Glyme-based Electrolytes Research Articles

On-Site Green Hydrogen Generation by Two-Step Water Splitting Enabled through Chemical-Electrochemical Zn-ZnO Cycles

Hydrogen (H2) is typically produced off-site for applications such as ammonia (NH3) production, steelmaking, and e-fuels synthesis. Following production, it undergoes compression or liquefaction and is transported in high-pressure tanks and tube trailers to the point of consumption. H2 compression and liquefaction are considered undesirable due to their high energy consumption, which accounts for over 30% of the energy used.1 Furthermore, transporting liquefied H2 in tube trailers requires high capital costs to insulate and maintain these tube trailers at cryogenic temperatures. The transportation and delivery of H2 can be avoided by using metal-water reactions to produce hydrogen on-site and on-demand directly at the point of consumption. Among metal-water reactions, the aluminum-water reaction given in Eq. 1 has been the subject of intense studies: 2Al + 6H2O --> 2Al(OH)3 + 3H2 + heat (Eq. 1).2 The generation of H2 on-site through the aluminum-water reaction faces two major issues. Firstly, the aluminum-water reaction (Eq. 1) produces an aluminum hydroxide solid by-product that cannot be recycled back to aluminum by the end user, rendering the aluminum-water reaction operates as a single-use system. Secondly, the energy content of the H2 produced through the aluminum-water reaction represents only around 50% of the total energy released from that reaction. The remaining 50% is lost as heat, thus limiting the energy efficiency of the aluminum-water reaction to a maximum of 50%.3 We propose a new and scalable method for generating hydrogen (H2) on-site and on-demand using a two-step water-splitting process that involves the zinc-water reaction. This innovative process allows for on-site and on-demand H2 generation and overcomes the challenges associated with the aluminum-water reaction. The first step of this process is the H2 evolution step, which is given by the following equation: Zn + H2O --> ZnO + H2 + heat (Eq. 2). The heat loss from this zinc-water reaction only accounts for approximately 18% of the total energy released during the reaction of Zn with water.2 The remaining 82% is effectively stored in H2, leading to a significantly higher zinc-to-hydrogen energy efficiency compared to the efficiency of aluminum-to-hydrogen conversion. The second stage of this process is the O2 evolution step, wherein the ZnO solid by-product undergoes electrochemical conversion, reverting to Zn through the following reaction: ZnO --> Zn + 1/2O2 (Eq. 3). This reduction step can be completed in just 5 minutes, ensuring a fast-charging characteristic that guarantees a continuous supply of H2 to the fuel cell and, consequently, uninterrupted power for mobile applications like vehicles and drones. We refer to these two steps as chemical-electrochemical Zn-ZnO cycles. This process can be repeated over multiple cycles to produce a large quantity of H2 using the same amount of Zn.During my talk, I will present this new chemical-electrochemical Zn-ZnO cycling process including the design concept, electrode fabrication methodology, and performance testing. We use various characterization techniques, including X-ray diffraction (XRD), scanning electron microscope (SEM), and focused ion beam (FIB) to investigate the microstructure and chemical composition of our materials. Electrochemical methods, in combination with gas chromatography and water displacement techniques, are used to investigate the cycle life, the H2 generation rate, and the yield.References(1) Armaroli, N.; Balzani, V. The Hydrogen Issue. ChemSusChem. 2011, 4 (1).(2) Lee, T.; Koh, H.; Ng, A. K.; Liu, J.; Stach, E. A.; Detsi, E. Ultrafine Nanoporous Aluminum by Electrolytic Dealloying of Aluminum-Magnesium Alloys in Glyme-Based Electrolytes with Recovery of Sacrificial Magnesium. Scr. Mater. 2022, 221, 114959.(3) Detsi, E.; Liu, J.; Kubota, J.; Fu, J.; Tao, J. Green Hydrogen Generation by Metal-Assisted Two-Step Water Splitting for Portable Hydrogen Power Stations, Hydrogen Refueling Stations, and Other Applications. U.S. Provisional Application, 63/600,171 - November 17, 2023.

