Zinc-bromine batteries (ZBBs) hold great potential for large-scale energy storage due to their high energy density, sustainability, and cost-effectiveness. However, the practical application of flowless ZBBs is hindered by self-discharge (SD) from uncontrolled bromine diffusion and the overlap of the Br⁻/Br2 redox potential with the oxygen evolution reaction (OER). Additionally, the limited solubility of bromine complexing agents (BCAs) in aqueous media poses a significant challenge. Here, we introduce a targeted localized presence (TLP) strategy, encapsulating hydrophobic BCAs within porous activated carbon electrodes to address these limitations. By examining three BCA structures, we demonstrate that TLP effectively reduces SD and increases coulombic efficiency. We show that the formation of hydrophobic phases within the pores can be controlled by manipulating the BCA alkyl chain length. This tailored TLP approach minimizes OER susceptibility and extends the voltage window to 2.7V (0.1M ZnBr2). Nuclear magnetic resonance analysis highlights the aggregation behavior of BCAs, elucidating their role in stabilizing the system. Remarkably, insoluble BCAs with hexyl side chains achieved >98% CE at 200 mAh/g over 1000 cycles at 1 A/g. This work presents a robust pathway for advancing aqueous zinc-halide batteries towards scalable and durable energy storage solutions.

Composite solid electrolytes with ceramic particles dispersed in polymeric matrices are promising for all-solid-state batteries, based on active metal anodes. However, a systematic analysis of the beneficial features that ceramic particles in polymeric electrolytes can provide, was never done so far. In this study, we offered electrochemical methods based on previous experience with liquid electrolytes to distinguish between the resistance of interfacial surface films and the resistance of charge transfer processes. In all-solid-state batteries, charge transfer and ion migration through surface films may have similar time constants, which makes electrochemical analyses of these systems a great challenge. We report herein on developing a method termed: "Range of Potentials Impedance Spectroscopy" (RPIS). The underlying concept of this method is that changes in cells potentials during their operation should accelerate the kinetics of charge transfer processes but should affect only moderately migration of ions through interfacial surface films. Consequently, it may be possible to evaluate separately resistances that reflect charge transfer and ionic migration processes. Here, we present the method using a specific case as a prototype: 30% weight of Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LTAP) was embedded in PEO 20 :LiTFSI matrices. (denoted as LATP30 electrolyte). LATP30-based Li||LiFePO 4 batteries show superior performance: after ~150 cycles, cells retained 84% of their original capacity in comparison to the same batteries, LATP free, that showed only 51% capacity retention after 150 cycles. At 5C, these cells with the composite polymeric electrolyte demonstrated 43% higher discharge capacity than their counterparts. In symmetric cells and all-solid-state batteries, LATP30 lowers the impedance of the electrode-electrolyte interfaces, conferring stability during cycling. By applying RPIS, we could identify the electrochemical barrier that the presence of LATP helps to lower. We discovered that LATP reduces both surface film and charge transfer resistances, enabling batteries to withstand prolonged cycling and high C-rates. These results have significant implications for further studies that should focus significantly on interfacial impedances as major barriers, rather than on bulk electrolyte resistance as a key factor. Reference: Ortal Breuer et al J. Electrochem. Soc. 2023, 170, 090509

Several decades after the invention of the flow Zn-Br2 systems persistent attempts have been made to develop stationary Zn-Br2 batteries. Such development should increase the energy density of the system simultaneously significantly reducing their cost and opening new challenges associated with the cell design and its performance. One of the major concerns is the rapid self-discharge of stationary systems leading to spontaneous charge loss during battery storage time. While self-discharge in flow cells is generally attributed to the chemical oxidation of the Zn anode, we show that the origin of self-discharge in a static configuration is completely different. By systematic investigations of activated carbon with different surface areas under varied charging conditions, mechanistic insights into this phenomenon were provided. Based on this understanding, we proposed herein an effective way to suppress the cathode's self-discharge by encapsulation of a bromine complexing agent inside the electrode's pore matrix. The modified electrodes unveil unique chemical kinetics of deaggregation of the stable fuse salt phase composed of bromine complexing agent and Br3− anions upon discharging. To the best of our knowledge, such a phenomenon has not been reported yet. The proposed system demonstrates high capacity (up to 300mAh/g) and impressive long-term stability.

