The salt-concentrated electrolytes offer superior properties beyond conventional dilute electrolytes yet suffer from high cost and viscosity that hinder their practical applications. A key strategy to address this challenge is to introduce a secondary solvent as a diluent that reduces the salt content while maintaining the local structure of salt-concentrated electrolytes, giving rise to localized high concentration electrolytes (LHCEs). Through a thorough investigation involving ~700 samples, we find that, the dielectric constant of solvent, a widely used parameter for electrolyte design, does not serve as a useful screening criterion for diluents; instead, donor number (DN) is an effective design parameter to achieve LHCE structure, i.e., the primary solvent must have DN > 10 and the diluent must have DN < 10. Correlating DN with solvent solubility leads to a simpler screening rule: Li-salt-insoluble solvents are diluents while Li-salt-soluble solvents become co-solvents. Both DN- and solubility-based design principles can be understood in an atomistic model of LHCE and are applicable to other electrolyte systems.

Na superionic conductor (NASICON)-type Na3(VO)2(PO4)2F (NVOPF) exhibits excellent cycling stability for high-voltage sodium ion batteries. Various strategies have been developed to form ion-exchanged NVOPF which can enhance the ionic and electronic conductivity. However, the underlying ion transport mechanism and complex structural transitions during battery operation remained uninvestigated. In this work, we prepared lithium-exchanged NVOPF (namely NLVOPF) which shows improved ionic conductivity and increased capacity at high discharging rates. Solid-state nuclear magnetic resonance (SSNMR) revealed the distinctive presence of two kinds of Li-exchanged sites in the NLVOPF, which are attributed to the occupied lithium ions at the Na1 and Na2 sites (namely Li1 and Li2, respectively). The Li1 site was metastably replaced in the first cycle, yet the Li2 site participated in ion insertion/extraction in the subsequent cycles. Our characterizations show that the dynamic doping of lithium in NLVOPF could contribute to the improved cycling stability and capacity retention.

Lithium-rich layered oxides (LLOs) that can support both cationic and anionic redox chemistry are promising cathode materials, but they often suffer from significant oxygen evolution when first charged to a high voltage, resulting in a large capacity loss and deteriorated durability in subsequent charge-discharge cycles. We reported a simple method to eliminate the irreversible anionic redox in Li1.2Mn0.54Co0.13Ni0.13O2 via low-potential charge-discharge activation (LOWPA), achieving an ultra-high reversible capacity of 322 mAh g-1 (corresponding to 1141 Wh kg-1) as well as improved cycling durability and rate capability. Combined experimental and theoretical investigations reveal that LOWPA enables a delicate control of the order-to-disorder transformation of the transition metal layers of LLOs, leading to a cation-disordered structure that can support reversible oxygen redox up to 4.8 V by forming a stable ozonic ion (O3-). This LOWPA approach is simple and effective, boosting the development of high-energy-density batteries based on the oxygen-redox chemistry.

The salt-concentrated electrolytes offer superior properties beyond conventional dilute electrolytes yet suffer from high cost and viscosity that hinder their practical applications. A key strategy to address this challenge is to introduce a secondary solvent as a diluent that reduces the salt content while maintaining the local structure of salt-concentrated electrolytes, giving rise to localized high concentration electrolytes (LHCEs). Through a thorough investigation involving ~700 samples, we find that, the dielectric constant of solvent, a widely used parameter for electrolyte design, does not serve as a useful screening criterion for diluents; instead, donor number (DN) is an effective design parameter to achieve LHCE structure, i.e., the primary solvent must have DN > 10 and the diluent must have DN < 10. Correlating DN with solvent solubility leads to a simpler screening rule: Li-salt-insoluble solvents are diluents while Li-salt-soluble solvents become co-solvents. Both DN- and solubility-based design principles can be understood in an atomistic model of LHCE and are applicable to other electrolyte systems.

The unsatisfactory electrochemical performance of Zn metal batteries (ZMBs) caused by uncontrollable Zn dendrite growth and detrimental parasitic reactions has significantly hindered their large‐scale applications. Herein, periodic hemispherical structures with a preferential exposure of Cu (100) crystal plane are designed and obtained using facile photolithography, which is followed by wet etching treatment. An exposed zincophilic Cu (100) crystal plane with low nucleation barriers acts as the preferred deposition site to induce homogeneous Zn deposition. Additionally, the periodic hemispherical structure with an enlarged surface area not only suppresses the Zn dendrite growth by reducing the local current density, but also synergistically buffers the volume expansion during the cycling process. As a result, the as‐prepared faceted Cu hemispherical electrodes achieve ultra‐stable Coulombic efficiency of over 99.9% for 1500 cycles at a current density of 5 mA cm −2 . This work has significant potential for the rational design of dendrite‐free Zn anodes to boost their potential for practical applications.

