Dilute Aqueous Electrolyte Research Articles

Long-duration aqueous Zn-ion batteries achieved by dual-salt highly-concentrated electrolyte with low water activity

Aqueous Zn-ion batteries have attracted much attention due to their unique high safety and low-cost merits. However, their practical applications are at a slow pace due to their short cycle life, which fundamentally results from the instability of the positive/negative electrode interface in the traditional dilute aqueous electrolytes with high water activity. Developing highly concentrated electrolyte (HCE) has been considered as an effective solution. Unlike previous studies of single salt-based HCE (SS-HCE), herein, a new dual-salt HCE (15 m ZnCl2 + 10 m NH4NH2SO3 DS-HCE) was proposed for the first time. DS-HCE was proven to simultaneously possess higher conductivity than traditional dilute electrolytes and ultralow water activity of SS-HCE by the regulation of dual high-concentration salts on the solvation structure, which renders the Zn||Zn symmetric cell the record-long cycling life of 2200 h compared with those with SS-HCE (30 m ZnCl2, 300 h) and other reported HCEs. Additionally, the Zn||NH4V4O10 full cell with DS-HCE demonstrated impressed rate capability within a wide-range current densities from 0.1 to 10 A g−1. Moreover, at the high current density of 5 A g−1, the full cell shows almost 100% capacity retention after 4000 cycles, which indicates the promising future of the DS-HCE system for long-duration aqueous Zn-ion batteries.

Electrophoresis Characterization of Nanoplastic Particle Surface Charge in Dilute Aqueous Electrolytes

Electrophoresis Characterization of Nanoplastic Particle Surface Charge in Dilute Aqueous Electrolytes

Dilute aqueous hybrid electrolyte endows a high-voltage window for supercapacitors

Developing aqueous electrolyte with wide electrochemical stability window (ESW) is one of the key technologies to boosting the energy density of aqueous electrochemical double-layer capacitors (EDLCs). However, expanding the ESW using super-concentrated electrolytes comes at the expense of cost, ionic conductivity and the mass density of the device. Herein, we selected a cost-effective and environmentally friendly molecular crowding agent, polyethylene glycol dimethyl ether (PEGDME-250), as the electrolyte additive designed to achieve high ESW at low salt concentrations. First, PEGDME can reduces the activity of water and increases the ESW of the electrolyte by forming hydrogen bonds with free water molecule. In addition, PEGDME does not have the interaction between terminal groups compared to conventional polyethylene glycols (PEG), which helps to reduce the viscosity and improve the ionic conductivity of the electrolyte. By adjusting the composition of the electrolyte, the optimal electrolyte with a high ESW of 2.96 V was achieved with the formula of 3 m NaClO4-25 % H2O-75 % PEGDME. The EDLCs assembled with this diluted aqueous electrolyte and YP-50 F electrodes presents a high operational voltage window of 2.4 V and outstanding cycle stability (>10000 cycles), and maintains excellent rate performance in a temperature range of −10–35 ℃.

A 2.4 V Aqueous Zinc-Ion Battery Enabled by the Photoelectrochemical Effect of a Modified BiOI Photocathode: Shattering the Shackle of the Electrochemical Window of an Aqueous Electrolyte.

Aqueous zinc-ion batteries emerge as a promising energy storage system with merits of high security, abundance, and being environmentally benign. But the low operating voltages of aqueous electrolytes restrict their energy densities. Previous reports have mostly focused on modifying the electrolytes to enlarge the operating voltages of aqueous zinc-ion batteries. However, either extra-expensive salts or potential safety hazards of organic additives are considered to be adverse for practical large-scale applications. Here, a proof-of-concept to enlarge the operating voltage of an aqueous zinc-ion battery by incorporating a well-designed semiconductor photocathode is proposed, which produces a photovoltage (Vph) across the semiconductor/liquid junction (SCLJ) interface to elevate the output voltage of zinc-ion battery under irradiation. The operating voltage of an aqueous zinc-ion battery can be markedly raised from 1.78 (thermodynamic limit) to 2.4 V when a BiOI nanoflake array photocathode with good surface modification is introduced, achieving a round-trip efficiency of 114.3% and a 34.8% increase of energy density compared to the theoretical value. The successive ionic layer adsorption and reaction modified surface effectively passivates surface trap defects of the BiOI photocathode and thus enlarges its Vph from 60 to 240 mV under irradiation. This study provides a design to enlarge the output voltages of aqueous zinc-ion batteries and other energy storage systems, providing insight into widening the voltage window, which is that the operating voltages are determined by photocathode under irradiation and not restricted by the electrochemical stability window of dilute aqueous electrolytes.

