Tuning electrochemical properties of NaMPO4 (M= Mn, Fe)

nanoparticles for their application in Na-ion Supercapacitors.

M.Tech project

Under the supervision of

Prof. Amreesh ChandraDepartment of Physics

IIT Kharagpur

By :

Charu Lakshmi T R

15PH62R07 1

Introduction

A supercapacitor is a compact, electrochemical capacitor that

can store an extremely high amount of energy compared to the

conventional capacitor .

Then it discharges that energy at rates demanded specially by

the application.

Its capacitance ranges upto 5000 farads.

Supercapacitors are finding their application in industries

ranging from defence to household appliances, automobiles to

communications, power grids to microelectronics, combustion

engines to rail locomotives

2

EDLC & Pseudocapacitor

Fig.1 Schematic representation of EDLC

Source : Wikipedia3

Why NaMPO4 was chosen

The strong P-O bonds increase the structural stability of the cathode,

characterised by good thermal stability.

Significantly larger electronegativity of the PO4 groups increases the

ionic character of the M-O bonds.

This decrease in covalency reduces the separation between the

bonding and antibonding orbitals and translates into an increased cell

potential which helps in tailoring the electrochemical performance of

a material.

( Ref: Materials Today, Volume 19, Number 2,

March 2016)

4

Fig.2: Schematic view of the (a) olivine type and (b) maricite-type

structure

Ref: CrytEngComm, 2013,15,9080

- Na ion - Mn ion - Oxygen ion

Schematic view

5

NaNO3 +

Mn(NO3)2·4H2O

+ NH4H2PO4

Solution combustion synthesis

of NaMnPO4

6

Stir @ 80˚C and

then add urea &

Set pH to 8

Heat @100 ˚C &

solid mass is

obtained

and then it was subjected to oven heating

@110˚C for 8 hrs + subsequent heating @ 600˚C

for 12 hrs

Semi chemical Synthesis of NaFePO4

Fe(NO3)2·4H2O

+ NH4H2PO4

+ NaNO3

Na : Fe : P = 1.05 : 0.97 : 1

7

Solid Mass

obtained

Subject it to oven heating

@ 350˚ C for 4 hrs

+ subsequent heating

@ 650˚ C for 10 hrs

Dissolve in water

& heat @100 ˚ C

Synthesis of PANI Coated NaFePO4

Sonicate for 15 min

8

2 gm NaFePO4

in 30 ml

ethanol

+ 10ml water

Add Aniline

Dropwise

Add 10 ml 1M

HCl + APS

Aniline : APS =

4:1

washed & was

collected then heated

@ 60˚c

Stirring

continued in

ice bath for 15

hrs

sonicate for 10 min

XRD Analysis

Average crystallite size was calculated using

Scherrer formula

It was approx 10 nm, 34 nm & 29nm for

NaMnPO4, bare and coated NaFePO4

respectively.

Fig.3: XRD of (a)NaMnPO4 (b) NaFePO4 (c) Coated NaFePO4

9

20 25 30 35 40 45

4000

6000

8000

10000

12000

* *

**

*

(222)

(240)

(122)

(221)

(012)

(002)

(031)

(211)

(220)

(121)(0

21)

(111)

Inte

ns

ity

( a

rb.

un

it)

2 Theta (Degree)

(011)

0 10

0

10

20 30 40 50 60

1600

2000

2400

2800

3200

*

*

*

(02

2)

(12

2)

(23

0)

(20

0)

(251

)

(01

3)

(400

)

(222

)

(03

1)

(211)

(12

2)

(111)

Inte

nsit

y (

Arb

Un

it)

2 Theta (Degree)

(02

0)

20 30 40 50 60

1400

1600

1800

2000

2200

(03

1)

(21

1)

(12

2)

(23

0)

(20

0)

(11

1)

(02

0)

Inte

nsit

y(A

rb.

un

it)

2 Theta (Degree)

(a) (b)

(c)

FTIR Analysis

The FTIR

spectrum of

coated NaFePO4

gets modified and

the peaks at

approx 1000 and

3400 cm-1

becomes distinct

as both NaFePO4

and PANI have

similar set of

peaks.

4000 3000 2000 1000 0

NaFePO4

PANI coated NaFePO4

Tra

nsm

itta

nce (

%)

Wave Number (cm-1)

Fig.4: FTIR spectra of NaFePO4 and PANI coated NaFePO4

10

SEM images

(a) (b)

Fig.5: SEM images of (a) NaMnPO4

(b)Bare and (c) coated NaFePO4

11

(c)

Electrochemical Results of

NaMnPO4

(a)

(b)

Fig.6 : Electrochemical measurements

a) CV curve b) charge-discharge curve

Current

density

(A/g)

Specific

capacitance(F/g)

2 7.009

1 8.198

0.5 10.663

0.25 17.976

12

13Fig. 7 : CV curves for Bare & Coated NaFePO4 in (a)& (b) 2M Na2SO4

and (c)& (d) 2M NaOH

(c)

(b)

(d)

