Preparation And Electrochemical Properties Of TiP₂O₇ Cathode Materials

With the rapid development of science and technology,the demand for batteries is increasing,at the same time,the requirements of the battery is also getting higher and higher.Lithium ion batteries,as a rechargeable battery,has the advantages of high specific capacity,good cycle performance,long service life,environment-friendly and energy saving,which has become a indispensable part in the new energy development.TiP₂O₇ has the stable three-dimensional frame structure which can improved its high rate discharge performance and cycle performance.And phosphorus's resource rich,low price,small environmental pollution and other advantages,has aroused great interest of researchers.In this paper,the method of synthesizing TiP₂O₇ and its modification are discussed.At first,we optimize the synthesis conditions of TiP₂O₇.Based on the selection of calcination temperature and titanium source,different designs were carried out to study the effects of different calcination temperatures and titanium sources on the physical and electrochemical properties of TiP₂O₇ materials.The results show that TiP₂O₇ at 800 ? and Ti?C4H9O?4 as titanium source have the highest discharge specific capacity and optimal cycle stability.Secondly,different amounts of acetylene black and with different amounts of sucrose as carbon source was used to dope and coat TiP₂O₇ for preparing TiP₂O₇/C,and the influence on the structure and electrochemical properties of TiP₂O₇ materials was investigated.It was found that TiP₂O₇/C synthesized by different amounts doping and coating are pure phase.In the doping and coating range between 1%and 10%,the first discharge capacity increases with the increase of doping carbon content,with the increase of the coating amount increases first and then decreases.When the amount of doped carbon and carbon coating are 10%and 5%,TiP₂O₇/C has the best electrochemical performance and has the highest capacity retention rate after 50 cycles at the current density of 0.05 C.Finally,AC impedance method was used to investigate the characteristics of the TiP₂O₇ electrode interface with the electrode potential changing in the process of second loop ion intercalation with lithium and sodium as the negative electrode respectively.It was found that when the lithium was the negative electrode,Nyquist diagram of the TiP₂O₇ electrode with Li+ further deintercalation finally formed another semicircle in the low frequency region which represents the electrode/electrolytes interface charge transfer process;when the sodium was the negative electrode,the entire frequency range of Nyquist diagram of the TiP₂O₇ electrode during charging and discharging process is mainly composed of semicircle in the high-frequency region?HFS?and a slightly inclined line in the low-frequency region?LFL?.There is no obvious charge transfer resistance in charge discharge process,the reason is probably because of TiP₂O₇ in 800 ? which can cause the collapse of the structure of calcination material,reduces the void radius inside the material,and the Na+ radius is greater than Li+,resulting in Na+ difficult to intercalate/deintercalate in TiP₂O₇ material.