Cobalt phosphide nanoparticles embedded in nitrogen- doped

Nano Res.

Electronic Supplementary Material

Cobalt phosphide nanoparticles embedded in nitrogen-doped carbon nanosheets: Promising anode materialwith high rate capability and long cycle life for sodium-ion batteries

Kai Zhang, Mihui Park, Jing Zhang, Gi-Hyeok Lee, Jeongyim Shin, and Yong-Mook Kang ()

Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 100-715, Republic of Korea

Supporting information to DOI 10.1007/s12274-017-1649-5

Figure S1 XRD pattern of the Co-MOF precursor.

Figure S2 XRD pattern of the Co@C composite. The broad peak at 22° corresponds to amorphous carbon, and the three sharp peaks at 44°, 51°, and 76° are indexed to standard JCPDS No. 15-806 which belongs to Co phase.

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Figure S3 EDS spectra of the CoP/carbon nanosheet composites prepared by one-step and two-step heat treatment, which are labelled as CoP-O and CoP-T, respectively.

Figure S4 Four-wire-resistor test results of CoP-O and CoP-T.

Conductivity is calculated by the following Eqs. (S1)−(S3) where ρ is the resistivity, κ is the conductivity, RES is

the resistance of the CoP disc, A is the cross-sectional area of the disc, and L is the thickness of the disc. The results

are listed in Table S3.

RES |(SAV-SBV)/Forcing current|= (S1)

RES A

L (S2)

1

(S3)

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Figure S5 EIS plots of pristine CoP-O and CoP-T electrodes.

Figure S6 SEM images of Co-MOF (a) and Co@C (b) composite.

Figure S7 TG and DSC curves of Co-MOF and the mixture of Co-MOF and P.


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The Co-MOF has an exothermic peak at 450 °C, however, two exothermic peaks are observed at 430 and

500 °C for Co-MOF + P mixture. The first peak corresponds to the reaction between the Co-MOF and P as well

as the sublimation of excessive P. The second peak refers to the carbonization process, and the carbonization

temperature increases because the Co-MOF is phosphorized.

Figure S8 EDS of the product obtained after annealing at 600 °C.

Figure S9 SEM images of the products obtained at various annealing temperatures and time.


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Figure S10 N2 adsorption–desorption isotherms of CoP-O (a) and CoP-T (b) samples.

Figure S11 TEM image of CoP-T composite.


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Figure S12 CV curves of CoP-O in the initial three cycles at a scan rate of 0.1 mV·s−1.

Figure S13 Charge–discharge curves (a) and cycling performance (b) of bare CNSs at 0.1 A·g−1.

Figure S14 Charge–discharge curves of CoP-O at 1st cycle when super P (conductive carbon) and PVDF binder were changed to acetylene black (AB) and sodium carboxymethylcellulose (NaCMC).

Figure S15 Charge–discharge curves of CoP-O at 50th, 100th, 150th, and 200th cycle.


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Figure S16 CV curves of CoP-O, CoP-T, and CoP-BM in a voltage range of 0.2–0.8 V during the oxidation process.

Scheme S1 Schematic illustration for different reaction mechanisms of CoP-O and CoP-BM.

Figure S17 Charge–discharge curves (a) and cycling performance (b) of CoP-BM at 0.1 A·g−1.

Figure S18 Charge–discharge curves (a) and cycling performance (b) of CoP-BM at 0.1 A·g−1.


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Figure S19 Rate capability comparison between this work and previous reports.

Figure S20 E(τ) vs. τ0.5 plots with the fitted line of CoP-O (a) and CoP-T (b).

Figure S21 Local amplification curves in the GITT profiles of CoP-O and CoP-T during a discharge ((a) and (b)) or charge ((c) and (d)) pulse based on Figs. 6(c) and 6(d).


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Figure S22 HRTEM image of CoP-O electrode after 500 cycles.

Table S1 ICP results of CoP-O and CoP-T samples

Co content (ppm) P content (ppm) CoP weight percent (wt.%) Atomic ratio of Co/P

CoP-O 374,287.17 200,946.59 58 1:1.02

CoP-T 378,390.85 200,722.78 58 1:0.99

Table S2 EA results of CoP-O and CoP-T samples

N weight percent (wt.%)

C weight percent (wt.%)

H weight percent (wt.%)

O weight percent (wt.%)

N weight percent in CNSs (wt.%)

CoP-O 6.9016 25.6540 0.6206 11.0075 15.6

CoP-T 6.3908 25.7310 0.8430 11.5194 14.4

Table S3 Comparison of ID/IG between previous reports and this work

ID/IG Ref.

MoS2/C nanocomposite 0.87–1.05 [S1]

CoS/C nanocomposite 1.04 [S2]

MnFe2O4@C nanofibers 1.15–1.18 [S3]

Li4Ti5O12/C nanocomposites 1.02–1.24 [S4]

Li3V2(PO4)3@C nanocomposite 0.93 [S5]

Sn4P3/RGO hybrids 1.42–1.50 [S6]

This work 1.42–1.43

Table S4 Four-wire-resistor test results of CoP-O and CoP-T samples

RES (Ω) A (m2) L (m) Resistivity (Ω·m) Conductivity (S·m−1)

CoP-O 2.6373 7.85 × 10−5 5.27 × 10−4 0.39 2.56

CoP-T 669.47 7.85 × 10−5 2.10 × 10−3 25 0.04


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References

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[S2] Zhou, L. M.; Zhang, K.; Sheng, J. Z.; An, Q. Y.; Tao, Z. L.; Kang, Y.-M.; Chen, J.; Mai, L. Q. Structural and chemical synergistic

effect of CoS nanoparticles and porous carbon nanorods for high-performance sodium storage. Nano Energy 2017, 35, 281–289.

[S3] Liu, Y. C.; Zhang, N.; Yu, C. M.; Jiao, L. F.; Chen, J. MnFe2O4@C nanofibers as high-performance anode for sodium-ion batteries.

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[S4] Zhu, Z. Q.; Cheng, F. Y.; Chen, J. Investigation of effects of carbon coating on the electrochemical performance of Li4Ti5O12/C

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[S5] Duan, W. C.; Hu, Z.; Zhang, K.; Cheng, F. Y.; Tao, Z. L.; Chen, J. Li3V2(PO4)3@C core-shell nanocomposite as a superior cathode

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[S6] Li, Q.; Li, Z. Q.; Zhang, Z. W.; Li, C. X.; Ma, J. Y.; Wang, C. X.; Ge, X. L.; Dong, S. H.; Yin, L. W. Low-temperature solution-

based phosphorization reaction route to Sn4P3/reduced graphene oxide nanohybrids as anodes for sodium ion batteries. Adv. Energy

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Cobalt phosphide nanoparticles embedded in nitrogen- doped