Transitioning from Regular Electrolytes to Solvate Ionic Liquids to High-Concentration Electrolytes: Changes in Transport Properties and Ionic Speciation.

Glyme-based lithium-ion electrolytes have received considerable attention from the scientific community due to their improved safety, as well as electrochemical and thermal stability over carbonate-based electrolytes. However, these electrolytes suffer from major drawbacks such as high viscosities. To overcome the challenges that hinder their full potential, the molecular description of glyme-based lithium electrolytes in the high-concentration regime, particularly in the solvate ionic liquid (SIL) and high-concentration electrolyte (HCE) regimes, is needed. In this study, model glyme-based electrolytes based on a lithium thiocyanate and either tetraglyme (G4) or a mixture of monoglyme (G1) and diglyme (G2) were investigated as a function of the solvent-to-lithium ratio using linear and nonlinear IR spectroscopies, in combination with ab initio computations as well as electrochemical methods . The transport properties reveal enhanced ionicities in the HCE and SIL regimes ([O]/[Li] ≤ 5) compared to the regular electrolytes (REs, with [O]/[Li] > 5) in both pure (G4) and mixed (G1:G2) glymes. IR and ab initio computations relate these larger ionicities to the higher concentration of charged aggregates in the HCE and SIL electrolytes ([O]/[Li] ≤ 5). Moreover, it was observed that the use of mixed glymes appears to have a minimal effect on the transport properties of REs but exhibits deleterious effects on SILs. Overall, the results provide a molecular framework for describing the local structure of lithium glyme-based electrolytes and demonstrate the key role that the nature of glyme solvation plays in the molecular structure and consequently the macroscopic properties of the Li-glyme SILs, HCEs, and REs.

Understanding the Solid-Electrolyte-Interface (SEI) Formation in Glyme Electrolyte Using Time-Of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

Lithium-ion batteries are commonly used for energy storage due to their long lifespan and high energy density, but the use of unsafe electrolytes poses significant health and safety concerns. An alternative source is necessary to maintain electrochemical efficacy. This research demonstrates new safe glyme-based electrolytes for silica/carbon (SiOx/C) nanocomposite derived from Australian rice husk (RH). The quality of SiOx/C was preserved by using deep eutectic solvent-based pre-treatment and single-step carbonization, which was confirmed through the X-ray analysis of the crystalline phase of silica. The electrochemical assessment of SiOx/C anode using various glyme-based electrolytes for LIBs was carried out. Among them, the resultant half cells based on diglyme electrolyte is superior to others with the first discharge capacity at 1274 mAh/g and a reversible discharge capacity of 759.7 mAh/g. Ex-situ SEM and Time-of-Flight Secondary Ion Mass Spectrometry (ToF- SIMS) analysis of the electrode indicated that diglyme not only improves the capacity but also sustains the electrode architecture for longer cycle life with more LiF-based components and also showed the absence of HF components. Importantly, the addition of fluoroethylene carbonate (FEC) additive enhanced the cycling stability. These results provide a new perspective on developing advanced SiOx/C anode using glyme electrolytes for Li-ion batteries.

Basic properties of glyme-based electrolytes doped with lithium 2,4,5-tricyanoimidazolide (LiTIM)

The article presents the electrolyte's basic physicochemical and electrochemical properties based on the new type of lithium salt for lithium batteries - lithium 2,4,5-tricyanoimidazolide (LiTIM). Two series of the electrolytes in diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether were obtained and their electrochemical properties were examined by means of impedance spectroscopy and cyclic voltammetry. Thermal and rheological properties of the electrolytes were tested with differential scanning calorimetry (DSC) and rheometric methods. Single crystal X-ray analysis was performed for LiTIM-crown ethers adducts used as models for solvent-separated and solvent-shared ionic species. Raman spectroscopy was used to obtain a more detailed insight into ionic interactions in the material. The electrochemical stability for the tetraglyme based electrolytes with a salt concentration higher than 0.4 M was 4.7 V vs Li. The high solubility of LiTIM in tetraglyme (up to 6.8 M) and the ability to form an amorphous, stable solution make the electrolyte an interesting candidate for advanced lithium batteries.

