Jahn Teller

DEVELOPMENT OF NON-AQUEOUS ASYMMETRIC HYBRID SUPERCAPACITORS BASED ON Li-ION INTERCALATED COMPOUNDS

GUIDE Dr.D.KALPANA, SCIENTIST,

BY

EEC DIVISION,

NAKKIRAN.A,

CECRI, KARAIKUDI.

An overview of previous presentation

• Introduction • Hybrid supercapacitors • Synthesis of LiMn2O4 and the same multidoped with Ni, Co and Cu • Physical characterization - XRD, SEM, FTIR • Cell Fabrication

Electrochemical Characterization techniques

• Cyclic voltammetry • Galvanostatic charge-discharge • Electrochemical impedance spectroscopy

Cyclic Voltammetry Before cycles: LiMn2O4

LiCo0.25Ni0.25Cu0.25Mn1.25O4

0.0010 1mV/s 2mV/s 5mV/s

0.0005

0.0010

1mV/s 2mV/s 5mV/s

0.0000

current(A)

current(A)

0.0005

-0.0005

0.0000

-0.0005

-0.0010 -0.0010

-0.0015 2000

1000

0 Voltage (mV)

-1000

-2000

2000

1000

0 voltage(mV)

-1000

-2000

Cyclic Voltammetry After 5000 cycles: LiMn2O4

LiCo0.25Ni0.25Cu0.25Mn1.25O4 0.0010

0.0010 1mV/s 2mV/s 5mV/s

1mV/s 2mV/s 5mV/s 0.0005 current(A)

current(A)

0.0005

0.0000

0.0000

-0.0005

-0.0005

-0.0010

-0.0010

2000

1000

0 voltage(mV)

-1000

-2000

2000

1000

0 voltage(mV)

-1000

-2000

Cyclic Voltammetry Scan rate = 5mV/s LiCo0.25Ni0.25Cu0.25Mn1.25O4

LiMn2O4 0.0010

0.0010

before cycles after 5000 cycles

0.0005

current(A)

current(A)

0.0005

before cycles after 5000 cycles

0.0000

0.0000

-0.0005

-0.0005

-0.0010

-0.0010

-0.0015

-0.0015 2000

1000

0 voltage(mV)

-1000

-2000

2000

1000

0 voltage(mV)

-1000

-2000

Cyclic Voltammetry Scan rate = 5mV/s

Before cycles: 0.0010

After 5000 cycles: 0.0010

LiMn O Li(CoNiCu)0.25Mn1.25O4 2

4

0.0005 current(A)

current(A)

0.0005

LiMn2O4 Li(CoNiCu)0.25Mn1.25O4

0.0000

0.0000

-0.0005

-0.0005 -0.0010

-0.0010

-0.0015 2000

1000

0 voltage(mV)

-1000

-2000

2000

1000

0 voltage(mV)

-1000

-2000

Formula used

Specific capacitance =

Average current Scan rate x Weight

Cyclic Voltammetry Results

Specific capacitance of LiMn2O4

Specific capacitance of LiMn1.25Co0.25Ni0.25Cu0.25O4

(F/g)

Condition

( F/g)

1mV/s

2mV/s

5mV/s

1mV/s

2mV/s

5mV/s

Before cycles

34

31

29

22

20

19

After 5000 cycles

27

22

18

18

16

15

Charge-Discharge Profiles of LiMn2O4 Current density = 500µA/cm2 2.4

2.4 2.2

cycle no.2

2.0

after 5000 cycles

2.0 1.8 1.6

voltage in V

Voltage(V)

1.6 1.2 0.8

1.4 1.2 1.0 0.8 0.6

0.4

0.4 0.2

0.0 900

1000 1100 1200 1300 1400 1500 1600 Time (sec)

0.0 700

750

800

850

900

950

Time in s

1000

1050

1100

1150

Charge-Discharge Profiles of LiCo0.25Ni0.25Cu0.25Mn1.25O4 Current density = 500µA/cm2 2.0

2.0

cycle no.3

1.6

1.6

1.4

1.4

1.2

1.2

1.0 0.8

1.0 0.8

0.6

0.6

0.4

0.4

0.2

0.2

6300

6350

6400

6450

6500

Time(sec)

6550

6600

after 5000 cycles

1.8

voltage in V

Voltage(V)

1.8

6650

0.0 450

500

550

600

Time in s

650

700

750

Formulae used Specific Capacitance =

Current x Discharge time Voltage x weight

Current x Voltage Specific Power = weight Current x Voltage x Discharge time Specific Energy = weight

Charge-Discharge results

LiMn2O4

LiMn1.25Co0.25Ni0.25Cu0.25O4

Condition Specific capacitance F/g

Specific power kW/kg

Specific energy kWh/kg

Specific capacitance F/g

Specific power kW/kg

Specific energy kWh/kg

Before cycles

14.55

200

21.98

5.36

110

5.8

After 5000 cycles

7.85

200

11.83

4.17

110

4.58

Columbic efficiency Vs Cycles

Coulombic efficiency (%)

Coulombic efficiency = discharge time/charging time 100 LiMn2O4 Li(CoNiCu)0.25Mn1.25O4 90

