a conductive binder for high-performance sn electrodes in ......pulverization of electrode and loss...

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Subscriber access provided by UNIVERSITY TOWN SHENZHEN ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Article A Conductive Binder for High-Performance Sn Electrodes in Lithium-ion Batteries Yan Zhao, Luyi Yang, Dong Liu, Jiangtao Hu, Lei Han, Zijian Wang, and Feng Pan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13692 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 24, 2017 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

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  • Subscriber access provided by UNIVERSITY TOWN SHENZHEN

    ACS Applied Materials & Interfaces is published by the American Chemical Society.1155 Sixteenth Street N.W., Washington, DC 20036Published by American Chemical Society. Copyright © American Chemical Society.However, no copyright claim is made to original U.S. Government works, or worksproduced by employees of any Commonwealth realm Crown government in the courseof their duties.

    Article

    A Conductive Binder for High-PerformanceSn Electrodes in Lithium-ion Batteries

    Yan Zhao, Luyi Yang, Dong Liu, Jiangtao Hu, Lei Han, Zijian Wang, and Feng PanACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13692 • Publication Date (Web): 21 Dec 2017

    Downloaded from http://pubs.acs.org on December 24, 2017

    Just Accepted

    “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are postedonline prior to technical editing, formatting for publication and author proofing. The American ChemicalSociety provides “Just Accepted” as a free service to the research community to expedite thedissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscriptsappear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have beenfully peer reviewed, but should not be considered the official version of record. They are accessible to allreaders and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offeredto authors. Therefore, the “Just Accepted” Web site may not include all articles that will be publishedin the journal. After a manuscript is technically edited and formatted, it will be removed from the “JustAccepted” Web site and published as an ASAP article. Note that technical editing may introduce minorchanges to the manuscript text and/or graphics which could affect content, and all legal disclaimersand ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errorsor consequences arising from the use of information contained in these “Just Accepted” manuscripts.

  • 1

    A Conductive Binder for High-Performance Sn

    Electrodes in Lithium-ion Batteries

    Yan Zhaoa, Luyi Yang

    a*, Dong Liu

    b, Jiangtao Hu

    a, Lei Han

    a, Zijian Wang

    a and Feng Pan

    a*

    a School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen

    518055, People’s Republic of China

    b BUCT-CWRU International Joint Laboratory, College of Energy, Beijing University of

    Chemical Technology, Beijing 100029, People’s Republic of China

    KEYWORDS

    Tin anode, Li-ion batteries, conductive binder, solid electrolyte interface, tin pulverization.

    ABSTRACT

    Tin (Sn) has been widely studied as a promising anode material for high energy and power

    density Li-ion batteries owing to its high specific capacity. In this work, a water-soluble

    conductive polymer is studied as a binder for nano-sized Sn anodes. Unlike conventional

    binders, this conductive polymer formed a conductive network, which maintained the

    mechanical integrity during the repeated charge and discharge processes despite the inevitable Sn

    particle pulverization. The resultant Sn anode without conductive additives showed a specific

    capacity of 593 mA h g-1

    after 600 cycles at the current density of 500 mA g-1

    , exhibiting better

    cycling stability as well as rate performance compared to the Sn anodes with conventional

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    binders. Furthermore, it was also found that the conductive binder enhanced the formation of

    stable solid electrolyte interphase (SEI) layers.

    1. INTRODUCTION

    Improving the energy density of lithium ion batteries (LIBs) is crucial to the development of

    electronic vehicles and consumer electronics.1–4

    The application of commercially available

    graphite anode is limited by its low theoretical capacity (372 mA h g-1

    ) and poor rate

    performance.5 These drawbacks have limited the application of LIBs in electric vehicles.

    Therefore, alternative anode materials with higher theoretical capacities are highly desired. As a

    non-toxic and abundant element, tin anode has attracted much attention because of its appealing

    theoretical capacity. In theory, one tin atom can store 4.4 lithium atoms to form Li22Sn5, resulting

    in a capacity of 992 mA h g-1

    .6 However, similar to silicon anode, tin anode suffers from massive

    volume change due to the large amount of lithium insertion and extraction, which leads to

    pulverization of electrode and loss of active material.7,8

    In order to improve the cycling stability of tin anode, some strategies have been implemented:

    (1) reduce the size of Sn particles to nanoscale to endure the high degree of volume change,6,9–11

