Search

Transition metal layered double hydroxides (LDHs) are widely used as high‐performance cathode materials for aqueous alkaline zinc (Zn) batteries. Yet, the strongly alkaline electrolytes may lead to undesirable rechargeability of the alkaline devices and environmental issues. Herein, as a research prototype, CoNi LDH material is designed with abundant H vacancies using electrochemical methods (denoted as CoNi LDH(v)). As a Zn‐ion battery cathode, CoNi LDH(v) exhibits promising electrochemical performances in mild ZnSO4 electrolyte, such as a good specific capacity of 185 mAh g−1 at the current density of 1.2 A g−1, a high average discharge potential of 1.6 V versus Zn2+/Zn, and a large energy density of 296.2 Wh kg−1 at the power density of 1894 W kg−1, outperforming most of the cathode materials for aqueous Zn‐ion batteries. Experimental and computational results indicate that the introduced H vacancies in the double hydroxide matrix induce the improved electronic conductivity and cation adsorption thermodynamics, endowing the double hydroxides with good electrochemical activity for reversible cation insertion. Structural and spectroscopy studies identify that CoNi LDH(v) experiences reversible H+/Zn2+ co‐intercalation mechanism in an aqueous ZnSO4 electrolyte. As far as it is known, it is the first report on transition‐metal‐based double hydroxides used for mild aqueous Zn‐ion batteries. [ABSTRACT FROM AUTHOR]

The Mn2+ dissolution of MnO2 cathode materials causes rapid capacity decay in aqueous zinc batteries. We herein show that the dissolved Mn2+ can be deposited back to the cathode with the aid of a suitable conductive agent. The active material is thus retained for energy storage, and this MnO2/Mn2+ redox process also provides capacity. In the Mn2+ free ZnSO4 electrolyte, MnO2 delivers 325 mA h g−1 capacity at 0.1 A g−1, and 90.4% capacity retention is achieved after 3000 cycles at 5 A g−1. Our work demonstrates an effective strategy to realize stable cycling of MnO2 cathodes in aqueous zinc batteries without Mn2+ additives. [ABSTRACT FROM AUTHOR]

Mn‐based materials for aqueous energy storage are reaching the capacity ceiling due to the limited Mn4+/Mn3+ redox. The disproportionation of Mn3+ often occurs, forming soluble Mn2+ and thus leading to severer capacity decays. Here, an amorphous manganese phosphate material [AMP, Na1.8Mn4O1.4(PO4)3] is fabricated using an electrochemical method for the first time. Benefitting from the open framework and the insoluble nature of Mn2+ in AMP, the Mn3+/Mn2+ and Mn4+/Mn3+ redox couples can participate in the charge storage processes. The AMP electrode shows a high capacity of 253.4 mAh g−1 (912.4 F g−1 or 912.4 C g−1) at the current density 1 A g−1 and good rate capability. Experimental results indicate AMP experiences a mixed charge storage mechanism (i.e., cation intercalation and conversion reactions) in Na2SO4 electrolyte. Besides, electrolyte engineering can effectively prevent the decomposition of AMP during cycling test, achieving capacity retention of 97% in 5000 cycles. Importantly, AMP can accommodate different cations (e.g., Mg2+, Ca2+, etc.), exhibiting great potential for aqueous energy storage. [ABSTRACT FROM AUTHOR]

The energy storage behavior of the Li3V2(PO4)3 cathode in zinc batteries is evaluated. The dissolution or decomposition into vanadium oxide in aqueous electrolytes is revealed. Using the optimal combination of water and acetonitrile solvents in electrolyte, those processes are effectively prevented without sacrificing the Zn2+ de/insertion kinetics. Further investigation demonstrates a water induced phase transformation into a VOPO4 type structure, which is still a polyanion material and preserves the high voltage. It delivers 128 mA h g−1 capacity at 1C with 1.45 V discharge voltage, and 87 mA h g−1 capacity is retained at 10C. A stable cycling is obtained for 1000 cycles. [ABSTRACT FROM AUTHOR]

Various cathode materials have been proposed for high‐performance rechargeable batteries. Vanadyl phosphate is an important member of the polyanion cathode family. VOPO4 has seven known crystal polymorphs with tunneled or layered frameworks, which allow facile cation (de)intercalations. Two‐electron transfer per formula unit can be realized by using VV/VIV and VIV/VIII redox couples. The electrochemical performance is closely related to the structures of VOPO4 and the types of inserted cations. This Review outlines the crystal structures of VOPO4 polymorphs and their lithiated phases. The research progress of vanadyl phosphate cathode materials for different energy storage systems, including lithium‐ion batteries, sodium‐ion batteries, potassium‐ion batteries, multivalent batteries, and supercapacitors, as well as the related mechanism investigations are summarized. It is hoped that this Review will help with future directions of using vanadyl phosphate materials for energy storage. [ABSTRACT FROM AUTHOR]