80

70

0

1000

2000

3000

No of cycles

4000

5000

Internal resistance Vs Cycles Internal resistance(ohm)

IR = ∆V/ ∆I LiMn2O4 Li(CoNiCu)0.25Mn1.25O4

800

700

600

500

400

300 0

1000

2000

3000

No of cycles

4000

5000

Specific Capacitance (F/g)

Specific capacitance Vs Cycles 20

16

LiMn2O4 Li(CoNiCu)0.25Mn1.25O

4

12

8

4

0 0

1000

2000

3000

No of cycles

4000

5000

Electrochemical Impedance spectroscopy Before cycles:

After 5000 cycles: -800

-8

LiMn2O4 Li(CoNiCu)0.25Mn1.25O4

-700

LiMn2O4 Li(CoNiCu)0.25Mn1.25O4

-600

-6 Zim(ohm)

Zim(ohm)

-500

-4

-2

-400 -300 -200 -100

0 4

6

8 Zre(ohm)

10

12

14

0 -200

0

200

400

Zre(ohm)

600

800

Impedance results LiMn2O4

LiMn1.25Co0.25Ni0.25Cu0.25O4

Condition Rs

Rct

Cdl

Rs

Rct

Cdl

ohm

ohm

mF/g

ofm

ohm

mF/g

Before cycles

5.128

0.2917

2.98

5.043

0.2394

3.14

After 5000 cycles

7.829

278

0.195

6.573

122.4

0.59

Structure Vs capacity fading • The structural stability of a host electrode to the repeated insertion and extraction of lithium is undoubtedly one of the key properties for ensuring that a lithium ion cell operates with good electrochemical efficiency • In transition metal oxides, both stability of the oxygen ion array and minimum displacements of the transition metal cations in the host are required to ensure good reversibility.

Structure of cubic SPINEL

Structural Change • the cubic symmetry of Li[Mn2]O4(space group Fd3m), in which the lithium ions occupy tetrahedral sites and Mn occupy the Octahedral sites • On cycling the lithium ions occupy octahedral sites of Mn ion ,So the cubic symmetry of LiMn2O4 is reduced to tetragonal Li2[Mn2]O4 (space group F41/ddm)

Cubic to tetragonal transition LiMn2O4

Li2Mn2O4

CUBIC [a=b=c]

TETRAGONAL

• This crystallographic distortion, which results in a 16% increase in the c/a ratio of the unit cell parameters • Average Oxidation state of cubic spinel is 3.5 • Average Oxidation state of tetragonal spinel is 3

Jahn Teller distortion When the ratio of Mn3+ increases ,it follows a disproportionate reaction 2Mn3+

Mn4+ + Mn2+

Where Mn2+ is an acid-soluble species .It dissolute into solution. And distrust its structural integrity during cycling.

Remedy • This multi-doped system maintains the average oxidation state of Mn ion between 3.5 to 4. • So JT distortion is reduced to the greater extend

Conclusions • The faster rate of capacity fading in pure substance than doped one may be attributed to the onset of Jahn-Teller distortion • The above point may be confirmed without any doubts soon after the arrival of XRD results for the sample after 5000 cycles.

Conclusions • The low IR in the case of doped substance is also a strong reason for its better performance • The impedance profiles too explain clearly that doped substance is a better candidate for supercapacitors than the pure one

Conclusions • With LiMn2O4 we were able to reach a high voltage of 2.4v, while the highest voltage that has ever been reported for this system is 1.8v • This high voltage may be attributed to the use of organic electrolyte – 1M LiClO4 in EC-PC

Lithium Cobaltate(LiCoO2) • Commercially successful • The layered structure of LiCoO2enables easy diffusion of Liions in and out of the structure

Synthesis Of Cathode Material

• Two cathode materials were synthesized, i) Pure LiCoO2 ii) LiCoO2 doped with Al - LiCo1-xAlxO2 ( x = 0.2, 0.4,…..0.8 ) • The cathode material was synthesized by soft combustion method • Compositions were taken on a stoichometric ratio based on following equations, • LiNO3 + Co(NO3)2.6H2O

LiCoO2 (for pure substance)

• LiNO3 + 0.8Co(NO3)2.6H2O + 0.2Al(NO3)2.9H2O

LiCo0.8Al0.2O2 (for doped substance)

Composition For Pure Substance Basis : 0.1 moles(9.8g) of product

Chemical

Weight

LiNO3

6.9 g

Co(NO3)2.6H2O

29.1 g

Glycine ( C2H5NO2)

15 g

Distilled Water

100 ml

Composition For Doped Substance Basis : 0.2 moles of product Chemical

Weight

LiNO3

13.8 g

Al(NO3)2.9H2O

15 g

Co(NO3)2.6H2O

46.56 g

Glycine ( C2H5NO2)

30 g

Distilled Water

100 ml

The Soft Combustion Process Weighing of required chemicals

Dissolve in 100ml distilled water Stir well at 600C Heat the mixture at 1000C for 8 hours

Product is formed following a soft combustion

Thermal Analysis

Future Work • Physical characterization of LiCoO2 • Cell fabrication • Electrochemical characterization • Comparison of LiMn2O4 and LiCoO2 using the available data

Thank you

Queries?