Jinglun Wang

Oligo(ethylene oxide)-functionalized trialkoxysilanes as novel electrolytes for high-voltage lithium-ion batteries

Oligo(ethylene oxide)-functionalized trialkoxysilanes were synthesized through hydrosilylation reaction by reacting trialkoxysilane with oligo(ethylene oxide) allyl methyl ether using PtO2 as a catalyst. The physical properties of these compounds, such as viscosity, dielectric constant, and ionic conductivity, were characterized. Among them, [3-(2-(2-methoxyethoxy)ethoxy)-propyl]triethoxysilane (TESM2) exhibited a commercial viable ionic conductivity of 1.14xa0mS cm−1 and a wide electrochemical window of 5.2xa0V. A preliminary investigation was conducted by using TESM2 as an electrolyte solvent for high-voltage applications in lithium-ion batteries. Using 1xa0M LiPF6 in TESM2 with 1xa0vol% vinyl carbonate as an electrolyte, LiCoO2/Li half-cell delivered a specific capacity of 153.9xa0mAh g−1 and 90xa0% capacity retention after 80xa0cycles (3.0–4.35xa0V, 28xa0mAxa0g−1); Li1.2Ni0.2Mn0.6O2/Li4Ti5O12 full cell exhibited the initial capacity of 161.3xa0mAh g−1 and 86xa0% capacity retention after 30xa0cycles (0.5–3.1xa0V, 18xa0mAxa0g−1).

Organosilicon functionalized quaternary ammonium ionic liquids as electrolytes for lithium-ion batteries

Organosilicon-functionalized quaternary ammonium ionic liquids (ILs) with oligo(ethylene oxide) substituent are designed and synthesized. Such properties as viscosity, conductivity, and thermal/electrochemical stability of these ILs are characterized. These ILs are miscible with the commercial carbonate electrolyte (EC: DECu2009=u20091:1(w/w), 1xa0M LiPF6) and are used as cosolvents to form hybrid electrolytes in proportions up to 30xa0vol%. By using such hybrid electrolytes, the LiFePO4/Li half cells exhibit no deterioration in specific capacity and cyclability, and the graphite/Li half cells show improved compatibility in the presence of lithium oxalyldifluoroborate. These hybrid electrolytes exhibit less flammability compared with the commercial baseline electrolyte, and thus improved safety for use in lithium-ion batteries.

Organosilicon functionalized glycerol carbonates as electrolytes for lithium-ion batteries

Two triethoxyl-/trimethoxyl-silyl functionalized glycerol carbonates and one disiloxanyl functionalized glycerol carbonate were synthesized through a cycloaddition reaction of carbon dioxide with allyl glycidyl ether followed by a hydrosilylation with the corresponding hydrosilanes. Their chemical structures were fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy and their basic physicochemical properties including dielectric constant, viscosity, ionic conductivity, apparent lithium transference number and electrochemical window, were systematically measured. Trimethoxysilyl functionalized glycerol carbonate as electrolyte solvent with LiPF6 (0.6 M) and lithium oxalyldifluoroborate (0.4 M) binary salts exhibited good cycling stability over 2.7–4.4 V in high-voltage-LiCoO2/graphite full cells. Disiloxane functionalized glycerol carbonate acted as an efficient electrolyte additive to improve the wetting property on the separator in Li/LiCoO2 cells.

Allyl cyanide as a new functional additive in propylene carbonate-based electrolyte for lithium-ion batteries

Allyl cyanide (AC) was investigated as a film-forming additive in propylene carbonate (PC)-based electrolytes for graphite anode in lithium-ion batteries. The film-forming behavior of AC was characterized with cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. By adding 2xa0wt% AC in the electrolyte of 1xa0M LiPF6-PC/DMC (1:1, in vol), the exfoliation of graphite anode was effectively suppressed over cycling. Graphite/Li half-cell showed an initial coulombic efficiency of 75xa0% and a specific capacity of 300xa0mAh/g after 48xa0cycles. A possible reductive polymerization mechanism of AC on the surface of graphite was proposed.

Dinitrile compound containing ethylene oxide moiety with enhanced solubility of lithium salts as electrolyte solvent for high-voltage lithium-ion batteries

A dinitrile compound containing ethylene oxide moiety (4,7-dioxa-1,10-decanedinitrile, NEON) is synthesized as an electrolyte solvent for high-voltage lithium-ion batteries. The introduction of ethylene oxide moiety into the conventional aprotic aliphatic dinitrile compounds improves the solubility of lithium hexafluorophosphate (LiPF6) used commercially in the lithium-ion battery industry. The electrochemical performances of the NEON-based electrolyte (0.8xa0M LiPF6u2009+u20090.2xa0M lithium oxalyldifluoroborate in NEON:EC:DEC, v:v:vu2009=u20091:1:1) are evaluated in graphite/Li, LiCoO2/Li, and LiCoO2/graphite cells. Half-cell tests show that the electrolyte exhibits significantly improved compatibility with graphite by the addition of vinylene carbonate and lithium oxalyldifluoroborate and excellent cycling stability with a capacity retention of 97xa0% after 50xa0cycles at a cutoff voltage of 4.4xa0V in LiCoO2/Li cell. A comparative experiment in LiCoO2/graphite full cells shows that the electrolyte (NEON:EC:DEC, v:v:vu2009=u20091:1:1) exhibits improved cycling stability at 4.4xa0V compared with the electrolyte without NEON (EC:DEC, v:vu2009=u20091:1), demonstrating that NEON has a great potential as an electrolyte solvent for the high-voltage application in lithium-ion batteries.

Synergistic film-forming effect of oligo(ethylene oxide)-functionalized trimethoxysilane and propylene carbonate electrolytes on graphite anode

Oligo(ethylene oxide)-functionalized trialkoxysilanes can be used as novel electrolytes for high-voltage cathode, such as LiCoO2 (4.35xa0V) and Li1.2Ni0.2Mn0.6O2 (4.6xa0V); however, they are not well compatible with graphite anode. In this study, a synergistic solid electrolyte interphase (SEI) film-forming effect between [3-[2-(2-methoxyethoxy)ethoxy]propyl]-trimethoxysilane (TMSM2) and propylene carbonate (PC) on graphite electrode was investigated. Excellent SEI film-forming capability and cycling performance was observed in graphite/Li cells using the electrolyte of 1xa0M LiPF6 in the binary solvent of TMSM2 and PC, with the PC content in the range of 10–30 vol.%. Meanwhile, the graphite/Li cells delivered higher specific capacity and better capacity retention in the electrolyte of 1xa0M LiPF6 in TMSM2 and PC (TMSM2:PCxa0=xa09:1, by vol.), compared with those in the electrolyte of 1xa0M LiPF6 in TMSM2 and EC (TMSM2:ECxa0=xa09:1, by vol.). The synergistic SEI film-forming properties of TMSM2 and PC on the surface of graphite anode was characterized by electrolyte solution structure analysis through Raman spectroscopy and surface analysis detected by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR) analysis.