Aqueous Rechargeable Batteries for Large-scale Energy Storage

Inducing Mn defects within MnTiO3 cathode for aqueous zinc-ion batteries

Layered manganese-based cathode materials are considered as one of the promising cathodes benefit from inherent low manufacturing cost, non-toxic and high safety in aqueous zinc-ion batteries (AZIBs). However, the sluggish reaction kinetics within layered cathodes is inevitable due to the poor electrical/ionic conductivity. Herein, MnTiO3 is reported as a new cathode material for AZIBs and in-situ induced Mn-defect within MnTiO3 during the first charging is desirable to improve the reaction kinetics to a great extent. Additionally, DFT calculations further demonstrate that MnTiO3 with manganese defects exhibits a uniform charge distribution at the defect sites, enhancing the attraction towards H+ and Zn2+ ions. Furthermore, it performs good cycling stability which can obtain 115 mA h g-1 even at 400 mA g-1 after 450 cycles and the discharge capacity reaches up to 233.8 mAh/g at 100 mA g-1 when Mn-defect MnTiO3 was employed as the cathode. This research could provide a new method for the development and mechanism research of cathode materials for AZIBs.

Deciphering the Effect of Microstructural Modification in Sodium Alginate-Based Solid Polymer Electrolyte by Unlike Anions

Microstructure modification in sodium alginate (NaAlg)-based solid polymer electrolytes by the perchlorate (ClO4-) and acetate (CH3COO-) anions of sodium salts has been reported. ClO4- participates in the structure-breaking effect via inter/intramolecular hydrogen bond breaking, while CH3COO- changes the amorphous phase, as evident from X-ray diffraction studies. The larger size and negative charge delocalization of ClO4- have a plasticizing effect, resulting in a lower glass transition temperature (Tg) compared to CH3COO-. Decomposition temperature is strongly dependent on the type of anion. Scanning electron microscopy images showed divergent modifications in the surface morphology in both electrolyte systems, with variations in salt content. The mechanical properties of the NaAlg-NaClO4 electrolyte systems are better than those of the NaAlg-CH3 COONa system, indicating weak interactions in the latter. Although most of the studies focus on the cation influence on conductivity, the interaction of the anion and its size certainly have an influence on the properties of solid polymer electrolytes, which will be of interest in the near future for sodium ion-based electrolytes in energy storage devices.

Mn2+/I- Hybrid Cathode with Superior Conversion Efficiency for Ultrahigh-Areal-Capacity Aqueous Zinc Batteries

Aqueous Zn-Mn²⁺ electrolysis batteries utilizing the two-electron-transfer reaction between Mn²⁺ and MnO₂ attract great attention because of their superior theoretical capacity (616 mAh g^-1). However, the low conductivity of deposited MnO₂ and the poor conversion efficiency of Mn²⁺/MnO₂ inevitably result in limited areal capacity and unsatisfied cycling stability, which have become the main hurdles of aqueous Zn-Mn²⁺ batteries' applications. Herein, we propose a novel Mn²⁺/I^- hybrid cathode that couples the triiodide/iodide redox with the Mn²⁺/MnO₂ redox to optimize the electrolysis kinetics. Because of the synergistically enhanced conversion reaction between Mn²⁺/I^- and the promoter effect of I^- to the dissolution of MnO₂, this hybrid cathode not only exhibits fast reaction kinetics, thus demonstrating ultrahigh rate capability (100 mA cm^-2), but also displays observably enhanced conversion efficiency up to 96.0% with excellent reversibility of 2000 cycles. Especially the superhigh areal capacity of 20 mAh cm^-2 with more than 100 cycles among the reported static Zn-Mn²⁺ electrolysis batteries is demonstrated. The excellent battery performance as well as the facile electrode hybridization approach designed here paves the way for the practical applications of aqueous Zn batteries.

A hybrid composite of H2V3O8 and graphene for aqueous lithium-ion batteries with enhanced electrochemical performance

Aqueous rechargeable lithium-ion batteries (ARLBs) are regarded as a competitive challenger for large-scale energy storage systems because of their high safety, modest cost, and green nature. A kind of modified composite material composed of H2V3O8 nanorods and graphene sheets (HVO/G) has been effectively made by a one-step hydrothermal method and following calcination at 523 K. XRD, SEM, TEM, and TG are used to determine the phase structures and morphologies of the composite materials. Owing to the advantage of the layered structure of H2V3O8 nanorods, the excellent conductivity of the graphene sheets, and the 3D network structure of the modified composite, the ARLBs with HVO/G can deliver an adequate specific capacity of 271 mA h g-1 at 200 mA g-1 and have a retention rate of 73.4% after 50 cycles. The average discharge capacity of ARLB with HVO/G as anode has a considerable improvement over that of HVO/CNTs and HVO, whatever the current rate used. Moreover, we find that the diffusion coefficient of lithium-ion increases by an order of magnitude through the theoretical calculation for HVO/G ARLB. The new ARLB with HVO/G electrode is a potential energy storage system with great advantages, such as simple preparation, easy assembly process, excellent safety and low-cost environmental protection.

