Study On Mxene-derived Materials As Cathode For Aqueous Zinc Ion Batteries

Vanadium oxide materials have been widely used as cathode for zinc ion batteries due to their high specific capacity.However,the lattice channels of most vanadium oxides are narrow,and they will suffer severe structural collapse after multiple cycles,resulting in poor reaction kinetics.The reaction kinetics can be improved by pre inserting metal ions or H₂O molecules into the V-O layer of vanadium oxide to expand the lattice channel and stabilize the structure.MXene has the characteristics of large specific surface area,many reactive sites,non toxicity and safety,especially the V valence state of V₂CT_x-MXene is low（+2,+3）,which can be obtained by hydrothermal oxidation of metal ions or H₂O intercalated vanadium oxides.In this paper,V₂CT_x-MXene was used as precursor to prepare H₂O molecular intercalated vanadium oxide（H₂V₃O₈）and Na+/H₂O molecular co intercalated sodium vanadate(Na₂V₆O₁₆·3H₂O).In addition,these two materials also have mixed valence state of V⁴⁺/V⁵⁺,so they have high electrochemical activity.The main research contents and results are as follows:1.Water pre-intercalated vanadium oxide nanorods（H₂V₃O₈）were synthesized by hydrothermal method using V₂CT_x-MXene as precursor and H₂O₂as oxidant.The layered structure of H₂V₃O₈has a large layer spacing（（200）surface layer spacing of 0.85nm）.When it is used as cathode for aqueous zinc ion batteries,it has good capacity(292 m Ah g^-1at 0.1 A g^-1),rate performance(133 m Ah g^-1at 2 A g^-1) and cycle stability(the capacity retention rate is 87.2%at 1000 cycles at 2 A g^-1)2.Na⁺and H₂O co-intercalated sodium vanadate nanorods(Na₂V₆O₁₆·3H₂O)were synthesized by using V₂CT_x-MXene as precursor,Na OH and H₂O₂as additives.The layered structure of Na₂V₆O₁₆·3H₂O has a large layer spacing（（100）surface layer spacing of 1.2nm）.When it is used as cathode for aqueous zinc ion batteries,it has good capacity(254.6 m Ah g^-1at 0.1 A g^-1)and rate performance 177.8 m Ah g^-1at 2 A g^-1).In addition,the effect of Na⁺on the stability of the cathode material was also studied.The results show that Na⁺can effectively inhibit its dissolution.The results show that the electrolyte system of 1M Zn SO₄+1M Na₂SO₄has the highest capacity retention rate(89.2%at 1000 cycles at 2 A g^-1).