Supporting Information for. Aqueous Mg-ion Battery Based on Polyimide Anode and Prussian. Blue Cathode

Transcription

1 Supporting Information for Aqueous Mg-ion Battery Based on Polyimide Anode and Prussian Blue Cathode L. Chen, J. L. Bao, X. Dong, D. G. Truhlar, Y. Wang,* C. Wang, Y. Xia * Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Institute of New Energy, ichem(collaborative Innovation Center of Chemistry for Energy Materials), Fudan University, Shanghai , China. ygwang@fudan.edu.cn, yyxia@fudan.edu.cn.. Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota , United States. Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742, United States. This PDF file includes: Experimental section Figure S1 to S17 Table S1 to S2 Experimental Section Synthesis and characterization of polyimide, PBN and PBC. Polyimide was prepared according to our previous report. Equimolar mixtures of 1,4,5,8- naphthalenetetracarboxylic dianhydride (NTCDA) and ethylene diamine (EDA) were reacted under reflux in the solvent of N-methylpyrrolidone (NMP) for 6 hours. The product was filtered, washed with ethanol and NMP several times, dried at 120 C in air for 12 hours, and then heated in nitrogen atmosphere for 8 hours at 1

2 300 C. PBN (denoted PBN as shorthand for Prussian blue nickel derivative) and PBC (denoted PBC as shorthand for Prussian blue copper derivative) nanoparticles were synthesized by a coprecipitation method 1. with 70 ml of aqueous nickel nitrate (for preparing PBN) or copper nitrate (for preparing PBC) and sodium ferrocyanide solutions (Sigma-Aldrich) were added into 60 ml of deionized water slowly, simultaneously and dropwise with uninterrupted stirring at room temperature for final concentrations of 40 mm nickel or copper nitrate and 20 mm sodium ferricyanide. The solid precipitate was vacuum filtered from solution, washed, and dried under vacuum at 120 C. The particle size and morphologies of the samples were characterized using an S-4800 scanning electron microscope (SEM) and a Joel JEM2011 transmission electron microscopy (TEM). The X-ray powder diffraction (XRD) patterns of the as-prepared materials were recorded were carried out using Bruker D8 Advanced diffractometer using Cu Kα radiation in a 2θ range of 10 to 90 with a step size of 0.02 and an exposition time of 0.2 s per step. The as-prepared polyimide was characterized by Fourier transform-infrared spectroscopy (FT-IR) measurements by a NICOLET 6700 FI-TR Spectrometer using a KBr pellet. Electrode preparation and electrochemical measurements. The working electrode was fabricated by compressing a mixture of the active materials (polyimide and PBN or PBC), conductive material (Ketjen Black, KB), and 2

3 binder (polytetrafluoroethylene) in the weight ratio of 6:3:1 onto a stainless steel grid at 10 MPa. The thickness of stainless steel grid was 0.08 mm and the mesh size was 150. A hydraulic machine has been used to press the samples together a and the pressing process was carried out by putting the film (active materials/kb/ PTFE) and stainless steel grid between two flat stainless steel plates whose surfaces were very smooth. Prior to assembly, the electrodes were dried at 120 C for 12 h under vacuum. For coin cell preparation, the electrode was punched into discs with a diameter of 12 mm and thickness of 0.1 mm. The loading of the anode material was around 5 mg; the active material is 3 mg in anode. The loading of the cathode is around 15 mg 9 mg was the active material. A 1 M MgSO 4 electrolyte solution was prepared by dissolving MgSO 4 in distilled water. Cyclic voltammetry (CV) was carried out using a three-electrode cell where active carbon and Ag/AgCl electrodes (0.197 V versus NHE) were used as the counter and reference electrodes, respectively. The CV measurements were carried out at several scan rates on a CHI660B electrochemical workstation. Galvanostatic charge/discharge cycling at several current densities was performed using a three-electrode cell where the counter and reference electrodes were active carbon and Ag/AgCl electrode respectively. The galvanostatic charge/discharge test of polyimide was carried out under N 2 flow in the absence of O 2. The galvanostatic charge/discharge measurements were performed at various constant current rates using a Solarton Instrument Model 1287 electrochemical interface. The stability test of discharged polyimide was carried out as follows. Polyimide electrode was first discharged to 0.8 V at a current of 1A g -1. Then, the open circuit 3

