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The binder plays a crucial role in maintaining the integrity and enhancing the conductivity of the electrode, although it accounts for a small weight fraction in the entire electrode. However, the conventional binder used in lithium-sulfur (Li-S) batteries fails to effectively tackle the challenges posed by the shuttle effect of lithium polysulfides, as well as the issues of poor conductivity and volume expansion of sulfur. These limitations greatly hinder the performance and overall efficiency of Li-S batteries. In this study, a waterborne polyurethane binder with lithium-ion (Li-ion) conductivity and an elastic 3D network structure is synthesized, integrating a diverse range of functional groups. The polyethylene glycol in the polyurethane binder significantly enhances the Li-ion conductivity due to its abundant electronegative oxygen atoms, consequently reducing the need for electrolyte. The presence of multi-functional polar groups endows the polymer binder with notable adsorption capability, effectively mitigating the undesirable shuttle effect. The 3D network formed by the crosslinking reaction between polyurethane and the aziridine crosslinker enables the accommodation of volume expansion during cycling. Benefitting from these characteristics, the designed waterborne binder endows the Li-S batteries with improved long-cycle stability and rate capability compared to polyethylene oxide and polyvinylidene fluoride binders under lean electrolyte conditions. A waterborne multifunctional 3D network binder is elaborately developed for lithium-sulfur batteries to accommodate the volume expansion, adsorb lithium polysulfides, and provide satisfactory Li-ion conductivity under lean electrolyte conditions.

The practical application of aqueous rechargeable batteries faces several challenges due to the limited stability window of electrolytes and parasitic side reactions, such as corrosion, passivation, gas evolution, and co-intercalations. The solid electrolyte interphase (SEI) formed at the electrode/electrolyte interface plays a critical role in determining interfacial properties and battery performance. Efforts are being made to develop effective SEIs, functionalize interphase layers, and explore various aqueous hybrid electrolytes that facilitate SEI formation. This review highlights the role of interphasial structures in aqueous batteries. First, common issues encountered by aqueous batteries and specific characteristics of aqueous lithium-ion, sodium-ion, zinc-ion, and aluminum-ion batteries are outlined. Then the tactics used to improve cycle stability of aqueous batteries are introduced and compared and the working principles and key parameters from the context of interphasial modification are discussed. Finally, constructive insights and suggestions for developing high-performance batteries are offered, with a focus on SEI formation and interphase layer design.

Among the many approaches to improve the performance of lithium-metal batteries, ternary polyethylene oxide/ionic liquid/lithium salt electrolytes offer several advantages such as low flammability, high conductivity ( vs. polyethylene oxide/lithium salt electrolytes) and, to a large extent, limiting the growth of dendrites at moderate currents. However, they suffer from relatively low mechanical strength for lithium metal confinement. Besides, the lithium transport numbers are very low, which is conducive to lithium depletion during plating at high current densities at the lithium/electrolyte interface. Thus, we show here that the combination of a ternary solid polymer electrolyte with a single-ion polymer-based conducting interlayer allows for a significant improvement of the cyclability of the lithium metal anode. This results in a strong improvement of the electrochemical performance of lithium-metal batteries using solid polymer electrolytes at 80 degrees C, with an 85% capacity retention after 350 cycles ( vs. 60% after 62 cycles for the uncoated anode). This is attributed, via focused ion beam-scanning electron microscopy and X-ray photoelectron spectroscopy, to a denser lithium deposit, better contact with the electrolyte and a reduced reactivity of electrolyte species with the interlayer.

The development and application of Electrochemical Quartz Crystal Microbalance (EQCM) sensing to study metal electroplating, especially for energy storage purposes, are reviewed. The roles of EQCM in describing electrode/electrolyte interface dynamics, such as the electric double-layer build-up, ionic/molecular adsorption, metal nucleation, and growth, are addressed. Modeling of the QCM sensor is introduced and its importance is emphasized. Challenges of metal electrode use, including side reactions and dendrite formation, along with their mitigation strategies are reviewed. Numerous factors affecting the electroplating processes, such as electrolyte composition, additives, temperature, and current density, and their influence on the electroplated metals' mass, structural, and mechanical characteristics are discussed. Looking forward, the need for deeper fundamental understanding and advancing simulations of the QCM signal response as a result of electroplating metal nanostructures is stressed. Further development and integration of innovative EQCM-strategies will provide unique future means to fundamentally understand and optimize metal electroplating for energy storage and application alike. Quartz Crystal Microbalance (QCM) in the study of metal electroplating for energy storage is reviewed herein. QCM's historical development, sensitivity in detecting minute metal changes, and integration with other techniques for electrolyte and additive screening are discussed. Innovative metal plating strategies, recent advancements in QCM, and future applications of high-throughput, automated research in material science and electrochemistry are highlighted. image

