Rechargeable Aqueous Zinc-ion Batteries Research Articles

Electrochemical constructing versatile ZnAl-LDH artificial interface layer coated (002)-textured Zn for highly reversible zinc anodes

Rechargeable aqueous zinc-ion batteries (AZIBs), renowned for their high safety, cost-effectiveness, and high energy density, are regarded as an alternative for large-scale energy storage. However, persistent challenges remain in achieving highly reversible AZIBs, primarily centered around the notorious issues associated with the Zn anode. Here, a zincophilic Zn-Al layered double hydroxide (ZnAl-LDH) artificial interface layer coated highly (002)-textured Zn metal anode (SZ/LDH@Zn) with an integrated design are successively constructed by electrochemical methods. Comprehensive characterizations and theoretical calculations reveal that the preferred (002)-textured Zn couping with the zincophilic ZnAl-LDH coating layer not only can effectively regulate the interfacial electric field and Zn2+ flux distribution, guiding a uniform and horizontal Zn2+ deposition but also provide inherent Zn2+ diffusion channels, accelerating its interfacial transport kinetics. Moreover, the ZnAl-LDH layer with good chemical stability acted as a robust physical barrier, impeding direct contact between the electrolyte and Zn anode, thus curbing interfacial side reactions. As a result, the SZ/LDH@Zn||SZ/LDH@Zn symmetric cell delivers unprecedented cycling stability of 5500 h (about 230 days) at 1 mA cm−2, 1 mA h cm−2. The SZ/LDH@Zn||Cu asymmetric cell achieves superior reversibility with a high average Coulombic efficiency of 99.85 % over 3800 cycles. More significantly, the SZ/LDH@Zn||NaV3O8·xH2O full cell with a low N/P ratio (3.62) exhibits an impressive areal capacity of 5.36 mA h cm−2 and reliable operation over 1500 cycles. This work offers a facile and controllable electrochemical coupling strategy to build a highly stable Zn metal anode.

Performances of MnO2 and SnO2 Coated MnO2 as Cathode Materials for Aqueous Rechargeable Zinc-ion Batteries

In this study, the micro-emulsion method was used to create the manganese-based cathode materials MnO2 and MnO2@SnO2. For the use as cathode materials in rechargeable zinc-ion batteries, MnO2 and SnO2 coated MnO2@SnO2 were synthesized. FT-IR, Powder X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), and UV-visible Spectroscopy were used to characterize the as-prepared materials. Electrochemical impedance spectroscopy (EIS), battery charge-discharge (BCD), and cyclic voltammetry (CV) techniques were used to investigate the electrochemical properties of the prepared cathode materials for aqueous rechargeable zinc-ion batteries (ARZIBs). The CV profiles were measured in the potential range of 2.1-1.0 V at a scan rate of 20 mV/s. A pair of redox peaks can be seen in the cycle of CV curves. Charge/discharge cycles of SnO2 coated MnO2@SnO2 electrodes are higher than those of pristine MnO2. SnO2 coated MnO2@SnO2 electrodes have better initial charge/discharge capacities than pristine MnO2 electrodes, which is a factor to take into account. In the first cycle, SnO2 coated MnO2@SnO2 electrode has a 26% higher charge capacity than the bare MnO2 electrode. The SnO2 coating on MnO2 may be the cause of the enhanced charge and discharge capabilities of MnO2@SnO2. J. of Sci. and Tech. Res. 5(1): 83-92, 2023

Understanding the hydrogen and halogen bonds of ionic liquids in regulating ion solvation and dynamic behaviors of aqueous zinc electrolytes

Despite their low cost and intrinsic safety, aqueous rechargeable zinc-ion batteries suffer from rapid performance deterioration originating from parasitic reactions and inhomogeneous deposition on the Zn anode. Halogen bonds share similarities with hydrogen bonds, yet their unique directionality, strength tunability, and hydrophobicity provide a promising approach for enhancing the reversibility of Zn anodes. Herein, a systematic comparison of ionic liquids with different anions, acetate (Ac−) and chloride (Cl−), is performed to explore the non-covalent interactions in regulating ion solvation and dynamic behaviors of electrolytes. Different from the Ac− possessing a strong capacity to form hydrogen bonds with water, the Cl−-water halogen bonds not only enable the structural diffusion of Zn2+ with better diffusion efficiency but also reduce the Zn2+ de-solvation energy barrier to promote uniform Zn nucleation. Consequently, the accelerated ions diffusion and homogeneous Zn deposition work in synergy to ensure high reversibility of Zn anode. These fundamental insights highlight the importance of hydrogen and halogen bonds in determining the dynamics and electrochemical behavior of electrolytes, providing theoretical guidance for the rational design of high-performance electrolytes.

