Reactivity of electrolytes for lithium-oxygen batteries with Li2O2

The stability of electrolytes is a significant limitation for cycle life performance in Li-O2 batteries. Since Li2O2 is generated at the cathode surface during cycling, an investigation of the thermal stability of common electrolytes with Li2O2 was conducted. All of the solvents investigated, including ethylene carbonate (EC), propylene carbonate (PC), dialkyl carbonates, dimethoxyethane (DME), tetraethylene glycol dimethyl ether, and acetonitrile, have good thermal stability in the presence of Li2O2. Many salts, including LiBF4, lithium bis(oxalaoto)borate (LiBOB), and lithium Bis(trifluoromethanesulfonyl)imide (LiTFSI), also have good stability in the presence of Li2O2. However, LiPF6 reacts rapidly with Li2O2 to generate OPF2OLi and LiF. © 2012 The Electrochemical Society

Investigation of the solid electrolyte interphase on MCMB and NG electrodes in lithium tetrafluorooxalatophosphate LiPF4C2O 4 based electrolyte

The performance of the novel lithium salt, lithium tetrafluorooxalatophopshate (LiPF4(C2O4)) has been investigated as electrolyte solution in carbonate solvents. Investigation of the performance of LiPF4(C2O4) electrolytes in the presence of different types of anode materials, Mesocarbon Microbead (MCMB) graphite and Nature Graphite (NG), has uncovered a dependence of a first cycle shoulder at 1.75 V and irreversible capacity on the structure of the anodic graphite. Andoes with more irreversible capacity have a thicker anode solid electrolyte interphase (SEI) which is most likely caused by differences in the surface of the graphite. Appropriate choice of graphite leads to first cycle efficiencies which are very similar for LiPF4(C 2O4) and LiPF6 electrolytes. © 2011 The Electrochemical Society

Two-step thermochromism in poly(3-docosoxy-4-methylthiophene): Mechanistic similarity to poly(3-docosylthiophene)

The two-step thermochromism in poly(3-docosoxy-4-methylthiophene) by using reflection and fluorescence spectroscopies and differential scanning calorimetry (DSC) was investigated. The polymer sample was prepared for DSC by drip-coating a solution of the polymer in tetrahydrofuran (THF) on the aluminum foil and evaporating the solvent. The polymer film was heated with a heat gun and rapidly quenched with liquid nitrogen to form the mesophase. Variable-temperature fluorescence spectra were recorded on Ocean Optics S2000 instrument with a blue LED light source (λ = 470 nm). The fluorescence spectrum (excited at 470 nm) of the mesophase contained a weak, broad emission with a maximum centered at ~650 nm. The emission band of the high temperature phase had peaks at 540 and 565 nm, with much greater intensity than the emission band of the mesophase

Methylene ethylene carbonate: Novel additive to improve the high temperature performance of lithium ion batteries

The preparation of methylene ethylene carbonate (MEC) and the incorporation of MEC into lithium ion batteries as an electrolyte additive were investigated. MEC is prepared in good yield by mercury catalyzed cyclization. Addition of low concentrations of MEC (1-2%) to 1 M LiPF 6 in 3:7 ethylene carbonate/ethyl methyl carbonate improves the capacity retention of lithium ion batteries cycled at elevated temperature (60 °C). Ex situ surface analysis (XPS and FTIR) of the electrodes supports the presence of poly(methylene ethylene carbonate) on the anode surface. Modification of the anode solid electrolyte interphase (SEI) correlates with significant improvements in the cycling performance at 60 °C. © 2011 Elsevier Ltd. All rights reserved. All rights reserved

Lithium ion battery graphite solid electrolyte interphase revealed by microscopy and spectroscopy

The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF6 electrolytes, the graphite SEI is nonuniform, ∼10-20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF. © 2013 American Chemical Society

Reduction reactions of carbonate solvents for lithium ion batteries

Lithium naphthalenide has been investigated as a one electron reducing agent for organic carbonates solvents used in lithium ion battery electrolytes. The reaction precipitates have been analyzed by IR-ATR and solution NMR spectroscopy and the evolved gases have been analyzed by GC-MS. The reduction products of ethylene carbonate and propylene carbonate are lithium ethylene dicarbonate and ethylene and lithium propylene dicarbonate and propylene, respectively. The reduction products of diethyl and dimethyl carbonate are lithium ethyl carbonate and ethane and lithium methyl carbonate and methane, respectively. Lithium carbonate is not observed as a reduction product. © 2014 The Electrochemical Society

Lithium Ion Battery Graphite Solid Electrolyte Interphase Revealed by Microscopy and Spectroscopy

The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D₂O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF₆ and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF₆ electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF₆ electrolytes, the graphite SEI is nonuniform, ∼10–20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF₆ electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF