Design and Comparative Study of O3/P2 Hybrid Structures for

Transcription

1 Supporting Information Design and Comparative Study of O3/P2 Hybrid Structures for Room Temperature Sodium-Ion Batteries Xingguo Qi, a,b,# Lilu Liu, a,b,# Ningning Song, c Fei Gao, d Kai Yang, d Yaxiang Lu, a * Haitao Yang, c * Yong-Sheng Hu, a,b * Zhao-Hua Cheng, c and Liquan Chen a,b a Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing , China b School of Physical Sciences, University of Chinese Academy of Sciences, Beijing , China c State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing , China d State Key Laboratory of Operation and Control of Renewable Energy & Storage Systems, China Electric Power Research Institute, Beijing , China Corresponding Authors * yxlu@iphy.ac.cn, htyang@iphy.ac.cn, yshu@aphy.iphy.ac.cn S-1

2 Experimental Section Materials Preparation: Layered Na x [Ni 0.2 Fe x-0.4 Mn 1.2-x ]O 2 (x=0.7~1.0) samples were prepared by a traditional solid state reaction. The starting materials, reagent-grade carbonate and oxides of Na 2 CO 3, NiO, Fe 2 O 3 and MnO 2, were weighed and grounded in an agate mortar according to the appropriate stoichiometric ratio (2% more Na 2 CO 3 in consideration of volatilization loss). After that, the mixture was pressed into a pellet under pressure of 5 MPa and then the pellets were heated at 950 o C for 24h in an alumina crucible in air, followed by natural cooling. Structure Characterizations: The crystal structure was identified by powder X-ray diffraction, the patterns of which were collected on an X-ray diffractometer (D8 Bruker) with Cu Kα radiation (λ= Å) in the scan range (2θ) of 10-80º. Rietveld refinement of XRD pattern was performed by General Structure Analysis System (GSAS) in order to get the detailed structural information. As for the in situ XRD test, a special battery case with an Al window was used and the voltage range was V and V with the current rate under 0.1C. The morphologies of samples were determined by scanning electron microscope (FEI SEM -S4800) and transmission electron microscope (JEOL ARM 200F). Charge Transfer Mechanism Characterizations: The X-ray photoelectron spectroscopy (XPS) were recorded with a spectrometer having Mg/Al Kα radiation (ESCALAB 250 Xi, ThermoFisher). All binding energies reported were corrected using the signal of the carbon at ev as an internal standard. The valence states of Fe from original and charged samples are determined by Mossbauer spectra which S-2

3 were taken with a Topologic System Inc. spectrometer with a 57 Co γ ray source, calibrated with α Fe at room temperature as standard. The model fitting was performed with MossWinn 3.0 software. Electrochemical Tests: Electrochemical studies were performed in CR2032 type cells, assembled in an argon filled glove-box. These working electrodes were prepared by mixing the active materials (70 wt.%), Super P (Timcal 20 wt.%) and the polyvinylidene fluoride (PVdF Alfa Aesar, 10 wt.%) binder and spreading the slurry on Al foil, then these electrodes were dried at 120 o C under vacuum for about 6 h so as to remove the absorbed water and solvent. The electrode is used as prepared without pressing and the average electrode mass loading is 4 mg/cm 2. Sodium foil (Alfa Aesar 99%), 1.0 M NaPF 6 /EC DMC (1:1 by volume with 2% FEC as additive, NaPF 6, EC, DMC, Alfa Aesar) and a glass fiber (Waterman CAT No ) is used as the counter electrode, electrolyte and separator, respectively. Electrochemical tests of the cells were carried out with a Land CT2001A battery test system (Wuhan Land Electronic Co. Ltd). In order to examine the electrochemical reaction of the cells, cyclic voltammetry was performed on a CHI600D Electrochemical Workshop (Shanghai, China) at a scan rate of 0.1 mv s 1. S-3

4 Supporting Figures Figure S1. SEM image of NNFM-0.78 with morphology of slices. Figure S2. Electrochemical performance of NNFM-0.7, NNFM-0.8, NNFM-0.9 and NNFM-1.0 (a) with current rate of 0.5 C, 1 C and (b) their rate performance (0.1C, 0.2C, 0.5C, 1C and 2C, 5 cycles in each current rate). S-4

5 Figure S3. The electrochemical profile of hard carbon with a current of 0.1C at the voltage range of V. Figure S4. XPS spectra of Mn 2p S-5

6 Figure S5. The structure stability of NNFM (a) Cycling performance of the material at 5C. (b) The electrochemical profile at 0.1C after 1000 cycles at 5C. (c) ex-situ XRD of the material at discharged state, after 1000 cycles at 5C. S-6

7 Supporting Tables Table S1. Crystallographic data and refinement parameters of the selected NFME P2 Structural formula Na Ni 0.2 Fe 0.38 Mn 0.42 O 2 Na Ni 0.2 Fe 0.38 Mn 0.42 O 2 Crystal system Trigonal Trigonal Space group P6 3 /mmc R-3m Lattice parameters a=b=2.919 Å, c= Å α=β=90 o, γ=120 o O3 a=b=2.952 Å, c= Å α=β=90 o, γ=120 o Volume Å Å 3 Phase fraction 31.74% 68.26% Rwp 9.44% Rp 7.02% χ In order to simplify the refinement, the content of Ni, Fe and Mn are made to be same, and only the sodium content is refined. Rwp, Rp and χ2 are in acceptable range, indicating the reliable result in this refinement. The phase fraction (molar ratio) of P2 is 31.74% for NNFM-0.78 and the calculated sodium content is Table S2. Detailed information of 57 Fe Mössbauer spectrometry for NNFM The value of CS is relative to α-fe at room temperature. CS (mm S -1 ) QS (mm S -1 ) Fraction (%) Valence Coordination As-prepa red Charged to 4.0 V Double % Fe Double % Fe Double % Fe Double % Fe Double % Fe Double % Fe S-7