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Development of Low cost, Eco Friendly Electrode Materials For Hybrid
Supercapacitor Applications
Karthikeyan Kaliyappan,Ph.D scholar,
Energy Conversion and Storage Processing Lab,Chonnam National University,
Gwangju.
What is Supercapacitors (SC)What is Supercapacitors (SC)
‘Super’ implies high capacitance values
SCs have the ability to store and release charge and deliver
high power densities over short periods of time
Stores energy efficiently and release energy very quickly
Can be used where short time backup power and peak power
needs are critical
Applications in hybrid power systems for EVs, memory back up
Bridges the gap between conventional capacitors and batteries
HistoryHistory
1957 – First supercapacitor developed with porous carbon electrode by general electronics1966 – Standard oil company patented a device that stored energy in double layer interface1978 – Memory backup devices1980 – Energy source2005 – Used to power emergency actuation systems for
doors in aircraft
Principle of a SupercapacitorPrinciple of a Supercapacitor
Capacitance Capacitance C = o r A/d
Double layer is generated when a voltage is applied to electro des in an electrolyte The charge separation occurs in molecular dimensions (few nanometers) resulting in extremely large capacitanceActivated carbon with high surface area (2000 m2/g)
Separator shocked in electrolyte
+ + + + ++ + + + + + ++ +
+ + + + ++ + + + + + ++ +- - - - -- - - - - - -- -
- - - - -- - - - - - -- -
Activated carbon electrode
Activated carbon electrode
Electrolyte
Properties of supercapacitors compared with batteries and Properties of supercapacitors compared with batteries and traditional capacitorstraditional capacitors
PropertyProperty CapacitorsCapacitors SCsSCs BatteriesBatteries
Charge – Discharge Charge – Discharge timetime
pico seconds to pico seconds to
milli secondsmilli secondsMilli seconds to Milli seconds to
minutesminutes1 to 10 hours1 to 10 hours
Operating Operating temperaturetemperature
- 20 to + 100 - 20 to + 100 oo C C - 40 to + 75 - 40 to + 75 oo C C - 20 to + 65 - 20 to + 65 oo C C
LifeLife > 10 > 10 88 Cycles Cycles 30,000 to 10 30,000 to 10 66 cycles cycles 150 to 1500 cycles150 to 1500 cycles
Power densityPower density 0.25 to 10,000 0.25 to 10,000
kW / kgkW / kg10 to 100 kW / kg10 to 100 kW / kg 0.005 to 0.4 0.005 to 0.4
kW / kgkW / kg
Energy densityEnergy density 0.01 to 0.05 0.01 to 0.05
Wh / kgWh / kg1 to 5 W h / kg1 to 5 W h / kg 8 to 600 W h / kg8 to 600 W h / kg
WeightWeight 1 to 10 g1 to 10 g 1 to 2 g1 to 2 g 1 g to over 10 kg1 g to over 10 kg
Comparison of Various Energy systemsComparison of Various Energy systems
AdvantagesAdvantages
Very high cell voltages possible High power density No special charging circuits required Can be charged and discharged in seconds Long cycle life No chemical reactions10 to12 years life
Classification of SupercapacitorsClassification of Supercapacitors
Need for Hybrid SupercapacitorNeed for Hybrid Supercapacitor
HEVs requires energy storage devices that can deliver higher power density as well as higher energy densities
Two kind of energy devicesTwo kind of energy devices
1. Secondary batteries can not be widely used in HEVs due to their low power density and short cycle life
2. Supercapacitors – Low energy density is the major problem By combining the energy density of a battery with a high By combining the energy density of a battery with a high power density of a super capacitor, much smaller and lighter power density of a super capacitor, much smaller and lighter battery could be used in carsbattery could be used in cars
High specific energy then ECs
• Cathode - Lithium intercalated compounds• Anode - High surface activated carbon
Lithium ion capacitorsLithium ion capacitors
Lithium materialsLithium materials LiMn2O4 LiCo1/3Ni1/3Mn1/3O2 High cost LiCoPO4 Toxic LiCoO2
Li4Ti5O12
Metal orthosilicates (LiMetal orthosilicates (Li22MSiOMSiO44, M = Fe, Mn), M = Fe, Mn)
Environmental Friendly Better thermal properties Competitive energy density Low cost Relatively high lithium-ion mobility
Preparation of LiPreparation of Li22MSiOMSiO4 4 (M=Fe and Mn)(M=Fe and Mn)
Solid State method Bulk production
Easy to handle
Pre calcination at 400 oC for 4h in air
Grinding and pellet
Li2MSiO4 (M=Fe and Mn)
LiOH Mn2O3 or FeC2O4 SiO2
Adipic Acid
Final calcination at 800 oC for 12h in argon
