Study on Solution Combustion Synthesis and Electrochemical Performance of V2O5-Cu as Cathode Materials for Aqueous Zinc-Ion Batteries

Study on Solution Combustion Synthesis and Electrochemical Performance of V2O5-Cu as Cathode Materials for Aqueous Zinc-Ion Batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study on Solution Combustion Synthesis and Electrochemical Performance of V 2 O 5 -Cu as Cathode Materials for Aqueous Zinc-Ion Batteries Jidong Ma, Xinya Gu, Kai Du, Wenjun Zhou, Jian Cui, Siyong Gu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4090795/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Aqueous zinc-ion batteries (AZIBs) are considered to be one of the most promising alternative energy sources due to their safety. Vanadium-based compounds, especially V 2 O 5 cathode materials, have been widely studied due to the advantages of suitable working voltage windows and highly reversible redox reactions. However, the poor conductivity of V 2 O 5 and its structural instability limit its application in AZIBs. In this paper, copper ions doped V 2 O 5 was synthesized by a simple one-step solution combustion synthesis method to improve its structural stability and electrochemical performance. The modified material expanded the interlayer spacing and increased the ionic diffusion rate, and increased the concentration of low valence vanadium and oxygen vacancy, thereby increasing the electron mobility and promoting the electrochemical reaction, resulting in an enhanced discharge specific capacity of the material. Zinc-ion batteries assembled with V 2 O 5 -Cu as the cathode material can provide a high discharge specific capacity of 300 mAh g − 1 at 4 A g − 1 , and have good cycling stability, with a capacity retention of 95% over 500 cycles. Aqueous Zinc-Ion Batteries Copper Ions Doping Solution Combustion Synthesis Figures Figure 1 Figure 2 Figure 3 1. Introduction Since the 1990s, aqueous zinc-ion batteries (AZIBs) based on V 2 O 5 have shown broad development prospects due to high specific capacity, cheap raw materials, and other advantages [ 1 – 5 ]. Like other insertion materials, this material also has a layered structure, which is advantageous for the intercalation and deintercalation of Zn ions. However, due to the poor conductivity and structural instability of V 2 O 5 , it becomes a bottleneck restricting application [ 6 – 9 ]. In order to improve the electrochemical performance of V 2 O 5 , metal ions doping can be employed to improve conductivity and stabilize its structure. Zheng et al. [ 10 ] doped aluminum ions into hydrated vanadium pentoxide by a one-step hydrothermal method to improve the stability of the entire material by forming stable Al-O bonds. The high interlayer spacing (13.4 Å) of the material may be mainly caused by the electrostatic repulsion between n-trivalent aluminum and n-pentavalent vanadium, which is beneficial to the rapid diffusion of zinc ions. The formation of V 4+ and the introduction of oxygen vacancies are also conducive to improving the electrical conductivity of the material. This material has an initial capacity of 380 mAh g -1 at 50 mA g -1 . At a high current of 4 A g -1 , the capacity of the material increased to 117% of its initial capacity after 200 cycles of activation, and the remaining capacity was still 107% of its initial capacity after 3000 cycles. Zhang et al. [ 11 ] used a simple solid-state chemical method to synthesize rod-shaped copper doped V 2 O 5 . Cu doping not only increases its volume, but also introduces abundant oxygen vacancies in the V 2 O 5 lattice, which facilitates rapid electron and ion transport during charge and discharge processes. The rod-shaped Cu doped V 2 O 5 shows a high discharge specific capacity of 293.1 mAh g -1 , which has a high discharge specific capacity and good cycling performance. The common methods for synthesizing V 2 O 5 include hydrothermal techniques, chemical vapor deposition, sol-gel method, soft template method, and supercritical solvent thermal reaction. However, these synthetic processes typically involve complex procedures, including long-term aging reactions, ethanol soaking processes, repeated washing and heating at different stages to obtain the final product [ 12 – 14 ]. Therefore, the development of a simple synthesis process with low-cost can improve its application in AZIBs. In this paper, V 2 O 5 (V 2 O 5 -Cu) electrode materials were synthesized in a one-step solution combustion synthesis method, and the morphology and structure of V 2 O 5 and V 2 O 5 -Cu materials were compared. The effect of Cu 2+ doping on the structure and electrochemical performance of AZIBs electrode material was investigated. The Cu 2 + doping in V 2 O 5 material can significantly enhance the interlayer spacing, facilitating the passage of more zinc ions and improving the transfer efficiency of zinc ions. The increase in oxygen vacancy concentration and V 4 + ratio after doping provides the material with more active sites for zinc ion storage. 2. Results and Discussion The facile and low-cost synthesis process is schematically illustrated in Fig. S1 . Figure 1 a compares the XRD patterns of V 2 O 5 and V 2 O 5 -Cu samples. From the figure, it can be seen that the comparative results between the prepared samples of V 2 O 5 , V 2 O 5 -Cu and the V 2 O 5 standard diffraction card (JCPDS NO.41-1426) show that the synthesized materials have identical peak positions to the standard card. And no obvious impurity peaks are observed, which indicates that the synthesized samples have high purity and good crystallinity. The diffraction peaks of V 2 O 5 at approximately 15.4°, 20.3° and 26.2° correspond to the (200), (001) and (110) crystal planes, respectively. According to the Bragg equation, the calculated d-values for the (001) crystal plane of V 2 O 5 -Cu and V 2 O 5 are 0.4384 nm and 0.4380 nm, respectively. This indicates that the introduction