    (2) introduce Sn into a conductive matrix (e.g. carbon) to cope with volume change and maintain

    the integrity of the electrode.12–17

    However, these mentioned methods emphasis on the design of

    Sn or Sn composite materials, the volume expansion is still inevitable. By using conductive

    binder instead of conventional binders such as polyacrylate acid (PAA),18

    poly(vinyldene

    difluoride) (PVDF)19

    and caboxymethyl cellulose (CMC)20

    , good electrical contact can be

    maintained despite the volume expansion.21

    It has been previously reported that the conductive

    binder significantly improved the electrochemical performance of Sn anodes.22,23

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    Sodium poly(9,9-bis(3-propanoate)fluorine) (PF-COONa) has been successfully applied in Si

    anodes as a conductive binder.24

    In the previous work, PF-COONa exhibited good mechanical

    adhesion, high electrolyte uptake and certain electric conductivity, and at the same time the polar

    groups of the binder could form strong chemical bonds with the hydroxyls on nanosized silicon

    particles. By employing it in Si anode, superior electrochemical performance was obtained,

    suggesting that PF-COONa is a promising binder for various anode materials that could be

    affected by the volume expansion.

    In this paper, the impact of the conductive binder on the electrochemical performance of Sn

    electrode is investigated. PF-COONa can firmly adhere to both Sn particles and Cu current

    collector to form an integrated structure. Above all, owing to the good conductivity of the binder,

    a carbon-free conductive network was formed. As a result, the electrode could still maintain

    good electric contact despite the significant volume changes after repeated cycling. The

    conductive binder can accommodate the huge volume change of tin particles as well as

    contribute to the formation of stable SEI films, hence greatly improved the electrochemical

    properties of Sn electrode. Using this conductive binder, the Sn electrode exhibited excellent

    long-term cycling capacity, stability as well as rate capability, which outperformed other

    conventional binders for pure Sn anode (see Table S1), indicating its great potential for high-

    capacity anode material with large volume changes.

    2. RESULTS AND DISSCUSSION

    Sn nanoparticles are used as-purchased without further treatments. Figure S1 displays the X-ray

    diffraction pattern of Sn nanoparticle with average size of 100 nm, where the major peaks can be

    well indexed to crystalline tin. The weak peaks of tetragonal SnO indicate the presence of a very

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    small amount of oxidized impurities. PF-COONa is prepared using the same method as described

    in the previous work. The infrared spectrum of Sn/PF-COONa in Figure S2 shows that different

    from the Si/PF-COONa electrodes, where the binder chemically bonds with Si particles, there is

    no chemical bond formed between Sn and PF-COONa. Therefore, the Sn particles are physically

    cohered by PF-COONa.The Sn/PF-COONa electrode consist of 80 wt% of Sn particles and 20

    wt% of PF-COONa. PF-COONa electrodes with different average Sn loading were prepared for

    different testing purposes.

    0 400 800 1200 16000.0

    0.5

    1.0

    1.5

    2.0

    2.5

    100 mA g-1

    1st

    2nd

    100th

    200th

    E/ V vs Li/Li+

    Specific capacity/ mA h g-1 0 50 100 150 200

    0

    300

    600

    900

    1200

    1500

    Specific capacity/ mA h g

    -1

    Cycle Number

    100 mA g-1

    0 200 400 6000

    300

    600

    900

    1200

    1500

    Specific capacity/ mA h g

    -1

    Cycle Number

    500 mA g-1

    (a) (b)

    (d)

    0 400 800 1200 16000.0

    0.5

    1.0

    1.5

    2.0

    2.5

    1st

    100th

    200th

    600th

    E/ V vs Li/Li+

    Specific capacity/ mA h g-1

    500 mA g-1(c)

    Figure 1. The 1st, 2nd, 100th and 200th cycle voltage profiles of the cells at the current densities

    of (a) 100 mA g-1

    and (c) 500 mA g-1

    ; cycling capacities (red-discharge, black-charge) of Sn/PF-

    COONa electrode at current densities of (b) 100 mA g-1

    and (d) 500 mA g-1

    . The loading of

    active material is approximately 0.6 mg cm-2

    .

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    Figure 1 shows The cycling performances of Sn/PFCOO-Na electrode (with Sn areal loading of

    approximately 0.6 mg cm-2

    ) at different cycling current densities. The voltage profiles of Sn/PF-

    COONa are shown in Figure 1a and Figure 1c, it can be seen that as the current density

    increased, very little overpotential due to DC polarization can be observed, which is an

    indication of good electronic contact in the electrode. For both cells, an irreversible discharge

    capacity of approximately 1500 mA h g-1

    was obtained at the first cycle, this phenomenon will be

    discussed in the following content. Figure 1b and Figure 1d demonstrate the cycling capacities

    of Sn/PF-COONa electrodes at current densities of 100 mA g-1

    and 500 mA g-1

    , respectively.

