Preparation And Electrochemical Performance Of TiP₂O₇and LiTi₂（PO₄）₃Electrode Materials For Lithium Batteries

TiP₂O₇with the superstructure and LiTi₂（PO₄）₃with the NASICON structure havebeen attracted much attention because of their stable three-dimensional frameworkstructures. TiP₂O₇and LiTi₂（PO₄）₃have a wide range of applications in lithium ionbatteries due to their low cost, safety, non-pollution, good cycle stability, and otheradvantages. However, TiP₂O₇and LiTi₂（PO₄）₃have poor conductivity, particularly lowelectronic conductivity, which results in a serious phenomenon of polarization of thematerials in electrochemical performance and limits their use in the practical application.Currently, the researchers generally improve the electrical conductivity of the materialsby carbon coating and/or doping modification.To improve the electronic conductivity of TiP₂O₇and LiTi₂（PO₄）₃materials, wehave synthesized their carbon-coated composites by annealing their precursors,respectively. The TiP₂O₇/C precursor was prepared via a solvothermal route, and theLiTi₂（PO₄）₃/C precursor was prepared by a co-precipitation method, using phyticacid asthe phosphorus and carbon sources. At the same time, we prepared pure TiP₂O₇andLiTi₂（PO₄）₃materials by changing phosphorus source or anneal conditions. The sampleswere charaeterized with XRD, SEM, FT-IR, TEM, UV/Vis, and elemental analysistechniques and further tested in the role of electrode materials lithium ion batteries.Flower-like TiP₂O₇/C composites were synthesized by using tetrabutyl titanate ortitanium tetrachloride as the titanium source and phytic acid as the phosphorus andcarbon source through a solvothermal route followed by anneal in nitrogen ambient.The influence of the solvothermal reaction time and calcination temperature to thestructure and morphology was investigated. In order to prove the excellentelectrochemical properties of carbon-coated composite samples, pure TiP₂O₇materialswere also prepared for comparison. The results show that TiP₂O₇/C composites aresuperior to TiP₂O₇in electrochemical properties. The TiP₂O₇/C composite materialsgive an initial discharge capacity of119.6mAh/g at a rate of0.1C, which is98.8%ofthe therotical capacity. The initial coulombic efficiency is74.2%.LiTi₂（PO₄）₃/C composite materials were prepared by a co-precipitation methodfollowed by anneal, using tetrabutyl titanate as the titanium source, lithium hydroxide aslithium source, and phytic acid as a phosphorus and carbon source. The influence of theanneal temperature was investigated. In order to prove the excellent electrochemical properties of carbon-coated composite sample, pure LiTi₂（PO₄）₃material was alsoprepared for comparison. The results show that LiTi₂（PO₄）₃/C composites are superiorto pure LiTi₂（PO₄）₃in electrochemical properties. The LiTi₂（PO₄）₃/C compositematerials give an initial discharge capacity of133.8mAh/g at a rate of0.1C, which is96.7%of the therotical capacity. The initial coulombic efficiency is94.6%.The carbon-coated TiP₂O₇and LiTi₂（PO₄）₃materials presented here have greatpotentials in the fields of environment and energy.