Preparation And Properties Of Layered And Tunneled Potassium Vanadate As Cathode Material For Calcium-ion Battery

Because lithium batteries have bottlenecks that cannot meet large-scale energy storage,there is an urgent need to explore low-cost,safer?no dendrite formation?and higher theoretical specific capacity multivalent positive ion batteries.Exploring a calcium ion material with high specific capacity and good cycle stability is of great significance to the development of calcium ion batteries.This article uses XRD,SEM,TEM,XPS and other characterization techniques,and uses electrochemical analysis and testing methods to systematically study the electrochemical performance of several potassium vanadate materials as calcium ion battery cathode materials in calcium nitrate electrolyte.First,the electrochemical performance of five potassium vanadate materials in 1M calcium nitrate electrolyte was systematically studied.Among them,the layered structure potassium vanadate K₂V₆O₁₆·2.7H₂O with the best comprehensive performance was obtained by hydrothermal synthesis.Layered structure potassium vanadate,the double-layered potassium vanadate K_0.5V₂O₅ has a relatively high initial capacity,and the discharge capacity can be close to 45 mAh g^-1 at a current density of 100 mA g^-1.The V₃O₈ layered potassium vanadate KV₃O₈ has no capacity attenuation after 200 cycles at a current density of 100 mA g^-1,the overall coulomb efficiency reaches 100%,but the maximum discharge capacity is only 17.9 mAh g^-1.Tunnel type potassium vanadate,?-Na_0.33V₂O₅ frame structure potassium vanadate K_0.25V₂O₅,200 cycles at a current density of 100 mA g^-1,the highest discharge capacity is only 18.7 mAh g^-1 and the capacity decline faster.With a large lattice spacing,potassium vanadate K₂V₈O₂₁,which has good performance as a positive electrode material for zinc ion batteries,underwent200 charge and discharge cycles at a current density of 100 mA g^-1,and its maximum discharge capacity was 5.7 mAh g^-1.Secondly,the electrochemical performance of layered structure potassium vanadate K₂V₆O₁₆·2.7H₂O as the positive electrode material of calcium ion battery in 5M calcium nitrate electrolyte at room temperature was determined.The potassium vanadate K₂V₆O₁₆·2.7H₂O electrode has a discharge capacity of up to 113.9 mAh g^-1 at a current density of 20 mA g^-1.At a current density of 50 mA g^-1,a discharge capacity of 94.0 mAh g^-1 was obtained,which maintained a capacity of 78.3%after 100 cycles.The cycle performance at a current density of 100 mA g^-1 can still achieve a discharge capacity of up to 60 mAh g^-1,and the capacity can still maintain 66.5%after 200 cycles,and its coulombic efficiency exceeds 99%.Analysis of the original state,the change of calcium ion intercalation and extraction state materials,through a series of characterization to verify its ability to embed and decalcify,a good description of the layered structure of potassium vanadate K₂V₆O₁₆·2.7H₂O after embedding and desorption can maintain a stable structure.