MXene-Bonded Activated Carbon as a Flexible. Electrode for High-Performance Supercapacitors

Transcription

1 Supporting information MXene-Bonded Activated Carbon as a Flexible Electrode for High-Performance Supercapacitors Lanyong Yu, Longfeng Hu, Babak Anasori, Yi-Tao Liu, Qizhen Zhu, Peng Zhang, Yury Gogotsi, *,, Bin Xu*, State Key Laboratory of Organic Inorganic Composites, Beijing Key Laboratory of Electrochemical Process and Technology for Materials, Beijing University of Chemical Technology, Beijing , China Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun , China AUTHOR INFORMATION Corresponding Author *B. Xu. address: binxumail@163.com Y. Gogotsi. address: gogotsi@drexel.edu 1

2 Experimental Synthesis of Ti 3 C 2 T x (MXene) nanosheets The preparation of the Ti 3 C 2 T x (MXene) nanosheets was described elsewhere [1]. Briefly, 0.99 g of LiF was added to 10 ml of HCl (9 M), followed by the slow addition of 1 g of Ti 3 AlC 2. After etching at 35 C for 24 h, the obtained Ti 3 C 2 T x (MXene) nanosheets were washed using deionized water until the ph is around 6. After 1 h sonication followed by 1 h centrifugation at 3500 rpm to separate the sediment, an aqueous dispersion containing the Ti 3 C 2 T x (MXene) nanosheets were obtained. Fabrication of MXene-bonded AC films Commercial activated carbon (AC), i.e. Maxsorb-3 (Kansai Thermochemical Co., Japan) with a surface area of 2786 m 2 g 1 and particle size of µm (Figure S1a) was used as the active material. The fabrication of the MXene-bonded films is illustrated in Figure 1. Briefly, the aqueous dispersions of Ti 3 C 2 T x (MXene) nanosheets and AC particles were mixed at different weight ratios, i.e., 1:1, 1:2 and 1:4, under sonication. The mixed dispersions were vacuum-filtered by using Celgard 3501 membranes, and then vacuum-dried at 80 C for 6 h to obtain free-standing, flexible films with a diameter of 40 mm. The films prepared with AC/MXene = 1:1, 2:1 and 4:1 were denoted as AC/MXene-1:1, AC/MXene-2:1 and AC/MXene-4:1 films, respectively. From the digital image of a representative MXene-bonded film (Figure 1), i.e., AC/MXene-2:1, it can be clearly seen that this hybrid film is free-standing and highly flexible due to the introduction of the MXene binder, and can be bent without cracking or breaking. For comparison, neat MXene films were fabricated according to the same procedures described above without the AC particles. The mass of all films was kept as 10 mg. 2

3 Characterization Scanning electron microscopy (SEM, Hitachi S4800) was used to observe the morphology and structure of the AC particles and the MXene-bonded AC films. The AC particle size was measured using the SEM image and averaging 50 particles using an image analysis software of Smile View. The conductivities of AC/MXene films and AC-PVDF were tested using a 4-point probes resistivity measurement system. X-ray diffraction (XRD) spectra was recorded on an X Pert-Pro MPD (PANalytical, the Netherlands) diffractometer with monochromatic Cu Ka radiation (λ =1.5418Å, the scanning speed was 5 o min -1 ). Nitrogen adsorption/desorption analysis (Micromeritics ASAP 2460) was used to measure the porosity parameters of the AC particles and MXene-bonded AC films. The surface area was calculated by BET (Brunauer Emmett Teller) method, while the pore size distribution was obtained using NLDFT model. Before measurements, the samples were outgassed under vacuum at 200 C for 10 h until the pressure was less than 5 µm Hg. Electrochemical measurements All the electrochemical tests were conducted in a symmetrical two-electrode capacitor. After cut into disks with a diameter of 10 mm and vacuum dried, the free-standing, flexible MXene-bonded AC films were directly used as electrodes without any metal current collectors for cells assembly. The control electrode, i.e. conventional PVDF (polyvinylidene fluoride)-bonded AC electrode, was prepared by mixing Maxsorb-3, carbon black and PVDF with a weight ratio of 80:10:10 in N-methyl-2-pyrrolidinone. Then the slurry was coated on the aluminum foil current collectors, cut into disks of 10 mm in diameter, and dried at 120 C for 6 h under vacuum. Two-electrode symmetric 3