Layered Co doped MnO2 with abundant oxygen defects to boost aqueous zinc-ion storage

Zinc Manganese oxide (Zn/MnO₂)-based aqueous battery is favored due to their high specific capacity, security and cost performance. Nevertheless, they usually problems of unstable cyclic structure and slow diffusion kinetics, restricting their practical application. Here, we have successfully synthesized a Co doped MnO₂ cathode material with abundant defects on a carbon cloth substrate. Through a simple hydrothermal method, the Co element can be lightly intercalated in the two-dimensional (2D) layered α-MnO₂ nanowires, inhibiting the structural transformation during the cycle and improve the stability of the material. Meanwhile, plasma technology facilitates the formation of oxygen vacancies in the electrode material, which not only accelerate electron diffusion but also improve the conductivity. Therefore, Zn/Co-MnO₂ battery can reach a specific capacity of 511 mAh g^-1 at 0.5A g^-1 and the retention rate accomplish 98% at high current density. This research puts forward a strategy of element doping and physical preparation of oxygen vacancies, which provides the possibility to develop reversible Zn/MnO₂-based aqueous battery cathode materials with high-performance.

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.

A Low Cost Aqueous Zn-S Battery Realizing Ultrahigh Energy Density

Rechargeable aqueous zinc ion batteries are enabled by the (de)intercalation chemistry, but bottlenecked by the limited energy density due to the low capacity of cathodes. In this work, carbon nanotubes supported 50 wt% sulfur (denoted as S@CNTs-50), as a conversional cathode, is employed and a high energy density aqueous zinc-sulfur (Zn-S) battery is constructed . In the electrolyte of 1 m Zn(CH3COO)2 (pH = 6.5) with 0.05 wt% I2 additive where I2 can serve as medium of Zn2+ ions to reduce the voltage hysteresis of S@CNTs-50 and stabilize Zn stripping/plating, S@CNTs-50 delivers a high capacity of 1105 mAh g-1 with a flat discharge voltage of 0.5 V, realizing an energy density of 502 Wh kg-1 based on sulfur, which is one of the highest values reported in aqueous Zn-based batteries that use mild electrolyte. Moreover, the chemical materials cost of this aqueous Zn-S battery can be lowered to be $45 kWh-1 due to the cheap raw materials, reaching to the level of pumped energy storage. Ex situ X-ray diffraction, Raman spectra, X-ray photoelectron spectrum, and transmission electron microscopy measurements reveal that sulfur cathode undergoes a conversion reaction between S and ZnS.

Monoclinic VO2(D) hollow nanospheres with super-long cycle life for aqueous zinc ion batteries

Vanadium dioxide (VO₂) is a very promising cathode material for aqueous zinc ion batteries (AZIBs) because of its high reversible specific capacity, excellent rate performance and fast diffusion kinetics. However, its long-term cycle stability and compatibility with electrolytes have not met expectations. In this study, another metastable phase of vanadium dioxide-monoclinic VO₂(D)-is demonstrated to be a better choice as a cathode for AZIBs. Electrochemical results revealed that the as-prepared VO₂(D) hollow nanospheres delivered high reversible discharge capacity (up to 408 mA h g^-1 at 0.1 A g^-1), exceptional rate performance (200 mA h g^-1 at 20 A g^-1), and long cyclic endurance stability (cycling for 30 000 cycles with a low capacity fading rate of 0.0023% per cycle) in inexpensive 3 M ZnSO₄ electrolyte. Furthermore, the electrochemical reaction mechanism was corroborated using ex situ XRD, HRTEM and XPS, showing that an interesting electrochemically induced phase transition from VO₂(D) to V₂O₅·xH₂O occured with the insertion/extraction of zinc ions. Finally, the prototype batteries assembled with our as-prepared VO₂(D) hollow nanospheres and the impressive performance of this electrode under high active material mass loading further reveal its high potential in practical applications.

Electrolytes and Electrolyte/Electrode Interfaces in Sodium-Ion Batteries: From Scientific Research to Practical Application

Sodium-ion batteries (SIBs) have drawn considerable interest as power-storage devices owing to the wide abundance of their constituents and low cost. To realize a high performance-price ratio, the cathode and anode materials must be optimized. As essential components of SIBs, electrolytes should have wide electrochemical windows, high thermal stability, and exceptional ionic conductivity. Therefore, improved electrolytes, based on various materials and compositions, are developed to meet the practical demands of SIBs, including organic electrolytes, ionic liquids, aqueous, solid electrolytes, and hybrid electrolytes. Although mature organic electrolytes are currently used in production, aqueous and solid electrolytes show advantages for future applications, as discussed here in detail. Current efforts in modifying electrolytes to optimize their interfacial compatibility with electrodes, leading to longer battery lifetimes and greater safety, are described. The advanced characterization techniques used to investigate the properties of electrolytes and interfaces are introduced, and the reaction processes and degradation mechanisms of SIBs are revealed. Furthermore, the practical prospects of SIBs promoted by high-quality electrolytes appropriately matched with electrodes are predicted and directions for developing next-generation SIBs are suggested.

Advanced Low-Cost, High-Voltage, Long-Life Aqueous Hybrid Sodium/Zinc Batteries Enabled by a Dendrite-Free Zinc Anode and Concentrated Electrolyte

Aqueous batteries are promising energy storage systems but are hindered by the limited selection of anodes and narrow electrochemical window to achieve satisfactory cyclability and decent energy density. Here, we design aqueous hybrid Na-Zn batteries by using a carbon-coated Zn (Zn@C) anode, 8 M NaClO₄ + 0.4 M Zn(CF₃SO₃)₂ concentrated electrolyte coupled with NASICON-structured cathodes. The Zn@C anode achieves stable Zn stripping/plating and improved kinetics without Zn dendrite formation due to the porous carbon film facilitating homogeneous current distribution and Zn deposition. Furthermore, the concentrated electrolyte offers a large electrochemical window (∼2.5 V) and permits stable cycling of cathodes. As a result, the hybrid batteries exhibit extraordinary performance including high voltage, high energy density (100-150 Wh kg^-1 for half battery and 71 Wh kg^-1 for full battery), and excellent cycling stability of 1000 cycles.