Preparation And Electrochemical Performances Of Potassium Titanium Phosphate

Potassium-ion batteries have good prospect in the field of large scale energy storage due to the low cost and abundant resources of potassium.Potassium titanium phosphate（KTi₂（PO₄）₃）is a new anode material for potassium-ion batteries with excellent structural stability,however,the low electrical conductivity greatly hinders its practical application.To address this problem,here,modified the KTi₂（PO₄）₃anode materials were prepared through the methods of carbon coating and constructing the composite with graphene.Furthermore,the two-dimensional transition metal carbon/nitride（MXene）was employed as highly conductive binder to optimize the KTi₂（PO₄）₃electrode.Finally,the KTi₂（PO₄）₃anode materials with good electrochemical performance were obtained.The main research results are as follows:（1）Carbon coated KTi₂（PO₄）₃ was prepared by one-step solvothermal method with perylene tetracarboxylic anhydride（PTCDA）as carbon source.The carbon coating layer can effectively inhibit the excessive growth of KTi₂（PO₄）₃grains and reduce the particle size,leading to the nano-scale KTi₂（PO₄）₃particles,which can provide massive active sites for K-ion storage.In addition,the carbon layer can form a highly conductive network and improve the electron transfer ability,leading to the improvement of the rate performance.As a result,the KTi₂（PO₄）₃with 6.4 wt%carbon coating shows a specific capacity of271.1 m Ah g^-1at 20 m A g^-1and 154.1 m Ah g^-1at 500 m A g^-1for potassium storage,a specific capacity of 53.6 m Ah g^-1can be maintained at 1A g^-1after 1000 cycles.Besides,as an anode material of lithium ion batteries,a reversible capacity of 585.5 m Ah g^-1could be obtained at 100m A g^-1,and after 1000 cycles,a specific capacity of 517.9 m Ah g^-1can be maintained and the capacity retention is about 88.3%.Even at a high current density of 5 A g^-1,the lithium storage capacity can still maintain286.1 m Ah g^-1.（2）The polydopamine coated KTi₂（PO₄）₃was synthesized by liquid-phase polymerization,and then a three-dimensional intermediate was constracted according to the hydrothermal reaction with graphene oxide.Further,the carbonization of polydopamine and the reduction of graphene oxide were realized by heating treatment.Finally,the KTP@C-r GO material was obtained.The three-dimensional structure effectively improved the electronic conductivity and ion diffusion.An initial potassium storage capacity of 235.3 m Ah g^-1is obtained,after the activation of five cycles,the capacity rises to 261.5 m Ah g^-1.After 70cycles,it still shows a specific capacity of 240.4 m Ah g^-1.At the same time,a specific capacity of 94.7 m Ah g^-1could be maintained after 1000cycles of at 1 A g^-1,which imply the good cycle performance of KTP@C-r GO.（3）The electrode was prepared by coating method,in which MXene as the conductive binder,KTi₂（PO₄）₃as the active material,Super-P as the conductive agent.Compared with the traditional PVDF or CMC binder,MXene has good conductivity,which will greatly improve the electrochemical performances.When the mass ratio of KTi₂（PO₄）₃,MXene and Super P is 7:1.5:1.5,a good rate performance was obtained,which is because that the existence of MXene can realize the rapid conduction of electrons on the plane,while the conductive agent Super P can realize the"point-to-point"transportation,which ensure the excelent electron conductivity of the whole electrode.As an anode for potassium ion batteries,the electrode delivered a capacity of 248.4 m Ah g^-1at 100m A g^-1.Even at a high current density of 2 A g^-1,the capacity can still maintain at 132.3 m Ah g^-1.At the same time,the electrode also shows good cycle performance,after 1000 cycles at 1 A g^-1,the specific capacity can still reach 153.8 m Ah g^-1,and the capacity rentention is about 95.4%.