Effect of Sulfate Electrolyte Additives on LiNi1/3Mn1/3Co1/3O2/Graphite Pouch Cell Lifetime: Correlation between XPS Surface Studies and Electrochemical Test Results

The role of prop-1-ene-1,3-sultone (PES) used alone or in combination with vinylene carbonate (VC) in LiNi1/3Mn1/3Co1/3O2(NMC)/graphite pouch cells was studied by correlating data from differential capacity (dQ/dV) analysis, gas chromatography/mass spectroscopy (GC−MS), ultrahigh precision coulometry, storage experiments and X-ray photoelectron spectroscopy. VC formed more stable and protective SEI films at both graphite and NMC surfaces due to the formation of a polymer of VC. For PES-containing electrolytes, the preferential reaction of PES led to the formation of SEI films with higher oxygen content at both graphite and NMC surfaces due to the additional oxygen contribution of sulfite species and substantially less LiF compared to control and VC electrolytes. PES also led to thicker SEI films at the NMC surface. When VC was combined with PES, features of the SEI films from both VC and PES were observed. The SEI film features for VC and PES used alone or in combination can explain the improved electrochemical performance as well as the lower production of gas observed with these additives compared to control electrolyte.

Section: Resultssupporting

confidence: 82%

Understanding the Role of Prop-1-ene-1,3-Sultone and Vinylene Carbonate in LiNi_1/3Mn_1/3Co_1/3O₂/Graphite Pouch Cells: Electrochemical, GC-MS and XPS Analysis

Madec

Petibon

Xia

et al. 2015

“…However, the peak spacing and widths were not a good match with the typical values obtained with this instrument. 47 It was then considered whether the two peaks may correspond to the reduced bipyridine adduct species, where the low BE peak corresponds to the aromatic carbon (C=C) and the higher BE peak corresponds to the carbon atoms directly bonded to nitrogen (C-N). The C-N peak is approximately expected to be at the same position as C-O.…”

Section: Resultsmentioning

confidence: 99%

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

Hall

Nie

Ellis

et al. 2016

Self Cite

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...

“…The sample holder was then transferred into the XPS system, without exposure to air, using a vacuum suitcase. 12 Electrodes were left under ultra-high vacuum overnight to allow for off-gassing of any remaining volatile components. The samples were then transferred to the analysis chamber of the XPS, which had a base pressure <2 × 10 −10 mbar, which was always at a pressure >2 × 10 −9 mbar during analysis.…”

mentioning

confidence: 99%

Quantifying, Understanding and Evaluating the Effects of Gas Consumption in Lithium-Ion Cells

Ellis

Allen

Thompson

et al. 2017

114

Lithium-ion cells produce a considerable amount of gas in their first cycle. If the gases are not removed in a degassing step, most are consumed by the cell over time. This phenomenon has never been investigated explicitly in the literature. In this paper, the evolution and subsequent consumption of gas in typical lithium-ion cells are measured by Archimedes' principle and gas chromatography. It is found that all evolved gases are subsequently consumed to some degree, except for saturated hydrocarbons. The consumption of gas occurs predominantly at the negative electrode, where the gases are reduced to form part of the solid-electrolyte interphase (SEI). Changes to the negative electrode SEI upon gas consumption are investigated using X-ray photoelectron spectroscopy. The effect of gas consumption on cell performance is studied with ultra-high precision charging and high voltage storage experiments. It is found that gas consumption does not result in measurable adverse effects to cell performance. Lithium-ion cells can produce a significant amount of gas during the first charge (in the formation cycle), as electrolyte and additives react at the surfaces of the charging electrodes to form passivating films. If lithium-ion cells are packaged in a flexible casing, these gases are normally removed by the manufacturer in a degassing step, to prevent deformation of the cell and to ensure uniform stack pressure on the electrodes. If the degassing step is omitted, a large portion of the gas evolved is consumed over time.1 The reactions that consume gas are presumably prevalent in hard-cased cylindrical cells, such as 18650 s, which are often hermetically sealed before the first charge, and therefore cannot be easily degassed. The reactions that consume gas are presumably less prevalent in pouch-type cells, which are degassed.Several authors have speculated about the fates of gases in lithiumion cells.2-5 There has been no work explicitly dedicated to understanding the phenomenon of gas consumption. There is no consensus as to whether the effects of gas consumption are beneficial or harmful to cell performance. For example, it has been argued by some that the consumption of CO 2 is beneficial to cells, as it reacts to form a passivating film on the negative electrode. 3,4,6 However it has also been argued that the consumption of CO 2 is detrimental to cells, as it may reduce at the negative electrode to form Li 2 C 2 O 4 , which causes continual self-discharge at high voltage. 2It is important for both scientists and manufacturers of lithium-ion cells to understand the causes and the effects of gas consumption. If gas consumption is quick, benign, or even beneficial to cell performance, then the time-consuming degassing step for lithium-ion pouch cells might be skipped. 7 The gases evolved in lithium-ion pouch cells could be left for consumption within the cell, perhaps leaving the pouch cell flat and rigid after several hours if all the gases were consumed. If gas consumption in a cell produces undesirable effects, such...