Interlayer engineering of a V₂O₅ anode toward high-rate and durable dual-ion batteries

Abstract

Dual-ion batteries (DIBs) have gained widespread attention thanks to their high operating voltage, low cost, and environmental friendliness. However, the development of DIBs is dramatically limited by the unsatisfactory rate capacity and cycling performance of anode materials. Herein, we adopted a water-incorporation approach to design a V₂O₅ anode with an extended interlayer gap (W-V₂O₅). The incorporated H₂O not only offered ample space and abundant channels for efficient ion/electron intercalation/diffusion, but also improved structural stability during the repeated charge and discharge processes. Consequently, the W-V₂O₅ electrode delivered an enhanced specific capacity (293.2 vs. 264.4 mA h g⁻¹ at 1C), rate property (48.2% vs. 24.6% from 1C to 70C), and cycling stability (96.8% vs. 74.6% over 1000 cycles). Furthermore, a DIBs device with fast kinetics was assembled with a graphite cathode and W-V₂O₅ NS anode, which could work normally in a wide range of current densities. This work opens a new avenue for designing layered materials for energy-storage devices with high rate and good durability.

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Introduction

With the deepening of contradiction between environmental problems and energy demand, there is an urgent need to develop advanced rechargeable devices with cost-effectiveness, superior performance, and green environmental performance.¹ Lithium-ion batteries (LIBs) have the advantages of large energy density, small self-discharge, long service life, memoryless effects, etc., and they have monopolized the electric vehicle and smart electronics markets.² However, in practice, the shortage of lithium resources has made the manufacturing costs soar,^3,4 while the preparation process of LIBs also causes pollution and damage to the environment;^5,6 thus, there is an urgently need to develop novel substitutes that have high quality and are inexpensive.^7,8 Alternatively, dual-ion batteries (DIBs, based on the working mechanism involving the storage of cations and anions separately in the anode and cathode during the charge/discharge process) represent a potential new energy-storage technology in the post-LIBs era, which brings the advantages of a high operating voltage, good safety, low cost, and environmental friendliness.^9,10 Graphitic carbon is the preferred cathode for DIBs because of its large capacity, high reaction potential, good stability, low price, and environmental friendliness, which are conducive properties for constructing DIBs with large energy density, high power density, and good durability.¹⁰ Several new DIB devices have been reported, consisting of a graphite cathode and battery-type anode (including graphite,^11,12 Co₃O₄,¹³ Ni₃S₂,¹⁴ MnO,¹⁵ KNi_0.1Co_0.9F₃,¹⁶ Al metal,¹⁷ Sn metal,¹⁸ WS₂,¹⁹ and MoS₂ ²⁰). Unfortunately, the power density and durability of DIBs devices have thus far remained unsatisfactory. Therefore, it is a huge challenge to design an advanced anode that can be assembled with graphite cathodes into high-performance DIB devices.

Orthorhombic vanadium pentoxide (α-V₂O₅) with a layered structure was constructed by edge- and corner-sharing highly distorted [VO₆] octahedrons and V₂O₅ sheets were held together via weak vanadium–oxygen interactions (van der Waals forces).^21,22 Because of its natural abundance, good safety, multiple oxidation states, and environmental friendliness, α-V₂O₅ is a cation-intercalation anode material with great development potential for DIBs.^23,24 The V⁵⁺/V⁴⁺ and V⁴⁺/V³⁺ redox couples are present in the Li⁺-intercalation reaction of α-V₂O₅, leading to a high theoretical capacity of 294 mA h g⁻¹ for the insertion of two lithium ions.²⁵ Moreover, the potential of α-V₂O₅ for intercalation is about 1.5–4.0 V vs. Li/Li⁺, which is smaller than that of graphite (>4.5 V vs. Li/Li⁺). This fully demonstrates that the α-V₂O₅ anode and graphite cathode can be assembled into a DIB device. Nevertheless, the further development and application of α-V₂O₅ suffer from its weak electrical conductivity (10⁻² to 10⁻³ S cm⁻¹) and low ionic diffusion coefficient (10⁻¹² to 10⁻¹³ cm² s⁻¹), which can lead to an inferior rate capability and cycling stability performance.^26–28 To overcome the above intrinsic drawbacks, many strategies have been applied, such as nanostructuring,²⁹ cation/molecule pillaring,³⁰ structural modification,²⁶ and oxygen defects.³¹ Nevertheless, the reported α-V₂O₅ electrodes delivered unsatisfactory energy-storage performance due to limited kinetics and lifespan. Thus, it is incredibly challenging to exploit advanced α-V₂O₅ electrodes to achieve high stability and rate performance.

Herein, we introduce H₂O molecules between the van der Waals layers of α-V₂O₅ nanosheets (NS) to extend the interlayer gap, and this sample was denoted as W-V₂O₅ NS. The introduced H₂O molecules were able to occupy the sites of the lattice oxygen, and served as interlayer pillars to stabilize the structure. Furthermore, the ionic channel dimension was also enlarged as the a (lattice parameter) of W-V₂O₅ NS (13.12 Å) was larger than that of α-V₂O₅ NS (11.516 Å). This is favorable for the rapid diffusion of ions and the fast conduction of electrons. Therefore, the W-V₂O₅ NS electrode exhibited an improved high specific capacity (293.2 vs. 264.4 mA h g⁻¹ at 1C), rate capability (8.2% vs. 24.6% from 1 to 70C), and cycling life (96.8% vs. 74.6% over 1000 cycles). Finally, a DIBs device was successfully assembled with the graphite cathode and W-V₂O₅ NS anode. The W-V₂O₅//graphite DIEs device could be operated well in the voltage range of 1.0–3.3 V with a short discharge time (0.1–2.5 h). Attributed to the fast kinetics and stable structure in the cycle process, the W-V₂O₅//graphite DIES device delivered a large energy density (481 W h kg⁻¹) and decent power capability (3.08 kW kg⁻¹) with good durability.

Experimental

Synthesis of α-V₂O₅ and W-V₂O₅ NS

In a typical procedure, vanadium oxytriisopropoxide (VOT, 1.0 mL) was first added into isopropanol (IPA, 40 mL) with mild stirring at room temperature. Then, commercial VO(acac)₂ powders (2.65 g) was dissolved into the above mixed solution, which was kept stirring until a uniform solution was formed. The prepared reaction solution and a piece of clean carbon cloth (2 cm × 3 cm) were placed in a Teflon-lined stainless-steel autoclave (50 mL), which was heated to 180 °C and the temperature was kept constant for 10 h in an oven. The as-synthesized sample was then rinsed thoroughly with de-ionized water at room temperature. After annealing at 300 °C for 5 h in air, we eventually obtained the α-V₂O₅ NS. To gain the W-V₂O₅ NS, the α-V₂O₅ NS sample was wholly immersed in 0.8 M n-butyl lithium in hexane for 24 h in a glove box in an Ar atmosphere. Finally, the obtained sample was thoroughly rinsed with de-ionized water, and then left to dry naturally in the atmosphere.

Electrochemical characterization

A CR2032 coin cell was used to measure the electrochemical performances of all the half-cells. The free-standing α-V₂O₅ and W-V₂O₅ NS were grown on carbon cloth to directly serve as electrodes (1.3 mg cm⁻²). The graphite electrode was made from the active material, binder, and super P carbon black. First, the active material, binder, and super P carbon black were mixed uniformly in a weight ratio of 8 : 1 : 1. Second, the above mixture was evenly coated on an Al foil conductive substrate. Finally, the sample was put into a vacuum drying oven and heated to 80 °C for 12 h (1.7 mg cm⁻²). This coin half-cells system comprised a separator (Celgard 2400), counter and reference electrode (Li metal foil), and electrolyte (2 M LiPF₆ dissolved in ethyl methyl carbonate).

