Extremely Stable Sodium Metal Batteries Enabled by Localized. High Concentration Electrolytes

Transcription

1 Supplementary Information for Extremely Stable Sodium Metal Batteries Enabled by Localized High Concentration Electrolytes Jianming Zheng, Shuru Chen, Wengao Zhao, Junhua Song, Mark H. Engelhard, Ji-Guang Zhang, * Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99354, USA Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99354, USA *Corresponding author. jiguang.zhang@pnnl.gov (J.-G. Zhang) S1

2 EXPERIMENTAL SECTION Materials. Sodium metal was obtained from Sigma-Aldrich Corporation. Sodium bis(fluorosulfonyl)imide (NaFSI) was purchased from Solvionic Corporation. NaPF 6 was obtained from Alfa Aesar. 1,2-dimethoxyethane (DME), ethylene carbonate (EC), and diethyl carbonate (DEC) were obtained from BASF Corporation. Bis(2,2,2-trifluoroethyl) ether (BTFE) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were ordered from Synquest Laboratories. The electrolytes were prepared by mixing the required amount of salt and solvent. The localized high concentration electrolyte (LHCE) electrolytes were prepared with DME:BTFE solvent ratios of 1:1, 1:2, and 1:3. The details of the electrolytes studied in this work are provided in Table S1. The concentration of the electrolytes is indicated by molarity (M, mol L -1 ). All the electrolyte preparation was carried out in a circulating-argonfilled glove box (MBraun LABmaster) (O 2 < 0.1 ppm and H 2 O < 0.1 ppm). Characterization. The ionic conductivity test of the electrolytes was performed on a fully integrated multichannel conductivity spectrometer (BioLogic MCS10) equipped with cells made of two parallel Pt electrodes. The viscosity (η) of the electrolytes was determined on a Brookfield DV-II+ Pro Viscometer at room temperature (22~23 C). Raman spectra were measured using a Horiba LabRAM HR Raman spectrometer with spectral resolution of 1 cm - 1. Morphology of Na deposited on a Cu current collector was observed using a Helios focused ion beam scanning electron microscope (SEM) at 5.0 kv. For sample preparation, the Na samples were rinsed with pure DME several times to remove residual electrolyte, and finally dried under vacuum. X-ray photoelectron spectroscopy (XPS) analysis was implemented with a Physical Electronics Quantera scanning X-ray microprobe, which was outfitted with a monochromatic Al Kα X-ray source (1,486.7 ev) for excitation. To avoid any unwanted S2

3 reactions with ambient oxygen and moisture, samples were transferred from the glovebox to the SEM and XPS instruments in a hermetically sealed container filled with Ar gas. Electrochemical testing. Electrochemical measurements were performed with R2032 coin-type batteries. The same amount (100 µl) of electrolyte was used in each cell. The Na Cu cells were constructed using Cu foil as working electrode, Na metal as counter electrode, and one piece of polyethylene (PE) membrane (from Asahi Kasei Corporation) as separator. In each cycle, 1.0 mah cm -2 of Na metal was deposited on the Cu current collector at 0.2 ma -2 or 1.0 ma cm -2, and then stripped until the voltage reached 1.0 V vs. Na/Na +. The coulombic efficiency (CE) of the Na Cu cells was tested using a high precision battery tester (Novonix Battery Testing Services, Inc.), and determined by dividing the charge for Na stripping from Cu substrate by the charge for Na deposition in the same cycle. Na Na symmetric cells were assembled using Na as both working and counter electrodes. After the cells were rested for 24 h, electrochemical impedance spectra were collected in a frequency range of 10 6 ~10-2 Hz with a potential perturbation of 10 mv using a 1255B Solartron frequency response analyzer coupled with a SI 1287 electrochemical interface. The charge/discharge performance of HCE and LHCEs were investigated in a full cell configuration using a Na 3 V 2 (PO 4 ) 3 /carbon (NVP/C) composite as cathode. The cathode was prepared by coating a slurry composed of wt% NVP/C composite (10% carbon in the composite), 10 wt% Super P, and 10 wt% polyvinylidene difluoride (PVDF) onto an Al foil substrate. The electrode loading was controlled at ca. 1.5 mg cm -2. The electrode was punched into discs and further dried under vacuum at 120 C overnight prior to cell assembling. Na NVP SMBs were then assembled using the NVP cathode, a Na metal foil as anode, and a piece of PE membrane as separator in an Ar-filled glove box. Cycling and rate performance tests were performed on a BT-2000 Arbin battery tester at 30 C. All the S3

