Polymer graphite composite anodes for Li-ion batteries
Basker Veeraraghavan, Bala Haran, Ralph White and Branko Popov
University of South Carolina, Columbia, SC 29208Plamen Atanassov
University of New Mexico,Albuquerque, NM 87131
Modification to the electrodeMild oxidation Coating with Ni, Pd
Modification to the electrolyteAddition of SO2, CO2
Other solvents like DMPC
Problem DefinitionElectrolyte decompositionSolvated lithium intercalation and reductionIrreversible reactions lead to
Losses in capacity / active lithium materialLowers cell energy densities, increases cell cost
Previous 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 polymerization
Approach
ExperimentalPreparation of PPy/Graphite composites
Dropwise addition of pyrrole into aqueous slurry of graphite at 0 C with nitric acid acting as an oxidizer for 40 h
Wash repeatedly with water and methanol and vacuum dried at 200C for 24h
Cell Preparation for testingElectrodes prepared by cold rolling using PTFE binder (10wt
%)
Whatman fiber used as separator and Li-foil used as counter and reference electrode
1M LiPF6 in EC/DMC (1:1 v/v) used as electrolyte
Experimental (Cont’d.)Electrochemical characterizationsCharge-discharge and cycling behaviors
Arbin Battery test system used for the testingCycling was performed between 2V and 5 mV at C/15 rate
(0.25 mA/cm2)Cyclic Voltammetry
CVs were performed from 1.6V to 0.01V at 0.05 mV/sElectrochemical Impedance Spectroscopy (EIS)
100kHz to 1mHz with 5mV PP signal
Physical characterizationsSEM micrographs TGA and BET analysis
TGA analysis of polymer compositeSFG10 samples
-0.0 150.0 300.0 450.0 600.0 750.0 900.0
Temperature
0
20
40
60
80
100
120
Weig
ht P
erce
nt (%
)
Bare5% PPy6% PPy7.8% PPy8.4% PPyPPy
Charge-discharge curves of polymer composite SFG10 samples
0 200 400 600 800
Specific Capacity (mAh/g)
0.0
1.0
2.0
3.0
4.0
Pote
ntia
l (V
vs L
i/Li+ )
Bare5% polymer6% polymer7.8% polymer8.4%polymer
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
(%)
056
7.88.4
485.9483.7471.7456.6432.5
232.7 309.3313.6310.1290.3
52.136.133.532.132.9
47.963.966.567.967.1
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)
056
7.88.4
284.6338.8359.8 362.3 359.0
9.848.98 8.557.787.69
21.6519.7618.8117.1216.92
626.1745.4791.6797.1789.8
Cyclic voltammograms of polymer composite SFG10 samples
0.0 0.4 0.8 1.2 1.6
Potential ( V vs Li/Li+)
-600
-500
-400
-300
-200
-100
0
100
200
300
400
Spec
ific
Curre
nt (m
A/g
)
Bare5% PPy6% PPy7.8% PPy8.4% PPy
SEM pictures of polymer composite SFG10 samples
Bare PPy/C
10 m 10 m
Impedance studies of polymer composite SFG10 samples
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Real Z (-g)
0.0
0.1
0.2
0.3
0.4
0.5
Imag
inar
y Z
(-g
)
Bare5% polymer6% Polymer7.8% Polymer8.4% Polymer
Impedance comparison of Bare and Polymer composites of SFG10.Impedance was done at unlithiated state for all the samples.
Equivalent circuit used to fit the experimental data
R
R R2
C2C
DPE1 DPE2
R – ohmic resistanceR1 – SEI layer resistance C1 – SEI layer capacitanceR2 – Polarization resistance C2 – Double layer capacitance
Equivalent circuit parameters for polymer composite electrode
Sample R(ohm) R1 (ohm) C1 (Farad) R2 (ohm) C2 (Farad)
Bare 7.9 197.4 2.3x10-7 17.7 4.3x10-6
5% PPy 7.6 27.1 4.7x10-6 14.8 4.3x10-6
6% PPy 7.9 21.7 7.0x10-6 12.1 4.5x10-6
7.8% PPy 7.8 13.9 7.2x10-6 10.4 7.0x10-6
8.4% PPy 8.3 8.7 8.2x10-6 9.1 9.9x10-6
Comparison of coulombic efficiencies for SFG10 samples
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0
Cycle number
90
91
92
93
94
95
96
97
98
99
100
Coul
ombi
c effi
eien
cy (%
)
Bare
7.8% PPy
Rate capability studies of composite SFG10 samples
0 5 10 15 20 25
Cycle number
0
100
200
300
400
Spec
ific
Cap
acity
(mA
h/g)
Bare
7.8% polymer
C/15 rate C/6 rate C/3 rate C rate C/15 rate
Cycle life studies of composite SFG10 samples
0 6 12 18 24 30 36
Cycle number
0
100
200
300
400Sp
ecifi
c Ca
paci
ty (m
Ah/
g)
Bare
7.8% PPy
Charge-Discharge curves of polymer compositeSFG10-15% sn samples
200 600 1000
Specific Capacity (mAh/g)
0.0
1.0
2.0
3.0
4.0Po
tent
ial (
V v
s Li/L
i+ )
SFG10-15%Sn15% Sn-PPy
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-PPy
485.9
456.6
719.9
606.2
232.7
310.1
350.8
370.4
52.1
32.1
51.3
38.9
47.9
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 composite
Charge 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 carbon
Polymer composite anode show better rate capability and longer cycle life
Acknowledgements
This 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.)