of Cu has a little change in the interlayer spacing of V 2 O 5 . Figure 1 b shows the Raman spectra of the V 2 O 5 and V 2 O 5 -Cu samples, and Fig. S2 shows the crystal structure of V 2 O 5 . It can be seen from the figure that oxygen atoms occupy four positions in a single [VO 5 ] layer. The Raman peak at 995 cm -1 is generated by the stretching vibration of the V = O 1 bond, while the peaks at 407 and 284 cm -1 can be attributed to the bending vibration of the V = O 1 bond [ 15 – 16 ]. The bending vibration peak of V-O 2 is located at 473 cm -1 , and the stretching vibration peak of V-O 3 is located at 693 cm -1 . The peaks at 524 and 308 cm -1 are the stretching and bending vibrations of the V-O 4 bond, respectively [ 17 – 19 ]. Due to the weak van der Waals force between adjacent [VO 5 ] layers, the external [VO 5 ]-[VO 5 ] vibration peaks appear at low wave numbers, specifically at 104, 147 and 199 cm -1 [ 14 ]. Compared with V 2 O 5 samples, the redshift of V 2 O 5 -Cu peak value and Raman spectral can be explained by lattice expansion, which leads to increased interatomic spacing and a relatively relaxed lattice. As a result, the vibration frequency is reduced. Consistent with the results of XRD analysis. As shown in Fig. 1 c, X-ray photoelectron spectroscopy (XPS) was employed to further determine the valence states of V, O and Cu elements in V 2 O 5 -Cu and V 2 O 5 . As shown in Fig. 1 d, the Cu 2p 3/2 and Cu 2p 1/2 peaks at 928.5 and 931.0 eV, respectively, are consistent with those observed in the literature for CuO [ 20 ], which can prove the existence of Cu 2+ ions. Cu 2+ has a ionic radius of 73 pm, which is larger than that of 54 pm for V 5+ . Copper ions dopped into the lattice of V 2 O 5 , which will cause an increase in the unit cell volume of V 2 O 5 [ 10 ]. This is the same as the XRD analysis results. Peak analysis was performed on the V 2 O 5 and V 2 O 5 -Cu samples (Fig. 1 e). The V 2p 3/2 peak of V 2 O 5 is located at 516.3 eV (V 4+ ) and 517.9 eV (V 5+ ), with a V 5+ /V 4+ ratio of 1:0.05. For V 2 O 5 -Cu, the ratio of V 5+ to V 4+ is 1:0.07. This indicates the presence of more low-valence vanadium in the V 2 O 5 -Cu samples. The increase in the peak area ratio of V 4+ indicates that the oxidation state of vanadium is lower, which may be due to the introduction of oxygen vacancies in V 2 O 5 -Cu. In order to maintain its electrical neutrality, the proportion of low-valence vanadium (V 4+ ) increases [ 21 ], which can enhance the electronic transition between V 4+ and V 5+ . Meanwhile, the conductivity of the electrode material is improved. Figure 1 f shows the O1s spectra of V 2 O 5 -Cu and V 2 O 5 samples, with the OI peak at 530.3 eV and the OII peak at 531.8 eV [ 22 ]. By comparing the integrated area ratios, it can be determined that V 2 O 5 -Cu has 1.6% more oxygen vacancies than V 2 O 5 . Oxygen vacancies play a crucial role in facilitating the kinetics of ion diffusion. Their generation and movement create additional space for ion diffusion, thereby accelerating ion migration and enhancing ionic conductivity. Additionally, oxygen vacancies serve as favorable active sites for nucleation during phase transitions in energy storage processes, providing supplementary sites for the storage of zinc ions [ 23 ]. The SEM images of V 2 O 5 and V 2 O 5 -Cu samples are shown in Fig. S3(a-b). It can be observed that undoped V 2 O 5 exhibits a block-like aggregation with an average particle size of 200 nm. V 2 O 5 -Cu is composed of numerous small plate-like structures arranged in a regular flake structure, with the average grain size of 100 nm for the tiny plate-like structures, so that the grain is refined. Grain refinement can increase the specific surface area of the material and enhance its electrochemical activity sites, which is conductive to improving the energy storage performance of the material [ 24 – 26 ]. Fig. S3(c-d) show the TEM images of the V 2 O 5 and V 2 O 5 -Cu samples, respectively. As measured by HRTEM in Fig. 2 a, the lattice fringe of the (110) plane of V 2 O 5 is 0.338 nm. In Fig. 2 b, the lattice fringes of the V 2 O 5 -Cu sample shows an interplanar spacing of 0.342 nm, indicating that the introduction of Cu 2+ increases its spacing, which is consistent with the above analysis results. In order to more intuitively display the distribution of Cu in the sample, the element distribution diagram of V 2 O 5 -Cu is shown in Fig. 2 (c-f), from which it can be observed that the copper element is uniformly distributed throughout the sample. As shown in Fig. 3 a, the electrochemical reaction kinetics of V 2 O 5 -Cu was studied by measuring CV test at different scan rates. As the scan rates increased from 0.2 mV s -1 to 1.0 mV s -1 , the oxidation and reduction peaks moved to higher and lower potential, respectively. According to the related b values of oxidation and reduction peaks are quantified according to the slope, as shown in Fig. 3 b. (The specific algorithm for calculating the b -value is provided in the supplementary material). The average b value of the peaks is about 0.6, indicating the presence of a diffusion-controlled Faradaic process and a capacitive process in the reaction. The curves show similar morphology at different scan rates, and the broadening of peaks in CV curves reflects the pseudocapacitive behavior, which is conducive to the rapid electrochemical reactions. Figure 3 c shows the second cycle CV curves of V 2 O 5 and V 2 O 5 -Cu as electrode materials for zinc-ion batteries at a scan rate of 0.1 mV s -1 , in the voltage range of 0.2–1.6 V. V 2 O 5 -Cu exhibits two major redox peaks around 1.11/0.84 V and 0.81/0.53 V, corresponding to the redox pairs of V 5+ /V 4+ and V 4+ /V 3+ , respectively [ 27 ]. The redox of the shoulder is irreversible, indicating the occurrence of side reactions. In addition, as shown in the figure, between the positive and negative peaks of the V 2 O 5 -Cu, a higher peak current density is observed compared to V 2 O 5 , which indicates better redox activity in V 2 O 5 -Cu [ 28 – 29 ]. In the V 2 O 5 -Cu electrode, the enhancement of charge transfer kinetics and involvement of active sites in electrochemical reactions were attributed to the increased proportion of V 4+ , leading to improved conductivity. Moreover, the heightened interlayer spacing in V 2 O 5 -Cu facilitates increased accommodation of zinc ions during the intercalation process, effectively diminishing the energy barrier in the diffusion mechanism. Ac impedance measurements of V 2 O 5 -Cu and V 2 O 5 samples to investigate the influence of copper ions on the charge transfer process. The results of the EIS test analysis are shown in Fig. 3 d. The illustration shows the simplified EIS fitting equivalent circuit, where Rct represents the charge transfer impedance, which mainly reflects the conductivity of electrons and ions; Rs represents the ohmic impedance; CPE 1 represents the Warburg impedance, which reflects the diffusion of Zn 2+ in the electrode material; and W 1 represents the double-layer capacitance. The impedance test of the three-electrode system consists of a semicircle in the high frequency region followed by a diagonal line in the low-frequency region matched with the charge transfer resistance ( Rct ) and the ion diffusion impedance, respectively. The fitting results of the two samples show that the charge transfer resistances ( Rct ) of V 2 O 5 and V 2 O 5 -Cu are 29.04 Ω and 9.18 Ω, respectively. The V 2 O 5 -Cu electrode exhibits a smaller charge transfer resistance, which indicates that electrons and ions transfer faster at the interface between the V 2 O 5 -Cu electrode and the electrolyte, mainly due to the addition of copper ions to improve the material' s conductivity and facilitate the transfer of electrons and ions at the liquid-solid interface [ 30 ]. The cycling performance of V 2 O 5 and V 2 O 5 -Cu electrodes at current densities of 8 A g -1 show in Fig. S4. At 8 A g -1 , the maximum discharge specific capacities of the two electrode materials are 125 and 232 mAh g -1 for V 2 O 5 and V 2 O 5 -Cu, respectively. After 1000 cycles, the capacity retention rates are 32% and 86% for V 2 O 5 and V 2 O 5 -Cu, respectively. Figure 3 e shows the rate performance of V 2 O 5 -Cu and V 2 O 5 . The average discharge specific capacities of V 2 O 5 at the current of 1, 2, 4 and 8 A g − 1 are 234, 219, 200 and 178 mAh g -1 , respectively. V 2 O 5 -Cu exhibits higher rate performance, with average discharge specific capacities of 271, 247, 214 and 199 mAh g -1 at the current of 1, 2, 4 and 8 A g -1 . Figure 3 f demonstrates that the V 2 O 5 -Cu electrode and V 2 O 5 electrode achieve efficiencies of over 100% in the initial several cycles. This can be attributed to the activation of the AZIBs at the beginning, which can be divided into the two steps listed below. As the charging and discharging progress, the electrolyte enters the interior of V 2 O 5 [ 31 ]. Simultaneously, the insertion/extraction of Zn 2+ and the phase transition of V 2 O 5 generate additional active sites. It can also be observed that the V 2 O 5 -Cu electrode exhibits better cycling capability compared to the V 2 O 5 electrode. The specific capacity of V 2 O 5 -Cu remains around 300 mAh g -1 at 4 A g -1 . After 500 cycles, the discharge specific capacity is 285 mAh g -1 (95.0% of the highest capacity), and the Coulombic efficiency is close to 100%. However, the specific capacity of V 2 O 5 remains around 180 mAh g -1 at 4 A g -1 , and it decreases to 139 mAh g -1 (77.2% of the highest capacity) after 500 cycles at 4 A g -1 . The enhanced discharge specific capacity and cycling stability of V 2 O 5 -Cu can be attributed to the increased interlayer spacing, improved electronic conductivity, and higher oxygen vacancy concentration. 3. Conclusions V 2 O 5 -Cu materials were synthesized in one step through a simple solution combustion synthesis method as the electrode material in AZIBs. The research results show that Cu 2+ doping in V 2 O 5 materials can significantly enhance the layer spacing, facilitate the deintercalation of zinc ions. Moreover, the elevation in oxygen vacancies concentration and the proportion of V 4+ following doping enhances active sites for charge transfer kinetics and engagement in the electrochemical reaction, consequently leading to an increase in electrical conductivity. After 500 cycles at 4 A g -1 , V 2 O 5 -Cu still maintained a higher specific capacity of 285 mAh g -1 (95.0% of the highest specific capacity), and the coulomb efficiency is close to 100%, surpassing V 2 O 5 with a capacity of 139 mAh g -1 (77.2% of the highest specific capacity). Declarations Author Contribution Xinya Gu (First Author): Conceptualization, Methodology, Software, Formal Analysis, Writing - Original Draft;Kai Du: Data Curation;Wenjun Zhou: Investigation;Jian Cui: Resources, Supervision;Siyong Gu: Software, ValidationHouan Zhang: Writing - Review & EditingJidong Ma (Corresponding Author): Conceptualization, Funding Acquisition, Resources, Supervision, Writing - Review & Editing. Acknowledgements This work is financially supported by the Natural Science Foundation of Fujian Province (2022J011269) and Fujian Provincial Key Laboratory of Functional Materials and Applications (No. fma2022005) . References M. Chen, S.C. Zhang, Z.G. Zou, S.L. Zhong, W.Q. Ling, J. Geng, F.A. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4090795","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":280375458,"identity":"635e4ede-be16-4c06-8899-e56ce3d91387","order_by":0,"name":"Jidong Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYHCChAM8QJIfymNsIFqLJEjpASK1MDCAtBgcIFaLbvuBhwfeVNyx23wjO036A4ON7IYDzM8e4NNidiYh4eCcM8+St505u03iAEOa8YYDbOYGeLUcSEg4zNt2ONnseC9Iy+HEDQd42CTwajn/AKLFuJkXpOU/EVpuQGyxM2AH23KAGC0PQH45nCBx5uxmizMGycYzD7OZEXBYTvKHNxWH7fln5G68UVFhJ9t3vPkZXi3ASEkAkYkNYA4oqJjxqwcC9gMg0p6gulEwCkbBKBi5AAD151Y/8oL2YgAAAABJRU5ErkJggg==","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jidong","middleName":"","lastName":"Ma","suffix":""},{"id":280375459,"identity":"3820ee70-55ee-4772-bfd4-f8dbc4e2069f","order_by":1,"name":"Xinya Gu","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xinya","middleName":"","lastName":"Gu","suffix":""},{"id":280375460,"identity":"5cd65648-7339-4504-9fd1-0e2413c0933b","order_by":2,"name":"Kai Du","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Kai","middleName":"","lastName":"Du","suffix":""},{"id":280375461,"identity":"53a28a06-edd5-45f7-930b-224d126808aa","order_by":3,"name":"Wenjun Zhou","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Wenjun","middleName":"","lastName":"Zhou","suffix":""},{"id":280375462,"identity":"318a110d-693b-4b9e-bedd-e57d0a1fa6ef","order_by":4,"name":"Jian Cui","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jian","middleName":"","lastName":"Cui","suffix":""},{"id":280375463,"identity":"1b4af443-00b3-45c2-a5b0-c288b575df5b","order_by":5,"name":"Siyong Gu","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Siyong","middleName":"","lastName":"Gu","suffix":""},{"id":280375464,"identity":"3325b039-7755-4706-9dd2-a8b75596cea8","order_by":6,"name":"Houan Zhang","email":"","orcid":"","institution":"Xiamen University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Houan","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2024-03-13 09:04:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4090795/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4090795/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52910522,"identity":"bfcca290-28b1-4e97-87cf-087a9a6c93fc","added_by":"auto","created_at":"2024-03-18 15:41:50","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":445418,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e XRD patterns of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. \u003cstrong\u003eb\u003c/strong\u003e Raman spectra of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e.\u003cstrong\u003e c\u003c/strong\u003e XPS full spectrum of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples. \u003cstrong\u003ed\u003c/strong\u003e XPS spectrum of Cu 2p in the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu sample. \u003cstrong\u003ee\u003c/strong\u003e XPS spectrum of V 2p\u003csub\u003e3/2\u003c/sub\u003e in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples.\u003cstrong\u003e f\u003c/strong\u003e XPS spectrum of O1s in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4090795/v1/945b29412db9cb6c30bdc963.jpg"},{"id":52910521,"identity":"cb5d0d45-e01e-41d0-bc7f-66daf717bee0","added_by":"auto","created_at":"2024-03-18 15:41:50","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1176886,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e HRTEM of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. \u003cstrong\u003eb\u003c/strong\u003e HRTEM of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu. \u003cstrong\u003ec\u003c/strong\u003e TEM of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu. \u003cstrong\u003ed-f \u003c/strong\u003eElemental distribution maps of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4090795/v1/e320a4e3362955a3937eacfe.jpg"},{"id":52911303,"identity":"6d1dbaf2-ccaf-499d-a07a-5f995751063b","added_by":"auto","created_at":"2024-03-18 15:49:50","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":460428,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e CV curves of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode at different scan rates. \u003cstrong\u003eb\u003c/strong\u003e Logarithmic plots of peak currents (log i) versus scan rates (log v) for the CV curves. \u003cstrong\u003ec\u003c/strong\u003e CV curves of the third cycle for V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrodes at a scan rate of 0.1 mV s\u003csup\u003e-1\u003c/sup\u003e and a potential range from 0.2 to 1.6 V. \u003cstrong\u003ed \u003c/strong\u003eCorresponding Nyquist plots of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrodes with the equivalent circuit insert. \u003cstrong\u003ee\u003c/strong\u003e Rate performance of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrodes. \u003cstrong\u003ef \u003c/strong\u003eCycling performance and coulombic efficiency of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrodes at a current density of 4 A g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4090795/v1/0db23ba0d35279191b623c4b.jpg"},{"id":53831009,"identity":"d544671e-a4a4-46b9-9991-452a0cbb8a7b","added_by":"auto","created_at":"2024-04-01 04:44:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":721732,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4090795/v1/ca66b96f-1828-4eae-b245-b8a16976e13f.pdf"},{"id":52910524,"identity":"0ae5ef44-062a-484c-abeb-5d46e3e0f6fb","added_by":"auto","created_at":"2024-03-18 15:41:50","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":533818,"visible":true,"origin":"","legend":"","description":"","filename":"SI.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4090795/v1/b7dc0b7ac593e33f73327556.