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Aqueous electrolytes were once the rule for the battery industry. Until the advent of lithium ion batteries, a majority of commercially relevant batteries utilized water as the solvent for ion exchange. The development of the intercalation‐based lithium ion battery upended the industrial aqueous electrolyte paradigm: the high energy density of the lithium‐ion battery was revolutionary but required the use of organic electrolytes capable of passivating strongly redox active electrodes. With the safety of organic electrolytes becoming an issue in the early 1990s, a small community re‐examined aqueous electrolytes for lithium ion batteries. The first such audacious attempt was by Dahn et al., who conceptualized an aqueous lithium‐ion battery chemistry based on electrode materials suitable for the narrow electrochemical stability window of water, sacrificing energy density and cycle life for safety and low cost. The concept of an aqueous lithium‐ion battery was revived in the mid‐2010s with “highly concentrated” electrolytes, expanding the electrochemical stability window of water to regions comparable with nonaqueous electrolytes. Since then, significant efforts have been made around the world, aiming to understand the nature of the interfacial stability in those high‐concentration electrolytes as well as to further make the system viable for practical batteries. This review summarizes these efforts in this emerging frontier of new battery chemistries.

Aqueous rechargeable zinc metal batteries promise attractive advantages including safety, high volumetric energy density, and low cost; however, such benefits cannot be unlocked unless Zn reversibility meets stringent commercial viability. Herein, we report remarkable improvements on Zn reversibility in aqueous electrolytes when phosphonium-based cations are used to reshape interfacial structures and interphasial chemistries, particularly when their ligands contain an ether linkage. This novel aqueous electrolyte supports unprecedented Zn reversibility by showing dendrite-free Zn plating/stripping for over 6400 h at 0.5 mA cm-2 , or over 280 h at 2.5 mA cm-2 , with coulombic efficiency above 99 % even with 20 % Zn utilization per cycle. Excellent full cell performance is demonstrated with Na2 V6 O16 ⋅1.63 H2 O cathode, which cycles for 2000 times at 300 mA g-1 . The microscopic characterization and modeling identify the mechanism of unique interphase chemistry from phosphonium and its functionalities as the key factors responsible for dictating reversible Zn chemistry.

Widespread commercial adoption of polymer electrolytes for lithium-ion batteries has been hindered by subpar transport properties, namely, ionic conductivities of

Polymerization via ultraviolet irradiation of LiTFSI21mH2O + PDA liquid mixtures turned most of these liquids into gels or solids. Here, LiTFSI21mH2O denotes a 21 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide, and PDA stands for a monomer of poly(ethylene glycol) diacrylate of Mn 575. Systematic thermoconductometric measurement on these electrolytes, both before and after the polymerization, showed the gel electrolytes to be considerably more conductive than their precursor liquid mixtures, especially at lower temperatures. A parallel measurement of glass transition temperature, θ g, revealed in these gel electrolytes a unique double glass transition enveloping two sub-transitions each with its own θ g’s. These and a number of other related experimental observations can be consistently and clearly explained based on the existence of a solution and a polymer substructure in the polymerized electrolytes, and on these substructures becoming codominant in the gels. The exceptional conductivity in these gel electrolytes points to a promising direction to formulating a polymer-supported aqueous electrolyte with a set of desirable physical traits and an uncompromising conductivity.

A thermoconductometric method, with a uniquely designed sample cell and an in situ polymerization procedure, was applied to a polymer-supported aqueous electrolyte of wPDA + (1−w)LiTFSI21mH2O, where w is in mass fraction, PDA stands for a monomer of poly(ethylene glycol) diacrylate of Mn 575, and LiTFSI21mH2O denotes a 21 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide. The thermoconductometry curves of temperature differential, Δθ, and conductivity, κ, were collected for these samples in the w range of (0, 0.5) and θ range of (−70, 60) °C. The Δθ curves yielded a partial phase diagram revealing a high degree of compatibility between PDA and LiTFSI21mH2O, and the κ curves formed for the unpolymerized and polymerized electrolytes a pair of data sets which were fitted to yield a pair of κ(w, θ) functions for the definition of a conductivity loss function upon polymerization. This function showed that a significant portion of the conductivity was retained upon polymerization in a large part of the (w, θ) space, where a safe and robust electrolyte with a decent conductivity could be formulated. Molecular and thermodynamic considerations were applied to correlate and discuss the results of the Δθ and κ measurements.

Recent success in extending the electrochemical stability window of aqueous electrolytes to 3.0 V by using 21 mol kg-1 “water-in-salt” (WiS) has raised a high expectation for developing safe aqueous Li-ion batteries. However, the most compatible Li4Ti5O12 anodes still cannot use WiS electrolyte due to the cathodic limit (1.9 V vs. Li/Li+). Herein, a UV-curable hydrophilic polymer is introduced to further extend the cathodic limit of WiS electrolytes and replace the separator. In addition, a localized strongly basic solid polymer electrolyte (SPE) layer is coated on the anode to promote the formation of an LiF-rich SEI. The synthetic impacts of UV-crosslinking and local alkaline SPE on the anodes extend the electrochemical stability window of the solid-state aqueous polymer electrolyte to ∼3.86 V even at a reduced salt concentration of 12 mol kg−1. It enables a separator-free LiMn2O4//Li4Ti5O12 aqueous full cell with a practical capacity ratio (P/N = 1.14) of the cathode and anode to deliver a steady energy density of 151 W h kg−1 at 0.5C with an initial Coulombic efficiency of 90.50% and cycled for over 600 cycles with an average Coulombic efficiency of 99.97%, which has never been reported before for an aqueous LiMn2O4//Li4Ti5O12 full cell. This flexible and long-duration aqueous Li-ion battery with hydrogel WiSE can be widely used as a power source in wearable devices and electrical transportations where both energy density and battery safety are of high priority. An ultra-thick LTO electrode with UV-curable polymer electrolyte as the binder is demonstrated as a solid state battery electrode. And a high-voltage (7.4 V) solid-state bipolar cell is assembled with a solid-state UV-curable polymer as the electrolyte.

