A Low-Cost High-Energy Potassium Cathode

Transcription

1 Supporting information A Low-Cost High-Energy Potassium Cathode Leigang Xue, Yutao Li, Hongcai Gao, Weidong Zhou, Xujie Lü, Watchareeya Kaveevivitchai, Arumugam Manthiram, and John B. Goodenough * Materials Science and Engineering Program and Texas Materials Institute, The University of Texas at Austin, Austin, TX 78712, USA Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA *jgoodenough@mail.utexas.edu Experimental Materials. Mn(NO 3 ) 2 solution (50 wt.%), K 4 Fe(CN) 6 3H 2 O, KCl, NaCl, KClO 4 were purchased from Sigma Aldrich. Propylene carbonate (PC) and fluoroethylene carbonate (FEC) electrolyte solvents were purchased from Merck. All materials were used as received. Cathode preparation. The K x MnFe(CN) 6 (x 2) was prepared by a precipitation method g Mn(NO 3 ) 2 solution (50 wt.%) was dissolved into 50 ml deionized water, 1.27 g K 4 Fe(CN) 6 3H 2 O and 17.8 g KCl were dissolved into 100 ml water. Mn(NO 3 ) 2 solution was added dropwise into the KCl/K 4 Fe(CN) 6 solution under magnetic stirring. The suspension was aged for 2 h before being filtered. The precipitate was washed with deionized water several times and then dried at 70 C overnight. For the bigger Na + -induced KMHCF particles, NaCl (7 g) and KCl (8.9 g) mixture was used instead, other conditions are same. The cathode electrodes were comprised of 60% cathode powder, 30% carbon black, and 10% Na-CMC binder (carboxymethylcellulose, Mw = g/mol, Alfa Aesar, USA). Distilled water was used as S1

2 solvent and the resultant slurry was thoroughly mixed and coated onto carbon-coated Al foil; the coating was dried under air overnight. All coin cells were assembled in an Ar-filled glovebox. ICP, TGA, SEM, STEM, EDS, Raman, Magnetic Susceptibility. The molar ratios of K, Mn and Fe were measured by inductive coupled plasma (ICP) analysis. Thermogravimetric analysis (TGA) was conducted from room temperature to 300 C at 10 C min -1 in a N 2 flow. The morphologies of the as-prepared poweders were investigated with a Hitachi S5500 SEM/STEM, and X-ray energy dispersive spectroscopy (EDS) analysis was conducted on an Oxford EDS spectrometer. The Raman spectroscopy was conducted with a 100, 0.9 N.A., objective lens and 488 nm laser excitation (Alpha 300, WITEC GmbH). A low incident power of µw and an acceleration time of 300 s were used to minimize heating effects and ensures good signal/noise ratio. The temperature dependence of magnetic susceptibility was measured in the temperature range K under a magnetic field H = 1 T with a commercial Superconducting Quantum Interference Device (SQUID) magnetometer (Quantum Design). XRD and Synchrotron. Powder X-ray diffraction (XRD) patterns were collected on a Rigaku MiniFlex 600 II. For ex-situ XRD, coin cells were disassembled in an Ar-filled glove box; the cathode was removed and rinsed thoroughly with PC. Then the electrodes were transferred out and dried for analysis. High-resolution synchrotron XRD data was collected at Sector 16 (HPCAT BM-D beamline) at Advanced Phonon Source (APS), Argonne National Laboratory (ANL). A monochromatic X-ray beam with wavelength of Å was used for the diffraction experiments. The diffraction data were recorded by a MAR345 image plate, and then the two dimensional images were integrated to one dimensional patterns with the Fit2D program. S2

3 Electrochemical tests. Cathodes were evaluated in CR2032 coin cells with a liquid K-Na anode, a liquid electrolyte composed of saturated KClO 4 in PC containing 10 wt% FEC, and a glass-fiber separator. The cells were cycled galvanostatically at room temperature with a LAND battery testing system. S3

