Intercalation Pseudocapacitance in Ultrathin VOPO4 Nanosheets ...
Supporting Information for
Intercalation Pseudocapacitance in Ultrathin VOPO4 Nanosheets: towards High-Rate Alkali-Ion Based Electrochemical Energy Storage Yue Zhu,† Lele Peng,† Dahong Chen, and Guihua Yu* Materials Science and Engineering Program, Department of Mechanical Engineering, The University of Texas at Austin, TX, 78712, USA *Correspondence should be addressed: [email protected] †
These authors contributed equally
Experimental Section Sample preparation: Bulk VOPO4·2H2O chunks were synthesized according to previous literature.1,2 Briefly, a mixture of V2O5 (4.8 g), H3PO4 (85%, 26.6 ml) and H2O (115.4 ml) was refluxed at 110 °C for 16 h. The resulting yellow precipitate was collected by centrifugation, washed several times with water and acetone, then dried in oven at 80 °C. To obtain exfoliated VOPO4 nanosheets, bulk VOPO4·2H2O chunks were first ground to approximately 1 µm in size then dispersed in 2-propanol with concentration about 2 mg/mL. The yellow dispersion was ultrasonicated in water for 30 min, during which color of the dispersion became faded, indicating successful formation of VOPO4 nanosheets. Cell assembly: The VOPO4 nanosheets electrode was prepared by adding Super P carbon and sodium carboxymethyl cellulose (CMC) directly into aforementioned 2-propanol dispersion after ultrasonication (weight ratio of VOPO4: Super P: CMC = 80: 15: 5). While heated to remove excess 2-propanol, the mixture was thoroughly mixed in Thinky centrifugal mixer to form a homogenous slurry, which was then casted on aluminium foil and dried in vacuum at 115 °C for 12 hrs. The bulk VOPO4·2H2O electrode was prepared by adding ground chunks, Super P carbon in CMC aqueous solution (the same weight ratio as nanosheets electrode), followed by similar mixing, casting and drying procedures. The typical mass loading was about 1.0 mg. CR2032 coin cells were assembled inside an Ar-filled glove box using metallic Li/Na as anode. For Li cells, Celgard 2500 was used as the separator, and LiPF6 in 1:1:1 ethylene carbonate, diethyl carbonate and dimethyl carbonate was used as the electrolyte. For Na cells, Waltman glassy fiber was used as the
separator, and 1 M NaClO4 dissolved in propylene carbonate with 2% fluoroethylene carbonate additive was used as the electrolyte. Materials characterization: X-ray powder diffraction patterns were performed on a Rigaku MiniFlex 600 equipped with Cu Kα radiation. SEM/STEM and TEM observations were carried out on a Hitachi scanning electron microspcope (S-5500) and JEOL transmission electron microscope (2010F), respectively. Electrochemical characterization was performed on LANHE battery cycler (CT2001A) and Bio-logic potentiostat (VMP3). All the coin cells were first charged/discharged at 0.1 C once before further tests.
Figure S1. Additional SEM/STEM images of ultrathin free standing VOPO4 nanosheets. a) SEM image showing one single nanosheet. b) STEM image showing several nanosheets.
Figure S2. Comparison of electrochemical stability in lithium storage devices between electrodes made from bulk chunks (black) and nanosheets (red), both were tested at 0.1 C rate.
Figure S3. Cyclic voltammetric profile of VOPO4 for lithium storage device at scan rate of 0.02 mV/s.
Figure S4. Charge/discharge profiles of the VOPO4 nanosheets electrode in lithium storage device at various current rates from 0.1 C to 10 C.
Figure S5. Kinetics analysis of the electrochemical behavior towards Na+ for the VOPO4 nanosheets electrode. a) CV curves at various scan rates, from 0.02 to 20 mV/s. b) Determination of the b-value using the relationship between peak current and scan rate. c) Separation of the capacitive and diffusion currents at a scan rate of 10 mV/s. d) Contribution ratio of the capacitive and diffusion-controlled charge at various scan rates.
Figure S6. Rate capability of sodium-ion cell made from bulk chunks at the C rate ranging from 0.1~10 C. After 10 C, the cell cannot go back to 0.1 C.
Figure S7. Top-view SEM images of VOPO4 nanosheets electrodes after 500 cycles at 5 C rate. a) In lithium storage device, morphology of VOPO4 nanosheets remained intact and the surface was smooth and clean. b) In sodium storage device, the surface of VOPO4 nanosheets became rather rough.
Figure S8. Top-view SEM image of VOPO4 nanosheets electrode before cycling test. Notice the nanosheet morphology remained intact during the electrode preparation.
References 1. Tietze, H. Aust. J. Chem. 1981, 34, 2035−2038. 2. Wu, C.; Lu, X.; Peng, L.; Xu, K.; Peng, X., Huang, J.; Yu, G.; Xie, Y. Nat. Commun. 2013, 4, 2431.
