Solid-State NMR and Electrochemical Dilatometry Study on Li[sup +] Uptake/Extraction Mechanism in SiO Electrode

Self Cite

An expanded graphite ͑e-MCMB, mesocarbon microbeads͒ having a wider interlayer spacing ͑d 002 = 0.404 nm͒ than that of common graphites is prepared by heat-treatment of an oxidized MCMB. When the e-MCMB electrode, which gives a negligible capacitance due to a small surface area, is polarized over a certain onset potential ͓4.6-4.8 V ͑vs Li/Li + ͒ for positive and 1.3-1.0 V for negative direction͔, it is electrochemically activated to be a high-capacitance positive and negative electrode for electrochemical capacitor. The activation process involves an ion intercalation into the interlayer space to generate ion-accessible sites. The intercalation is evidenced by the presence of a voltage plateau in the charge-discharge profiles, and by the widening of the interlayer distance ͑by in situ X-ray diffraction study͒ and concomitant electrode swelling ͑by electrochemical dilatometry͒ that occur at the same potential region. The electrochemically activated e-MCMB particles carry slitlike pores of ca. 0.45 nm in the mean interlayer distance, into which ions very likely enter either bare or with partial solvent shells with a mixed adsorption/ intercalation charge storage behavior. A full cell fabricated with two e-MCMB electrodes delivers a volume specific capacitance of 30-24 F mL Until now, electric double-layer capacitors ͑EDLCs͒, which deliver a higher rate capability and longer cycle life as compared to the modern secondary batteries, have been used as the energy storage device for memory back-up systems. [1][2][3][4][5][6] Recently, the markets for EDLCs have been extended to the higher power and higher energy systems such as hybrid electric vehicles. Energy density of the present EDLC, however, does not meet the market's need. Hence, to exploit such new applications, it is necessary to develop electrode materials having a higher energy density than the conventional ones.The energy density of EDLC is given by E = 1/2 CV 2 , where C stands for the capacitance per volume or weight, and V the working voltage. An enlargement in either C or V can thus be the way to achieve a high energy density in EDLCs. 3,5,7 One way to increase the cell voltage is the use of nonaqueous electrolytes. Normally, the cell voltage of EDLCs employing aqueous electrolytes is below 1.2 V, which can, however, be enlarged up to 3.0 V by using nonaqueous electrolytes. The other approach to increase the energy density is the employment of high-capacitance electrode materials, which are normally high-surface-area conductive materials as the electric double layer is formed at the electrode/electrolyte interface.

Section: Methodsmentioning

confidence: 99%

Electrochemical Activation of Expanded Graphite Electrode for Electrochemical Capacitor

Ka¹,

Oh²

2008

Self Cite

“…However, the electrodes used in Type A, B and C cells were all heavily calendared (to achieve maximum energy density) and as such, it is believed that particle expansion will cause overall cell expansion, as is observed in this work. In all cases, the Si-containing component of the electrodes showed a potential/Li content curve which matched that of amorphous Si 1,15,18 after the first lithiation since the materials were not driven into the Li 15 Si 4 phase based on the negative/positive electrode balance. Pouch cells were received from the respective manufacturers sealed without electrolyte.…”

mentioning

confidence: 86%

“…Silicon is an attractive negative electrode material for increasing the energy-density of lithium-ion cells due to its significantly higher specific and volumetric capacity than graphite (3579 mAh/g for silicon and 2194 Ah/L for Li 15 Si 4 vs. 372 mAh/g for graphite and 719 Ah/L for LiC 6 ).…”

mentioning

confidence: 99%

“…1,11 Such volume changes have been observed with electrochemical dilatometry techniques for Si-graphite composite electrodes, 7,12,13 graphite electrodes 14 and SiO electrodes. 15 A full cell, with such a composite negative electrode paired with a positive electrode, will be affected by the volume change of the positive electrode as it charges and discharges. For example, LiCoO 2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 positive electrodes have been shown to experience volume changes of a few percent during charge and discharge.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Volume, Pressure and Thickness Evolution of Li-Ion Pouch Cells with Silicon-Composite Negative Electrodes