4 Weight % Temperature / o C Figure S1. Thermogravimetric (TGA) curves of KMHCF measured under N 2 atmosphere. S4

5 K a Fe K Mn Fe cps / ev Na b c KeV Figure S2. Energy dispersive X-ray (EDX) spectra of (a) potassium manganese hexacyanoferrate powder (KMHCF) prepared by using K + precursors; (b) sodium manganese hexacyanoferrate powder prepared by using Na + precursors. (c) When Na + can K + co-exist with a molar ratio of 1:1 in the solution, only K + peak is observed, indicating only K + is precipitated. S5

6 a b Intensity c theta Figure S3. XRD patterns of (a) potassium manganese hexacyanoferrate powder prepared by using K + precursors; (b) sodium manganese hexacyanoferrate powder prepared by using Na + precursors. (c) When Na + can K + co-exist with a molar ratio of 1:1 in the solution, XRD shows it is potassium manganese hexacyanoferrate powder, indicating only K + is precipitated. S6

7 Weight % Temperature / o C Figure S4. Thermogravimetric (TGA) curve of NI-KMHCF measured under N 2 atmosphere. S7

8 Experiment Fitting Difference Bragg Position θ Figure S5. Synchrotron radiation pattern (λ= Å) and Rietveld refinement of K 1.70 Mn[Fe(CN) 6 ] H 2 O powder. S8

9 NI-KMHCF Raman Intensity 2175 KMHCF Wavenumber / cm -3 Figure S6. Raman spectra of KMHCF and NI-KMHCF. S9

10 a b χ 1 /mol emu KMHCF Fitting χ 1 /mol emu NI-KMHCF Fitting T T Figure S7. Magnetic susceptibility versus temperature of (a) KMHCF and (b) NI-KMHCF. S10

11 st 100 th 20 th Voltage / V st 100 th 20 th Capacity / mah g -1 Figure S8. Charge/discharge curves of KMHCF powder at 1 C. S11

12 Table S1. Atomic positions of KMHCF from Rietveld refinement of X-ray diffraction pattern Atom Site x, y, z Occupation K 4e ,0.4376, Mn 2d 0.5,0, Fe 2a 0,0, C1 4e ,0.1427, C2 4e ,0.8009, C3 4e ,0.0082, N1 4e ,0.6683, N2 4e , , N3 4e ,0.0341, a = Å, b= Å, c= Å, and α = γ = 90, β = Rp = 5.33, Rwp = 6.03, and CHI 2 = 0.35 S12

13 Table S2. Atomic positions of NI-KMHCF from Rietveld refinement of X-ray diffraction pattern Atom Site x, y, z Occupation Na 4e ,0.4367, * K 4e ,0.4367, Mn 2d 0.5,0, Fe 2a 0,0, C1 4e ,0.1318, C2 4e ,0.8153, C3 4e ,0.0088, N1 4e ,0.6588, N2 4e , , N3 4e ,0.0302, a = Å, b= Å, c= Å, and α = γ = 90, β = Rp = 4.79, Rwp = 5.12, and CHI 2 = 0.17 * Confirmed by ICP S13

14 Table S3. Comparison between potassium manganese hexacyanoferrate powder prepared by using K + precursors, and sodium manganese hexacyanoferrate powder prepared by using Na + precursors. K x MnFe(CN) 6 Na y MnFe(CN) 6 Theoretical ideal formula K 2 MnFe(CN) 6 Na 2 MnFe(CN) 6 Theoretical capacity 156 mah g mah g -1 Discharge voltage 3.6 ~ 4.0V (vs. K + /K) 3.4 V(vs. Na + /Na) Structure monoclinic monoclinic Actual formula K 1.89 Mn[Fe(CN) 6 ] H 2 O Na 1.72 Mn[Fe(CN) 6 ] H 2 O a = Å, a = Å, Lattice parameter b= Å, c= Å, b = Å, c = Å, β = β = S14