In recent years, there have been extensive debates regarding the charging mechanism of MnO2 cathodes in aqueous Zn electrolytes. The discussion centered on several key aspects including the identity of the charge carriers contributing to the overall capacity, the nature of the electrochemical process, and the role of the zinc hydroxy films that are reversibly formed during the charging/discharging. Intense studies are also devoted to understanding the effect of the Mn2+ additive on the performance of the cathodes. Nevertheless, it seems that a consistent explanation of the α-MnO2 charging mechanism is still lacking. To address this, a step-by-step analysis of the MnO2 cathodes is conducted. Valuable information is obtained by using in situ electrochemical quartz crystal microbalance with dissipation (EQCM-D) monitoring, supplemented by solid-state nuclear magnetic resonance (NMR), X-ray diffraction (XRD) in Characterization of Materials, and pH measurements. The findings indicate that the charging mechanism is dominated by the insertion of H3O+ ions, while no evidence of Zn2+ intercalation is found. The role of the Mn2+ additive in promoting the generation of protons by forming MnOOH, enhancing the stability of Zn/α-MnO2 batteries is thoroughly investigated. This work provides a comprehensive overview on the electrochemical and the chemical reactions associated with the α-MnO2 electrodes, and will pave the way for further development of aqueous cathodes for Zn-ion batteries.

Aqueous electrolytes offer enhanced safety and environmental friendliness for next-generation energy storage systems, but a narrow electrochemical stability window limits their application. This study provides a comprehensive analysis of the relationship between water activity and the electrochemical stability window of aqueous electrolytes, critically examining current expansion strategies. Our investigation reveals that stability window expansion is primarily driven by kinetic factors rather than thermodynamic ones. We demonstrate that decreasing water activity predominantly affects the oxygen evolution reaction, with minimal impact on hydrogen evolution. This asymmetric effect is quantified through Tafel analysis, showing a significant decrease in exchange current density with reduced water activity. Notably, this study is the first to establish a direct correlation between water activity and the electrochemical stability window for aqueous electrolytes, providing fundamental insights into how water activity influences electrode reaction kinetics and overall system stability. We critically evaluate existing approaches to reducing water activity, including high-concentration electrolytes, water-in-salt systems, and hydrophobic ions. While these methods widen the electrochemical window, they lead to decreased ionic conductivity and increased viscosity. In "water-in-salt" electrolytes, conductivity drops to levels comparable to organic electrolytes while viscosity increases exponentially. This work challenges the focus on maximizing stability windows at the expense of other crucial properties. We argue for a balanced approach in aqueous electrolyte design, considering factors such as ionic mobility, salt solubility, viscosity, operational temperature range, and electrochemical stability.

The discovery of the Ti 3 C 2 T x compounds (MXenes) a decade ago opened new research directions and valuable opportunities for high‐rate energy storage applications. The unique ability of the MXenes to host various mono‐ and multivalent cations and their high stability in different electrolyte environments including aqueous, organic, and ionic liquid solutions, promoted the rapid development of advanced MXene‐based electrodes for a large variety of applications. Unlike the vast majority of typical intercalation compounds, the electrochemical performance of MXene electrodes is strongly influenced by the presence of co‐inserted solvent molecules, which cannot be detected by conventional current/potential electrochemical measurements. Furthermore, the electrochemical insertion of ions into MXene interspaces results in strong coupling with the intercalation‐induced structural, dimensional, and viscoelastic changes in the polarized MXene electrodes. To shed light on the charging mechanisms of MXene systems and their associated phenomena, the use of a large variety of real‐time monitoring techniques has been proposed in recent years. This review summarizes the most essential findings related to the charging mechanism of Ti 3 C 2 T x electrodes and their potential induced structural and mechanical phenomena obtained by in situ investigations.