    After long cycling, stable capacities of 762 mA h g-1

    (200 cycles, 100 mA g-1

    ) and 593 mA h g-1

    (600 cycles, 500 mA g-1

    ) have been delivered. The stable capacities showed that the integrity of

    the electrodes was well maintained after long cycling, suggesting good adhesive property of PF-

    COONa for Sn nanoparticles. In addition, it can be observed that both cells exhibit excellent

    coulombic efficiency during long cycling, indicating good electrochemical stability of the binder.

    0 100 200 300 400 500

    0

    300

    600

    900

    1200

    1500

    Sn/AB/PVDF

    Sn/PF-COONa

    Specific capacity/ mA h g

    -1

    Cycle Number

    200 mA g-1

    Sn/AB/CMC-Na

    0 5 10 15 20 250

    300

    600

    900

    1200

    1500

    Sn/AB/PVDF

    100 mA g-11000 mA g

    -1500 mA g-1200 mA g-1

    Specific capacity/ mA h g

    -1

    Cycle Number

    100 mA g-1

    Sn/PF-COONa

    Sn/AB/CMC-Na

    40 μm

    (c)

    (a) (b)

    (d)

    40 μm

    (e)

    20 μm

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    Figure 2. Cycling performances (a) and rate performances (b) of Sn/PF-COONa, Sn/AB/CMC-

    Na and Sn/AB/PVDF electrode. SEM images of Sn/PF-COONa electrode (c), Sn/AB/CMC-Na

    electrode (d) and Sn/AB/PVDF electrode (e) after cycling. The loading of active material is

    approximately 1 mg cm-2

    .

    In order to prove the advantage of using this conductive binder over traditional binder,

    Sn/acetylene black (AB)/CMC-Na and Sn/AB/PVDF (8:1:1 in weight) electrodes were prepared

    and compared with Sn/PF-COONa electrode. In this case, all electrodes were prepared with

    higher loading of active material (approximately 1 mg cm-1

    ). From the long cycling

    performances shown in Figure 2a, it can be seen that the first cycle coulombic efficiency of

    Sn/PF-COONa is lower than that of Sn/AB/CMC-Na and Sn/AB/PVDF, which could be

    attributed to several factors: 1. the n-type doping of PF-COONa; 2. the formation of more stable

    SEI layer. After 50 cycles, the capacity of Sn/PF-COONa trended to become stable and a

    capacity of 518 mA h g-1

    was achieved after 500 cycles; in contrast, the capacity of

    Sn/AB/CMC-Na and Sn/AB/PVDF showed rapid declining trends after initial cycles, especially

    for PVDF, the capacity dropped to less than 100 mA h g-1

    after 10 cycles, which can be

    attributed to the swelling property of PVDF18,26

    . This wide difference indicates that PF-COONa

    has superior cycling stability over the traditional combination of AB/CMC-Na and AB/PVDF.

    Figure 2b compares the rate performances of Sn/PF-COONa, Sn/AB/CMC-Na and

    Sn/AB/PVDF electrodes. It can be seen that at 100 mA g-1

    , 200 mA g-1

    , 500 mA g-1

    and 1000

    mA g-1

    , similar capacity variation trends were exhibited by Sn/PF-COONa (1087, 1036, 883 and

    767 mA h g-1

    ) and Sn/AB/CMC-Na (892, 793, 679 and 592 mA h g-1

    ), indicating similar rate

    capabilities of two electrodes. Similar to the results from Figure 2a, Sn/AB/PVDF anode resulted

    in the poorest capacities at all currents. This result shows that without conductive additives, PF-

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    COONa not only acts as binder, but also exhibits excellent conductivity that could accommodate

    high-rate tests. Furthermore, the post-mortem SEM images (Figure 2c and Figure 2d) showed

    that after cycling the Sn/PF-COONa electrode demonstrated a smooth surface while a much

    more uneven surface is resulted from the Sn/AB/CMC-Na and Sn/AB/PVDF electrodes. For the

    first time, the conductive polymer has been found to promote the formation of stable SEI layer.

    This difference in surface topography could be attributed to that the electronic conductivity of

    PF-COONa facilitated the formation of a homogeneous and stable SEI layer on the Sn electrode.

