Engineering a High-Energy-Density and Long Lifespan Aqueous Zinc

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Energy, Environmental, and Catalysis Applications

Engineering a High Energy-density and Long Lifespan Aqueous Zinc Battery via Ammonium Vanadium Bronze Duan Bin, Yao Liu, Beibei Yang, Jianhang Huang, Xiaoli Dong, Xiao Zhang, Yong-Gang Wang, and Yong-Yao Xia ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b03159 • Publication Date (Web): 15 May 2019 Downloaded from http://pubs.acs.org on May 18, 2019

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ACS Applied Materials & Interfaces

Engineering a High Energy-density and Long Lifespan Aqueous Zinc Battery via Ammonium Vanadium Bronze Duan Bina, Yao Liua, Beibei Yanga, Jianhang Huanga, Xiaoli Donga, Xiao Zhangc, Yonggang Wanga* and Yongyao Xiaa,b* aDepartment

of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative

Materials, Institute of New Energy, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Fudan University, Shanghai 200433, China. bKey

Laboratory of the Ministry of Education for Advanced Catalysis Materials, Department of Chemistry,

Zhejiang Normal University Jinhua 321004. cState

Key Laboratory Base of Eco-chemical Engineering, College of Chemistry and Molecular

Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China. *E-mail: [email protected]; [email protected] KEYWORDS：Aqueous rechargeable zinc batteries, Ammonium vanadium bronze, NH4+ insertion, Electrochemical stability, High energy density, High power density

ABSTRACT: Aqueous rechargeable zinc batteries (ARZBs) are desirable for energy storage devices owing to the low cost and abundance of Zn anode, but their further development is limited by a dearth of ideal cathode materials that can simultaneously possess the high capacity and stability. Herein, we employ a layered structure of ammonium vanadium bronze (NH4)0.5V2O5 as the cathode material for ARZBs. The large interlayer distance supported by the NH4+ insertion not only facilitates the Zn2+ ion intercalation/de-

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intercalation, but also improves electrochemical stability in ARZBs. As a result, the layered structural (NH4)0.5V2O5 cathode delivers a large capacity up to 418.4 mAh g-1 at a current density of 0.1 A g-1. A reversible capacity of 248.8 mAh g-1 is still remained after 2000 cycle and a capacity retention of 91.4 % was kept at 5 A g-1. Furthermore, in comparison with previously reported Zn ion batteries, the Zn/(NH4)0.5V2O5 battery achieves a prominent high energy density of 418.4 Wh kg-1 while delivering high power density of 100 W kg-1. The results would enlighten and push the ammonium vanadium compounds to a brand new stage for the application of aqueous batteries.

1. INTRODUCTION Given the looming demands of further portable electronics, electrochemical energy storage (EES) is pivotal to dominate the sustainable prosperity of modern society, which triggered the search for reliable and low-cost battery technology.[1-2] Although lithium-ion batteries (LIBs) indeed provide huge potential for EES owing to the high energy and power densities in marketplace, the increasing concerns about lithium resource (scarce abundance and uneven distribution), toxicity and safety derived from organic electrolytes cannot meet their large-scale application in stationary grid storage.[3-7] Because of these issues, aqueous rechargeable batteries (ARBs), which possess inexpensive and high operational safety electrolytes, and provide a higher ionic conductivity in aqueous electrolyte compared with organic electrolytes, are the attractive choices.[3] Despite the substantial applications of lead-acid aqueous batteries, the unfavorable environmental concern on the use of lead, coupled with the low energy density (~75 Wh kg-1), have deviated away from the parameters of EES. The past efforts in ARBs have always focused on the alkaline cations, such as Li+, Na+ and K+ system. Among beyond these systems, multivalent ion (Mg2+, Zn2+, Al3+) based aqueous battery systems, have attracted significant interests due to their high energy density (Zn: ~5851 mAh mL-1, Mg: ~3833 mAh mL-1, Al: ~8046 mAh mL-1 ).[4] Particularly, aqueous rechargeable Zn batteries (ARZBs) are expected to emerge as the front-runner to replace both LIBs and lead-acid batteries in virtue of the following