The introduction of the water-in-salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re-evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter-ions), surprisingly, the dominant factor influencing its electrochemical performance, including long-term electrode stability, is the type of the co-ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Composite solid electrolytes with ceramic particles dispersed in a polymer matrix are considered a correct choice for all-solid-state batteries. These electrolytes balance the high ionic conductivity of superionic-ceramic conductors and the elasticity of polymers. Here, Li||LiFePO 4 batteries with 30 wt% of LATP embedded in PEO 20 :LiTFSI show superior performance at elevated temperature. After ∼150 cycles, cells retained 84% of their original capacity compared to only 51% for batteries with no additive. At 5 C cells demonstrate 43% higher capacity. In symmetric cells with blocking and non-blocking electrodes and all-solid-state batteries LATP lowers the impedance of the electrode-electrolyte interface ensuring cycling stability. LATP improves performance by stabilization of the cathode-electrolyte interface, apparently the major contributor to the cell impedance.

The exploration of cathode and anode materials that enable reversible storage of mono and multivalent cations has driven extensive research on organic compounds. In this regard, polyimide (PI)-based electrodes have emerged as a promising avenue for the development of post-lithium energy storage systems. This review article provides a comprehensive summary of the syntheses, characterizations, and applications of PI compounds as electrode materials capable of hosting a wide range of cations. Furthermore, the review also delves into the advancements in PI based solid state batteries, PI-based separators, current collectors, and their effectiveness as polymeric binders. By highlighting the key findings in these areas, this review aims at contributing to the understanding and advancement of PI-based structures paving the way for the next generation of energy storage systems.

The use of fast surface redox storage (pseudocapacitive) mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so quite rapidly. Yet, few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Here we demonstrate that two-dimensional transition metal carbides (MXenes) can operate at rates exceeding those of conventional EDLCs, but still provide higher volumetric and areal capacitance than carbon, electrically conducting polymers or transition metal oxides. We applied two distinct designs for MXene electrode architectures with improved ion accessibility to redox-active sites. A macroporous Ti3C2Tx MXene film delivered up to 210 F g−1 at scan rates of 10 V s−1, surpassing the best carbon supercapacitors known. In contrast, we show that MXene hydrogels are able to deliver volumetric capacitance of ∼1,500 F cm−3 reaching the previously unmatched volumetric performance of RuO2. Pseudocapacitors based on redox-active materials have relatively high energy density but suffer from low power capability. Here the authors report that two-dimensional transition metal carbides exhibit high gravimetric, volumetric and areal capacitance values at high charge/discharge rates.

Large grid energy storage devices are critical for the success of the clean and sustainable energy revo-lution. As Li-ion batteries are earmarked for electric vehicles and portable devices such as laptops and cellphones, other electrochemical systems should be developed that enable cost-effective, safe, and durable large-scale energy storage. Due to the low cost and non -flammability of aqueous electrolyte solutions, much effort is being put into the development of 'beyond-Li' batteries and super capacitors that can work in these environments. Here, we propose new proton batteries comprising an acetic acid electrolyte solution, NiII [FeIII(CN)6]2/3$4H2O Prussian blue analog cathodes, and Ti3C2Tx MXene anodes. Both electrodes were investigated independently to discover ideal settings for the electrochemical performance and stability. Significant attention was given to the cathodes' protons storage mechanism. In-situ electrochemical quartz crystal microbalance with dissipation revealed that in acetic acid, hy-dronium and proton insertion contribute to charge storage, whereas in sulfuric acid-based electrolyte solutions, the main charge carriers are bare protons. 4.5 M acetic acid solution provided the best per-formance in terms of electrodes' capacitance and rate capability. The battery systems presented here show a promising direction but require further intensive optimization efforts. This research opens the way for research and development of novel proton batteries based on solutions containing common weak acids for more cost-effective and environmentally friendly energy storage systems.(c) 2022 Elsevier Ltd. All rights reserved.