Bridging Aqueous and Organic Electrolytes: Intercalation Mechanism of TiS2 in Sustainable Aqueous Li-Ion Batteries

Aqueous Li-ion batteries (ALiBs) are a promising alternative for large-scale grid storage owing to water's non-flammability, low cost, and ease of purification. However, the narrow electrochemical stability window (ESW) of water (1.23 V) significantly limits the energy density of ALiBs, compared to their non-aqueous counterpart. The use of a highly concentrated electrolyte, such as 21 mol kg-1 (molality, m) of LiTFSI in water, known as the “water-in-salt” (WiS) electrolyte, can widen the water ESW to ~3 V, but its high cost and low environmental sustainability hinder the commercialization of ALiBs. Therefore, we explored the feasibility of cycling layered TiS2 anodes in ALiBs containing dilute electrolytes (i.e. 2 m LiTFSI in water).We obtained a reversible discharge capacity of ca. 80 mAh g-1 at a current density of 50 mA g-1. By employing three-electrode cycling with online electrochemical mass spectrometry, we identified potential-dependent gas evolution from the cell triggered by multiple chemical/electrochemical reactions, such as (1) solvent co-intercalation, (2) partial TiS2 exfoliation, and (3) TiS2-catalyzed water splitting in dilute aqueous electrolytes. We also identified a completely different potential profile of TiS2, when cycled in an aqueous electrolyte, with two distinct redox plateaus at 2.95 V and 2.88 V, followed by a sloping region until 2.3 V (all vs. Li+/Li0). Recall that in classic non-aqueous electrolytes, TiS2 shows a characteristic sloping profile centered at ca. 2.2 V, the peculiar potential profile suggests a different intercalation mechanism of TiS2 in aqueous electrolytes.In this presentation, we will share our latest findings from complementary physicochemical and computational methods to tackle the complex interfacial reactivity between layered anodes and aqueous electrolytes. Operando synchrotron X-ray diffraction data revealed the reversible uptake-release of water molecules between TiS2 layers, which was also confirmed energetically favorable by theoretical modeling. By introducing triethyl phosphate (TEP) as a co-solvent, we successfully tuned the electrochemical intercalation behavior of TiS2 from purely Li-intercalation (as in non-aqueous systems, when using only TEP as the solvent) to hydrated-Li-intercalation (as in concentrated and dilute aqueous electrolytes, when using water/TEP mixtures as the solvent). These findings suggest that solvent co-intercalation can be a promising strategy for ALiBs. The general implication of these results on the electrode-electrolyte interface and interphase in aqueous batteries will be systematically discussed in the talk. Overall, our work provides new perspectives on developing sustainable energy storage technologies. Figure 1

High-Rate Electrochemical Energy Storage of MXene in Neutral Aqueous Electrolytes

Increasing demand for electrochemical energy storage devices with high energy density, high power density, and long lifespan has posed significant challenges for developing suitable electrodes and electrolyte systems with fast charge transport kinetics and superior cycling stability.1 As one of the promising electrode materials explored recently, MXenes (Mn+1XnT x ) are a group of two-dimensional transition metal carbides and/or nitrides, in which M is early transition metal, X presents C and/or N, T x stands for the surface groups such as =O, -OH, -Cl or -F. They exhibit excellent high-rate performance in electrochemical energy storage applications due to their unique properties: superior electronic conductivity (~15 000 S cm-1) and large interlayer spacing (~1 nm).2 The charge storage mechanism and performance of the MXenes electrode is highly dependent on the electrode and electrolyte composition. For example, Ti3C2T x has shown rapid pseudocapacitive (de)intercalation of protons and transformation between the oxygen surface groups (=O) and hydroxyl (-OH) groups in acidic aqueous electrolytes.3,4 As a result, Ti3C2T x exhibits an ultrahigh volumetric capacitance of 1500 F cm-3 in H2SO4 electrolyte.5 In less corrosive neutral aqueous electrolytes, the cation intercalation is accompanied by negligible charge transfer, leading to ultrafast charge storage.6 Consequently, a moderate capacitance with superior cycling stability is reported in neutral electrolytes compared to acidic electrolytes. In contrast to dilute aqueous electrolyte, which has a limited electrochemical stability window (ESW), the highly concentrated water-in-salt (WIS) electrolyte possesses a large ESW (∼3.0 V) owing to the depressed activity of free water. Besides, the unique solvation structure of WIS electrolyte induces a novel intercalation of fully-solvated Li+ at positive potential and increases the capacitance of MXene.7 As a result, WIS electrolyte helps overcome the drawback of the low energy density of MXene in neutral aqueous electrolytes.In our research, we explored the impact of MXene structure and a novel electrolyte system on the pseudocapacitive performance of MXene. The charge storage behavior of Ti3C2T x in a molecular crowding electrolyte was explored. Interestingly, Ti3C2T x displayed one pair of redox peaks with low polarization, differing from both dilute neutral aqueous electrolyte and WIS electrolyte, which may be attributed to the intercalation of Polyethylene glycol (PEG)-solvated Li+ cluster. The in situ X-ray diffraction are employed to better understand the charge storage process. We also constructed a MXene/polymer heterostructure with enlarged interlayer spacing. The unique heterostructure delivered a significantly enhanced rate performance in neutral aqueous electrolyte. (a high capacitance retention of 81% at 10 A g-1)Reference: Simon, P. & Gogotsi, Y. Nature Materials 7, 845–854 (2008).Anasori, B. et al. Nature Reviews Materials 2, 16098 (2017).Mu, X. et al. Advanced Functional Materials 29, 1902953 (2019).Zhan, C. et al. J. Phys. Chem. Lett. 9, 1223–1228 (2018).Lukatskaya, M. R. et al. Nat Energy 2, 1–6 (2017).Ando, Y. et al. Advanced Functional Materials 30, 2000820 (2020).Wang, X. et al. ACS Nano 15, 15274–15284 (2021).

Interfacial Chemistry in Aqueous Lithium-Ion Batteries with Dilute Aqueous Electrolytes: A Case Study with V2O5

Aqueous lithium ion batteries (ALIBs) are promising candidates for large-scale energy storage systems, benefiting from the intrinsic safe and environmentally friendly properties of aqueous electrolytes. However, its practical application is impeded due to the narrow electrochemical stability windows (ESWs) of aqueous electrolytes. Despite that increasing electrolyte concentration can achieve a wide ESW with the protection of SEI layer, it brings numerous disadvantages induced by excessive salt as well. Therefore, understanding the SEI formation mechanism and further widening the ESWs of dilute aqueous electrolytes are critical for the breakthrough of next-generation ALIBs.Herein, the interphase chemistry of V2O5 electrode with dilute aqueous electrolyte was systematic investigated by conducting various Operando characterizations with LMO||V2O5 cell system. Dynamic SEI, which consists of Li2CO3, LiF and V2O4, was formed during charge and disappeared during the following discharge, which is strongly affected by electrolyte pH fluctuation. Moreover, its evolution process is reversible during cycling. There are several impacts affect the pH fluctuation during cycling. First, V2O5 dissolution, which turns electrolyte into acidic before cycling, and is aggravated by electrolyte concentration decrease. Second, proton/hydronium ion insertion, which takes place on electrode surface in dilute electrolyte, while it is suppressed by concentration increase due to reduced proton concentration. Third, the redox reaction of dissolved V2O5, which is controlled by both potential and electrolyte pH change according to the V-H2O poubaix diagram. Along with the anode potential decrease and the alkalinisation of electrolyte, V2O4 is formed on anode surface by the reduction of HV10O28 5- and V4O12 4- and this reduction process further produces hydroxide ion into electrolyte. Last, the carbon oxidation, which takes place on cathode side during charge and on anode side during the final discharge. Therefore, the acidification of electrolyte during cycling is detrimental to SEI stability in aqueous electrolytes. This systematic research work provides new perspectives to the understanding of the interphase chemistry evolution in aqueous Li-ion batteries using dilute electrolytes, which guides the building of effective SEI layer in aqueous Li-ion batteries and beyond. Figure 1

