Preparation And Energy Storage Performance Of Aqueous Zinc Ion Batteries Based On V₂O₅ Cathodes

Lithium ion batteries are the main energy storage device currently because of their high energy density,operating voltage and the good long-term cycle stability.However,the further large-scale application of lithium ion batteries is limited by the scarce reserves and uneven distribution of the lithium source and low electrolyte safety.A range of alternative energy storage devices have emerged,such as supercapacitors and multivalent metal ion batteries.Among them,aqueous zinc ion batteries have become one of the hottest spots for research due to the abundant zinc resources,neutral and non-toxic electrolyte,high capacity and good energy storage performance.One of the focal points in research on zinc ion batteries is to optimize the cathode materials for their limited capacity,narrow voltage window and poor cycling performance,which are decisive for the energy storage performance.All the popular cathode materials have their own advantages and disadvantages,so the corresponding optimization strategies have different focuses.In this paper,V₂O₅ with a high theoretical capacity and layered morphology is selected as the host material to accommodate the zinc ion(Zn²⁺)intercalation/deintercalation,and the energy storage performance is improved through two different synthesis strategies with the purpose of improving the long-term cycle stability while keeping the synthesis cost low.The studies are as follows:（1）V₂O₅·3H₂O with poly（3,4-ethylenedioxythiophene）:poly（styrene sulfonate）（PEDOT:PSS）as the additive（P-VO）was synthesized by a simple one-step hydrothermal method.The P-VO samples were tested using a series of morphological and structural characterizations.Electrochemical tests were then applied to investigate the energy storage performance and diffusion mechanism of the P-VO cathode.Finally,the structural changes of the P-VO cathode during the electrochemical reaction and the formation of by-products were investigated using the ex situ X-ray diffraction technique.The test results show that the intercalation/deintercalation efficiency of Zn²⁺in V₂O₅·3H₂O is improved thanks to the larger interlayer spacing and more O vacancies.As a result,the aqueous zinc ion battery based on a P-VO cathode delivers a capacity of up to 424.3 m Ah g^-1 at 0.2 A g^-1 and maintains 89.4%of the maximum capacity after2000 cycles at a current density of 5.0 A g^-1,demonstrating the good long-term cycle stability.（2）To further explore the cost-effective cathode material with a simpler system composition,V₂O₅·3H₂O with Zn²⁺pre-intercalated（Z-VO）was synthesized by a simple one-step hydrothermal method.The Z-VO samples were tested by a range of morphological and structural characterizations.The energy storage performance and diffusion mechanism of the batteries empolying Z-VO cathodes were then investigated by electrochemical methods.The results show that the capacitive response accounts for a high proportion in the battery reaction,and the pre-intercalated Zn²⁺acted as"pillars"widens the interlayer spacing of V₂O₅·3H₂O and increases the intercalation/deintercalation efficiency of Zn²⁺.As a result,the aqueous zinc ion battery with Z-VO as the cathode material provides a capacity of 424.5 m Ah g^-1 at 0.2 A g^-1and maintains 94.1%of its maximum capacity after 4000 cycles at a current density of5.0 A g^-1.Even when the current density increases to 20.0 A g^-1,the battery still achieves the maximum capacity of 150.0 m Ah g^-1 and 96.4%capacity retention after10000 cycles,demonstrating the good long cycle stability and rate performance.