Electrolyte Formulations Based on Dinitrile Solvents for High Voltage Li-Ion Batteries

Density functional theory (DFT) was used to investigate the effect of electrolyte additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl ethylene sulfite (VES), and ethylene sulfite (ES) in propylene carbonate (PC)-based Li-ion battery electrolytes on SEI formation at graphitic anodes. The higher desolvation energy of PC limits Li + intercalation into graphite compared to solvated Li + in EC. Li + (PC) 3 clusters are found to be unstable with graphite intercalation compounds and become structurally deformed, preventing decomposition mechanisms and associated SEI formation in favor of co-intercalation that leads to exfoliation. DFT calculations demonstrate that the reduction decomposition of PC and electrolyte additives is such that the first electron reduction energies scale as ES > VES > VEC >PC. The second electron reduction follows ES > VES > VEC > VC > PC. The reactivity of the additives under consideration follows ES > VES > VEC > VC. The data demonstrate the supportive role of certain additives, particularly sulfites, in PC-based electrolytes for SEI film formation and stable cycling at graphitic carbon-based Li-ion battery anodes without exfoliation or degradation of the anode structure. The lithium ion battery has been one of the primary power sources driving the digital age, and witnessed a resurgence in interest with the advent of nanoscale materials and advances in cell performance. [1][2][3][4][5][6] Much of the processes and mechanisms underpinning carbonate-based electrolytes in Li-ion batteries, particularly at the anode, still need to be resolved. 7,8 Some commonly used organic solvents are ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) etc. These organic electrolytes are decomposed during intercalation of lithium ions into graphite anode, resulting in the formation of the crucial solid electrolyte interphase (SEI) film. [9][10][11] This film plays an important role in determining capacity retention, cycle life and safety concerns in lithium ion batteries.12,13 SEI films typically comprise Li 2 O, Li 2 CO 3 and related carbonates, LiF (depending on salt used), and polymer phases together with olefins.14 Effective SEI films provide stable surface passivation without significant reduction in electron conduction (higher transfer resistance). On carbon (graphite) anodes, stable SEI films are crucial for stable cycling and are formed below ∼0.8 V vs. Li + /Li. In practical applications of lithium-ion batteries, the selection of the electrode material is critical, particularly when using high surface area nanomaterials. 15 Enhanced chemical stability against electrolyte oxidation and reduction, high ionic conductivity, high boiling points, and low melting points are required, as well as the ability to solvate a wide range of lithium salts such as LiPF 6 , LiBF 4 or LiClO 4 , 16-21 in aprotic and organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), their mixtures, and ...

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The Role of Carbonate and Sulfite Additives in Propylene Carbonate-Based Electrolytes on the Formation of SEI Layers at Graphitic Li-Ion Battery Anodes

Bhatt¹,

O’Dwyer²

2014

“…In addition, one of the main issues with high voltage batteries is the instability of common aprotic electrolytes at voltage above 4.5 V. 6,7 The stability of the electrolyte/cathode interphase is related to the chemistry of electrolyte solvents and salts and also to the chemistry of the components of the cathode.…”

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confidence: 99%

Analysis of the Interphase on Carbon Black Formed in High Voltage Batteries

Younesi

Christiansen

Scipioni

et al. 2015

Carbon black (CB) additives commonly used to increase the electrical conductivity of electrodes in Li-ion batteries are generally believed to be electrochemically inert additives in cathodes. Decomposition of electrolyte in the surface region of CB in Li-ion cells at high voltages up to 4.9 V is here studied using electrochemical measurements as well as structural and surface characterizations. LiPF 6 and LiClO 4 dissolved in ethylene carbonate:diethylene carbonate (1:1) were used as the electrolyte to study irreversible charge capacity of CB cathodes when cycled between 4.9 V and 2.5 V. Synchrotron-based soft X-ray photoelectron spectroscopy (SOXPES) results revealed spontaneous partial decomposition of the electrolytes on the CB electrode, without applying external current or voltage. Depth profile analysis of the electrolyte/cathode interphase indicated that the concentration of decomposed species is highest at the outermost surface of the CB. It is concluded that carboxylate and carbonate bonds (originating from solvent decomposition) and LiF (when LiPF 6 was used) take part in the formation of the decomposed species. Electrochemical impedance spectroscopy measurements and transmission electron microscopy results, however, did not show formation of a dense surface layer on CB particles. The growth of earth's population with concomitant increase in energy consumption require development of renewable energy conversion technologies coupled with advanced energy storage systems like lithium batteries.1,2 In order to increase the power density in Li-ion batteries, much research is focused on developing cathode materials that can operate at high voltages (above 4.5 V vs. Li/Li + ) with a high capacity, high cycling stability, and good rate capability.3-5 However, at high voltages, all the components of positive electrodes including the Al current collector, polymer binders, conductive additives, and other possible additives have an increased risk of degradation. In addition, one of the main issues with high voltage batteries is the instability of common aprotic electrolytes at voltage above 4.5 V. 6,7 The stability of the electrolyte/cathode interphase is related to the chemistry of electrolyte solvents and salts and also to the chemistry of the components of the cathode.Carbon black (CB) additives are one of the main constituents of cathodes, added to increase the electrical percolation and thus the electronic conductivity. 8,9 Though the weight percentage of CB in commercial batteries is generally very small, it composes a rather large part of the internal surface area of a cathode due to its small particle size (≈50 nm), low density, and high surface area. CBs are generally thought of being an electrochemically inert additive in cathodes, but few studies have investigated the role of CBs at high voltages and have indicated that CBs exhibit irreversible electrochemical reactions resulting in appreciable irreversible charge capacities. [10][11][12][13][14][15][16][17][18] This charge capacity is attributed to oxid...

