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Nanocomposite LiFePO4·Li3V2(PO4)3/C synthesized by freeze-drying assisted sol-gel method and its magnetic and electrochemical properties

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  • ReceivedJul 11, 2017
  • AcceptedSep 11, 2017
  • PublishedOct 27, 2017

Abstract

Nano-sized LiFePO4·Li3V2(PO4)3/C was synthesized via a sol-gel route combining with freeze-drying. X-ray diffraction results show that this composite mainly consists of olivine LiFePO4 and monoclinic Li3V2(PO4)3 phases with small amounts of V-doped LiFePO4 and Fe-doped Li3V2(PO4)3. The magnetic properties of LiFePO4·Li3V2(PO4)3/C are significantly different from LiFePO4/C. Trace quantities of ferromagnetic impurities and Fe2P are verified in LiFePO4/C and LiFePO4·Li3V2(PO4)3/C by magnetic tests, respectively. LiFePO4·Li3V2(PO4)3/C possesses relatively better rate capacities and cyclic stabilities, especially at high charge-discharge rates. The initial discharge capacities are 136.4 and 130.0 mA h g−1, and the capacity retentions are more than 98% after 100 cycles at 2 C and 5 C, respectively, remarkably better than those of LiFePO4/C. The excellent electrochemical performances are ascribed to the mutual doping of V3+ and Fe2+, complementary advantages of LiFePO4 and Li3V2(PO4)3 phases, the residual high-ordered carbon and Fe2P with outstanding electric conductivity in the nanocomposite.


Funded by

the National Natural Science Foundation of China(21673051)

Guangdong Province Science & Technology Bureau(2014A010106029,2014B010106005,2016A010104015)

Guangzhou Science & Innovative Committee(201604030037)

the Youth Foundation of Guangdong University of Technology(252151038)

the link project of the National Natural Science Foundation of China and Guangdong Province(U1401246)

and the Science and Technology Program of Guangzhou City of China(201508030018)


Acknowledgment

This work was supported by the National Natural Science Foundation of China (21673051), Guangdong Province Science & Technology Bureau (2014A010106029, 2014B010106005 and 2016A010104015), Guangzhou Science & Innovative Committee (201604030037), the Youth Foundation of Guangdong University of Technology (252151038), the link project of the National Natural Science Foundation of China and Guangdong Province (U1401246), and the Science and Technology Program of Guangzhou City of China (201508030018).


Interest statement

The authors declare that they have no conflict of interest.


Contributions statement

Liu L designed the experiments and wrote the initial manuscript; Xiao W and Guo J performed the experiments with support from Liu L, Cui Y and Chen Y; Shi Z and Chou S guided the work. All authors contribute to analysis of the data and advice for the paper writing.


Author information

Liying Liu received her PhD degree in 2006 from Northeastern University. Then she joined Guangdong University of Technology as a lecturer until now. Meanwhile, she worked as a post-doctoral fellow in Mcnair Technology Co., Ltd. from 2008 to 2010, as a visiting fellow at University of Wollongong in Australia from 2016 to 2017. Her research focuses on energy storage materials for batteries.


Zhicong Shi is a professor at Guangdong University of Technology, where he presently serves as the Head of Department of New Energy Materials and Devices and the Director of Guangdong Engineering Centre for New Energy Materials and Devices. He received his PhD in physical chemistry from Xiamen University in 2005. His current research interests include novel materials for batteries, supercapacitors and fuel cells.


ShuLei Chou is a senior research fellow in ISEM at University of Wollongong (UOW). He obtained his Bachelor (1999) and Master degree (2004) in Nankai University, China. His PhD degree was received from UOW with the best thesis award in 2010. His research has been focused on energy storage materials for battery applications, especially on novel composite materials, new binders and new electrolytes for Li/Na batteries.


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  • Figure 1

    XRD (a) and Rietveld refinement results of LFP/C (b) and LFP·LVP/C (c), partial zoom of XRD diagrams (d).

  • Figure 2

    Raman spectra of LFP/C (a) and LFP·LVP/C (b).

  • Figure 3

    SEM images of LFP/C (a and b) and LFP·LVP/C (c and d); TEM (e) and HRTEM (f) of LFP·LVP/C.

  • Figure 4

    Magnetization curves of LFP/C (a) and LFP·LVP/C (b), the insets are temperature dependences of the reciprocal of magnetic susceptibilities of LFP/C and LFP·LVP/C, respectively.

  • Figure 5

    First and 100th charge-discharge curves of LFP/C (a and b) and LFP·LVP/C (c and d); cycle performances of LFP/C (e) and LFP·LVP/C (f).

  • Figure 6

    Nyquist plots of LFP/C and LFP·LVP/C at open circuit potential before charge-discharge tests (a) and after 100 cycles to the cut-off voltage of 2.5 V at 1 C rate (b).

  • Figure 7

    CV curves of LFP/C (a) and LFP·LVP/C (b) at varied scan rates; linear fittings of Ip vs. v1/2 of LFP/C (c) and LFP·LVP/C (d) corresponding to different redox peaks.

  • Table 1   Refined unit-cell parameters (, , : three lengths of unit cell; : volume of unit cell, : R-factor) for LFP/C and LFP·LVP/C

    Samples

    a (Å)

    b (Å)

    c (Å)

    V 3)

    Measured phase content (wt.%)

    Theoretical phase content (wt.%)

    R (%)

    LFP/C

    10.3280(2)

    6.0080(1)

    4.6951(1)

    291.3

    7.21

    LFP in LFP·LVP/C

    10.3995(0)

    6.0760(6)

    4.7281(4)

    298.8

    28.8(0.3)

    27.9

    8.93

    LVP in LFP·LVP/C

    8.5324(9)

    8.5900(5)

    11.9633(6)

    876.8

    71.2(0.5)

    72.1

  • Table 2   Values of calculated

    Peaks

    a

    b

    c

    d

    LFP/C

    1.62×10–12

    1.56×10–12

    LFP in LFP·LVP/C

    5.31×10–12

    2.02×10–11

    LVP in LFP·LVP/C

    6.32×10–11

    1.37×10–10

    8.67×10–10

    1.57×10–10

    5.29×10–10

    2.38×10–10

    LVP/C [32]

    2.34×10–11

    5.66×10–11

    8.62×10–11

    1.04×10–10

    1.02×10–10

    2.04×10–10

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