Kinetic nature of electrochemical plasticization

The electrochemical plasticization (EP) of metallic materials has been known for decades, but the underlying mechanisms, especially the kinetic mechanisms, remain unclear. Herein, the kinetic nature of EP has been investigated by employing the electrochemical cold drawing of single-crystal copper (in a 0.35 mol L–1 dilute sulfuric acid aqueous electrolyte and with a current density of 0.67 × 10−2 A cm−2) through microstructural characterizations and reactive force field molecular dynamic simulations. The results intuitively reveal that the surface-loosened atoms, due to the selective corrosion dissolution, acts as the sources of dislocations to accelerate the formation of dislocations in a multi-slip manner, which then rapidly move toward the inside, and react with the internal early-formed dislocations to undergo abnormal slip of Lomer-Cottrell locks, cross-slip, and annihilation, leading the dislocation entanglements to reconfigure into the movable short-range wavy dislocations and their density to reduce, thus resulting in the softening and the weakening of work-hardening. These findings provide in-depth insights into the kinetic mechanism of EP, which will inevitably accelerate the development and engineering applications of new metal processing technologies based on EP as well as get a deeper understanding of stress corrosion cracking.

Enhancing pseudocapacitive intercalation in Ti3C2T x MXene with molecular crowding electrolytes

The growing demand for safe, cost-efficient, high-energy and high-power electrochemical energy storage devices has stimulated the development of aqueous-based supercapacitors with high capacitance, high rate capability, and high voltage. 2D titanium carbide MXene-based electrodes have shown excellent rate capability in various dilute aqueous electrolytes, yet their potential window is usually narrower than 1.2 V. In this study, we show that the potential window of Ti3C2T x MXene can be efficiently widened to 1.5 V in a cost-effective and environmentally benign polyethylene glycol (PEG) containing molecular crowding electrolyte. Additionally, a pair of redox peaks at −0.25 V/−0.05 V vs. Ag (cathodic/anodic) emerged in cyclic voltammetry after the addition of PEG, yielding an additional 25% capacitance. Interestingly, we observed the co-insertion of the molecular crowding agent PEG-400 during the Li+ intercalation process based on in-situ x-ray diffraction analysis. As a result, Ti3C2T x electrodes presented an interlayer space change of 4.7 Å during a complete charge/discharge cycle, which is the largest reversible interlayer space change reported so far for MXene-based electrodes. This work demonstrates the potential of adding molecular crowding agents to improve the performance of MXene electrodes in aqueous electrolytes and to enlarge the change of the interlayer spacing.

A Universal Descriptor in Determining H2 Evolution Activity for Dilute Aqueous Zn Batteries

AbstractLarge‐scale energy storage with aqueous Zn batteries (AZBs) have bright future, but their practical application is impeded by H2 evolution reaction (HER), which results in poor stability of Zn–metal anodes. Here, using linear sweep voltammetry in dilute salt aqueous electrolytes, it is discovered that as the salt concentration decreases, HER is gradually suppressed, which is contrary to prior beliefs. Combining calculations and experiments, it is demonstrated that HER derives predominantly from the sum of Zn2+‐solvated water rather than the average amount of water in the Zn2+‐solvation structural unit or free water without interaction with Zn2+, which answers the puzzle from above. This result, which differs fundamentally from the previous understandings, sheds new light on the mysterious role of water chemistry in controlling HER and contributes to a more rational design of advanced electrolytes for AZBs.

