Latest Advances in High-Voltage and High-Energy-Density Aqueous Rechargeable Batteries

A Cu-Ag double-layer coating strategy for stable and reversible Zn metal anodes

Structuring a stable artificial coating to mitigate dendrite growth and side reactions is an effective strategy for protecting the Zn metal anode. Herein, a Cu-Ag double-layer metal coating is constructed on the Zn anode (Zn@Cu-Ag) by simple and in-situ displacement reactions. The Cu layer enhances the bond between the Ag layer and Zn substrate by acting as an intermediary, preventing the Ag coating from detachment. Concurrently, the Ag layer serves to improve the corrosion resistance of Cu metal. During plating, the initial Cu sheets and Ag particles on the surface of Zn@Cu-Ag electrode gradually transform into a flat and smooth layer, resulting in the formation of AgZn, AgZn3, and (Ag, Cu)Zn4 alloys. Alloys play a multifunctional role in inhibiting dendrite growth and side reactions due to decreased resistance, low nucleation barrier, enhanced zincophilicity, and strong corrosion resistance. Consequently, the Zn@Cu-Ag symmetric cell exhibits continuous stable performance for 3750 h at 1 mA cm-2. Furthermore, the Zn@Cu-Ag||Zn3V3O8 full cell achieves an initial capacity of 293.4 mAh g-1 and realizes long cycling stability over 1200 cycles. This work provides new insight into the engineering of an efficient artificial interface for highly stable and reversible Zn metal anodes.

Optimization of an Artificial Solid Electrolyte Interphase Formed on an Aluminum Anode and Its Application in Rechargeable Aqueous Aluminum Batteries

Electrochemical cells that incorporate aluminum (Al) as the active material have become increasingly popular due to the advantages of high energy density, cost-effectiveness, and superior safety features. Despite the progress made by research groups in developing rechargeable Al//MxOy (M = Mn, V, etc.) cells using an aqueous Al trifluoromethanesulfonate-based electrolyte, the reactions occurring at the Al anode are still not fully understood. In this study, we explore the artificial solid electrolyte interphase (ASEI) on the Al anode by soaking it in AlCl3/urea ionic liquid. Surprisingly, our findings reveal that the ASEI actually promotes the corrosion of Al by providing chloride anions rather than facilitating the transport of Al3+ ions during charge/discharge cycles. Importantly, the ASEI significantly enhances the cycling stability and activity of Al cells. The primary reactions occurring at the Al anode during the charge/discharge cycle were determined to be irreversible oxidation and gas evolution. Furthermore, we demonstrate the successful realization of urea-treated Al (UTAl)//AlxMnO2 cells (discharge operating voltage of ∼1.45 V and specific capacity of 280 mAh/g), providing a platform to investigate the underlying mechanisms of these cells further. Overall, our work highlights the importance of ASEI in controlling the corrosion of Al in aqueous electrolytes, emphasizing the need for the further development of electrolytic materials that facilitate the transport of Al3+ ions in rechargeable Al batteries.

Heterostructures of MXenes and transition metal oxides for supercapacitors: an overview

MXenes are a large family of two dimensional (2D) materials with high conductivity, redox activity and compositional diversity that have become front-runners in the materials world for a diverse range of energy storage applications. High-performing supercapacitors require electrode materials with high charge storage capabilities, excellent electrical conductivity for fast electron transfer, and the ability of fast charging/discharging with good cyclability. While MXenes show many of these properties, their energy storage capability is limited by a narrow electrochemically stable potential window due to irreversible oxidation under anodic potentials. Although transition metal oxides (TMOs) are often high-capacity materials with high redox activity, their cyclability and poor rate performance are persistent challenges because of their dissolution in aqueous electrolytes and mediocre conductivity. Forming heterostructures of MXenes with TMOs and using hybrid electrodes is a feasible approach to simultaneously increase the charge storage capacity of MXenes and improve the cyclability and rate performance of oxides. MXenes could also act as conductive substrates for the growth of oxides, which could perform as spacers to stop the aggregation of MXene sheets during charging/discharging and help in improving the supercapacitor performance. Moreover, TMOs could increase the interfacial contact between MXene sheets and help in providing short-diffusion ion channels. Hence, MXene/TMO heterostructures are promising for energy storage. This review summarizes the most recent developments in MXene/oxide heterostructures for supercapacitors and highlights the roles of individual components.