Keywords: cathode materials; polyanions; rechargeable batteries; supercapacitors; vanadyl phosphate EN cathode materials polyanions rechargeable batteries supercapacitors vanadyl phosphate 1 1 1 07/04/20 20200702 NES 200702 B The vanadyl phosphate materials b have various crystal structures, which allow reversible cation (de)intercalation. Cathode materials, polyanions, rechargeable batteries, supercapacitors, vanadyl phosphate. [Extracted from the article]

[Display omitted] • Prepare a novel hierarchical structured cathode for aqueous zinc batteries. • The hierarchical cathode shows ultra-long cycle life. • Nanorod arrays on the hierarchical cathode regulate the local electric field. • Tip effect accumulates protons near the surface to inhibit the side reaction. Vanadium-based oxides are promising cathode candidates for aqueous zinc batteries, but their cycling stability is unsatisfactory. Herein, a unique hierarchical structured zinc vanadate material, with amorphous nanorod arrays standing on crystalline lamellar plates, is produced by the in-situ electrochemical conditioning from a H 0.39 V 2 O 5 precursor. The hierarchical cathode achieves a high capacity of 536 mAh/g at 0.1 A/g and 344 mAh/g at 5 A/g. Importantly, a long life of 10,000 cycles with 88% capacity retention is realized at 5 A/g. Finite-element analysis shows that the tip effect of the nanorod arrays accumulates protons near the surface of the hierarchical cathode. The resulting locally low-pH environment prevents vanadium dissolution and formation of inactive Zn 3 V 2 O 7 (OH) 2 ·nH 2 O during cycling, which ensures the high cycling stability. This work presents insights into local pH regulation to optimize the cycling stability of cathode materials in aqueous zinc batteries. [ABSTRACT FROM AUTHOR]

Research on anode materials with high capacitive performance is lagging behind that of cathode materials, which has severely hindered the development of high-efficient energy storage devices. Compared with other anode materials, Fe 3 O 4 exhibits highly desirable advantages due to its low cost, high theoretical capacity and preferable electronic conductivity of ∼10 2 S cm −1 . Herein, hierarchical honeycomb Fe 3 O 4 is integrated on functionalized exfoliated graphite through electrochemical deposition and the following chemical conversion. The hierarchical honeycomb Fe 3 O 4 is constructed by the oxide nanorods, which are assembled by a number of nanoparticles. This unique porous structure not only ensures fast ion diffusion in the electrode, but also provides large amount of active sites for electrochemical reactions. The exfoliated graphene atop the graphite base can act as 3D conductive scaffold to facilitate the electron transport of the electrode. Therefore, FEG/Fe 3 O 4 exhibits large specific capacitances of 327 F g −1 @1 A g −1 and 275 F g −1 @10 A g −1 . Good cycling stability is also achieved due to the flexibility of the graphene substrate. The assembled asymmetric device using FEG/Fe 3 O 4 as anode can deliver a high energy density of 54 Wh kg −1 . [ABSTRACT FROM AUTHOR]