4 voltage of Mg-P was measured as a function of time for two days. Finally it was charged back to 0 V at the same current density. The whole experiment was carried out under N 2 flow to protect it from being oxidized by oxygen dissolved in the aqueous solution. This experiment was performed by using the Solarton Instrument Model 1287 electrochemical interface. Aqueous Mg-ion battery fabrication and electrochemical measurements A fully sealed aqueous Mg-ion battery with polyimide anode and PBN or PBC cathode was assembled in an open environment. The anode and cathode were separated by a nonwoven-fabric separator (as used in commercial Ni-MH batteries), and a 1 M MgSO 4 aqueous solution was used as electrolyte. A CR2016-type coin cell was used the sealed battery test used. The capacity was determined using only the weight of the active materials. The self-discharge test was carried out as follows. First, we charged the aqueous Mg-ion battery at a current density of 1A g -1 until the voltage was up to 1.55V, then we let this charged battery rest for 20 hours, and finally we discharged the cell, again at 1A g -1. Computational details The polyimide is truncated to a monomer structure P (shown in Fig. 1C) for computational modeling. The binding energies between P 2- anion and metal cation M m+ (M m+ =Li +, Na +, Mg 2+ ) were calculated by density functional theory using the following equation: 4

5 E bind = 2 m E(Mm+ )+ E(P 2 ) E(M 2/m P) (1) where is the binding energy, and M 2/n P represents the bound complex. Changes in vibrational and conformational energy upon binding were neglected. All of the calculations were carried out in aqueous phase with the solvent treated by the implicit universal solvation model SMD 2 which is based on the quantum mechanical charge density of the solute, a polarized continuum treatment of the bulk solvent and atomic surface tensions representing the interaction of the solute with the first solvation shell. Geometry optimizations and single-point energy calculations were carried out with the meta-gga density functional M06 3 with the 6-31+G(d, p) all-electron basis set. All the calculations were performed using the Gaussian 09 4 software package, and the integrals over density functionals were evaluated with ultrafine integration grids. 5

6 Fig. S1 Fig. S1 Schematic representation and operating principles of Mg batteries. (a) Rechargeable Mg-metal battery; (b) Rechargeable Mg-ion battery. It has been well demonstrated that there is no dendrites formation on Mg-metal electrode during the charge/discharge cycling, however, the formation of passivating layers (Fig. S1a) is also the key challenge to implement Mg as an efficient anode for rechargeable batteries. The rocking chair type Mg-ion batteries without any Mg-metal electrode can solve this problem fundamentally (Fig. S1b). 6

7 Fig. S2 Fig. S2 FT-IR spectrum of as-prepared polyimide (P) The Fourier transform infraredspectroscopy (FT-IR) spectrum of as-prepared polyimide (P) was characterized with a NICOLET 6700 FT-IR Spectrometer using KBr pellets. The absorption bands at 1350 and 1581 cm -1 can be assigned to the vibration of imide C-N and naphthalene respectively. The sharp absorption peaks at 1702, 1670 and 771 cm -1 can be attributed to the vibration of the imide C=O bond (Fig. S2). From the FT-IR spectrum, it can be detected that the characteristic absorption bands of the imide group are consistent with previous reports 5-7, which thus confirms the successful preparation of polyimide (P). 7

8 Fig. S3 Fig. S3 Energy binding of 2Na-P with different molecular structure. For 2Li-P and 2Na-P, we use the lowest-energy structure, in which the two metal cations are in trans positions, to compute the binding energies. The two cis- isomers (a, b) of 2Na-P (Fig. S3) are 0.33 and 0.68 kcal/mol energetically higher than the lowest-energy isomer (trans-) (c). 8

9 Fig. S4 Fig. S4 X-ray powder diffraction pattern of PBN. X-ray powder diffraction patterns for this precipitated powder PBN can be indexed as a single cubic phase without crystalline impurities, which are in agreement with the previous report 8. 9

10 Fig. S5 Fig. S5 SEM and TEM images of PBN. (a, b) SEM images of PBN; (c, d) TEM images of PBN. These images show an average particle size of PBN is about 50 nm. 10

11 Fig. S6 Fig. S6 Thermogravimetric curve of the as-prepared PBN. TGA measurment was conducted at a rate of 5 C min -1 in Ar atmosphere. The significant mass loss at 100 o C is attributed to the water content of the sample indicating that the sample PBN contains 22% of water. 11