One of the biggest hurdles to realise high-performance Li-metal batteries is the instability of Li metal towards all relevant electrolytes. Now, an approach is reported to improve Li cells’ stability by upshifting the Li electrodes’ potential to reduce their voltage gap with the electrolyte electrochemical stability windows.

The optimal performance of organic electrodes for aqueous batteries requires their full compatibility with selected electrolyte solutions. Electrode materials having 1-3-dimensional structures of variable rigidity possess a confined space in their structure filled with water and electrolyte solutions. Depending on the rigidity and confined space geometry, insertion and extraction of ions into electrode structures are often coupled with incorporation/withdrawal of water molecules. Aside from the scientific interest in understanding the charging mechanism of such systems, co-insertion of solvent molecules affects strongly the charge storage capability of the electrodes for energy storage devices. We present herein in situ electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) investigations of polyaniline (PANI) electrodes operating in various aqueous Na+-containing electrolytes, namely, Na2SO4, NaClO4, NaBF4, and NaPF6. Careful analysis of the EQCM-D results provides a dynamic snapshot of the mixed anionic/protonic fluxes and the accompanying water molecules' insertion/extraction to/from the PANI electrodes. Based on our observations, it was found that the charging mechanism, as well as the capacity values, strictly depends on the electrolyte pH, the chaotropic/kosmotropic character of the anionic dopants, and the amount of the extracted water molecules. This study demonstrates the effectiveness of analysis by EQCM-D in selecting electrolytes for batteries comprising organic electrodes.

Netanel Shpigel, Mikhael D Levi, Sergey Sigalov, Doron Aurbach, Leonid Daikhin and Volker Presser 1 Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel 2 School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat Aviv 69978, Israel 3 INM—Leibniz Institute for New Materials, 66123 Saarbrücken, Germany 4 Department of Materials Science and Engineering, Saarland University, 66123 Saarbrücken, Germany

Extensive efforts are currently underway to develop safe and cost-effective electrolytes for large-scale energy storage. In this regard, water-based electrolytes may be an attractive option, but their narrow electrochemical stability window hinders their realization. Although highly concentrated fluorinated electrolytes have been shown to be highly effective in suppression of water splitting, enabling significant widening of the applied potential range, they utilize expensive salts (e.g., lithium bis(trifluoromethane sulfonyl) imide [LiTFSI] or lithium trifluoromethane sulfonate [LiOTf]); hence, they cannot be considered for practical applications. Here, we demonstrate a cost-effective aqueous electrolyte solution combining 14 M LiCl and 4 M CsCl that allows stable operation of a 2.15-V battery comprising a TiO2 anode and LiMn2O4 cathode. Addition of CsCl to the electrolyte plays a double role in system stabilization: the added chloride anions interact with the free water molecules, whereas the chaotropic cesium cations adsorb at the electrified interface, preventing hydrogen formation.

The emerging interest in aqueous rechargeable batteries has led to significant progress in the development of next-generation electrolytes and electrode materials enabling reversible and stable insertion of various multivalent ions into the electrode's bulk. Yet, despite its abundance, high salt solubility, and small ionic radius, the use of manganese ions for energy storage purposes has not received sufficient attention. Herein, we present the use of Mo6S8 (Chevrel phase) as an anode for Mn2+ insertion. By careful optimization of the electrolyte solution, high-capacity values exceeding 90 mAh/g and long-term stability (more than 1500 cycles) have been obtained. Based on in situ XRD analysis, the charging mechanism and the associated structural changes occurring during Mn2+ insertion have been carefully studied. Finally, we demonstrate for the first time a rocking chair aqueous Mn-ion battery comprising a Chevrel anode and NiHCF cathode.