[Display omitted] • A high donor number electrolyte additive of N -methylpyrrolidone is demonstrated for aqueous Zn batteries. • It preferential adsorbs on both electrode surface and generates stable electrode-electrolyte interface. • Side reactions are inhibited and uniform Zn deposition is realized at Zn electrode. • Stable Zn plating-stripping is achieved for 1100 h, and coulombic efficiency reaches 99.5 %. • Vanadium dissolution is prevented for the V 6 O 13 ·H 2 O cathode, which enhances cycling stability. Aqueous Zn batteries provide high safety and low cost. However, the Zn metal anode experiences various side reactions and dendritic growth in aqueous electrolytes. Herein, we regulate the interfaces at both Zn anode and vanadium oxide cathode in aqueous batteries with a high donor number electrolyte additive. The N -methylpyrrolidone (NMP) molecule with the donor number of 27.3 is introduced to the ZnSO 4 electrolyte at the low concentration of 5 %. It preferentially adsorbs on both electrode surface and induces electrode–electrolyte interfaces composed of mixed organic and inorganic species. Thanks to the effective protection of solid-electrolyte interface (SEI) on Zn anode, the corrosions from electrolytes are inhibited, and 99.5 % coulombic efficiency of plating-stripping is realized. The Zn deposition behavior is also modified, which ensures uniform Zn growth and stable Zn plating-stripping for 1100 h. Meanwhile, the cathode-electrolyte interface (CEI) at the V 6 O 13 ·H 2 O cathode effectively suppresses vanadium dissolution, and the capacity retention over cycling is enhanced. Our work presents an effective strategy to simultaneously promote the electrochemical performance of both electrodes in aqueous Zn batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • The leucoemeraldine-emeraldine-pernigraniline reactions of PANI are realized by Nernst shift. • The pernigraniline hydrolysis is inhibited with low water activity in electrolyte. • The PANI cathode delivers 221 mAh g−1 capacity at 0.2 A g−1 in aqueous Zn batteries. • A stable capacity retention of 96.6% is achieved after 1000 cycles at 3 A g−1. Polyaniline (PANI) is a promising cathode material for aqueous zinc batteries. However, only half available capacity based on the leucoemeraldine-emeraldine redox reaction can be used. Further oxidation to pernigraniline requires potential exceeding the top voltage limit of aqueous solutions, and the hydrolysis of pernigraniline leads to PANI degradation. Herein, we show that the redox potential of emeraldine-pernigraniline reaction is effectively shifted within electrolyte voltage window by tuning ion activities in electrolyte based on Nernst shift, so that both redox processes of PANI are realized for energy storage in aqueous zinc cells. Meanwhile, the pernigraniline hydrolysis is inhibited with limited water activity in the concentrated electrolyte, and the long-term stability in ensured. The PANI electrode delivers a high capacity of 221 mAh g−1 at 0.2 A g−1 and maintains 118 mAh g−1 at 5 A g−1 in aqueous zinc batteries. An excellent capacity retention of 96.6% is achieved after 1000 cycles with 99.7% coulombic efficiency. The energy storage processes as well as the active dopants on PANI are identified by a series of characterizations. The work demonstrates an effective strategy to realize energy storage with redox couples outside the voltage window of conventional electrolytes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A conversion-type CuO cathode is proposed for aqueous zinc batteries. • Two-electron transfers based on Cu2+-Cu redox reaction are realized. • The Cu2+ dissolution is suppressed by shifting the dissolution equilibrium. • Stable retentions of both capacity and voltage are achieved. • The electrode delivers 180 mAh g−1 capacity at 100 mA g−1. Cathode materials with conversion reaction would offer higher theoretical capacities than intercalation-type materials. Copper-based materials can undergo two electron transfers from the redox couples of Cu2+/Cu+ and Cu+/Cu, which at the same time provides desirable redox potentials as cathode materials for aqueous zinc batteries. However, most Cu2+ components are soluble in water, leading to the continuous loss of active material and capacity decay upon cycling. Herein, we prevent Cu2+ dissolution with fundamental equilibrium principles. The CuO cathode experiences rapid capacity decay within few cycles in conventional zinc electrolytes upon the formation of soluble charged products. The dissolution equilibrium is effectively shifted to the left by increasing the concentration of the associated anion TFSI- in the electrolyte of 21 m LiTFSI + 1 m Zn(TFSI) 2 , and Cu2+ is confined in the cathode in the forms of Cu(TFSI) 2 and CuO. A stable capacity retention of 91.2% realized after 300 cycles, and the stable evolution of differential capacity curves furthermore demonstrates the well-preserved energy storage process. A good capacity of 180 mAh g−1 is achieved at 100 mA g−1. This work provides a feasible strategy to suppress active material dissolution and highlights the potential utilization of copper-based conversion cathode materials for aqueous zinc batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quinone sites are introduced to PANI by a facile electrochemical method. • Polymer chains transform into expanded coil conformation at the same time. • Quinone provides extra redox sites, and expanded polymer enhances conductivity. • The electrode delivers 186 mAh g−1 capacity with quinone at 1.4 V and PANI at 1.1 V. • A stable capacity retention of 88.0% is achieved after 1500 cycles. Rechargeable aqueous batteries with zinc metal anodes are promising energy storage systems owing to their high safety and low lost. A suitable cathode material is in urgent demand. Organic materials offer adjustable electrochemical activity, and conducting polymers provide good electrical conductivity. Herein, we combine those advantages in one cathode material by the controlled introduction of quinone-type active sites onto polyaniline (PANI) nanorod-arrays through a facile electrochemical treatment. The process simultaneously transforms the polymer with a compact coil conformation into an expanded coil structure, resulting in facilitated electron transportations and charge transfer processes. In comparison to the original PANI, the electrochemically treated Q-PANI electrode exhibits extra electrochemical activity from quinone sites as well as enhanced capacity from PANI itself. Q-PANI delivers a high capacity of 186 mAh g−1 at 0.2 A g−1. Upon long-term cycling, 88.0% capacity retention is achieved after 1500 cycles at 2 A g−1. Detailed mechanism studies demonstrate the redox reaction on quinone sites at 1.4 V and nitrogen centers in PANI at 1.1 V. The work proposes a potential pathway towards high performance electrode materials for zinc batteries. [ABSTRACT FROM AUTHOR]