Louli

Trussler

et al. 2017

153

125

In-situ volume, pressure and thickness measurements were performed on Li-ion pouch cells with various silicon-composite negative electrodes to quantify electrode volume expansion. Li(Ni 1-x-y Co x Al y )O 2 /SiO-graphite, LiCoO 2 /Si Alloy-graphite and Li(Ni 1-x-y Co x Al y )O 2 /nano Si-C pouch cells were tested in this work. Archimedes-type in-situ volume measurements and in-situ thickness measurements showed cell expansion during charge and contraction during discharge due to electrode lithiation and de-lithiation. An in-situ pressure measurement was used to measure the effect of electrode volume expansion on volumetricallyconstrained pouch cells. The volume expansion and contraction profiles measured exhibit a non-linear, asymmetric behavior as a function of cell state of charge for all cell types. To explain this, calculations of the volume expansion contribution of each electrode component were performed. Based on the results of the calculations, conclusions about the mechanisms contributing to the measured expansion profiles can be made. Silicon is an attractive negative electrode material for increasing the energy-density of lithium-ion cells due to its significantly higher specific and volumetric capacity than graphite (3579 mAh/g for silicon and 2194 Ah/L for Li 15 Si 4 vs. 372 mAh/g for graphite and 719 Ah/L for LiC 6 ).1,2 However, unlike graphite in which lithium intercalates in a structurally benign process, silicon alloys with lithium, significantly altering its structure resulting in a large volume expansion of 280%.3 Previous studies have shown how this volume expansion can be detrimental to electrodes by causing constituent particles to electrically disconnect from their current collectors, particles to fracture, and damage to the SEI-all of which result in large capacity fade.1,3-5 Confining silicon to nano-sized domains can reduce internal stress on particles to avoid fracture which can mitigate some of these effects.1,2,6,7 Efforts to reduce electrical disconnection of particles often involve making composites of Si-containing electrode materials with more volumetrically benign materials such as graphite.7-10 This effort aims to take advantage of the high capacity of silicon, while diminishing the overall volume expansion of the composite electrode material.Composite Si-graphite electrodes will experience a volume expansion during silicon lithiation. Additionally, the graphite componentalthough to a much smaller extent-will experience a volume expansion, as it has been shown to expand by 10% during lithium insertion.1,11 Such volume changes have been observed with electrochemical dilatometry techniques for Si-graphite composite electrodes, 7,12,13 graphite electrodes 14 and SiO electrodes. 15 A full cell, with such a composite negative electrode paired with a positive electrode, will be affected by the volume change of the positive electrode as it charges and discharges. For example, LiCoO 2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O 2 positive electrodes have been shown to experience volume changes of ...

“…[20][21][22] In recent years, several studies of Si-based anodes have integrated some electrochemical dilatometry results. 16,[23][24][25][26][27][28][29][30][31][32] However, the dilatometric responses are rarely analyzed in detail.The role of the binder is very critical for Si electrodes to maintain the electrode architecture despite the large Si volume change and thereby to achieve long cycle life.8 Although carboxymethyl cellulose * Electrochemical Society Member. z E-mail: roue@emt.inrs.ca (CMC) is not an elastomeric binder, it has been shown to significantly improve the cycling performance of Si electrodes.…”

mentioning

confidence: 99%

Impact of the Slurry pH on the Expansion/Contraction Behavior of Silicon/Carbon/Carboxymethylcellulose Electrodes for Li-Ion Batteries

Tranchot

Idrissi

Thivel

et al. 2016

Electrochemical dilatometry experiments were performed on silicon/carbon/carboxymethylcellulose (Si/C/CMC) composite electrodes prepared with pH7 and buffered pH3 slurries. It was shown that the pH3 electrode better accommodates the severe volume change of the micrometric Si particles, inducing a much better capacity retention with cycling (70% after 10 cycles compared to only 6% for the pH7 electrode). During the first discharge (lithiation), a maximum electrode thickness expansion of ∼170% was observed for the pH3 electrode compared to ∼330% for the pH7 electrode. A lower irreversible expansion was also observed at the end of the 1 st cycle (∼50% compared to ∼180% for the pH7 electrode). It was explained by the fact that the pH3 of the slurry, which is known to favor the formation covalent bonds between the Si particles and the CMC chains, greatly improves the cohesive strength of the electrode as supported by the higher hardness and elastic modulus of the pH3 electrode. When the discharge capacity was limited to 1200 mAh g −1 , a progressive and irreversible swelling of the pH3 electrode was observed upon prolonged cycling, which was attributed to the accumulation of solid electrolyte interface (SEI) products. Silicon is a very attractive active material for Li-ion battery anodes due to its ∼10 times higher gravimetric capacity and ∼3 times higher volumetric capacity than conventional graphite anode (i.e., 3579 mAh g −1 and 2190 mAh cm −3 for Li 15 Si 4 compared to 372 mAh g −1 and 719 mAh cm −3 for LiC 6 ). However, obtaining commercially viable Sibased anodes is very challenging due to the large volume expansion of Si during its lithiation (∼280% from Si to Li 15 Si 4 ).1 This leads to the fracture and rearrangement of the Si particles, inducing the rupture of the electrical network in the composite electrode. As a result, a rapid capacity decay with cycling is observed.2 The large Si volume change also induces an instability of the solid electrolyte interface (SEI), which continuously grows with cycling, decreasing the coulombic efficiency (CE) and increasing the electrode impedance.3 To address these issues, numerous strategies have been investigated for several years as reviewed in Refs. 4-8 with a few significant successes in the improvement of the cycle life of Si-based electrodes (>1000 cycles, at least in half-cell).9-15 Actually, further work is still required to tackle the issue of SEI stability and to obtain low-cost Si-based electrodes with practical relevant surface, gravimetric and volumetric capacities.Considering that the volume change of Si-based electrodes largely contributes to their degradation, monitoring their expansion and contraction with cycling is highly relevant to evaluate the impact of the composite electrode formulation and morphology, and cycling conditions on this process. For this purpose, a simple and efficient method consists of integrating a non-contact gap sensor 16 or a contact displacement transducer 17 to the electrochemical cell, which permits a measurement of any ver...