Highly Stable Al Metal Anode Enabled by Surface Chemical Passivation for Long-Life Aqueous Al Metal Batteries

Aqueous aluminum (Al) metal batteries (AMBs) have received much attention due to their high volumetric energy density, low cost, and high safety. However, the practical application of aqueous AMBs is limited by the electrochemical reversibility of the Al anode, which is often deteriorated by corrosion. Herein, we developed a dense passivation layer based on Mn/Ti/Zr compounds on the Al metal anode by a rapid surface passivation strategy. The passivation layer can effectively uniform Al deposition, increase corrosion resistance, and significantly enhance the cycling stability of Al anodes in both symmetric and full cells. Symmetric cells assembled with the treated Al electrodes exhibit stable cycling for over 300 cycles at 0.1 mA cm^-2 and 0.05 mA h cm^-2, and a 600-cycle life is achieved for a prototype full cell. This work provides a versatile remedy for the limited cycle life of Al metal anodes for rechargeable aqueous batteries.

BiOIO3@Zn3(PO4)2·4H2O Heterojunction with Fast Ionic Diffusion Kinetics for Long-Life "Rocking-Chair" Zinc Ion Batteries

Increasing insertion host materials are developed as high-performance anodes of "rocking-chair" zinc ion batteries. However, most of them show unsatisfactory rate capabilities. Herein, layered BiOIO₃ is reported as an excellent insertion host and a zinc ion conductor, i.e., Zn₃(PO₄)₂·4H₂O (ZPO), is introduced to construct a BiOIO₃@ZPO heterojunction with a built-in electric field (BEF). Both ZPO and a BEF obviously enhance Zn²⁺ transfer and storage, which is proven by theoretical calculations and experimental studies. The conversion-type mechanism of BiOIO₃ is revealed through ex situ characterizations. The optimized electrode exhibits a high reversible capacity of 130 mAh g^-1 at 0.1 A g^-1, a low average discharge voltage of 0.58 V, an ultrahigh rate performance with 68 mAh g^-1 at 5 A g^-1 (52% of capacity at 0.1 A g^-1), and an ultralong cyclic life of 6000 cycles at 5 A g^-1. Significantly, the BiOIO₃@ZPO//Mn₃O₄ full cell shows a good cyclic life of 67 mAh g^-1 over 1000 cycles at 0.1 A g^-1. This work provides a new insight into the design of anodes with excellent rate capability.

How About Vanadium-Based Compounds as Cathode Materials for Aqueous Zinc Ion Batteries?

Aqueous zinc-ion batteries (AZIBs) stand out among many monovalent/multivalent metal-ion batteries as promising new energy storage devices because of their good safety, low cost, and environmental friendliness. Nevertheless, there are still many great challenges to exploring new-type cathode materials that are suitable for Zn²⁺ intercalation. Vanadium-based compounds with various structures, large layer spacing, and different oxidation states are considered suitable cathode candidates for AZIBs. Herein, the research advances in vanadium-based compounds in recent years are systematically reviewed. The preparation methods, crystal structures, electrochemical performances, and energy storage mechanisms of vanadium-based compounds (e.g., vanadium phosphates, vanadium oxides, vanadates, vanadium sulfides, and vanadium nitrides) are mainly introduced. Finally, the limitations and development prospects of vanadium-based compounds are pointed out. Vanadium-based compounds as cathode materials for AZIBs are hoped to flourish in the coming years and attract more and more researchers' attention.

Transition-Metal Dichalcogenides in Electrochemical Batteries and Solar Cells

The advent of new nanomaterials has resulted in dramatic developments in the field of energy production and storage. Due to their unique structure and properties, transition metal dichalcogenides (TMDs) are the most promising from the list of materials recently introduced in the field. The amazing progress in the use TMDs for energy storage and production inspired us to review the recent research on TMD-based catalysts and electrode materials. In this report, we examine TMDs in a variety of electrochemical batteries and solar cells with special focus on MoS₂ as the most studied and used TMD material.

Charge Carriers for Aqueous Dual-Ion Batteries

Environmental and safety concerns of energy storage systems call for application of aqueous battery systems which have advantages of low cost, environmental benignity, safety, and easy assembling. Among the aqueous battery systems, aqueous dual-ion batteries (ADIBs) provide high possibility for achieving excellent battery performance. Compared with the "rocking chair" batteries with only one type of carrier involved in the charging and discharging, ADIBs with both cations and anions as charge carriers possess diverse selections of electrodes and electrolytes. Charge carriers are the basis of the configuration of ADIBs. In this Review, cations and anions that could be applied in ADIBs are demonstrated with corresponding electrode materials and favorable electrolytes. Some insertion mechanisms are emphasized to provide insights for the possibilities to enhance the practical performances of ADIBs.

Chloride-Free Electrolytes for High-Voltage Magnesium Metal Batteries: Challenges, Strategies, and Perspectives

The demand for high-energy-density and safe energy storage devices has spurred increasing interest in high-voltage rechargeable magnesium batteries (RMB). As electrolytes are the bridge connecting the cathode and anode materials, the development of high-voltage electrolytes is the key factor in realizing high-voltage RMBs. This concept presents an overview of three chloride-free electrolyte systems with wide electrochemical windows, together with the degradation mechanisms and modification strategies at the anode/electrolyte interphase. Finally, future directions in stabilizing Mg anodes and realizing high-voltage RMBs are highlighted.