Highly 002-Oriented Dendrite-Free Anode Achieved by Enhanced Interfacial Electrostatic Adsorption for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) are gaining recognition as promising next-generation energy storage solution, due to their intrinsic safety and low cost. Nevertheless, the advancement of AZIBs is greatly limited by the abnormal growth of zinc dendrites during cycling. Electrolyte additives are effective at suppressing zinc dendrites, but there is currently no effective additive screening criterion. Herein, we propose employing the interfacial electrostatic adsorption strength of zinc ions for the initial screening of additives. Subsequently, dendrite-free plating is achieved by employing the anionic surfactant sodium dodecyl benzenesulfonate (SDBS) to enhance electrostatic adsorption. The cycled zinc anode exhibited a dense plating morphology and a high (002) orientation (I002/I101 = 22). The Zn||MnO2 full cell with SDBS exhibited a capacity retention of 85% after 1000 cycles at 1 A g-1. Furthermore, an instantaneous nucleation model and continuous nucleation model (CNM) are constructed to reveal the microscale plating/stripping dynamics under the scenarios of weak adsorption and strong adsorption. The CNM accurately explains the self-optimizing reconstruction of electrodes resulting from enhanced electrostatic adsorption. Our exploration was extended to other anionic surfactants (sodium dodecyl sulfate and disodium laureiminodipropionate), confirming the effectiveness of strong electrostatic adsorption in the screening of electrolyte additives.

Regulating zinc hydroxide sulfate (0 0 1) preferential growth and Zn (0 0 2) deposition by trace dibenzenesulfonimide additive toward long cycle lifespan for aqueous Zn-ion batteries

Regulating the zinc hydroxide sulfate (ZHS) growth orientation to construct interface layer with electronic insulation and high flux of Zn2+ is an efficient way to suppress parasitic side reactions and Zn dendrite in rechargeable aqueous zinc-ion batteries (ZIBs). Herein, a novel ZnSO4-based electrolyte with dibenzenesulfonimide (BBI) additive is proven able to maintain long-time cycle stabilities of Zn anode. The combination of experimental and precise testing technologies demonstrated that BBI additive can guide a surface-preferred ZHS (001) and Zn (002) crystal plane, as well as prevent the Zn corrosion and dendrite growth to smooth Zn deposition by adjusting the solid-phase interface energy. As a result, the Zn||Cu cells deliver an extended cycling lifespan over 1500 cycles with 99.7 % Coulombic efficiency at the current density of 2 mA cm−2, demonstrating an ultra-stable plating/stripping behavior. More encouragingly, the cyclic stability of Zn-MnO2 battery with the ZnSO4-BBI electrolyte can deliver a specific capacity of ∼165 mAh g−1 after 200 cycles at 1 C. This study clearly elucidates the interface behaviors to stabilize Zn anode, which contributes to a deep insight into the additive regulation mechanisms and brings a promising approach to solve the anode nuisance in aqueous metal batteries.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Continued efforts towards the decarbonization of the power sector through an uptake of renewable energy generation, namely solar and wind, play a key role in the fight against climate change. However, due to their variable nature, the simultaneous implementation of energy storage solutions capable of ensuring a reliable delivery of energy at any time of day is of the utmost importance. Aqueous rechargeable zinc-ion batteries (RZIBs) are a promising technology for this end. Offering several advantages over lithium-ion batteries in terms of cost, environmental impact, and material abundance, the investment in RZIB research continues to grow. However, the realization of commercial RZIBs is currently hindered by the lack of cathode materials with adequate performance for long-term storage solutions. This is the case for manganese (e.g., MnO2, Mn2O3, Mn3O4) and vanadium (e.g., V2O5, VO2) based oxides, which exhibit considerable capacity fade during realistic charge and discharge times. While simple transition metal oxides (MyOx, M=transition metal) are one of the most studied classes of materials for RZIB cathodes, a literature survey shows that there are still many unexplored redox active elements and redox pairs which may be employed in next-generation RZIBs. Therefore, to accelerate the discovery of these novel cathode systems, we mapped the theoretical Zn intercalation potential for simple oxides from 12 different transition metals using Density Functional Theory (DFT) calculated thermodynamic properties. The screened elements were chosen upon considering their commercial availability, toxicity, price, and existence of previously reported structures containing zinc. During the present analysis, the feasibility of Zn intercalation for each system was accounted for by analyzing the atomic arrangement in the charged and discharged phases. Experimentally obtained Pourbaix Diagrams were also used to probe the electrochemical stability of the cathodes in aqueous solution, with the possibility of electrolyte degradation (oxygen or hydrogen evolution reaction) and competing reactions (metal dissolution or solid phase change) also considered. Experimental validation of the computationally predicted potentials was also done for select materials. The result for the 35+ redox pairs evaluated in this study provides a clear roadmap for the future development of RZIBs cathodes.

