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