While the solid-electrolyte-interphase (SEI) originating from carbonate-based electrolytes has been extensively studied due to the success of Li-ion batteries, significantly less is known about the SEI formed in ether-based electrolytes, which have become increasingly important for many “beyond-Li ion” batteries, including lithium-sulfur and other lithium metal battery systems. Li dendrite growth and poor cycling efficiencies related to high rate and/or high capacity cycling of lithium are two of the primary factors limiting practical application of Li metal anodes. Similar to graphite in Li-ion batteries, these behaviors are inextricably linked to the mechanism for SEI formation, the resulting interphase chemistry, and the film stability during cycling—all of which require further understanding. Employing both computational and experimental means in this effort, we investigated the reduction chemistry of dimethoxyethane (DME) and 1,3-dioxolane (DOL) on the surface of metallic lithium. We determined that ether-based SEIs are layer-structured, with an outer organic/polymeric layer consisting of lithium oligoethoxides with C-C-O or O-C-O linkages and an inner layer of simple inorganic oxides (Li2O). Remarkably, although Li+ is preferentially solvated by DME, it is the cyclic DOL that primarily contributes to the interphase chemistry. This selective electrochemical reduction of ether solvents is corroborated by precise calculation of transition state structures and energies, providing a valuable guide for future design and manipulation of Li anode interphasial chemistries.

Extensive efforts have been made to seek new battery chemistries based on multivalent working ions, with the aim to replace the mature lithium-ion batteries. These efforts were initially driven by the pursuit of higher capacity/energy, better safety and lower cost, and more recently have significantly intensified with the increasing concerns over the climate change, the limited resources of Co and Ni, and the anxieties over geopolitical as well as ethical risks of the corresponding supply chain. But how far are we from a practical multivalent battery? This talk rigorously examines the achievements made in MV batteries as reported in the current literature, while attempting to explore a pathway through the fog-of-war ahead of us.

The investigation of ion-solvent interaction in electrolytes is crucial for basic understanding of ion transport through the bulk electrolyte as well as interphase formation processes on both electrodes, which dictate performances of lithium ion batteries (LIBs). In this report, nuclear magnetic resonance (NMR) was used to study the solvation behaviors of two typical lithium salts (lithium hexafluorophosphate, or LiPF6, and lithium tetrafluoroborate, or LiBF4) dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) mixtures. With increasing salt concentration and DMC percentage in both systems, 19F NMR experiences an upfield shift along with decreasing J 31 P − 19 F and J 11 B − 19 F , which evidence the stronger interaction between the Li+ and F− in an environment with diminishing presence of high dielectric medium. The quadrupolar relaxation of 11B dominates the 19F relaxation mechanism and demonstrates that LiBF4 mainly exists as ion pairs in solution either at high salt concentration or in a medium of low polarity. 7Li, 19F, 1H NMR diffusion measurements were conducted to characterize the relative mobility of cation, anion and solvent molecules, the results of which support the conclusion above. Salt concentration and solution polarity have a much stronger effect on cation-anion aggregation and solvation in the LiBF4 system than in the LiPF6 system.

Magnesium-based batteries possess potential advantages over their lithium counterparts. However, reversible Mg chemistry requires a thermodynamically stable electrolyte at low potential, which is usually achieved with corrosive components and at the expense of stability against oxidation. In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg2+ cannot penetrate such interphases. Here, we engineer an artificial Mg2+-conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/V2O5 full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.

Combining theoretical and experimental approaches, we investigate the solvation properties of Li+ ions in a series of ether solvents (dimethoxyethane, diglyme, triglyme, tetraglyme, and 15-crown-5) and their subsequent effects on the solid-state lithium–sulfur reactions in subnano confinement. The ab initio and classical molecular dynamics (MD) simulations predict Li+ ion solvation structures within ether solvents in excellent agreement with experimental evidence from electrospray ionization-mass spectroscopy. An excellent correlation is also established between the Li+-solvation binding energies from the ab initio MD simulations and the lithiation overpotentials obtained from galvanostatic intermittent titration techniques (GITT). These findings convincingly indicate that a stronger solvation binding energy imposes a higher lithiation overpotential of sulfur in subnano confinement. The mechanistic understanding achieved at the electronic and atomistic level of how Li+-solvation dictates its electrochemic...