A low-cost dilute aqueous hybrid electrolyte for low-temperature supercapacitors

A low-cost dilute aqueous hybrid electrolyte for low-temperature supercapacitors

Dilute Aqueous Hybrid Electrolyte with Regulated Core‐Shell‐Solvation Structure Endows Safe and Low‐Cost Potassium‐Ion Energy Storage Devices

AbstractHigh‐concentration “water‐in‐salt” (WIS) electrolytes with the wider electrochemical stability window (ESW) can give rise to safe, non‐flammable, and high‐energy aqueous potassium‐ion energy storage devices, thus highlighting the prospect for applications in grid‐scale energy storage. However, WIS electrolytes usually depend on highly concentrated salts, leading to serious concerns about cost and sustainability. Here, an aqueous low‐concentration‐based potassium‐ion hybrid electrolyte is demonstrated with the regulated core‐shell‐solvation structure by using an aprotic solvent, i.e., trimethyl phosphate, to limit the water activity. This aqueous hybrid electrolyte has a low salt concentration (1.6 mol L−1) of potassium trifluoromethanesulfonate but with an expanded ESW up to 3.4 V and the nonflammable property. Based on this dilute aqueous hybrid electrolyte, electrochemical double‐layer capacitors are capable of working within a large voltage range (0–2.4 V) at a wide range of temperatures from −20 to 60 °C. An aqueous potassium‐ion battery consisting of an organic 3,4,9,10‐perylenetetracarboxylic diimide anode, Prussian blue K1.5Mn0.61Fe0.39[Fe(CN)6]0.77·H2O cathode and this dilute aqueous hybrid electrolyte can operate well at rates between 0.2 and 4.0 C and deliver a high energy density of 66.5 Wh kg−1 as well as a durable cycling stability with a capacity retention of 84.5% after 600 cycles at 0.8 C.

Hydrogen-Bond Restructuring of Water-in-Salt Electrolyte Confined in Ti3C2Tx MXene Monitored by Operando Infrared Spectroscopy.

Highly concentrated water-in-salt aqueous electrolytes exhibit a wider potential window compared to conventional, dilute aqueous electrolytes. Coupled with MXenes, a family of two-dimensional transition metal carbides and nitrides with impressive charge storage capabilities, water-in-salt electrolytes present a potential candidate to replace flammable and toxic organic solvents in electrochemical energy storage devices. A new charge storage mechanism was recently discovered during electrochemical cycling of Ti3C2Tx MXene electrodes in lithium-based water-in-salt electrolytes, attributed to intercalation and deintercalation of solvated Li+ ions at anodic potentials. Nevertheless, direct evidence of the state of Li+ solvation during cycling is still missing. Here, we investigate the hydrogen bonding of water intercalated between MXene layers during electrochemical cycling in a water-in-salt electrolyte with operando infrared spectroscopy. The hydrogen-bonding state of the confined water was found to change significantly as a function of potential and the concentration of Li+ ions in the interlayer space. This study provides fundamentally new insights into the electrolyte structural changes while intercalating Li+ in the MXene interlayer space.

Low-Temperature Aqueous Na-Ion Batteries: Strategies and Challenges of Electrolyte Design

Aqueous Na-ion batteries (ANIBs) are considered to be promising secondary battery systems for grid-scale energy storage applications and have attracted widespread attention due to their unique merits of rich resources of Na, as well as the inherent safety and low cost of aqueous electrolytes. However, the narrow electrochemical stability widow and high freezing point of traditional dilute aqueous electrolytes restrict their multi-scenario applications. Considering the charge-storage mechanism of ANIBs, the optimization and design of aqueous Na-based electrolytes dominate their low-temperature performance, which is also hot off the press in this field. In this review, we first systematically comb the research progress of the novel electrolytes and point out their remaining challenges in ANIBs. Then our perspectives on how to further improve the low-temperature performance of ANIBs will also be discussed. Finally, this review briefly sheds light on the potential direction of low-temperature ANIBs, which would guide the future design of high-performance aqueous rechargeable batteries.