W-V₂O₅//graphite DIES device tests were also conducted with CR2032 coin cells. In this DIES device, the graphite electrode acted as the cathode, and the W-V₂O₅ NS electrode was the anode. The mass ratio of graphite and W-V₂O₅ NS was about 2.5 : 1. The battery assembly was completed in a glove box filled with Ar. The concentration of H₂O and O₂ in the glove box was strictly controlled below 0.1 ppm.

A CHI 760E electrochemical workstation was used to collect the electrochemical performance data, including cyclic voltammetry (CV) curves, galvanostatic charge–discharge (GCD) profiles, Mott–Schottky plots, electrochemical impedance spectroscopy (EIS) spectra, and galvanostatic intermittent titration technique (GITT) curves.

Material characterization

Transmission electron microscopy (TEM, FEI Tecnai G2 F30) and field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800) were used to analyze the microscopic topography. X-Ray diffraction (XRD, Bruker D8) was used to study the crystal structure. Raman spectroscopy, thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) were conducted on Renishaw inVia, Netzsch DSC-204 F1, and Thermo Nicolet 670 systems, respectively. The structural properties of the surrounding unpaired electrons were explored by electron paramagnetic resonance (EPR, A300-10–12 Bruker). An ASAP 2020 PLUS HD88 instrument was applied to obtain the N₂ adsorption/desorption isotherms. The elemental composition and surface electronic state were investigated by X-ray photoelectron spectroscopy (XPS), synchrotron-based X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) analysis, and ultraviolet photoemission spectroscopy (UPS), which were performed on the Photoemission Endstation (BL10B beamline).

Results and discussion

Fig. 1a illustrates the technology for extending the interlayer gaps of the α-V₂O₅ NS. First, the α-V₂O₅ NS was grown on carbon fiber cloth (Fig. S1†) through a hydrothermal method and annealing treatment. Then the sample was completely immersed in 0.8 M n-butyl lithium in hexane for 24 h, which could reduce the V species as a result of lithium-ion intercalation.^31,32 Finally, the sample was transferred to water. In this step, the sample is oxidized caused by the Li⁺ extraction, and the hydrogen ions in the water are reduced to hydrogen gas simultaneously. Through such a redox process, H₂O molecules can successfully occupy the positions of the lattice oxygen, thereby expanding the interlayer gaps in α-V₂O₅ NS. Compared to the original sample (Fig. S2a†), the W-V₂O₅ NS still retained the nanosheet array structure with a rougher surface that was caused by the mechanical strains from the expansion of the interlayer space (Fig. 1b). For more details about the microstructure, the W-V₂O₅ NS was characterized by TEM. The morphology of the W-V₂O₅ was a nanosheet with a rough surface, as noted in Fig. 1c. The surface of the nanosheets had many tiny pores, which increased the specific surface area of the W-V₂O₅ NS, as confirmed by the BET surface area measurements (Fig. S3†). The distinct diffraction rings in the selected area electron diffraction (SAED) pattern mean that the W-V₂O₅ NS is polycrystalline (insert in Fig. 1c). We could accurately identify these diffraction rings as the (200), (001), (101), and (111) planes of the orthorhombic V₂O₅ (JCPDS 41-1426). Specifically, interlayer gap belonging to the W-V₂O₅ NS was determined to be 0.656 nm (Fig. 1d), which was much larger than that of the original α-V₂O₅ NS (0.576 nm, Fig. S2c†), confirming that the incorporated H₂O can expand the interlayer gaps of α-V₂O₅ NS. Additionally, the V, O, and C elements were uniformly distributed throughout the W-V₂O₅ NS, as confirmed by the energy dispersive spectroscopy (EDS) results in Fig. 1e–g. The crystal structure evolution along with the interlayer gap expansion could be probed through the XRD analyses. All the characteristic peaks of α-V₂O₅ NS in Fig. 2a matched well with the orthorhombic V₂O₅ (JCPDS 41-1426), and its lattice parameters a, b, and c were 11.516, 3.5656, and 4.3727 Å, respectively. No other impurity peaks were detected, indicating that the α-V₂O₅ NS was of very high purity. In the case of the W-V₂O₅ NS, similar diffraction peaks were maintained but shifted to lower angles. Specifically, the (200) peak shifted from 15.3° to 14.4°, indicating that the interlayer distance was expanded from 0.576 to 0.656 nm, which was in accordance with the HRTEM results. The interlayer distance of W-V₂O₅ NS was enlarged by 0.08 nm, much larger than that caused by oxygen defects,³¹ indicating the incorporated H₂O had a better effect on expanding the interlayer gap compared to the oxygen defect. The widened interlayer distance would effectively promote Li⁺ insertion and extraction, which can be highly beneficial for boosting the lithium-ion storage performance.⁹ Moreover, the chemical bonding information of α-V₂O₅ and W-V₂O₅ NS could be found in the FTIR spectra (Fig. S4†). For the α-V₂O₅ NS, three characteristic peaks were observed, which were located at 1018 cm⁻¹ (V=O stretching vibration), 835 cm⁻¹ (V–O–V symmetric stretching), and 531 cm⁻¹ (V–O–V asymmetric stretching).^33,34 Obviously, the V–O–V bonds exhibited a blue-shift in W-V₂O₅ NS due to the stress variation and lattice distortion. Moreover, the presence of V=O at 990 cm⁻¹ for the W-V₂O₅ NS indicated the reduction state (V⁴⁺) of vanadium. Additionally, two characteristic peaks attributed to O–H stretching vibration were observed at 3450 and 1622 cm⁻¹, indicating the successful incorporation of H₂O molecules between the van der Waals interlayers. As shown in Fig. S5,† all the Raman peaks of α-V₂O₅ NS were well consistent with the layered structure of orthorhombic V₂O₅ ^35,36 (Table S1†). Clearly, after incorporating H₂O molecules, the Raman peaks became weaker and broader, and some of the peaks were shifted to lower wave numbers and even disappeared. These results confirmed that the incorporation of H₂O could disturb the crystal arrangement of the [VO₆] octahedrons and form oxygen defects in the W-V₂O₅ NS.

Fig. 1 (a) Diagram of the process for extending the interlayer gap. (b) SEM image; inset is a magnification of the SEM image, (c) TEM image; inset is the SAED pattern, (d) high-resolution TEM image (HRTEM), and (e–g) C, V, and O elements mapping for W-V₂O₅ NS.

Fig. 2 (a) XRD patterns; (b) V 2p and (c) O 1s spectra; (d) V K-edge and (e) O K-edge XANES spectra; and (f) radial distribution functions for α-V₂O₅ and W-V₂O₅ NS.

XPS was further carried out to ascertain the chemical composition and valence state in α-V₂O₅ and W-V₂O₅ NS. The XPS survey spectra in Fig. S6a† reveal that V, O, and C elements coexisted in both samples. Importantly, the Li 1s signal could not be detected for W-V₂O₅ NS (Fig. S6b†), indicating there was no Li-containing compound in the W-V₂O₅ NS, and excluding the possibility for prelithiation. The V 2p spectra of the α-V₂O₅ and W-V₂O₅ NS are displayed in Fig. 2b. Two peaks appeared at 517 and 525 eV, corresponding to the spin–orbit of V 2p_3/2 and V 2p_1/2, respectively, which could be divided into two peaks of V⁵⁺ and V⁴⁺.^35,37 After the incorporation of H₂O molecules, the intensities of the V⁴⁺ peaks increased significantly, while the intensities of the V⁵⁺ peaks decreased obviously, which was ascribed to the partial reduction from V⁵⁺ to V⁴⁺ in the process of the H₂O molecules incorporation. Meanwhile, the V⁵⁺ peak of W-V₂O₅ NS was shifted to a lower binding energy, which also proved the existence of oxygen vacancies.³¹ Based on the peak areas of W-V₂O₅ NS, the ratio between V⁴⁺ and V⁵⁺ was calculated to be 1 : 1.5, giving an average oxidation state of +4.6. The O 1s spectra of α-V₂O₅ and W-V₂O₅ NS are compared in Fig. 2c. For both samples, the peak of lattice oxygen was located at 529.9 eV, while the peak at 531.2 eV was assigned to the oxygen defect with a low oxygen coordination.³⁸ Notably, the defect oxygen peak for W-V₂O₅ NS was much stronger compared with α-V₂O₅ NS, indicating that water molecules were successfully incorporated into the W-V₂O₅ NS. Additionally, the W-V₂O₅ NS manifested a peak for surface adsorbed water located at 532.8 eV, which facilitated improved wettability and reactivity.³⁹ Moreover, the oxygen defects in W-V₂O₅ NS could be confirmed again by the EPR spectra in Fig. S7,† which displayed an intensive peak at g = 2.0 for the W-V₂O₅ NS. As demonstrated by the Mott–Schottky plots in Fig. S8,† the oxygen vacancies in the W-V₂O₅ NS could effectively enhance the electrical conductivity. Moreover, the incorporated H₂O molecules in W-V₂O₅ NS could be further verified by the TGA curves (Fig. S9†). Based on a weight loss of 0.79 wt%, the formula of W-V₂O₅ was determined as V₂O_4.92·0.08H₂O. Combined with the TGA and XPS analysis results, the molar amounts of incorporated H₂O and oxygen defects were approximately equal. Consequently, the introduced H₂O molecules could substitute for the lattice oxygen in W-V₂O₅ NS, serve as interlayer pillars to stabilize the structure, and affect the charge-shielding effect by reducing the interaction with the surrounding framework.⁴⁰

Furthermore, XANES measurements were performed to evaluate the valence state and structural environment change of V in α-V₂O₅ and W-V₂O₅ NS. A small pre-edge peak (A) was detected in the V K-edge XANES spectra, representing the electronic dipole-forbidden transition from the 1s to 3d orbital (Fig. 2d). However, when the local symmetry of the vanadium–oxygen coordination is structurally distorted, resulting in the hybridization of p–d orbitals, the above-mentioned electron transfer will be permitted in this situation. Simultaneously, a main absorption edge peak (B) also appeared in Fig. 2d, which was associated with the dipole-allowed electron transition from the 1s to 4p orbital. It is worth noting that the change in chemical coordination had an important influence on the intensity of the pre-edge peak, whose position was closely related to the oxidation state of V. In comparison with α-V₂O₅ NS, the absorption edge of W-V₂O₅ NS moved to a lower photon energy, which suggested a higher electron density around the V sites.^1,40 Additionally, the intensity of the pre-edge peak was much weaker than that of α-V₂O₅ NS. This proved that the local asymmetry around V was reduced, which was due to the interaction between the incorporated H₂O and terminal O in [VO₆].⁴¹ This result was also verified by the V L edges XANES spectra in Fig. S10.† The V L_III edges of the W-V₂O₅ NS were shifted to lower energy compared to the α-V₂O₅ NS, suggesting a higher electron density.⁴² The O K-edge XANES spectra were further obtained for the two samples and are shown in Fig. 2e. The energy region of 528–537 eV referred to the hybridization of O 2p with V 4d states, which was split into t_2g and e_g peaks. Evidently, the W-V₂O₅ NS exhibited a much stronger e_g peak compared with α-V₂O₅ NS, which indicated a more electron-rich state at the V sites caused by oxygen vacancies.⁴³ Besides, the UPS spectra of α-V₂O₅ and W-V₂O₅ NS are depicted in Fig. S11.† It is clear that the center of the d-band of W-V₂O₅ NS was closer to the Fermi level (EF). This indicated that the introduced H₂O molecules had a forceful interaction with the terminal O of [VO₆], which would have a great influence on the valence band structure.⁴⁴ The R space curves obtained from k²χ(k) by FT for EXAFS are illustrated in Fig. 2f, and provide data for further exploring the bonding and coordination. Here, V–O, O–O, and V–V bonds in [VO₆] were detected for the α-V₂O₅ and W-V₂O₅ NS, located at 1.72, 2.86, and 3.01 Å, respectively.⁴⁵ Notice that the curve characteristics of both samples were highly similar, which confirmed that the H₂O incorporation did not cause crystal phase transformation again. Additionally, the FT peaks of W-V₂O₅ NS were all weaker than those of α-V₂O₅ NS, which implied that W-V₂O₅ NS had an increased disorder (or decreased coordination number).⁴⁶ As a consequence, the water incorporation would be able to enhance the electron density localization around the V atoms effectively.

To evaluate the advantages of the expanded interlayer gap, the α-V₂O₅ and W-V₂O₅ NS were directly used as cathodes for half-cell electrochemical performance testing. When the battery is deeply discharged, an irreversible ω-phase Li_xV₂O₅ (2 < x < 3) will be formed, which would be detrimental for cycle life. Thus, in order to prevent the above situation, we selected an electrochemical working voltage between 2.0 and 4.0 V (vs. Li/Li⁺). The CV curves of α-V₂O₅ and W-V₂O₅ NS are shown in Fig. 3a, which were collected at 0.2 mV s⁻¹ for the 3rd cycle. Compared with the α-V₂O₅ NS, the CV curve of W-V₂O₅ NS exhibited a greater current density and area, suggesting that W-V₂O₅ NS had better kinetics and capacity.⁴⁷ Three pairs of redox peaks were observed in both electrodes, representing a three-step intercalation and intercalation process. During the cathodic process, the sample underwent the following transformations: α-V₂O₅ → ε-Li_0.5V₂O₅ (3.35 V), ε-Li_0.5V₂O₅ → δ-LiV₂O₅ (3.35 V), and δ-LiV₂O₅ → γ-Li₂V₂O₅ (3.35 V).⁴⁸ Conversely, the sample went through a reversible conversion in the anodic process: γ-LiV₂O₅ → δ-Li₂V₂O₅ (2.60 V), δ-Li₂V₂O₅ → ε-Li_0.5V₂O₅ (3.27 V), and ε-Li_0.5V₂O₅ → α-V₂O₅ (3.46 V).²⁶ Moreover, compared with the α-V₂O₅ NS, the first five CV curves of the W-V₂O₅ NS electrode overlapped much more (Fig. S12†), signifying the good reversibility and durability. The electrochemical reactions for both electrodes during charging and discharging can be represented as follows:²⁶

V₂O₅ + 0.5Li⁺ + 0.5e⁻ ⇌ ε-Li_0.5V₂O₅ (1)

ε-Li_0.5V₂O₅ + 0.5Li⁺ + 0.5e⁻ ⇌ δ-LiV₂O₅ (2)

δ-LiV₂O₅ + Li⁺ + e⁻ ⇌ γ-Li₂V₂O₅ (3)

Fig. 3 (a) CV curves, (b) GCD curves, (c) rate performance, (d) cycling performance, and (e) Li⁺ diffusion coefficient of the α-V₂O₅ and W-V₂O₅ NS electrodes. (f) Nyquist plots at different potentials, (g) CV curves, (h) log(i) vs. log(v) plots, and (i) capacitive contribution ratio for the W-V₂O₅ NS electrode.