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properties of Zn, which including its abundance and high theoretical capacity (~820 mAh g-1), low electrochemical potential of Zn/Zn2+(-0.76 V vs. standard hydrogen electrode), stability and nontoxicity.[1619]

Motivated by these advantages, a series of cathode materials mainly focused on manganese-based oxides

(α-, β-, γ-, and δ-types MnO2), prussian blue analogs, and Na3V2(PO4)3 have been demonstrated. However, the long-life aqueous Zn/MnO2 battery has been prevented by Mn2+ dissolution induced in drastic capacity fading. And rest of them often provided the limited capacity and energy density, and unsatisfactory cycling performance.[20-26] Impressively, owing to the multivalence state of vanadium from +2 to +5, as well as different vanadium oxide frameworks arise from several coordination polyhedral, vanadium-based compounds have been extensively utilized as the electrode to insert Li+ and Na+ ion for lithium/sodium batteries.[27-29] In previous studies, these class of layered materials, such as V2O5·H2O, Zn0.25V2O5·nH2O, Ca0.25V2O5·nH2O, H2V3O8, LiV3O8, Na2V6O16·3H2O, VS2, have been served as the host materials for ARZBs.[30-36] In fact, most of them delivered a limited capacity less than 400 mAh g-1, while remaining superior rate performance and long-life stability. Although Cation (Zn2+, Ca2+, Mg2+ and K+) preintercalated vanadium oxides frameworks have been demonstrated improved ARZBs performance, these metal-ions with large atomic mass can cause the relatively low theoretical capacity, and an unstable structure with rapid decline in capacity upon cycling. Most recently, Yang et al have developed a LixV2O5·nH2O material by arranging the Li+ in the interlayers of V2O5·nH2O, which achieved high capacities and excellent cycling performance for the current ARZBs[37]. Driven by these hints, many layered structural of vanadium bronze materials that composed of intercalations inside edge- and corner-shared VO6 layers, which have sparked renewed investigation in the insertion of Zn ion due to their lower toxicity, higher ionic and electronic conductivities than V2O5.[38] Ammonium vanadium bronze material has been available for electrode materials in organic electrolyte for these Li+/Na+/Mg2+ batteries, whereas significant improvement in high capacity and cycling stability has not been achieved yet. In most recently paper, Wei et al and Tang et al used the (NH4)2V10O25·8H2O with the same structure as bilayered V2O5·nH2O



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displayed a long cycling performance for ARZBs[39-40], it did not deliver a huge capacity since the relatively large volume and small interplanar spacing. During our manuscript submission, Tang et al reported three kinds of ammonium vanadate including NH4V4O10, NH4V3O8 and (NH4)2V3O8, they found that the NH4V4O10 with largest interplanar spacing of 9.8 Å displayed the best electrochemical performance in ARZBs[41]. We explored a hydrothermal method for the rapid synthesis of (NH4)0.5V2O5 nanoflakes, this layered structural of (NH4)0.5V2O5 by inserting the NH4+ ion exhibited an interplanar spacing of 12.2 Å, which can provide the highest theoretical Zn-storage capacity of 492.3 mAh g-1 (based on the vanadium valence state from V4.75+ to V3+), which can be considered as a promising high-capacity cathode in ARZBs with a long-life performance and high rate capability. 2. EXPERIMENTAL SECTION 2.1. Preparation of (NH4)0.5V2O5 nanoflakes. The ammonium vanadium bronze was synthesized via a conventional hydrothermal reaction. First, a mixture of solution was prepared from 2.5538 g of NH4VO3 (Sigam-Aldrich, 99.9%) and 3.199 g of oxalic acid dehydrate (Sigam-Aldrich, 99%) dissolved in 40 mL distilled water. Then the above solution was stirred at 60 °C for 1 h to get yellow-green solution. The mixture was transferred into a 100 mL Teflon lined stainless steel autoclave. The autoclave was sealed into a stainless steel tank and kept at 180 °C for 24 h. After that, the blue-green products was collected by filtration, purified with distilled water and ethanol three times, respectively. Finally, the products is dried at 80 °C overnight. 2.2. Material Characterization. Powder X-ray diffraction (XRD) patterns were collected on a Bruker D8 Focus Power X-ray diffractometer with Cu Kα (λ = 0.15405 nm) radiation (40 kV, 40 mA). SEM images were obtained on a JSM-6390 microscope from JEOL working at 1 kV acceleration voltage. TEM, HRTEM images and EDS mapping were obtained through a Tecnai G2 F20 S-Twin (America FEI) microscopy operating at 200 kV. XPS was tested on a XSAM800 Ultra spectrometer. The obtained sample was also