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eStudy on Solution Combustion Synthesis and Electrochemical Performance of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu as Cathode Materials for Aqueous Zinc-Ion Batteries\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSince the 1990s, aqueous zinc-ion batteries (AZIBs) based on V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e have shown broad development prospects due to high specific capacity, cheap raw materials, and other advantages [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Like other insertion materials, this material also has a layered structure, which is advantageous for the intercalation and deintercalation of Zn ions. However, due to the poor conductivity and structural instability of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, it becomes a bottleneck restricting application [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In order to improve the electrochemical performance of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, metal ions doping can be employed to improve conductivity and stabilize its structure. Zheng et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] doped aluminum ions into hydrated vanadium pentoxide by a one-step hydrothermal method to improve the stability of the entire material by forming stable Al-O bonds. The high interlayer spacing (13.4 \u0026Aring;) of the material may be mainly caused by the electrostatic repulsion between n-trivalent aluminum and n-pentavalent vanadium, which is beneficial to the rapid diffusion of zinc ions. The formation of V\u003csup\u003e4+\u003c/sup\u003e and the introduction of oxygen vacancies are also conducive to improving the electrical conductivity of the material. This material has an initial capacity of 380 mAh g\u003csup\u003e-1\u003c/sup\u003e at 50 mA g\u003csup\u003e-1\u003c/sup\u003e. At a high current of 4 A g\u003csup\u003e-1\u003c/sup\u003e, the capacity of the material increased to 117% of its initial capacity after 200 cycles of activation, and the remaining capacity was still 107% of its initial capacity after 3000 cycles. Zhang et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] used a simple solid-state chemical method to synthesize rod-shaped copper doped V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. Cu doping not only increases its volume, but also introduces abundant oxygen vacancies in the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e lattice, which facilitates rapid electron and ion transport during charge and discharge processes. The rod-shaped Cu doped V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e shows a high discharge specific capacity of 293.1 mAh g\u003csup\u003e-1\u003c/sup\u003e, which has a high discharge specific capacity and good cycling performance. The common methods for synthesizing V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e include hydrothermal techniques, chemical vapor deposition, sol-gel method, soft template method, and supercritical solvent thermal reaction. However, these synthetic processes typically involve complex procedures, including long-term aging reactions, ethanol soaking processes, repeated washing and heating at different stages to obtain the final product [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Therefore, the development of a simple synthesis process with low-cost can improve its application in AZIBs.\u003c/p\u003e \u003cp\u003eIn this paper, V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu) electrode materials were synthesized in a one-step solution combustion synthesis method, and the morphology and structure of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu materials were compared. The effect of Cu\u003csup\u003e2+\u003c/sup\u003e doping on the structure and electrochemical performance of AZIBs electrode material was investigated. The Cu\u003csup\u003e2\u0026thinsp;+\u003c/sup\u003e\u0026thinsp;doping in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e material can significantly enhance the interlayer spacing, facilitating the passage of more zinc ions and improving the transfer efficiency of zinc ions. The increase in oxygen vacancy concentration and V\u003csup\u003e4\u0026thinsp;+\u003c/sup\u003e\u0026thinsp;ratio after doping provides the material with more active sites for zinc ion storage.\u003c/p\u003e"},{"header":"2. Results and Discussion","content":"\u003cp\u003eThe facile and low-cost synthesis process is schematically illustrated in Fig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea compares the XRD patterns of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples. From the figure, it can be seen that the comparative results between the prepared samples of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e standard diffraction card (JCPDS NO.41-1426) show that the synthesized materials have identical peak positions to the standard card. And no obvious impurity peaks are observed, which indicates that the synthesized samples have high purity and good crystallinity. The diffraction peaks of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e at approximately 15.4\u0026deg;, 20.3\u0026deg; and 26.2\u0026deg; correspond to the (200), (001) and (110) crystal planes, respectively. According to the Bragg equation, the calculated d-values for the (001) crystal plane of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e are 0.4384 nm and 0.4380 nm, respectively. This indicates that the introduction of Cu has a little change in the interlayer spacing of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb shows the Raman spectra of the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples, and Fig. S2 shows the crystal structure of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. It can be seen from the figure that oxygen atoms occupy four positions in a single [VO\u003csub\u003e5\u003c/sub\u003e] layer. The Raman peak at 995 cm\u003csup\u003e-1\u003c/sup\u003e is generated by the stretching vibration of the V\u0026thinsp;=\u0026thinsp;O\u003csub\u003e1\u003c/sub\u003e bond, while the peaks at 407 and 284 cm\u003csup\u003e-1\u003c/sup\u003e can be attributed to the bending vibration of the V\u0026thinsp;=\u0026thinsp;O\u003csub\u003e1\u003c/sub\u003e bond [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. The bending vibration peak of V-O\u003csub\u003e2\u003c/sub\u003e is located at 473 cm\u003csup\u003e-1\u003c/sup\u003e, and the stretching vibration peak of V-O\u003csub\u003e3\u003c/sub\u003e is located at 693 cm\u003csup\u003e-1\u003c/sup\u003e. The peaks at 524 and 308 cm\u003csup\u003e-1\u003c/sup\u003e are the stretching and bending vibrations of the V-O\u003csub\u003e4\u003c/sub\u003e bond, respectively [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Due to the weak van der Waals force between adjacent [VO\u003csub\u003e5\u003c/sub\u003e] layers, the external [VO\u003csub\u003e5\u003c/sub\u003e]-[VO\u003csub\u003e5\u003c/sub\u003e] vibration peaks appear at low wave numbers, specifically at 104, 147 and 199 cm\u003csup\u003e-1\u003c/sup\u003e [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Compared with V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples, the redshift of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu peak value and Raman spectral can be explained by lattice expansion, which leads to increased interatomic spacing and a relatively relaxed lattice. As a result, the vibration frequency is reduced. Consistent with the results of XRD analysis.