Properties of solid electrolyte interphase formed by prop-1-ene-1,3-sultone on graphite anode of Li-ion batteries

The use of electrolyte additives to form a passive solid-electrolyte interphase (SEI) at one or both electrodes is a common method for improving lithium-ion cell lifetime and performance. This work follows the chemical and electrochemical processes involved in SEI formation on graphite electrodes for two Lewis acid-base adducts, pyridine boron trifluoride (PBF) and pyridine phosphorus pentafluoride (PPF). The combination of experimental methods (electrochemistry, in situ volumetric measurements, gas chromatography, isothermal microcalorimetry, and X-ray photoelectron spectroscopy) with quantum chemistry models (density functional theory) provides new insight into the interfacial chemistry. PBF and PPF are reduced at ∼1.3 V vs. Li/Li + and ∼1.4 V, respectively. This is followed by radical coupling to form 4,4 -bipyridine adducts, hydrogen transfer to ethylene carbonate solvent molecules, and reduction of the solvent to produce lithium ethyl carbonate. The reduced bipyridine adducts, Li 2 (PBF) 2 Over the past decade, the predominant electrolyte solution used in lithium-ion cells has remained lithium hexafluorophosphate (LiPF 6 ) salt dissolved in some blend of organic carbonate solvents.1 This is not, however, an indication that advances in cell solution chemistry have stagnated, but it is rather a result of a major shift to focus on electrolyte additives. By adding just a few weight percent of the right compounds to the electrolyte solution before cells are filled, one can significantly improve charge-discharge cycling performance, extend calendar lifetime, decrease detrimental gas formation, and improve lithium-ion cell safety. [1][2][3][4][5] This move to electrolyte additives has the rather practical aspect that the battery industry can tweak performance with minimal changes to their existing supply chains for LiPF 6 and solvents.1 This article will focus on Li(Ni a Mn b Co 1−a−b )O 2 (NMC)/graphite cells, for which vinylene carbonate (VC), [6][7][8][9][10] prop-1-ene-1,3-sultone (PES), [8][9][10][11][12][13][14][15] methylene methane disulfonate (MMDS), tris(trimethylsilyl) phosphite (TTSPi), 16,17 and triallyl phosphate (TAP) 18,19 are among the best reported additives. Recently, Nie et al. introduced a series of Lewis acid-base adducts that may be used individually or as part of an additive blend. [20][21][22] In particular, pyridine boron trifluoride (PBF) and pyridine phosphorus pentafluoride (PPF) offer improved charge capacity retention after cycling at high temperature and high cell voltage. 20 It is these latter two additives that will be closely examined in this article, chosen because they are still quite new and, so far, relatively unstudied.If one is to optimize the solution chemistry in lithium-ion cells for various applications (high temperature, high power, etc.), it is clearly desirable to have thoroughly characterized the chemical and electrochemical reactions in a cell, including all those of the various electrolyte additives. Unfortunately, such a detailed understanding of the many proces...

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Surface-Electrolyte Interphase Formation in Lithium-Ion Cells Containing Pyridine Adduct Additives

Hall

Nie

Ellis

et al. 2016

“…z E-mail: jeff.dahn@dal.ca X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), Li et al 14 found sulfur-containing species in the SEI on the graphite electrode, which indicated the importance of PES in forming the protective SEI. Sano et al 15 showed that the SEI on the graphite electrode in cells with DTD contained a polyethylene oxide (PEO) like polymer and Li 2 S-like compounds.…”

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Ternary Electrolyte Additive Mixtures for Li-Ion Cells that Promote Long Lifetime and Less Reactivity with Charged Electrodes at Elevated Temperatures

Xia

Dahn

2015

(NMC111)/graphite and Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells demonstrate superb performance when ternary blends of electrolyte additives are added to the cells. These ternary blends contain one of vinylene carbonate (VC) or prop-1-ene-1,3-sultone (PES) plus a sulfur containing molecule and tris(trimethylsilyl) phosphite (TTSPi). Here, the excellent charge-discharge capacity retention of cells containing these ternary blends of additives is demonstrated at both 45 • C and 55 • C by comparison to cells with only VC or PES additives alone. The impact of a number of sulfur-and phosphorous-containing electrolyte additives on the reactivity of charged electrode materials with electrolyte at elevated temperatures was studied using accelerating rate calorimetry (ARC). The electrolyte additives, methylene methanedisulfonate (MMDS) and TTSPi, dramatically reduce the reactivity between lithiated (charged) graphite and electrolyte. Lithium-ion cells used in electrified vehicles require longer calendar and cycle lifetime than those used in portable electronics (e.g. laptops and cell phones). In addition, cell used in electrified vehicles can reach high temperatures, so improved tolerance of Li-ion cells to high temperature exposure is also desired. One method of extending lifetime and temperature tolerance of Li-ion cells is to use electrolyte additives in order to suppress parasitic reactions between charged electrodes and electrolyte.1,2 Vinylene carbonate (VC), a popular electrolyte additive, has been shown to improve Li-ion cell performance. 3,4 Recently, some novel sulfur-containing and phosphorouscontaining electrolyte additives have also been shown to be able to increase lifetime, control impedance growth and suppress gas production, etc. for Li-ion cells. Xia et al. 5 showed that the addition of ethylene sulfate (DTD) or trimethylene sulfate (TMS) to Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC111)/graphite pouch cells could increase coulombic efficiency (CE) and decrease impedance after cycling compared to cells without additives. Methylene methanedisulfonate (MMDS) has been shown to be able to greatly decrease the impedance of NMC111/graphite cells after cycling and slow the rate of parasitic reactions at the Li x MO 2 electrode according to storage results.6 Xia et al.7 also showed that prop-1-ene-1,3-sultone (PES) could increase CE, decrease charge end point capacity slippage and suppress gas production during cycling for NMC111/graphite pouch cells. Sinha et al. 8 showed that the CE of NMC111/graphite pouch cells was improved and impedance was reduced when tris(trimethylsilyl) phosphate (TTSP) or tris(trimethylsilyl) phosphite (TTSPi) was added to the electrolyte. In a massive study of over 110 electrolyte additive combinations tested in NMC111/graphite pouch cells, Wang et al. showed that ternary electrolyte additive blends containing one or more of VC or PES, one or more of DTD, MMDS, ES or TMS and one or more of TTSP or TTSPi led to cells with excellent performance. Electrolyte additives improve...

