Sodium-ion batteries are emerging as a highly promising technology for large-scale energy storage applications. However, it remains a significant challenge to develop an anode with superior long-term cycling stability and high-rate capability. Here we demonstrate that the Na þ intercalation pseudocapacitance in TiO 2 /graphene nanocomposites enables high-rate capability and long cycle life in a sodium-ion battery. This hybrid electrode exhibits a specific capacity of above 90 mA h g -1 at 12,000 mA g -1 (B36 C). The capacity is highly reversible for more than 4,000 cycles, the longest demonstrated cyclability to date. First-principle calculations demonstrate that the intimate integration of graphene with TiO 2 reduces the diffusion energy barrier, thus enhancing the Na þ intercalation pseudocapacitive process. The Na-ion intercalation pseudocapacitance enabled by tailor-deigned nanostructures represents a promising strategy for developing electrode materials with high power density and long cycle life.

class of materials show great potential for the insertion/extraction of multivalent ions (Zn 2+ , Mg 2+ , Al 3+ ) owing to the characteristic of large layer spacing and high conductivity. Among all the TMDs, VS 2 is a typical family member of TMDs with hexagonal system, which shows similar crystal structure to that of graphite lamellar with an interlayer spacing of 5.76 Å. [25,30] There is a vanadium layer between two sulfur layers to form a kind of sandwich structure. In VS 2 crystal structure, each V atom is arranged around six S atoms and connected with S atoms with covalent bonds. The interlayer spacing of VS 2 is so large that enables the convenient insertion/extraction of lithium ions (0.69 Å), sodium ions (1.02 Å), zinc ions (0.74 Å) or their solvation sheath in electrolyte. However, to the best of our knowledge, there is no report about VS 2 as the electrode materials for ZIBs.Herein, the VS 2 nanosheets are synthesized via a facile hydrothermal reaction (Supporting Information), which deliver a high capacity of 190.3 mA h g −1 at a current density of 0.05 A g −1 and exhibit long-term cyclic stability as the cathode for ZIBs. The electrochemical reaction mechanism of such VS 2 electrodes is further investigated systematically through a series of measurements including ex situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), in situ Raman, ex situ transmission electron microscopy (TEM). A reversible insertion/extraction process can be observed from all aspects. Both the ex situ TEM and ex situ XRD results demonstrate that the interlayer space of VS 2 can self adapt to the intercalation of Zn 2+ with an expansion along the c-axis (only 1.73%) and a slightly shrink along the a-and b-axes, which plays a key role in the realization of long-life ZIBs. All the above evidences reveal that the VS 2 is a promising cathode material with high capacity and good cyclic stability for ZIBs.The crystal structure of the as-prepared VS 2 is tested by XRD. All characteristic peaks are in accordance with the standard card of VS 2 (JCPDS NO. 01-089-1640) (Figure 1a). The Raman spectrum of the VS 2 in the range of 100-1100 cm −1 is shown in Figure 1b. Six peaks located at 140.4, 192.0, 282.0, 406.6, 687.8, and 993.2 cm −1 are observed, which correspond to the rocking and stretching vibrations of V-S bonds or their combination. [25] The morphology and microstructures of as-prepared VS 2 are investigated by field emission scanning electron microscopy (SEM) and high-resolution TEM (HRTEM). As shown in Figure 1c, The VS 2 flowers are assembled by nanosheets with a diameter of 5-8 µm and a thickness of 50-100 nm. The d-spacing calculated from selected area electron diffraction (SAED) patterns are 2.89 and 1.64 Å (Figure 2f), which match the d-spacing values of (002) and (110) crystal planes of VS 2 , respectively. TEM and corresponding HRTEM images in Figure 2e show VS 2 nanosheets with a d-spacing of ≈5.76 Å,The continuous researches of energy-storage devices have gained considerable attention in our world ...

Hard carbon is one of the most promising anode materials for sodium‐ion batteries, but the low Coulombic efficiency is still a key barrier. In this paper, a series of nanostructured hard carbon materials with controlled architectures is synthesized. Using a combination of in situ X‐ray diffraction mapping, ex situ nuclear magnetic resonance (NMR), electron paramagnetic resonance, electrochemical techniques, and simulations, an “adsorption–intercalation” mechanism is established for Na ion storage. During the initial stages of Na insertion, Na ions adsorb on the defect sites of hard carbon with a wide adsorption energy distribution, producing a sloping voltage profile. In the second stage, Na ions intercalate into graphitic layers with suitable spacing to form NaC x compounds similar to the Li ion intercalation process in graphite, producing a flat low voltage plateau. The cation intercalation with a flat voltage plateau should be enhanced and the sloping region should be avoided. Guided by this knowledge, nonporous hard carbon material has been developed which has achieved high reversible capacity and Coulombic efficiency to fulfill practical application.

The development of manganese dioxide as the cathode for aqueous Zn-ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll-coated α-MnO as the cathode is proposed. The graphene scroll is uniformly coated on the MnO nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg (382.2 mA h g ) at 0.3 A g can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn-ion battery so far, and good long-term cycling stability with 94% capacity retention after 3000 cycles at 3 A g are achieved. Meanwhile, a two-step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO framework is proved by in situ X-ray diffraction, galvanostatic intermittent titration technique, and X-ray photoelectron spectroscopy characterizations. The graphene scroll-coated metallic oxide strategy can also bring intensive interests for other energy storage systems.