Furthermore, the improved capacity for the W-V₂O₅ NS electrode could be further demonstrated with the GCD curves, which were measured at 1C (294 mA g⁻¹) and are depicted in Fig. 3b. Each charge or discharge curve had three voltage platforms, and each voltage platform corresponded to an electrochemical reaction, which agreed with the results of the CV curves. Compared with the α-V₂O₅-NS electrode, the W-V₂O₅ NS electrode not only manifested a higher discharge voltage plateau, but also a lower charge voltage plateau. Additionally, the W-V₂O₅ NS electrode released a large capacity of 293 mA h g⁻¹, which was very near to the theoretical capacity of 294 mA h g⁻¹. Such a value was better than for the α-V₂O₅ NS electrode (268 mA h g⁻¹) and a recently reported cathode material (Table S2†).^31,49–52Fig. 3c shows the high-rate capabilities for α-V₂O₅ and W-V₂O₅ NS electrodes, which are important for developing high-performance LIBs, while the representative charge and discharge curves are displayed in Fig. S13.† When the current density was changed from 1C to 70C, a capacity retention of up to 48.2% was achieved by the W-V₂O₅ NS electrode. This value was superior to the α-V₂O₅ NS electrode (24.6% capacity retention) and the-state-of-art V₂O₅-based electrode presented in Table S2.† In addition, the W-V₂O₅ NS electrode displayed better cycle durability than the α-V₂O₅ NS electrode (Fig. 3d), whereby the W-V₂O₅ NS electrode could still maintain a large capacity of up to 253.7 mA h g⁻¹ (96.8% capacity retention) over 1000 cycles at 5C. By comparison, the α-V₂O₅ NS electrode showed an inferior specific capacity of 163.3 mA h g⁻¹ (74.6% capacity retention) over 1000 cycles under the same test conditions. Furthermore, the W-V₂O₅ NS electrode was further cycled at 40C to study the advanced long-term durability (Fig. S14†). A capacity retention of up to 85.7% was achieved by the W-V₂O₅ NS electrode after 2000 cycles, and such a value was better than the α-V₂O₅ NS electrode (57.1% capacity retention) and other V₂O₅-based electrodes (Table S2†).

The influence of the introduced H₂O molecules on the reaction kinetics was further assessed by GITT and EIS. The lithium-ion diffusion coefficient (D_Li⁺) of the α-V₂O₅ and W-V₂O₅ NS electrode were obtained through GITT (Fig. 3e), and their GITT charge–discharge curves are displayed in Fig. S15.† The D_Li⁺ value in the W-V₂O₅ NS electrode was 3.4 × 10⁻¹¹ cm² s⁻¹, greatly surpassing the α-V₂O₅ NS electrode (1.1 × 10⁻¹² cm² s⁻¹). The enlarged ion diffusion channel is one important reason for the greatly improved D_Li⁺ in the W-V₂O₅ NS electrode. Another important reason is the shielding effect of the introduced H₂O molecules, which can eliminate the electrostatic interaction between the V₂O₅ lattice and lithium ions.^53,54 At the same time, EIS was performed for α-V₂O₅ and W-V₂O₅ NS electrodes at different voltages in the cathodic process (Fig. 3f and S16†). As the potential increased from 2.0 to 4.0 V vs. Li/Li⁺, the Ohmic resistance (R_s) was very stable, while the charge-transfer resistance (R_ct) increased first and then decreased (Fig. S17†). The W-V₂O₅ NS electrode revealed an obviously smaller R_s and R_ct compared with the α-V₂O₅ NS electrode, suggesting a faster electron-transfer speed. Additionally, kinetics analysis was conducted to further explore the capacitive behavior of α-V₂O₅ and W-V₂O₅ NS electrodes. In the scan rate range of 0.1–2.0 mV s⁻¹, the W-V₂O₅ NS electrode could maintain the shape of the CV curve without significant changes (Fig. 3g), revealing a quick responsiveness to high-speed scanning for LIBs. The formula i = av^b can be used to assess the capacitive effect,⁵⁵ which considers the current density (i), scan rate (v), and two parameters (a, b), whereby when b is equal to 0.5 and 1.0, the capacitive effect is a diffusion-controlled process and surface-controlled process, respectively. The calculated b values from peak 1 to peak 6 were 0.76, 0.86, 0.83, 0.79, 0.84, and 0.82, respectively (Fig. 3h). These values were all between 0.5 and 1.0, indicating that the capacitive effect of the W-V₂O₅ NS electrode was a mixture of diffusion-controlled and surface-controlled processes. Besides, the capacitance contribution could be further quantitatively differentiated into capacitive-controlled effects and diffusion-controlled effects by applying the formula i (V) = k₁v + k₂v^1/2.⁵⁶ As the scan rate ranged from 0.1 to 2.0 mV s⁻¹, the capacitive contributions in the W-V₂O₅ NS electrode were 50.6%, 54.2%, 61.0%, 67.8%, 73.1%, 76.7%, and 83.2% (Fig. 3i). This shows that the diffusion-controlled process played a dominant role in the capacitance behavior. It can be seen from Fig. S18† that the capacitive contribution in the W-V₂O₅ NS electrode was larger than in the α-V₂O₅ NS electrode, revealing enhanced rapid electron and ion migration, which were beneficial for delivering excellent rate performance.

Subsequently, a W-V₂O₅//graphite DIES device was fabricated by applying the W-V₂O₅ NS anode and graphite cathode (Fig. 4a). In the process of charging, the anion PF₆⁻ migrated from the electrolyte to the cathode, and intercalated with the graphite cathode to generate the graphite intercalation compound C_x(PF₆). Simultaneously, the cation Li⁺ migrated from the electrolyte to the anode, and intercalated with the V₂O₅ anode to form the compound Li_xV₂O₅. Conversely, the PF₆⁻ and Li⁺ were deintercalated from the graphite and V₂O₅, respectively, and returned to the electrolyte during discharge. The electrochemical performances of the graphite cathode are displayed in Fig. S19,† which manifested its large specific capacity (124 mA h g⁻¹), high discharge potential (4.6 V), favorable rate capability (111 mA h g⁻¹ at 1 A g⁻¹), and superior lifespan (91.3% capacity retention over 1500 cycle). Therefore, the designed W-V₂O₅//graphite DIES is expected to have potential as an energy-storage device with high performance.

Fig. 4 Electrochemical performances of W-V₂O₅//graphite DIES device. (a) Schematic illustration, (b) CV curves, (c) charge and discharge curves, (d) rate capability compared with recent works,^18,57–66 and (e) cycling performance; inset is the selected charge and discharge curves.

