Dinitrile–Mononitrile-Based Electrolyte System for Lithium-Ion Battery Application with the Mechanism of Reductive Decomposition of Mononitriles

Abstract

The development of electrolytes capable of performing at a high voltage (>5 V) is essential for the advancement of lithium-ion batteries. In the present work, we have investigated a dinitrile–mononitrile-based electrolyte system that can offer electrochemical stability up to 5.5 V at room temperature. The electrolytes consist of 1.0 M lithium bis­(trifluoromethane)­sulfonamide in various volume proportions of glutaronitrile, a dinitrile, and butyronitrile, a mononitrile (10/0; 8/2; 6/4; 4/6; 2/8; 10/0). The ionic conductivity of the electrolytes was found to be 3.1 × 10–3–10.6 × 10–3 S cm–1 at 30 °C, comparable with commercially used carbonate-based electrolytes. However, butyronitrile reacts with Li metal to give 3-amino-2-ethylhex-2-ene-nitrile, 2,6-dipropyl-5-ethylpyrimidin-4-amine, and oligomers/polymers. These compounds have been characterized by nuclear magnetic resonance techniques, and based on these findings, a plausible mechanism of reactivity of mononitriles toward Li metal has been proposed. Finally, 5 wt % of vinylene carbonate is added to the glutaronitrile/butyronitrile (6/4 ratio) system to inhibit the reductive decomposition of butyronitrile. The resultant electrolyte system is used in the assembly of several coin cells consisting of a LiFePO4 composite cathode and a Li metal anode. The cells perform up to 3 C charge/discharge rate with reasonably good discharge capacity and also display a cycle life of more than 100 cycles at a 0.5 C rate with capacity retention above 95% at room temperature.

Adiponitrile–Lithium Bis(trimethylsulfonyl)imide Solutions as Alkyl Carbonate‐free Electrolytes for Li4Ti5O12 (LTO)/LiNi1/3Co1/3Mn1/3O2 (NMC) Li‐Ion Batteries

“…[7][8][9][10][11] In addition, their wide electrochemical window ( % 6V vs. Li/ Li + ) [7,8,[10][11][12] makes them suitable foru se with high voltage cathodest oi ncreaset he energy density.D initriles also exhibit good solvating properties owing to the CN groups and are commercially available at ar elativelyc heap price with ah igh degree of purity.A monga liphatic dinitriles, adiponitrile (ADN, n = 4) has already been proposed as an electrolyte solvent, [7] with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)a st he lithium salt in aM CMB( mesocarbon microbeads)/LiCoO 2 cell. [7][8][9][10][11] In addition, their wide electrochemical window ( % 6V vs. Li/ Li + ) [7,8,[10][11][12] makes them suitable foru se with high voltage cathodest oi ncreaset he energy density.D initriles also exhibit good solvating properties owing to the CN groups and are commercially available at ar elativelyc heap price with ah igh degree of purity.A monga liphatic dinitriles, adiponitrile (ADN, n = 4) has already been proposed as an electrolyte solvent, [7] with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)a st he lithium salt in aM CMB( mesocarbon microbeads)/LiCoO 2 cell.…”

“…Aliphatic dinitriles (NC(CH) 2 ) n CN) belong to as olvent family, which may be used as an electrolyte solvent and replace, at least partially,c onventionale lectrolytes based on alkyl carbonates.R ecently,s ome reports have pointed out the advantages of dinitriles as electrolyte solvents owing to their high boiling points, high flash points, and low vapor pressures. [7][8][9][10][11] In addition, their wide electrochemical window ( % 6V vs. Li/ Li + ) [7,8,[10][11][12] makes them suitable foru se with high voltage cathodest oi ncreaset he energy density.D initriles also exhibit good solvating properties owing to the CN groups and are commercially available at ar elativelyc heap price with ah igh degree of purity.A monga liphatic dinitriles, adiponitrile (ADN, n = 4) has already been proposed as an electrolyte solvent, [7] with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI)a st he lithium salt in aM CMB( mesocarbon microbeads)/LiCoO 2 cell. However,b ecause of the inability of ADNt of orm as table and conductive solid electrolyte interphase (SEI) layer on the negative electrode, ethylene carbonate (EC) or SEI-forming additives have to be added to the electrolyte blend.…”

In Situ Polymerized Electrolytes with Fully Cross-Linked Networks Boosting High Ionic Conductivity and Capacity Retention for Lithium Ion Batteries

“…Nevertheless, the capacity of the cell decayed rapidly after the 30th cycle under 0.5 C as shown in Figure S9b, which may be a consequence of the decomposition of SN. 63,64 In this study, the precursor directly contacted lithium metal during the polymerization, which accelerated the side reaction between SN and lithium metal and would further lead to the formation of nitrile anions. Considering that the nitrile carbon in SN is electrophilic, which is easily attacked by the formed nucleophile nitrile anions and may further react with other SN, the side reaction would continuously generate a variety of complicated compounds, resulting in the gradual consumption of the electrolyte.…”

Comparative Study of Physical Properties and CO2 Solubility of Ammonium and Sulfonium Ionic Liquids in Mixture with Glutaronitrile

“…Mixtures of ILs with protic molecular solvents such as water, alcohols, amides, and so forth ,, or aprotic solvents such as ACN, alkylcarbonates, DMSO, or DMF , improve the properties of ILs by lowering their viscosity and promoting ionic dissociations while retaining their thermal and electrochemical properties, unlike mineral salts, whose solubility in molecular solvents is often limited (close to 1–2 mol L –1 ) . ILs often composed of asymmetrical organic cations are much more soluble or miscible in all proportions. ,, The cross-interactions between ion liquid ions and molecular solvent molecules depend on several factors: the presence of a labile proton, the size of ions, the nature of the heteroatom (S, N, P) in the cation (sulfonium, ammonium, or phosphonium), , the length of the carbon chain of the cation or anion, , and also the properties of the molecular solvent chosen to make the mixture. , Among the solvents suitable for electrochemical applications, nitriles and more specifically dinitriles , have emerged as a base for electrolytes for batteries, , supercapacitors, and other energy storage applications. , Among dinitriles, glutaronitrile (GLN) is emerging as an electrochemically stable and safe solvent very suitable for various applications − …”

“…1,20,21 The crossinteractions between ion liquid ions and molecular solvent molecules depend on several factors: the presence of a labile proton, the size of ions, the nature of the heteroatom (S, N, P) in the cation (sulfonium, ammonium, or phosphonium), 22,23 the length of the carbon chain of the cation or anion, 24,25 and also the properties of the molecular solvent chosen to make the mixture. 26,27 Among the solvents suitable for electrochemical applications, nitriles and more specifically dinitriles 28,29 have emerged as a base for electrolytes for batteries, 29,30 supercapacitors, 31 and other energy storage applications. 32,33 Among dinitriles, glutaronitrile (GLN) is emerging as an electrochemically stable and safe solvent very suitable for various applications 34−37 Among the selection criteria of electrolytes for energy storage or conversion applications 38 or for other gas-phase processes, 39,40 it is their ability to solubilize gases and in particular, CO 2 , SO 2 , H 2 , and O 2 that can qualify them for this purpose.…”