Lithium ion phosphate

1. 1
Arun Kumar
Department of Physics and Institute for Functional Nanomaterials, University
of Puerto Rico, San Juan, PR-00931
Rechargeable Li-ion batteries based on Olivine-structured
(LiFePO4) cathode materials
20 August 2012 UPRRP

2. 2
 Introduction
Some basics!
Emergence of Li-(ion) rechargeable batteries
Current status of cathode materials
 Motivation
 Experimental details
 Results and discussions
 Summary
Outline

3. 3
About Batteries
Introduction
Chemical reactions leads to electrical energy
 Convert chemical energy to electrical energy
Collection of ´cells´ to get the required voltage
A Cell is comprised of
Cathode (Undergoes reduction)
Anode (Undergoes oxidation)
Electrolyte ( ionic conductor)
Active component
Inactive component

4. 4
Cells
Primary
Chemical reaction is irreversible
Reactions eat up the active material
Schematic of a primary
half cell
Anode Cathode
A A+
+ e
C + e C-
EA,Oxidation
EC,Reduction
ELECTROLYTE
ECELL = EA,OX+EC,RED
Some basics
Topic of this talk
Secondary
Chemical reaction is reversible
Active material remains!!

5. 5

6. 6
Rechargeable lithium ion battery : Schematic
Li ion shuttles between anode and
cathode
During charging Li ions move from
cathode to anode
During discharge Li ions gets
intercalated into cathode
X Li + + x e - + Li yM X Liy+x MX
Charge
Discharge
X Li + + x e - + Li yM X Liy+x MX
Charge
Discharge
∆G= -nFE
For maximum (+ve) E, cathode has to be highly oxidizing and anode has to be highly reducing
Cathode –Intercalation compound
Anode - Li metal (Li battery) not safe
or another intercalation compound (Li
ion battery)

7. 7
Theoretical capacity
Important concept in reference to the quality of the active material
Faraday’s first law of electrolysis:
F = N.e
Gram equivalent = MW/n
F = 965000 C ≡ 26.8 Ah
LiCoO2 : MW = 99.9 and n =1
so, 99.9 g of LiCoO2 is capable of delivering 26.8 Ah
i.e. theoretical capacity of LiCoO2 is 26.8Ah/99.9 g = 268 mAh/g
LiCoO2+ Li+
+ e-
LiCoO2
LiC6 Li+
+ C6
+
e-
Theoretical
1 e-
Practical
0.5-0.6 e-
Out put voltage : 3.6 V NO
of e-
or Li+
Molecular weight
(Kg)
How to optimize such system ?How to optimize such system ?

8. 8
Electrolyte
eVoc = μA -μC <Eg
At high current densities, the ionic motion
within an electrode and/or across an
electrode/electrolyte interface is too slow for the
charge distribution to reach equilibrium, that is
why the reversible capacity decreases with
increasing current density in the battery
The electrolyte must satisfy several additional
requirements
such as:
A Li-ion conductivity σLi>10-4
S/cm over the
temperature range of battery operation.
 An electronic conductivity σe<10-10
S/cm.
Chemical stability with respect to the electrodes,
including the ability to form rapidly a
solid/electrolyte-interface (SEI) layer where kinetic
stability is required because the electrode
potential lies outside the electrolyte window.
 Safe materials, i.e., preferably nonflammable and
non explosive if short-circuited.
 Low toxicity and low cost.

9. 9
Energy density (Wh) = Capacity (Ah) × Voltage (V)
Large work function (highly oxidizing)
+ maximize cell voltage.
 Insertion/extraction of a large amount of lithium
+ maximize the capacity.
High cell capacity + high cell voltage = high energy density
 Reversible lithium insertion/extraction process.
+ make it rechargeable
 No structural changes
+This prolongs the lifetime of the electrode.
 Good electronic and Li+
ionic conductivities.
+ improves the rate capability
 Chemically stable over the entire voltage range
+ No reaction with the electrolyte.
 Inexpensive, environmentally benign and light weight.
+safe, friendly, portability
Cathode: Material requirements