A zinc-conducting chalcogenide electrolyte

A solid-state zinc-ion battery can fundamentally eliminate dendrite formation and hydrogen evolution on the zinc anode from aqueous systems. However, enabling fast zinc ion ⁺ conduction in solid crystals is thought to be impossible. Here, we demonstrated a fluorine-doping approach to achieving fast Zn²⁺ transport in mesoporous Zn_yS_1-xF_x. The substitutional doping of fluoride ion with sulfide substantially reduces Zn²⁺ migration barrier in a crystalline phase, while mesopore channels with bounded dimethylformamide enable nondestructive Zn²⁺ conduction along inner pore surface. This mesoporous conductor features a high room-temperature Zn²⁺ conductivity (0.66 millisiemens per centimeter, compared with 0.01 to 1 millisiemens per centimeter for lithium solid-state electrolyte) with a superior cycling performance (89.5% capacity retention over 5000 cycles) in a solid zinc-ion battery and energy density (0.04 watt-hour per cubic centimeter) in a solid zinc-ion capacitor. The universality of this crystal engineering approach was also verified in other mesoporous zinc chalcogenide materials, which implies various types of potential Zn²⁺-conducting solid electrolytes.

Yttrium-preintercalated layered manganese oxide as a durable cathode for aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) are regarded as competitive alternatives for large-scale energy storage on account of cost-effectiveness and inherent safety. In particular, rechargeable Zn-MnO₂ batteries have drawn increasing attention due to high manufacturing readiness level. However, obtaining MnO₂ with high electrochemical activity and high cyclic stability toward Zn²⁺/H⁺ storage still remains challenging. Herein, we reveal that incorporating yttrium ions (Y³⁺) into layered MnO₂ can regulate the electronic structure of the MnO₂ cathode by narrowing its band gap (from 3.25 to 2.50 eV), thus boosting the electrochemical performance in RAZIBs. Taking advantage of this feature, the optimized Y-MnO₂ (YMO) sample exhibits greater capacity (212 vs. 152 mA h g^-1 at 0.5 A g^-1), better rate capability (94 vs. 61 mA h g^-1 at 8 A g^-1), reduced charge-transfer resistance (79 vs. 148 Ω), and promoted mass transfer kinetics (3.13 × 10^-11vs. 2.37 × 10^-11 cm² s^-1) in comparison with Y-free MnO₂ (MO). More importantly, compared to MO, YMO-0.1 exhibits enhanced energy storage capability by nearly 40% (309 vs. 222 W h kg^-1) and stable cycle performance (94 vs. 52 mA h g^-1 after 3000 cycles). In situ Raman microscopy further reveals that the presence of Y³⁺ endows MnO₂ with remarkable electrochemical reversibility during charge/discharge processes. This work highlights the importance of the Y³⁺ preintercalation strategy, which can be further developed to obtain better cathode materials for aqueous batteries.

A Double-Functional Additive Containing Nucleophilic Groups for High-Performance Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted attention for their low cost and environmental friendliness. Unfortunately, commercialization has been hampered by several problems with dendrite growth and side reactions. Herein, we select sodium tartrate (TA-Na) as a dual-functional electrolyte additive to enhance the reversibility of AZIBs. The tartrate anions are preferentially adsorbed on the Zn surface, and then the highly nucleophilic carboxylate will coordinate with Zn2+ to promote the desolvation of [Zn(H2O)6]2+, leading to uniform Zn deposition on the beneficial (002) plane and inhibiting side reactions and dendrite growth. Consequently, the Zn|Zn cells show a long-term cycling stability of over 1500 cycles at 0.5 mA cm-2. Moreover, the Ta-Na additive improves the performance of Zn||MnO2 full cells, evidenced by a cycling life of 1000 cycles at 1 A g-1 under practical conditions with a limited Zn anode (negative/positive capacity ratio of 10/1) and controlled electrolyte (electrolyte/capacity ratio of 20 μL mAh-1).

The Influence of a Binder in a Composite Electrode: The Case Study of Vanadyl Phosphate in Aqueous Electrolyte

Layered VOPO₄·2H₂O is synthesized by the sonochemical method. An X-ray powder diffraction is used to examine the crystal structure, while scanning electron microscopy is used to reveal the morphology of the powder. The crystal structure refinement is performed in the P4/nmmZ space group. The electrochemical intercalation of several cations (Na⁺, Mg²⁺, Ca²⁺, and Al³⁺) in saturated nitrate aqueous solutions is investigated. The most notable reversible activity is found for the cycling in aluminium nitrate aqueous solution in the voltage range from -0.1 to 0.8 V vs. SCE. During the preparation of the electrode, it is observed that the structure is prone to changes that have not been recorded in the literature so far. Namely, the use of conventional binder PVDF in NMP solution deteriorates the structure and lowers the powder's crystallinity, while the use of Nafion solution causes the rearrangement of the atoms in a new crystal form that can be described in the monoclinic P2₁/c space group. Consequently, these structural changes affect electrochemical performances. The observed differences in electrochemical performances are a result of structural rearrangements.

