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

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Unwanted lithium plating on the graphite anode of lithium ion batteries can reduce the cycle life and safety of lithium ion batteries. Increased charging rates, lower temperatures, thicker electrodes, lower Li-ion diffusion constant and larger graphite particles all increase the propensity for unwanted lithium plating. In this work, a variety of electrolyte additives and electrolytes, which extend lifetime during low rate cycling, were used in Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC111/graphite) pouch cells subjected to high rate charging at 20 • C. It was found that additives and electrolytes which increased the negative electrode area-specific resistance, R negative , decreased the onset current, I u , for unwanted lithium plating. Here, the processes of ion desolvation, electron and ion transport through the solid electrolyte interphase and contact resistance are lumped into the R negative . Under conditions where R negative is the dominant factor determining when unwanted Li plating occurs, the onset current for lithium plating could be well predicted by the expression: I u = 0.080 V x S/R negative , where S is the geometric electrode surface area. R negative is easily determined using negative electrode coin-type symmetric cells. This simple rule-of-thumb relation will help guide researchers seeking to select electrolyte additives that simultaneously increase lifetime and also allow fast charging. Unwanted lithium plating can occur in Li-ion cells at high charge rates due to the close working potential of the graphite anode to metallic lithium. If the lithium ions and corresponding electrons cannot intercalate within the graphite particles fast enough, then metallic lithium can deposit on the surface of the graphite anode. Unwanted lithium plating is one mechanism that can limit the lifetime of lithiumion cells. Even worse, plated Li can form dendrites which may pierce the separator and affect the safety of lithium-ion cells. 1,2The propensity for unwanted lithium plating depends on many factors such as electrolyte components, 3 cell design (e.g., anode/cathode ratios, thickness and porosity of the graphite anode), 4 cell history and age (e.g., thickening of the negative electrode solid electrolyte interphase (SEI)) 5 and harsh charging conditions (e.g., high charge rates, low temperature and overcharge).6-8 Among these factors, the electrolyte used in lithium-ion cells not only determines the ionic conductivity but also plays a significant role in determining the properties of the SEI films.9,10 Therefore, the electrolyte components (i.e., Li salt, solvents and additives) can strongly affect unwanted lithium plating.The choice of appropriate electrolyte additives is an efficient and simple way to improve the lifetime of Li ion batteries by modifying the SEI properties.11 Vinylene carbonate (VC) has been commonly used as an additive for forming a robust negative electrode SEI and has been shown to improve the cycle life and calendar life of Li-ion cells.12-14 Ethylene sulfite (ES) was reported to form a...

“…[18][19][20] The additive triallyl phosphate (TAP) is reported to improve the high-voltage performance.…”

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confidence: 99%

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confidence: 99%

Effects of Electrolyte Additives and Solvents on Unwanted Lithium Plating in Lithium-Ion Cells

Liu

Petibon

et al. 2017

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“…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.…”

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confidence: 99%

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

Hall

Nie

Ellis

et al. 2016

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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...

“…In another publication, 14 they found that the introduction of 1% VC to the methoxyethyl methyl sulfone system could provide similar cycling performance to 1.0 M LiPF 6 /EC:DMC (1:1 by volume) in LiCoO 2 /graphite full cells cycled between 3.0 to 4.2 V. Abouimrane et al 6 demonstrated that tetramethylsulfone can be used with EMC as a co-solvent and LiPF 6 Recently, our group has begun studying the effect of electrolyte additives and different solvents in Li[Ni 0.42 Mn 0.42 Co 0. 16 ]O 2 (NMC442)/graphite pouch cells which are balanced for 4.7 V. [16][17][18][19] Ma et al 16 found that NMC442/graphite pouch cells with 2% VC added to 1 M LiPF 6 EC:EMC showed dramatic impedance growth when cycled to 4.3 V and above. The addition of 2% prop-1-ene-1,3-sultone (PES) or 2% PES +1% methylene methanedisulfonate (MMDS) +1% tris(trimethylsilyl) phosphite (TTSPi) ("PES-211") proved to be beneficial in suppressing impedance growth when cells were cycled up to and above 4.4 V. 17 Petibon et al 19 • C for at least several weeks without dramatic capacity loss.…”

