Direct Atomic-Scale Confirmation of Three-Phase Storage Mechanism in Li 4 Ti 5 O 12 Anodes for Room-Temperature Sodium-Ion Batteries

Transcription

1 SUPPLEMENTARY INFORMATION FOR Direct Atomic-Scale Confirmation of Three-Phase Storage Mechanism in Li 4 Ti 5 O 12 Anodes for Room-Temperature Sodium-Ion Batteries Authors: Yang Sun 1,*, Liang Zhao 1,*, Huilin Pan 1,*, Xia Lu 1, Lin Gu 2, Yong-Sheng Hu 1, Hong Li 1, Michel Armand 1, Yuichi Ikuhara 3,4,5, Liquan Chen 1, Xuejie Huang 1 Affiliations: 1 Key Laboratory for Renewable Energy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing , China 2 Laboratory for Advanced Materials & electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing , China 3 WPI Advanced Institute for Materials Research, Tohoku University, Sendai , Japan 4 Institute of Engineering Innovation, The University of Tokyo, Tokyo , Japan 5 Nanostructures Research Laboratory, Japan Fine Ceramic Centre, Nagoya , Japan * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to L.G. ( l.gu@aphy.iphy.ac.cn) or to Y.-S.H. ( yshu@iphy.ac.cn).

2 Supplementary Figures: a b SEI 20 nm c 9 nm d SEI 9 nm 30 nm 10 nm Supplementary Figure S1 TEM images of the discharged/charged Li 4 Ti 5 O 12 nanoparticles in the first cycle. (a,b) TEM images at discharged state. (c,d) TEM images at recharged state. The Li 4 Ti 5 O 12 /Na half-cell was discharged to 0.5 V and then recharged to 3 V at a current rate of C/10. The cycled Li 4 Ti 5 O 12 electrodes were washed several times by DMC solvent. Li 4 Ti 5 O 12 nano-particles were then scraped from the Li 4 Ti 5 O 12 electrodes for the TEM measurements.

3 Voltage (V) V Capacity (mah/g) Supplementary Figure S2 GITT curves of the Li 4 Ti 5 O 12 electrode in a half cell. The applied current rate was C/10 in an interval of 30 min, with a relaxation period of 12 h. Solid and dotted lines correspond to the GITT result and open circuit voltage, respectively. The green dashed line represents the average voltage of sodium insertion.

4 a C1 C2 C3 b Computational Error (%) Lattice Volume Lattice Parameter c Calculated Voltage (V) 2.4 Calculated voltage Exp. 1.55V 0 C1 C2 C3 C1 C2 C3 Supplementary Figure S3 Structural optimization of stoichiometric Li 4 Ti 5 O 12. (a) Schematic illustration of three stoichiometric Li 4 Ti 5 O 12 models with different Li 16d distributions. Ti 16d O 6, Li 16d O 6 octahedra are plotted in blue and yellow, respectively. (b) The computational error of lattice parameters with respect to the experimental value, using the structure models shown in a. (c) The calculated Li insertion voltage based on the structure models shown in a. Since the 16d sites of Li 4 Ti 5 O 12 are randomly occupied by 1/6 Li atoms and 5/6 Ti atoms, a 1a 3b 1c supercell was constructed to satisfy the stoichiometry. The supercell contains two formula units of Li 4 Ti 5 O 12 and therefore, three different Li 16d distributions were considered. Computational results show that the C3 configuration with two farthermost Li 16d ions has the lowest energy. Furthermore, both the lattice parameter (with an error of less than 1%) and the insertion voltage (theoretical value 1.54 V vs. experimental value 1.55 V) of Li 4 Ti 5 O 12 could be well reproduced by the C3 model. Accordingly, the C3 model was adopted in further calculations.