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characterized by Raman spectroscopy (LABRAM-1B) and FT-IR spectroscopy (NICOLET 6700) respectively. 2.3. Electrochemical Characterization. The electrode was fabricated by mixed well with active materials (70%), acetylene black (20%) and polytetrafluoroethylene binder (10%) to produce a homogeneous slurry, and then form a suitable film by the roll press machine. Prior to press onto a titanium grid, the films were dried in a vacuum oven at 80 °C for 12 h. The mass loading of the films was controlled to be 2~3 mg cm-2. Cyclic voltammetry (CV) test was performed on an AUTOLAB PGSTAT302N potentiostat model workstation. The full aqueous ZIBs cell was assembled in CR2016-type coin cell, in which Zn metal foil (0.03 mm) and 2 M ZnSO4 solution were used as the anode electrolyte, respectively. The galvanostatic charge-discharge and cycling stability were conducted on a computer controlled by a Hukuto Denko battery system (HJ series) at room temperature. The thermodynamic equilibrium (or close-to equilibrium) zinc-ion intercalation voltages were estimated by using Wuhan LAND charge/discharge system operating in the galvanostatic intermittent titration technique (GITT) mode.

3. RESULTS AND DISCUSSION As illustrated in Figure 1a, we demonstrated a detailed study on electrochemical zinc storage by employing the obtained (NH4)0.5V2O5 cathode, coupled with metallic zinc anode and 2 M ZnSO4 electrolyte. The asymmetric and symmetric stretching of V-O-V bond, V=O stretching of distorted octahedral, and N-H mode of NH4+ group correspond to the obtained sample are confirmed by Fourier-transform infrared spectroscopy (FTIR, Figure S2) and Raman spectrum (Figure S3). In Figure 1b, Rietveld refinement XRD result reveals that, the diffraction lines of (NH4)0.5V2O5 sample are well indexed to the monoclinic phase (NH4)0.5V2O5 (space group C 2/m) with the lattice parameters, a=12.204 (Å), b=3.755 (Å), c=9.877 (Å), similar to the previous report.[42] The refined atomic parameters and selected interatomic distances are presented in Table S1. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images are shown in Figure 1c