The CV curves were obtained from the 2nd, 4th, 6th, and 8th cycles of the W-V₂O₅//graphite DIES device, and the scan rate was set at 0.5 mV s⁻¹ (Fig. 4b). These CV curves revealed two anode and two cathode peaks, which signified a multistep anion and cation intercalation/deintercalation process. A high coincidence of these CV curves could be identified, indicating a good reversibility and stability during anion and cation intercalation/deintercalation. As expected, the elaborated W-V₂O₅//graphite DIES device delivered high capacities of 248, 236, 224, 212, 200, 188, 176, 164, and 152 mA h g⁻¹ at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.1, and 1.5 A g⁻¹, respectively (Fig. 4c). The W-V₂O₅//graphite DIES device demonstrated a high specific capacity and superior rate capability (Fig. 4d), which substantially outweighed most other reported DIES devices at comparable current densities, such as EG//P-HCNs (210 mA h g⁻¹ at 0.1 A g⁻¹),⁵⁷ coronene//NTO@G (161 mA h g⁻¹ at 0.05 A g⁻¹),⁵⁸ graphite//PTCDI-G (121 mA h g⁻¹ at 0.25 A g⁻¹),⁵⁹ graphite//Al (105 mA h g⁻¹ at 0.05 A g⁻¹),⁶⁰ graphite//graphite (103 mA h g⁻¹ at 0.1 A g⁻¹),⁶¹ P-PANI//N-PDHC (96 mA h g⁻¹ at 0.1 A g⁻¹),⁶² graphite//Al (90 mA h g⁻¹ at 0.2 A g⁻¹),⁶³ pK2TP//EG (69 mA h g⁻¹ at 0.2 A g⁻¹),⁶⁴ graphite//Sn (67 mA h g⁻¹ at 0.05 A g⁻¹),¹⁸ MoS₂//C-G (65 mA h g⁻¹ at 0.2 A g⁻¹),⁶⁵ and graphite//LTO (40 mA h g⁻¹ at 0.01 A g⁻¹).⁶⁶ Furthermore, when the current density varied from 0.1 to 1.5 A g⁻¹, the capacity retention of the W-V₂O₅//graphite device was as high as 70.4%, suggesting good charge-transfer kinetics and high reversibility. Moreover, the W-V₂O₅//graphite DIES device exhibited excellent cycling durability (84% retention) and released a capacity of up to 143 mA h g⁻¹ over 1500 cycles at 1.0 A g⁻¹ (Fig. 4e), which surpasses most reported DIES devices, for instance, EG//P-HCNs (121 mA h g⁻¹ at 0.5 A g⁻¹ over 1500 cycles),⁵⁷ graphite//PTCDI-G (116.3 mA h g⁻¹ at 0.25 A g⁻¹ over 300 cycles),⁵⁹ graphite//Al (91.52 mA h g⁻¹ at 0.2 A g⁻¹ over 200 cycles),⁶⁰ graphite//Al (86.93 mA h g⁻¹ at 0.2 A g⁻¹ over 500 cycles),⁶³ P-PANI//N-PDHC (75 mA h g⁻¹ at 0.1 A g⁻¹ over 100 cycles),⁶² and pK2TP//EG (63 mA h g⁻¹ at 0.5 A g⁻¹ over 200 cycles).⁶⁴ As depicted in the inset of Fig. 4, the GCD curves of the 1st, 380th, 940th, and 1500th cycles displayed little capacity attenuation, revealing a good durability property for the W-V₂O₅//graphite DIES device again. Additionally, the W-V₂O₅//graphite DIES device possessed an admirable coulombic efficiency, which behaved very smoothly and infinitely approached 100% throughout the whole electrochemical process.

The combination of fast kinetics with superb capacity led to the W-V₂O₅//graphite DIES device obtaining a peak energy density of 481.1 W h kg⁻¹ at 0.19 kW kg⁻¹, as shown in Fig. 5 (based on the total mass of active materials). Such a value surpasses the recently reported DIES devices, such as PANI//PDI-EDA (29.5 W h kg⁻¹),⁶⁷ LMO//N-NS/nS (30 W h kg⁻¹),⁶⁸ coronene//NTO@G (78 W h kg⁻¹),⁵⁸ graphite//Al (113 W h kg⁻¹),⁶⁰ graphite//LTO (150 W h kg⁻¹),⁶⁶ graphite//Al (178 W h kg⁻¹),⁶³ EG//P-HCNs (180 W h kg⁻¹),⁵⁷ graphite//graphite (190 W h kg⁻¹),⁶¹ MCMB//Al (210 W h kg⁻¹),⁶⁹ graphite//PTCDI-G (230 W h kg⁻¹),⁵⁹m-PTPA//Zn (235 W h kg⁻¹),⁷⁰ and P-PANI//N-PDHC (295 W h kg⁻¹).⁶² Beyond that, the W-V₂O₅//graphite DIES device also provided a top power density of up to 3.08 kW kg⁻¹, which is comparable to that of supercapacitors.^71–73 Additionally, we also manufactured a lithium-ion full-cell with a commercial Li₃VO₄ positive electrode and W-V₂O₅ negative electrode for comparison (Fig. S20†). Obviously, the W-V₂O₅//graphite DIES device was superior to the W-V₂O₅//Li₃VO₄ LIB device in terms of both energy density and power density. Encouragingly, the W-V₂O₅//graphite DIES device could be employed to power light-emitting diode (LED) indicators (inset in Fig. 5), which confirmed the potential application of the fabricated W-V₂O₅//graphite DIES in portable electronics devices.

Fig. 5 Ragone plots of the W-V₂O₅//graphite DIES device compared with other recently reported DIES devices.^{57–63,66–73} Inset is the image of an LED indicator lit up by the W-V₂O₅//graphite DIES device.

Conclusions

To sum up, we reported a simple and effective H₂O-incorporation approach to design a V₂O₅ anode with an extended interlayer gap. This strategy could strongly stimulate the lithium-storage performance of the W-V₂O₅ NS electrode, greatly boosting its rate capability and cycle life. The introduced H₂O molecules served as interlayer pillars to expand the interlayer gaps and stabilize the structure, which could offer large space and abundant channels for ion diffusion and electron transport, thus promoting the rapid electrochemical kinetics. Moreover, the introduced H₂O molecules could eliminate the electrostatic interaction between the V₂O₅ lattice and lithium ions. This could effectively buffer the volume variation of the W-V₂O₅ NS electrode in the charge–discharge cycle process, thereby validly enhancing its cycling durability. Additionally, because the lattice oxygen in W-V₂O₅ NS was replaced by the equivalent mole of H₂O molecules, the enhanced rate performance and durability were not a trade-off for the capacity. More importantly, a DIES device was assembled by coupling the anion-intercalation graphite cathode and cation-intercalation W-V₂O₅ NS anode, which could combine fast kinetics with intercalation-type charge storage. Delightfully, an admirable energy density and power density were achieved by the W-V₂O₅//graphite DIES device, which were as high as 481.1 W h kg⁻¹ and 3.08 kW kg⁻¹, respectively. This work can provide a reference and ideas about the interlayer engineering strategy for designing fast-kinetics and long-life layered electrode materials in DIBs and other energy-storage systems.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We acknowledge the Basic and Applied Basic Research Project of Guangdong Province (2019A1515110827), Science and Technology Planning Project of Guangzhou (202102080169), Education Commission of Guangdong Province (2022ZDZX3048), Advanced Functional Materials Scientific Research and Technical Service Team (X20190197), Undergraduate research projects of Guangdong Industry Polytechnic College (XSKYL202208), and Exquisite Education Project of Guangdong Industry Polytechnic College (JZYR202120).

