polymer graphite composite anodes for li-ion batteries

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Polymer graphite composite anodes for Li-ion batteries. Basker Veeraraghavan, Bala Haran, Ralph White and Branko Popov University of South Carolina, Columbia, SC 29208 Plamen Atanassov University of New Mexico, Albuquerque, NM 87131. Problem Definition. Previous approaches. - PowerPoint PPT Presentation

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  • Polymer graphite composite anodes for Li-ion batteriesBasker Veeraraghavan, Bala Haran, Ralph White and Branko PopovUniversity of South Carolina, Columbia, SC 29208Plamen AtanassovUniversity of New Mexico,Albuquerque, NM 87131

  • Problem DefinitionElectrolyte decompositionSolvated lithium intercalation and reductionIrreversible reactions lead toLosses in capacity / active lithium materialLowers cell energy densities, increases cell costModification to the electrodeMild oxidation Coating with Ni, PdModification to the electrolyteAddition of SO2, CO2Other solvents like DMPCPrevious approaches

  • ObjectivesTo prepare PPy/C composite which will reduce the initial irreversible capacity To improve the conductivity and the coulombic efficiency of the electrode To obtain material with better rate capability and good cycle life Produce a matrix of PPy which forms a conducting backbone for the graphite particles by in-situ polymerizationApproach

  • ExperimentalPreparation of PPy/Graphite compositesDropwise addition of pyrrole into aqueous slurry of graphite at 0 C with nitric acid acting as an oxidizer for 40 hWash repeatedly with water and methanol and vacuum dried at 200C for 24hCell Preparation for testingElectrodes prepared by cold rolling using PTFE binder (10wt%)Whatman fiber used as separator and Li-foil used as counter and reference electrode1M LiPF6 in EC/DMC (1:1 v/v) used as electrolyte

  • Experimental (Contd.)Electrochemical characterizationsCharge-discharge and cycling behaviorsArbin Battery test system used for the testingCycling was performed between 2V and 5 mV at C/15 rate (0.25 mA/cm2)Cyclic VoltammetryCVs were performed from 1.6V to 0.01V at 0.05 mV/sElectrochemical Impedance Spectroscopy (EIS)100kHz to 1mHz with 5mV PP signalPhysical characterizationsSEM micrographs TGA and BET analysis

  • TGA analysis of polymer compositeSFG10 samples

  • Charge-discharge curves of polymer composite SFG10 samples

  • Change in irreversible capacity loss with PPy loading at C/15 rate

    Amount of PPy loading (wt%) Initial lithiation capacity (mAh/g) Initial de-lithiation capacity (mAh/g) Overall irreversible Capacity (%) Initial coulombic efficiency (%)

    0567.88.4485.9483.7471.7456.6432.5232.7 309.3313.6310.1290.352.136.133.532.132.947.963.966.567.967.1

  • Comparison of surface area and capacity for polymer composite electrodes

    Amount of PPy loading (wt%)Reversible Capacity (mAh/g) Specific Surface area (m2/g) Volumetric Surface area (m2/cm3) Volumetric Capacity (mAh/cm3)

    0567.88.4284.6338.8359.8 362.3 359.09.848.98 8.557.787.6921.6519.7618.8117.1216.92626.1745.4791.6797.1789.8

  • Cyclic voltammograms of polymer composite SFG10 samples

  • SEM pictures of polymer composite SFG10 samplesBarePPy/C

  • Impedance studies of polymer composite SFG10 samples

  • Equivalent circuit used to fit the experimental dataRW ohmic resistanceR1 SEI layer resistance C1 SEI layer capacitanceR2 Polarization resistance C2 Double layer capacitance

  • Equivalent circuit parameters for polymer composite electrode

    SampleRW(ohm)R1 (ohm)C1 (Farad)R2 (ohm)C2 (Farad)Bare7.9197.42.3x10-717.74.3x10-65% PPy7.627.14.7x10-614.84.3x10-66% PPy7.921.77.0x10-612.14.5x10-67.8% PPy7.813.97.2x10-610.47.0x10-68.4% PPy8.38.78.2x10-69.19.9x10-6

  • Comparison of coulombic efficiencies for SFG10 samples

  • Rate capability studies of composite SFG10 samples

  • Cycle life studies of composite SFG10 samples

  • Charge-Discharge curves of polymer compositeSFG10-15% sn samples

  • Comparison of irreversible capacities for bare and polymer composite SFG10 samples

    Sample Initial lithiation capacity (mAh/g)Initial de-lithiation capacity (mAh/g)Irreversible capacity (%) Initial coulombic efficiency (%) Bare Bare-PPy

    15% Sn

    15% Sn-PPy485.9 456.6

    719.9

    606.2232.7

    310.1

    350.8

    370.452.1

    32.1

    51.3

    38.947.9

    67.9

    48.7

    61.1

  • ConclusionsPolypyrrole on SFG10 graphite results in high performance anodes for use in Li-ion batteriesIrreversible capacity is reduced up to 7.8% PPy compositeCharge discharge studies are supported by CV dataReduction in irreversible capacity seen during cathodic scanPolymer composite anodes show better conductivity and lower polarization resistance compared to virgin carbonPolymer composite anode show better rate capability and longer cycle life

  • AcknowledgementsThis work was funded by the Dept. of Energy division of Chemical Science, Office of Basic Energy Sciences and, in part, by Sandia National Laboratories

    (Sandia National Laboratories is a multi-program laboratory operated by Sandia corp., a Lockheed Martin Company, for the U.S. Dept. of Energy under Contract DE-AC04-94AL85000.)

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