12 Fig. S7 Fig. S7 Electrochemical impedance spectroscopic (EIS) measurement of PBN and Polyimide electrode. (a) Nyquist plots obtained from EIS measurement of PBN electrode; (b) Nyquist plots obtained from EIS measurement of Polyimide electrode. The electrochemical impedance spectroscopic (EIS) measurement of PBN (Fig. S7a) and Polyimide (Fig. S7b) was performed at the open circuit potential in the frequency range of Hz and AC signal amplitude of 5mV. The obtained Nyquist plot (-Z vs. Z ) is given in Fig. S7. The Nyquist plot consists of a high frequency semicircle and a low frequency spike. Typically, the high frequency semicircle is associated with the internal resistance of electrode, interface resistance and charge transfer resistance. We have found that Polyimide has a much bigger semicircle radius than PBN, which indicates a much higher resistance. In the low frequency region, typical linear shape of Nyquist plot can be observed where the slope gradually changes from 45 to 90 with decrease of AC frequency, indicating that the Mg-intercalation in the PBN and Polyimide is not controlled by the diffusion process, also confirmed by cyclic voltammetry test. 12

13 Fig. S8 Fig. S8 Charge/discharge curves of PBN. The first 5 galvanostatic charge/discharge curves of PBN at the current of 1A g -1 between the voltage of -0.2 and 0.75 V is shown in this picture. It is noticeable that, in the first charge process of both PBN, it is the Na ions extract from the structure, while in the discharge process the Mg ions inserted into the open framework structure. It can be observed that, the specific capacity of the first charge process is about 50 mah g -1, while the discharge capacity is about 56 mah g -1. Since the second cycle, the charge/discharge capacity is both 56 mah g -1, and the coulombic efficiency for PBN is near to 100 %. 13

14 Fig. S9 Fig. S9 Charge/discharge curves of PBN before and after changing the electrolyte. To confirm the Mg 2+ intercalation is more favourable than the re-intercalation of extracted Na +, we carried out another experiment. At first, we charged and discharged the PBN cathode material between the window of -0.2V to 0.75V (vs. Ag/AgCl) at the current rate of 1A g -1 for several circles in 1M MgSO 4 electrolyte. Then, we charged the PBN cathode to 0.75V, and hold on the voltage for 10 minutes, during this process, the ions (Mg 2+ or Na + if has) will extracted from the structure. Then we changed the electrolyte with new 1M MgSO 4 electrolyte, and washed the PBN electrode with DI water, then charge/discharge the same PBN electrode. We compared the charge/discharge curves before and after changing the electrolyte. After we changing the electrolyte, there is no Na + ion in the electrolyte, and the Fig. S9 show that, the charge/discharge curves are almost the same before and after changing the electrolyte, 14

15 which indicate that the extracted Na ion is negligible. Fig. S10 Fig. S10 Charge/discharge curves of aqueous PBN/Polyimide full Mg ion battery. We constructed another Mg ion PBN/Polyimide battery, first we charged/discharged the PBN electrode in a three electrode system and then use the same electrode to construct a full PBN/Polyimide aqueous Mg ion battery. The Fig. S10 show the charge/discharge curves at the current density of 1 A g -1, it can worked very well without the Na ion, and it is almost the same as the Fig. 5b. So we can confirm that the PBN battery is a truly Mg-ion battery. The current density (A g -1 ) is calculated based on the weight of anode material. The capacity (mah g -1 ) is calculated based on the total weight of cathode and anode material. 15

16 Fig. S11 Fig. S11 Charge/discharge curves of aqueous Mg-ion battery based on PBN/polyimide at the current density of 0.02 A g -1 (0.15C). The first 50 charge/discharge curves of aqueous Mg-ion cell based on PBN/polyimide showed in the Fig. S11. It deliver a capacity of 37 mah g -1 at the first cycle. The cycle stability is also very good at the low current rate, the coulombic efficiency is about 98%, which is for the electrolysis of water from the electrolyte. The current density (A g -1 ) is calculated based on the weight of anode material. The capacity (mah g -1 ) is calculated based on the total weight of cathode and anode material. 16

17 Fig. S12 Fig. S12 X-ray powder diffraction pattern of PBC. X-ray powder diffraction patterns for this precipitated powder PBC can be indexed as a single cubic phase, which are in agreement with the previously reported. While according to the peak located at around 29 degree, there is some impurity 1,9. 17

18 Fig. S13 Fig. S13 SEM and TEM images of PBC. (a, b) SEM images of PBC; (c, d) TEM images of PBC. These images show an average particle size about 50 nm of these nanoparticles of PBC. 18

19 Fig. S14 Fig. S14 Thermogravimetric curve of the as-prepared PBC. It was test at a rate of 5 C min -1 in Ar atmosphere. It indicated that the PBC sample contain about 20% water. 19