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confidence: 99%

“…16 ]O 2 (NMC442)/graphite pouch cells which are balanced for 4.7 V. [16][17][18][19] Ma et al 16 found that NMC442/graphite pouch cells with 2% VC added to 1 M LiPF 6 EC:EMC showed dramatic impedance growth when cycled to 4.3 V and above. The addition of 2% prop-1-ene-1,3-sultone (PES) or 2% PES +1% methylene methanedisulfonate (MMDS) +1% tris(trimethylsilyl) phosphite (TTSPi) ("PES-211") proved to be beneficial in suppressing impedance growth when cells were cycled up to and above 4.4 V. 17 Petibon et al 19 • C for at least several weeks without dramatic capacity loss. Thus, electrolyte additives, concentrated salts and atypical solvents all can play a part in the successful implementation of high voltage Li-ion cells.…”

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confidence: 99%

Sulfolane-Based Electrolyte for High Voltage Li(Ni_0.42Mn_0.42Co_0.16)O₂(NMC442)/Graphite Pouch Cells

Xia

Self

et al. 2015

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Ethylene carbonate (EC)-free electrolyte composed of sulfolane (SL), ethylmethyl carbonate (EMC) and vinylene carbonate (VC) was studied in Li(Ni 0.42 Mn 0.42 Co 0.16 )O 2 (NMC442)/graphite pouch cells using in situ measurements of gas evolution, ultra high precision coulometry (UHPC), automated storage experiments, long-term cycling and electrochemical impedance spectroscopy (EIS). Although cells using 1 M LiPF 6 in SL:EMC 3:7 (w:w) do not function at all, the addition of only 1% VC allows the cells to operate normally. In situ gas measurements show that NMC442/Graphite pouch cells containing SL:EMC:VC electrolyte produce less gas during formation than cells containing control (1 M LiPF 6 EC:EMC 3:7 (w:w)) electrolyte or 2% VC in control electrolyte. Cycling and storage experiments show that cells containing SL:EMC:VC electrolytes can provide better performance than control electrolyte without additives and similar performance to state-of-the-art electrolyte with the ternary additive blend 2% prop-1-ene-1,3-sultone (PES) +1% methylene methanedisulfonate (MMDS) +1% tris(trimethylsilyl) phosphite (TTSPi) ("PES-211") in EC:EMC 3:7 (w:w). The SL:EMC:VC system needs to be further explored with additional additives and from a safety perspective. The development of high voltage Li-ion batteries is one of the best ways to increase their energy density. However, this simple approach has proven to be difficult since electrolyte solvents and additives are unstable at high potentials and the parasitic degradation of these components results in gas evolution, severe impedance growth, low coulombic efficiency (CE) and poor capacity retention.1-4 Therefore, the development of high voltage electrolyte systems is one of the major bottlenecks in the path of Li-ion cells with high energy density.There have been many efforts to develop high voltage electrolyte systems. Some examples include: sulfone-based electrolytes; 5,6 room temperature ionic liquid-based electrolytes; 7 fluorinated electrolytes; 8 nitrile-based electrolytes; 9 as well as electrolyte additives that can properly passivate the positive electrode surface.10 Sulfone-based solvents were first reported in rechargeable lithium batteries by Matsuda et al in 1985. 11 The oxidation potentials of sulfones are generally higher than 5.0 V vs. Li/Li + , independent of the sulfone structure. 12The oxidation potentials of sulfones can be further increased when they are functionalized with strong electron-withdrawing groups. (442)/graphite cells with highly concentrated lithium bis(fluorosulfonyl)imide (LiFSI) in ethyl acetate electrolyte (no EC present) could be cycled to 4.2 V and 4.4 V at 40• C for at least several weeks without dramatic capacity loss. Thus, electrolyte additives, concentrated salts and atypical solvents all can play a part in the successful implementation of high voltage Li-ion cells.Here, the sulfolane (SL) -ethylmethyl carbonate (EMC) -vinylene carbonate (VC) system is shown to be viable in NMC442/graphite pouch cells that can be cycled to 4.5 V for s...