10. 10
Price, safety and low toxicity are strong arguments that Fe based cathode
should provide significant technological advantages in a Li-ion system
over LiCoO2 or LiNiO2 systems
But..All are not good with Fe based cathode material???
Low electronic conductivity!!
Candidates for cathodes
Compound
Capacity:
theo./Pract.
(mAh/gm)
Working
Voltage(V)
Cycleability
Energy
density
( Wh/kg)
Conductivity Drawbacks
LiMn2O4 148/120 3.8 300 100 10-5
S/cm Severe capacity fading
LiMnO2 285/140 4.0
Very difficult to
stabilize in layered
structure
LiCoO2 270/140-150 3.7 400 180 10-3
S/cm Expensive, toxic
LiNiO2 270/140 3.9
Severe cation mixing,
thermal instability at
the charged state
LiFePO4 170/165 3.4 1000 130 10-10
S/cm
Low electronic
conductivity

11. 11
Structure of olivine LiFePO4
The structure consists of corner-shared
FeO6 octahedral and edge-shared LiO6 octahedra
running parallel to the b-axis, which are linked
together by the PO4 tetrahedral .
The triphylite LiFePO4 belongs to the olivine
family of lithium ortho-phosphates with an
orthorhombic lattice structure in the space
group Pnma.
Structure(using ICSD software)

12. 12

13. 13

14. 14
LiCoO2 and their substituted versions adapt the α-NaFeO2-type
structure (space groupR3 m ), which is a layered, rhombohedral
structure in which the lithium ions can move quite freely in the
two-dimensional planes perpendicular to the c-axis. In this
structure, ~0.6 Li can be extracted and inserted during the charge
and discharge cycles, Further extraction leads to irreversible
collapse of the structural framework

15. 15
 Introduction
Some basics!
Emergence of Li-(ion) rechargeable batteries
Current status of cathode materials
 Motivation
 Experimental details
 Results and discussions
 Summary
Outline

16. 16
• High Performance:
Provides a High Theoretical capacity of ~170 mAh/g and
a High Practical capacity as high as ~ 165 mAh/g.
• Extremely Safe/Stable Chemistry
High intrinsic safety, non-explosive
High thermal stability
• High Discharge Rate Capability
• Extraordinary Long Cycle Life
• No memory effect
• Environment Friendly
• Non-toxic, non-contaminating-no rare metals
• Wide working temperature range
• From -45°C to 70°C ( Extremely cold and extremely hot
weather will not affect its performance)
Motivation
 Realization of high electronic conductivity in LiFePO4

17. 17
Improving
Conductivity of
LiFePO4
SONY (2001)
• Synthesis of small particle
LiFePO4 (50-100nm)
Armand et. al. (2001)
• Carbon coating of LiFePO4
particle (carbon~ 4-12%)
L.Nazar el. al. (2001)
•C-matrix composite influence on
LiFePO4
Y-M.Chiang et. al. (2002)
•Doped LiFePO4 (Nb5+Zr4+Al3+)
8 – fold order of magnitude increase in conductivity )
Advances in the conductivity of LiFePO4

18. 18
Nanomaterial structure
Advantage
The smaller particle size increases the rate of lithium insertion/extraction because of the short
diffusion length for lithium-ion transport within the particles, resulting in enhanced rate capability.
The smaller particle size enhances the electron transport in the electrode, resulting in enhanced rate
capability.
The high surface area leads to enhanced utilization of the active materials, resulting in higher
capacity.
The smaller particle size aids a better accommodation of the strain during lithium
insertion/extraction, resulting in improved cycle life
Disadvantage
Complexities involved in the synthesis methods employed could increase the processing cost,
resulting in higher manufacturing cost
High surface area may lead to enhanced side reactions with the electrolyte, resulting in high
irreversible capacity loss and capacity fade during cycling
The smaller particle size and high surface to volume ratio could lead to low packing density,
resulting in low volumetric energy density
Electrochemical impedance spectroscopy (EIS) can reflect
the electrochemical characteristics and inner structure more
accurately .