20 Fig. S15 Fig. S15 Charge/discharge curves of PBC. The first 5 galvanostatic charge/discharge curves of PBC at the current of 1A g -1 between the voltage of 0 and 0.95 V is shown in this picture. It is noticeable that, in the first charge process of both PBC, it is the Na ions extract from the structure, while in the discharge process the Mg ions inserted into the open framework structure. It can be observed that, the specific capacity of the first charge process is about 225 mah g -1, while the discharge capacity is about 50 mah g -1. We speculated that, the extra capacity comes from the overcharge of the impurities of PBC (Fig. S12). Since the second cycle, the charge/discharge capacity is both 50 mah g -1, and the coulombic efficiency for PBC is near to 100 %. 20

21 Fig. S16 Fig. S16 Rate and cycle performance of PBC in 1M MgSO 4 aqueous electrolyte (a) galvanostatic charge/discharge curves of PBC at several current densities between the voltage of 0 and 0.95 V; (b) cycle life of the PBC at the current of 1A g -1 within the voltage of 0V and 0.95 V. PBC delivers a good rate performance in aqueous Mg ions solution, which could be charged and discharged at a current density up to 10 A g -1, while maintaining about a half of the discharge capacity at the current of 0.1 A g -1 (Fig. S16a). Furthermore, it reveals excellent capacity retention, which could be maintain 60% after 1000 cycles (Fig. S16b). 21

22 Fig. S17 Fig. S17 Electrochemical performance of aqueous Mg-ion cell based on PBC/polyimide (P). (a) Galvanostatic charge/discharge curves at several current densities between 0 and 1.55V; (b, c) Cycle and coulombic performance of the aqueous Mg-ion battery at the current of 2A g -1 between 0 and 1.55V. The current density (A g -1 ) is calculated based on the weight of anode material. The capacity (mah g -1 ) is calculated based on the total weight of cathode and anode material. For the low coulombic efficiency of PBC at the first cycle, before applied as the cathode materials to assemble a full battery, it was charged/discharged using a 22

23 three-electrode cell in 1 M MgSO 4 aqueous solution at the current 1A g -1 (Fig. S15). The balancing weight ratio of PBC to polyimide (P) was 3:1, it was calculated using the charge capacity 50 mah g -1 of PBN at the second charge/discharge cycle, and discharge capacity 148 mah g -1 of the polyimide (P) at the first charge/discharge cycle with the current density of 1 A g -1. The charge/discharge profiles reveal an average operation voltage at 1.3V, which is higher than the battery based on the PBN and polyimide (P). This batttery also exhibited an excellent rate performance, 15 ma h g -1 retained when the current density up to 10A g -1. The Charge/discharge cycling at a current density of 2A g -1 demonstrated the high stability of this aqueous Mg-ion battery, which nearly perfectly maintained its specific capacity over the first 100 cycles, and the capacity retention is about 60 percent after 5000 charge/discharge cycles. The coulombic efficiency remained 100% among the whole cycle process, indicating that there is no gas evolution. 23

24 Table S1 A summary of operation voltages of some Mg-metal batteries and batteries using aqueous electrolyte Battery type Average cell voltage Capacity / (V) Energy density Mg x Mo 3 S 4 / Mg mah/g Mg x Mo 6 S 8 n Se n (n= 0, 1, 2) / Mg mah/g CoS/ Mg mah/g Mg 1.03 Mn 0.97 SiO 4 / Mg mah/g MgCoSiO 4 / Mg mah/g S/ Mg mah/g MoS 2 / Mg mah/g TiSe 2 / Mg mah/g PAQS/Mg mah/g α-mno 2 /Mg mah/g CSM-PAn/Mg mah/g V 2 O 5 /Mg mah/g Lead acid Wh/kg Ni-Cd Wh/kg Ni-MH Wh/kg LiMn 2 O 4 /LiTi 2 (PO 4 ) Wh/kg LiFePO 4 /LiTi 2 (PO 4 ) Wh/kg LiMn 2 O 4 /Activated Carbon Wh/kg 24

25 Table S2 Cartesian coordinates (in Å) for optimized structures of P, P 2-, 2Li-P, 2Na-P and Mg-P at M06/6-31+G(d,p) in water. Truncated polyimide (P): Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

26 P 2- : Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

27 2Na-P (lowest-energy structure): Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

28 2Na-P (0.33 kcal/mol higher than the lowest-energy structure) Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

29 2Na-P (0.68 kcal/mol higher than the lowest-energy structure) Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

30 2Li-P: Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

31 Mg-P: Center Atomic Atomic Coordinates (Angstroms) Number Number Type X Y Z

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