| LiTi2(PO4)3as superionic conductor with the NASICON structure is regarded as a promising candidate for aqueous lithium ion battery anode materials, due to its stable charge and discharge platform, excellent cycle stability and it de/intercalates Li ions at an appropriate potential. However LiTi2(PO4)3has intrinsic drawback of low electronic conductivity, which account for largely deterioration of anode material and especially on its electrochemical properties, and limit its practical use. The electrical conductivity of between LiTi2(PO>4)3particles by carbon coating increased, thus the electronic conductivity is enhanced apparently and electronic properties improved largely of LiTi2(PO4)3, especially has excellent cycle stability in aqueous solution electrolyte. Through the metal ion doping can change the LiTi2(PO4)3particle internal crystal structure and electrical conductivity.In this paper, the LiTi2(PO4)3, LiTi2(PO4)3/C and Li13Al0.3Ti1.7(PO4)3powder were systhesized by microwave assisted Sol-Gel method as anode materials. Then the optimal synthetic conditions were obtained and discussed. The samples were characterized by thermogravimetry and differential thermal analysis(TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), specific surface area analysis and Laser particle sizer analysis. Moreover, the charge and discharge platform, capacity and cycle performance of the samples were studied by AC impedance, cycle voltammetry and galvanostatic charge and discharge tests.The LiTi2(PO4)3with spinel structure were synthesized with lithium acetate, tetrabutyl titanate, phosphoric acid, absolute ethyl alcohol as raw materials. The effects of amount of raw materials, heat treatment temperature and soaking time on properties of sample were studied. Then, the synthesis mechanism was studied. The results show that pure phase sample LiTi2(PO4)3was synthesized when the mole ratio of reactants (lithium acetate:phosphoric acid:etrabutyl titanate) is1.05:2:3.5. When heat treatment temperature was600℃and soaking time was15min, the grain size of sample was42.25nm. The average volume size of samples was between l00nm and300nm.The charge and discharge platform of samples was very stable. When the sintering temperature was600℃, the first discharge capacity was 123.4mAh/g at0.1C.After10th cycle, the discharge capacity retained at109.3mAh/g. The ratio of capacity retention was89.3%. The tap density of LiTi2(PO4)3sample was2.1g/ml. With tap density increasing, the volume capacity is apparently enhanced and better electrochemical performance is obtained.The LiTi2(PO4)3/C with spinel structure were synthesized with lithium acetate, tetrabutyl titanate, phosphoric acid, absolute ethyl alcohol as raw materials, amylaceum and citric acid as carbon source respectinely. The effects of various carbon sources on properties of sample were studied. The results showed that when citric acid was used as carbon source, the obtained samples exhibit excellent electrochemical performance, while when amylaceum was used, the samples polarized seriously during charge-discharge process. Cyclic voltammetry and AC impendence measurement results found that the redox potential interval and charge transfer resistance of the sample was decreased, indicating the enhancement of electrode reaction reversibility and electrochemical performance. By studying the influence of carbon content on the performance of LiTi2(PO4)3, the result indicated that with the carbon content increasing, the quantity of amorphous substance increase which led to the intensity of characteristic peaks of XRD appreciably reduce. The particle sizes of the sample became small and the specific surface area increased with increasing the carbon content. The sample added by5%carbon has the largest surface area of14.5673m2/g, which showed an initial discharge capacity of130.6mAh/g under0.1C rate.The Li1.3Alo.3Ti17(PO4)3with spinel structure were synthesized with lithium acetate, tetrabutyl titanate, phosphoric acid, absolute ethyl alcohol and aluminium as raw materials. When heat treatment temperature was600℃, the pariticle size uniform distribution. By infrared absorption spectrum analysis, we can conclude that1395cm-1place absorption peaks for Al-0key telescopic vibration absorption peaks, showing that composite Al had been injected into chemical composition. |
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