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec, X-ray photoelectron spectroscopy (XPS) was employed to further determine the valence states of V, O and Cu elements in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed, the Cu 2p\u003csub\u003e3/2\u003c/sub\u003e and Cu 2p\u003csub\u003e1/2\u003c/sub\u003e peaks at 928.5 and 931.0 eV, respectively, are consistent with those observed in the literature for CuO [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e], which can prove the existence of Cu\u003csup\u003e2+\u003c/sup\u003e ions. Cu\u003csup\u003e2+\u003c/sup\u003e has a ionic radius of 73 pm, which is larger than that of 54 pm for V\u003csup\u003e5+\u003c/sup\u003e. Copper ions dopped into the lattice of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, which will cause an increase in the unit cell volume of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]. This is the same as the XRD analysis results. Peak analysis was performed on the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee). The V 2p\u003csub\u003e3/2\u003c/sub\u003e peak of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e is located at 516.3 eV (V\u003csup\u003e4+\u003c/sup\u003e) and 517.9 eV (V\u003csup\u003e5+\u003c/sup\u003e), with a V\u003csup\u003e5+\u003c/sup\u003e/V\u003csup\u003e4+\u003c/sup\u003e ratio of 1:0.05. For V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu, the ratio of V\u003csup\u003e5+\u003c/sup\u003e to V\u003csup\u003e4+\u003c/sup\u003e is 1:0.07. This indicates the presence of more low-valence vanadium in the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples. The increase in the peak area ratio of V\u003csup\u003e4+\u003c/sup\u003e indicates that the oxidation state of vanadium is lower, which may be due to the introduction of oxygen vacancies in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu. In order to maintain its electrical neutrality, the proportion of low-valence vanadium (V\u003csup\u003e4+\u003c/sup\u003e) increases [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e], which can enhance the electronic transition between V\u003csup\u003e4+\u003c/sup\u003e and V\u003csup\u003e5+\u003c/sup\u003e. Meanwhile, the conductivity of the electrode material is improved. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ef shows the O1s spectra of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples, with the OI peak at 530.3 eV and the OII peak at 531.8 eV [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. By comparing the integrated area ratios, it can be determined that V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu has 1.6% more oxygen vacancies than V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. Oxygen vacancies play a crucial role in facilitating the kinetics of ion diffusion. Their generation and movement create additional space for ion diffusion, thereby accelerating ion migration and enhancing ionic conductivity. Additionally, oxygen vacancies serve as favorable active sites for nucleation during phase transitions in energy storage processes, providing supplementary sites for the storage of zinc ions [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe SEM images of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples are shown in Fig. S3(a-b). It can be observed that undoped V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e exhibits a block-like aggregation with an average particle size of 200 nm. V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu is composed of numerous small plate-like structures arranged in a regular flake structure, with the average grain size of 100 nm for the tiny plate-like structures, so that the grain is refined. Grain refinement can increase the specific surface area of the material and enhance its electrochemical activity sites, which is conductive to improving the energy storage performance of the material [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. Fig. S3(c-d) show the TEM images of the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu samples, respectively. As measured by HRTEM in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea, the lattice fringe of the (110) plane of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e is 0.338 nm. In Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb, the lattice fringes of the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu sample shows an interplanar spacing of 0.342 nm, indicating that the introduction of Cu\u003csup\u003e2+\u003c/sup\u003e increases its spacing, which is consistent with the above analysis results. In order to more intuitively display the distribution of Cu in the sample, the element distribution diagram of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(c-f), from which it can be observed that the copper element is uniformly distributed throughout the sample.