Lithium-ion batteries are commonly charged following the constant current -constant voltage (CC-CV) protocol. Current flow during charging implies an equivalent ionic flow through the battery materials. Intercalation and de-intercalation of Li + are accompanied by concentration gradients that are reflected by the rise in the cells’ potentials that is required to maintain the constant current during the CC regime. In this work, two new pulsed charging protocols were tested. Firstly, a square current pulse is applied to the cell until the cut-off voltage is reached, followed by a pulsed square voltage protocol (PV). The second methodology keeps the same current pulse, however, after the limiting voltage was reached, the pulsing regime consisted in alternating between a maximum voltage value and a minimum, non-zero, constant current value. Different voltage pulse widths and frequencies were tested, in order to study the maximum electrodes’ capacity, the time required to reach that capacity, the contribution of each individual step (i.e. PC and PV) to the total electrodes’ capacity, and the thermal variations for each. The second pulsing mode produced capacity values 7%–8% higher than in the classical CC–CV protocol, and in charging times periods from 5%–25% faster, without compromising the batteries’ cycle life.

The purpose of this paper is to suggest frontier inter-disciplinary research directions that can be considered as important horizons of modern electrochemistry in the field of energy storage and conversion. We selected several topics that call for advancements in solid-state, interfacial, analytical and energy-related electrochemical science. A dramatic improvement in the performance of energy storage and conversion devices is needed to meet the urgent demands of our society. Significantly more efficient devices are needed to meet two major challenges: electro-mobility, namely electrochemical propulsion of electric vehicles, and the ability to store and convert large quantities of energy generated from sustainable sources such as sun and wind. We suggest promotion of breakthroughs in several important directions. The examples chosen include: Development of novel in-situ methodologies for design and testing composite electrodes for advanced energy storage devices; Improving the electrochemical performance of high specific capacity, but hard to control, LiNiO2 cathodes for advanced lithium ion batteries designed for electric vehicles, with a quantitative goal of stable specific capacity >230 mAh/g with a charging potential lower than 4.3 V; Advancing aqueous electrochemical systems for large energy storage based on sodium electrochemistry; Promoting development of batteries based on multivalent active metals with magnesium as the most advanced example. There is a strong incentive to promote fundamental and practical progress in the field of rechargeable Mg batteries using new electrodes' configurations and advanced electroanalytical methods. All these directions require deep efforts in basic, fundamental studies, in order to reach important practical goals.

The need for improved batteries and supercapacitors, which are not based on lithium compounds, promotes significant research efforts to find suitable alternative systems based on various mono and multivalent cations capable of delivering high energy and power density with good long-term stability. The progress in aqueous Zn-ion batteries and supercapacitors obtained over the past years lead to the development of new structures and compounds that enable revisable hosting of Zn-ions while keeping good structural integrity. Yet, as aqueous electrolytes involve also the generation and co-insertion of protons it is necessary to carefully define what is the charge storage mechanism in these Zn insertion compounds. In this work, the use of Ti3C2Tx as an anode for the Zn-ion system was evaluated for the first time in different ZnCl2 concentrations. Remarkable changes in the charge storage mechanism and the performance of the Ti3C2Tx electrodes were observed by moving from dilute Zn electrolytes (1 M) to higher concentrations. The high acidity of the concentrated ZnCl2 solutions results in an additional charge storage mechanism that arises from redox interactions between the MXene and the released protons and hence enhanced capacity values (60 mAh/g with good rate capability and capacity retention of 89.4% after 9000 cycles). In-situ EQCM-D measurements were employed to shed light on the charge storage mechanism of the Ti3C2Tx and the exact identity of the charge carrier inserted into the electrodes. The demonstrated EQCM-D based analysis provides precise quantification of the Zn-ion to proton ratio in the examined system and can be further applied for other aqueous Zn-ion electrodes and multivalent systems as well.