    0 500 1000 1500 20000

    500

    1000

    1500

    2000

    1st cycle

    10th cycles

    20th cycles

    initial

    -Z'' (ohm)

    Z' (ohm)

    Sn/AB/CMC-Na

    0 500 1000 1500 2000 25000

    500

    1000

    1500

    2000

    2500

    1st cycle

    10th cycle

    20th cycle

    initial

    -Z'' (ohm)

    Z' (ohm)

    Sn/CNT/PF-COONa

    0 500 1000 1500 2000 2500

    500

    1000

    1500

    2000

    2500

    1st cycle

    10th cycle

    20th cycle

    initial

    -Z'' (ohm)

    Z' (ohm)

    Sn/CNT/PVDF

    (a)(a)(a)(a) (b)(b)(b)(b)

    (c)(c)(c)(c) (d)(d)(d)(d)

    0 50 100 1500

    400

    800

    1200

    Sn/CNT/PVDF

    Sn/CNT/CMC-Na

    Specific capacity/ mA h g

    -1

    Cycle Number

    200 mA h g-1

    Sn/CNT/PF-COONa

    Figure 3. Cycling performances of cells using different binders (a). Impedance spectra of cells

    using PF-COONa (b), CMC-Na (c) and PVDF (d) at different cycle numbers. The loading of

    active material is approximately 2.5 mg cm-2

    .

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    Furthermore, the cycling performance of Sn/carbon nanotube (CNT)/PF-COONa,

    Sn/CNT/CMC-Na and Sn/CNT/PVDF electrodes with higher Sn loading (2.5 mg cm-2

    ) was also

    tested. As shown in Figure 3, at the current density of 200 mA g-1

    , the capacity of Sn/CNT/PF-

    COONa was retained at around 555 mA h g-1

    after 150 cycles. In contrast, capacities of 254 mA

    h g-1

    and 87 mA h g-1

    were obtained from Sn/CNT/CMC-Na and Sn/CNT/PVDF respectively.

    Therefore, the electrochemical performance of Sn electrode can be further improved by adding

    conductive CNT. In addition, alternative current (AC) impedance spectroscopy was used to

    measure the impedance of the cells at different cycle number. As shown in Figure 3, three cells

    showed similar charge transfer impedance initially. However, as cycle number increased, the cell

    using PF-COONa exhibited much lower impedance compared to the cells using CMC-Na and

    PVDF. This result not only proved the formation of stable SEI layer, but also indicated that PF-

    COONa served as a conductive network in the electrode.

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    (a) (b)

    400 nm

    (c)

    200 nm 200 nm

    0.0 0.5 1.0 1.5 2.0 2.5-30

    -20

    -10

    0

    10

    20

    I/ µµ µµA

    E/ V vs Li/Li+

    Cycle 1

    Cycle 2

    Cycle 3

    Cycle 4

    (d)

    Figure 4. (a) Cyclic voltammogram of single-dispersed Sn/PF-COONa electrode at the scanning

    rate of 0.1 mV s-1

    ; SEM images of single-dispersed Sn/PF-COONa electrode (b) before and (c)

    after cycling; SEM image of highly pulverized Sn nano particles after cycling (d).

    To observe the morphology, change of Sn nanoparticles after cycling, single-dispersed electrodes

    were prepared where the Sn weight content is 12.5 %. Figure 4a shows the cyclic

    voltammogram (CV) of the single-dispersed electrode at the scan rate of 0.1 mV s-1

    . During the

    first cathodic sweep, two broad peaks at 1.5 V and 0.75 V vs Li/Li+ can be attributed to the n-

    type doping of the polyfluorene structure, which enhances the conductivity of PF-COONa;24

    while the cathodic peak and the at 0.3 V vs Li/Li+ can be attributed to both Sn reduction and the

    formation of the solid-electrolyte interface film. This result corresponds to the irreversible

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    discharge capacity during the first galvanostatic cycling. From the second cycle, three

    reproducible cathodic peaks can be found at 0.66 V, 0.62 V and 0.41 V vs Li/Li+, which can be

    explained by the formation of LixSn alloy.8 As for the anodic sweep, four oxidation peaks can be

    found at 0.45 V, 0.60 V, 0.72 V and 0.78 V vs Li/Li+, which can be assigned to the dealloying of

    LixSn.8 As a result, Sn particles underwent a full lithiation/delithiation process in this system.