Highly Reversible Zinc Metal Anode in a Dilute Aqueous Electrolyte Enabled by a pH Buffer Additive.

Aqueous zinc-ion batteries have drawn increasing attention due to the intrinsic safety, cost-effectiveness and high energy density. However, parasitic reactions and non-uniform dendrite growth on the Zn anode side impede their application. Herein, a multifunctional additive, ammonium dihydrogen phosphate (NHP), is introduced to regulate uniform zinc deposition and to suppress side reactions. The results show that the NH4 + tends to be preferably absorbed on the Zn surface to form a "shielding effect" and blocks the direct contact of water with Zn. Moreover, NH4 + and (H2 PO4 )- jointly maintain pH values of the electrode-electrolyte interface. Consequently, the NHP additive enables highly reversible Zn plating/stripping behaviors in Zn//Zn and Zn//Cu cells. Furthermore, the electrochemical performances of Zn//MnO2 full cells and Zn//active carbon (AC) capacitors are improved. This work provides an efficient and general strategy for modifying Zn plating/stripping behaviors and suppressing side reactions in mild aqueous electrolyte.

Highly Reversible Zinc Metal Anode in a Dilute Aqueous Electrolyte Enabled by a pH Buffer Additive

AbstractAqueous zinc‐ion batteries have drawn increasing attention due to the intrinsic safety, cost‐effectiveness and high energy density. However, parasitic reactions and non‐uniform dendrite growth on the Zn anode side impede their application. Herein, a multifunctional additive, ammonium dihydrogen phosphate (NHP), is introduced to regulate uniform zinc deposition and to suppress side reactions. The results show that the NH4+tends to be preferably absorbed on the Zn surface to form a “shielding effect” and blocks the direct contact of water with Zn. Moreover, NH4+and (H2PO4)−jointly maintain pH values of the electrode‐electrolyte interface. Consequently, the NHP additive enables highly reversible Zn plating/stripping behaviors in Zn//Zn and Zn//Cu cells. Furthermore, the electrochemical performances of Zn//MnO2full cells and Zn//active carbon (AC) capacitors are improved. This work provides an efficient and general strategy for modifying Zn plating/stripping behaviors and suppressing side reactions in mild aqueous electrolyte.

Monolayer Thiol Engineered Covalent Interface toward Stable Zinc Metal Anode.

Interface engineering of zinc metal anodes is a promising remedy to relieve their inferior stability caused by dendrite growth and side reactions. Nevertheless, the low affinity and additional weight of the protective coating remain obstacles to their further implementation. Here, aroused by DFT simulation, self-assembled monolayers (SAMs) are selectively constructed to enhance the stability of zinc metal anodes in dilute aqueous electrolytes. It is found that the monolayer thiol molecules relatively prefer to selectively graft onto the unstable zinc crystal facets through strong Zn-S chemical interactions to engineer a covalent interface, enabling the uniform deposition of Zn2+ onto (002) crystal facets. Therefore, dendrite-free anodes with suppressed side reactions can be achieved, proven by in situ optical visualization and differential electrochemical mass spectrometry (DEMS). In particular, the thiol endows the symmetric cells with a 4000 h ultrastable plating/stripping at a specific current density of 1.0 mA cm-2, much superior to those of bare zinc anodes. Additionally, the full battery of modified anodes enables stable cycling of 87.2% capacity retention after 3300 cycles. By selectively capping unstable crystal facets with inert molecules, this work provides a promising design strategy at the molecular level for stable metal anodes.