Hierarchical MXene/transition metal oxide heterostructures for rechargeable batteries, capacitors, and capacitive deionization

2D MXenes have attracted considerable attention due to their high electronic conductivity, tunable metal compositions, functional termination groups, low ion diffusion barriers, and abundant active sites. However, MXenes suffer from sheet stacking and partial surface oxidation, limiting their energy storage and water treatment development. To solve these problems and enhance the performance of MXenes in practical applications, various hierarchical MXene/transition metal oxide (MXene/TMO) heterostructures are rationally designed and constructed. The hierarchical MXene/TMO heterostructures can not only prevent the stacking of MXene sheets and improve the electronic conductivity and buffer the volume change of TMOs during the electrochemical reaction process. The synergistic effect of conductive MXenes and active TMOs also makes MXene/TMO heterostructures promising electrode materials for energy storage and seawater desalination. This review mainly introduces and discusses the recent research progress in MXene/TMO heterostructures, focusing on their synthetic strategies, heterointerface engineering, and applications in rechargeable batteries, capacitors, and capacitive deionization (CDI). Finally, the key challenges and prospects for the future development of the MXene/TMO heterostructures in rechargeable batteries, capacitors, and CDI are proposed.

Theory-Driven Design of a Cationic Accelerator for High-Performance Electrolytic MnO2 -Zn Batteries

Aqueous electrolytic MnO₂ -Zn batteries are considered as one of the most promising energy-storage devices for their cost effectiveness, high output voltage, and safety, but their electrochemical performance is limited by the sluggish kinetics of cathodic MnO₂ /Mn²⁺ and anodic Zn/Zn²⁺ reactions. To overcome this critical challenge, herein, a cationic accelerator (CA) strategy is proposed based on the prediction of first-principles calculations. Poly(vinylpyrrolidone) is utilized as a model to testify the rational design of the CA strategy. It manifests that the CA effectively facilitates rapid cations migration in electrolyte and adequate charge transfer at electrode-electrolyte interface, benefiting the deposition/dissolution processes of both Mn²⁺ and Zn²⁺ cations to simultaneously improve kinetics of cathodic MnO₂ /Mn²⁺ and anodic Zn/Zn²⁺ reactions. The resulting MnO₂ -Zn battery regulated by CA exhibits large reversible capacities of 455 mAh g^-1 and 3.64 mAh cm^-2 at 20 C, as well as a long lifespan of 2000 cycles with energy density retention of 90%, achieving one of the best overall performances in the electrolytic MnO₂ -Zn batteries. This comprehensive work integrating theoretical prediction with experimental studies provides opportunities to the development of high-performance energy-storage devices.

Defect regulated spinel Mn3O4 obtained by glycerol-assisted method for high-energy-density aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) show great potential as a competitive candidate for reliable energy storage by virtue of cost-effectiveness, high safety, and environmental friendliness. However, unsatisfactory cycle stability of cathode material impedes the development of high-performance RAZIBs. This study reveals a strategic polyol-mediated process by using glycerol as the solvent for solvothermal reaction. After heat treatment in air, Mn-deficient Mn₃O₄ spinel (D-Mn₃O₄) can be obtained with rich Mn valence states (Mn²⁺/Mn³⁺/Mn⁴⁺), expanded crystal structure, high surface area, and good electrolyte compatability. Compared to well-crystallized Mn₃O₄, the presence of manganese vacancies in D-Mn₃O₄ enables lower charge-transfer resistance (86.0 vs 196.5 Ω), reduced activation energy for ion insertion (30.9 vs 50.4 kJ mol^-1), and boosted solid-state ion diffusivity (9.45 × 10^-12 vs 4.61 × 10^-14 cm² s^-1). Therefore, D-Mn₃O₄ exhibits promising electrochemical performance with high capacity (284 mAh g^-1), high specific energy (388.5 Wh kg^-1) and stable cycle retention (87% after 200 cyclesat 0.3 A g^-1). On the contrary, the well-crystallized Mn₃O₄ sample suffers from severe capacity fading with only 48% capacity retention. Moreover, the specific energies obtained after 200 cycles are 336.1 and 166.0 Wh kg^-1 for D-Mn₃O₄ and Mn₃O₄, respectively. The drastic differences between the electrochemical performance of D-Mn₃O₄ and Mn₃O₄ manifest that the existing manganese vacancies in Mn₃O₄ spinel structure enhance energy storage capability.