Among the aqueous rechargeable batteries, Zn 2+ -based batteries exhibit a series of unique attributes for large-scale energy storage: (i) feasibility of using low-cost Zn metal anode with a high theoretical specific capacity of 819 mA h g −1 ; (ii) replacement of the traditional alkaline electrolytes by mild neutral electrolytes, mitigating the environmental disruption and recycling costs; and (iii) low redox potential of Zn/Zn 2+ (−0.76 V vs standard hydrogen electrode) and two-electron transfer mechanism during cycling responsible for the high energy density. [6,22,23] However, the zinc system also has long-standing challenges, such as the unstable cathode and anode structures in the aqueous environment. On the cathode side, the cycling stability is related to how zinc ions and the electrolyte react with the cathode materials, which is much more complex as compared to the lithium-ion systems. An initial attempt on the hexacyanoferrate system delivered a limited capacity (≈60 mA h g −1 ), although a high operation voltage of ≈1.7 V was achieved. [23][24][25][26][27][28] Recently, Pan et al. demonstrated that the manganese oxide cathode goes through a chemical conversion reaction with the zinc species and H 2 O rather than the simple intercalation process, delivering a high capacity of ≈285 mA h g −1 and an operating voltage of ≈1.44 V. [29] Nazar's group developed a Zn 0.25 V 2 O 5 ·nH 2 O cathode material, which displayed a specific energy of ≈250 Wh kg −1 (based on cathode) and a high capacity of 220 mA h g −1 at 15 C (1 C = 300 mA g −1 ). [30] During cycling, the structural water in Zn 0.25 V 2 O 5 ·nH 2 O was revealed to exchange with Zn 2+ reversibly, thus resulting in good kinetics and rate performance. Furthermore, some other studies have also suggested the importance of H 2 O in metal ion intercalation. [23,31] During cycling, the solvating H 2 O works as a charge shield for the metal ions (Al 3+ , Mg 2+ , Li + , etc.), reducing their effective charges and hence their interactions with the host frameworks. [32,33] This strategy has been investigated to enhance the capacity and rate capability of Li + , Na + , and Mg 2+ batteries. [34][35][36][37][38][39] In this paper, we present a systematic and detailed study of the role of H 2 O in bilayer V 2 O 5 ·nH 2 O (n ≥ 1) as a prototype cathode material for zinc batteries. By coupling the electrochemical measurements, thermogravimetric/differential BatteriesLarge-scale energy storage systems are critical for the integration of renewable energy and electric energy infrastructures. [1][2][3] Among numerous candidates, lithium-ion batteries with organic electrolytes are one of the most attractive options due to their high energy density [4][5][6][7][8][9][10] and mature markets. [11,12] However, for grid scale energy storage, the cost of lithium-ion batteries is still too high, [13,14] and the use of the flammable organic electrolyte in large format batteries poses a severe safety and environmental concern. [15] As an alternative, low-cost aqueous batteries wi...

Aqueous Zn‐ion batteries (ZIBs) have received incremental attention because of their cost‐effectiveness and the materials abundance. They are a promising choice for large‐scale energy storage applications. However, developing suitable cathode materials for ZIBs remains a great challenge. In this work, pioneering work on the designing and construction of aqueous Zn//Na0.33V2O5 batteries is reported. The Na0.33V2O5 (NVO) electrode delivers a high capacity of 367.1 mA h g−1 at 0.1 A g−1, and exhibits long‐term cyclic stability with a capacity retention over 93% for 1000 cycles. The improvement of electrical conductivity, resulting from the intercalation of sodium ions between the [V4O12]n layers, is demonstrated by single nanowire device. Furthermore, the reversible intercalation reaction mechanism is confirmed by X‐ray diffraction, Raman, X‐ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis. The outstanding performance can be attributed to the stable layered structure and high conductivity of NVO. This work also indicates that layered structural materials show great potential as the cathode of ZIBs, and the indigenous ions can act as pillars to stabilize the layered structure, thereby ensuring an enhanced cycling stability.

Expanding hydrated vanadate with transition metal cations collectively promotes and catalyzes fast and more Zn-ion intercalation in aqueous batteries.

With the rapid development of energy storage devices, aqueous battery with noncombustion properties and instinct safe features has received great attentions and Zn anode is investigated intensively due to its high theoretical capacity (820 mAh g−1), and low negative potential (−0.762 V vs SHE). However, the unavoidable gas evolution hinders the cyclability and the application in the commercial field. Herein, the atomic layer deposition of TiO2 coating is first demonstrated as the protection layer of metallic zinc anode. The corrosion of zinc plate is significantly suppressed, leading to less gas evolution and Zn(OH)2 byproduct formation. The reduced gas generation on the outer surface of the zinc plate will maintain the effective contact area between the electrolyte and anode and leads to an improved coulombic efficiency. In this way, the Zn anode with 100 ALD cycles TiO2 protection shows reduced overpotential (72.5 mV) at 1 mA cm−2 for Zn–Zn symmetrical battery and additionally, the protection of TiO2 extended the Zn–MnO2 battery cycling performance up to 1000 cycles with the capacity retention of 85% at current density of 3 mA cm−2. The novel design of atomic layer deposition protected metal zinc anode brings in new opportunities to the realization of the ultrasafe aqueous zinc metal batteries.