Electrochemical analysis

0.0 0.2 0.4 0.6 0.8 1.0

-0.0004

-0.0002

0.0000

0.0002

0.0004

0.0006

Cu

rren

t (A

)

Voltage (V)

5mV/s (coated)

5mV/s

0.0 0.2 0.4 0.6 0.8 1.0

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

Cu

rren

t (A

)

Voltage (V)

200mV/s (coated)

200mV/s

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

Cu

rren

t (A

)

Voltage (V)

5mV/s coated

5mV/s

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-0.008

-0.004

0.000

0.004

0.008

Cu

rren

t (A

)

Voltage (V)

200mV/s (coated)

200mV/s

(a)

CD curves of Bare & Coated NaFePO4

14

(a)

Fig. 8 : CD curves for bare and coated NaFePO4 in (a)

,(b) 2M Na2SO4 and (c),(d) 2M NaOH

(b)

(c) (d)

0 50 100 150 200 250 300 350

0.0

0.2

0.4

0.6

0.8

1.0

1.2

V

olt

ag

e (

V)

Time (Sec)

0.5 A/g

0.75 A/g

1 A/g

2 A/g

3A/g

0 50 100 150 200 250

-0.4

-0.2

0.0

0.2

0.4

0.6

Vo

ltag

e (

V)

Time (Sec)

0.75A/g

1A/g

2A/g

3/g

0 100 200 300 400 500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Vo

ltag

e (

V)

Time (Sec)

0.5A/g

0.75A/g

1A/g

2A/g

3A/g

0 50 100 150 200 250 300 350 400

-0.4

-0.2

0.0

0.2

0.4

0.6

Vo

ltag

e (

V)

Time (Sec)

0.5A/g

0.75A/g

1A/g

2A/g

3A/g

Current

density

Specific Capacitance (F/g)

a) For

NaFePO4

Pani

coated

b) For

NaFePO4

Pani

coated

0.5A/g 65.78 84.05 57.05 67.25

0.75A/g 54.13 76.03 53.96 66.36

1A/g 50.84 71.85 49.74 59.62

2A/g 29.33 47.30 45.69 58.31

3A/g 20.74 34.74 42.51 57.87

Electrochemical Results

for bare and coated NaFePO4

Specific Capacitance in a) 2M Na2SO4 and b) 2M NaOH 15

0.5 1.0 1.5 2.0 2.5 3.0

20

30

40

50

60

70

80

90

Sp

ecif

ic C

ap

acit

an

ce (

F/g

)

Current Density (A/g)

NaFePO4

Pani Coated NaFePO4

0.5 1.0 1.5 2.0 2.5 3.0

40

45

50

55

60

65

70

Sp

ecif

ic C

ap

acit

an

ce (

F/g

)

Current Density (A/g)

NaFePO4

Pani Coated NaFePO4

Fig.9 (a) Change in specific

capacitance of NaFePO4 for

different scan rates and

Specific capacitance vs. current

density plot of NaFePO4 and PANI

coated NaFePO4

in (b) 2M Na2SO4 and (c) 2M NaOH

electrolyte solution

Change in specific capacitance

16

(a) (b)

0 25 50 75 100 125 150 175 200 225

10

20

30

40

50

60

70

Sp

ecif

ic C

ap

acit

an

ce (

F/g

)

Scan Rate (mV/S)

2 M Na2SO4

2 M NaOH

(c)

Cycling stability

0 200 400 600 800 1000

55

60

65

70

S

pecif

ic C

ap

acit

an

ce (

F/g

)

Cycle Number

0 200 400 600 800 1000

66

68

70

72

74

76

78

80

Sp

ecif

ic C

ap

acit

an

ce (

F/g

)

Cycle Number

Fig.10 : Cycling curve for (a) NaFePO4 and (b) PANI coated

NaFePO4

• Charging and discharging were carried out at 3A/g for 1000

cycles.

• The capacitance in the first cycle was 62 F/g and 72.8 F/g ,

which remained nearly stable.

17

(a) (b)

Conclusions

NaFePO4 acts as a supercapacitive material in 2M

Na2SO4.

There was a clear increase in the specific capacitance

of the material after coating with conducting polymer.

But the capacitance obtained has to be more to

compete with other active materials like the olivines,

spinels, oxides etc.

18

Future Aspects

This being a battery material, much work is not done on

its use as a Supercapacitor electrode material. So,

The mass loading on the electrode can be reduced, so as

to get higher capacitance.

Particle size can be tuned further so as to increase the

surface area

The percentage of monomer used can be varied to find

out the effect on the capacitance.

19

Acknowledgement

I hereby acknowledge the support of

Prof. Amreesh Chandra .

Prof. Krishna Kumar, HOD of physics dept.

Prof. Achintya Dhar, Facaulty advisor.

CRF , IIT Kharagpur

My Labmates; Md. Aqueel Akhtar, Inderjeet Singh, Prasenjit

Haldar, Vikas Sharma, Sudipta Biswas, Ananya

Chowdhury,Debabrata Mandal, Shivangi Shree, Prateek

Srivastava.

20

Thank you

21