Showing papers by "K. M. Abraham published in 1997"

Highly Conductive PEO-like Polymer Electrolytes

Abstract: Polymer electrolyte membranes comprising poly(vinylidene fluoride)−hexafluoropropene (PVdF−HFP) copolymer plasticized with a solution of LiSO3CF3, LiN(SO2CF3)2, or LiPF6 in oligomeric poly(ethylene glycol) dimethyl ethers (PEGDME, Mw = 250, 400, and 500) were prepared by hot-melt-rolling or solvent-casting techniques. Since the electrolytes containing PEGDME400 and PEGDME500 are “dry” with essentially no volatile components up to 150 °C, we have dubbed them PEO-like. Their thermal stability, mechanical strength, conductivity, electrochemical stability window, and Li/electrolyte interface stability were characterized. Plasticizing PVdF−HFP with the PEGDME/LiX solutions disordered the polymer structure leading to polymer electrolytes having lower crystallinity than the polymer host itself. The mechanical strength of the electrolyte membranes varied depending on the PVdF content. Tensile strength (stress) as high as 420 psi at an elongation-at-break value (strain) of 75% was observed. The conductivities of t...

Characterization of some polyacrylonitrile-based electrolytes

Abstract: Polyacrylonitrile (PAN)-based electrolytes have been prepared by encapsulating Li salt solutions. The conductivity of these electrolytes is governed by a combination of factors including the relative amounts of PAN, EC, PC and the Li salt, and temperature. A conductivity of about 4.5 x 10{sup -3}{Omega}{sup -1} cm{sup -1} at 30 {degrees}C was exhibited by EC-rich electrolytes containing both LiN(SO{sub 2}CF{sub 3}){sub 2} and LiPF{sub 6}. The cationic transference numbers, measured using a dc polarization method coupled with impedance spectroscopy, were found to be between 0.2 and 0.3 for electrolytes containing LiN(CF{sub 3}SO{sub 2}){sub 2} and LiPF{sub 6}. The tensile strength of the electrolytes was observed to increase from 60 to 140 lb/in.{sup 2} upon incorporation of the thermally activated cross-linking agent ethylene glycol dimethacrylate. Cyclic voltammetry on Pt electrodes has shown that these electrolytes have an inherent oxidation stability window extending up to about 5 V versus Li{sup +}/Li. On Al, Ni, and Cu electrodes, however, oxidation was observed at lower potentials because of metal corrosion reactions. Copper was reversibly oxidized at 3.5 V, irrespective of the Li salt present in the electrolyte. On the other hand, the nature of the Li salt influenced the corrosion potentials of Al andmore » Ni. Nickel was found to be stable up to 4.2 V in the presence of LiAsF{sub 6}, whereas it was oxidized at about 3.5 and 4 V when the electrolyte contained LiN(SO{sub 2}CF{sub 3}){sub 2} and LiSO{sub 3}CF{sub 3} showing oxidation at {le}4 V. The electrochemical stability of the electrolytes was further verified in Li/LiMn{sub 2}O{sub 4} cells. 10 refs., 15 figs., 9 tabs.« less

Passivation-free solid state battery

Abstract: This invention pertains to passivation-free solid-state rechargeable batteries composed of Li4 Ti5 O12 anode, a solid polymer electrolyte and a high voltage cathode. The solid polymer electrolyte comprises a polymer host, such as polyacrylonitrile, poly(vinyl chloride), poly(vinyl sulfone), and poly(vinylidene fluoride), plasticized by a solution of a Li salt in an organic solvent. The high voltage cathode includes LiMn2 O4, LiCoO2, LiNiO2 and LiV2 O5 and their derivatives.