Cerium-polysulfide redox flow battery with possible high energy density enabled by MFI-Zeolite membrane working with acid-base electrolytes

A pH change can enable high-energy-density RFB (redox flow battery) in an aqueous medium. Nevertheless, a membrane to prevent the ion crossover is needed. This study adopted cerium and polysulfide in an acid-base combined electrolyte with an MFI-Zeolite membrane as a separator. The increased potential with pH change is described by the OCP (open circuit potential) difference, which varies by 0.8 V for the combination of acid-acid and acid-base electrolyte. A decrease of 350 mV at the redox peak potential of Ce³⁺/Ce⁴⁺ and a 10 mV negative potential shift for S₄^2-/2S₂^2- highlights the pH effect between the combination of acid-acid and acid-base electrolyte indicates the influence of pH leading in half-cell of anodic than the opposite cathodic side. The UV-visible spectral analysis for Ce³⁺ and S₄^2- ions displacement shows that cerium and sulfur ions do not migrate to each other half-cell through an MFI-Zeolite membrane. As a result, the current efficiency of 94%, voltage, and energy efficiency of 40%-43% were attained at a current density of 10 mA cm^-2. Moreover, the acid-base composition of the Ce/S system showed an energy density of 378.3 Wh l ^-1.

Vanadium oxides obtained by chimie douce reactions: The influences of transition metal species on crystal structures and electrochemical behaviors in zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have received increasing attention due to cost-effectiveness and inherent safety. A wide variety of advanced cathode materials have been revealed with promising performance in RAZIBs. However, these materials usually require sophisticated procedures at high temperatures, which greatly limit further practical application. Herein, a chimie douce approach is adopted to prepare vanadium oxides from V₂O₅ suspension with the addition of various transition metal cations (Mn²⁺, Zn²⁺, Ag⁺, and Fe³⁺) by simple liquid-solid mixing under ambient conditions. For the cases of Mn²⁺ and Zn²⁺, the dissolution-recrystallization process takes place leading to layered Mn_0.31V₃O₇·1.40H₂O (MnVO) and Zn_0.32V₃O₇·1.52H₂O (ZnVO). The use of Ag⁺ forms tunneled Ag_0.33V₂O₅ (AgVO), and the present of Fe³⁺ stays mainly unreacted V₂O₅. The underlying reaction chemistries are proposed, for which the pH values of precursor solutions are found to be a key factor. Among the prepared materials, layered vanadium oxides exhibit promising battery performance. Particularly, MnVO delivers 340 and 217 mAh g^-1 at 1 and 8 A g^-1, respectively. A specific capacity of 164 mAh g^-1 can be retained after 500 cycles at 1 A g^-1. By contrast, AgVO and FeVO demonstrate inferior performance with retaining only 89 and 20 mAh g^-1 after 500 cycles.

Aluminum-copper alloy anode materials for high-energy aqueous aluminum batteries

Aqueous aluminum batteries are promising post-lithium battery technologies for large-scale energy storage applications because of the raw materials abundance, low costs, safety and high theoretical capacity. However, their development is hindered by the unsatisfactory electrochemical behaviour of the Al metal electrode due to the presence of an oxide layer and hydrogen side reaction. To circumvent these issues, we report aluminum-copper alloy lamellar heterostructures as anode active materials. These alloys improve the Al-ion electrochemical reversibility (e.g., achieving dendrite-free Al deposition during stripping/plating cycles) by using periodic galvanic couplings of alternating anodic α-aluminum and cathodic intermetallic Al2Cu nanometric lamellas. In symmetric cell configuration with a low oxygen concentration (i.e., 0.13 mg L−1) aqueous electrolyte solution, the lamella-nanostructured eutectic Al82Cu18 alloy electrode allows Al stripping/plating for 2000 h with an overpotential lower than ±53 mV. When the Al82Cu18 anode is tested in combination with an AlxMnO2 cathode material, the aqueous full cell delivers specific energy of ~670 Wh kg−1 at 100 mA g−1 and an initial discharge capacity of ~400 mAh g−1 at 500 mA g−1 with a capacity retention of 83% after 400 cycles.

Co-substitution in a Prussian blue analog with a hollow heterostructure for ultrahigh capacity and rate capability aqueous Zn2+ batteries

Nickel and manganese co-substitution in a hollow Prussian blue nanocubes has been successfully carried out via utilizing a high-concentration polymer template, with an ultrahigh capacity of 138.4 mA h g−1 at 0.05 A g−1 in an aqueous zinc-ion battery.