Intercalation Pseudocapacitance in Ultrathin VOPO4 Nanosheets: towards High-Rate Alkali-Ion Based Electrochemical Energy Storage Yue Zhu,† Lele Peng,† Dahong Chen, and Guihua Yu* Materials Science and Engineering Program, Department of Mechanical Engineering, The University of Texas at Austin, TX, 78712, USA *Correspondence should be addressed: [email protected] †
These authors contributed equally
Experimental Section Sample preparation: Bulk VOPO4·2H2O chunks were synthesized according to previous literature.1,2 Briefly, a mixture of V2O5 (4.8 g), H3PO4 (85%, 26.6 ml) and H2O (115.4 ml) was refluxed at 110 °C for 16 h. The resulting yellow precipitate was collected by centrifugation, washed several times with water and acetone, then dried in oven at 80 °C. To obtain exfoliated VOPO4 nanosheets, bulk VOPO4·2H2O chunks were first ground to approximately 1 µm in size then dispersed in 2-propanol with concentration about 2 mg/mL. The yellow dispersion was ultrasonicated in water for 30 min, during which color of the dispersion became faded, indicating successful formation of VOPO4 nanosheets. Cell assembly: The VOPO4 nanosheets electrode was prepared by adding Super P carbon and sodium carboxymethyl cellulose (CMC) directly into aforementioned 2-propanol dispersion after ultrasonication (weight ratio of VOPO4: Super P: CMC = 80: 15: 5). While heated to remove excess 2-propanol, the mixture was thoroughly mixed in Thinky centrifugal mixer to form a homogenous slurry, which was then casted on aluminium foil and dried in vacuum at 115 °C for 12 hrs. The bulk VOPO4·2H2O electrode was prepared by adding ground chunks, Super P carbon in CMC aqueous solution (the same weight ratio as nanosheets electrode), followed by similar mixing, casting and drying procedures. The typical mass loading was about 1.0 mg. CR2032 coin cells were assembled inside an Ar-filled glove box using metallic Li/Na as anode. For Li cells, Celgard 2500 was used as the separator, and LiPF6 in 1:1:1 ethylene carbonate, diethyl carbonate and dimethyl carbonate was used as the electrolyte. For Na cells, Waltman glassy fiber was used as the
separator, and 1 M NaClO4 dissolved in propylene carbonate with 2% fluoroethylene carbonate additive was used as the electrolyte. Materials characterization: X-ray powder diffraction patterns were performed on a Rigaku MiniFlex 600 equipped with Cu Kα radiation. SEM/STEM and TEM observations were carried out on a Hitachi scanning electron microspcope (S-5500) and JEOL transmission electron microscope (2010F), respectively. Electrochemical characterization was performed on LANHE battery cycler (CT2001A) and Bio-logic potentiostat (VMP3). All the coin cells were first charged/discharged at 0.1 C once before further tests.
Figure S1. Additional SEM/STEM images of ultrathin free standing VOPO4 nanosheets. a) SEM image showing one single nanosheet. b) STEM image showing several nanosheets.
Figure S2. Comparison of electrochemical stability in lithium storage devices between electrodes made from bulk chunks (black) and nanosheets (red), both were tested at 0.1 C rate.
Figure S3. Cyclic voltammetric profile of VOPO4 for lithium storage device at scan rate of 0.02 mV/s.
Figure S4. Charge/discharge profiles of the VOPO4 nanosheets electrode in lithium storage device at various current rates from 0.1 C to 10 C.
Figure S5. Kinetics analysis of the electrochemical behavior towards Na+ for the VOPO4 nanosheets electrode. a) CV curves at various scan rates, from 0.02 to 20 mV/s. b) Determination of the b-value using the relationship between peak current and scan rate. c) Separation of the capacitive and diffusion currents at a scan rate of 10 mV/s. d) Contribution ratio of the capacitive and diffusion-controlled charge at various scan rates.
Figure S6. Rate capability of sodium-ion cell made from bulk chunks at the C rate ranging from 0.1~10 C. After 10 C, the cell cannot go back to 0.1 C.
Figure S7. Top-view SEM images of VOPO4 nanosheets electrodes after 500 cycles at 5 C rate. a) In lithium storage device, morphology of VOPO4 nanosheets remained intact and the surface was smooth and clean. b) In sodium storage device, the surface of VOPO4 nanosheets became rather rough.
Figure S8. Top-view SEM image of VOPO4 nanosheets electrode before cycling test. Notice the nanosheet morphology remained intact during the electrode preparation.
References 1. Tietze, H. Aust. J. Chem. 1981, 34, 2035−2038. 2. Wu, C.; Lu, X.; Peng, L.; Xu, K.; Peng, X., Huang, J.; Yu, G.; Xie, Y. Nat. Commun. 2013, 4, 2431.
