The role of two homologous cyclic sulfate electrolyte additives, trimethylene sulfate (or 1,3,2-dioxathiane-2,2-dioxide, TMS) and ethylene sulfate (or 1,3,2-dioxathiolane-2,2-dioxide, DTD), used either alone or in combination with vinylene carbonate (VC) on the lifetime of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC)/graphite pouch cells was studied by correlating data from gas chromatography/mass spectroscopy (GC−MS), dQ/dV analysis, ultrahigh precision coulometry, storage experiments, and X-ray photoelectron spectroscopy. For VC alone, more stable and protective SEI films were observed at the surface of both electrodes due to the formation of a polymer of VC, which results in higher capacity retention. For TMS, similar chemical SEI compositions were found compared to the TMS-free electrolytes. When VC was added to TMS, longer cell lifetime is attributed to VC. For DTD, a cell lifetime that competes with VC was explained by a preferential reduction potential and a much higher fraction of organic compounds in the SEI films. When VC was added to DTD, the contribution of both additives to the SEI films is consistent with the initial reactivity observed from dQ/dV and GC−MS analysis.

LiCoO2/graphite and Li[Ni1/3Mn1/3Co1/3]O2/graphite pouch cells and Li[Ni1-x-yMnxCoy]O2/graphite 18650 cells were made with varying concentrations of vinylene carbonate (VC) and studied using high precision coulometry, extended cycling as well as electrochemical impedance spectroscopy (EIS). As expected, adding increased concentrations of VC (up to 6 wt%) to the control electrolyte resulted in improved coulombic efficiency, decreased charge endpoint slippage and longer cycle life. However, high concentrations of VC led to larger charge transfer resistance, especially at the graphite negative electrode. Understanding how varying amounts of VC impact cell lifetime and impedance allows for optimized electrolyte formulations to be found for different applications that may balance lifetime and power demands.

Li [Ni 0.4 Mn 0.4 Co 0.2 ]O 2 (NMC442)/graphite pouch cells containing various electrolyte additives, either singly or in combination, were studied using cycling experiments up to 4.4 and 4.5 V coupled with simultaneous electrochemical impedance spectroscopy (EIS) measurements. The impedance of most cells increased dramatically at 4.4 and 4.5 V, but was nearly reversible over one cycle. However, during continued cycling, the impedance of all cells slowly increased at all potentials. Electrolyte additives were found to dramatically affect this behavior. The impacts of adding prop-1-ene-1,3-sultone (PES), vinylene carbonate (VC), triallyl phosphate (TAP), methylene methane disulfonate (MMDS), ethylene sulfate (DTD) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) to 1M LiPF 6 ethylene carbonate:ethyl methyl carbonate (EC:EMC) electrolyte were studied. PES-containing cells had dramatically lower impedance and better capacity retention than VC and TAP-containing cells during both 4.4 and 4.5 V experiments. When MMDS, DTD and/or TTSPi were added in combination with PES, the performance was improved further. Finally, continuous charge-discharge cycling was compared to cycling with a 24-hour hold applied at the top of charge at 4.4 V. The high voltage hold led to severe impedance growth which could be partially overcome through the use of optimal additive combinations. Lithium-ion (Li-ion) batteries are currently used in phones, laptop computers and, more recently, electric vehicles. It is well known that electrolyte additives can have a dramatic effect on the performance and lifetime of Li-ion batteries.1,2 Vinylene carbonate (VC) is perhaps the most famous and widely used additive and has been shown to improve cycle and calendar life of Li-ion cells.3 VC is less effective, however, when used in cells cycling to potentials above 4.2 V 4 or at elevated temperatures.5 Sulfur-containing additives have recently been investigated by several research groups in the hopes of overcoming the temperature sensitivity of VC and extending the usable voltage range of Li-ion cells. [6][7][8] Prop-1-ene-1,3-sultone (PES) has been shown to function as a stable solid electrolyte interphase (SEI)-forming additive that improved coulombic efficiency (CE), reduced charge end point capacity slippage and self-discharge rates. 8,9 PES nearly eliminated all gas production during storage at 4.2 V and 60• C, whereas VC did not. 9,10The work by Xia et al. 9 and Nelson et al. 10 demonstrated the superiority of PES over VC as an electrolyte additive in NMC/graphite cells. Methylene methane disulfonate (MMDS) has been shown to reduce electrolyte oxidation at the positive electrode and reduce the volume of gas produced, as well as decrease the impedance and rate of parasitic reactions when compared to cells without MMDS.6,11 The additive ethylene sulfate or 1,3,2-dioxathiolane-2,2-dioxide (DTD) has been shown to function as a film-forming additive for the SEI on the negative electrode.12,13 The additive tris-(trimethyl-silyl) phosphite (TTSPi) has bee...