(Battery Student Slam 8 Award Winner) A Simple and Fast Method to Assemble Flexible and Stable Quasi-Solid-State Zn Ion Pouch Cell

Aqueous zinc-ion batteries (AZIBs) have been investigated intensively as effective energy storage devices that are environmentally friendly, safe, and have a lower cost than current Li-ion batteries.[1-5] Being outstandingly safe due to usage of non-organic electrolyte, AZIBs could also be used as power supply for wearable electronics. This also put high standard requirements in terms of flexibility, stability and electrochemical performance to AZIBs. On the other hand, the general challenges, such as the formation of the dendrites on the Zn anodes, hydrogen evolution and side reactions, have been obstructing the practical application of AZIBs. In this presentation, a simple method to assemble quasi-solid-state Zn ion pouch cell with excellent mechanical performance, flexibility and electrochemical performance was developed, combining in-situ electrodeposition of MnO2 cathode and aramid nano fiber-based hydrogel with Zn plate as anode. In-situ and cycling measurements of the electrodeposition of MnO2 on carbon nanotube mat shows excellent capacitance and superior cycling stability. In addition, Kevlar derivatized aramid nanofiber-based hydrogel shows extremely strong strength when combined with polyvinyl alcohol, which prolonged the lifetime of the cell by preventing Zn dendrite growth largely.[5,6] Moreover, the method to assemble the AZIBs pouch cell enables us to optimize the process, decrease the steps, and save time effectively by taking advantage of hydrogel formation stage and avoiding conventional verbose slurry-casting-drying steps. This work paves an efficient path to assemble flexible and stable AZIBs pouch cells with high capacity and cycling stability.[1] Tang, Boya, et al. "Issues and opportunities facing aqueous zinc-ion batteries." Energy & Environmental Science 12.11 (2019): 3288-3304.[2] Li, Chang, et al. "Toward practical aqueous zinc-ion batteries for electrochemical energy storage." Joule 6.8 (2022): 1733-1738.[3] Yu, Feng, et al. "An aqueous rechargeable zinc-ion battery on basis of an organic pigment." Rare Metals 41.7 (2022): 2230-2236.[4] Lin, Yuexing, et al. "Dendrite-free Zn anode enabled by anionic surfactant-induced horizontal growth for highly-stable aqueous Zn-ion pouch cells." Energy & Environmental Science 16.2 (2023): 687-697.[5] Wang, Peng, and Petru Andrei. "High Performance Separator and Hydrogel Based on Aramid Fibers for Zn Ion Batteries." Electrochemical Society Meeting s 242. No. 4. The Electrochemical Society, Inc., 2022.[6] Xu, Lizhi, et al. "Water‐rich biomimetic composites with abiotic self‐organizing nanofiber network." Advanced Materials 30.1 (2018): 1703343.

Development of Organic Positive Electrodes for Rechargeable Aqueous Zinc-Ion Batteries for Stationary Energy Storage Systems