4 cells were assembled at room temperature, among which two electrodes were same in both composition and mass and separated by polypropylene membrane with 1 mol L 1 Et 4 NBF 4 /AN as the electrolyte in an argon-filled glove box with water and oxygen contents less than 0.1 ppm. Galvanostatic charge/discharge (GCD) profiles were recorded on Arbin BT2000 battery test equipment between V. Cyclic voltammetry (CV) were carried out at electrochemical workstation CHI1100C and electrochemical impedance spectroscopy (EIS) were performed on the electrochemical workstation CS350 with frequency from 0.01 Hz to 20 khz with ±10 mv voltage amplitude. The specific gravimetric capacitances (C m, F g -1 ) from the GCD curves were calculated by the formula: C m = 4It/ Vm [2], where I is the discharge current (A), t is the discharge time (s), V is the potential change in discharge process (V) and m is the total mass of the two electrodes excluding the current collector (g). The volumetric capacitance (C v, F cm -3 ) was calculated by equation C v = C m ρ, in which ρ is the electrode density (g cm -3 ). The energy density against two electrodes in device was calculated by the formula: E = C m V 2 /8, where V is the operating voltage. The power densities of the device (P) against two electrodes were calculated from the formula: P = E/ t, where t is the discharge time [3]. The specific capacitances from the CV curves were calculated by integrating the discharge portion using the following equation: C m = ʃ, where i is the current (A), V is the voltage window (V), v is the scan rate (mv s -1 ), and m is the mass of the one electrode excluding the current collector (g) [4]. It should be noted that, all the data were based on the total mass of the electrodes excluding the current collector (aluminum foil for AC-PVDF electrode) unless mentioned. 4

5 Table S1. The porosity parameters, conductivity and capacitance of AC-PVDF, MXene film and AC/MXene films in 1 mol L -1 Et 4 NBF 4 /AN. Sample S BET (m 2 g -1 ) V total (cm 3 g -1 ) Conductivity (S cm -1 ) Density (g cm -3 ) Capacitance at 0.1 A g -1 C m (F g -1 ) C v (F cm -3 ) AC-PVDF MXene film AC/MXene-1: AC/MXene -2: AC/MXene -4:

6 Figure S1. SEM image (a), nitrogen adsorption/desorption isotherms (b) and pore size distribution (c) of AC particles. Figure S2. TEM images of MXene sheets (a, b) and SEM image of MXene film (c). Figure S3. SEM image of AC-PVDF electrode. 6

7 Intensity / a.u. AC AC/MXene-1:1 AC/MXene-2:1 AC/MXene-4: Theta / o MXene Figure S4. XRD patterns of AC particles, MXene film, and AC/MXene films. Figure S5. Nitrogen adsorption/desorption isotherms (a) and pore size distributions (b) of AC-PVDF, MXene film and AC/MXene films. 7

8 Figure S6. CV curves of AC/MXene-1:1 film (a) and AC-PVDF electrode (b) at 5 mv s -1. Figure S7. (a) V-t curves of AC/MXene-2:1 film at current densities of A g -1, (b) rate performance of AC/MXene-2:1 film, (c) V-t curves of AC-PVDF electrode at current densities of 50 and 75 A g -1, and (d) CV curves of AC-PVDF electrode at different scan rates. 8

9 References (1) Alhabeb, M.; Maleski, K.; Anasori, B.; Lelyukh, P.; Clark, L.; Sin, S.; Gogotsi, Y. Guidelines for Synthesis and Processing of 2D Titanium Carbide (Ti 3 C 2 T x MXene), Chem. Mater. 2017, 29, (2) Hu, L.; Ma, L.; Zhu, Q,; Yu, L.; Wu, Q.; Hu, C.; Qiao, N.; Xu, B. Organic salt-derived nitrogen-rich, hierarchical porous carbon for ultrafast supercapacitors. New J. Chem. 2017, 41, (3) Yu, D.; Goh, K.; Wang, H.; Wei, L.; Jiang, W.; Zhang, Q.; Dai, L.; Chen, Y. Scalable synthesis of hierarchically structured carbon nanotube-graphene fibres for capacitive energy storage. Nat. Nanotechnol. 2014, 9, (4) Lin, Z.; Barbara, D.; Taberna, P. L.; Van Aken, K. L.; Anasori, B.; Gogotsi, Y.; Simon, P. Capacitance of Ti 3 C 2 T x MXene in ionic liquid electrolyte. J. Power Sources 2016, 326,