“…5 The possibility of using adiponitrile and glutaronitrile as electrolyte solvents was investigated thoroughly.…”

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“…Based on the results of reference 3, it is possible that nitriles as electrolyte additives can be potential candidates to improve cycle life because results in the literature showed that EC:DMC mixed with nitrile co-solvents has high electrochemical stability up to around 5.0 V and starts to be oxidized at around 5.5 V vs. Li/Li + , while pure EC:DMC starts to be oxidized suddenly at around 4.5 V. [4][5][6][7] Nigahara et al reported that 1.0 M LiBF 4 EC:DMC:sebaconitrile (25:25:50 by vol %) showed the best electrochemical compatibility with positive electrode materials such as LiMn 2 O 4 and LiCoPO 4 in experiments involving the nitriles: glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, sebaconitrile and dodecanedinitrile at high voltage. 4 Duncan et al showed that dinitriles with shorter carbon chain length between nitrile groups gave higher capacities in Li-ion cells than dinitriles with longer carbon chain between nitrile groups because the shorter dinitriles showed higher ionic conductivity than the longer dinitriles.…”

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“…4 Duncan et al showed that dinitriles with shorter carbon chain length between nitrile groups gave higher capacities in Li-ion cells than dinitriles with longer carbon chain between nitrile groups because the shorter dinitriles showed higher ionic conductivity than the longer dinitriles. 5 The possibility of using adiponitrile and glutaronitrile as electrolyte solvents was investigated thoroughly. [6][7] However, the electrochemical characteristics of Li-ion cells, when nitriles are used as electrolyte additives (less than 5 wt%), have not been thoroughly investigated yet.…”

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confidence: 99%

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The Effect of Some Nitriles as Electrolyte Additives in Li-Ion Batteries

Kim

Dahn

2015

The effect of the nitrile electrolyte additives, succinonitrile (SN), adiponitrile (AN) and pimelonitrile (PN) was studied using High Precision Charger at Dalhousie University, automated cell storage and AC impedance. Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC111/graphite) cells containing the nitrile electrolyte additives showed no significant effect on the cycling between 2.8 V and 4.2 V and storage at 4.2 V at 60. ± 0.1 • C. However, when the high cutoff voltage increased to 4.5 V in Li [Ni 0.4 Mn 0.4 Co 0.2 ]O 2 /graphite (NMC442/graphite) cells, the addition of 2 wt% SN and 2 wt% vinylene carbonate (VC) reduced the reversible capacity loss and gas generation during storage experiments at 60. ± 0.1 • C compared to 2 wt% VC alone. The addition of 2 wt% SN also caused a large impedance growth during the 4.5 V storage period, but that could be suppressed by the addition of 1 wt% ethylene sulfite (ES) + 1 wt% tris(trimethlysilyl) phosphite (TTSPi) or 2 wt% trimethylene sulfate (TMS) + 2 wt% TTSPi. This work shows that SN leads to meaningful improvements in storage properties at voltages higher than 4. The incorporation of electrolyte additives is one of the approaches for improving the cycle life and calendar life of Li-ion cells.1-2 Recently, Burns et al. suggested that the addition of one or more electrolyte additives can lead to longer cycle life by suppressing electrolyte oxidation at the positive electrode.3 Burns et al. reported that electrolyte oxidation products created at the positive electrode migrate to the negative electrode and are reduced on the surface of the negative electrode as a solid layer of undesired material. As the layer becomes thicker during the cycle test, ion transport to the bulk of the negative electrode is reduced, which leads to "cycle life failure".Based on the results of reference 3, it is possible that nitriles as electrolyte additives can be potential candidates to improve cycle life because results in the literature showed that EC:DMC mixed with nitrile co-solvents has high electrochemical stability up to around 5.0 V and starts to be oxidized at around 5.5 V vs. Li/Li + , while pure EC:DMC starts to be oxidized suddenly at around 4.5 V. 4 Duncan et al. showed that dinitriles with shorter carbon chain length between nitrile groups gave higher capacities in Li-ion cells than dinitriles with longer carbon chain between nitrile groups because the shorter dinitriles showed higher ionic conductivity than the longer dinitriles. 5 The possibility of using adiponitrile and glutaronitrile as electrolyte solvents was investigated thoroughly.6-7 However, the electrochemical characteristics of Li-ion cells, when nitriles are used as electrolyte additives (less than 5 wt%), have not been thoroughly investigated yet.Here, the possibility of using 2 wt% of succinonitrile (SN), adiponitrile (AN) or pimelonitrile (PN) as an electrolyte additive is considered. Storage and cycling experiments at 60• C using Li [Ni 0.33 8 A paper about the effect of SN on * Electrochemical Society Fellow. z ...