The rising concern towards the amount of anthropogenic carbon emissions and their effects on the environment has motivated the transition away from fossil fuels. The implementation of renewable energy sources has promoted the decarbonization of the power sector, but the variability of wind and solar energy necessitates the parallel deployment of high-performance energy storage infrastructure to ensure a reliable on-demand supply of green electricity to the grid. To this end, aqueous rechargeable zinc-ion batteries (ZIBs) are a promising new option for stationary energy storage owing to their high safety and low cost, when compared to established storage technologies like lithium-ion batteries. However, ZIBs are still limited by several technological challenges that hinder their uptake for commercial energy storage installations. In particular, the positive electrode materials, mostly comprised of metal oxides, are restraining the energy density and stability of the batteries and are yet under investigation. Low cost, long cycle life, and natural abundance are required properties of materials used in batteries for stationary energy storage. The search for materials with these properties has motivated the investigation of alternatives to metal oxides. One group of materials attracting considerable research attention is organic compounds which offer advantages like their natural abundance and high theoretical capacities. In this work, we developed an organic positive electrode for ZIBs using carbonyl groups as redox-active centers to provide energy storage capacity at round-trip energy efficiencies that are higher than the conventionally utilized manganese oxide electrodes. Furthermore, we investigated the effects of the conductive carbon additive on the deliverable capacity of the battery and elucidated the charge storage mechanism of this positive electrode material through detailed characterization. The results indicated that both Zn2+ and H+ are involved in the energy storage process of this organic electrode material. In addition to studying the energy storage process, degradation mechanisms were identified through nuclear magnetic resonance (NMR) and mass spectroscopy (MS). Both dissolution of the reduced form of the active material from the electrode and the formation of unwanted decomposition products are important contributors to the capacity fade of the battery. The technological and scientific insights provided in this presentation will thereby contribute towards the development of high-performance and naturally abundant electrode materials for the next generation of ZIBs to enable clean energy grid storage.

Structural Evolution of Manganese Prussian Blue Analogue in Aqueous ZnSO4 Electrolyte.

Among different Prussian Blue Analogues (PBAs), manganese hexacyanoferrate (MnHCF), with open framework and two abundant electroactive metal sites, exhibits high potential for the grid-scale aqueous rechargeable zinc-ion batteries (ARZIBs) application. Until now, the intercalation mechanism of Zn2+ into MnHCF has not been clearly illustrated. In this work, combining different synchrotron X-ray techniques, the structural and microscopic evolution of MnHCF in 3 m ZnSO4 electrolyte is comprehensively studied, and a thorough understanding of the intercalation/release dynamic, in terms of local and long-range domain, is provided. The elemental distribution and structural information of Fe, Mn, Zn inside MnHCF electrodes is obtained from the X-ray fluorescence (XRF) elemental maps and X-ray absorption spectroscopy (XAS). The in-depth analysis of extended X-ray absorption fine structure (EXAFS) signals confirm that the rearrangement of Mn site, evidencing the cleavage of the Mn─N bond with the formation of a Mn─O bond, in an octahedral environment. The phase transformation of MnHCF takes place exclusively during the 1st cycle, and a mixture of rhombohedral and cubic zinc hexacynoferrate (ZnHCF) phases are formed during the first charge process. Thereafter, the newly formed cubic ZnHCF phase becomes the only stable one, existing in the subsequent cycles and exhibiting excellent electrochemical stability.

Effect of pre-inserted monovalent cations on vanadium-based cathode materials for rechargeable aqueous zinc-ion batteries

Understanding the effect of pre-inserted cations in vanadium-based from a comprehensive perspective plays a vital role in exploring novel cathode materials for Zn-ion storage. In this work, we provide a study of monovalent cations (i.e., Na+, K+, and NH4+) on the Zn2+ storage behaviors of proton-substituted vanadates (i.e., NaVO, KVO, and NH4VO), revealing the intrinsic property (e.g., hydration capacity, bonding strength) of monovalent ions has a significant impact on the amount of pre-inserted cations and crystal water in stacked V–O layers, as well as the morphology of the obtained products, and the structural evolution during the activated process. Due to the enhancement of the ion-diffusion kinetics and stronger capacitance properties from the synergistic effect by pre-inserted Na+ ions and crystal water, the NaVO cathode exhibits superior rate performance and better energy efficiency (60.87 % at 10 A g−1), delivers a high specific capacity of 427.0 mAh g−1 at 0.2 A g−1 and retains 74.3 % of capacity after 1900 cycles at 2 A g−1. Moreover, the correlation between the pre-inserted cations in the cathode and the issues (e.g., side-products and dendrites) of the Zn anode has been revealed, providing new insight into designing high-performance cathodes for Zn ion batteries.

Construction of an n-Type Fluorinated ZnO Interfacial Phase for a Stable Anode of Aqueous Zinc-Ion Batteries.

