In Situ Conductivity, Impedance Spectroscopy, and Ex Situ Raman Spectra of Amorphous Silicon during the Insertion/Extraction of Lithium

Pollak, Elad; Salitra, Gregory; Baranchugov, V.; Aurbach, Doron

doi:10.1021/jp0729563

Cited by 220 publications

(193 citation statements)

References 37 publications

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“…Apart from suffi cient ionic conductivity this also indicates suffi cient electronic conductivity, likely because the inserted Na ions and associated doping lead to a better electronic conductivity of the electrode. Similar effects have been reported on lithiation of Si, [ 25,26 ] and theoretical studies on Na ion insertion in Si based materials. [ 14,16 ] To obtain insight in the equilibrium potentials during sodiation and desodiation the galvanostatic intermittent titration technique (GITT) is utilized.…”

supporting

confidence: 82%

Reversible Na‐Ion Uptake in Si Nanoparticles

Swaans²,

Basak

et al. 2015

Advanced Energy Materials

110

103

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appear to be nicely spherical, whereas the surface layer has been oxidized. A native oxidation layer grows on the surface of individual Si nanoparticles when they are exposed to traces of air after synthesis. The presence of such limited pacifying oxide layer appeared of advantage for the further processing in air. The average thickness of the oxidation layer is around 1.2 nm, and it is amorphous when observed by X-ray diffraction (XRD) (Figure 1 c), i.e., only peaks corresponding to crystalline Si are visible. For a particle with a size of 20 nm Si in diameter and 1.2 nm outer layer of SiO 2 , the volume percentage of SiO 2 is 28.8%. Raman spectra (Figure 1 d) on the sample report that both crystalline and amorphous Si exist and the amount of amorphous Si is signifi cant (c-Si:a-Si = 0.39:0.61; quantitative analysis in the Supporting Information). To determine the amount of oxygen in the sample, thermogravimetric analysis (TGA) is carried out by heating the Si NP sample under a mixture of O 2 /Ar gas and fully oxidizing Si into SiO 2 . The result indicates that the amount of Si accounts for 69.0 wt% of the sample ( Figure S2, Supporting Information), i.e., Si:SiO 2 = 0.83:0.17 in mole. Meanwhile, the volume fraction from the estimated mass ratio above is 28.2% and is in good quantitative agreement with the one estimated from TEM.Galvanostatic tests on the Si NP electrode are performed using different dis-/charge currents between applied potentials of 0.01 and 2.8 V. In this paper, all specifi c currents applied are calculated with respect to the mass of Si. De-/sodiation capacities of Si stated in this paper are the capacities after subtracting the capacity of the super P carbon black ( Figure S3, Supporting Information), and excluding inactive SiO x inside the sample.Figure 2 a demonstrates an initial sodiation capacity of 1027 mAh g −1 for Si at 20 mA g −1 , which is higher than the theoretical capacity (954 mAh g −1 for NaSi). A large part of this initial capacity is attributed to the irreversible formation of a solid electrolyte interface (SEI) layer on the surface of Si in combination with some decomposition of electrolyte, and possibly also the irreversible formation of sodium silicate from reaction with SiO 2 . The subsequent Na ion extraction process achieves a capacity up to 270 mAh g −1 , indicating that a signifi cant Na fraction is stored reversibly, next to the large irreversible part. For the subsequent few cycles the sodiation capacity decreases from above 410 mAh g −1 to around 300 mAh g −1 but the desodiation capacity is relatively stable around 260 mAh g −1 . The Coulombic effi ciency grows gradually to >90%, after which the de-/sodiation capacity becomes relatively stable. After 100 cycles the reversible capacity retention reaches 248 mAh g −1 , which is 92% of the fi rst desodiation capacity; and the Coulombic efficiency declines slowly to 87% in this cycle test. Additionally, Figure 1 e shows that after charge/discharge for 100 cycles Si particles in this electrode got fractured into small g...