Electroactive interfaces distinguish electrochemistry from chemistry and enable electrochemical energy devices like batteries, fuel cells, and electric double layer capacitors. In batteries, electrolytes should be either thermodynamically stable at the electrode interfaces or kinetically stable by forming an electronically insulating but ionically conducting interphase. In addition to a traditional optimization of electrolytes by adding cosolvents and sacrificial additives to preferentially reduce or oxidize at the electrode surfaces, knowledge of the local electrolyte composition and structure within the double layer as a function of voltage constitutes the basis of manipulating an interphase and expanding the operating windows of electrochemical devices. In this work, we focus on how the molecular-scale insight into the solvent and ion partitioning in the electrolyte double layer as a function of applied potential could predict changes in electrolyte stability and its initial oxidation and reduction reactions. In molecular dynamics (MD) simulations, highly concentrated lithium aqueous and nonaqueous electrolytes were found to exclude the solvent molecules from directly interacting with the positive electrode surface, which provides an additional mechanism for extending the electrolyte oxidation stability in addition to the well-established simple elimination of "free" solvent at high salt concentrations. We demonstrate that depending on their chemical structures, the anions could be designed to preferentially adsorb or desorb from the positive electrode with increasing electrode potential. This provides additional leverage to dictate the order of anion oxidation and to effectively select a sacrificial anion for decomposition. The opposite electrosorption behaviors of bis(trifluoromethane)sulfonimide (TFSI) and trifluoromethanesulfonate (OTF) as predicted by MD simulation in highly concentrated aqueous electrolytes were confirmed by surface enhanced infrared spectroscopy. The proton transfer (H-transfer) reactions between solvent molecules on the cathode surface coupled with solvent oxidation were found to be ubiquitous for common Li-ion electrolyte components and dependent on the local molecular environment. Quantum chemistry (QC) calculations on the representative clusters showed that the majority of solvents such as carbonates, phosphates, sulfones, and ethers have significantly lower oxidation potential when oxidation is coupled with H-transfer, while without H-transfer their oxidation potentials reside well beyond battery operating potentials. Thus, screening of the solvent oxidation limits without considering H-transfer reactions is unlikely to be relevant, except for solvents containing unsaturated functionalities (such as C═C) that oxidize without H-transfer. On the anode, the F-transfer reaction and LiF formation during anion and fluorinated solvent reduction could be enhanced or diminished depending on salt and solvent partitioning in the double layer, again giving an additional tool to manipulate the order of reductive decompositions and interphase chemistry. Combined with experimental efforts, modeling results highlight the promise of interphasial compositional control by either bringing the desired components closer to the electrode surface to facilitate redox reaction or expelling them so that they are kinetically shielded from the potential of the electrode.

Using molecular dynamics simulations, small-angle neutron scattering, and a variety of spectroscopic techniques, we evaluated the ion solvation and transport behaviors in aqueous electrolytes containing bis(trifluoromethanesulfonyl)imide. We discovered that, at high salt concentrations (from 10 to 21 mol/kg), a disproportion of cation solvation occurs, leading to a liquid structure of heterogeneous domains with a characteristic length scale of 1 to 2 nm. This unusual nano-heterogeneity effectively decouples cations from the Coulombic traps of anions and provides a 3D percolating lithium-water network, via which 40% of the lithium cations are liberated for fast ion transport even in concentration ranges traditionally considered too viscous. Due to such percolation networks, superconcentrated aqueous electrolytes are characterized by a high lithium-transference number (0.73), which is key to supporting an assortment of battery chemistries at high rate. The in-depth understanding of this transport mechanism establishes guiding principles to the tailored design of future superconcentrated electrolyte systems.

Summary Although recent efforts have expanded the stability window of aqueous electrolytes from 1.23 V to >3 V, intrinsically safe aqueous batteries still deliver lower energy densities (200 Wh/kg) compared with state-of-the-art Li-ion batteries (∼400 Wh/kg). The essential origin for this gap comes from their cathodic stability limit, excluding the use of the most ideal anode materials (graphite, Li metal). Here, we resolved this "cathodic challenge" by adopting an "inhomogeneous additive" approach, in which a fluorinated additive immiscible with aqueous electrolyte can be applied on anode surfaces as an interphase precursor coating. The strong hydrophobicity of the precursor minimizes the competitive water reduction during interphase formation, while its own reductive decomposition forms a unique composite interphase consisting of both organic and inorganic fluorides. Such effective protection allows these high-capacity/low-potential anode materials to couple with different cathode materials, leading to 4.0 V aqueous Li-ion batteries with high efficiency and reversibility.

A super-concentrated aqueous electrolyte, “water-in-bisalt (WiBS)”, consisting of 21 m lithium bis(trifluoromethanesulfonyl)imide and 7 m lithium trifluoromethanesulfonate on the most concentrated end, was measured for its electrolytic conductivity κ and glass transition temperature Tg in wide ranges of salt concentration m and temperature θ, with Tg as an indicator for the electrolyte viscosity. The measured κ–(m, θ) data in its entirety was fitted with an extended Casteel–Amis equation for an accurate functional representation, and the κ–θ data for the most concentrated electrolytes were fitted with the Vogel–Fulcher–Tammann equation for an evaluation of the activation energy Ea and vanishing mobility temperature T0. The resultant values of κ and T0 are compared and correlated with Tg, and the possibility of the formation of a water–salt liquid structure under these super-concentrated environments is discussed.

Sodium ion batteries are on the cusp of being a commercially available technology. Compared to lithium ion batteries, sodium ion batteries can potentially offer an attractive dollar-per-kilowatt-hour value, though at the penalty of reduced energy density. As a materials system, sodium ion batteries present a unique opportunity to apply lessons learned in the study of electrolytes for lithium ion batteries; specifically, the behavior of the sodium ion in an organic carbonate solution and the relationship of ion solvation with electrode surface passivation. In this work the Li+ and Na+-based solvates were characterized using electrospray mass spectrometry, infrared and Raman spectroscopy, 17O, 23Na and pulse field gradient double-stimulated-echo pulse sequence nuclear magnetic resonance (NMR), and conductivity measurements. Spectroscopic evidence demonstrate that the Li+ and Na+ cations share a number of similar ion–solvent interaction trends, such as a preference in the gas and liquid phase for a solvation shell rich in cyclic carbonates over linear carbonates and fluorinated carbonates. However, quite different IR spectra due to the PF6− anion interactions with the Na+ and Li+ cations were observed and were rationalized with the help of density functional theory (DFT) calculations that were also used to examine the relative free energies of solvates using cluster – continuum models. Ion–solvent distances for Na+ were longer than Li+, and Na+ had a greater tendency towards forming contact pairs compared to Li+ in linear carbonate solvents. In tests of hard carbon Na-ion batteries, performance was not well correlated to Na+ solvent preference, leading to the possibility that Na+ solvent preference may play a reduced role in the passivation of anode surfaces and overall Na-ion battery performance.

