Tuning glycolide as an SEI-forming additive for thermally robust Li-ion batteries

The effects of a ternary electrolyte additive system on Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells balanced for 4.7 V was thoroughly investigated. The additive system consisted of 2% prop-1-ene-1,3-sultone (PES) + 1% methylene methane disulfonate + 1% tris-(trimethylsilyl)-phosphite (TTSPi) which is denoted "PES211". "PES211" significantly improved the capacity retention, impedance and gas evolution of NMC442/graphite pouch cells cycled at constant current up to 4.4 V or 4.5 V. X-ray photoelectron spectroscopy results suggest more stable and passivating SEI films at both graphite and NMC442 surfaces due to the preferential electrochemical reaction of PES and MMDS as well as the preferential chemical reaction of TTSPi at the graphite surface. "PES211" modifies the reactivity of the LiPF 6 salt at the graphite surface and hinders its degradation at high potential. However, during extended exposure to 4.5 V, less passivating SEI films were observed leading to extensive electrolyte degradation, capacity loss, impedance increase and gas evolution even for NMC442/graphite pouch cells containing "PES211". + which lead to large cell impedance and short lifetime.1,2 To overcome this limitation, the use of electrolyte additives is one of the most simple, economical and effective approaches.3,4 Electrolyte additives are known to hinder unwanted parasitic reactions of electrolyte solvents and/or salts that occur during cycling/storage at the electrolyte/electrode interfaces by modifying the Solid Electrolyte Interphase (SEI). 5Vinylene carbonate (VC) 6 is perhaps the most famous and widely used additive as it has been shown to greatly improve cycle/calendar life and thermal stability of different Li-ion systems.7-13 However, the charge-discharge capacity loss, impedance and gas evolution of cells containing VC all increase at high potentials 14 and high temperatures 15 due to extensive electrolyte degradation. To overcome these limitations and enable the use of high voltage Li-ion cells, sulfurcontaining additives have been recently proposed by different research groups. [16][17][18][19][20] Prop-1-ene-1,3-sultone (PES, Figure 1) was first proposed as a SEI film forming additive by Li et al. 21,22 in LiCoO 2 /graphite cells using PC-based electrolyte. Later, they showed that using PES in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (1:2 by weight) electrolyte also greatly improved the capacity retention of LiNi 0.5 Mn 1.5 O 4 /Li half cells compared to control cells 23 and in LiMn 2 O 4 /graphite cells tested at 60• C compared to cells using VC. 24For this later case, PES was also found to lower the gas production by a factor of 3 after 150 cycles at 60• C compared to the use of VC. Li et al. attributed the beneficial effects of PES to its preferential reaction and the formation of more protective and stable SEI films at both electrode surfaces. Xia et al. 25 and Nelson et al. 26 also demonstrated the superiority of PES over VC as an electrolyte additive for 1 M LiPF 6 in EC:EMC (3:7 by weig...

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confidence: 99%

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confidence: 99%

The Effects of a Ternary Electrolyte Additive System on the Electrode/Electrolyte Interfaces in High Voltage Li-Ion Cells

Madec

Nelson

et al. 2016

“…5,7,10,12 For instance, storage experiments 14 and high precision coulometry 15 showed that VC decreases the rate of electrolyte oxidation at the positive LiCoO 2 electrode. However, the performance and/or gas evolution of cells containing VC degrade at high voltage 16 and high temperatures 17 due to extensive electrolyte degradation. The benefit of using VC as an SEI film forming additive arises from its polymerizable vinyl group.…”

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confidence: 99%

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

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.

“…NMC/graphite cells do not normally function well when charged to high potential (>4.3 V), however, appropriate electrolyte additives have been investigated for use in cells operating at high voltage. 1,2 Although vinylene carbonate (VC) is one of the most widely used electrolyte additives, it is less effective when used in cells cycling to high voltage 3 or at elevated temperatures. 4 The superiority of prop-1-ene-1,3-sultone (PES) over VC in NMC/graphite cells has been demonstrated by Xia et al 5 and Nelson et al 6 Ternary combinations of electrolyte additives are superior to PES alone, particularly PES combined with a sulfur-containing additive (either methylene methane disulfonate [MMDS] or 1,3,2-dioxathiolane-2,2-dioxide [DTD]) and tris-(trimethyl-silyl) phosphite (TTSPi).…”

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confidence: 99%

Effects of Upper Cutoff Potential on LaPO₄-Coated and Uncoated Li[Ni_0.42Mn_0.42Co_0.16]O₂/Graphite Pouch Cells

Nelson¹,

Abarbanel²,

Xia³

et al. 2015

Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite pouch cells, with and without a LaPO 4 coating on the positive electrode active material, containing the additives prop-1-ene-1,3-sultone, 1,3,2-dioxathiolane-2,2-dioxide and tris-(trimethyl-silyl) phosphite were studied using chargehold-discharge cycling experiments up to potentials between 4.4 and 4.5 V at 40 • C. Simultaneous electrochemical impedance spectroscopy measurements were made during cycling. The effects of a 24 hour hold at the top of charge at upper cutoff voltages of 4. 4, 4.425, 4.45, 4.475, and 4.5 V on the impedance and capacity retention of both LaPO 4 -coated and uncoated cells were investigated. All coated cells cycled above 4.4 V exhibited severe capacity fade and large impedance growth over 80 cycles. Uncoated cells cycled to 4.45 V and below exhibited small capacity fade and virtually no impedance growth. Although uncoated cells above 4.45 V were superior to coated cells, capacity fade and impedance growth were present. Impedance growth remains one of the biggest obstacles to high voltage NMC/graphite lithium-ion cells. Lithium-ion (Li-ion) cells are currently used in phones, laptop computers and, more recently, electric vehicles (EV). Electrolyte additives can have a dramatic effect on the cycling performance and calendar life of Li-ion cells. In addition to achieving longer lifetimes and better capacity retention, it is important to increase the voltage range of Li-ion cells which will increase their energy density. In order to reduce the cost of batteries for EV and grid energy storage applications, the use of NMC instead of LiCoO 2 (LCO) as a positive electrode material is advantageous due to the reduced amount of cobalt, an expensive component, in NMC. NMC/graphite cells do not normally function well when charged to high potential (>4.3 V), however, appropriate electrolyte additives have been investigated for use in cells operating at high voltage. 1,2Although vinylene carbonate (VC) is one of the most widely used electrolyte additives, it is less effective when used in cells cycling to high voltage 3 or at elevated temperatures. 4 The superiority of prop-1-ene-1,3-sultone (PES) over VC in NMC/graphite cells has been demonstrated by Xia et al. 5 and Nelson et al. 6 Ternary combinations of electrolyte additives are superior to PES alone, particularly PES combined with a sulfur-containing additive (either methylene methane disulfonate [MMDS] it is important to study and understand the performance of these additives when used in cells undergoing experiments representative of "real-life" Li-ion cell use. Nelson et al. studied the effect of ternary combinations of PES, MMDS or DTD and TTSPi (all added at 1 or 2% by weight to control electrolyte) on the impedance and cycling performance of NMC442 cells up to 4.4 and 4.5 V.1 Cells containing the ternary mixture with MMDS showed very low impedance and excellent capacity retention when cycled continuously up to 4.5 V.1 These cells, however, exhibited severe capacity fade and large impedance grow...