Reduction mechanisms of additives on Si anodes of Li-ion batteries

Hoz, Julibeth M. Martínez de la; Balbuena, Perla B.

doi:10.1039/c4cp01948b

Cited by 89 publications

(110 citation statements)

References 40 publications

(146 reference statements)

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“…A number of FEC decomposition routes have been proposed and most include LiF and CO 2 (or Li 2 CO 3 ). 15,[19][20][21] There have been claims in the literature that LiF is central to FEC's benefit, 15,21 which would suggest F-containing additives as beneficial to Si cycling. On the other hand VC is also seen as beneficial to Si cycling and does not contain any F. 22 In screenings of electrolyte additives, VC was shown to lead to considerable gassing with ongoing cycling 23 and CO 2 is part of proposed decomposition routes.…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand VC is also seen as beneficial to Si cycling and does not contain any F. 22 In screenings of electrolyte additives, VC was shown to lead to considerable gassing with ongoing cycling 23 and CO 2 is part of proposed decomposition routes. 20 FEC can also lead to gassing particularly at high temperatures with CO 2 as the main component. 24 The present results suggest that the possible production of CO 2 by FEC and VC should be considered when considering mechanisms by which they improve the cycle life of Si-based materials.…”

Section: Discussionmentioning

confidence: 99%

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The Effect of Carbon Dioxide on the Cycle Life and Electrolyte Stability of Li-Ion Full Cells Containing Silicon Alloy

Krause

Chevrier

Jensen

et al. 2017

J. Electrochem. Soc.

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Carbon dioxide is shown to be an effective additive to standard Li-ion electrolyte for extending the cycle life of full pouch cells containing an engineered silicon alloy. CO 2 was introduced to pouch cells by adding a few milligrams of dry ice to cells before sealing. The cells contained composite negative electrodes formulated with 15 to 17 wt% of an engineered silicon alloy and a LiCoO 2 positive electrode. Parasitic electrolyte reactions were measured in-situ by isothermal micro-calorimetry and high precision coulometry and compared to cells containing 1-fluoro ethylene carbonate (FEC). Extended cycling of cells containing CO 2 were compared to cells containing FEC. Cell gas generation and gas consumption were measured by applying the Archimedes principle. A new approach using small tubes in pouch cells to differentiate volume changes from gassing and solid expansion is introduced. Cells with CO 2 showed significantly lower parasitic thermal power, improved coulombic efficiency and better capacity retention compared to cells containing electrolytes with FEC. The gas generation/consumption experiments showed that Si alloy reacts with CO 2 during cycling until it is fully consumed. Combining FEC and CO 2 reduces the consumption rate of CO 2 . Microscopy of cross-sectioned cycled electrodes showed a thin SEI layer and minimal silicon alloy erosion. The combined work establishes CO 2 as a powerful precursor to an effective SEI layer on silicon alloys. Finally, CO 2 is shown to be an effective SEI former for graphite in EC-free electrolytes. The desire to increase energy density in Li-ion cells has fueled the research and development of silicon and silicon-based materials as a component of Li-ion negative electrodes. In most cases, however, only small amounts of silicon or silicon alloy are used largely because of the generally inferior cycle life of silicon compared to graphite. While there can be several reasons for the inferior cycle life of silicon and silicon alloys one important contributor to poor cycle life is the erosion of the silicon particle by parasitic electrolyte reactions. [1][2][3] Because of the volume changes Si experiences during cycling, continuous passivation is required at the surface and the demands on the electrolyte system are greater than for graphite.Carbon dioxide (CO 2 ) has been described as an effective electrolyte additive in metallic Li cells many years ago. 4 In that work it was shown that cycling efficiencies of the Li electrode were greatly increased in the presence of CO 2 . With the development of Li-ion cell chemistry the use of CO 2 was also explored early on. [5][6][7] In a few papers on the subject it was shown that the CO 2 generators, known as pyrocarbonates, were effective in forming SEI layers on graphite. 8,9 More recently a patent by workers at Sanyo has described the effect of electrolytes containing CO 2 on the cycle life of sintered negative electrodes containing silicon. 10In the course of our work on the erosion of silicon alloys our interest was drawn to the ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The Effect of Carbon Dioxide on the Cycle Life and Electrolyte Stability of Li-Ion Full Cells Containing Silicon Alloy

Krause

Chevrier

Jensen

et al. 2017

J. Electrochem. Soc.

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“…22,[26][27][28]30,31,36,[46][47][48][49] A mechanism which would be consistent with this β-value will be presented below. Another important aspect of the FEC consumption analysis in Si-Li vs. Li-Li cells is that the FEC consumption per electrode during charge/discharge cycling only depends on the overall exchanged coulombs.…”