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and 1d, respectively, obviously depicting the formation of ubiquitous (NH4)0.5V2O5 nanoflakes. Besides, the thickness of (NH4)0.5V2O5 nanoflakes is only about 2.1 nm via atomic force microscope (AFM) analysis (Figure S4). A high-resolution (HRTEM) image is provided in Figure 1e, from which the interplanar distance of lattice fringes can be calculated to be 0.375 nm, corresponding to the spacing of the (010) plane of the monoclinic (NH4)0.5V2O5 species. The selected area electron diffraction (SAED) pattern (Figure 1e insert) manifests that d-spacing of (NH4)0.5V2O5 nanoflakes are 0.276, 0.371, and 0.883 nm, which may match with the d-spacing values of (400), (110) and (001) crystal planes, respectively. The detailed X-ray photoelectron spectroscopy (XPS) spectra provides the surface composition and element valence of (NH4)0.5V2O5 material, as presented in Figure S5. The corresponding peaks of V, O and N are observed (Figure S5a), whereas the presence of H element is not appeared due to the absence free electron outside of H+. Figure S5b-5d presents the appearance of N 1s and O 1s peaks at around 401.4 and 530.0 eV, respectively. The V 2p spectrum in Figure S5c clearly indicated, two peaks are observed at 517.4 and 524.6 eV, which are characteristic of V5+ 2p3/2 and V5+ 2p1/2, respectively, and the peak located at 516.2 eV with less intensity is indicative of the appearance of certain amount of V4+.[43] Obviously, the mixed valence states of V5+/V4+ can be measured by the above result in this pristine material. As known, many oxide materials have been demonstrated that the introduction of mixed valence states into material lattice leads to improved high electrochemical performance. [44-45] The electrochemical performances of the Zn/(NH4)0.5V2O5 battery were studied using CR2016 coin-type assembled cells. Figure 2a displays the CV of (NH4)0.5V2O5 electrode with 2 M ZnSO4 electrolyte in a voltage range of 0.4-1.6 V (vs Zn2+/Zn). The CV curve shows feature two pairs of cathodic and anodic peaks at 0.79/0.6 and 0.82/1.02 V, respectively, indicating a multi-step Zn2+ de/intercalation behavior in (NH4)0.5V2O5. When the current density is maintained at 0.2 A g-1, the initial three charge/discharge profiles are presented in Figure 2b. Two distinct sloping plateau between open-circuit voltage and 0.4 V are observed, derived from the reduction of V5+/V4+ to V3+. It is also revealed that first discharge capacity of 341.7 mAh g-1 and sequential charge capacity of


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385.4 mAh g-1 are delivered with an initial Coulombic efficiency (CE) of 88.7 %. In the following cycles, a higher discharge capacity of 386.9 and 396.6 mA h g-1 is obtained on the second and third cycle, respectively, and the CE quickly increases to 98 % in the second cycle. It is speculated that the increased CE values during initial cycling in aqueous batteries could be ascribed to the completion of side reactions. Specific in Figure 2c, a lower CE is observed in the initial cycles at a low applied current of 0.1 A g-1 and then a higher CE approaching ~100% in the subsequent cycles . Because the kinetic reaction is very slow at low current density, and it is easy to generate other side reaction that cause the larger irreversibility in this process [46-47]. The cycling performance of Zn/(NH4)0.5V2O5 battery at 0.2 A g-1 for 50 cycles was presented in Figure 2c, in which a stable CE of ~100 % was remained after 10 cycles. Moreover, a high capacity retention of 80.5% (against the highest capacity) is available at the end of 50 cycles. We also investigated the Zn-ion storage behavior of (NH4)0.5V2O5 by CV tested with different scan rate, and the result were shown Figure 2d. With the increase of scan rate, it can be found that cathodic peaks positively shifted to higher potential and anodic peak negatively shifted to lower potential. Theoretically, the voltammetric response of the activeelectrode materials at various scan rates can be described using the following equation: i = ανb Where i is the measured current at a fixed potential, ν is sweep rate. The semi-infinite diffusion is reflected by which the peak current i varies with ν1/2 (that is, b = 0.5), while capacitive process in which it varies with ν (that is, b = 1). As shown in Figure 2e, a good linear relationship between the peak current and scan rate reveals that slopes for peak 1, 2, 3, and 4 are 0.87, 0.85, 0.80 and 0.70, respectively, suggesting that the ionic diffusion and pseudocapacitance are synchronously predominant for Zn2+ storage in (NH4)0.5V2O5 electrode. In order to quantitatively measure their contribution in this process, we assumed that response current is a combination of diffusion-controlled and capacitive reactions derived from the following equation.[48] i=k1ν+ k2ν1/2