Aqueous rechargeable zinc-ion batteries have become an ideal solution for the next generation of energy storage systems due to their low cost and high safety. However, the uncontrollable zinc dendrites and harmful side reactions of metal zinc anodes hinder the further development of aqueous zinc-ion batteries. In this work, the artificial fluoride zinc oxide (F-ZnO) interface phase is integrated in situ on the surface of zinc foil. The F-ZnO interface phase significantly inhibits the side reactions on the surface of the zinc electrode by reducing the direct contact between the electrolyte and the surface of the zinc foil. In addition, F-ZnO modified by a small amount of F doping shows enhanced conductivity and electron transport capacity, avoiding the accumulation of high concentration Zn2+ on the anode surface, and ultimately promoting the efficient nucleation and orderly deposition of a zinc anode. The cycle life of the symmetrical cell based on F-ZnO is as high as 2600 cycles at an area current density of 4 mA cm-2, which is much better than that of a commercial pure Zn electrode. The modified F-ZnO@Zn anode truly achieves the purpose of prolonging the anode's life.

Ultrathin Zn(002) textured zinc anodes for dendrite-free and hydrogen evolution-inhibited zinc batteries

For practical rechargeable aqueous zinc-ion batteries, the long-term cycling stability of the zinc anode remains significantly constrained by its low utilization efficiency and the persistent challenge of hydrogen evolution. This study demonstrates the fabrication of ultrathin zinc electrodes with a robust Zn (002) texture while ensuring an adequate supply of zinc metal for use as an anode material. This approach effectively suppresses the tendency of zinc atoms to undergo deposition transformation due to dislocation-induced phenomena. Compared to zinc foils with higher deposition amount, the ultrathin Zn anode exhibits enhanced resistance to dendrite growth and interfacial side reactions. Assembled symmetrical cells based on this ultra-thin Zn anode show a cycle life of 1750 h (1 mAcm−2, 0.5 mAhcm−2), maintaining stable cycling for over 100h even at a high depth of discharge (DOD) of 46.23%. Additionally, the full cell couple with V10O24 exhibits a high initial capacity of 429.6 mAh g−1 and a capacity retention of 75.8% after 1000 cycles.

Construction of an anti-anionic-depletion layer to mitigate the tip deposition effect for dendrite-free zinc anode

Rechargeable aqueous zinc-ion batteries have been plagued by the well-known problem of zinc dendrite formation. This issue mainly arises from the inherent depletion of anions in the vicinity of the zinc anode during deposition process, leading to a strong spatial electric field that influences Zn2+ cations deposition and triggers dendrite growth. Herein, the anti-anionic-depletion strategy is proposed that involves anions anchored in the surface region of zinc anode to mitigate the adverse effects of the spatial electric field and inhibit dendrite growth. By theoretical calculations and experimental verification, layered double hydroxides (LDHs) materials were selected to immobilize SO42- anions and construct a protective coating layer against anion depletion (anti-anionic-depletion layer). Furthermore, the deposition flux of Zn2+ cations was also regulated by in-situ growing LDH nanosheets. Benefiting from these modifications, the in-situ grown ZnAl-LDH modified electrode (Zn@ZnAl) exhibits outstanding stability (5500 cycles at 40 mA cm−2), and shows negligible capacity degradation in both Zn-Mn full cells and zinc hybrid capacitors.

Unlocking the performance degradation of vanadium-based cathodes in aqueous zinc-ion batteries

Vanadium-based materials stand out as promising cathode options for rechargeable aqueous zinc-ion batteries (ZIBs), primarily because of their high capacity and superior rate capability. Nevertheless, the utilization of vanadium-based cathodes in advancing ZIBs toward commercial viability is hindered by their insufficient stability and a notable lack of comprehension of the mechanisms driving capacity degradation. Herein, we identified the formation of Zn3(OH)2V2O7·2H2O (ZOV) as a key contributor to the capacity decay of vanadium-based cathodes. Through a series of compelling experiments, we revealed that dissolved vanadium ions react with zinc salts or layered zinc hydroxide (formed from H+ insertion) during the immersion or cycling of vanadium-based cathodes in aqueous electrolytes, ultimately leading to the formation of detrimental ZOV. Strong evidence shows that ZOV is inactive for Zn2+ storage owing to the presence of the pure tetrahedral frameworks of vanadium. To suppress the formation of ZOV, adjustments were made to the electrolyte composition, including the solvents and solutes. Consequently, the absence of ZOV enables an impressive capacity retention of 85 % in the ZnSO4 electrolyte after 150 cycles at 0.2 A g−1. Overall, this study directly unlocks the capacity decay mechanism in vanadium-based cathodes and offers valuable insights for the design of innovative electrolytes and novel vanadium-based cathode materials for ZIBs.