Highly concentrated solutions of lithium salts in water have made sweeping strides from the time in the early 2010s where aqueous electrolytes could operate a battery within an electrochemical window no more than 1.5V wide. In this presentation, we discuss the construction of a lithium ion battery using graphite as the anode and LiCoO2 as the cathode to make a cell with a 4.2V potential. The primary electrolyte is a water:trimethylphosphate hybrid with a water mole fraction of 0.44 and LiTFSI salt at a concentration of 9 molal. This aqueous hybrid electrolyte can be formed into a gel electrolyte by directly polymerizing acrylate-based monomers and crosslinkers dissolved in the electrolyte. We demonstrate that by protecting the graphite anode using an acrylate gel with a fluoroethylene carbonate-based liquid electrolyte, the battery cell can be cycled repeatedly between 3.0V and 4.2V just like a cell using organic carbonate electrolytes. The advantage of the aqueous hybrid electrolyte is that it is non-flammable, and a cell using aqueous gel electrolytes can withstand damage and even be cut open while operating with no risk of fire or explosion. The manufacturing and performance characteristics of the aqueous 4V battery will be discussed as well as the interfacial issues that come about with the use of aqueous gel electrolytes in a 4V-capable battery system.

A system of electrolytes using water as a solvent was successfully used to support a typical lithium-ion battery chemistry that operates at 3.7V–4.2 V using standard ultraviolet-cured acrylic-based polymers as hydrophobic barriers. The aqueous electrolyte is contained in a system of poly(ethylene glycol) acrylate polymers crosslinked to produce an electrolyte gel that has electrochemical properties similar to that of the liquid phase component. The electrolyte gels have elastic moduli in the kPa range, making them soft enough to tolerant flexing, cutting, and blunt force impacts while keeping the electrodes covered and safe from shorting. While batteries based on water-in-salt electrolyte provides intrinsic safety that is otherwise unavailable from typical non-aqueous electrolytes, acrylate-based aqueous gel electrolytes offer the potential of large-scale manufacturing owing to the relatively low volatility of the electrolyte components and the low complexity of the proposed manufacturing process.

Ionic conductivity needs to be improved significantly for solid polymer electrolytes to be considered competitive alternatives to organic liquid electrolytes for battery technology. The strategy employed here is to promote polymer microstructures that facilitate ion transport by developing an amorphous rather than crystalline polymer matrix. To this end the transport, thermal, and electrochemical properties of solid polymer electrolytes incorporating ionic liquid (ILSPEs) are investigated. ILSPEs are fabricated into homogenous films using a hot-pressing procedure and are composed of a blend of poly (ethylene oxide) (PEO), triethylsulfonium bis(trifluoromethylsulfonyl)imide ionic liquid (S2TFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt. The goal of this work is to establish composition-property relationships that enable the ambient temperature operation of ILSPEs in a lithium metal battery. Optimized ILSPE compositions are able to achieve a high total ionic conductivity and Li+ transference number, 0.96 mS/cm at 22 °C and 0.31 at 60 °C respectively, that meet commercial benchmarks. The ILSPEs also show resistance to oxidation, with passivation up to 4.5 V (vs. Li+), and long-term stability with lithium metal, which enable good rate performance during room temperature cycling with a lithium metal anode and lithium iron phosphate cathode. Initial tests with higher potential lithium cobalt oxide cathode demonstrate promising performance.

Silicon (Si) has been well recognized as a promising candidate to replace graphite because of its earth abundance and high‐capacity storage, but its large volume changes upon lithiation/delithiation and the consequential material fracturing, loss of electrical contact, and over‐consumption of the electrolyte prevent its full application. As a countermeasure for rapid capacity decay, a composite electrode of graphite and Si has been adopted by accommodating Si nanoparticles in a graphite matrix. Such an approach, which involves two materials that interact electrochemically with lithium in the electrode, necessitates an analytical methodology to determine the individual electrochemical behavior of each active material. In this work, a methodology comprising differential plots and integral calculus is established to analyze the complicated interplay among the two active batteries and investigate the failure mechanism underlying capacity fade in the blend electrode. To address performance deficiencies identified by this methodology, an aluminum alkoxide (alucone) surface‐modification strategy is demonstrated to stabilize the structure and electrochemical performance of the graphite‐Si composite electrode. The integrated approach established in this work is of great importance to the design and diagnostics of a multi‐component composite electrode, which is expected to be high interest to other next‐generation battery system.

Highly conductive elastic composites were constructed using multistep solution-based fabrication methods that included the deposition of a nonwoven polymer fiber mat through solution blow spinning and nanoparticle nucleation. High nanoparticle loading was achieved by introducing silver nanoparticles into the fiber spinning solution. The presence of the silver nanoparticles facilitates improved uptake of silver nanoparticle precursor in subsequent processing steps. The precursor is used to generate a second nanoparticle population, leading to high loading and conductivity. Establishing high nanoparticle loading in a microfibrous block copolymer network generated deformable composites that can sustain electrical conductivities reaching 9000 S/cm under 100% tensile strain. These conductive elastic fabrics can retain at least 70% of their initial electrical conductivity after being stretched to 100% strain and released for 500 cycles. This composite material system has the potential to be implemented in wearable electronics and robotic systems.

