Why is tris(trimethylsilyl) phosphite effective as an additive for high-voltage lithium-ion batteries?

Han, Young‐Kyu; Yoo, Jaeik; Yim, Taeeun

doi:10.1039/c5ta01253h

Cited by 114 publications

(131 citation statements)

References 52 publications

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“…Besides Me 3 SiF (TMSF), two more decomposition compounds: Me 3 SiOH (TMSOH) and Me 3 SiOSiMe 3 (TMSOTMS) have also been observed in the 1 H-NMR spectra of the TMSPi-containing electrolyte, 18 indicating that the highly electrophilic TMS group acts not selectively as a F À receptor, but rather as an receptor for all anions. Hence, it can be suspected that TMSPi may also directly react with the LiPF 6 salt or with the hydrolysis reaction products of LiPF 6 .…”

mentioning

confidence: 99%

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

Tao

Hahn

et al. 2016

RSC Adv.

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The tris(trimethylsilyl) phosphite (TMSPi) is considered as an ideal electrolyte additive for lithium ion batteries. In this work, its positive effect as well as its failure mechanism in a LiPF 6 containing electrolyte was studied by means of selected electrochemical, structural and analytical techniques. The LiNi 0.5 Co 0.2 Mn 0.3 O 2 /graphite cells with TMSPi as electrolyte additive were cycled between 2.8 and 4.6 V.Thanks to the compact cathode electrolyte interphase formed by the oxidative decomposition of TMSPi in a freshly prepared TMSPi containing electrolyte, both the discharge capacity and the cycling stability of cells were enhanced. However, our results also show that TMSPi actually reacts with LiPF 6 at room temperature. TMSPi is consumed by this spontaneous reaction after aging for certain time. In addition, a part of the fluorophosphates, generated from the hydrolysis of LiPF 6 , is bonded to one or two TMS groups, causing a decrease in the fluorophosphate content in the CEI film. Consequently, the cycling stability of the lithium ion cells with aged TMSPi containing electrolyte deteriorates. The obtained results offer important insights into the practical application of TMSPi, which means that TMSPi can only be used as an effective additive in a freshly prepared LiPF 6 containing electrolyte.

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confidence: 99%

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

Tao

Hahn

et al. 2016

RSC Adv.

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“…In this work, both of these components are evaluated separately, with the passivation determined during the potentiostatic hold, and the functionality determined during the z E-mail: zzhang@anl.gov post-hold cycling. In this way, this protocol distinguishes cathode passivation from other known mechanisms of performance improvement through the use of additives, including HF scavenging, [33][34] anode solid-electrolyte interphase (SEI) formation, 20,24,33 or prevention of transition metal ion dissolution. 26 For every electrolyte oxidation reaction, there is a compensating reduction reaction, and charge neutrality dictates that the electron transfer will not lead to net charging of either the electrolyte or the electrode.…”

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confidence: 99%

The Role of Additives in Improving Performance in High Voltage Lithium-Ion Batteries with Potentiostatic Holds

Tornheim

et al. 2017

J. Electrochem. Soc.

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In this work, various electrolyte additives designed for enhanced performance at high voltages were evaluated with elevated temperature potentiostatic holds with LiNi 0.5 Co 0.2 Mn 0.3 /Li 4 Ti 5 O 12 full cells to determine their effect on the high voltage stability. Of the additives investigated, many showed increased oxidation current through the 60 hour potentiostatic holds test, and adversely affected both the capacity retention and interfacial impedance. Improved high voltage performance was observed with two additives, vinylene carbonate (VC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), which was attributed to two different mechanisms of improvement. This work investigates some conclusions in the available literature of an additive molecule that decomposes on the charged cathode surface and passivates the surface against electrolyte oxidation. With the goal of increasing battery energy density for transportation applications, layered transition metal oxides cathodes of the form LiMO 2 (M = Ni, Co, Mn) have received significant attention.1-7 While these cathode materials have a high theoretical gravimetric capacity of ∼280 mAh/g, 8 achieving the high capacity of these materials requires very high charging voltages (>4.5V vs. Li + /Li), 2-4 above the stability range of conventional carbonate electrolytes.9,10 Enabling the additional high voltage capacity of the cathode materials requires new electrolytes that provide additional stability at high voltages at the charged cathode surface.The approach to creating compatible electrolytes has mainly fallen along two separate paths: either increasing the intrinsic anodic stability of the electrolyte, [11][12][13][14][15][16][17] or using a sacrificial component in small amounts (an additive) to "passivate" the cathode surface and inhibit continual electrolyte oxidation.18 20,32 have shown evidence of decomposition on various high voltage cathode surfaces through a variety of surface characterization techniques, including attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS).However, this cathode "passivation" is conventionally inferred through a combination of experimental results, such as increased capacity retention, voltammetric methods indicating a lower anodic stability attributed to additive oxidation, changes to the XPS and/or FTIR spectra of the cathode that include components of the additive, and decreased impedance after cycling. While the results provided by the previously mentioned characterization methods can be reconciled with the conclusion that cathode "passivation" led to the improvement, this mechanistic process can be more accurately evaluated by monitoring the electrolyte oxidation current at a charged cathode surface through potentiostatic holds. A passivation layer will limit electron transfer from the electrolyte to the charged cathode surface. By this definition, this layer must have both a minimal electron conductivity as well as a minimal diffusio...