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Where k1 and k2 are adjustable parameters, they can be obtained from the line fitting of ν1/2 versus i (ν)*ν-1/2. As a result, 53.7% of the total current is attributed to the capacitive contribution at 0.2 mV s-1 (Figure 2f). The ratios of capacitive contribution at every scan rate are displayed in Figure S6. Notably, the capacitive contribution ratio raises to 58.7, 60.7, 63.8 and 66.8% along with the increasing scan rate from 0.4, 0.6, 0.8 and 1 mV s-1, respectively, demonstrating a dominant position of capacitive behavior at high scan rate. Galvanostatic intermittent titration (GITT) technique is established to determine the diffusion coefficient of DZn2+ in the (NH4)0.5V2O5 material (Detailed description shown in Supporting Information). Obtained from Figure S7, the average DZn2+ value in the discharge and charge process are approximately 1.05*10-8 and 0.46*10-8 cm2 s-1, respectively. The diffusion coefficient of DZn2+ material on the whole intercalation reaction is in the range of 10-8 to 10-9, which is higher than the Li diffusion coefficient in the reported commercial electrode including the 1D Li diffuser LiFePO4 cathode, Li4Ti5O12 anode, and other cathode for ARZBs[31,32,49-50]. We then apply (NH4)0.5V2O5 cathode for ARZBs to evaluate the rate capability performance and long-term stability. Figure 3a presents the rate capability of Zn/(NH4)0.5V2O5 battery with increased current density varied from 0.1 to 20 A g-1 and returned to 0.1 A g-1. At each rate, it was found that the discharge capacity slowly decreased with cycles. When returned back to 0.1 A g-1, the discharge capacity is still 379.6 mAh g-1, which maintains 88.0 % of the initial capacity at 0.1 A g-1. The galvanostatic charge/discharge profiles from 0.1 to 20 A g-1 are presented in Figure 3b, in which a discharge capacity of 418.4 mAh g-1 is obtained at 0.1 A g-1, higher that of many ARZBs under the same condition.[26,30,35,43,51] This battery displays discharge capacities of 394.8, 358.9, 333.1, 305.0 and 252.1 mAh g-1at 0.2, 0.5, 1, 2 and 5 A g-1, respectively. Surprisingly, it delivers a high discharge capacity of ~204.1 mAh g-1at 10 A g-1, keep an impressive discharge capacity of ~153.5 mAh g-1 at a high rate up to 20 A g-1 due to the fast Zn2+ ion migration. This superior rate capability could exceed that of most previously V-based materials.[31,32,34,35,48,52-53] The prolong


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cycling and Coulombic efficiency of the Zn/(NH4)0.5V2O5 battery at 5 A g-1 are shown in Figure 3c. The battery shows gradually increased capacity in the initial 100 cycles, which may be derived from the activation of (NH4)0.5V2O5 flake. After certain cycles, the (NH4)0.5V2O5 cathode displays a constant capacity of 240-260 mAh g-1 with a high Coulombic efficiency of approaching 100%, maintaining a discharge capacity of 248.8 mAh g-1 after 2000 cycles (~91.4 % capacity retention against the maximum capacity). The corresponding voltage profile of Zn/(NH4)0.5V2O5 battery at 5 A g-1 is presented in Figure S8. The comparison of the capacity and cycle life of recently reported vanadium-based cathode materials is presented in Table S2. Furthermore, another good cycle life of this battery at 10 A g-1 is show in Figure S9, where a highest discharge capacity fade from 214.5 to 191.8 mAh g-1 after 3000 cycles (a high capacity retention of 89.5%). It is worthwhile to note that very few materials can simultaneously achieve an outstanding rate capability and long lifespan. The NH4+ inserted in layered structural (NH4)0.5V2O5 can further expanding the interlayer space for facile Zn2+ intercalation. The Ragone plots in Figure 3d further indicates the excellent rate performance of Zn/(NH4)0.5V2O5