    Owing to the low thickness of the electrode, the morphology of Sn particles can be observed

    using SEM. By comparing the SEM images of Sn/PF-COONa electrodes before and after cycling

    in Figure 4b and Figure 4c, it can be seen that after cycling, the surface of Sn nanoparticles has

    become much rougher, suggesting the start of pulverization. It is also observed for some particles,

    smaller subgrains are formed on the surface, indicating a higher degree of pulverization (see

    Figure 4d). Therefore, it can be inferred that after long-term galvanostatic cycling, highly

    pulverized nanoparticles will be inevitably resulted and the use of conductive binder is a

    practical solution.

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    Scheme 1. Schematic illustration of the Sn anodes in the processes of lithiation/delithiation using

    (upper) AB and non-conductive polymer and (lower) conductive binder.

    As shown in Scheme 1, when using the conventional binder/conductive material combination,

    the pulverized particles may will lose electronic contact with the conducting network, leading to

    capacity fading. By contrast, the conductive material will provide a conducting network, which

    facilitates electron transfer pathways for pulverized Sn particles, hence greatly reducing the

    capacity loss.

    3. CONCLUSION

    In summary, a water-soluble conductive polymer (PF-COONa) is investigated as a promising

    binder for nano-sized Sn anode. The Sn/PF-COONa electrodes demonstrated excellent reversible

    capacities of 762 mA g-1

    and 593 mA g-1

    at the current density of 100 mA h g-1

    and 500 mA h g-

    1after long cycling, respectively. By comparing the electrochemical performances of Sn electrode

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    using PF-COONa as binder and those using conventional binder, PF-COONa delivered

    significantly better cycling capacities and very similar rate capability. After examining the

    cycled electrodes, it can be seen that pulverization of Sn particles generally exists during the

    cycling. It is believed that the superior electrochemical performance is due to the conductive

    binder provides a conductive network, which will keep the pulverized Sn particles from losing

    electronic contact. Furthermore, the use of PF-COONa promotes the formation of stable SEI

    layer, which can be also attributed to its excellent performance. In this case, it is reasonable to

    speculate that this type of binder can generally boost the performance of anode materials with

    large volume changes. Therefore, this work not only demonstrates a polymeric binder for Sn

    anode with great commercialization potential, but also provide guidance on designing Sn-based

    electrodes.

    4. EXPERIMETAL PROCEDURES

    Preparation and characterization of materials:

    Preparation of 2,7-Dibromo-9,9-bis(3-tert-butyl propanoate)fluorine (M1): Firstly, 5 g

    (76.1mmol) of 2,7-dibromofluorene and 300mg (0.94 mmol) of tetrabutylammonium bromide

    (TBAB) were mixed in 35 mL toluene solution. Then 8 mL of 50 wt% NaOH aqueous solution

    was injected dropwise into the above solution under N2 atmosphere. After half an hour, 8 g (62.5

    mmol) of tert-butyl acrylate was slowly added. The solution was vigorously stirred at RT for 12h.

    After the reaction completed, the products were extracted by dichloromethane and washed with

    water three times. The organic solution was dried over aqueous Na2SO4 and further concentrated

    under reduced pressure. The crude product was purified by column chromatography using ethyl

    acetate: petroleum ether (1:50) in order to obtain a white solid (M1) with a 60% yield. 1H NMR

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    (400 M Hz, CDCl3), δ(ppm): 7.68-7.50 (m, 6H); 2.30 (t, 4H); 1.46 (t, 4H); 1.33 (s, 18H). 13

    C

    NMR (400 MHz, CDCl3), δ(ppm): 172.2, 150.1, 139.2, 131.2, 126.2, 122.2, 121.6, 80.5, 54.2,

    34.5, 29.9, 28.

    Preparation of 2,7-bis(4,4,5,5-tetrameth-yl-1,3,2-dioxaborolan-2-yl)-9,9-bis (3-tert- butyl

    propanoate)fluorine (M2): 6.912 g (12 mmol) of M1, 6.0 g (60 mmol) of anhydrous KOAc and

    6.4 g (25.2 mmol) of bis(pinacolato)diboron were added into 80 mL anhydrous DMF,

    subsequently 300 mg of Pd(dppf)2Cl2 was added quickly under a nitrogen atmosphere. The

    reaction was conducted in the dark condition at 90 °C for 10 h. The completed mixture was

    poured into deionized water and extracted with dichloromethane. The obtained organic solution

    was washed with deionized water seven times and then dried with aqueous MgSO4. After

    concentration under reduced pressure, the product was purified via column chromatography

    (ethyl acetate: hexane = 1: 20) to obtain a white product (M2) with a 75% yield. 1H NMR (400

    M Hz, CDCl3), δ(ppm): 7.84-7.72 (m, 6H); 2.39 (t, 4H); 1.44-1.39 (m, 28H); 1.31 (s, 18H). 13

    C

    NMR (400 MHz, CDCl3), δ(ppm): 172.8, 147.8, 143.8, 134.3, 129.0, 119.6, 83.8, 76.68, 53.5,

    34.4, 29.92, 28.0, 25.0.