References

1. H. Z. Zhang, W. X. Wu, Q. Y. Liu, F. Yang, X. Shi, X. Q. Liu, M. H. Yu and X. H. Lu, Interlayer Engineering of α–MoO₃ Modulates Selective Hydronium Intercalation in Neutral Aqueous Electrolyte, Angew. Chem., Int. Ed., 2021, 60, 896–903.
2. M. Yu, R. Dong and X. Feng, Two-dimensional carbon-rich conjugated frameworks for electrochemical energy applications, J. Am. Chem. Soc., 2020, 142, 12903–12915.
3. F. Wang, O. Borodin, T. Gao, X. L. Fan, W. Sun, F. D. Han, A. Faraone, J. A. Dura, K. Xu and C. S. Wang, Highly reversible zinc metal anode for aqueous batteries, Nat. Mater., 2018, 17, 543–549.
4. J. X. Zheng, Q. Zhao, T. Tang, J. F. Yin, C. D. Quilty, G. D. Renderos, X. T. Liu, Y. Deng, L. Wang, D. C. Bock, C. Jaye, D. H. Zhang, E. S. Takeuchi, K. J. Takeuchi, A. C. Marschilok and L. A. Archer, Reversible epitaxial electrodeposition of metals in battery anodes, Science, 2019, 366, 645–648.
5. C. F. Liu, Z. Neale, J. Q. Zheng, X. X. Jia, J. J. Huang, M. Y. Yan, M. Tian, M. S. Wang, J. H. Yang and G. Z. Cao, Expanded hydrated vanadate for high-performance aqueous zinc-ion batteries, Energy Environ. Sci., 2019, 12, 2273–2285.
6. L. T. Ma, S. M. Chen, C. B. Long, X. L. Li, Y. W. Zhao, Z. X. Liu, Z. D. Huang, B. B. Dong, J. A. Zapien and C. Y. Zhi, Achieving high-voltage and high–capacity aqueous rechargeable zinc ion battery by incorporating two–species redox reaction, Adv. Energy Mater., 2019, 9, 1902446.
7. F. Wan and Z. Q. Niu, Design strategies for vanadium–based aqueous zinc-ion batteries, Angew. Chem., 2019, 131, 16508–16517.
8. L. Li, Z. Hu, Y. Lu, C. C. Wang, Q. Zhang, S. Zhao, J. Peng, K. Zhang, S. L. Chou and J. Chen, Angew. Chem., Int. Ed., 2021, 60, 13050–13056.
9. M. H. Yu, H. Shao, G. Wang, F. Yang, C. L. Liang, P. Rozier, C.-Z. Wang, X. H. Lu, P. Simon and X. L. Feng, Interlayer gap widened α-phase molybdenum trioxide as high-rate anodes for dual-ion-intercalation energy storage devices, Nat. Commun., 2020, 11, 1–9.
10. Y. M. Sui, C. F. Liu, R. C. Masse, Z. G. Neale, M. Atif, M. AlSalhi and G. Z. Cao, Dual-ion batteries: The emerging alternative rechargeable batteries, Energy Storage Mater., 2020, 25, 1–32.
11. X. Li, X. W. Ou and Y. B. Tang, 6.0 V high-voltage and concentrated electrolyte toward high energy density K-based dual-graphite battery, Adv. Energy Mater., 2020, 10, 2002567.
12. K. M. Song, J. F. Liu, H. L. Dai, Y. Zhao, S. H. Sun, J. Y. Zhang, C. D. Qin, P. F. Yan, F. Q. Guo, C. Y. Wang, Y. L. Cao, S. F. Li and W. H. Chen, Atomically dispersed Ni induced by ultrahigh N-doped carbon enables stable sodium storage, Chem, 2021, 7, 2684–2694.
13. L. Sui, X. Y. Shi, T. Deng, H. Yang, H. Y. Liu, H. Chen, W. Zhang and W. T. Zheng, Integrated Co₃O₄/carbon fiber paper for high-performance anode of dual-ion battery, J. Energy Chem., 2019, 37, 7–12.
14. S. Wang, J. G. Tu, J. S. Xiao, J. Zhu and S. Q. Jiao, 3D skeleton nanostructured Ni₃S₂/Ni foam@RGO composite anode for high-performance dual-ion battery, J. Energy Chem., 2019, 28, 144–150.
15. L. N. Wu, S. Y. Shen, Y. H. Hong, C. H. Shen, F. M. Han, F. Fu, X. D. Zhou, L. Huang, J. T. Li and S. G. Sun, Novel MnO–Graphite Dual-Ion Battery and New Insights into Its Reaction Mechanism during Initial Cycle by Operando Techniques, ACS Appl. Mater. Interfaces, 2019, 11, 12570–12577.
16. Q. L. Xu, R. Ding, W. Shi, D. F. Ying, Y. F. Huang, T. Yan, P. Gao, X. J. Sun and E. H. Liu, Perovskite KNi_0.1Co_0.9F₃ as a pseudocapacitive conversion anode for high-performance nonaqueous Li-ion capacitors and dual-ion batteries, J. Mater. Chem. A, 2019, 7, 8315–8326.
17. X. F. Tong, F. Zhang, B. F. Ji, M. H. Sheng and Y. B. Tang, Carbon-coated porous aluminum foil anode for high-rate, long-term cycling stability, and high energy density dual-ion batteries, Adv. Mater., 2016, 28, 9979–9985.
18. B. F. Ji, F. Zhang, X. H. Song and Y. B. Tang, A novel potassium-ion-based dual-ion battery, Adv. Mater., 2017, 29, 1700519.
19. S. Bellani, F. X. Wang, G. Longoni, L. Najafi, R. Oropesa-Nunez, A. E. Del Rio Castillo, M. Prato, X. D. Zhuang, V. Pellegrini, X. L. Feng and F. Bonaccorso, WS₂–graphite dual-ion batteries, Nano Lett., 2018, 18, 7155–7164.
20. C. Y. Cui, Z. X. Wei, J. T. Xu, Y. Q. Zhang, S. H. Liu, H. K. Liu, M. L. Mao, S. Y. Wang, J. M. Ma and S. Dou, Three-dimensional carbon frameworks enabling MoS₂ as anode for dual ion batteries with superior sodium storage properties, Energy Storage Mater., 2018, 15, 22–30.
21. R. Enjalbert and J. Galy, A refinement of the structure of V₂O₅, Acta Crystallogr., 1986, 42, 1467–1469.
22. X. Zhao, L. Mao, Q. H. Cheng, F. F. Liao, G. Y. Yang, X. H. Lu and L. Y. Chen, Interlayer engineering of preintercalated layered oxides as cathode for emerging multivalent metal-ion batteries: zinc and beyond, Energy Storage Mater., 2021, 38, 397–437.
23. H. B. Geng, M. Cheng, B. Wang, Y. Yang, Y. F. Zhang and C. C. Li, Electronic structure regulation of layered vanadium oxide via interlayer doping strategy toward superior high-rate and low-temperature zinc-ion batteries, Adv. Funct. Mater., 2020, 30, 1907684.
24. Y. J. Zhu, M. Yang, Q. Y. Huang, D. R. Wang, R. B. Yu, J. Y. Wang, Z. J. Zheng and D. Wang, V₂O₅ textile cathodes with high capacity and stability for flexible lithium-ion batteries, Adv. Mater., 2020, 32, 1906205.
25. C. R. Wang, L. Zhang, M. Al-Mamun, Y. H. Dou, P. Liu, D. W. Su, G. X. Wang, S. Q. Zhang, D. Wang and H. J. Zhao, A Hollow-Shell Structured V₂O₅ Electrode-Based Symmetric Full Li-Ion Battery with Highest Capacity, Adv. Energy Mater., 2019, 9, 1900909.
26. D. L. Chao, X. H. Xia, J. L. Liu, Z. X. Fan, C. F. Ng, J. Y. Lin, H. Zhang, Z. X. Shen and H. J. Fan, A V₂O₅/conductive-polymer core/shell nanobelt array on three-dimensional graphite foam: a high-rate, ultrastable, and freestanding cathode for lithium-ion batteries, Adv. Mater., 2014, 26, 5794–5800.
