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Supporting Information

Nanoscale Surface Modification of Battery Electrodes by Electroless Deposition with Improved Performance for Na-ion battery

Abhishek Lahiri, Mark Olschewski, René Gustus, Natalia Borisenko, Frank Endres

Institute of Electrochemistry, Clausthal University of Technology, Arnold-Sommerfeld-Str. 6,

38678, Clausthal-Zellerfeld, Germany

Experimental Section

1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) and 1-butyl-

1-methylpyrrolidinium bis(fluorosulfonyl)amide ([Py1,4]FSI) were purchased in the highest

available quality from Io-Li-Tec (Germany) and Solvionic, respectively, and were used after

drying under vacuum at 100 oC to remove the water content to below 2 ppm.

GeCl4 (99.999 %), SbCl3 (99.99 %) and NaFSI (99.9 %) were purchased from Alfa Aesar,

Sigma-Aldrich and Solvionic, respectively. The working electrode in the experiment was a

copper plate. Prior to the experiments, the copper plate was cleaned in isopropanol and

acetone to remove surface contaminations. Platinum wire was used as a counter electrode. For

the reference electrode a platinum wire was immersed into the respective ionic liquid

electrolyte and placed inside a glass frit. The electrochemical cell was either a three electrode

cell in a glass beaker or a Teflon cell which was clamped over a Teflon-covered Viton O-ring

onto the substrate, yielding a geometric surface area of 0.3 cm2. Prior to the experiments, the

Teflon cell and the O-ring were cleaned in a mixture of 50:50 vol% of concentrated H2SO4

and H2O2 (35 %) followed by refluxing in distilled water.

The electrochemical measurements were performed in an argon-filled glove box with water

and oxygen contents of below 2 ppm (OMNI-LAB from Vacuum Atmospheres) by using a

VersaStat II (Princeton Applied Research) potentiostat/galvanostat controlled by powerCV.

The entire scan rate during cyclic voltammetry was 1 mV sec-1. After the constant potential

deposition, the deposit was washed in isopropanol to remove any remaining ionic liquid.

For preparation of anode, Ge was electrodeposited at -2.2 V vs. Pt for 30 minutes from

0.25 M GeCl4 in [Py1,4]TFSI . After the electrodeposition was done, the remaining ionic liquid

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2016

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in the cell was removed and the electrodeposited germanium was washed in the pure ionic

liquid inside of the glove box. For surface modification, the electrodeposited Ge was exposed

to 0.1 M SbCl3-[Py1,4]TFSI for 10 minutes for the galvanic displacement reaction to take

place. After 10 minutes, the electrolyte was removed and the deposited material was again

washed with pure [Py1,4]TFSI. For battery testing, half-cell setups were made with the

electrodeposited material as the working electrode and a sodium metal as the counter

electrode. The two electrodes were separated with a Celgrad 2400 membrane and the

electrolyte used was 1 M NaFSI/[Py1,4]FSI. The galvanostatic charge-discharge cycles were

performed using VersaStat 3 (Princeton Applied Research) potentiostat/galvanostat.

Raman spectra were recorded by a Bruker Senterra Raman microscope using 50X objective

with a laser excitation of 532 nm. Photoelectron spectra (XPS) were obtained using an

ultrahigh vacuum (UHV) apparatus with a base pressure below 1x10-10 hPa. The sample was

irradiated using the Al K alpha line (photon energy of 1486.6 eV) of a non-monochromatic

X-ray source (Omicron DAR 400). Electrons emitted were detected by a hemispherical

analyser (Omicron EA125) under an angle of 45° to the surface normal with a calculated

resolution of 0.83 eV for detail spectra and 2.07 eV for survey spectra. All XPS spectra were

displayed as a function of the binding energy with respect to the Fermi level.

Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) were carried

out in a Scanning Auger Microscope (Omicron NanoSAM) with a base pressure below

10-10 hPa. AES was performed with a primary electron energy of 5 keV using a hemispherical

analyser. All SEM images were taken with an energy of 5 keV and an incident electron beam

of 1.5 nA. For XPS, SEM and AES analysis the sample was etched by argon ions accelerated

to 1 keV by an Omicron ISE 5 ion source to clean residual ionic liquid on the surface.

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Figure S1: Change in potential measured on exposing electodeposited (Ed) Ge in

0.1 M SbCl3-[Py1,4]TFSI

Figure S2: EDX spectra of (a) electrodeposited Ge (b) electroless deposited Sb on Ge from

0.1 M SbCl3-[Py1,4]TFSI

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Figure S3: XPS survey spectra of Ge (blue) and Sb modified Ge (green)

Figure S4: XPS detail spectra for Sb modified Ge before cycling (black squares) and Gaussian peak fits for (a) Ge 3d structure (b) Sb 3d and O 1s. Peak fits allow distinguishing Sb 3d5/2 (green lines) and O 1s features

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Figure S5: XPS Survey spectra before (green and blue spectra) and after cycling. Cycled Ge

deposit as black line and Sb modified Ge as red line

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Figure S6: Sb 3d and O 1s detail spectra for Sb modified Ge before and after cycling (red data

points) in comparison

Figure S7: SEM image of Sb modified Ge after first full charge recorded at beam energy

of 5 kV showing layered structure of SEI