Rationally Designed in-Situ Gelled Polymer-Ceramic Hybrid Electrolyte Enables Superior Performance and Stability in Quasi-Solid-State Lithium-Sulfur Batteries

Despite boasting giant leaps in performance improvement over the years, the current commercial standard, Li-ion batteries, are fast approaching their theoretical limits. Meanwhile, Lithium-Sulfur (Li-S) batteries offering ultra-high theoretical energy density (～2600 Whkg-1), cost-effectiveness, and nontoxicity are being seen as promising alternatives. Despite their plentiful advantages, the practicality of Li-S batteries has been largely stymied by several challenges: a) deleterious polysulfide dissolution and ‘shuttle effect’, b) significant volume change of S cathodes during cycling, c) safety concerns with flammable traditional glyme-based electrolyte, and d) the instability of Li anode. To mitigate these challenges, researchers have explored all-solid-state electrolytes, but their poor Li-ion conductivity, high interfacial impedance, and need for expensive, exotic materials and complex fabrication procedures severely limit their practical application.To overcome these challenges, we propose an in-situ gelled polymer-ceramic hybrid silsesquioxane-based electrolyte system. The gelled matrix, thermally crosslinked post cell fabrication, immobilizes the glyme-based liquid electrolyte and exhibits high liquid-like ionic conductivities (1.03 mS.cm-1), low interfacial impedance, and high oxidative potential (>4.5V vs. Li/Li+) . In this study, in addition to vastly decreased flammability, we report superior Li-ion conductivity compared to state-of-art solid-state Li-S electrolytes. This high ionic conductivity translated to a significantly improved specific capacity of 1050 mAh.gS-1 at 0.2 C, elevated Coulombic efficiencies (>98.5%), and elevated rate kinetics. The gelled electrolytes exhibited stable cycling in a large temperature range (-10oC - 60 oC). Moreover, polysulfide permeation studies and subsequent DFT calculations revealed that the gelled electrolyte exhibited strong chemical absorptivity to lithium polysulfides due to the polar silsesquioxane core, which translated to superior capacity retention (>80% over 200 cycles). Further, post- mortem XPS characterization studies revealed the formation of stable SEI at the anode and cathode, and SEM of cycled anodes showed reduced dendritic formations. Finally, the electrolyte was tested in practical pouch cell architecture, and the cells demonstrated excellent reliability even under mechanical stress. This work successfully reports a robust, rationally designed gelled electrolyte system for developing safe and high-performance quasi-solid state Li-S batteries.

The Mg Electrode Cycling Mechanism in Simple Salt Glyme Electrolytes

The lithium-ion battery (LIB) has been at the forefront of innovations in energy storage since its commercialisation over 30 years ago. As we reach the practical specific capacity limit of current state-of-the-art materials, novel and innovative battery technologies are required to satiate the requirements of energy intensive applications such as electric vehicles. 1 The use of a lithium metal negative electrode has been proposed to increase the energy density, however the high reactivity causes poor cycling performance due to electrolyte degradation, dendrite formation and safety issues. 2 The magnesium electrode offers a solution that has double the theoretical volumetric capacity of the lithium electrode while simultaneously mitigating dendritic growth, reducing raw material costs and greatly increasing sustainability. 3,4 Previous work has shown that traditional LIB electrolytes are not compatible with magnesium metal, and the plating and stripping mechanism that underpins how magnesium electrodes cycle is poorly understood. 5 Here we explored the mechanism of magnesium plating and stripping in glyme-based electrolytes with a range of additional additives. We show that in the pure electrolyte solution, interphase formation is critical to stable cycling but that this is accompanied by significant degradation and accumulation of inactive Mg.6 We establish the three-dimensional chemical composition of Mg deposits in the different electrolyte formulations using a combination of focused ion beam-scanning electron microscopy (FIB-SEM), energy dispersive x-ray spectroscopy (EDX) and transmission electron microscopy (TEM). We use these findings to develop a mechanistic understanding that explains the electrochemical cycling performance of magnesium metal negative electrodes. In situ electrochemical quartz crystal microbalance (EQCM) measurements are used to evaluate the plating and stripping efficiency of the electrodes and to identify non-electrochemical degradation reactions between Mg and the electrolyte solutions.