Ethylene carbonate is a co-solvent used in virtually every lithium ion cell produced today because it enables operation of both the positive and negative electrodes. Most battery scientists believe ethylene carbonate is essential. Surprisingly, totally removing all ethylene carbonate from typical organic carbonate-based electrolytes and adding small amounts of electrolyte additives creates cells that are better than those containing ethylene carbonate. For example an electrolyte of only 2% vinylene carbonate and 98% ethyl methyl carbonate, with selected additives, provides excellent performance to Li[Ni 0.4 Mn 0.4 Co 0.2 ]O 2 /graphite cells cycled up to 4.4 V which increases their energy density by at least 10%. The cells have low impedance, low rates of electrolyte oxidation, good graphite passivation, low gas generation, acceptable conductivity and low cost. This discovery opens an entirely new space for electrolyte development.

The effects of electrolyte additives singly or in combination on Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells have been systematically investigated and compared using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), an automated storage system, gas evolution measurements and selected long-term cycling experiments. The results of testing Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells with different electrolyte additives singly or in combination were measured and the results for over 110 additive sets are compared. A "Figure of Merit" approach is used to rank the effectiveness of the additives and their combinations. The combination of vinylene carbonate (VC) and/or prop-1-ene-1,3 sultone (PES), a sulfur containing additive, such as methylene methane disulfonate (MMDS), as well as either tris(-trimethly-silyl)-phosphate (TTSP) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) as additives in the electrolyte can give cells with extremely high coulombic efficiency, excellent storage properties, low impedance and superior long term cycling at 55 • C. Additive mixtures such as 2% PES + 1% MMDS + 1% TTSPi are especially excellent in all respects. It is hoped that this comprehensive report sets a benchmark for future studies by others and can be used as a guide and reference for the comparison of other electrolyte additives singly or in combination.

LiCoO 2 /graphite and LiNi 0.33 Mn 0.33 Co 0.33 O 2 /graphite Li-ion pouch-type cells filled with 1 M LiPF 6 EC: EMC (3:7 by weight) with the additives vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) were prepared. Some cells underwent partial or complete formation while others underwent full formation followed by charge-discharge cycling or high potential storage. Following a simple liquid-liquid extraction step, the mass ratios of the organic components of the electrolyte were analyzed using gas chromatography (GC) coupled with electron impact mass spectroscopy (MS). This semi-quantitative method proved to be very effective for the removal of the LiPF 6 from the electrolyte, thus preventing damage to the gas chromatograph and mass spectrometer. It also allowed for a quick and simple assessment of the consumption of additives as a function of state of charge and cycling. The purpose of this paper is to make this method widely available to the Li-ion battery research community.

The effectiveness of Prop-1-ene-1,3-sultone (PES) and Vinylene carbonate (VC) as electrolyte additives in Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC)/graphite pouch cells was studied using in situ measurements of gas evolution, ultra high precision coulometry (UHPC), automated storage experiments and electrochemical impedance spectroscopy (EIS). Gas measurements show that cells containing PES produce less gas than cells containing 2% VC during formation and much less gas during elevated temperature storage (60 • C) at 4.2 V. UHPC cycling and storage results show that cells containing 2% PES have higher coulombic efficiency, lower charge end point capacity slippage and smaller voltage drop during storage than cells containing 2% VC. The combination of VC and PES shows even better cycling performance than the single additives, however, at the expense of much higher impedance. EIS studies of positive and negative electrode symmetric cells show that the introduction of PES or VC to control electrolyte affects the individual electrode impedances in a similar way: both increase the negative electrode impedance and decrease the positive electrode impedance. Based on these experiments we suggest that PES is a very useful additive for NMC/graphite Li-ion pouch cells that may encounter high temperatures during storage and cycling.

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...