诛仙手游套装有属性吗:Journal of the Chilean Chemical Society - HYDROTHERMAL SYNTHESIS OF SILVER EMBEDDED LIFEPO4/C1

Journal of the Chilean Chemical Society

versión On-line ISSN0717-9707

J. Chil. Chem. Soc. v.55 n.2 Concepción jun. 2010

doi: 10.4067/S0717-97072010000200006 

J. Chil. Chem. Soc, 55, N° 2 (2010), págs.: 176-178

HYDROTHERMAL SYNTHESIS OF SILVER EMBEDDED LIFEPO₄/C¹

LIANLIANG WANG^a,b

^a Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, 10008, PR China
^b Graduate University of Chinese Academy of Sciences, Beijing, 100049, PR China

ABSTRACT

Silver embedded LiFePO₄/C were preparad by direct hydrothermal synthesis of Li₂CO₃ FeSO₄ and H₃PO₄ in mixed solution of Glucose and Ag(NH₃)₂OHSamples were characterized by XRD, SEM and galvanostaticcharge-discharge test. Results show that silver particles are locatedin the inner part of synthesized diamond-like and rectangularparticles. The reversible capacities of prepared samples are 141.3mAh g^-1 and no capacity loss are detected after 800 cycles at 1C.

Key words: Li-ionbatteries; LiFePO.; Hydrothermal; Silver

INTRODUCTION

Lithium iron phosphate (LiFePO₄)has received considerable attention as a cathode material forlithium ion batteries because of its low toxicity and good capacityretention [1-2]. The performance of LiFePO₄, however, islimited by its poor electronic conductivity and by the inability oflithium ions to diffuse easily through the LiFePO₄/FePO₄interface [3], which can result in a significant loss of capacity athigh discharge currents. Most of the research groups take measuresof preparing fine particles [4-7], coating the particles withelectrically conductive materials [7-9] and doping other atoms [10-11 ] to overcome these limitations and good electrochemicalperformance are achieved. L. N. Wang et al [7] developed a simple, onestep rheological phase reaction to synthesize LiFePO₄/Cpowders using PEG as the carbon source, and its electrochemicalperformance is satisfactory. In the paper, two approaches havedeveloped to overcome this problem. One is to prepare evenlydistributed diamond-like and rectangular LiFePO₄/Cparticles by hydrothermal method, the other is to embed silver particlesin the inner part of the particles in addition to coat LiFePO₄ particles with carbon. Li₂CO₃is developed as the lithium resources in the hydrothermal methodwhich is seldom and most of the previous papers take LiOH or CH₃COOLi which are unstable to air, and so it limited the industrialized application. C.H. Mi et al [8] try to prepare LiFePO₄/C+Agcomposite particles by Sol-gel and Co-precipitation method buthydrothermal method can prepare particles with special morphologyeasier by controlling different experimental parameters. On the otheraspect, wrapped silver particles and surface coated carbon improvethe conductivity of LiFePO₄ effectively.

EXPERIMENTAL

Silver embedded LiFePO₄/C were prepared by direct hydrothermal synthesis of Li₂CO₃, FeSO₄ and H₃PO₄ in the stoichiometric ratio of 1.5 : 1.0 : 1.0 and 1.5 : 1.0 : 3.0. First, Glucose was added into Ag(NH₃)₂OH solution to obtain silver particle along with stirring and Ag : LiFePO₄ = 1: 99(wt%). Second, FeSO. was mixed with Ascorbic acid in order to avoid Fe²⁺ was oxidized to Fe³⁺. Third, Li₂CO₃ and H₃PO₄were mixed with different molar ratios. At last, all solutions werequickly transferred to Parr reactor for up to lOh at 180 °C, and allthe reactions are under the protection of N₂ (99.9%purity). After the samples were cooled, the precipitates werefiltered and dried at 65 °C for 8h in vacuum oven. Dried samples werefired at 750 °C for 5h to decompose residual glucose and ascorbicacid.

In order totestify the existence of conducting silver particles, preparedsamples were dissolved in 11.6 mol/L HC1 solution, stirred andfiltered, residue of samples were obtained separately.

Samplesand residue were characterized by X-ray diffraction using aPANalytical X Pert PRO diffractometer with Cu Ka radiation. SEMobservation of samples were performed on a JEOL scanning electrodemicroscope(JSM-5610LV),

Electrodeswere made by dispersing 85wt.% active materials, 8wt.% carbon blackand 7wt.% polyvinylidenefiuoride(PVDF) binder in1-Methyl-2-pyrrolidone solvent to form a slurry. The slurry was thenspread uniformly on to a electrode slice and dried in the vacuum ovenat 65°C for at least 12h. the cells were assembled in an argónfilled glove-box(MBraun, Unilab, USA). The electrolyte was 1M LiPF₆in a mixture of ethylene carbonate(EC) and dimethylcarbonate(DMC)(1: 1 by volume). The cells were galvanostaticallycharged and discharged in the voltage range of 2.7-4.2V versus Li/Li⁺ counter electrode.