4 Na NVP cells were cycled in a voltage range between 2.7 and 3.7 V vs. Na/Na +. Long-term cycling was carried out at C/3, 5C, 10C, or 20C, after 3 formation cycles at C/10. Rate performance testing was carried out with a constant charge at C/5 and a gradual increase in discharge C rates after the initial 5 charge/discharge cycles at C/10 (1C = 120 ma g -1 ). The specific capacity was determined on the basis of the active mass of NVP/C composite. a 100 J = 1 ma cm -2 Efficiency (%) b M NaFSI/DME-BTFE(1:3) M NaFSI/DME-BTFE(1:1) Cycle number 100 J = 1 ma cm -2 Efficiency (%) M NaFSI/DME-BTFE(1:3) M NaFSI/DME-BTFE(1:1) Cycle number Figure S1. zoom-in version of the CE data (shown in Figure 2a) of Na Cu cells (a) at early cycles and (b) during long-term cycling at 1 ma cm -2 after 2 formation cycles at 0.2 ma cm -2 with an areal capacity of 1 mah cm -2. S4

5 a Voltage (V vs. Na/Na + ) st cycle 50 th cycle 100 th cycle th cycle 200 th cycle 250 th cycle 1 ma cm -2 b Voltage (V vs. Na/Na + ) Figure S2. Na deposition/stripping profile evolution at 1 ma cm -2 after 2 formation cycles at 0.2 ma cm -2 with an areal capacity of 1 mah cm -2. (a) ; (b) 2.1 M NaFSI/DME-BTFE (1:2) Capacity (mah cm -2 ) st cycle 50 th cycle 100 th cycle th cycle 200 th cycle 250 th cycle 1 ma cm Capacity (mah cm -2 ) S5

6 Figure S3. SEM images of Na deposited on Cu electrode using 1 M NaPF6/EC-DEC (1:1 v:v) at 1 ma cm-2 with an areal capacity of 1 mah cm-2. (a) 5000X; (b) 10,000X. Figure S4. SEM images of Na deposited on Cu electrode using (NaFSI:DME molar ratio 1:5) at 1 ma cm-2 with an areal capacity of 1 mah cm-2. (a) 5000X; (b) 10,000X. S6

7 a b c 3.1 M NaFSI/ DME-BTFE(1:1) 2.1 M NaFSI/ DME-BTFE(1:2) d 1.5 M NaFSI/ DME-BTFE(1:3) Figure S5. SEM images of Na deposited on Cu electrodes at 0.2 ma cm-2 with an areal capacity of 1 mah cm-2: (a) HCE (); (b) LHCE (3.1 M NaFSI/DMEBTFE (1:1)); (c) LHCE (2.1 M NaFSI/DME-BTFE (1:2)); (d) LHCE (1.5 M NaFSI/DMEBTFE (1:3)). S7

8 0.2 a HCE () b J = 1 ma cm -2 LHCE (3.1 M NaFSI/DME-BTFE(1:1)) Potential (V) J = 1 ma cm -2 c LHCE () -0.2 J = 1 ma cm d LHCE (1.5 M NaFSI/DME-BTFE(1:3)) -0.2 J = 1 ma cm Time (h) Figure S6. Long-term cycling of Na deposition/stripping of Na Na cells at 1.0 ma cm -2 after initial two cycles at 0.2 ma cm -2 ; (a) HCE (); (b) LHCE of 3.1 M NaFSI/DME-BTFE (1:1); (c) LHCE of 2.1 M NaFSI/DME-BTFE (1:2); and (d) LHCE of 1.5 M NaFSI/DME-BTFE (1:3). S8