Toward Sustainable Li-S Battery Using Scalable Cathode and Safe Glyme-Based Electrolyte.

The search for safe electrolytes to promote the application of lithium-sulfur (Li-S) batteries may be supported by the investigation of viscous glyme solvents. Hence, electrolytes using nonflammable tetraethylene glycol dimethyl ether added by lowly viscous 1,3-dioxolane (DOL) are herein thoroughly investigated for sustainable Li-S cells. The electrolytes are characterized by low flammability, a thermal stability of ∼200 °C, ionic conductivity exceeding 10-3 S cm-1 at 25 °C, a Li+ transference number of ∼0.5, electrochemical stability window from 0 to ∼4.4 V vs Li+/Li, and a Li stripping-deposition overpotential of ∼0.02 V. The progressive increase of the DOL content from 5 to 15 wt % raises the activation energy for Li+ motion, lowers the transference number, slightly limits the anodic stability, and decreases the Li/electrolyte resistance. The electrolytes are used in Li-S cells with a composite consisting of sulfur and multiwalled carbon nanotubes mixed in the 90:10 weight ratio, exploiting an optimized current collector. The cathode is preliminarily studied in terms of structure, thermal behavior, and morphology and exploited in a cell using standard electrolyte. This cell performs over 200 cycles, with sulfur loading increased to 5.2 mg cm-2 and the electrolyte/sulfur (E/S) ratio decreased to 6 μL mg-1. The above sulfur cathode and the glyme-based electrolytes are subsequently combined in safe Li-S batteries, which exhibit cycle life and delivered capacity relevantly influenced by the DOL content within the studied concentration range.

An efficient upcycling of graphite anode and separator for Na-ion Batteries via solvent-co-intercalation process

The need for efficient energy storage devices has led to a boom in Li-ion battery production, which will be a threat in the future to the global ecosystem in the form of toxic waste if not recycled properly. Herein, we report the electrochemical performance of recycled and fresh polyolefin separators in a glyme-based electrolyte for a recovered graphite/Na3V2(PO4)3-based Na-ion full-cell. An in-depth investigation of the electrolyte stability with tetraethylene glycol dimethyl ether and diethylene glycol dimethyl ether-based electrolytes and the compatibility with polyolefin separators has been done, with successful sodium-plating stripping for 350+ hours. Cycling stabilities with >99.9 % Coulombic efficiency for 250+ cycles have been observed in both half-and full-cell configurations, with robust capacity retention for the full-cell at a current of 1 A g−1.

Co-Intercalation Batteries (CoIBs): The Use of TiS2 As Electrode for Solvent Co-Intercalation in Sodium-Ion Batteries