RESULTS AND DISCUSSION

Most of the reported papers about hydrothermal method took LiOH as Lithium resource and using Li₂CO₃ as starting materials was seldom. Reactions using Li₂CO₃ as starting materials in this paper could be described as followers:

Reaction (1) was difficult and not complete because partial products were LiH₂PO₄, and Li₂HPO₄. NH₃XH₂O was added in to mixed solution until pH value was 7 in reaction (2) in order to get LiFePO₄ grain easier. Obtained sample from reaction (1) was called sample 1 and the other one was sample 2.

XRD patterns of samples and residue of samples were shown in Fig.1 and 2.We performed a cell refinement to samples using MDI Jade 5.0software. Samples were indexed in the orthorhombic system with spacegroup Pmnb and cell parameters of sample 1 was, a = 6.017(1) ?, b =10.34(57) ?, c = 4.709(8) ? and V = 293.1(9) ?³, sample 2 was, a = 6.010(2) ?, b = 10.350(5) ?, c = 4.70(45) ? and V = 292.6(7) ?³. Fig.2showed XRD patterns of residue of samples. Ag and AgCl were detectedand AgCl should be come from the reaction of HC1 and minor silversalt contained in samples.

Morphology for prepared samples were observed on SEM, as shown in Fig.3,samples were uniformly distributed. Sample 1 was composed of diamondand slightly agglomerated particles, particle síze was 1-5μm.Particles of sample 2 was rectangular and agglomerated, grain sizewas 1-8μm.

Electrochemical performance of prepared samples were shown in Fig.4.Cycle performance of sample 1 are better than that of sample 2.After 1, 400, 500 and 800 cycles, the specific capacity of sample 1are 111.1, 122.5, 133.2 and 141.3 mAh g^-1 separately at lC(lC=150mA g^-1) ; after 1, 400 and 800 cycles, the specific capacity are 87.4, 89.6 and 80.7 mAh g^-1 separately at 15C. The specific capacity of sample 2 are 129.5,130.6 and 126.3 mAh g^-1 separately at 1C after 1, 200 and 300 cycles. Good cycle performance were achieved and it might because that LiFePO₄ grain grow up on the surface of reduced silver particles since Ag(NH₃)₂⁺ ions were firstly reduced to Ag under stirring and Wrapped silver particles enhance the conductivity of LiFePO₄.

CONCLUSIONS

Diamond-like and rectangular particles of silver embedded LiFePO₄/Cwere successfully synthesized through hydrothermal reactions. Atambient temperature, the discharge capacitíes of sample 1 are 141.3mAh g^-1, and no capacity loss were detected after 800 cyclesat 1C. Good electrochemical performance could be correlated withwrapped silver particles which might lead to the enhancement ofconductibility of individual particle.

 

ACKNOWLEDGEMENTS

Thiswork was supported by the Key Technologies Research and DevelopmentProgram of Qinghai Province, China (fund No. 2006-G-168).

 

REFERENCES

1.    A. K. Padhi, K. S. Nanjundaswamy, J. B. Goodenough, J. Electrochem. Soc. 144, 1188,(1997).        [ Links ]

2.    J. K. Kim, G. Cheruvally, J. W. Choi, J. Power Sources. 166, 211,(2007).        [ Links ]

3.    A. S. Andersson, J. O. Thomas, J. Power Sources. 97-98, 498, (2001).        [ Links ]

4.    Z. L. Wang, S. R. Su, C. Y. Yu, J. Power Sources. 184, 633, (2008).        [ Links ]

5.    B. Jin, H. B. Gu, Solid State Ionics. 178, 1907, (2008).        [ Links ]

6.    J. J. Chen, M. J. Vacchio, S.J. Wang, Solid State Ionics. 178, 1676, (2008).        [ Links ]

7.    L. N. Wang, X. C. Zhan, Z. G. Zhang, et al. J Alloys Compd. 456, 461, (2008).        [ Links ]

8.    C. H. Mi, Y. X. Cao, X. G. Zhang, Powder Technol. 181, 301, (2008).        [ Links ]

9.    R. Dominko, M. Gaberscek, J. Drofenik, J. Power Sources. 119-121, 770, (2003).        [ Links ]

10.  J. Barker, M. Y. Saidi, J.L. Swoyer, Solid-State Lett. 6, A53, (2003).        [ Links ]

11.   C.S. Ho, B. P. Sung, H. Jang, Electrochim. Acta 53, 7946, (2008).        [ Links ]

 

(Received: March 31,2009 - Accepted: January 25,2010)

* e-mail address: wlianliang@yahoo.com