“…z E-mail: jeff.dahn@dal.ca VC by fluoroethylene carbonate (FEC) or difluoro ethylene carbonate (DiFEC). 15 EC-free, linear alkyl carbonate-electrolytes with SEIenabling additives have been shown to have acceptable conductivity, acceptable ability to dissolve LiPF 6 , good wetting of the separator, good tolerance to high voltage and their use leads to Li-ion cells with long cycle and calendar lifetime, when compared to EC-containing electrolytes with state-of-the-art electrolyte additive packages. 14 In an effort to further improve EC-free 1 M LiPF 6 in EMC:VC 98:2 electrolyte, various additives to this electrolyte were carefully studied in NMC442/graphite Li-ion pouch cells.…”

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“…The additives selected for this study are well-known in the literature and have been shown to improve the quality of the negative electrode SEI or to reduce parasitic reactions at high voltage in NMC442/graphite cells. The additives used in this study were prop-1-ene,1,3-sultone (PES), 15,16 methylene methanedisulfonate (MMDS), 17 propanediol cyclic sulfate (trimethylene sulfate -TMS), 18 1,3,2-dioxathiolan-2,2-oxide (ethylene sulfate -DTD), 18 tris(trimethylsilyl) phosphite (TTSPi), 19 Tris(trimethylsilyl) phosphate (TTSP), 19 pyridine boron trifluoride (PBF), 20 pyridine phosphorus pentafluoride (PPF), 21 maleic anhydride (MA), 22 succinic anhydride (SA), 23 4-(trifluoromethyl) benzonitrile (4-TB), 24 hexamethylene diisocynate (HDI) 25 and triallyl phosphate (TAP). 26 The chemical structures of these additives are shown in Figure 1.…”

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See 1 more Smart Citation

Improving Linear Alkyl Carbonate Electrolytes with Electrolyte Additives

Xia

Glazier

Petibon

et al. 2017

The effectiveness of some selected electrolyte additives were studied in ethylene carbonate-free linear alkyl carbonate electrolyte mixtures containing 1 M LiPF 6 /ethylmethyl carbonate: vinylene carbonate (98:2 w:w). The electrolytes were used in Li(Ni 0.4 Mn 0.4 Co 0.2 )O 2 /graphite pouch type Li-ion cells tested to 4.5 V at elevated temperature. The results showed that cells with linear alkyl carbonate electrolytes outperformed cells with EC-based electrolytes having state-of-the-art additive blends and cells with fluorinated electrolytes during short-term and long-term cycling at elevated temperatures. The addition of triallyl phosphate or pyridine phosphorus pentafluoride as electrolyte additives to the EC-free electrolyte provided cells with better capacity retention during long-term cycling than cells containing vinylene carbonate alone. These results suggest that small quantities of electrolyte additives can be used to create EC-free, linear alkyl carbonate electrolytes that perform well at high voltages. Energy-dense, long-lasting lithium-ion cells are in high demand for electric vehicles, portable electronics and many other important technologies. The easiest way to increase the energy density of a conventional lithium-ion cell is to increase its upper charge cutoff potential when certain layered oxide positive electrode materials are used. However, increasing the upper cutoff potential normally decreases cell lifetime because the rate of unwanted parasitic reactions like electrolyte oxidation increase with potential. Parasitic reactions involving ethylene carbonate (EC)-a ubiquitous co-solvent in lithiumion electrolytes-at high potential has proven to be one of the most important factors to overcome. 1Until recently, EC has been regarded as an essential component of lithium-ion electrolytes and it has been used in nearly all commercial Li-ion cells produced today. EC was first considered as an electrolyte co-solvent by Elliot in 1964 2 and was used as an electrolyte component in cells with lithiated graphite electrodes by Fong et al. in 1990. 3 EC was found to preferentially react with Li + and electrons at the surface of the graphite electrode prior to lithium intercalation, forming a solid electrolyte interface (SEI) on the surface of the graphite electrode that then allowed the reversible intercalation and de-intercalation of lithium ions into the graphite electrode at very low potentials (<0.20 V).3-5 It was generally believed that the graphite electrode could not be electrochemically lithiated in most common solvents, including ethers, esters, butyrolactones and propylene carbonate, without the sacrificial reaction of EC to form the SEI. 6While the passivation of graphite is virtually complete during the first few cycles, the remaining EC in the electrolyte can be oxidized at high voltages, causing the performance of cells containing EC to diminish as the upper charge voltage increases above 4.4 V.7,8 Electrolyte oxidation at the positive electrode at high potentials can lead to salt consum...