Cathodic Electrodeposition of MOF Films Using Hydrogen Peroxide

Metal-organic framework (MOF) films can be made by cathodic electrodeposition, where a Brønsted base is formed electrochemically which deprotonates the MOF linkers that are present in solution as undissociated/partially dissociated weak acids. However, the co-deposition of metal and the narrow range of possible metal nodes limit the scope of this method. In this work, we propose the use of hydrogen peroxide (hydrogen peroxide assisted cathodic deposition or HPACD), to overcome these limitations. Electrochemical measurements indicate that in DMF, hydrogen peroxide is reduced to superoxide anions that deprotonate the carboxylic ligands. This single-electron reduction happens at much higher potentials than all previous reported methods. This prevents the co-deposition of metal and extends the range of possible metal nodes. Various pure MOF films (HKUST-1, MIL-53(Fe) and MOF-5) were prepared via this approach. HPACD was also used for the preparation of patterned MOF films and of flexible Cu-BTC coated paper membranes which reject 99.1 % of Rose Bengal from water with a permeance of 8.4 L m^-2  h^-1  bar^-1 .

Electrode-Less MnO2 -Metal Batteries with Deposition and Stripping Chemistry

Electrode materials are key components in typical batteries, where the electrodes are generally fabricated onto current collectors in solid forms and are isolated by a separator. However, the preparation of the electrodes increases the fabrication complexity, which speeds down their large-scale production. Here, series of static electrode-less MnO₂ -metal batteries are presented that are facilely fabricated by using carbon current collectors and electrolytes. The MnO₂ -metal batteries are operated in dual-deposition/stripping chemistries of Mn²⁺ /MnO₂ on the cathode and M/M^x+ on the anode. The MnO₂ -Cd/Zn/Cu batteries exhibit remarkable rates up to 200 C, excellent reversibility of 15 000 cycles, and realistic gravimetric and volumetric energy densities of 93.7 Wh kg^-1 and 134 Wh L^-1 , respectively. Impressively, the MnO₂ -Cd battery can achieve over 160 000 cycles in the high current pulse test, showing promises in the applications of electrical vehicle's start-stop and large-scale energy storage.

Agar Acts as Cathode Microskin to Extend the Cycling Life of Zn//α-MnO2 Batteries

The Zn/MnO₂ battery is a promising energy storage system, owing to its high energy density and low cost, but due to the dissolution of the cathode material, its cycle life is limited, which hinders its further development. Therefore, we introduced agar as a microskin for a MnO₂ electrode to improve its cycle life and optimize other electrochemical properties. The results showed that the agar-coating layer improved the wettability of the electrode material, thereby promoting the diffusion rate of Zn²⁺ and reducing the interface impedance of the MnO₂ electrode material. Therefore, the Zn/MnO₂ battery exhibited outstanding rate performance. In addition, the agar-coating layer promoted the reversibility of the MnO₂/Mn²⁺ reaction and acted as a colloidal physical barrier to prevent the dissolution of Mn²⁺, so that the Zn/MnO₂ battery had a high specific capacity and exhibited excellent cycle stability.

Long cyclic stability of acidic aqueous zinc-ion batteries achieved by atomic layer deposition: the effect of the induced orientation growth of the Zn anode

Aqueous Zn-ion batteries with economical ZnSO₄ solution as the electrolyte suffer from a tremendous tendency of dendrite formation under mildly acidic conditions; moreover, utilization of Zn(CF₃SO₃)₂ delivers superior performance, but is expensive. Herein, we optimize the ZnSO₄ electrolyte by inducing 50 μL of 10 M sulfuric acid in 10 mL electrolyte, which can achieve long cycle life (1000 h at 0.1 mA cm^-2, 300 h at 1 mA cm^-2 and 250 h at 10 mA cm^-2) when the Zn foil is protected by three metallic oxides deposited by atomic layer deposition (ALD). The nucleation behaviour of the (002) facet has proved to play a critical role in the reversible lifespan. The Al₂O₃ layer would restrict the stripping procedure, leading to the highest overpotential, while the TiO₂ layer and Fe₂O₃ layer tended to strip all orientations but the (002) facet. Al₂O₃@Zn demonstrated a preference for a compact hillock-like (101) orientation texture in the deposition procedure, while TiO₂@Zn and Fe₂O₃@Zn were favourable to obtain a smooth terrace texture. Additionally, symmetric cells with Fe₂O₃@Zn expressed the lowest overpotential (31.64 mV) and minimal voltage hysteresis (23.6 mV) at 1 mA cm^-2. A Zn-MnO₂ battery with Fe₂O₃@Zn also displayed superior capacity, which could reach 280 mA h g^-1 at a current density of 1 A g^-1. The diffusion coefficient of Zn²⁺ discloses that among the three ALD layers, full cells with Fe₂O₃@Zn are the most favourable for diffusion of Zn²⁺ in acidic electrolyte.

