Mechanism On Zn²⁺ Intercalation Into The Active Interface Of V₂O₅ Thin Films And Its Application In Electrochromic Devices

In recent years,the integration of electrochromic technology with other advanced technologies has created a strong impetus for the development of electrochromic technology.The dual-function electrochromic device integrating electrochromic and energy storage has attracted much attention.Vanadium pentoxide is currently regarded as an ideal candidate for the fusion of electrochromism and energy storage because of its a bipolar and multi-color electrochromic characteristic in electrochromism as well as a functional trait in cathode materials for energy storage batteries.Herein,a flexible ZPEM/V2O5/ITO electrochromic device and a rigid ITO/V2O5/ZGE/PB/ITO complementary electrochromic device were constructed using a quasi-solid freestanding Zn2+-based polymeric electrolyte membrane(ZPEM)electrolyte and a liquid Zn(CF3SO3)2-PC as the electrolyte,respectively.Both of these devices enjoy a electrochromic characteristic and a energy storage feature.The morphologies,microstructures,compositions,resistance transformation,pseudocapacitance characteristics,electrochromic and electrochemical properties of the V2O5 thin films based on Zn2+/V2Os active interface system are systematically investigated.Mechanism on Zn ion intercalation into V2O5 is demonstrated.The main research content is as follows:1.The V2O5 thin films were synthesized on ITO/PET and ITO/Glass substrates by electrochemical deposition.The as-deposited V2O5 thin films show a structural feature of nonapolycrystalline embedded amorphous matrix on the nanoscale in addition to a layered structue with a large interlayer distance of 1.299 nm,which can provide a free channel for zinc ion injection and extraction.Improved electrochromic cyclic stability of V2O5 thin films is mostly ascribed to a buffering effect of the nanocrystal-in-glass structue,which can accommodate the local stress concentraiton of the host V2O5 and alleviate the structural collapse of the host V2O5 induced by the zinc ion insertion/extraction.2.The results based on XRD patterns,Raman spectra and X-ray photoelectron spectroscopy analysis show that the interlayer distance of the V2O5 thin films decreases from 1.330 nm to 1.205 nm with decreasing the bleached/colored voltages of+2.0 V to-0.5 V,which results from the change of the interacion force between the layers induced by the zinc ion insertion/extraction.The Raman vibrational modes of(V2O2)n,V-O3 bonds,V2O5 phase and V2-O in the V2O5 thin films are respectively inactive and active in the colored and bleached states,which is ascribed to the reversible redox reactions accompanied with double injection/extraction of zinc ions/electrons.The content of Vs+component increases from 4.29%to 90.40%with the increase of the applied voltages from-0.5 V to+2.0 V,and accordingly V4+and V3+component decreases.The reversible redox reaction of V4+and V5+at Zn2+/V2O5 active interface is demonstrated.3.The Zn2+/V2O5 system shows a typical pseudocapacitive behavior and a characterisitc of the dominance of the capacitive charge in the total capacitance.Impressively,highly reversible multi-electrochromism among greenish blue,yellowish green,greenish yellow,faint yellow,yellowish orange and reddish orange is observed in the V2O5 thin films.Also,a high optical transmittance modulation(?T=67.01%)and a highest transmittance of up to 94.86%is exhibited.Moreover,a good performance with a fast colored/bleached time of 20.94/34.35 s and a high coloration efficiency of 28.57 cm2C-1 is obtained by in situ time-dependent transmittance spectra.Such excellent electrochromic properties is origined from the large interlayer spacing and the buffering effect of amorphous phase in V2O5,the strong electrostatic interactions between Zn2+and V2O5 alleviates the structural collapse of the V2O5 thin film,and a water which plays a role of potential lubrication in the migration of Zn2+through the V2O5 films4.The V2O5 single layer and SnO2/V2O5 bilayer electrodes are used to analyze electrochromic and electrochemical properties by introducing the SnO2 interfacial layer.The addition of SnO2 interfacial layer can improve the diffusion and transport capacity of Zn2+at the V2O5 active interface,optical modulation(up to 84%)and coloration efficiency(from 64.36 cm2 C-1 to 117.35 m2 C-1).5.A flexible ZPEM/V2O5/ITO electrochromic device and a rigid ITO/VN2O5/ZGE/PB/ITO complementary electrochromic device were respectively assembled via a direct bonding method and a vacuum infusion method.The flexible ZPEM/V2O5/ITO electrochromic device manifests a five multi-electrochromism,a high optical transmittance modulation(?T=57.88%)and a highest transmittance of up to 71.63%.In addition,the device enjoys a high performance with a short colored/bleached time of 35.48 s/32.52 s,a high coloration efficiency of 36.91 cm2C-1 and a high capacitance retention ratio decayed to 82.35%of the initial state after 2000 charge and discharge cycles.Moreover,the device shows excellent energy storage characteristics such as a maximum energy density of 12.54?Wh cm-2,a maximum specific capacitance of 51?F cm-2 and a typical pseudocapacitive behavior.The electrochromic performance of the ITO/V2O5/ZGE/PB/ITO complementary electrochromic devices can be improved by introducing the SnO2 interfacial layer.The open circuit voltage of the two types of fully bleached(+2.0 V)devices is measured to be ~1.60 V,and a couple of the devices in series can light up a 3.0-V-rated light-emitting diode(LED).These results demonstrate that the electrochromic devices based on Zn2+/V2O5 system possess a dual-function of electrochromism and energy storage.