With the rising demand for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have become an attractive alternative with the promise of improved safety, reduced cost, and lower environmental impact.1 However, the larger ion size of sodium cation has major consequence on the battery chemistry, which provides several challenges and opportunities for designing electrode materials and electrolyte solutions.2 Graphite is the currently most used anode material in LIBs. However, its use in SIBs, with traditional carbonate-based electrolytes, results in very poor specific capacities due to unfavorable thermodynamic processes.3 A strategy around this problem is to choose different solvents: Ethers and in particular glymes can exhibit a co-intercalation behavior into the graphite structure by forming ternary graphite intercalation compounds.4, 5 Although the co-intercalation of solvent molecules with sodium cation leads to a large increase in the graphite framework, the cycle life and rate capability of the reaction are excellent.Regardless of this, there is a lack of evidence for a comparable reaction with other electrode materials. Hence, it would be of interest to identify a cathode material that operates via this same mechanism. A battery based on solvent co-intercalation at both electrodes can have minimized charge-transfer resistances due to the absence of desolvation steps, and great cycle life. Thus, such a system can show high power density over many cycles. It has also been shown that stripping of the solvation shell can be the rate limiting step for battery operation, especially at subzero temperatures.6 Such a solvent co-intercalation battery (CoIB) could therefore be more energy efficient compared to other batteries or could enable a better low-temperature performance.Transition metal dichalcogenides (TMDs) have emerged as promising anode materials owing to their low cost, high electric conductivity, good thermal stability and environmental friendliness. Among them, titanium sulphide (TiS2), with a two-dimensional framework, exhibits several advantages such as a high conductivity (compare to other metal oxides), a larger interlayer distance (0.569 nm) compared to graphite (0.335 nm) and high stability. 7 Several papers have reported on the use of TiS2 as an anode material for SIBs, and observed that the voltage profiles and electrochemical behaviour of the system is highly dependent on the choice of electrolyte. However, this has seldomly been explicitly stated and the cause of the electrolyte dependence has never been investigated. By using operando and in-situ techniques such as Operando XRD and dilatometry, Na-diglyme complexes were showed to co-intercalate, similar as graphite, into TiS2. In contrast, no signs of solvent co-intercalation are observed in cyclic ethers and conventional carbonate-based electrolytes – where instead the redox reaction with TiS2 results in the formation of different NaxTiS2 compounds.As we identified TiS2 as “co-intercalation electrode” in glyme-based electrolytes it served to create the first ever solvent co-intercalation battery (CoIB – pronounced Co-IB) which was done by pairing TiS2 (positive electrode) with graphite (negative electrode).8 This work could enable the development of highly energy efficient batteries with minimum charge transfer resistances and References I. Hasa, S. Mariyappan, D. Saurel, P. Adelhelm, A. Y. Koposov, C. Masquelier, L. Croguennec and M. Casas-Cabanas, J. Power Sources, 2021, 482, 228872. P. Adelhelm, P. Hartmann, C. L. Bender, M. Busche, C. Eufinger and J. Janek, Beilstein Journal of Nanotechnology, 2015, 6, 1016-1055. B. Jache and P. Adelhelm, Angew. Chem., 2014, 126, 10333-10337. B. Jache, J. O. Binder, T. Abe and P. Adelhelm, Physical Chemistry Chemical Physics, 2016, 18, 14299-14316. M. Goktas, C. Bolli, J. Buchheim, E. J. Berg, P. Novák, F. Bonilla, T. f. Rojo, S. Komaba, K. Kubota and P. Adelhelm, ACS applied materials & interfaces, 2019, 11, 32844-32855. S. S. Zhang, K. Xu and T. R. Jow, Journal of Power Sources, 2003, 115, 137-140. Q. Yun, L. Li, Z. Hu, Q. Lu, B. Chen and H. Zhang, Adv. Mater., 2020, 32, 1903826. G. A. Ferrero, G. Avall, K. A. Mazzio, Y. Son, K. Janssen, S. Risse and P. Adelhelm, Adv. Energy Mater., 2022, 2202377. an improved low temperature performance, where the charge transfer can become rate limiting. Figure 1

4V-class Magnesium-ion pseudocapacitors fabricated using an in situ inverse-charging process

Pseudocapacitors can deliver much more improved energy densities than those (<4% of typical lithium-ion batteries) of the electrochemical double layer (EDL) capacitors. Nevertheless, surface-limited redox behaviors based on typical monovalent-ion charge carriers exhibit insufficient energy densities, necessitating a new high-performance electrochemical system based on a feasible cell configuration. In this study, 4 V-class multivalent magnesium-ion pseudocapacitors (MIPs) were fabricated from mass-producible nanocarbon electrodes and a glyme-based electrolyte system via an in situ electrochemical oxidation process. A redox-free nanocarbon electrode was electrochemically tuned into a pseudocapacitive nanocarbon anode (PNA) using a well-controlled oxidation process, showing an approximately four times higher specific capacitance value (∼196F g−1) compared with its initial EDL capacitance. The dual experimental and theoretical analysis results elucidate that the pseudocapacitance originates from the strong chemisorption ability with divalent magnesium-ions by the concerted effect of surface carbonyl functional groups and topological carbon defects. The high-capacitance PNA can work in a wide voltage range of 4 V. Therefore, the PNA-based MIP showed a high specific energy density of 167 Wh kg−1, which is much higher than those (46 ∼ 145 Wh kg−1) of previously reported alkali-ion capacitors. Additionally, a high cycling performance of the MIP full cell was achieved over 5,000 cycles.