The solid electrolyte interphase（SEI） with strong mechanical strength and high ion conductivity is highly desired for Li metal batteries, especially for harsh anode-free batteries. Herein, we report a pragmatic approach to the in-situ construction of high-quality SEI by applying synergistic additives of Li NO 3 and ethylene sulfite（ES） in the electrolyte. The obtained SEI exhibits a high average Young’s modulus（9.02GPa） and exchanging current density(4.59 mA cm -2 ), which are 3.0 and 1.2 times as large as those using the sole additive of LiNO 3 , respectively. With this improved SEI, Li-dendrite growth and side reactions are effectively suppressed, leading to an ultra-high Coulombic efficiency（CE） of 99.7% for Li plating and stripping. When applying this improved electrolyte in full cells, it achieves a high capacity retention of 89.7%for over 150 cycles in a LiFePO 4 ||Li battery(～12 mg cm -2 cathode, 50 μm Li) and of 44.5% over 100 cycles in a LiFePO 4 ||Cu anode-free battery.

The solid electrolyte interface (SEI) formed on the anode is one of the key factors that determine the life span of sodium metal batteries (SMBs). However, the continuous evolution of SEI during charging/discharging processes complicates the fundamental understanding of its chemistry and structure. In this work, we studied the underlying mechanisms of the protection effect offered by the SEI derived from sodium difluoro(oxalato)borate (NaDFOB). In situ nuclear magnetic resonance (NMR) shows that the prior reduction of DFOB anion contributes to the SEI formation, and it suppresses the decomposition of carbonate solvents. Depth-profiling x-ray photoelectron spectroscopy and high-resolution solid-state NMR reveal that the DFOB anion is gradually turned into borate and fluoride-rich SEI with cycling. The protection effect of SEI reaches the optimum at 50 cycles, which triples the life span of SMB. The detailed investigations provide valuable guidelines for the SEI engineering.

Salt-concentrated aqueous electrolytes show a wider electrochemical window than conventional aqueous electrolytes, yet still suffer from significant hydrogen evolution reaction (HER) at <1.9 V versus Li+/Li. Introducing organic compounds was reported to alleviate HER, but all reported organic additives are flammable, inevitably compromising the safety property. Here, we report a new all nonflammable-ingredient aqueous electrolyte via hybridizing with nonflammable methylurea. The structurally asymmetric methylurea molecules possessing both donor and acceptor functional groups regulate the hydrogen bonding network, resulting in peculiar nano scale core-shell-like clusters. Such unique solution structure allows localized super-high salt concentration in the electrolyte and suppresses HER at 0.5 V versus Li+/Li, achieving a 4.5 V electrochemical window. Under a harsh testing condition with low electrolyte loading, no excess Li resource, no electrode precoating, and conventional aluminum current collectors, this electrolyte realizes a stable cycling of a rocking-chair NbO2 vertical bar LiMn2O4 full cell (175 Wh kg(-1)) without compromising the safety property.

A simple electrolyte formula of “single salt single solvent” —1 M LiDFOB in ES—enables the stable operation of an NCM622|Li full cell (2.5 mA h cm −2 , N/P = 4) under harsh conditions of high voltage (4.6 V) and wide temperature range (−30 to 60 °C).

The continuous reduction of electrolytes by Li metal leads to a poor lifespan of lithium metal batteries(LMBs). Low Coulombic efficiency(CE) and safety concern due to dendrite growth are the challenging issues for LMB electrolyte design. Novel electrolytes such as highly concentrated electrolytes(HCEs) have been proposed for improving interphase stability. However, this strategy is currently limited for high cost due to the use of a large amount of lithium salts as well as their high viscosity, reduced ion mobility, and poor wettability. In this work, we propose a new type of electrolyte having a moderate concentration. The electrolyte has the advantage of HCEs as the anion is preferentially reduced to form inorganic solidelectrolyte-interphase(SEI). Such optimization has been confirmed through combined spectroscopic and electrochemical characterizations and supported with the first-principle molecular dynamics simulation. We have shown the intrinsic connections between solution structure and their electrochemical stability. The 2.0 M LiDFOB/PC electrolyte, as predicted by our characterizations and simulations, allows stable charge–discharge of LNMO|Li cells at 5C for more than 1500 cycles. The 2.0 M electrolyte generates a dense layer of SEI containing fluoro-oxoborates, Li 3 BO 3 , LiF, Li 2 CO 3 , and some organic species effectively passivating the lithium metal, as confirmed by electron microscopy, X-ray photoelectron spectroscopy,and solid-state nuclear magnetic resonance.

The performance of lithium batteries is heavily governed by the transport of ions within the electrolytes. Commercial liquid electrolytes, however, generally exhibit a low lithium‐ion transference number, causing concentration polarization, side reactions, and deteriorated battery performance. Herein, a novel class of electrolyte additives based on particles of metal–organic framework is proposed to immobilize the anions while allowing efficient transport of lithium ions in the electrolytes. The use of such additives effectively increases the lithium‐ion transference number, enhances the rate capability, and prolongs the cycling life, which provides a facile yet effective strategy toward lithium batteries with dramatically improved performances.