Section: Cellmentioning

confidence: 99%

“…It will be shown that FEC nearly suppresses the reduction of any other electrolyte component, which is consistent with the previous literature and suggests that the rate of FEC reduction is greater than the reduction of EC and linear carbonates. [26][27][28][29][30][31] Furthermore, due to the continuous consumption of FEC quantified by 19 F-NMR, the number of charge/discharge cycles over which silicon anodes can by stabilized by FEC is directly proportional to the total moles of FEC per gram of anode electrode, rather than the FEC concentration in the electrolyte. As a consequence, 10-20% wt FEC additive are highly effective when examined at the high electrolyte/active material weight ratios commonly used in small-scale test cells (e.g., coin cells), but are predicted to not provide long-term protection under the much lower electrolyte/active material weight ratios used in commercial cells.…”

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confidence: 99%

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confidence: 99%

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Consumption of Fluoroethylene Carbonate (FEC) on Si-C Composite Electrodes for Li-Ion Batteries

Jung

Metzger

Haering

et al. 2016

J. Electrochem. Soc.

262

311

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The electrolyte additive fluoroethylene carbonate (FEC) is known to significantly improve the lifetime of Li-ion batteries with silicon anodes. In this work, we show that FEC can indeed improve the lifetime of silicon-carbon composite anodes but is continuously consumed during electrochemical cycling. By the use of 19 F-NMR spectroscopy and charge/discharge cycling we demonstrate that FEC is only capable to stabilize the cell performance as long as FEC is still remaining in the cell. Its total consumption causes a significant increase of the cell polarization leading to a rapid capacity drop. We show with On-line Electrochemical Mass Spectrometry (OEMS) that the presence of FEC in the electrolyte prohibits the reduction of other electrolyte components almost entirely. Consequently, the cumulative irreversible capacity until the rapid capacity drop correlates linearly with the specific amount of FEC (in units of μmol FEC /mg electrode ) in the cell. The latter quantity therefore determines the lifetime of silicon anodes rather than the concentration of FEC in the electrolyte. By correlating the cumulative irreversible capacity and the specific amount of FEC in the cell, we present an easy tool to predict how much cumulative irreversible capacity can be tolerated until all FEC will be consumed in either half-cells or full-cells. We further demonstrate that four electrons are consumed for the reduction of one FEC molecule and that one carbon dioxide molecule is released for every FEC molecule that is reduced. Using all information from this study and combining it with previous reports in literature, a new reductive decomposition mechanism for FEC is proposed yielding CO 2 , LiF, In the emerging market of electric vehicles (EVs), the development of batteries with higher energy density and improved cycle-life is essential.1 However, their penetration of the mass market significantly depends on cost and the available driving range.2 The US Advanced Battery Consortium (USABC) defined the target value of 235 Wh/kg (at a C/3 rate) on a battery level until 2020.3 As outlined in the recent review by Andre et al., 4 reaching this goal requires an increase of the energy density of today's batteries by a factor of roughly 2 to 2.5 and can only be achieved by the development and integration of novel anode and cathode active materials. A critical element to reach this goal is the implementation of anode active materials with much higher specific capacity than currently used graphite anodes (372 mAh/g 1,5,6 ), with silicon being considered as the most likely next generation anode material due to its high natural abundance and very high theoretical specific capacity of roughly 3600 mAh/g (corresponding to the Li 15 Si 4 phase 7 ). The alloying of silicon with lithium is accompanied by large structural changes, resulting in a volume increase by 310% upon full lithiation.5,7-11 These huge volumetric changes upon lithium insertion and extraction are responsible for the generally shorter cycle-life of silicon electrode materials comp...

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Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance

Sina

Alvarado

Shobukawa

et al. 2016

Adv Materials Inter

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Fluoroethylene carbonate (FEC) as an electrolyte additive can considerably improve the cycling performance of silicon (Si) electrodes in Li-ion batteries. However, the fundamental mechanism for how FEC contributes to solid electrolyte interphase (SEI) morphological changes and chemical composition is not well understood. Here, scanning transmission electron microscopy coupled with electron energy loss spectroscopy gives a comprehensive insight as to how FEC affects the SEI evolution in terms of composition and morphology throughout electrochemical cycling. In the fi rst lithiation cycle, the electrode cycled in ethylene carbonate (EC): diethylene carbonate (DEC) forms a porous uneven SEI composed of mostly Li 2 CO 3 . However, the electrode cycled in EC/DEC/FEC is covered in a dense and uniform SEI containing mostly LiF. Interestingly, the intrinsic oxide layer (Li x SiO y ) is not observed at the interface of electrode cycled in EC/DEC/FEC after 1 cycle. This is consistent with fl uoride anion formation from the reduction of FEC, which leads to the chemical attack of any silicon-oxide surface passivation layer. Furthermore, surface sensitive helium ion microscopy and X-ray photoelectron spectroscopy techniques give further insights to the SEI composition and morphology in both electrodes cycled with different electrolytes.

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Reduction mechanisms of additives on Si anodes of Li-ion batteries

Cited by 89 publications

References 40 publications

The Effect of Carbon Dioxide on the Cycle Life and Electrolyte Stability of Li-Ion Full Cells Containing Silicon Alloy

The Effect of Carbon Dioxide on the Cycle Life and Electrolyte Stability of Li-Ion Full Cells Containing Silicon Alloy

Consumption of Fluoroethylene Carbonate (FEC) on Si-C Composite Electrodes for Li-Ion Batteries

Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance

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