enhanced using MBA-(MgCl2)2-(AlCl3)2 + LiCl/THF non-nucleophilic electrolyte with 677.9 mAh g−1 specific capacity and 75.9% cycling stability after 85 cycles at 0.1C. More effective CEI layers formed on the cathode with a lower electrode/electrolyte internal resistance play a key effect on the enhanced electrochemical performance. This work will attract extensive study on Mg-S batteries containing easily prepared electrolytes with a combination of S@pPAN cathode.

Progress of Non-Nucleophilic Electrolytes for Magnesium/Sulfur Battery

Progress of Non-Nucleophilic Electrolytes for Magnesium/Sulfur Battery

Non-Nucleophilic Electrolyte Based on Ionic Liquid and Magnesium Bis(diisopropyl)amide for Rechargeable Magnesium-Ion Batteries

A non-nucleophilic electrolyte for rechargeable Mg-ion batteries is developed by the reaction of magnesium bis(diisopropyl)amide and 1-ethyl-3-methylimidazolium tetrachloroaluminate ionic liquid in...

Stripping and Plating a Magnesium Metal Anode in Bromide-Based Non-Nucleophilic Electrolytes.

A non-nucleophilic Hauser base hexamethyldisilazide (HMDS) magnesium electrolyte possesses inherent properties required for a magnesium-sulfur battery. However, the development of full cell batteries using HMDSCl-based electrolytes is still hampered by a low coulombic efficiency. A new electrolyte formulation of non-nucleophilic HMDS magnesium containing bromide as a halide instead of chloride was obtained through a simple and straightforward synthesis route. The electrochemistry of magnesium was investigated through plating and stripping in three different HMDSBr-based electrolytes: Mg(HMDS)Br, Mg(HMDS)Br-BEt3 , and Mg(HMDS)Br-AlEt3 dissolved in tetrahydrofuran. The different magnesium species present in the electrolytes were determined using NMR. Weak electron-withdrawing Lewis acids, BEt3 and AlEt3 were used intentionally and their impact was investigated. Contrary to expectation, the substitution of chloride by bromide does not drastically narrow the electrochemical stability window. HMDSBr-based electrolytes demonstrated long-term (1000 cycles) stable reversibility and highly efficient (≈99 %) magnesium plating/tripping without a high ratio of bromide compared with the MgHMDSCl-based electrolytes. The aprotic electrolyte shows comparatively high anodic stability (≈2.4 V vs. Mg/Mg2+ ) and high ionic conductivity of 1.16 mS cm-1 at room temperature. Plating of magnesium with low overpotential (<188 mV) revealed a morphology dependence on the electrolyte type with a shiny metallic homogenous layer, suggesting a rational balance between the nucleation and growth process in HMDSBr-based electrolytes.

Highly Efficient Non-Nucleophilic Mg(CF3SO3)2-Based Electrolyte for High-Power Mg/S Battery.

The application of high-energy Mg/S batteries was obstructed by the insufficiency of low-cost and non-nucleophilic electrolyte. In this work, a non-nucleophilic electrolyte was prepared by facilely dissolving Mg(CF3SO3)2, MgCl2, and AlCl3 in 1,2-dimethoxyethane (DME). The equilibrium species of the MTB electrolyte mainly comprise [Mg2(μ-Cl)2(DME)4]2+ and [(CF3SO3)AlCl3]-, which are generated by dehalodimerization reaction and Lewis acid-base reaction, respectively. The electrolyte exhibits a highly efficient reversible Mg deposition/dissolution, low overpotential of around 250 mV, and good oxidative stability up to 3.5 V after conditioning. The conditioning process that the active [Mg2(μ-Cl)2(DME)4]2+ species transforms into [Mg3(μ3-Cl)(μ2-Cl)2(DME)7]3+ was demonstrated, owing to the irreversible deposition of Al3+ on Mg foil. More importantly, this electrolyte exhibited good compatibility and kinetics for reversible Mg/MgSx redox, resulting in a high specific capacity of 866 mAh g-1 at 200 mA g-1 and high power density of 550 W kg-1. This work offers a new direction for low-cost, non-nucleophilic electrolyte and paves the way to explore high-power Mg/S batteries.

Vat Orange 11—Based Organic Cathode Material for High Rate Rechargeable Magnesium Battery

Mg-ion batteries are of immense interest owing to their dendrite free chemistry, low cost and high energy density and often comparable to the existing Li-ion batteries. Organic molecules as electrodes, are well-explored in alkali metal ion batteries as they are less expensive, environment friendly and amenable to redox potential-tuning. But these molecules are rarely used for secondary Mg-ion batteries and they continue to attract attention. In the present studies, an organic dye, vat orange 11, is explored as a cathode material for non-aqueous secondary Mg-ion battery in different electrolytes. The electrolyte with salt-controlled dissolution approach turns out to be very good in terms of capacity recovery with long cycle life. It shows an excellent rate performance up to a discharge current of 4000 mA g−1 with high cycling stability (1000 cycles at 500 mA g−1 current density). Further, high capacity and high rate performance are observed using a non-nucleophilic electrolyte based on an ionic liquid. The possible mechanism of Mg2+ uptake is studied using ex situ FTIR spectroscopy that shows a transformation between carbonyl (–C=O) and enolate (–C=O−) functional groups during charge-discharge cycles. The present studies initiate the use of vat-based dye molecules in rechargeable Mg-ion batteries.

(Invited) Magnesium Organic Batteries

Magnesium insertion cathodes are predominantly based on chalcogenide materials and possess low energy density due to high molecular weight and low operational voltage. Redox active organic material can be considered as an alternative material, which due to open structure caused by relatively weak intermolecular forces possess much higher gravimetrical energy density. Although, their drawback can be low volumetric energy density since polymers have low density, latter can be compensated with high volumetric density of Mg metal. Redox active organic molecules were considered as a cathode for rechargeable Mg batteries more than decades ago, however their practical application in two electrode cell has been demonstrated with discovery of non-nucleophilic electrolytes which enable reversible stripping and deposition of metallic magnesium. Several different redox active organic materials show potential application, but the most promising direction is use of conjugated carbonyls since predicted theoretical energy density can exceed 700 Wh/kg and batteries show working potential of 2V. Reduction of conjugated carbonyl compounds occurs through the reversible reduction of carbonyl bond as it has been demonstrated by ATR-IR operando measurements. In this presentation, an overview of recent achievements on the field of magnesium organic batteries will be discussed with a focus on remaining problems that has to be solved in the future. Acknowledgement: This work is supported HONDA R&D Europe and by the Slovenian Research Agency (research core funding No. P2-0393 and research project J2-8167).

Electrochemical performance and redox mechanism of naphthalene-hydrazine diimide polymer as a cathode in magnesium battery

A magnesium (Mg) battery in the combination with the redox active polymers possesses attractive electrochemical properties as a future battery technology. This concept has been demonstrated by using quinone based polymers and the non-nucleophilic electrolytes, while polyimides were rarely investigated. In this work, a naphthalene-hydrazine diimide polymer (NP) has been tested as a cathode material for Mg organic battery in two different electrolytes. Average discharge voltage of the Mg-NP battery is 1.70 V with Coulombic efficiency above 99% in the TEGDME/DOL based electrolyte. The electrochemical mechanism was studied by in operando ATR IR spectroscopy and confirmed by DFT calculation of the IR spectra. We confirmed redox activity of carbonyl moieties, which undergo reversible reduction to enolate anion. Moreover, in operando IR spectroscopy shows charge delocalization in the reduced form since none of the bonds has pure single/double bond character.