Polyanion-type sodium superionic conductor (NA-SICON) Na3V2(PO4)(2)F (NVOPF) is a promising cathode material for sodium ion batteries (SIBs). However, NVOPF shows relatively low specific capacity and poor long-term performance at high rates. Herein, we report a remarkable improvement of NVOPF cathode material by introducing a surface coating of reduced graphene oxide (RGO). The RGO-coated Na3V2O2(PO4)(2)F cathode (hereafter denoted as NVOPF@RGO) delivers outstanding high-rate capability (93.6 mAh g(-1) at 60 C) and ultralong cycle stability (similar to 87% retention after 10 000 cycles at 50 C). This surface-enhanced material also exhibits excellent full-cell performance when coupled with the Fe1-xS anode, which sustains a 94.3 mAh g(-1) specific capacity after 900 cycles at 20 C. The battery performance and stability of NVOPF@RGO are among the best in the state-of-the-art NASICON-based SIBs. Electrochemical measurements have shown that the coated RGO on NVOPF not only enhances its electric conductivity but also increases the apparent sodium ion diffusivity notably. We confirmed the structural reversibility and revealed the long/short-range structural evolutions of NVOPF@RGO upon electrochemical cycling by multinuclear solid-state nuclear magnetic resonance (ssNMR) combined with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques.

Boron sources in forms of SiB4/FeB/TiB2 were used to react with LiF/LiH under hydrogen atmosphere to investigate their effectiveness for synthesizing LiBH4, a promising hydrogen storage material. Fourier transform infrared (FTIR) study revealed the formation of B-H bond vibrations in these hydrogenated systems, and it demonstrated the generation of LiBH4. When using FeB and TiB2, few amounts of B-H bonds were formed in the hydrogenated samples either reacting with LiH or LiF. When utilizing SiB4, the formation of B-H bonds was promoted for both systems mixing with LiH and LiF. The results imply that a stepwise process of LiBH4-x -> LiBH4 possibly took place during the hydrogenation process. Importantly, SiB4 LiH system exhibited the best hydrogenation performance. At moderate conditions of 250 degrees C and 10 MPa H-2, LiBH4 was successfully synthesized from this system. A facile synthesis pathway, SiB4(s) + 4LiH(s) + 6H(2)(g) -> 4LiBH(4)(s) + Si(s), having a Delta H-r(m) of -65 kJ/mol H-2, was proposed. This study supports that the chemical state of boron in the reactant is an important factor affecting the generation of LiBH4. A hydrogenation reaction between SiB4 and CaH2 or MgH2 may be also applicable for synthesizing Ca(BH4)(2) or Mg(BH4)(2), which are regarded as potential hydrogen storage materials. (C) 2018 Elsevier Ltd. All rights reserved.

Graphene oxides (GOs) are layered carbon materials composed of a mixture of oxygenated functional groups that can react with different molecules. Alkyl diamine molecules (ethylenediamine, butanediamine, or hexanediamine) can insert into the layers of GO and systematically expand its interlayer spacing from 0.762 nm to over 1.030 nm. In this work, we found that CO2 uptake maximizes at the interlayer spacing of 0.860 nm in GOs cross-linked by diamines. We characterized the subtle chemical and compositional differences among samples by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state NMR. In situ 13C NMR was applied at variable temperatures to investigate the adsorption mechanisms of CO2, which revealed both physically and chemically adsorbed CO2 in diamine-cross-linked GO matrices. In particular, we observed the unique state of CO2 that are physically trapped in GO layers with 0.860 nm spacing by van der Waals interactions. This state of CO2 was not observed in GOs ...

A LiBH4–H3BO3 destabilization system shows significantly lower temperature, rapid kinetics, pure hydrogen and high capacity through [BH4]−⋯[OH]− interaction.

A compact and conductive solid-electrolyte interphase formed by NaDFOB enables high performance of sodium metal batteries.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Surface and interfacial chemistry is of fundamental importance in functional nanomaterials applied in catalysis, energy storage and conversion, medicine, and other nanotechnologies. It has been a perpetual challenge for the scientific community to get an accurate and comprehensive picture of the structures, dynamics, and interactions at interfaces. Here, some recent examples in the major disciplines of nanomaterials are selected (e.g., nanoporous materials, battery materials, nanocrystals and quantum dots, supramolecular assemblies, drug-delivery systems, ionomers, and graphite oxides) and it is shown how interfacial chemistry can be addressed through the perspective of solid-state NMR characterization techniques.

Owing to almost unmatched volumetric energy density, Li-based batteries have dominated the portable electronic industry for the past 20 years. Not only will that continue, but they are also now powering plug-in hybrid electric vehicles and zero-emission vehicles. There is impressive progress in the exploration of electrode materials for lithium-based batteries because the electrodes (mainly the cathode) are the limiting factors in terms of overall capacity inside a battery. However, more and more interests have been focused on the electrolytes, which determines the current (power) density, the time stability, the reliability of a battery and the formation of solid electrolyte interface. This review will introduce five types of electrolytes for room temperature Li-based batteries including 1) non-aqueous electrolytes, 2) aqueous solutions, 3) ionic liquids, 4) polymer electrolytes, and 5) hybrid electrolytes. Besides, electrolytes beyond lithium-based systems such as sodium-, magnesium-, calcium-, zinc- and aluminum-based batteries will also be briefly discussed.