9 0.4 a HCE () b J = 2 ma cm -2 LHCE (3.1 M NaFSI/DME-BTFE(1:1)) Potential (V) c J = 2 ma cm -2 LHCE () -0.2 J = 2 ma cm d LHCE (1.5 M NaFSI/DME-BTFE(1:3)) -0.2 J = 2 ma cm Time (h) Figure S7. Long-term cycling of Na deposition/stripping of Na Na cells at 2.0 ma cm -2 after initial two cycles at 0.2 ma cm -2 ; (a) HCE (); (b) LHCE of 3.1 M NaFSI/DME-BTFE (1:1); (c) LHCE of 2.1 M NaFSI/DME-BTFE (1:2); and (d) LHCE of 1.5 M NaFSI/DME-BTFE (1:3). S9

10 Figure S8. Digital images showing the wettability difference of HCE () and LHCE (2.1 M NaFSI/DME-BTFE (1:2)). a) Side view; b) Surface view. The result demonstrates that the LHCE of 2.1 M NaFSI/DME-BTFE (1:2) shows significantly improved wettability as compared to HCE of. S10

11 Capacity (mah g -1 ) C/10 20C Cycle number 1.5 M NaFSI/DME-BTFE(1:3) Figure S9. Comparison of cycling performance Na Na 3 V 2 (PO 4 ) 3 batteries using dilute 1.7 M NaFSI/DME and LHCE of 1.5 M NaFSI/DME-BTFE (1:3) at 20C after 3 formation cycles at C/10 in the voltage range of 2.7~3.7 V (30 C). S11

12 a 100 C/10 C/3 Capacity (mah g -1 ) M NaFSI/DME-BTFE(1:3) 3.1 M NaFSI/DME-BTFE(1:1) b Voltage (V vs. Na/Na + ) d Voltage (V vs. Na/Na + ) Cycle number Increased polarization 1 st 25 th 50 th 100 th 150 th 200 th Specific capacity (mah g -1 ) Stabilized 1 st 25 th 50 th 100 th 150 th 200 th Specific capacity (mah g -1 ) Specific capacity (mah g -1 ) Figure S10. (a) Cycling performance of Na Na 3 V 2 (PO 4 ) 3 batteries at C/3 after 3 formation cycles at C/10 at 30 C in the voltage range of 2.7~3.7 V. (b-e) Voltage profile evolutions of Na NVP batteries using (b) electrolyte, (c) 3.1 M NaFSI/DME-BTFE (1:1), (d) 2.1 M NaFSI/DME-BTFE (1:2) and (e) 1.5 M NaFSI/DME-BTFE (1:3). c Voltage (V vs. Na/Na + ) e Voltage (V vs. Na/Na + ) M NaFSI/DME-BTFE(1:1) Stabilized 1 st 25 th 50 th 100 th 150 th 200 th 1.5 M NaFSI/DME-BTFE(1:3) Stabilized 1 st 25 th 50 th 100 th 150 th 200 th Specific capacity (mah g -1 ) S12

13 a Capacity (mah g -1 ) b Capacity (mah g -1 ) Figure S11. Cycling performance of Na Na 3 V 2 (PO 4 ) 3 batteries using HCE and different LHCEs at (a) 5C, and (b) 10C after 3 formation cycles at C/10 at 30 C in the voltage range of 2.7~3.7 V. C/10 5C M NaFSI/DME-BTFE(1:3) M NaFSI/DME-BTFE(1:1) Cycle number C/10 10C M NaFSI/DME-BTFE(1:3) M NaFSI/DME-BTFE(1:1) Cycle number S13

14 a Intensity (a. u.) Na1s -O KLL -O KLL -F KLL -F KLL -F1s -Na KLL -O1s Na KLL -C1s -S2s -S2p -Na2s -Na2p b c d Atomic concentration (%) C1s N1s Dilute O F1s Na1s S2p Sputter time (nm) Atomic concentration (%) Binding Energy (ev) C1s N1s HCE O F1s Na1s S2p Sputter time (nm) Figure S12. XPS analysis of the SEI debris on Cu electrodes cycled in different electrolytes. (a) Wide-scan XPS spectra after the 10 th stripping, and (b-d) corresponding atomic concentrations for (b) ; (c) ; (d) 2.1 M NaFSI/DME- BTFE (1:2). Atomic concentration (%) C1s N1s LHCE O F1s 60 Na1s S2p Sputter time (nm) S14