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, the electrochemical reaction kinetics of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu was studied by measuring CV test at different scan rates. As the scan rates increased from 0.2 mV s\u003csup\u003e-1\u003c/sup\u003e to 1.0 mV s\u003csup\u003e-1\u003c/sup\u003e, the oxidation and reduction peaks moved to higher and lower potential, respectively. According to the related b values of oxidation and reduction peaks are quantified according to the slope, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb. (The specific algorithm for calculating the \u003cem\u003eb\u003c/em\u003e-value is provided in the supplementary material). The average \u003cem\u003eb\u003c/em\u003e value of the peaks is about 0.6, indicating the presence of a diffusion-controlled Faradaic process and a capacitive process in the reaction. The curves show similar morphology at different scan rates, and the broadening of peaks in CV curves reflects the pseudocapacitive behavior, which is conducive to the rapid electrochemical reactions. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the second cycle CV curves of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu as electrode materials for zinc-ion batteries at a scan rate of 0.1 mV s\u003csup\u003e-1\u003c/sup\u003e, in the voltage range of 0.2\u0026ndash;1.6 V. V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu exhibits two major redox peaks around 1.11/0.84 V and 0.81/0.53 V, corresponding to the redox pairs of V\u003csup\u003e5+\u003c/sup\u003e/V\u003csup\u003e4+\u003c/sup\u003e and V\u003csup\u003e4+\u003c/sup\u003e/V\u003csup\u003e3+\u003c/sup\u003e, respectively [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. The redox of the shoulder is irreversible, indicating the occurrence of side reactions. In addition, as shown in the figure, between the positive and negative peaks of the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu, a higher peak current density is observed compared to V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, which indicates better redox activity in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. In the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode, the enhancement of charge transfer kinetics and involvement of active sites in electrochemical reactions were attributed to the increased proportion of V\u003csup\u003e4+\u003c/sup\u003e, leading to improved conductivity. Moreover, the heightened interlayer spacing in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu facilitates increased accommodation of zinc ions during the intercalation process, effectively diminishing the energy barrier in the diffusion mechanism.\u003c/p\u003e\n\u003cp\u003eAc impedance measurements of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e samples to investigate the influence of copper ions on the charge transfer process. The results of the EIS test analysis are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed. The illustration shows the simplified EIS fitting equivalent circuit, where \u003cem\u003eRct\u003c/em\u003e represents the charge transfer impedance, which mainly reflects the conductivity of electrons and ions; \u003cem\u003eRs\u003c/em\u003e represents the ohmic impedance; \u003cem\u003eCPE\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e represents the Warburg impedance, which reflects the diffusion of Zn\u003csup\u003e2+\u003c/sup\u003e in the electrode material; and \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e represents the double-layer capacitance. The impedance test of the three-electrode system consists of a semicircle in the high frequency region followed by a diagonal line in the low-frequency region matched with the charge transfer resistance (\u003cem\u003eRct\u003c/em\u003e) and the ion diffusion impedance, respectively. The fitting results of the two samples show that the charge transfer resistances (\u003cem\u003eRct\u003c/em\u003e) of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu are 29.04 Ω and 9.18 Ω, respectively. The V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode exhibits a smaller charge transfer resistance, which indicates that electrons and ions transfer faster at the interface between the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode and the electrolyte, mainly due to the addition of copper ions to improve the material' s conductivity and facilitate the transfer of electrons and ions at the liquid-solid interface [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe cycling performance of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrodes at current densities of 8 A g\u003csup\u003e-1\u003c/sup\u003e show in Fig. S4. At 8 A g\u003csup\u003e-1\u003c/sup\u003e, the maximum discharge specific capacities of the two electrode materials are 125 and 232 mAh g\u003csup\u003e-1\u003c/sup\u003e for V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu, respectively. After 1000 cycles, the capacity retention rates are 32% and 86% for V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu, respectively. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee shows the rate performance of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. The average discharge specific capacities of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e at the current of 1, 2, 4 and 8 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are 234, 219, 200 and 178 mAh g\u003csup\u003e-1\u003c/sup\u003e, respectively. V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu exhibits higher rate performance, with average discharge specific capacities of 271, 247, 214 and 199 mAh g\u003csup\u003e-1\u003c/sup\u003e at the current of 1, 2, 4 and 8 A g\u003csup\u003e-1\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef demonstrates that the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrode achieve efficiencies of over 100% in the initial several cycles. This can be attributed to the activation of the AZIBs at the beginning, which can be divided into the two steps listed below. As the charging and discharging progress, the electrolyte enters the interior