Understanding the solvation structures of glyme-based electrolytes by machine learning molecular dynamics

Glyme-based electrolytes are of great interest for rechargeable lithium metal batteries due to their high stability, low vapor pressure, and non-flammability. Understanding the solvation structures of these electrolytes at the atomic level will facilitate the design of new electrolytes with novel properties. Recently, classical molecular dynamics (CMD) and ab initio molecular dynamics (AIMD) have been applied to investigate electrolytes with complex solvation structures. On one hand, CMD may not provide reliable results as it requires complex parameterization to ensure the accuracy of the classical force field. On the other hand, the time scale of AIMD is limited by the high cost of ab initio calculations, which causes that solvation structures from AIMD simulations depend on the initial configurations. In order to solve the dilemma, machine learning method is applied to accelerate AIMD, and its time scale can be extended dramatically. In this work, we present a computational study on the solvation structures of triglyme (G3) based electrolytes by using machine learning molecular dynamics (MLMD). Firstly, we investigate the effects of density functionals on the accuracy of machine learning potential (MLP), and find that PBE-D3 shows better accuracy compared to BLYP-D3. Then, the densities of electrolytes with different concentration of LiTFSI are computed with MLMD, which shows good agreement with experiments. By analyzing the solvation structures of 1 ns MLMD trajectories, we found that Li+ prefers to coordinate with a G3 and a TFSI− in equimolar electrolytes. Our work demonstrates the significance of long-time scale MLMD simulations for clarifying the chemistry of non-ideal electrolytes.

AMOEBA Polarizable Force Field for Molecular Dynamics Simulations of Glyme Solvents.

Classical molecular dynamics (MD) simulations of electrolyte systems are important to gain insight into the atom-scale properties that determine the battery-relevant performance. The recent Tinker-HP software release enables efficient and accurate MD simulations with the AMOEBA polarizable force field. In this work, we developed a procedure to construct a universal AMOEBA model for the solvent family of glymes (glycol methyl ethers), which involves a refinement scheme for valence parameters by fitting the AMOEBA-derived atomic forces to those computed at the DFT level. The refined AMOEBA model provides a good description of both local and nonlocal properties in terms of the spectroscopic response of glyme molecules, as well as the liquid glyme density and dielectric constant. In addition, the complexation energies of alkali and alkaline-earth metal cations with tetraglyme molecules obtained from AMOEBA calculations are in good agreement with DFT results, demonstrating the suitability of the developed AMOEBA model for an accurate simulation of glyme-based battery electrolytes. We also expect the procedure to be transferable to the development of AMOEBA models for other battery electrolyte systems.

Leveraging impurities in recycled lead anodes for sodium-ion batteries

In recent years, the supply chain shock due to the rapid rise of the lithium-ion battery has made alternative chemistries, such as sodium-ion batteries, appealing for low-cost and large-scale energy storage. Meanwhile, the falling popularity of lead acid batteries has potential consequences for the price of scrap lead and its penetration into waste streams. In this work, we upcycle lead alloys from a used lead acid battery into a next-generation sodium-ion system for ultra-low-cost rechargeable batteries. Through evaluation of sodium storage capacity and rate capability, we study the rich interplay of Pb-Sb-Sn microstructure and properties which can be controlled through simple heat treatment of unrefined powders to reach a maximum specific capacity of 522 mAh.g -1 . When cycled in the presence of glyme-based electrolytes, the ternary alloys nanostructure to facilitate an optimal balance of power and cycle life. These findings that demonstrate how defects can be leveraged to improve performance bring exciting implications for reducing cost and mitigating volume expansion in other high-value commodities, like tin or silicon.