system compared with previously reported state-of-the-art

cathode materials. As observed, our system possesses the highest energy densities up to 418.4 Wh kg-1 at a power density of 100 W kg-1 (In terms of the mass of positive materials). Even the energy density of 151.1 Wh kg-1, the (NH4)0.5V2O5 cathode still obtains a power density of almost 20000 W kg-1. The minimal energy loss (energy density vs. power density) for this battery is superior to reported cathode materials such as α-MnO2,[24] Na0.33V2O5,[51] Zn0.25V2O5,[31] H2V3O8,[32] Na2V6O16·3H2O[35], Zn2(OH)VO4 [54]for ARZBs. The mechanism of zinc storage for Zn/(NH4)0.5V2O5 battery was systematically investigated using elemental mapping, XPS, SEM, TEM, and in-situ XRD analysis. Figure 4a displays EDX mapping of the (NH4)0.5V2O5 electrode after the first charge/discharge process. Obviously, the V, N and O elements are evenly distributed in (NH4)0.5V2O5 nanoflakes matrix. Further results clearly reveal that the appearance and disappearance of element zinc upon the first charge/discharge



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reaction, demonstrating the successful Zn-ion intercalation/de-intercalation process. The oxidation state of N, V and Zn in the first discharge and charge states were determined by XPS measurement (Figure 4a-c). As observed in Figure 4a, no single peak of Zn was observed in the as-prepared sample. When discharged to 0.4 V, the main two peaks around at ~1021.8 and ~1044.9 eV are detected in the Zn 2p region and the associated intensity extremely decreases in the subsequent charge state, which further verifies the effective Zn2+ intercalation into (NH4)0.5V2O5 nanoflakes. The detection of feeble Zn signal in the latter charge may attributed the residual zinc sulfate from the electrode. The V5+ signal along with weak V4+ component jointly constructs the V 2p XPS region in the pristine state, which displayed in Figure 4b. However, a lower peak with binding energy of 515.7 eV also appeared, which is attributed to the formation of V3+ that originated from the reduction of V5+ and V4+ due to the zinc ion intercalation. When charging, the V 2p spectra can resume the pristine state, reflecting a high reversibility. As shown in Figure 4c, the signal intensities of N 1s spectrum upon discharge/charge are strongly weaken than the pristine material, which could be originated from the occupation of Zn ion in the former sites of NH4+, which is also produced similar results by Hong et al.[38] In addition, the SEM images (Figure S10) indicate that the entire surface of the Zn anode after the first cycle discharge/charge is slightly rougher with dendrite-free surface morphology, in comparison with the pristine Zn foil. The corresponding EDX spectrum (Figure S11) shows that the Zn foil surface contains mainly Zn metal, additional existence of S and O elements could be ascribed to the penetration of ZnSO4 electrolyte. The morphology of (NH4)0.5V2O5 cathode during the discharge/charge process is also used to evaluate the structural stability of materials, as shown in Figure S12. Like to the original (NH4)0.5V2O5 nanoflakes, the (NH4)0.5V2O5 cathode still maintains similar structure without deterioration after insertion (0.4 V) and extraction (1.6 V). Figure S13 presents the HRTEM images of the (NH4)0.5V2O5 cathode with a subtle lattice spacing change of the (010) plane from pristine state to discharge/charge state. Upon discharging to 0.4 V, the corresponding (010) lattice spacing of discharged product increase to