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supporting

confidence: 82%

Reversible Na‐Ion Uptake in Si Nanoparticles

Swaans²,

Basak

et al. 2015

Advanced Energy Materials

110

103

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“…The semicircle on the EIS spectrum of Si-1100-800 is smaller than that on the spectrum of Si-1100-620, indicating that Si-1100-800 has a lower charge transfer resistance. [ 56 ] Figure 5 . (a) Raman spectra of Si-1100-620 and Si-1100-800 around carbon region; (b) XPS spectra of Si-1100, Si-1100-620 and Si-1100-800; (c) Raman spectra of Si-1100, Si-1100-620 and Si-1100-800 around the silicon region.…”

Section: Full Papermentioning

confidence: 99%

Influence of Silicon Nanoscale Building Blocks Size and Carbon Coating on the Performance of Micro‐Sized Si–C Composite Li‐Ion Anodes

Dai

Gordin

et al. 2013

Advanced Energy Materials

176

153

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Silicon has been intensively pursued as the most promising anode material for Li‐ion batteries due to its high theoretical capacity of 3579 mAh/g. Micro‐sized Si–C composites composed of nanoscale primary building blocks are attractive Si‐based anodes for practical application because they not only achieve excellent cycling stability, but also offer both gravimetric and volumetric capacity. However, the effects of key parameters in designing such materials on their electrochemical performance are unknown and how to optimize them thus remains to be explored. Herein, the influence of Si nanoscale building block size and carbon coating on the electrochemical performance of the micro‐sized Si–C composites is investigated. It is found that the critical Si building block size is 15 nm, which enables a high capacity without compromising the cycling stability, and that carbon coating at higher temperature improves the first cycle coulombic efficiency (CE) and the rate capability. Corresponding reasons underlying electrochemical performance are revealed by various characterizations. Combining both optimized Si building block size and carbon coating temperature, the resultant composite can sustain 600 cycles at 1.2 A/g with a fixed lithiation capacity of 1200 mAh/g, the best cycling performance with such a high capacity for micro‐sized Si‐based anodes.

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“…Amongst anode candidates, [1][2][3][4][5][6] silicon is especially attractive owing to its high specific capacity (3579 mAh/g for lithiation to the amorphous phase limit of Li 15 Si 4 vs. 372 mAh/g for graphite to composition LiC 6 ) and high natural abundance. 2,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] However, silicon electrodes suffer from accelerated capacity fade compared to established intercalation electrodes, which is attributed to losses originating from fracture and fragmentation induced by the nearly 300% particle volume expansion upon lithiation. 4,25 The general trend toward nanoscaling of silicon has been motivated almost entirely by these considerations.…”

mentioning

confidence: 99%

Electrochemical Charge Transfer Reaction Kinetics at the Silicon-Liquid Electrolyte Interface

Swamy¹,

Chiang²

2015

J. Electrochem. Soc.

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Since the gravimetric lithiation capacity of silicon is roughly ten times that of graphite, while their mass densities are comparable, for the same particle size the current density required to cycle a silicon electrode at a given C-rate is about ten times greater than that of graphite. Depending on the magnitude of the corresponding Butler-Volmer exchange current density, jo, such high current densities may cause the charge transfer kinetics at the silicon-electrolyte interface to become rate limiting. Previously reported values of jo for Si differ by about 10 orders of magnitude. Here we report jo measurements using electrochemical impedance spectroscopy (EIS) for single crystal electronically conductive silicon wafers with well-defined (100) and (111) orientations and active surface areas. The electrochemical cycling regime was designed to avoid artifacts due to stress-induced surface cracking of Si upon lithiation. The exchange current density of the silicon-electrolyte interface is found to be 0.1 ± 0.01 mA/cm2 when using electrolyte consisting of 1 M LiPF6 in EC/DMC (1/1 by wt) + FEC (10 wt%) + VC (2 wt%). These results are then used to illustrate the dependence of kinetic overpotential on particle size and C-rate for silicon compared to lower volumetric capacity compounds such as graphite.

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In Situ Conductivity, Impedance Spectroscopy, and Ex Situ Raman Spectra of Amorphous Silicon during the Insertion/Extraction of Lithium

Cited by 220 publications

References 37 publications

Reversible Na‐Ion Uptake in Si Nanoparticles

Reversible Na‐Ion Uptake in Si Nanoparticles

Influence of Silicon Nanoscale Building Blocks Size and Carbon Coating on the Performance of Micro‐Sized Si–C Composite Li‐Ion Anodes

Electrochemical Charge Transfer Reaction Kinetics at the Silicon-Liquid Electrolyte Interface

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