Interfacial Chemistry and Electrolyte Approaches for Enabling Metal Anode Batteries

Continuous solid electrolyte interphase (SEI) and dendrite growth, as well as formation of ion blocking interfaces are some of the crucial issues preventing the commercialization of batteries depending on the implementation of Li/Na/K/Mg/Ca metal anodes.[1,2] In the first part of my talk, I will focus on the chemistry of formed interfaces, including growth and ion transport control. Second part of my talk deals with bulk liquid, polymer and hybrid electrolyte molecular structure approaches for circumventing dendrite formation.Understanding of the SEI growth on alkali and alkaline earth metals in contact with liquid electrolytes under open circuit potential conditions important for shelf aging is still in its infancy. I will show that the SEI formed on Li in contact with glyme-based electrolyte grows via reaction-controlled mechanism that is rapidly substituted by the diffusion-controlled one.[3] The ionic transport and stability of the complex composite SEI material under current is highly dependent on the salt chemistry, with detrimental effects of LixSy and positive effects of the Li3N constituents. Most recent ion transport and morphological studies show that the initial SEI formed in contact with liquid electrolytes on Li, Na and Mg is nanoporous.[4,5] Based on the electrochemical impedance spectroscopy measurements in symmetric cells and related equivalent circuit models, I will discuss potential growth mechanism via SEI densification. Finally, I will present a possibility of using gas/solid synthesis for preparation of sulfide-based artificial SEIs for both liquid-based and solid-state batteries.[6]Dendrite formation on alkali and alkaline earth metal anodes is closely related to the ion concentration gradients formed near the electrodes in contact with the electrolytes. I will discuss the method to circumvent this problem by using electrolytes with high cationic transference number. In soft matter electrolytes this is possible when (i) interfacial effect enables preferential anionic adsorption in liquid/solid electrolytes,[7] (ii) the size and steric effects control the association and mobility of the anion in the liquid electrolytes,[8] (iii) ion transport proceeds through percolating amorphous clusters in polymer-in-salt electrolytes. [9]

Insights into Cationic Transference Number Values and Solid Electrolyte Interphase Growth in Liquid/Solid Electrolytes for Potassium Metal Batteries.

Liquid/solid battery electrolytes make separators dispensable and enable a high cationic transference number with liquid-like room temperature ionic conductivity. This work gives insights into electrochemical behavior (galvanostatic polarization and time-dependent impedance spectroscopy) of liquid/solid electrolytes containing potassium salts in battery cells enclosing potassium metal anodes. Very high potassium transference numbers (t K = 0.88) are observed in carbonate-based electrolytes, linked with long-term mechanical instability of the solid electrolyte interphase on the potassium anode. In the case of glyme-based electrolytes, electrochemical behavior indicates the existence of the highly porous solid electrolyte interphase and additional surface porosity of the potassium electrode.

Ultrafine nanoporous aluminum by electrolytic dealloying of aluminum-magnesium alloys in glyme-based electrolytes with recovery of sacrificial magnesium

Air-free electrolytic dealloying using non-aqueous electrolytes is a sustainable method for creating nanoporous Al (NP-Al) with highly reactive nanoscale-sized ligaments from Al-Mg parent alloys while simultaneously recovering the sacrificial Mg. However, this synthesis strategy is limited in versatility by the low number of available non-aqueous electrolytes that can conduct Mg ions and has so far only been proven to work with all-phenyl complex (APC) electrolyte derived from in situ reaction between two equivalents of Lewis base C₆H₅ClMg and one equivalent of Lewis acid AlCl3 in tetrahydrofuran (THF) solvent. Here we demonstrated that a new electrolyte consisting of MgCl2/AlCl3/Mg(TFSI)2 (or MACT) in glyme-based solvents recently introduced in the Mg-ion battery community can also be used to create NP-Al. This alternative electrolyte exhibits higher electrochemical performance than APC and can create ultrafine NP-Al with ≈ 6–14 nm ligament size, which is smaller than the ≈ 10–20 nm ligament size commonly achieved using APC.

