Research On Vanadium Oxide/Ti₃C₂T_x Compsites In Aqueous Zinc-ion Batteries

With the continuous consumption of non-renewable sources,energy scarcity has become one of the major problems in the sustainable development of human society.The exploitation and fabrication of safe,low-cost and economical rechargeable batteries are quite urgent for the storage of renewable sources such as wind and solar energy.Rechargeable aqueous zinc-ion batteries（ZIBs）are attracting more and more attention since zinc anode displays high theoretical capacity,safety in the water,and low cost.Vanadium oxides are widely used as ZIBs cathode materials due to their large theoretical capacity and low voltage window.Based on the above points,there are four kinds of materials including Ni_0.22V₂O₅·n H₂O,Ni_0.22V₂O₅·n H₂O/Ti₃C₂T_xnanocomposites,NH₄V₃O₈and NH₄V₃O₈/Ti₃C₂T_xnanocomposites were prepared as ZIBs cathode materials.The main research contents of this paper are as follows:（1）Ni_0.22V₂O₅·n H₂O nanomaterials were prepared by a one-step hydrothermal method.The structure and morphology of Ni_0.22V₂O₅·n H₂O were characterized by material testing method.Nanomaterials were used as cathode materials for ZIBs,and their electrochemical properties were tested.The state of the electrode during the electrochemical process was further characterized by in-situ XRD and ex-situ XRD testing methods.（2）In order to further explore the possibility of improving the charge-discharge specific capacity of Ni_0.22V₂O₅·n H₂O,Ni_0.22V₂O₅·n H₂O/Ti₃C₂T_xnanocomposites were prepared by a one-step hydrothermal method.The prepared material was used as an electrode to further test whether the charge-discharge specific capacity of the electrode material could be improved after MXene compounding.（3）NH₄V₃O₈nanomaterials were prepared by ultrasonic intercalation method for the first time,and the structure and morphology of the prepared materials were characterized,and the electrochemical properties were also tested as ZIBs cathode.（4）In order to further improve the electrochemical properties of NH₄V₃O₈nanomaterials,NH₄V₃O₈/Ti₃C₂T_xnanocomposite materials were prepared by ultrasonic intercalation method for the first time,and the structure and morphology of the prepared materials were characterized,and the electrochemical properties were also analyzed.The results obtained in this paper are as follows:（1）Ni_0.22V₂O₅·n H₂O（Ni VO）has a typical layered structure.Ni VO has a nanoribbon morphology with a width of less than one hundred nanometers and a length of several hundred nanometers.（2）At a current density of 0.2 A g^-1,the discharge specific capacity of Ni VO reaches 296.7m Ah g^-1.At a current of 5 A g^-1,the capacity is still 168.7 m Ah g^-1after 5000 cycles.（3）The electrode states during the electrochemical process of Ni VO were tested by in-situ XRD and ex-situ XRD.The interplanar spacing of the Ni VO electrode gradually decreased during the discharge process,and then returned to the original position during the charging process.The reversible change in the interplanar spacing indicates that the electrode has good electrochemical stability.（4）The interplanar spacing of the Ni_0.22V₂O₅·n H₂O/Ti₃C₂T_xnanocomposites increased to different degrees,and the interplanar spacing of Ni VO-T3 increased to 0.104 nm.（5）The Ni VO-T3 nanocomposite exhibits superior performance than Ni VO in terms of charge-discharge capacity.The initial discharge capacity is 367.8 m Ah g^-1,and the maximum discharge specific capacity is 388 m Ah g^-1.The capacity decay is 26.8m Ah g^-1in the first 30 cycles,and the capacity decay rate is 7.2%.（6）NH₄V₃O₈material has excellent electrochemical performance,and the initial discharge capacity is 311.7m Ah g^-1.The discharge capacity was 226.7m Ah g^-1after 1000 cycles,and the capacity retention rate was 72.7%.However,the cycle stability is not satisfactory,and the decay is fast.After 2000 cycles,the discharge capacity of the electrode is207.3m Ah g^-1,and the capacity retention rate at this time is 66.6%.（7）The NH₄V₃O₈-Ti₃C₂T_xcomposite（NH₄V₃O₈-T）is a two-dimensional nanosheet material with a length of 100 nanometers and a thickness of about 73 nanometers.NH₄V₃O₈-T exhibits ultra-high discharge specific capacity and excellent cycle stability when used as electrode material.At a current density of 0.2A g^-1,the discharge specific capacity can be as high as 410m Ah g^-1.The specific capacity of the NH₄V₃O₈-T electrode is389.4m Ah g^-1after 2000 cycles,with a decay of 21m Ah g^-1,and the capacity retention rate is 94%.