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0.390 nm due to the Zn ion insertion. Subsequently, the contracted crystal structure could recover to its original state upon Zn ion removal, which agrees well with the XPS and EDX mapping results. Figure S14 depicts the FTIR spectra obtained at various state for the (NH4)0.5V2O5 electrode upon the fifth cycle. The intensity of V-O-V, V=O and N-H bonds located at 500, 1004, and 1399.5 cm1

decreases when discharge to 0.4 V and could gradually increases until charge to 1.6 V. These

peaks are closely related to the layered structure, which can affect the structure transformation during the insertion/extraction of Zn2+ into VO6 layers [32]. We also used time-resolved in situ synchrotron XRD technique to track the transformation and evolution of crystal structure on the (NH4)0.5V2O5 phases. As shown in Figure 5a, the three main peaks corresponding to (NH4)0.5V2O5 electrode at 36.2, 38.4, and 40.1° slightly shift to higher 2θ values during the complete discharge (0.4 V), and gradually shift to the lower position until the initial state (1.6 V). The positive shifts is an indicative of the decrease in interplanar distance, which could be attributed to the powerful electrostatic interaction among the intercalated zinc ions and VO6 layers. In contrast, a negative shift in the 2θ value of 28.6° occurs during discharge and then returns to original position at the fully charged state of 1.6 V, which suggested that the lattice parameters changed with the increasement of discharge depth. Upon a complete discharge state, an interplanar spacing of the (111) plane from 1.6 to 1.7 Å is an indicative of zinc ion successful intercalation in the corresponding reaction. Concordantly, we can see from Figure 5b that, a new set of peaks located at 16.2 and 27.6° gradually emerge and their intensity reach a maximum upon discharge to 0.4 V, then weaken and disappear in subsequent charge process, which is a characteristics of phase separation reaction rather than solid solution reaction. Under a phase separation mechanism, the insertion/extraction is speculated in Figure 5c. When voltage ranged from 1.6 to 0.4 V, a new phase of Znx(NH4)0.5V2O5 is gradually produced from the increase insertion of Zn ion, and reconverted to (NH4)0.5V2O5 phase along with the Zn ion extraction. Obviously, the XRD pattern after complete charge state is almost identical to original electrode before



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electrochemical reaction, thereby reflecting the high reversibility and stability of layered structural (NH4)0.5V2O5 material. Occasionally, the special intercalation mechanism involves the proton or water molecular co-intercalation/deintercalation into structure of host material. However, it was found that no Zn4SO4(OH)6·4H2O phase was formed during the in situ synchrotron XRD measurement, which is different from the co-intercalation/deintercalation mechanism of H+ and Zn accordance with the previously report [23, 48, 55]. The reaction of this battery can be demonstrated by the following electrochemical reaction: Cathode: xZn2++2xe-+(NH4)0.5V2O5 ↔ Znx(NH4)0.5V2O5, Anode: xZn↔xZn2++2xe-, where x represents the number of Zn2+ than can be reversibly inserted into the (NH4)0.5V2O5. Herein, a practical number of 2.97 is obtained when vanadium valence state could be transferred into V3+.

4. CONCLUSION In summary, we have successfully synthesized a kind of (NH4)0.5V2O5 nanoflakes material, and assembled as aqueous Zn/(NH4)0.5V2O5 battery. The layered structure along with the wide valence state of vanadium could promote the accommodation and transportation of Zn ion for ARZBs. The (NH4)0.5V2O5 cathode exhibited amazing rate capability with large reversible capacities of 418.4 and 252.1 mAh g-1 at 0.1 and 5 A g-1, respectively, and kept excellent cycle life of 2000 cycles with persistent Coulombic efficiencies of ~100%. Such high energy density up to 418.4 Wh kg-1 at power density of 100 W kg-1 is one of the best cathode among the reported ARZBs, which may offer guidance for enriching layered-typed materials of multivalent ion storage application. ASSOCIATED CONTENT


