The Li-O 2 Battery with a Dimethylformamide Electrolyte

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1 The Li-O 2 Battery with a Dimethylformamide Electrolyte Yuhui Chen, Stefan A. Freunberger, Zhangquan Peng, Fanny Bardé and Peter G. Bruce* School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST, U.K. Toyota Motor Europe, Technical Centre, Hoge Wei 33 B, B-1930 Zaventem, Belgium Supplementary information EXPERIMENTAL SECTION Electrochemical measurements Dimethylformamide was distilled over a packed bed column and dried for several days over freshly activated molecular sieves (type 4 Å). The water content was 4 ppm (determined using a Mettler-Toledo Karl Fischer titration apparatus). For DMA and NMP the same solvent purification procedure was carried out. Battery grade lithium perchlorate LiClO 4 (Aldrich) and LiN(SO 2 CF 3 ) 2 (LiTFSI) (Aldrich) was dried at 140 C under vacuum overnight prior to being used for preparing the electrolytes. A 3-electrode configuration in a five-neck glass cell was used to investigate cycling. A composite carbon working electrode (WE), silver wire reference (RE), separated from the working electrolyte by porous vycor glass, and lithium iron phosphate (LFP) composite counter electrode (CE), were employed. The composite carbon electrode was composed of Super P (TIMCAL) : PTFE (Aldrich) in an 8:2 (m/m) ratio, and was prepared by coating pastes composed of carbon, binder, and 2-propanol onto a stainless steel mesh current collector, i.e. 80 mg carbon, 20mg PTFE and 2 ml 2-propanol. The electrodes had typically a thickness of m. The LFP counter electrode was composed of LFP nano-powder : Super P : PTFE in an 8:1:1 (m/m) ratio and was prepared in the same way. The electrodes were vacuum-dried at 200 C for 24 hours. LFP was used instead of Li metal, as the former is more stable in contact with DMF, hence the use of a 3-electrode cell and silver wire reference to measure the voltage of the cathode. The LFP CE had a capacity at least twice the observed capacity of the WE. The silver wire RE was calibrated with ferrocene solution after every measurement and the cathode potential quoted vs Li + /Li. Nanoporous gold (NPG) electrode foils were prepared by dealloying white gold leaf by floating it on a bath of concentrated nitric acid for 5 minutes, following a published procedure. 54 This process resulted in a freestanding thin film of NPG. The NPG was dried by heating under vacuum at 150 C overnight. All handling was carried out in an Argon filled glove box. Pure oxygen was bubbled through the flask for 10 minutes prior to the electrochemical measurements, which were performed at room temperature using a VMP3 (Biologic, USA) electrochemical work station. DEMS The in-situ electrochemical cell for differential electrochemical mass spectrometry is based on a Swagelok design. The 3-electrode cell consisted of a Super P carbon composite working electrode, silver reference, electrolyte (0.1 M LiClO 4 in DMF) soaked into a glass fibre separator (Whatman) and a LFP counter electrode. The volume of electrolyte was chosen to completely soak the pores of the CE, separator and WE. 1

2 Mass spectrometry analysis was carried out to examine the gases evolved on discharge and charge using a Thermofisher mass spectrometer, described previously. 32 The setup was calibrated for Ar, O 2, CO 2, H 2, N 2 and H 2 O using calibration mixtures in steps over the anticipated concentration ranges to capture nonlinearity and cross-sensitivity (0-10% Ar/O 2 in each other plus ppm of the other gases). Detection limits are <1 ppm. For typical discharge/charge currents relative gas evolution corresponding to < 0.1 % of the O 2 consumed/evolved is readily detected. Ultrapure He was used for the background. All calibration and quantification was performed using in-house software. Quantification of NO was done using relative sensitivity values vs. O 2 taken from the data base of the MS manufacturer. PXRD, FTIR and NMR Examination of electrodes involved first disassembling the cell, rinsing the cathode twice with dry acetonitrile and removing the acetonitrile under vacuum. Powder X-ray diffraction (PXRD) was carried out using a STOE STADI/P diffractometer operating in transmission mode with a primary beam monochromator and position sensitive detector. Cu Kα 1 radiation (λ= Å) was employed. The samples were contained in an airtight X-ray holder. FTIR measurements were carried out on a Nicolet 6700 spectrometer (Thermo Fisher Scientific) in transmission with a CsI pellet in a N 2 filled glove box. For solution phase 1 H NMR analysis the previously rinsed and dried electrodes were extracted with D 2 O and then the extracted solution examined on a Bruker Avance II 400 spectrometer. 2

3 Figure S1. 1 H NMR spectra of solution extracted by washing the composite electrode with D 2 O after cycling in 0.1 M LiClO 4 in DMF (a) 1 st discharge, (b) 1 st cycle (c) 2 nd discharge, (d) 2 nd cycle and (e) 5 th discharge. 3

4 Figure S2. In-situ DEMS of a cell containing 0.1 M LiClO 4 in DMF and a Super P carbon-ptfe composite electrode (a) 2 nd discharge and (b) 2 nd recharge, scan rate 0.05 mvs -1. Note the NO and H 2 O fluxes are magnified by 10 3 to make them visible on the same plot. Figure S3. FTIR spectra of Super P carbon-ptfe composite electrodes cycled in 0.1 M LiTFSI in DMF, rate 70 mag -1 (carbon). Spectra in red correspond to the pristine electrode and electrodes at the end of charge after the indicated number of cycles. 4

5 Figure S4. 1 H NMR spectra of solution extracted by washing the composite electrode with D 2 O after cycling in 0.1 M LiTFSI in DMF (a) 1 st discharge, (b) 1 st cycle, (c) 2 nd discharge, (d) 2 nd cycle and (e) 5 th discharge. 5

6 Figure S5. In-situ DEMS of a cell containing 0.1 M LiTFSI in DMF at a Super P carbon-ptfe composite electrode discharged and recharged, (a) 1 st discharge, (b) 1 st recharge, (c) 2 nd discharge, (d) 2 nd recharge, (e) 5 th discharge and (f) 5 th recharge, scan rate 0.05 mvs -1. Gas fluxes are still rising at 4.2V at which point charging was stopped to avoid possible electrolyte oxidation. Note the NO and H 2 O fluxes are magnified by 10 3 to make them visible on the same plot. 6

7 Figure S6. 1 H NMR spectra of solution extracted by washing the nanoporous gold electrode with D 2 O after cycling in 0.1 M LiClO 4 in DMF (a) 1 st discharge, (b) 5 th discharge. Figure S7. FTIR spectra of Super P carbon-ptfe composite electrodes discharged in 0.1 M LiClO 4 in DMA and in NMP, rate 70 mag -1 (carbon). 7

8 Figure S8 PXRD patterns (Cu Kα) of Super P carbon-ptfe composite electrodes discharged in 0.1 M LiClO 4 in DMA and in NMP. Figure S9 1 H NMR spectra of solution extracted by washing the composite electrode with D 2 O after discharging in 0.1 M LiClO 4 (a) in DMA and (b) in NMP. References (32) Freunberger, S. A.; Chen, Y.; Peng, Z.; Griffin, J. M.; Hardwick, L. J.; Bardé, F.; Novák, P.; Bruce, P. G. J. Am. Chem. Soc. 2011, 133, (54) Ding, Y.; Kim, Y. J.; Erlebacher, J. Adv. Mat. 2004, 16,