Electrode FabricationElectrode Fabrication
AnodeAnode: 70% of Li2MnSiO4 or Li2FeSiO4
20% of Ketjen Black
10% of Teflonized acetylene black
CathodeCathode: 70% of Activated carbon
20% of Ketjen Black
10% of Teflonized acetylene black
SeparatorSeparator: Celgard 3401
ElectrolyteElectrolyte: 1 M LiPF6 in EC:DMC (1:1 vol%)
The mass ratio of cathode to anode was about 2:1
Cell FabricationCell FabricationCoin type cell - CR 2032
X-Ray diffraction PatternsX-Ray diffraction Patterns
10 20 30 40 50 60 70 80
Li2FeSiO
4
Li2MnSiO
4
Inte
nsity
(a
u.u
nits
)
2 (degree)
The broad peaks indicate that in neither case the crystallinity is good
Orthorhombic unit cell in space group Pmn2 typical of phases with the low temperature Li3PO4 structure type
The two compounds are isostructural
Size of the particles Size of the particles
= 0.9/cos
Li2FeSiO4 – 62 nm
Li2MnSiO4 – 150 nm
Well-developed particles
Narrow size distribution
Better for diffusion of lithium ions
Compound Average particle size (nm)
Li2FeSiO4 50 - 75
Li2MnSiO4 100-150
(a)
(b)
(a) - Li2FeSiO4
(b) - Li2MnSiO4
SEM ImagesSEM Images
CV test was employed to find out the capacitive performance of the material• Voltage window - 0-3 V • Scan rates – 2, 5, 10 and 20 mV/s
The rectangular-like behavior revels that both have good capacitive behavior and high reversibility The curve remains in good rectangular like shape even at high scan rates
0.0 0.5 1.0 1.5 2.0 2.5 3.0
-6
-3
0
3
6
9Li
2FeSiO
4/AC capacitor
a - 2 mV/sb - 5 mV/sc - 10 mV/sd - 20 mV/s
d
cba
Cur
rent
(m
A)
Voltage (V)0.0 0.5 1.0 1.5 2.0 2.5 3.0
-6
-3
0
3
6
9
Li2MnSiO
4/AC capacitor
d
cb
a
a - 2 mV/sb - 5 mV/sc - 10 mV/sd - 20 mV/s
Cur
rent
(m
A)
Voltage (V)
CV StudiesCV Studies
Specific capacitanceSpecific capacitance
CSC = I/s*m
I = Applied current (A)
S – Scan Rate (mV/s)
M – weight of the active material
Li2FeSiO4/AC Cell Li2MnSiO4/AC Cell
Scan rate (mV/s)
Csc (F/g) Scan rate (mV/s)
Csc (F/g)
2 58.1 2 76.92
5 42.6 5 64.13
10 40.8 10 48.07
20 36.2 20 38.15
Charge Discharge Characteristics Charge Discharge Characteristics
0 2000 4000 6000 8000 100000
1
2
3Li
2FeSiO
4/AC Cell
Vol
tage
(V
)
Time (sec)0 2500 5000 7500 10000
0
1
2
3 Li2MnSiO
4/AC Cell
Vo
ltag
e (
V)
Time (s)
Linear and symmetrical feature can be observed from curves Excellent electrochemical reversibility and good capacitance behavior Both systems have low ohmic drop
Discharge Specific capacitanceDischarge Specific capacitance
Sdc = 4 (I * t) /(V * M) R = Vcharge – Vdischarge/2l
The average internal resistanceThe average internal resistance
Li2FeSiO4/AC Cell Li2MnSiO4/AC Cell
Current Density (mA/cm2)
Discharge Capacitance
(F/g)
Current Density (mA/cm2)
Discharge Capacitance
(F/g)1 1 43.2
2 2 34.8
4 4 33.5
6 6 32
8 8 30.6
10 10 30
Resistance (Ω) 58 Resistance (Ω) 70
0 200 400 600 800 10000
20
40
60
80
100
120
0
20
40
60
80
100
120Li
2MnSiO
4/AC Cell
C
oulo
mbi
c E
ffic
ienc
y (%
)
Dis
char
ge C
apac
itanc
e (F
/g)
Cycle Number 0 200 400 600 800 1000
20
40
60
80
100
20
40
60
80
100Li
2FeSiO
4/AC Cell
(b)
C
oulo
mbi
c ef
fici
ency
(%
)
Dis
char
ge C
apac
itanc
e (F
/g)
Cycle Number
Li2FeSiO4/AC Cell Li2MnSiO4/AC Cell
Cycle Number Discharge Capacitance (F/g)
Cycle Number Discharge Capacitance (F/g)
1 49.5 1 43.2
1000 43.5 2 36.7
Capacity loss (%) 12 Capacity loss (%) 15
Columbic Efficiency (%) More then 99.5 Columbic Efficiency (%)
More then 99.5
Li2FeSiO4/AC Cell Li2MnSiO4/AC Cell
Energy density (Wh/kg)
Power Density (W/kg)
Energy density (Wh/kg)
Power Density (W/kg)
54 150
43 300
41 600
40 900
38 1200
37 1500
10 20 30 40 500
5
10
15
20Li
2MnSiO
4/AC Cell
-Zim
a (o
hm)
Zreal
(ohm)5 10 15 20
0
3
6
9
12
Li2FeSiO
4/AC Cell
-Zim
a (ohm
)
Zreal
(ohm)
System Solution Resistance (Ω)
Charge transfer Resistance
(Ω)
Capacitance (F/g)
C = -1/2pfZimm
Conductivity (S/cm)
σ = δ/Rct * A
Li2FeSiO4/AC Cell 40
Li2MnSiO4/AC Cell 56
Electrochemical impedance spectroscopy Electrochemical impedance spectroscopy
Nano sized low cost, less toxic materials Li2MSiO4 (M = Fe and Mn) have been developed for hybrid supercapacitor application.
Hybrid EC capacitors gives about 43.2 and 49.5 F/g specific capacitance based on the electrode active-material in 1 M LiPF6 in EC:DMC
Delivered high Specific energy and Specific power then conventional EDLC.
Both system exhibited excellent cycling performance (more then 1000 cycles) with more then 99.5% efficiency
ConclusionConclusion