Aqueous zinc–bromine (Zn–Br₂) batteries feature operational safety and high-energy and high-power densities, but suffer from polybromide dissolution in the cathode and the low reversibility of Zn metal in the anode. Here, we demonstrate that these challenges can be simultaneously tackled by using a fully exploited imidazolium bromide (MPIBr). An in-depth analysis demonstrates that MPIBr enhances both the reversibility and kinetics of Zn anodes. This enhancement arises from MPI⁺ cations participating in the formation of an H₂O-scarce inner Helmholtz plane, suppressing water-associated side reactions. Additionally, electron-donating Br⁻ ions contribute to the Zn²⁺-solvation sheath, forming [Zn(H₂O)₅Br]⁺ that promotes Zn²⁺ migration and faster interfacial kinetics. Furthermore, the robust chelation between the MPI⁺ cation and Br_x⁻ species significantly impedes shuttling. Notably, the Br⁻ anion and Zn²⁺ cation in the electrolyte can construct a dual-plating Zn–Br₂ battery, eliminating the necessity for active materials on both the cathode and anode. The as-prepared dendrite-free and shuttle-free dual-plating Zn–Br₂ batteries demonstrate stable cycling for 1000 cycles even under 100% depth of discharge. This work deepens the understanding of electrolyte composition on electrode interfaces, driving the advancement of high-performance and cost-effective Zn-halogen batteries.

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)₂)- and magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)₄]₂)-based electrolytes, each with and without MgCl₂, on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM−D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip)₄]₂-based electrolytes, highly efficient and interphase-free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so-called initial conditioning process. With the more reactive Mg(TFSI)₂-based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode

Aqueous lithium-ion batteries (ALIBs) are promising for large-scale energy storage systems because of the cost-effective, intrinsically safe, and environmentally friendly properties of aqueous electrolytes. Practical application is however impeded by interfacial side-reactions and the narrow electrochemical stability window (ESW) of aqueous electrolytes. Even though higher electrolyte salt concentrations (e.g., water-in-salt electrolyte) enhance performance by widening the ESW, the nature and extent of side-reaction processes are debated and more fundamental understanding thereof is needed. Herein, the interfacial chemistry of one of the most popular electrode materials, V₂O₅, for aqueous batteries is systematically explored by a unique set of operando analytical techniques. By monitoring electrode/electrolyte interphase deposition, electrolyte pH, and gas evolution, the highly dynamic formation/dissolution of V₂O₅/V₂O₄, Li₂CO₃ and LiF during dis-/charge is demonstrated and shown to be coupled with electrolyte decomposition and conductive carbon oxidation, regardless of electrolyte salt concentration. The study provides deeper understanding of interfacial chemistry of active materials under variable proton activity in aqueous electrolytes, hence guiding the design of more effective electrode/electrolyte interfaces for ALIBs and beyond.

Anode-free zinc batteries offer reduced weight and simplified production compared to traditional zinc metal batteries, but challenges such as dendrite formation and parasitic reactions limit their efficiency and cycle life. In this study, we present an effective strategy to form a zincophilic interphase in situ via indium co-deposition during cycling, using InCl3 as an electrolyte additive. Zinc plating/stripping processes were investigated using operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and hydrodynamic spectroscopy, combined with other ex situ techniques. Our findings demonstrate that the indium-containing electrolyte additive has three functions: it induces oriented zinc deposition through prenucleation, suppresses the hydrogen evolution reaction by forming an indium intermediate layer, and suppresses zinc hydroxide sulfate (ZHS) formation by consuming OH– with In2O3/InOOH formation. These advantages result in a decreased overpotential and higher Coulombic efficiency, enhancing the design of highly reversible anode-free zinc batteries.

Rechargeable magnesium batteries could provide future energy storage systems with high energy density. One remaining challenge is the development of electrolytes compatible with the negative Mg electrode, enabling uniform plating and stripping with high Coulombic efficiencies. Often improvements are hindered by a lack of fundamental understanding of processes occurring during cycling, as well as the existence and structure of a formed interphase layer at the electrode/electrolyte interface. Here, a magnesium model electrolyte based on magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)₂) and MgCl₂ with a borohydride as additive, dissolved in dimethoxyethane (DME), was used to investigate the initial galvanostatic plating and stripping cycles operando using electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). We show that side reactions lead to the formation of an interphase of irreversibly deposited Mg during the initial cycles. EQCM-D based hydrodynamic spectroscopy reveals the growth of a porous layer during Mg stripping. After the first cycles, the interphase layer is in a dynamic equilibrium between the formation of the layer and its dissolution, resulting in a stable thickness upon further cycling. This study provides operando information of the interphase formation, its changes during cycling and the dynamic behavior, helping to rationally develop future electrolytes and electrode/electrolyte interfaces and interphases.

Layered TiS₂ has been proposed as a versatile host material for various battery chemistries. Nevertheless, its compatibility with aqueous electrolytes has not been thoroughly understood. Herein, we report on a reversible hydration process to account for the electrochemical activity and structural evolution of TiS₂ in a relatively dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate in TiS₂ layers together with Li⁺ cations, forming a hydrated phase with a nominal formula unit of Li_0.38(H₂O)_2−δTiS₂ as the end-product. We unambiguously confirm the presence of two layers of intercalated water by complementary electrochemical cycling, operando structural characterization, and computational simulation. Such a process is fast and reversible, delivering 60 mAh g^–1 discharge capacity at a current density of 1250 mA g^–1. Our work provides further design principles for high-rate aqueous Li-ion batteries based on reversible water cointercalation.