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?