Combining theoretical and experimental approaches, we investigate the solvation properties of Li

With the correlation between Li+ solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. As of now, most studies are dedicated to the solvation of Li+, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. As a mirror effort to prior Li+ solvation studies, this work focuses on the interactions between carbonate-based solvents and two anions (hexafluorophosphate, PF6–, and tetrafluoroborate, BF4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.

ConspectusAs one of the landmark technologies, Li-ion batteries (LIBs) have reshaped our life in the 21stcentury, but molecular-level understanding about the mechanism underneath this young chemistry is still insufficient. Despite their deceptively simple appearances with just three active components (cathode and anode separated by electrolyte), the actual processes in LIBs involve complexities at all length-scales, from Li+ migration within electrode lattices or across crystalline boundaries and interfaces to the Li+ accommodation and dislocation at potentials far away from the thermodynamic equilibria of electrolytes. Among all, the interphases situated between electrodes and electrolytes remain the most elusive component in LIBs.Interphases form because no electrolyte component (salt anion, solvent molecules) could remain thermodynamically stable at the extreme potentials where electrodes in modern LIBs operate, and their chemical ingredients come from the sacrificial decompositions of electrolyte comp...

A microscale battery comprised of mechanically exfoliated molybdenum disulfide (MoS2) flakes with copper connections and a sodium metal reference was created and investigated as an intercalation model using in situ atomic force microscopy in a dry room environment. While an ethylene carbonate-based electrolyte with a low vapor pressure allowed topographical observations in an open cell configuration, the planar microbattery was used to conduct in situ measurements to understand the structural changes and the concomitant solid electrolyte interphase (SEI) formation at the nanoscale. Topographical observations demonstrated permanent wrinkling behavior of MoS2 electrodes upon sodiation at 0.4 V. SEI formation occurred quickly on both flake edges and planes at voltages before sodium intercalation. Force spectroscopy measurements provided quantitative data on the SEI thickness for MoS2 electrodes in sodium-ion batteries for the first time.

Suppressing lithium (Li) dendrite growth is one of the most critical challenges for the development of Li metal batteries. Here, we report for the first time the growth of dendrite-free lithium films with a self-aligned and highly compacted nanorod structure when the film was deposited in the electrolyte consisting of 1.0 M LiPF6 in propylene carbonate with 0.05 M CsPF6 as an additive. Evolution of both the surface and the cross-sectional morphologies of the Li films during repeated Li deposition/stripping processes were systematically investigated. It is found that the formation of the compact Li nanorod structure is preceded by a solid electrolyte interphase (SEI) layer formed on the surface of the substrate. Electrochemical analysis indicates that an initial reduction process occurred at ∼ 2.05 V vs Li/Li(+) before Li deposition is responsible for the formation of the initial SEI, while the X-ray photoelectron spectroscopy indicates that the presence of CsPF6 additive can largely enhance the formation of LiF in this initial SEI. Hence, the smooth Li deposition in Cs(+)-containing electrolyte is the result of a synergistic effect of Cs(+) additive and preformed SEI layer. A fundamental understanding on the composition, internal structure, and evolution of Li metal films may lead to new approaches to stabilize the long-term cycling stability of Li metal and other metal anodes for energy storage applications.

The development of aqueous solutions containing comparatively high amounts of dissolved salts has brought water, an unlikely solvent, into the ongoing development of new battery chemistries. Aqueous electrolytes have the advantage of being inherently non-flammable materials, while demonstrating high cation transference number behavior and cation conductivity in the range of 1-10 mS/cm2 in the case of Li+. As a reaction medium, highly concentrated aqueous electrolytes allow for polymerization reactions such as radical polymerization to occur, and it has been demonstrated that the kinetics of these reactions are fast enough to allow rapid processing into films of solid gel electrolytes. While lithium ion batteries were one of the first applications of aqueous gel electrolytes, we have synthesized gel electrolytes for the increasingly popular sodium and zinc systems as well. This talk will focus on the kinetics of polymerization of various radicalized monomers, the formation and properties of the solid gels that result, and the electrochemical behavior and application tree that follow using the new electrolyte materials.

A reversible dual-graphite intercalation chemistry with simultaneous accommodation of Li+ and PF6− in graphitic structures is enabled for the first time by a high voltage electrolyte based on a fluorinated solvent and additive, which is capable of supporting the chemistry at 5.2 V with high efficiency. This all-graphite battery promises an energy storage device of low cost, high safety and high environmental friendliness that are critical for large scale energy harvesting/storage needs.

To understand how Li(+) interacts with individual carbonate molecules in nonaqueous electrolytes, we conducted natural abundance (17)O NMR measurements on electrolyte solutions of 1 M LiPF6 in a series of binary solvent mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC). It was observed that the largest changes in (17)O chemical shift occurred at the carbonyl oxygens of EC, firmly establishing that Li(+) strongly prefers EC over DMC in typical nonaqueous electrolytes, while mainly coordinating with carbonyl rather than ethereal oxygens. Further quantitative analysis of the displacements in (17)O chemical shifts renders a detailed Li(+)-solvation structure in these electrolyte solutions, revealing that maximum six EC molecules can coexist in the Li(+)-solvation sheath, while DMC association with Li(+) is more "noncommittal" but simultaneously prevalent. This discovery, while aligning well with previous fragmental knowledge about Li(+)-solvation, reveals for the first time a complete picture of Li(+) solvation structure in nonaqueous electrolytes.