Bismuth Nanoparticles Confined in Carbonaceous Nanospheres as Anodes for High-Performance Potassium-Ion Batteries

Bismuth (Bi) has been considered as a promising alloying-type anode for potassium-ion batteries (PIBs), owing to its high theoretical capacity and suitable working voltage plateaus. However, Bi suffers from dramatic volume fluctuation and significant pulverization during the discharge/charge processes, resulting in fast capacity decay. Herein, we synthesize Bi nanoparticles confined in carbonaceous nanospheres (denoted as Bi@C) for PIBs by first utilizing BiOCl nanoflakes as a hard template and a Bi precursor. The construction of the loose structure buffers the mechanical stresses resulting from the volume expansion of Bi during the alloying reaction and avoids the fracture of the electrode structure, thus improving the cycling performance. Moreover, the carbonaceous layers increase the electronic conductivity and disperse the Bi nanoparticles, enhancing the charge transportation and ionic diffusion, which further promotes the rate capability of Bi@C. It exhibits a superior capacity (389 mAh g^-1 at 100 mA g^-1 after 100 cycles), excellent cycling stability (206 mAh g^-1 at 500 mA g^-1 over 1000 cycles), and an improved rate capability (182 mAh g^-1 at 2.0 A g^-1). This work provides a new structuring strategy in alloying materials for boosting reversible and stable potassium-ion storage.

"Water-in-Salt" Electrolytes for Supercapacitors: A Review

"Water-in-salt" (WIS) electrolytes, which have more salt than the solvent in both mass and volume, show promising prospects for application in supercapacitors due to their wide electrochemical stability window (about 3 V), considerable ion transport, high safety, low cost, and environmental friendliness. This Review summarizes the advances, progress, and challenges of WIS electrolytes in supercapacitors. The working mechanisms, reason for the wide electrochemical stability window, typical systems, challenges, and modification strategies of the WIS electrolytes in supercapacitors are discussed. Moreover, the application of WIS electrolytes in symmetric and asymmetric supercapacitors are presented. Finally, perspectives and the future development direction of WIS electrolytes are given. This Review is expected to provide inspiration and guidance for designing WIS electrolytes with advanced performance and push forward the development of high-performance aqueous supercapacitors with high cell voltage, good rate performance, and thus high energy density and power density.

Anticatalytic Strategies to Suppress Water Electrolysis in Aqueous Batteries

Aqueous electrolytes are the leading candidate to meet the surging demand for safe and low-cost storage batteries. Aqueous electrolytes facilitate more sustainable battery technologies due to the attributes of being nonflammable, environmentally benign, and cost effective. Yet, water's narrow electrochemical stability window remains the primary bottleneck for the development of high-energy aqueous batteries with long cycle life and infallible safety. Water's electrolysis leads to either hydrogen evolution reaction (HER) or oxygen evolution reaction (OER), which causes a series of dire consequences, including poor Coulombic efficiency, short device longevity, and safety issues. These are often showstoppers of a new aqueous battery technology besides the low energy density. Prolific progress has been made in the understanding of HER and OER from both catalysis and battery fields. Unfortunately, a systematic review on these advances from a battery chemistry standpoint is lacking. This review provides in-depth discussions on the mechanisms of water electrolysis on electrodes, where we summarize the critical influencing factors applicable for a broad spectrum of aqueous battery systems. Recent progress and existing challenges on suppressing water electrolysis are discussed, and our perspectives on the future development of this field are provided.

An Artificial Polyacrylonitrile Coating Layer Confining Zinc Dendrite Growth for Highly Reversible Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-metal-based batteries are an attractive alternative to lithium-ion batteries for grid-scale energy-storage systems because of their high specific capacity, low cost, eco-friendliness, and nonflammability. However, uncontrollable zinc dendrite growth limits the cycle life by piercing the separator, resulting in low zinc utilization in both alkaline and mild/neutral electrolytes. Herein, a polyacrylonitrile coating layer on a zinc anode produced by a simple drop coating approach to address the dendrite issue is reported. The coating layer not only improves the hydrophilicity of the zinc anode but also regulates zinc-ion transport, consequently facilitating the uniform deposition of zinc ions to avoid dendrite formation. A symmetrical cell with the polymer-coating-layer-modified Zn anode displays dendrite-free plating/stripping with a long cycle lifespan (>1100 h), much better than that of the bare Zn anode. The modified zinc anode coupled with a Mn-doped V2 O5 cathode forms a stable rechargeable full battery. This method is a facile and feasible way to solve the zinc dendrite problem for rechargeable aqueous zinc-metal batteries, providing a solid basis for application of aqueous rechargeable Zn batteries.

