Preparation And Lithium Storage Properties Of Zn-V-O/C Composites

Recent developments of portable electronic devices?PEDs?and medium-to large-scale applications including high-power electric vehicles?EVs?and smart grid energy technologies have increased intensively demands for LIBs with longer cycle life,higher power capacities and improved energy densities.It is well known that electrode materials,both anode and cathode,play decisive roles in LIB performances.Vanadium oxides?MVOs?have been drawing more and more attention,as their particular properties make them suitable for application as anode materials for LIBs.However,further enhancement in electrochemical performances of MVO electrodes is still essential to suit the urgent demand of practical requirements.In the first part,Zn₃V₂O₇?OH?2·2H₂O microspheres were prepared by using a water-in-oil?w/o?microemulsion method.Subsequently,PVP was coated onto the surface of the Zn₃V₂O₇?OH?2·2H₂O microspheres.Finally,the microspheres were annealed under Ar,during which time the PVP was transformed into carbon coating on the constituent nanoplates.At the same time,the unique hollow nanoplate structure was fabricated on the microspheres via PVP assisted heterogeneous contraction effect.when evaluated as the anode material for LIBs,the as-synthesized porous hollow nanoplate-assembled Zn₃V₃O₈/C showed excellent electrochemical performance.In the whole process of the first discharge,the specific discharge capacity of Zn₃V₃O₈/C microspheres reaches to 1022 mAh/g with a corresponding Coulombic efficiency?CE?of 58.8% at a current density of 400 m A/g.As the current rate increases from 100 to 200,400,800,and 1600 mA/g,the discharge capacity decreases slightly from 905,880,771,587 to 506 mAh/g,and even at the high rate of 3200 mA/g,the as-synthesized material can still maintain a stable reversible capacity of 380 mAh/g.In the second part,Zn–V precursor nanospheres can gradually in situ anchored on the GONPs to obtain Zn-V precursor/GONPs.Then,the as-prepared Zn-V precursor/GONPs are further calcined at 350 ? in Ar atmosphere to obtain crystalline Zn₃V₂O₈ with porous properties,at the same time,the GONPs are completely reduced into GNPs.Finally,the hybrid Zn₃V₂O₈/GNPs with a lot of pores within the nanoparticles have been prepared successfully.Benefiting from the above remarkable synergistic effects,as expected,the asprepared Zn₃V₂O₈/GNPs composite exhibits superior electrochemical performances as anode material when evaluated in LIBs.The Zn₃V₂O₈/GNPs-50 can deliver good rate capacity with attractive discharge capacities of 824,745,640,554 and 403 mAh/g when the specific currents are increased stepwise to 200,400,800,1600 and 3200 mA/g,respectively.