A new super-concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra-high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO2 as the anode material, and a 2.5 V aqueous Li-ion cell based on LiMn2 O4 and carbon-coated TiO2 delivered the unprecedented energy density of 100 Wh kg(-1) for rechargeable aqueous Li-ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the "water-in-salt" electrolyte further pushed the energy densities of aqueous Li-ion cells closer to those of the state-of-the-art Li-ion batteries.

In electrolytes with unique electrochemical signature, the structure of Li+ solvation sheath was quantitatively analyzed in correlation with its electrochemical behavior on graphitic anodes. For th...

In any electrochemical device, the interface between electrolyte and electrode should be the only “legitimate” location where redox reactions happen. Particularly in Li ion batteries, these interfaces become “interphases” due to the reactivity of the electrode materials used, and they mainly consist of chemical species from the sacrificial decomposition of electrolyte components. Since the emergence of Li ion technology, it has been recognized that interphase on graphitic anodes, usually referred as SEI (solid electrolyte interphase) after its electrolyte attributes, is the key component supporting the reversibility of Li+-intercalation chemistry. Research attention focused on this component during the past two decades has led to substantial understanding about both its chemistry and mechanism. This article summarizes these progresses, and elaborates on the relatively recent insights, including the effect of Li+-solvation sheath structure on the interphasial processes at graphitic anode. A new strategy of forming a more desirable interphase is also discussed.

Using a mass spectrum technique and an "SEI-marker", we successfully established a direct link between Li+-solvation sheath structure and the interphasial processes occurring at graphitic anode.

We demonstrate an unusual electrochemical reaction of sulfur with lithium upon encapsulation in narrow-diameter (subnanometer) single-walled carbon nanotubes (SWNTs). Our study provides mechanistic insight on the synergistic effects of sulfur confinement and Li+ ion solvation properties that culminate in a new mechanism of these sub-nanoscale-enabled reactions (which cannot be solely attributed to the lithiation-delithiation of conventional sulfur). Two types of SWNTs with distinct diameters, produced by electric arc (EA-SWNTs, average diameter 1.55 nm) or high-pressure carbon monoxide (HiPco-SWNTs, average diameter 1.0 nm), are investigated with two comparable electrolyte systems based on tetraethylene glycol dimethyl ether (TEGDME) and 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5). Electrochemical analyses indicate that a conventional solution-phase Li-S reaction occurs in EA-SWNTs, which can be attributed to the smaller solvated [Li(TEGDME)]+ and [Li(15-crown-5)]+ ions within the EA-SWNT diameter. In stark contrast, the Li-S confined in narrower diameter HiPco-SWNTs exhibits unusual electrochemical behavior that can be attributed to a solid-state reaction enabled by the smaller HiPco-SWNT diameter compared to the size of solvated Li+ ions. Our results of the electrochemical analyses are corroborated and supported with various spectroscopic analyses including operando Raman, X-ray photoelectron spectroscopy, and first-principles calculations from density functional theory. Taken together, our findings demonstrate that the controlled solid-state lithiation-delithiation of sulfur and an enhanced electrochemical reactivity can be achieved by sub-nanoscale encapsulation and one-dimensional confinement in narrow-diameter SWNTs. Fil: Fu, Chengyin. University Of California Riverside; Estados Unidos Fil: Oviedo, María Belén. University Of California Riverside; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Zhu, Yihan. Zhejiang University Of Technology; China Fil: von Wald Cresce, Arthur. U. S. Army Research Laboratory; Estados Unidos Fil: Xu, Kang. U. S. Army Research Laboratory; Estados Unidos Fil: Li, Guanghui. University Of California Riverside; Estados Unidos Fil: Itkis, Mikhail E.. University Of California Riverside; Estados Unidos Fil: Haddon, Robert C.. University Of California Riverside; Estados Unidos Fil: Chi, Miaofang. Oak Ridge National Laboratory; Estados Unidos Fil: Han, Yu. King Abdullah University Of Science And Technology; Arabia Saudita Fil: Wong, Bryan M.. University Of California Riverside; Estados Unidos Fil: Guo, Juchen. University Of California Riverside; Estados Unidos