15 a F 1s b F 1s NaF c F 1s NaF NaF d S 2p Li2Sx e S 2p f -SO2- -SO2- Li2Sx S 2p -SO2- Li2Sx g N 1s h N 1s i Binding energy (ev) N 1s Na3N Na3N Na3N j C 1s k C 1s l C 1s O=C-OR C-O C-C O=C-OR C-O C-C O=C-OR C-O C-C m Na 1s n Binding energy (ev) Na 1s o Na 1s p O 1s Na KLL auger O=C-OR q O 1s Na KLL auger O=C-OR r O 1s Na KLL auger O=C-OR Binding energy (ev) Binding energy (ev) Binding energy (ev) Figure S13. XPS analysis of the SEI debris on Cu electrodes cycled in different electrolytes. (a) Narrow-scan XPS spectra after the 10 th stripping for: (a,d,g,j,m,p) ; S15

16 (b,e,h,k,n,q) ; (c,f,i,l,o,r) 2.1 M NaFSI/DME-BTFE (1:2). The three spectra in each graph were collected at various sputtering depth points (,,, from bottom to top) as shown in Figure S12. a Voltage (V vs. Na/Na + ) c Specific capacity (mah g -1 ) M NaFSI/DME-TTE(1:1) J = 0.2 ma cm Areal capacity (mah cm -2 ) 100 C/10 C/ M NaFSI/DME-TTE(1:1) Cycle number b CE (%) d Specific capacity (mah g -1 ) Cycle number C/10 J = 1 ma cm M NaFSI/DME 2.3 M NaFSI/DME-TTE(1:1) C/3 2.3 M NaFSI/DME-TTE(1:1) Charge Discharge Cycle number Figure S14. (a) Initial deposition/stripping profiles at 0.2 ma cm -2 of Na Cu cells using HCE () and LHCE with TTE as diluent (2.3 M NaFSI/DME-TTE (DME:TTE molar ratio 1:1)). (b) Cycling CE of Na Cu cells using HCE () and LHCE (2.3 M NaFSI/DME-TTE) at 1.0 ma cm -2 after 3 formation cycles at 0.2 ma cm -2. (c) Cycling performance of Na Na 3 V 2 (PO 4 ) 3 batteries using HCE () and LHCE (2.3 M NaFSI/DME-TTE) at C/3 after 3 formation cycles at C/10 at 30 C in the voltage range of 2.7~3.7 V. (d) Charge/discharge capacities vs. cycle number of Na Na 3 V 2 (PO 4 ) 3 batteries using LHCE (2.3 M NaFSI/DME-TTE). S16

17 Table S1. Compositions and physicochemical properties of the electrolytes investigated in this work. Electrolyte component DME:BTFE M (mol/l) Viscosity (cp) (22~23 C) Conductivity (ms cm -1 ) (25 C) NaFSI:DME 1: :1 molar ratio NaFSI/DME:BTFE 1: NaFSI/DME:BTFE 1: NaFSI/DME:BTFE 1: NaFSI/DME (1:5) NaPF 6 /EC-DEC (EC:DEC 1:1 v:v) Table S2. Fitted result of electrolyte resistance (R e ) and interfacial resistance (R in ) of the electrochemical impedance spectra as shown in Figures 4a-c. High concentration electrolyte (HCE) Localized high concentration electrolyte (LHCE) NVP NVP R e / Ω R in / Ω Na Na R e / Ω R in / Ω Na NVP R e / Ω R in / Ω S17

18 Table S3. Information of the price and supplier of the NaFSI salt and BTFE and TTE diluents. Chemical Price Supplier BTFE $795 for 100 g Synquest Laboratories TTE $115 for 100 g Synquest Laboratories NaFSI $595. for 50 g Solvionic S18