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Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Characterization of the prepared (NH4)0.5V2O5 material, including FT-IR, Raman spectra, XPS, AFM, SEM, EDX, HRTEM, and electrochemical tested data. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected]. Author Contributions The manuscript was written through contributions of all authors. Notes Any additional relevant notes should be placed here. ACKNOWLEDGMENT This work was partially supported by the National Natural Science Foundation of China (No. 21622303， 21333002, 21805126) and National Key Research and Development Plan (2016YFB0901500). REFERENCES (1) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical Energy Storage for the Grid: A Battery of Choices. Science, 2011, 334, 928-934. (2) Lu, W.; Yuan, Z.; Zhao, Y.; Li, X.; Zhang, H.; Vankelecom, F. J. High-Performance Porous Uncharged Membranes for Vanadium Flow Battery Applications Created by Tuning Cohesive and Swelling Forces. Energy & Environ. Sci, 2016, 9, 2319-2325. (3) Larcher, D.; Tarascon. J. M. Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem, 2015, 7, 19-29. (4) Yu, H.; Qian, Y.; Qtani, M.; Tang, D.; Guo, S.; Zhu, Y.; Zhou, H. S. Study of the Lithium/nickel Ions Exchange in the Layered LiNi0.42Mn0.42Co0.16O2 Cathode Material For Lithium Ion Batteries: Experimental and



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Aqueous Zinc Ion Batteries. Adv. Energy. Mater, 2019, 1900083.

FIGURES

Figure 1. (a) Schematic illustration of the aqueous Zn/(NH4)0.5V2O5 battery. (b) Rietveld refinement of the XRD pattern of (NH4)0.5V2O5. (c) SEM, (d) TEM, (e) HR-TEM images and SAED pattern of (NH4)0.5V2O5.



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Figure 2. Characterization of ARZBs with 2 M ZnSO4 electrolyte. (a) The first CV curve of (NH4)0.5V2O5 at a scan rate of 0.2 mV s-1, (b) galvanostatic charge and discharge profiles of the (NH4)0.5V2O5 cathode at a current density of 0.2 A g-1, (c) the cycling performance and coulombic efficiency of the (NH4)0.5V2O5 cathode at 0.2 A g-1, (d) CV curves of (NH4)0.5V2O5 cathode at different scan rates of 0.2, 0.4, 0.6, 0.8 and 1 mV s-1 (peak 1 and peak 2 is the reduction peaks, peak 3 and peak 4 is the oxidation peaks, respectively), (e) the corresponding plots of log(peak current) versus log (scan rate) based on the main four peaks. (f) The ratio of capacitive and diffusion controlled capacities at multiple scan rates.


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Figure 3. Electrochemical performance of ARZBs based on (NH4)0.5V2O5 cathode. (a) Rate performance of (NH4)0.5V2O5 electrode at various current densities from 0.1 to 20 A g-1, (b) galvanostatic charge/discharge curves of the (NH4)0.5V2O5 electrode at various current densities. (c) Cycling performances of (NH4)0.5V2O5 electrode at 5 A g-1, (d) Comparison of the Ragone plots of aqueous Zn/(NH4)0.5V2O5 battery with other advanced ARZBs, in terms of the mass of cathodes only.

21 ACS Paragon Plus Environment


Figure 4. TEM-EDX element mapping image and high-resolution XPS spectra of Zn2p (a), V2p (b) and N 1s (c) of (NH4)0.5V2O5 electrode at the pristine state and full first discharge (0.4 V) and charge state (1.6 V).


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Figure 5. (a) The galvanostatic charge/discharge curve of Zn/(NH4)0.5V2O5 battery at 0.04 A g-1 (left), In-situ XRD measurements obtained through the whole angle, the corresponding enlarge regions of 15.8-16.4°, 26.0-42.0°, respectively (right). (b) Twodimensional plots of 15.8-16.4°, and 26.0-42.0° intensity reflections versus time and 2 theta (different colour zones mark two-phase regions where there are different intensities diffraction peaks). (c) An illustration of Zn ion insertion/extraction into (NH4)0.5V2O5 upon electrochemical discharge/charge process.



Graphic for manuscript


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Engineering a High-Energy-Density and Long Lifespan Aqueous Zinc

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