Future advancements in energy storage systems (lithium-ion batteries/LIBs and beyond) rely on the development of novel materials, innovative electrode/device architectures and scalable processing techniques or a combination thereof. In this talk, I will discuss my work on each of these three aspects including in situ characterization of planar devices as well as the development of nanomaterials and additive-free electrode architectures via alternative manufacturing processes such as dry/cold pressing and extrusion printing, respectively. Operando studies can elucidate the reaction behavior of battery electrodes during operation; however, specialized electrochemical cells are required to study these materials in their natural environment (in situ). In this study, a planar microscale battery with an open cell configuration was designed to investigate the structural evolution and concomitant solid electrolyte interphase formation of model electrode-electrolyte systems, such as Na-MoS2.1 By coupling an atomic force microscope with the planar electrochemical cell platform, real-time topographical observations of MoS2 electrodes during sodiation are readily achieved, which leads to crucial information regarding battery operation at the nanoscale. The use of advanced in situ/operando techniques with this newly developed planar battery configuration can elucidate the electrochemical behavior of numerous electrode-electrolyte systems, particularly for alkali-metal-ion batteries, during cycling. The drive towards lighter electric vehicles with longer ranges requires the development of higher energy density systems beyond conventional LIBs, such as lithium-oxygen (Li-O2) batteries. To increase battery performance for practical applications, high mass loading electrodes are advantageous as long as optimal battery reactions are maintained throughout the entirety of the “thick” electrode. Here, I present a facile, alternative electrode processing method known as dry/cold pressing, where a highly porous and compressible carbon nanomaterial (holey graphene or hG) enables the formation of mechanically robust, high mass loading electrodes for Li-O2 batteries.2-3 Dry pressing hG, the compressible matrix, with incompressible materials also enables the preparation of unique mixed and stacked/sandwich electrode architectures under binder- and solvent-free conditions.3 The enhancements in electrochemical performance demonstrate the promise of dry pressed electrode architectures and the reported additive-free processing method for advanced electrochemical energy storage systems. Additive manufacturing (AM) techniques also show promise towards the fabrication of complex 3D designs for advanced electrochemical devices. In particular, the development of inexpensive, sustainable (aqueous), and easily processable material ink systems and the use of a facile and low-cost fabrication process, such as extrusion-based 3D printing, are advantageous for scalable battery manufacturing. In this work, hierarchically porous electrode architectures are readily extruded using additive-free, aqueous graphene oxide-based (GO) ink compositions and demonstrated as the first 3D printed Li-O2 cathodes.4 The development of a nanoporous GO material enabled trimodal porosity (nano-micro-macropores) within the 3D printed mesh architecture, which provides facile mass/ionic transport pathways and enhances active-site utilization during battery operation. The results demonstrate the potential of AM techniques towards the scalable fabrication and improvement of advanced energy storage devices through structurally conscious designs as well as tailored material compositions. References: SD Lacey, J Wan, A Cresce, SM Russell, J Dai, W Bao, K Xu and L Hu, “Atomic Force Microscopy Studies on Molybdenum Disulfide Flakes as Sodium-ion Anodes,” Nano Letters, 15 (2) 1018-1024 (2015). Y Lin, B Moitoso, C Martinez-Martinez, ED Walsh, SD Lacey, JW Kim, L Dai, L Hu and JW Connell, “Ultrahigh-Capacity Lithium-Oxygen Batteries Enabled by Dry-Pressed Holey Graphene Air Cathodes,” Nano Letters, 17 (5), 3252-3260 (2017) SD Lacey, ED Walsh, E Hitz, J Dai, JW Connell, L Hu and Y Lin, “Highly compressible, binderless and ultrathick holey graphene-based electrode architectures,” Nano Energy, 31, 386-392 (2017). SD Lacey, DJ Kirsch, Y Li, JT Morgenstern, BC Zarket, Y Yao, J Dai, LQ Garcia, B Liu, T Gao, S Xu, SR Raghavan, JW Connell, Y Lin and L Hu, “Extrusion-based 3D Printing of Hierarchically Porous Advanced Battery Electrodes,” Advanced Materials, 30 (12), 1705651 (2018).

Efforts were made to differentiate the contributions to the so-called "ion transfer" barrier at the electrolyte/graphite junction from two distinct processes: (1) desolvation of Li(+) before it enters graphene interlayer and (2) the subsequent migration of bare Li(+) through the ad hoc interphase. By leveraging a scenario where no substantial interphase was formed on Li(+) intercalation hosts, we were able to quantify the distribution of "ion transfer" activation energy between these two interfacial processes and hence identify the desolvation process of Li(+) as the major energy-consuming step. The result confirmed the earlier belief that the rate-determining step in the charging of a graphitic anode in Li(+) intercalation chemistry relates to the stripping of solvation sheath of Li(+), which is closely interwoven with the interphasial resistance to Li(+) migration.

Sodium ion batteries present a meaningful opportunity to apply knowledge gained from lithium ion batteries. In order to produce functional sodium ion batteries that present real advantages compared to today’s commercial lithium ion batteries, the sodium ion and its interactions in solution must be exploited. From previous work on the subject, our work has shown fundamental differences in the solvation of Na+ as compared to Li+. Specifically, we were able to show that Na+ experiences weaker attractive forces and longer bond lengths between itself and its solvent molecules in organic and aqueous solution, which affects contact ion pairing and aggregation behavior. In this work, we will explore the relationship between ion-solvent interactions as they relate to the transference number and electrochemical stability of sodium organic and aqueous electrolytes. Ion interaction has a significant effect on the reduction potential of both solvent molecules and anions, and so there may be opportunities to take advantage of Na+ to affect both transference number and stability with the goal of producing effective electrolytes for sodium ion batteries.

Water-in-salt electrolytes (WiSE) are one of a growing family of water-based lithium ion electrolytes that use high concentrations of non-hydrolyzable lithium salts such as LiTFSI. WiSE are non-flammable and have a much wider electrochemical stability window than typical dilute aqueous electrolytes through two anion-based mechanisms: the formation of a passive anode layer through the decomposition of the TFSI- anion and exclusion of water by the anion from the cathode surface. This work details the formation of a polymer gel network containing WiSE as its liquid phase using commercially available polymer and crosslinker components. WiSE gel electrolytes are thought to be a natural evolution of the water-in-salt concept, as a WiSE gel should allow for WiSE-containing batteries to decouple themselves from typical cylindrical and prismatic battery form factors. Cycling performance and mechanical properties of the gel electrolytes will be discussed, along with fundamental investigations into the electrode-electrolyte interface and the minimization of charge-transfer resistance. Additionally, the kinetics of gel reactions in WiSE as a solvent will be discussed.