of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. Simultaneously, the insertion/extraction of Zn\u003csup\u003e2+\u003c/sup\u003e and the phase transition of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e generate additional active sites. It can also be observed that the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu electrode exhibits better cycling capability compared to the V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e electrode. The specific capacity of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu remains around 300 mAh g\u003csup\u003e-1\u003c/sup\u003e at 4 A g\u003csup\u003e-1\u003c/sup\u003e. After 500 cycles, the discharge specific capacity is 285 mAh g\u003csup\u003e-1\u003c/sup\u003e (95.0% of the highest capacity), and the Coulombic efficiency is close to 100%. However, the specific capacity of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e remains around 180 mAh g\u003csup\u003e-1\u003c/sup\u003e at 4 A g\u003csup\u003e-1\u003c/sup\u003e, and it decreases to 139 mAh g\u003csup\u003e-1\u003c/sup\u003e (77.2% of the highest capacity) after 500 cycles at 4 A g\u003csup\u003e-1\u003c/sup\u003e. The enhanced discharge specific capacity and cycling stability of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu can be attributed to the increased interlayer spacing, improved electronic conductivity, and higher oxygen vacancy concentration.\u003c/p\u003e"},{"header":"3. Conclusions","content":"\u003cp\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu materials were synthesized in one step through a simple solution combustion synthesis method as the electrode material in AZIBs. The research results show that Cu\u003csup\u003e2+\u003c/sup\u003e doping in V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e materials can significantly enhance the layer spacing, facilitate the deintercalation of zinc ions. Moreover, the elevation in oxygen vacancies concentration and the proportion of V\u003csup\u003e4+\u003c/sup\u003e following doping enhances active sites for charge transfer kinetics and engagement in the electrochemical reaction, consequently leading to an increase in electrical conductivity. After 500 cycles at 4 A g\u003csup\u003e-1\u003c/sup\u003e, V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu still maintained a higher specific capacity of 285 mAh g\u003csup\u003e-1\u003c/sup\u003e (95.0% of the highest specific capacity), and the coulomb efficiency is close to 100%, surpassing V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e with a capacity of 139 mAh g\u003csup\u003e-1\u003c/sup\u003e (77.2% of the highest specific capacity).\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eXinya Gu (First Author): Conceptualization, Methodology, Software, Formal Analysis, Writing - Original Draft;Kai Du: Data Curation;Wenjun Zhou: Investigation;Jian Cui: Resources, Supervision;Siyong Gu: Software, ValidationHouan Zhang: Writing - Review \u0026amp; EditingJidong Ma (Corresponding Author): Conceptualization, Funding Acquisition, Resources, Supervision, Writing - Review \u0026amp; Editing.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work is financially supported by the Natural Science Foundation of Fujian Province (2022J011269) and Fujian Provincial Key Laboratory of Functional Materials and Applications (No. fma2022005) .\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eM. 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Compd. 863: 8. http://doi.org/10.1016/j.jallcom.2021.158761\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Aqueous Zinc-Ion Batteries, Copper Ions Doping, Solution Combustion Synthesis","lastPublishedDoi":"10.21203/rs.3.rs-4090795/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4090795/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAqueous zinc-ion batteries (AZIBs) are considered to be one of the most promising alternative energy sources due to their safety. Vanadium-based compounds, especially V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e cathode materials, have been widely studied due to the advantages of suitable working voltage windows and highly reversible redox reactions. However, the poor conductivity of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and its structural instability limit its application in AZIBs. In this paper, copper ions doped V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e was synthesized by a simple one-step solution combustion synthesis method to improve its structural stability and electrochemical performance. The modified material expanded the interlayer spacing and increased the ionic diffusion rate, and increased the concentration of low valence vanadium and oxygen vacancy, thereby increasing the electron mobility and promoting the electrochemical reaction, resulting in an enhanced discharge specific capacity of the material. Zinc-ion batteries assembled with V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e-Cu as the cathode material can provide a high discharge specific capacity of 300 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 4 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and have good cycling stability, with a capacity retention of 95% over 500 cycles.\u003c/p\u003e","manuscriptTitle":"Study on Solution Combustion Synthesis and Electrochemical Performance of V2O5-Cu as Cathode Materials for Aqueous Zinc-Ion Batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-18 15:41:45","doi":"10.21203/rs.3.rs-4090795/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"71aeb6ef-74ce-41e5-98fd-d775f719302b","owner":[],"postedDate":"March 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-01T04:44:31+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-18 15:41:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4090795","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4090795","identity":"rs-4090795","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}