27. J. H. Lee, J. M. Kim, J. H. Kim, Y. R. Jang, J. A. Kim, S. H. Yeon and S. Y. Lee, Toward Ultrahigh-Capacity V₂O₅ Lithium-Ion Battery Cathodes via One-Pot Synthetic Route from Precursors to Electrode Sheets, Adv. Mater. Interfaces, 2016, 3, 1600173.
28. Q. Liu, Z. F. Li, Y. D. Liu, H. Y. Zhang, Y. Ren, C. J. Sun, W. Q. Lu, Y. Zhou, L. Stanciu, E. A. Stach and J. Xie, Graphene-modified nanostructured vanadium pentoxide hybrids with extraordinary electrochemical performance for Li-ion batteries, Nat. Commun., 2015, 6, 1–10.
29. P. G. Bruce, B. Scrosati and J. M. Tarascon, Nanomaterials for rechargeable lithium batteries, Angew. Chem., Int. Ed., 2008, 47, 2930–2946.
30. B. Ju, H. J. Song, H. Yoon and D. W. Kim, Amorphous hydrated vanadium oxide with enlarged interlayer spacing for aqueous zinc-ion batteries, Chem. Eng. J., 2021, 420, 130528.
31. X. Peng, X. M. Zhang, L. Wang, L. S. Hu, S. H. S. Cheng, C. Huang, B. Gao, F. Ma, K. F. Huo and P. K. Chu, Hydrogenated V₂O₅ nanosheets for superior lithium storage properties, Adv. Funct. Mater., 2016, 26, 784–791.
32. J. H. Zhang, H. X. Zhang, M. M. Liu, Q. C. Xu, H. Jiang and C. Z. Li, Cobalt-stabilized oxygen vacancy of V₂O₅ nanosheet arrays with delocalized valence electron for alkaline water splitting, Chem. Eng. Sci., 2020, 227, 115915.
33. D. Chen, X. H. Rui, Q. Zhang, H. B. Geng, L. Y. Gan, W. Zhang, C. C. Li, S. M. Huang and Y. Yu, Persistent zinc-ion storage in mass-produced V₂O₅ architectures, Nano Energy, 2019, 60, 171–178.
34. Z. H. Wang, P. Liang, R. G. Zhang, Z. M. Liu, W. Y. Li, Z. G. Pan, H. Yang, X. D. Shen and J. Wang, Oxygen-defective V₂O₅ nanosheets boosting 3D diffusion and reversible storage of zinc ion for aqueous zinc-ion batteries, Appl. Surf. Sci., 2021, 562, 150196.
35. K. Chen, G. D. Zhang, L. P. Xiao, P. W. Li, W. L. Li, Q. C. Xu and J. Xu, Polyaniline Encapsulated Amorphous V₂O₅ Nanowire-Modified Multi-Functional Separators for Lithium-Sulfur Batteries, Small Methods, 2021, 5, 2001056.
36. J. Liu, H. Xia, D. F. Xue and L. Lu, Double-shelled nanocapsules of V₂O₅-based composites as high-performance anode and cathode materials for Li ion batteries, J. Am. Chem. Soc., 2009, 131, 12086–12087.
37. C. Z. Liu, J. H. Yao, Z. G. Zou, Y. W. Li and G. Z. Cao, Boosting the cycling stability of hydrated vanadium pentoxide by Y³⁺ pillaring for sodium-ion batteries, Mater. Today Energy, 2019, 11, 218–227.
38. H. D. Chen, J. J. Huang, S. H. Tian, L. Liu, T. F. Qin, L. Song, Y. P. Liu, Y. N. Zhang, X. G. Wu, S. L. Lei and S. L. Peng, Interlayer Modification of Pseudocapacitive Vanadium Oxide and Zn(H₂O)_n²⁺ Migration Regulation for Ultrahigh Rate and Durable Aqueous Zinc-Ion Batteries, Adv. Sci., 2021, 8, 2004924.
39. W. D. Qiu, Y. L. Tian, Z. C. Lin, S. T. Lin, Z. Q. Geng, K. T. Huang, A. H. Lei, F. C. Huang, H. J. Feng, F. Z. Ding and X. H. Lu, High rate and ultralong life flexible all-solid-state zinc ion battery based on electron density modulated NiCo₂O₄ nanosheets, J. Energy Chem., 2022, 70, 283–291.
40. N. N. Liu, X. Wu, L. S. Fan, S. Gong, Z. K. Guo, A. S. Chen, C. Y. Zhao, Y. C. Mao, N. Q. Zhang and K. N. Sun, Intercalation Pseudocapacitive Zn²⁺ Storage with Hydrated Vanadium Dioxide toward Ultrahigh Rate Performance, Adv. Mater., 2020, 32, 1908420.
41. E. B. Deeva, A. Kurlov, P. M. Abdala, D. Lebedev, S. M. Kim, C. P. Gordon, A. Tsoukalou, A. Fedorov and C. R. Müller, In situ XANES/XRD study of the structural stability of two-dimensional molybdenum carbide Mo₂CT_x: Implications for the catalytic activity in the water–gas shift reaction, Chem. Mater., 2019, 31, 4505–4513.
42. S. J. Deng, Y. Zhang, D. Xie, L. Yang, G. Z. Wang, X. S. Zheng, J. F. Zhu, X. L. Wang, Y. Yu, G. X. Pan, X. H. Xia and J. P. Tu, Oxygen vacancy modulated Ti₂Nb₁₀O_29−x embedded onto porous bacterial cellulose carbon for highly efficient lithium ion storage, Nano Energy, 2019, 58, 355–364.
43. Y. Gogotsi and P. Simon, True performance metrics in electrochemical energy storage, Science, 2011, 334, 917–918.
44. Y. Nakayama, K. Morii, Y. Suzuki, H. Machida, S. Kera, N. Ueno, H. Kitagawa, Y. Noguchi and H. Ishii, Origins of improved hole-injection efficiency by the deposition of MoO₃ on the polymeric semiconductor poly (dioctylfluorene-alt-benzothiadiazole), Adv. Funct. Mater., 2009, 19, 3746–3752.
45. H. Morikawa, M. Miyake, S. I. Iwai, K. Furukawa and A. Revcolevschi, Structural analysis of molten V₂O₅, J. Chem. Soc., Faraday Trans. 1, 1981, 77, 361–367.
46. Y. X. Zeng, Z. Z. Lai, Y. Han, H. Z. Zhang, S. L. Xie and X. H. Lu, Oxygen-vacancy and surface modulation of ultrathin nickel cobaltite nanosheets as a high-energy cathode for advanced Zn-ion batteries, Adv. Mater., 2018, 30, 1802396.
47. L. Q. Mai, Q. Y. An, Q. L. Wei, J. Y. Fei, P. F. Zhang, X. Xu, Y. L. Zhao, M. Y. Yan, W. Wen and L. Xu, Nanoflakes-Assembled Three-Dimensional Hollow-Porous V₂O₅ as Lithium Storage Cathodes with High-Rate Capacity, Small, 2014, 10, 3032.
48. A. Q. Pan, H. B. Wu, L. Yu and X. W. Lou, Emplate-free synthesis of VO₂ hollow microspheres with various interiors and their conversion into V₂O₅ for lithium-ion batteries, Angew. Chem., 2013, 125, 2282–2286.
49. S. F. Xu, H. C. Dai, S. L. Zhu, Y. C. Wu, M. X. Sun, Y. Chen, K. Fan, C. Y. Zhang, C. L. Wang and W. P. Hu, A branched dihydrophenazine-based polymer as a cathode material to achieve dual-ion batteries with high energy and power density, eScience, 2021, 1, 60–68.
50. J. M. Son, S. Oh, S. H. Bae, S. Nam and I. K. Oh, A Pair of NiCo₂O₄ and V₂O₅ Nanowires Directly Grown on Carbon Fabric for Highly Bendable Lithium-Ion Batteries, Adv. Energy Mater., 2019, 9, 1900477.