Stabilizing Zinc Hexacyanoferrate Cathode by Low Contents of Cs Cations for Aqueous Zn-Ion Batteries.

Exploring cathode materials with excellent electrochemical performance is crucial for developing rechargeable aqueous zinc ion batteries (RAZIBs). Zinc hexacyanoferrate (ZnHCF), a promising candidate of cathode materials for RAZIBs, suffers from severe electrochemical instability issues. This work reports using low contents of alkaline metal cations as electrolyte additives to improve the cycle performance of ZnHCF. The cations with large sizes, particularly Cs+, changes the intercalation chemistry of ZnHCF in RAZIBs. During cycling, Cs+ cations co-inserted into ZnHCF stabilize the host structure. Meanwhile, a stable phase of CsZn[Fe(CN)6] forms on the ZnHCF cathode, suppressing the loss of active materials through dissolution. ZnHCF gradually converts to an electrochemically inert Zn-rich phase during long-term cycling in aqueous electrolyte, leading to irreversible capacity loss. Introducing Cs+ in the electrolyte inhibits this conversion reaction, resulting in the extended lifespan. Owing to these advantages, the capacity retention rate of ZnHCF/Zn full batteries increases from the original 7.0 % to a high value of 54.6 % in the electrolyte containing 0.03 M of Cs2SO4 after 300 cycles at 0.25 A ⋅ g-1. This research provides an in-depth understanding of the electrochemical behavior of ZnHCF in aqueous zinc electrolyte, beneficial for further optimizing ZnHCF and other metal hexacyanoferrates.

CNT Composite β-MnO2 with Fiber Cable Shape as Cathode Materials for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) have developed into one of the most attractive materials for large-scale energy storage owing to their advantages such as high energy density, low cost, and environmental friendliness. Nevertheless, the sluggish diffusion kinetics and inherent impoverished conductivity affect their practical application. Herein, the β-MnO2 composited with carbon nanotubes (CNT@M) is prepared through a simple hydrothermal approach as a high-performance cathode for AZIBs. The CNT@M electrode exhibits excellent cycling stability, in which the maximum specific discharge capacity is 259 mA h g-1 at 3 A g-1, and there is still 220 mA h g-1 after 2000 cycles. The specific capacity is obviously better than that of β-MnO2 (32 mA h g-1 after 2000 cycles). The outstanding electrochemical performance of the battery is inseparable from the structural framework of CNT and inherent high conductivity. Furthermore, CNT@M can form a complex conductive network based on CNTs to provide excellent ion diffusion and charge transfer. Therefore, the active material can maintain a long-term cycle and achieve stable capacity retention. This research provides a reasonable solution for the reliable conception of Mn-based electrodes and indicates its potential application in high-performance AZIB cathode materials.

High-capacity K+-pillared layered manganese dioxide as cathode material for high-rate aqueous zinc-ion battery

Sluggish kinetics and severe structural instability of manganese-based cathode materials for rechargeable aqueous zinc-ion batteries (ZIBs) lead to low-rate capacity and poor cyclability, which hinder their practical applications. Pillaring manganese dioxide (MnO2) by pre-intercalation is an effective strategy to solve the above problems. However, increasing the pre-intercalation content to realize stable cycling of high capacity at large current densities is still challenging. Here, high-rate aqueous Zn2+ storage is realized by a high-capacity K+-pillared multi-nanochannel MnO2 cathode with 1 K per 4 Mn (δ-K0.25MnO2). The high content of the K+ pillar, in conjunction with the three-dimensional confinement effect and size effect, promotes the stability and electron transport of multi-nanochannel layered MnO2 in the ion insertion/removal process during cycling, accelerating and accommodating more Zn2+ diffusion. Multi-perspective in/ex-situ characterizations conclude that the energy storage mechanism is the Zn2+/H+ ions co-intercalating and phase transformation process. More specifically, the δ-K0.25MnO2 nanospheres cathode delivers an ultrahigh reversible capacity of 297 mAh g−1 at 1 A g−1 for 500 cycles, showing over 96 % utilization of the theoretical capacity of δ-MnO2. Even at 3 A g−1, it also delivered a 63 % utilization and 64 % capacity retention after 1000 cycles. This study introduces a highly efficient cathode material based on manganese oxide and a comprehensive analysis of its structural dynamics. These findings have the potential to improve energy storage capabilities in ZIBs significantly.