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“…20 Detailed mechanistic investigations on the use of TMSPi as an electrolyte additive are limited [17][18][19]22 and in all reported systems the observed benefits of TMSPi have been attributed to two common traits: formation of a protective film on the cathode, and elimination of HF from the electrolyte. While the reaction of HF with trimethylsilyl (TMS) groups is well documented both experimentally 18,22 and computationally, 19,23,25 the formation of TMSPi-based surface films is poorly understood. Even less is known about the effects of triethylphosphite (TEPi) (Figure 1) in LIB cells: the compound has been shown to benefit cells by acting as an oxygen scavenger 28 and as a flame retardant.…”

Section: The Electrolyte Plays a Vital Role In Lithium Ion Battery (Lmentioning

confidence: 99%

Tris(trimethylsilyl) Phosphite (TMSPi) and Triethyl Phosphite (TEPi) as Electrolyte Additives for Lithium Ion Batteries: Mechanistic Insights into Differences during LiNi_0.5Mn_0.3Co_0.2O₂-Graphite Full Cell Cycling

Peebles

Sahore

Gilbert

et al. 2017

J. Electrochem. Soc.

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Tris(trimethylsilyl) phosphite (TMSPi) has emerged as an useful electrolyte additive for lithium ion cells. This work examines the use of TMSPi and a structurally analogous compound, triethyl phosphite (TEPi), in LiNi 0.5 Mn 0.3 Co 0.2 O 2 -graphite full cells, containing a (baseline) electrolyte with 1.2 M LiPF 6 in EC:EMC (3:7 w/w) and operating between 3.0-4.4 V. Galvanostatic cycling data reveal a measurable difference in capacity fade between the TMSPi and TEPi cells. Furthermore, lower impedance rise is observed for the TMSPi cells, because of the formation of a P-and O-rich surface film on the positive electrode that was revealed by X-ray photoelectron spectroscopy data. Elemental analysis on negative electrodes harvested from cycled cells show lower contents of transition metal (TM) elements for the TMSPi cells than for the baseline and TEPi cells. Our findings indicate that removal of TMS groups from the central P-O core of the TMSPi additive enables formation of the oxide surface film. This film is able to block the generation of reactive TM-oxygen radical species, suppress hydrogen abstraction from the electrolyte solvent, and minimize oxidation reactions at the positive electrode-electrolyte interface. In contrast, oxidation of TEPi does not yield a protective positive electrode film, which results in inferior electrochemical performance. The electrolyte plays a vital role in lithium ion battery (LIB) cells -not only must it enable Li+ ion transport between the electrodes, it should also form passivating layers (such as the solid electrolyte interphase (SEI) on graphite), and remain stable under the oxidizing and reducing conditions at the positive and negative electrodes, respectively. While conventional carbonate-based electrolytes meet the requirements of commercial LIB cells, the next generation of cathode materials will require high-voltage operating conditions (>4.5 V vs. Li/Li + ) in order to meet the demands of higher energy and power. At these higher voltages, the conventional electrolytes experience severe oxidation leading to rapid performance loss and cell failure. Approaches to mitigate electrolyte oxidation at the positive electrode (cathode) include the (i) use of electrolytes with higher oxidation potentials which are intrinsically stable at higher voltages;

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Why is tris(trimethylsilyl) phosphite effective as an additive for high-voltage lithium-ion batteries?

Abstract: Tris(trimethylsilyl)phosphite exhibits outstanding performance as an electrolyte additive for high-voltage lithium-ion batteries on the strength of its distinct molecular properties.

Cited by 114 publications

References 52 publications

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

The Role of Additives in Improving Performance in High Voltage Lithium-Ion Batteries with Potentiostatic Holds

Tris(trimethylsilyl) Phosphite (TMSPi) and Triethyl Phosphite (TEPi) as Electrolyte Additives for Lithium Ion Batteries: Mechanistic Insights into Differences during LiNi_0.5Mn_0.3Co_0.2O₂-Graphite Full Cell Cycling

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Why is tris(trimethylsilyl) phosphite effective as an additive for high-voltage lithium-ion batteries?

Abstract: Tris(trimethylsilyl)phosphite exhibits outstanding performance as an electrolyte additive for high-voltage lithium-ion batteries on the strength of its distinct molecular properties.

Cited by 114 publications

References 52 publications

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

Lifetime limit of tris(trimethylsilyl) phosphite as electrolyte additive for high voltage lithium ion batteries

The Role of Additives in Improving Performance in High Voltage Lithium-Ion Batteries with Potentiostatic Holds

Tris(trimethylsilyl) Phosphite (TMSPi) and Triethyl Phosphite (TEPi) as Electrolyte Additives for Lithium Ion Batteries: Mechanistic Insights into Differences during LiNi0.5Mn0.3Co0.2O2-Graphite Full Cell Cycling

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Tris(trimethylsilyl) Phosphite (TMSPi) and Triethyl Phosphite (TEPi) as Electrolyte Additives for Lithium Ion Batteries: Mechanistic Insights into Differences during LiNi_0.5Mn_0.3Co_0.2O₂-Graphite Full Cell Cycling