    Synthesis of sodium Poly[9,9-bis(3-propanoate)fluorine)] (PF-COONa): A mixture containing

    1.741 g (3mmol) of M1 and 2.023 g (3 mmol) of M2, 35 mg Pd(PPh3)4, and several drops of

    Aliquat 336 was added to a flask. Then 12 mL 2 M Na2CO3 solution and 36 mL THF was added

    and the flask was degassed by three freeze–pump–thaw cycles. The mixture was heated to 85 oC

    for 72 h under Ar and after cooling down to RT, the crude product was precipitated from

    methanol and dried under vacuum. Then the obtained material was dissolved in 200 mL

    dichloromethane containing 15% trifluoroacetic acid. The mixture was stirred at room

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    temperature for 24h. And after the solvent removed under reduced pressure, 200 mL 0.5 M

    aqueous Na2CO3 solution was added, stirred for 6h and dialyzed against water for several times.

    The product was obtained via freeze-dry with a 75% yield. 1H NMR (400 M Hz, CDCl3) δ (ppm):

    7.92-7.76 (br, 6H); 2.45 (br, 4H); 1.45 (br, 4H).

    Fourier transform infrared (FTIR) spectroscopy was performed on a Nicolet Avatar 360

    spectrophotometer. The surface morphology of the electrodes was characterized by a scanning

    electron microscope (SEM, ZEISS Supra 55). The crystal structure of Sn nanoparticles was

    analyzed by XRD using a Bruker D8-Advantage powder diffractometer (Cu-Kradiation) with 2θ

    from 20° to 90° at 0.2 s per step.

    Electrochemical measurements:

    All electrodes in this work were prepared using casting method. Firstly, Sn nanoparticles

    (Aladdin, 99.99% metals basis ≤100nm) was dispersed in the 2% PF-COONa solution and

    stirred vigorously for 24 hours. Then slurry is casted onto the Cu foil current collector and dried

    naturally at room temperature. After cut into pieces, the electrodes are dried at 110 °C under

    vacuum for removing remained H2O content. The electrodes with PVDF, CMC-Na binders and

    CNT additives were prepared by using same procedures.

    All of coin cells were fabricated in an Ar-filled dry-box. Coin cells (2032) were used as to

    assemble half cells. Li foil (99.9%) was used as the negative electrode. 1.2 M LiPF6 in ethylene

    carbonate (EC): diethylene carbonate (DEC) (1:1 w/w) with additive of 10 wt% fluoroethylene

    carbonate (FEC) was used as electrolyte. Galvanostatic cycling was conducted in the voltage

    range between 0.01 V and 1 V at room temperature using a battery test system (Newell, China).

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    The CV measurements were performed at the scan rate of 0.1 mV s-1

    from 0.01 V to 2 V on an

    electrochemical workstation (CHI 604E, CH Instruments).

    ASSOCIATED CONTENT

    Supporting Information

    Performance comparison of PF-COONa with other reported binders; XRD pattern of Sn; infrared

    spectra of Sn, Sn/PF-COONa and PF-COONa; cycling capacities of Sn/SWCNT/PF-COONa

    electrode.

    AUTHOR INFORMATION

    Corresponding Author

    *E-mail: [email protected]

    *E-mail: [email protected]

    Author Contributions

    The manuscript was written through contributions of all authors. All authors have given approval

    to the final version of the manuscript.

    Notes

    The authors declare no competing financial interest.

    ACKNOWLEDGMENT

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    The research was financially supported by National Materials Genome Project

    (2016YFB0700600), Guangdong Innovation Team Project (No. 2013N080) and Shenzhen

    Science and Technology Research Grant (peacock plan KYPT20141016105435850, No.

    JCYJ20151015162256516, JCYJ20150729111733470).

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    Table of Contents:

    0 100 200 300 400 5000

    300

    600

    900

    Specific capacity/ mA h g

    -1

    Cycle Number

    Conventional binder

    AB

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