51. X. B. Yu, G. Y. Zhao, C. Liu, C. L. Wu, H. H. Huang, J. J. He and N. Q. Zhang, A MoS₂ and Graphene Alternately Stacking van der Waals Heterostructure for Li⁺/Mg²⁺ Co-Intercalation, Adv. Funct. Mater., 2021, 31, 2103214.
52. Y. L. Shan, L. Xu, Y. J. Hu, H. Jiang and C. Z. Li, Internal-diffusion controlled synthesis of V₂O₅ hollow microspheres for superior lithium-ion full batteries, Chem. Eng. Sci., 2019, 200, 38–45.
53. H. J. Lee, J. Shin and J. W. Choi, Intercalated water and organic molecules for electrode materials of rechargeable batteries, Adv. Mater., 2018, 30, 1705851.
54. D. Kundu, B. D. Adams, V. Duffort, S. H. Vajargah and L. F. Nazar, A high-capacity and long-life aqueous rechargeable zinc battery using a metal oxide intercalation cathode, Nat. Energy, 2016, 1, 1–8.
55. V. Augustyn, J. Come, M. A. Lowe, J. W. Kim, P.-L. Taberna, S. H. Tolbert, H. D. Abruña, P. Simon and B. Dunn, High-rate electrochemical energy storage through Li⁺ intercalation pseudocapacitance, Nat. Mater., 2013, 12, 518–522.
56. J. L. Liu, J. Wang, C. H. Xu, H. Jiang, C. Z. Li, L. L. Zhang, J. Y. Lin and Z. X. Shen, Advanced energy storage devices: basic principles, analytical methods, and rational materials design, Adv. Sci., 2018, 5, 1700322.
57. X. Y. Wang, S. F. Wang, K. X. Shen, S. G. He, X. H. Hou and F. M. Chen, Phosphorus-doped porous hollow carbon nanorods for high-performance sodium-based dual-ion batteries, J. Mater. Chem. A, 2020, 8, 4007–4016.
58. S. Y. Dong, Z. F. Li, I. A. Rodríguez-Pérez, H. Jiang, J. Lu, X. G. Zhang and X. L. Ji, A novel coronene//Na₂Ti₃O₇ dual-ion battery, Nano Energy, 2017, 40, 233–239.
59. Z. D. Huang, Y. Hou, T. R. Wang, Y. W. Zhao, G. J. Liang, X. L. Li, Y. Guo, Q. Yang, Z. Chen, Q. Li, L. T. Ma, J. Fan and C. Y. Zhi, Manipulating anion intercalation enables a high-voltage aqueous dual ion battery, Nat. Commun., 2021, 12, 1–11.
60. X. L. Zhang, Y. B. Tang, F. Zhang and C. S. Lee, A novel aluminium-graphite dual-ion battery, Adv. Energy Mater., 2016, 6, 1502588.
61. Y. Wang, Y. J. Zhang, S. Wang, S. Y. Dong, C. Q. Dang, W. C. Hu and D. Y. Yu, Ultrafast Charging and Stable Cycling Dual-Ion Batteries Enabled via an Artificial Cathode-Electrolyte Interface, Adv. Funct. Mater., 2021, 31, 2102360.
62. Z. Q. Sun, K. J. Zhu, P. Liu, H. X. Li and L. F. Jiao, Optimized Cathode for High-Energy Sodium-Ion Based Dual-Ion Full Battery with Fast Kinetics, Adv. Funct. Mater., 2021, 31, 2107830.
63. L. Xiang, X. W. Ou, X. Y. Wang, Z. M. Zhou, X. Li and Y. B. Tang, Highly concentrated electrolyte towards enhanced energy density and cycling life of dual-ion battery, Angew. Chem., Int. Ed., 2020, 59, 17924–17930.
64. A. Yu, Q. G. Pan, M. Zhang, D. H. Xie and Y. B. Tang, Fast rate and long life potassium-ion based dual-ion battery through 3D porous organic negative electrode, Adv. Funct. Mater., 2020, 30, 2001440.
65. H. L. Zhu, F. Zhang, J. R. Li and Y. B. Tang, Penne-like MoS₂/carbon nanocomposite as anode for sodium-ion-based dual-ion battery, Small, 2018, 14, 1703951.
66. X. Y. Shi, S. S. Yu, T. Deng, W. Zhang and W. Zheng, Unlock the potential of Li₄Ti₅O₁₂ for high-voltage/long-cycling-life and high-safety batteries: Dual-ion architecture superior to lithium-ion storage, J. Energy Chem., 2020, 44, 13–18.
67. Y. P. Zhu, J. Yin, A. H. Emwas, O. F. Mohammed and H. N. Alshareef, An Aqueous Mg²⁺-Based Dual-Ion Battery with High Power Density, Adv. Funct. Mater., 2021, 31, 2107523.
68. J. M. Park, M. Jana, P. Nakhanivej, B.-K. Kim and H. S. Park, Facile multivalent redox chemistries in water-in-bisalt hydrogel electrolytes for hybrid energy storage full cells, ACS Energy Lett., 2020, 5, 1054–1061.
69. F. Zhang, B. F. Ji, X. F. Tong, M. H. Sheng, X. L. Zhang, C. S. Lee and Y. B. Tang, A dual-ion battery constructed with aluminum foil anode and mesocarbon microbead cathode via an alloying/intercalation process in an ionic liquid electrolyte, Adv. Mater. Interfaces, 2016, 3, 1600605.
70. H. Z. Zhang, L. F. Zhong, J. H. Xie, F. Yang, X. Q. Liu and X. H. Lu, A COF-like N-rich conjugated microporous polytriphenylamine cathode with pseudocapacitive anion storage behavior for high-energy aqueous zinc dual-ion batteries, Adv. Mater., 2021, 33, 2101857.
71. S. M. Chen, L. T. Ma, K. Zhang, M. Kamruzzaman, C. Y. Zhi and J. A. Zapien, A flexible solid-state zinc ion hybrid supercapacitor based on co-polymer derived hollow carbon spheres, J. Mater. Chem. A, 2019, 7, 7784–7790.
72. Y. Z. Jiao, H. T. Zhang, H. L. Zhang, A. Liu, Y. X. Liu and S. J. Zhang, Highly bonded T-Nb₂O₅/rGO nanohybrids for 4 V quasi-solid state asymmetric supercapacitors with improved electrochemical performance, Nano Res., 2018, 11, 4673–4685.
73. C. Zhou, Y. W. Zhang, Y. Y. Li and J. P. Liu, Construction of high-capacitance 3D CoO@polypyrrole nanowire array electrode for aqueous asymmetric supercapacitor, Nano Lett., 2013, 13, 2078–2085.

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Footnotes

† Electronic supplementary information (ESI) available: SEM image, TEM image, N₂ adsorption–desorption isotherm, FTIR spectra, Raman spectra, Raman peak assignment, survey and Li 1s XPS spectra, EPR spectra, Mott–Schottky plots, TGA curves, V L edges XANES spectra, UPS spectra, CV curves, comparison of electrochemical performance, charge and discharge profiles, cycling performance, GITT charge discharge curves, Nyquist plots, R_s and (b) R_ct as a function of potential, CV curves, log(i) vs. log(v) plots, capacitive contribution for α-V₂O₅ and W-V₂O₅ sample. Electrochemical performance of the graphite cathode and W-V₂O₅//Li₃VO₄ device. See DOI: https://doi.org/10.1039/d2qi02080g

‡ These authors contributed equally to this work.

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