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With the growth of demand for flexible devices, the development of flexible electrodes used in energy storage devices has attracted much attention of researchers. In this work, a thin flexible cathode of Prussian blue analogue@polyaniline rooted in carbon cloth has been fabricated. The Prussian blue analogue (PBA) is an electrochemically active material grafted on flexible carbon cloth substrates, which had been precoated with polyaniline. Polyaniline as an intermediate layer can not only improve the overall electronic conductivity of the electrode but also enhance the adhesion and load of the PBAs. The electrochemical properties of the flexible cathode with a "sandwich" structure were determined in half-cells, with a superior capacity of 151 mA h·g-1 and a striking cyclability with 96% capacity retention over 100 cycles at 100 mA h·g-1. This work proposes a novel perspective for the structural construction and material synthesis of flexible positive electrodes and gives new options for the practical application of flexible batteries.

Prussian blue analogues are potential competitive energy storage materials due to their diverse metal combinations and wide three-dimensional ion channels. Here, we prepared a new highly crystalline monoclinic nickel-doped cobalt hexacyanoferrate via a feasible and simple one-step co-precipitation method. In the process of sodium-ion de-intercalation, three stable charge and discharge platforms, which are consistent with the cyclic voltammetry performance, are seen for the first time, showing the function of nickel ions in Prussian blue. Furthermore, the charge transfer and structural evolution caused by the transmission of sodium ions were well revealed via ex situ XRD, ex situ XPS, and in situ EIS studies. Simulation calculations are performed relating to the energy band structure and the highest-occupied bonding orbitals of the system in different charge states, revealing the charge and discharge mechanism of the nickel-doped material and the reason for the emergence of the new platform at low voltages. In addition, NaNi0.17Co0.83Fe(CN)6 also delivers a striking capacity of 146 mA h g-1 and superior cyclability, with 93% capacity retention over 100 cycles; it can be considered as a promising alternative cathode material for use in sodium-ion batteries.

Low-cost manganese hexacyanoferrate (NMHCF) possesses many favorable advantages including high theoretical capacity, ease of preparation, and robust open channels that enable faster Na+ diffusion kinetics. However, high lattice water and low electronic conductivity are the main bottlenecks to their pragmatic realization. Here, we present a strategy by anchoring NMHCF on reduced graphene oxide (RGO) to alleviate these problems, featuring a specific discharge capacity of 161/121 mA h g–1 at a current density of 20/200 mA g–1. Moreover, the sodiation process is well revealed by ex situ X-ray diffraction, EIS and Car–Parrinello molecular dynamics simulations. At a rate of 20 mA g–1, the hard carbon//NMHCF/RGO full cell affords a stable discharge capacity of 84 mA h g–1 (based on the weights of cathode mass) over 50 cycles, thus highlighting NMHCF/RGO an alternative cathode for sodium-ion batteries.

Designing Prussian blue with optimally exposed crystal planes and confining it in a conductive matrix are critical issues for improving its sodium storage performance, and will result in much improved sodium ion adsorption and diffusion, together with improved electron mobility. Here, we firstly illustrate through DFT simulations that the {100} lattice planes and [100] direction of the KxFeFe(CN)6 crystal are the preferred occupation sites and diffusion route for sodium ions. In addition, through coupling with RGO, KxFeFe(CN)6 electrodes exhibit better electronic conductivity. Accordingly, {100} plane-capped cubic K0.33FeFe(CN)6 wrapped in RGO was fabricated using a facile CTAB-assisted method. Due to the highly robust framework, higher specific surface area, greatly reduced number of lattice water defects and conductive RGO coating, K0.33FeFe(CN)6/RGO exhibits superior electrochemical performance in sodium-ion batteries. As a cathode, the RGO-coated K0.33FeFe(CN)6 yields an initial discharge–charge capacity of 160 mA h g−1 at a rate of 0.5C, and an excellent capacity retention of 92.2% at 0.5C and 90.1% at 10C after 1000 and 500 cycles. Furthermore, XRD, DFT simulation, XANES and EXAFS verified that the structural changes during the Na-ion insertion–extraction processes are highly reversible. All these results suggest that {100} plane-capped K0.33FeFe(CN)6/RGO has excellent potential as a cathode for sodium-ion batteries.

Establishing advanced sodium-ion batteries (SIBs) with high energy density and eco-friendly electrode materials are still far from satisfactory due to the large-size of sodium-ions and sluggish redox kinetics during electrochemical processes. Herein, a novel ultrafast kinetics net electrode assembled via MoSe2/MXene heterojunction is synthesized by a simple hydrothermal method followed by thermal annealing. Featuring the Van der Waals force interaction between MoSe2 and MXene, the volumetric change during the sodium ions insertion/extraction courses is effectively restrained, and the reaction kinetics is greatly enhanced further. Meanwhile, both the high electrical and ion conductivity (lower diffusion barrier between Na+/MXene ~0.066 eV) provided by the unique MXene based net heterostructure of our hybrid materials, as evidenced by DFT calculations, are beneficial to the transportation of sodium ions, thus enabling an outstanding rate and long-cycling capability. As a result, the fabricated cells exhibit high reversible capacities of 490 mAh g−1 at 1 A g−1, as well as 250 mAh g−1 at a high current of 10 A g−1 with a coulombic efficiency of 99.8%, indicating the excellent electrochemical performance of our hybrid materials, especially at high current. This novel net MoSe2/MXene heterostructure, combined with our simple synthesis strategy together, are expected to have great potential in sodium-ions storage application.

Prussian blue analogs are receiving intense attention due to their high theoretical energy density and low cost, but their real applications are still hampered by poor electronic conductivity and cycling stability. Here, Na[Formula: see text]Ni[Formula: see text]Mn[Formula: see text]Fe(CN)6 wrapped with graphene was synthesized by a facile co-precipitation method. The existence of RGO not only significantly increases the conductivity of the cathode, but also makes the framework much more robust during long cycling process. As the cathode, the Na[Formula: see text]Ni[Formula: see text]Mn[Formula: see text]Fe(CN)6/RGO is able to deliver a high initial discharge capacity of 120[Formula: see text]mA[Formula: see text]h[Formula: see text]g[Formula: see text] at a current density of 20[Formula: see text]mA[Formula: see text]g[Formula: see text] with superior capacity retention of 96.7% after 100 cycles. Even at a current density of 1000[Formula: see text]mA[Formula: see text]g[Formula: see text], the cell still delivers a capacity of 86[Formula: see text]mA[Formula: see text]h[Formula: see text]g[Formula: see text], indicating outstanding rate capability. The results and the facile synthesis method enable Na[Formula: see text]Ni[Formula: see text]Mn[Formula: see text]Fe(CN)6/RGO to the competitive for a future energy storage system.