Microporous activated carbon derived from azulmic acid precursor with high sulfur loading and its application to lithium-sulfur battery cathode

We have previously reported that an effective activation method for azulmic acid carbon (AZC: AZC is a carbide of azulmic acid, a nitrogen-containing organic material) as a precursor can produce microporous activated carbon. By improving the activation method of AZC, we succeeded in producing an AZC-based activated carbon that can support a larger amount of sulfur than that of previously reported one while keeping its microporous property. We have found that the present AZC activated carbon has a BET specific surface area of 2633 m2 g−1 and a pore volume of 1.286 cc g−1 and can contain up to 70 wt.% sulfur when an optimum alkaline activator and activation temperature are used. The cathode of this activated carbon can be stably charged and discharged in a lithium-sulfur battery with a glyme-based electrolyte. The present highly sulfur-filled microporous AZC is a promising sulfur host material for lithium sulfur batteries.

Enabling 100C Fast-Charging Bulk Bi Anodes for Na-Ion Batteries.

It is challenging to develop alloying anodes with ultrafast charging and large energy storage using bulk anode materials because of the difficulty of carrier-ion diffusion and fragmentation of the active electrode material. Herein, a rational strategy is reported to design bulk Bi anodes for Na-ion batteries that feature ultrafast charging, long cyclability, and large energy storage without using expensive nanomaterials and surface modifications. It is found that bulk Bi particles gradually transform into a porous nanostructure during cycling in a glyme-based electrolyte, whereas the resultant structure stores Na ions by forming phases with high Na diffusivity. These features allow the anodes to exhibit unprecedented electrochemical properties; the developed Na-Bi half-cell delivers 379mAhg-1 (97% of that measured at 1C) at 7.7Ag-1 (20C) during 3500 cycles. It also retained 94% and 93% of the capacity measured at 1C even at extremely fast-charging rates of 80C and 100C, respectively. The structural origins of the measured properties are verified by experiments and first-principles calculations. The findings of this study not only broaden understanding of the underlying mechanisms of fast-charging anodes, but also provide basic guidelines for searching battery anodes that simultaneously exhibit high capacities, fast kinetics, and long cycling stabilities.

On the Practical Applications of the Magnesium Fluorinated Alkoxyaluminate Electrolyte in Mg Battery Cells.

High-performance electrolytes are at the heart of magnesium battery development. Long-term stability along with the low potential difference between plating and stripping processes are needed to consider them for next-generation battery devices. Within this work, we perform an in-depth characterization of the novel Mg[Al(hfip)4]2 salt in different glyme-based electrolytes. Specific importance is given to the influence of water content and the role of additives in the electrolyte. Mg[Al(hfip)4]2-based electrolytes exemplify high tolerance to water presence and the beneficial effect of additives under aggravated cycling conditions. Finally, electrolyte compatibility is tested with three different types of Mg cathodes, spanning different types of electrochemical mechanisms (Chevrel phase, organic cathode, sulfur). Benchmarking with an electrolyte containing a state-of-the-art Mg[B(hfip)4]2 salt exemplifies an improved performance of electrolytes comprising the Mg[Al(hfip)4]2 salt and establishes Mg[Al(hfip)4]2 as a new standard salt for the future Mg battery research.

Realization of high cycle life bismuth oxychloride Na-ion anode in glyme-based electrolyte

Two-dimensional bismuth oxychloride (BiOCl) is recently explored as an anode in rechargeable alkali-ion batteries because its layered structure facilitates ionic diffusion and higher specific capacities. However, its application is mainly challenged by rapid capacity decay originating from particle pulverization and unstable solid electrolyte interphase (SEI). Herein, we demonstrate the higher cycling stability of BiOCl anode in Na-ion batteries (NIBs) by simply coupling it with diglyme-based electrolyte. The BiOCl anode delivers reversible capacities greater than 295 mA h g−1 for 650 cycles at 100 mA g−1. It also displays excellent rate performances (∼278 and 267 mA h g−1 at 200 and 500 mA g−1, respectively) and higher durability under different current rates. Such stellar performance of BiOCl anode is attributed to the formation of stable SEI and maintenance of electrode integrity as revealed by the post-mortem studies. Besides, the electrochemical (de)sodiation mechanism of BiOCl anode is also clarified through in-operando X-ray diffraction (XRD) studies, which reveals the reversible formation of Bi ↔ NaBi ↔ cubic-Na3Bi phases. This report emphasizes the importance of electrolyte engineering as an excellent way to build stable SEI and achieve high-performance advanced alloy anodes for NIB application.