Despite the potential advantages it brings, such as wider liquid range and lower cost, propylene carbonate (PC) is seldom used in lithium-ion batteries because of its sustained cointercalation into the graphene structure and the eventual graphite exfoliation. Here, we report that cesium cation (Cs(+)) directs the formation of solid electrolyte interphase on graphite anode in PC-rich electrolytes through its preferential solvation by ethylene carbonate (EC) and the subsequent higher reduction potential of the complex cation. Effective suppression of PC-decomposition and graphite-exfoliation is achieved by adjusting the EC/PC ratio in electrolytes to allow a reductive decomposition of Cs(+)-(EC)m (1 ≤ m ≤ 2) complex preceding that of Li(+)-(PC)n (3 ≤ n ≤ 5). Such Cs(+)-directed interphase is stable, ultrathin, and compact, leading to significant improvement in battery performances. In a broader context, the accurate tailoring of interphasial chemistry by introducing a new solvation center represents a fundamental breakthrough in manipulating interfacial reactions that once were elusive to control.

Ring opening metathesis polymerization (ROMP) with Grubbs's catalyst was used to synthesize narrow polydispersity (PDI)diblock copolymers of norbornene (NOR) and norbornenedicarboxylic acid (NORCOOH). Norbornene (NOR) and 5-norbornene-2,3,-dicarboxylic acid bis trimethylsilyl ester (NORCOOTMS) were used as precursor monomers for thepolymerization. [NORCOOTMS] m /[NOR] n was converted to [NORCOOH] m /[NOR] n by precipitating the polymer solution in a mixture of methanol, acetic acid, and water. The conversion to 5-norbornene-2,3-dicarboxylic acid was evidenced by 1 H NMR. By polymerizing the bulkier NORCOOTMS precursor monomer first, lower PDIs were observed for the completed [NORCOOH] m /[NOR] n block copolymers in comparison to copolymers where the NOR block was polymerized first. The PDI of the diblock copolymers of [NORCOOH] m /[NOR] n decreased with increase in block length ofthe precursor NORCOOTMS monomer. This study shows that the PDI can be controlled by selecting a monomer with appropriate functionality as the starting block of the block copolymer to control the rate of propagation, R p , as an alternative of using additives to change the reactivity of the catalyst.

The solvation of cations and anions in a lithium-containing electrolyte was studied using electrospray ionization mass spectrometry (ESI-MS) combined with nuclear magnetic resonance (NMR) and electrochemical testing. The purpose of these experiments was to develop an understanding of the solvation of the small, hard Li+ cation and the more cryptic nature of the solvation of poorly-coordinating anions such as PF6- and BF4-. It has long been held that the passivation of graphitic anodes in lithium ion batteries is a solvation-driven process, meaning that whatever solvent molecules surround the Li+ cation will provide the raw material for the formation of the solid electrolyte interphase (SEI) layer. Because the SEI is a critical component, and because a binary solvent system is normally used in lithium batteries, it is necessary to understand the competitive nature of lithium solvation. Conversely, the anion can be chemically active even if poorly coordinating; therefore, it was desired to see if a competitive solvation condition exists for the anion as well. Results indicate that Li+ has a strong preference for cyclic carbonates like ethylene carbonate (EC) over linear carbonates, where the anions had a mixed preference. It is thought that anion solvent preference might dictate oxidative chemistry that occurs on the cathode, while the anion also significantly participates in the formation of SEI on the anode.

The formation of self-assembled ZnO nanoclusters using diblock copolymers, is reported. The diblock copolymers, consisting of a majority polymer (norbornene) and a minority polymer (norbornene-dicarboxcylic acid), were synthesized with a block repeat unit ratio of 400/50, to obtain spherical microphase separation and hence a spherical morphology for the metal oxide nanoclusters. The self-assembly of the inorganic nanoparticles was achieved at room temperature in the liquid phase, using ZnCl2 precursor dopant and wet chemical processing compatible with semiconductor manufacturing to convert to ZnO. FTIR and XPS spectroscopy, confirmed the association of the ZnCl2 precursor with the minority block and the formation of ZnO, while TEM showed the spherical morphology of ZnO nanoparticles as targeted, and a relatively narrow size distribution ranging between 7 and 15 nm.

Currently used lithium ion batteries for portable electronics utilize flammable and often toxic non-aqueous electrolytes in order to achieve high energy densities. They also require a low humidity manufacturing environment resulting in an increased cost. Aqueous electrolytes have recently emerged as potential intrinsically nonflammable alternatives after their electrochemical stability window was expanded beyond 3.0 V by employing a new class of “Water-in-Salt” electrolytes. In such super-concentrated electrolyte, the decomposition of salt anion occurs preferentially on the anode before hydrogen evolution takes place, creating a kinetic protection against electrochemical decomposition via a dense solid electrolyte interphase (SEI). In this presentation, results from classical molecular dynamics (MD) simulations using a polarizable APPLE&P force field are analyzed in order to examine in detail the ion transport mechanism in bis(trifluoromethane sulfonyl)imide (LiTFSI-water) “Water-in-Salt” electrolytes (WiSE) for safe, green and low cost aqueous lithium ion batteries. They are complemented by Born Oppenheimer MD simulations of smaller systems that yield similar structural features. Simulations revealed an unusually low activation energy and fast ion transport for highly concentrated solutions even at low temperatures that is quite different from the dramatic increase of the activation energy for conductivity found in traditional battery electrolytes. A high conductivity and lithium transference number in WiSE is attributed to the formation of fast ion transporting pathways that are connected to the unexpected structure of WiSE electrolytes, which was confirmed by small angle neutron scattering experiments (SANS). The ability of MD simulations to describe dynamics of ion and solvent in WiSE electrolytes was further validated via pfg-NMR and conductivity measurements, while IR spectroscopy measurements provide a comprehensive picture of the salt electrolyte aggregation that is coupled with ion transport. The connection between the double layer structure of WiSE electrolytes and its electrochemical stability will be briefly discussed.