5 I obs Intensity (a.u.) Excluded Region θ ( ) I calc I obs -I calc Bragg positions of Li4/Li7 Bragg positions of Na6Li R p =17.0 R wp =16.9 R exp =5.74 Supplementary Figure S4 Rietveld refinement of XRD pattern for the chemically sodiated Li 4 Ti 5 O 12 sample. Red circles, black, and blue lines correspond to the observed, calculated and difference, respectively. The vertical blue and red bars correspond to the Bragg peaks of Li4/Li7 and Na6Li phases, respectively. As the sealed Kapton film results in two broaden peaks and there is no peak position from Li7/Li4 or Na6Li phase, we excluded this region (20-28 ) to obtain reasonable refinement result. The structure can be fully indexed into Li 7 Ti 5 O 12 (or Li 4 Ti 5 O 12, as they are indistinguishable especially for nano-particles with broadened peaks) and Na 6 LiTi 5 O 12 two phases, with a ratio of 55.5:44.5. The vertical blue and red bars show the expected positions of Bragg reflections for Li7 (R Bragg = 2.74%, R f = 2.05%) and Na6Li (R Bragg = 6.82%, R f = 4.95%) phases, respectively. Refined lattice parameters for Li7 and Na6Li phases are ca Å and 8.72 Å, respectively, demonstrating a volume expansion of 12.5% for Na6Li phase with respect to Li7 phase.

6 LTO (311) LTO (400) LTO (111) discharge charge θ(⁰), λ = nm Voltage (V) Supplementary Figure S5 Peak shifts of Li4/Li7 phase during discharge/charge. The in situ synchrotron XRD data illustrated here are the same as shown in Figure 4, but the (111), (311) and (400) peaks of Li4/Li7 phase are magnified to give a clear illustration of the peak shift during discharge/charge.

7 a b c Ti 8a site O O Ti Li Li d e f Ti O 16c site O Ti Li g h i Ti 16c site O Na O Ti Supplementary Figure S6 Simulated STEM images. (a-c) The simulated HAADF, ABF images and the corresponding ABF line-profile for Li 4 Ti 5 O 12, respectively. (d-f) The simulated HAADF, ABF images and the corresponding ABF line-profile for Li 7 Ti 5 O 12, respectively. (g-i) The simulated HAADF, ABF images and the corresponding ABF line-profile for Na 6 LiTi 5 O 12, respectively.

8 b a [001] Straight line across the atomic column along the [110] direction Ti2 column O column 16c site d Straight line c Ti1 column 8a site Practical line across the atomic columns [110] [110] Supplementary Figure S7 Arrangement of atomic columns in lithiated/sodiated Li4Ti5O12 nano-particles. If we connect the atomic columns in Figure 5a along the [ 1 10] direction, it should be a straight line in the perfect lattice of Li4/Li7/Na6Li phase, as shown in (a). However, both the half- (b) and fully-sodiated (c) nano-particles show visible discrepancy from this arrangement. In contrast, in the lithiated case presented in (d), we see that the lattice arrangement of atomic columns is almost perfect and this should be ascribed to the zero-strain feature in the phase transition between Li4 and Li7 phases. Scale bar in (b-d), 2nm.

9 Na6Li peak Li4/Li7 peak (333) Intensity (a.u.) (111) (113) (004) Cu foil (440) Discharge to 0.5 V Covered film Charge to 3 V θ (Degrees) Supplementary Figure S8 Ex situ XRD patterns of the Li 4 Ti 5 O 12 electrode in the 10 th cycle. The (111), (113), (004), (333) and (400) peaks corresponding to Na6Li and Li4/Li7 phases are marked by red and blue dotted line, respectively. The peak positions of both Na6Li and Li4/Li7 phases are exactly the same as that of the first cycle, indicating that the three-phase reaction mechanism is still evident.

10 Charge 2.4 Voltage (V) Discharge Capacity (mahg -1 ) Supplementary Figure S9 The first charge/discharge profiles of Li 4 Ti 5 O 12 //Na 3 V 2 (PO 4 ) 3 /C sodium full cell at a current rate of C/10.