| Pyrophosphate is one of the most promising anode materials at present.However,it has disadvantages such as poor electronic conductivity,volume expansion during cycling,low Coulombic efficiency,fast self-discharge,and rapid capacity decay.The preparation of pyrophosphates with high electrochemical activity and high capacity is one of the research hotspots in recent years.In this work,a vacancy-controlled approach was employed to improve the electrochemical activity of pyrophosphate anode materials.Taking titanium pyrophosphate,zinc pyrophosphate and manganese pyrophosphate as the research objects,the defects were introduced by different solvothermal times,different calcination atmospheres and different molar ratios,respectively,and modified as anode materials to improve the electrochemical performance of lithium and sodium ion batteries,the specific work is as follows:（1）The oxygen-deficient TiP2O7-y was prepared by solvothermal method.X-ray powder diffraction（XRD）analysis indicated that the solvothermal reaction time affects the concentration of oxygen vacancies in TiP2O7-y.Infrared spectroscopy（FT-IR）indicated that the presence of oxygen vacancies caused a blue-shift of the P-O bond.Electron paramagnetic resonance（EPR）and X-ray photoelectron spectroscopy（XPS）tests confirmed that the material contained oxygen vacancies.The TiP2O7-y prepared after solvothermal reaction for 18 h showed a discharge specific capacity of 828.4 mAh g-1 in the first cycle at a current density of 0.5 A g-1,and maintained a discharge capacity of 209.7 mAh g-1 at 5 A g-1.Oxygen vacancies not only enhance the electronic conductivity of TiP2O7-y but also increase the mobility of Li+。（2）Zn2P2O7-y was synthesized by solvothermal reaction and calcination treatment.Zn2P2O7-y with different oxygen vacancy concentrations was synthesized by calcination in different atmospheres,and the effect of different oxygen vacancy concentrations on the electrochemical performance of Zn2P2O7-y was investigated.EPR and XPS tests proved that the synthesized Zn2P2O7-y contained oxygen vacancies.Electrochemical tests show that Zn2P2O7-y modified by argon-hydrogen atmosphere has the best electrochemical performance.When the current density is 1 A g-1,the discharge specific capacity of Zn2P2O7-y is as high as 361.4 mAh g-1,while the discharge specific capacity of Zn2P2O7-y calcined in air is only 206.4 mAh g-1.The reason is mainly attributed to the loss of some oxygen atoms during calcination in a reducing atmosphere to generate a large number of oxygen vacancies,and the generation of oxygen vacancies increases Li+intercalation sites,thereby enhancing the electronic conductivity and capacity of Zn2P2O7-y.（3）Oxygen-deficient Mn2-xP2O7-y was synthesized by using manganese acetate tetrahydrate as the manganese source with different molar ratios and ammonium dihydrogen phosphate.EPR and XPS tests proved that the synthesized Mn2-xP2O7-y contained oxygen vacancies.Mn2-xP2O7-y introduces abundant oxygen vacancies and manganese vacancies,which can adjust the electronic structure and reduce the resistance of charge transport.At the same time,the modification of surface oxygen vacancies can reduce the activation energy required for the electrode reaction,while the vacancies of manganese ions and oxygen vacancies can provide additional reactive sites.When the current density is 1 A g-1,the discharge specific capacity of Mn1.93P2O7-y is 424.2 mAh g-1,while the discharge specific capacity of Mn2P2O7-y is only 176.1 mAh g-1 under the same conditions.The sodium-ion battery assembled with Mn2P2O7-y and sodium sheets also showed excellent electrochemical performance.When the current density was 0.1 A g-1,the discharge capacity of Mn1.93P2O7-y was 33.0 mAh g-1,while The discharge capacity of Mn2P2O7-y under the same conditions is only 26.9 mAh g-1。... |
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