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Ultrathin conformal polycyclosiloxane films to improve silicon cycling stability

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Science Advances  19 Jul 2019:
Vol. 5, no. 7, eaaw4856
DOI: 10.1126/sciadv.aaw4856
  • Fig. 1 Surface characterization of pV4D4-coated and uncoated silicon electrodes.

    FTIR-ATR spectra of (A) the V4D4 monomer and (B) the pV4D4-coated thin film silicon electrodes. (C) Normalized XPS survey spectra and (D) normalized high-resolution spectra of uncoated and 25-nm pV4D4–coated silicon thin films. CPS, counts per second.

  • Fig. 2 Electrochemical characterization of pV4D4-coated silicon electrodes.

    (A) Lithiation capacity and (B) coulombic efficiency of pV4D4-coated silicon films cycled against lithium metal from 0.05 to 1.5 V at 25°C at a rate of C/10 for the first two cycles and then at 1C after. Electrolyte was 1.0 M LiPF6 in 1:1:1 EC:EMC:DMC. (C) First cycle voltage profiles and (D) first and (E) second cycle differential capacity curves of pV4D4-coated silicon electrodes. (F) Differential capacity curves of 45-nm pV4D4–coated silicon electrodes.

  • Fig. 3 Rate capability of pV4D4-coated and uncoated silicon electrodes.

    Lithiation capacity of pV4D4-coated silicon electrodes during a variable rate test. Cells were cycled four times at C/10, C/5, C/3, 1C, and lastly at C/10 each.

  • Fig. 4 EIS of pV4D4-coated and uncoated silicon electrodes.

    EIS spectra of silicon electrodes coated with (A) 0-nm, (B) 25-nm, and (C) 45-nm pV4D4 films. Three electrode potentiostatic EIS measurements were performed after the silicon electrodes had been lithiated to 50 mV. Silicon electrodes acted as the WE, while lithium metal foil acted as the CE and the RE. Electrolyte used was 1 M LiPF6 in 1:1:1 EC:EMC:DMC. Cell temperature was maintained at 25°C.

  • Fig. 5 Post-cycling surface characterization of pV4D4-coated and uncoated silicon electrodes.

    (A) FTIR-ATR and (B) XPS survey spectra of uncoated and 25-nm pV4D4–coated silicon electrodes after 30 cycles against lithium metal from 0.05 to 1.5 V at 25°C at 1C using 1.0 M LiPF6 in 1:1:1 EC:EMC:DMC as electrolyte. Electrodes were rinsed in DMC and dried at 80°C for 48 hours. (C) Carbon, (D) fluorine, and (E) lithium high-resolution scans of the cycled electrodes are shown. Scanning electron micrographs are shown for (F) as-deposited Si electrodes, (G) as-deposited 25-nm pV4D4–coated Si electrodes, (H) Si electrodes after 30 cycles, and (I) 25-nm pV4D4–coated Si electrodes after 30 cycles.

  • Table 1 Summary of initial and final cycling data for pV4D4-coated silicon electrodes.

    Average (de)lithiation capacity and average coulombic efficiency at cycles 1 and 100 for (un)coated silicon electrodes.

    Coating thickness (nm)Cycle 1Cycle 100
    Charge capacity
    (mAh g−1)
    Discharge capacity
    (mAh g−1)
    Coulombic efficiencyCharge capacity
    (mAh g−1)
    Discharge capacity
    (mAh g−1)
    Coulombic efficiency
    02705 ± 2044174 ± 27864.8 ± .6442 ± 92472 ± 9793.5 ± .2
    152491 ± 1073428 ± 22672.8 ± 1.7565 ± 12605 ± 1393.5 ± .1
    252685 ± 1053670 ± 13973.2 ± .8729 ± 46776 ± 4793.9 ± .4
    352632 ± 283720 ± 2870.7 ± .2482 ± 24516 ± 2793.4 ± .2
    4516859828333593.2

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaaw4856/DC1

    Fig. S1. FTIR of the V4D4 monomer and the 200-nm pV4D4 film.

    Fig. S2. Anomalous cycling behavior observed with thick (45 nm) pV4D4 films.

    Fig. S3. Micrograph of the uncoated copper foil.

    Table S1. Spectral reflectivity measurements of the pV4D4-coated silicon in various media.

    Table S2. XPS data for (un)cycled (un)coated silicon electrodes.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. FTIR of the V4D4 monomer and the 200-nm pV4D4 film.
    • Fig. S2. Anomalous cycling behavior observed with thick (45 nm) pV4D4 films.
    • Fig. S3. Micrograph of the uncoated copper foil.
    • Table S1. Spectral reflectivity measurements of the pV4D4-coated silicon in various media.
    • Table S2. XPS data for (un)cycled (un)coated silicon electrodes.

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