Temperature-dependent structure and performance evolution of “water-in-salt” electrolyte for supercapacitor

“Water-in-salt” (WIS) electrolytes exhibit enlarged electrochemical stability windows compared to conventional dilute aqueous electrolytes, which helps to achieve high-voltage aqueous electrochemical energy storage devices. However, the ultra-high concentration of WIS electrolytes raises a serious concern about their temperature availability. Herein, we demonstrate the correlation of the temperature-dependent electrochemical performance of different-concentration electrolytes with their solvation structures and intermolecular interactions as elaborated via Raman spectroscopy and molecular dynamics simulations. The 21 m (mol kg−1) WIS electrolyte is advantageous in the high-temperature range of >25 °C, whereas the 5 m WIS electrolyte shows superior low-temperature performance, remaining a stable gel state even at −30 °C ascribed to the muscular hydrogen bond network. The electrochemical performance evaluation of carbon supercapacitors assembled with different-concentration WIS electrolytes further verify our findings. This study provides guidance to choose suitable WIS electrolytes for electrochemical energy storage devices working at different temperatures.

Aqueous Electrolytes with Hydrophobic Organic Cosolvents for Stabilizing Zinc Metal Anodes.

Rechargeable aqueous zinc (Zn) batteries are promising for large-energy storage because of their low cost, high safety, and environmental compatibility, but their implementation is hindered by the severe irreversibility of Zn metal anodes as exemplified by water-induced side reactions (H2 evolution and Zn corrosion) and dendrite growth. Here, we find that the introduction of a hydrophobic carbonate cosolvent into a dilute aqueous electrolyte exhibits a much stronger ability to address the reversible issues facing Zn anodes than that with hydrophilic ones. Among the typical carbonates (ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate (DEC)), DEC as the most hydrophobic additive enables the strongest breaking of water's H-bond network and replaces the solvating H2O in a Zn2+-solvation sheath, which significantly reduces the water activity and its decomposition. Additionally, DEC molecules preferentially adsorb onto the Zn surface to create an H2O-poor electrical double layer and render a dendrite-free Zn2+-plating behavior. The formulated hybrid 2 m Zn(OTf)2 + 7 m DEC electrolyte endows the Zn electrode with an ability to achieve high cycling stability (over 3500 h at 5 mA cm-2 with 2.5 mA h cm-2) and supports the stable operation of Zn||V2O5·nH2O full battery. This efficient strategy with hydrophobic cosolvent suggests a promising direction for designing aqueous battery chemistries.

Highly Reversible Zn Metal Anode Stabilized by Dense and Anion‐Derived Passivation Layer Obtained from Concentrated Hybrid Aqueous Electrolyte

AbstractZinc metal is considered a promising anode material for aqueous zinc ion batteries. However, it suffers from dendrite growth, corrosion, and low coulombic efficiency (CE) during plating/stripping. Herein, a concentrated hybrid (4 m Zn(CF3SO3)2 + 2 m LiClO4) aqueous electrolyte (CHAE) to overcome the challenges facing the Zn anode is reported. The developed electrolyte achieves dendrite‐free Zn plating/stripping and obtains an excellent CE of ≈100%, surpassing the previously reported values. The combination of synchrotron‐based in operando transmission X‐ray microscopy, X‐ray diffraction, and ex situ X‐ray photoelectron spectroscopy analyses indicate that the denser, anion‐derived passivation layer formed using the CHAE facilitates homogeneous current distribution and better prevents freshly deposited Zn from directly contacting the electrolyte than the looser, solvent‐derived layers formed from a dilute hybrid aqueous electrolyte (DHAE). The beneficial effects of the CHAE on the compact, dense, and stable salt‐anion‐derived passivation layer can be attributed to its unique solvation structure, which suppresses the water‐related side reactions and widens the electrochemical potential window. In the hybrid Zn||LiFePO4 configuration, the CHAE‐based cell delivered a stable performance of CE >99% and capacity retention >90% after 285 cycles. In contrast, the DHAE‐based cell exhibits capacity retention of <65% after 170 cycles.