Rice powder template for hausmannite Mn3O4 nanoparticles and its application to aqueous zinc ion battery.

In this study, a simple calcination route was adopted to prepare hausmannite Mn3O4 nanoparticles using rice powder as soft bio-template. Prepared Mn3O4 was characterized by Fourier Transform Infra-Red Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray microanalysis (EDX), Powder X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Brunauer-Emmett-Teller (BET) and Solid state UV-Vis spectroscopic techniques. Mn-O stretching in tetrahedral site was confirmed by FTIR and Raman spectra. % of Mn and O content supported Mn3O4 formation. The crystallinity and grain size was found to be 68.76% and 16.43 nm, respectively; tetragonal crystal system was also cleared by XRD. TEM clarified the planes of crystal formed which supported the XRD results and BET demonstrated mesoporous nature of prepared Mn3O4 having low pore volume. Low optical band gap of 3.24 eV of prepared Mn3O4 nanoparticles indicated semiconductor property and was used as cathode material to fabricate CR-2032 coin cell of Aqueous Rechargeable Zinc Ion Battery (ARZIB). A reversible cyclic voltammogram (CV) showed good zinc ion storage performance. Low cell resistance was confirmed by Electrochemical Impedance Spectroscopy (EIS). The coin cell delivered high specific discharge capacity of 240.75 mAhg-1 at 0.1 Ag-1 current density. The coulombic efficiency was found to be 99.98%. It also delivered excellent capacity retention 94.45% and 64.81% after 300 and 1000 charge-discharge cycles, respectively. This work offers a facile and cost effective approach for preparing cathode material of ARZIBs.

Three-dimensional mixed-valence polyoxovanadates@polyaniline architecture towards high-performance rechargeable aqueous zinc-ion batteries cathode

Aqueous zinc ion batteries (AZIBs) are toward promising candidates of energy storage systems for their low cost, high safety and eco-friendliness, whereas the sluggish reaction kinetics and unstable internal structure of cathode materials greatly limited the practical application of AZIBs. Herein, we employ the three-dimensional mixed-valance polyoxovanadates [Co3(H2O)12][VIV10VV8O42(SO4)]·24H2O (CoVO) coated with polyaniline (PANI) as stable zinc ion storage material (denoted as CoVO@PANI). The 3D highly porous CoVO framework constructs multidimensional interconnected Zn2+ migration channels, and the high conductivity of PANI facilitates the formation of oxygen defects during in-situ polymerization process and inhibits the polyoxovanadates dissolution. Density functional theory calculation reveals that PANI significantly regulates the electronic property of the CoVO host, further promoting the electron/ion transfer kinetics and thus contributing to high-effciency Zn2+ storage performance. As expected, the optimized as-fabricated CoVO@PANI60 cathode exhibits a high reversible capacity of 456.8 mAh g−1 at 0.1 A g−1 and long-term cyclability with capacity retention of 90.4 % after 1500 cycles at 10 A g−1.

On the origin of enhanced electrochemical kinetics in guest-ions pre-intercalated layered vanadium oxides: Interlayer spacing vs lattice distortion

Cathode materials of highly stable structure and high capacity are essentially required for aqueous rechargeable zinc ion batteries (ARZIBs), where layered vanadium oxide hydration (VOH) is one of the most promising cathode materials for reversible zinc ion intercalation/deintercalation. Previous studies have shown that both the interlayer spacing and the Zn-ion storage performance can be altered by the pre-intercalation of certain guest ions between the layers of VOH. In addition to previous discussions on the increase in effective Zn2+ storage as a result of the widening in interlayer spacing after guest ion pre-intercalation, there is a variation in the exposed active O sites, which are shown to be equally important. In the metal ion pre-intercalated layered vanadium oxides, there is a delicate balance between the interlayer spacing and lattice distortion, depending on the type and amount of pre-intercalated metal ions. In particular, those pre-intercalated guest ions with high electronegativity can steadily shift towards the VO layers and break the V-O bonds leading to exposed active O sites. The high electronegativity endows the combination of guest ions with newly exposed O sites. These active O sites give rise to an inhomogeneous distribution of the charge density, leading to an improvement in electrochemical performance. The present study demonstrates the complicated interplays of more than one parameter in the guest ion pre-intercalated layered vanadium oxides, going much beyond the simple widening in inter-layer spacing.