Electrokinetic-Driven Fast Ion Delivery for Reversible Aqueous Zinc Metal Batteries with High Capacity

Aqueous zinc (Zn) metal batteries (ZMBs) are considered a promising candidate for grid-scale energy storage due to their freedom from fire hazards. However, a limited reversibility of Zn metal electrode caused by dendritic Zn growth has hindered the advent of high-capacity Zn metal batteries (>4 mAh cm^-2 ). Herein, it is reported that fast electrokinetic Zn-ion transport extremely improves the Zn metal reversibility. It is revealed that a negatively charged porous layer (NPL) provides the electrokinetic Zn-ion transport by surface conduction, and consequently impedes the depletion of Zn-ion on electrode surface as indicated by numerical simulations and overlimiting current behavior. Due to the quick Zn-ion delivery, a dendrite-free and densely packed Zn metal deposit is accommodated inside its pores. With the introduction of the NPL, the cycling stability of Zn symmetric cell is enhanced by 21 times at 10 mA cm^-2 /10 mAh cm^-2 . Average Coulombic efficiency of 99.6% is achieved over 500 cycles for electrodeposition/stripping at 30 mA cm^-2 /5 mAh cm^-2 on NPL-Cu electrode. Furthermore, a high-capacity Zn/V₂ O₅ full cell with the NPL exhibits an extraordinary stability over 1000 cycles at a capacity of 4.8 mAh cm^-2 .

Operation Mechanism in Hybrid Mg-Li Batteries with TiNb2O7 Allowing Stable High-Rate Cycling

We studied the structural evolution and cycling behavior of TiNb₂O₇ (TNO) as a cathode in a nonaqueous hybrid dual-salt Mg-Li battery. A very high fraction of pseudocapacitive contribution to the overall specific capacity makes the material suitable for ultrafast operation in a hybrid battery, composed of a Mg-metal anode, and a dual-salt APC-LiCl electrolyte with Li and Mg cations. Theoretical calculations show that Li intercalation is predominant over Mg intercalation into the TNO in a dual-salt electrolyte with Mg²⁺ and Li⁺, while experimentally up to 20% Mg cointercalation was observed after battery discharge. In hybrid Mg-Li batteries, TNO shows capacities which are about 40 mA h g^-1 lower than in single-ion Li batteries at current densities of up to 1.2 A g^-1. This is likely due to a partial Mg cointercalation or/and location of Li cations on alternative crystallographic sites in the TNO structure in comparison to the Li-intercalation process in Li batteries. Generally, hybrid Mg-Li cells show a markedly superior applicability for a very prolonged operation (above 1000 cycles) with 100% Coulombic efficiency and a capacity retention higher than 95% in comparison to conventional Li batteries with TNO after being cycled either under a low (7.75 mA g^-1) or high (1.55 A g^-1) current density. The better long-term behavior of the hybrid Mg-Li batteries with TNO is especially pronounced at 60 °C. The reasons for this are an appropriate cathode electrolyte interface containing MgCl₂ species and a superior performance of the Mg anode in APC-LiCl electrolytes with a dendrite-free, fast Mg deposition/stripping. This stable interface stands in contrast to the anode electrolyte interface in Li batteries with a Li anode in conventional carbonate-containing electrolytes, which is prone to dendrite formation, thus leading to a battery shortcut.

Laboratory Operando XAS Study of Sodium Iron Titanite Cathode in the Li-Ion Half-Cell

Electrochemical characterization of the novel sodium iron titanate Na_0.9Fe_0.45Ti_1.55O₄ was performed upon cycling in the Li-ion half-cell. The material exhibited stable cycling in the voltage range 2–4.5 V, and the number of alkali ions extracted per formula unit was approximately half of the Na stoichiometry value. Using laboratory X-ray absorption spectrometry, we measured operando Fe K-edge X-ray absorption spectra in the first 10 charge–discharge cycles and quantified the portion of charge associated with the transition metal redox reaction. Although 3d metals are commonly accepted redox-active centers in the intercalation process, we found that in all cycles the amount of oxidized and reduced Fe ions was almost 20% less than the total number of transferred electrons. Using density functional theory (DFT) simulations, we show that part of the reversible capacity is related to the redox reaction on oxygen ions.

Assessment of All-Electric General Aviation Aircraft

The purpose of this paper is to describe the upcoming changes that will bring the transition from piston engines to all-electric aircrafts. The article focuses on the differences in operation of small general aviation aircrafts. This topic is timely, as the first all-electric aircraft was certified by the European Union Aviation Safety Agency (EASA) in 2019. As there are no data concerning this new type of operation available, the data have been derived from other applicable sources. At first, we compared the energy consumption of the same aircraft with the piston engine, and then afterwards with the retrofitted all-electric variant. Our results focus on the difference in fuel price, which is discussed in the context of electricity price comparison with AVGAS prices. Moreover, we discuss the environmental impacts, especially concerning electricity source mix and emissions produced (we estimate both with and without life-cycle assessment). In the discussion, we compare the results and identify the benefits of an all-electric solution. Furthermore, several operational restrictions of all-electric aircrafts are discussed.