19. 19
 Introduction
Some basics!
Emergence of Li-(ion) rechargeable batteries
Current status of cathode materials
 Motivation
 Experimental details
 Results and discussions
 Summary
Outline

20. 20
Synthesis of LiFePO4
Ammonium
dihydrogen
phosphate
Lithium carbonate
High Energy
Ball Milling (8-
24H) ,(500 rmp
10h)
Organic removal at 350°C- 8-
12h
Sintering at 650°C-3 h
(crystallization)
Iron Oxalate
dihydrate
Carbon coated Powder synthesis through solid state route
 Carbon coated ( HEBM)
 RTA effect
Zinc oxide

21. 21
Schematic of CR2032 coin cell
Working electrode (cathode)
Active powder – 80 wt%
Carbon black – 10 wt%
PVDF binder – 10 wt%
Current collector- Al
Electrolyte
LiPF6 – 1M
EC : DMC- 1:1
Anode
Li foil
Structural Characterizations:
X-ray diffraction,
Raman spectroscopy
Electrochemical Characterizations:
Cyclic voltammetry, Charge discharge ,
rate -capability and EIS study
Coin cell assembled in our group
Experiment: coin cell fabrication

22. 22
 Introduction
Some basics!
Emergence of Li-(ion) rechargeable batteries
Current status of cathode materials
 Motivation
 Experimental details
 Results and discussions
 Summary
Outline

23. 23
X-ray diffraction analysis-I
15 20 25 30 35 40 45
C/LiFePO4
221,041
022
012
140
211
131
031
200
111
101
120
011
Intensity(au)
2Θ(degree)
020 (a)
LiFePO4
Li3Fe2(PO4)3 impurities indicating incomplete
reduction of Fe3+
to Fe2+
.
Refined parameters
 Phase pure orthorhombic
LiFePO4 + complete reduction of
Fe3+
to Fe2+
.
15 20 25 30 35 40 45
221,041
022
012
140
211
131
031
200
111
101
120
011
Intensity(au)
2Θ (degree)
020
15 20 25 30 35 40 45 50 55
Intensity(a.u.)
2Θ°
(a) 8h
(b)12h
(c) 16h
(d) 20h
(e) 24h
(a)
(b)
(c)
(d)
(e)

24. 24
20 30 40 50 60
0
100
200
300
400
500
600
700
800
42.0 42.5 43.0
0
20
40
60
80
100
120
140
160
Intensity(a.u.)
2θ
*
Intensity(a.u.)
2Θ
**
* Fe2
P
Carbon coating and rapid thermal
annealing effects
Fe2P is an impurity, which is
highly conducting . It helps to
improve the Electrochemical
properties.
15 20 25 30 35 40 45 50 55
LiFe0.09
4Zn0.06
PO4
/C
2Θ
Intensity
(b)
LiFe0.97
Zn0.03
PO4
/C
(a)
 All the XRD peaks could be indexed based
on a orthorhombic unit cell (Pnma).
 No evidence of additional crystalline phases
(crystalline carbon or other phases) were
seen from the XRD.
 The increase in the unit cell parameters is
due to the formation of LiFePO4.
X-ray diffraction analysis-II

25. 25
X-ray diffraction analysis-III
10 15 20 25 30 35 40 45 50 55
0
200
400
600
800
Intensity(arb.units)
2θ (Degrees)
Iobserved
ICalculated
Iobs-Ical
(a)
Element Wyckoff x y z s.o.f
Li 4a 0 0 0 1.00
Fe 4c 0.281 0.25 0.025 1.00
P 4c 0.095 0.25 0.582 1.00
O1 4c 0.097 0.25 0.258 1.00
O2 4c 0.457 0.25 0.781 1.00
O3 8d 0.342 0.537 0.215 1.00
Rwp (%) 17.9
Rp (%) 12.6
Goodness of Fit
(GOF)
1.6
Lattice
Parameters
a 10.314 Ǻ
b 6.002 Ǻ
c 4.693 Ǻ
The only phase observed is
LiFePO4.
The Rietveld refinement
indicates that the iron is
completely ordered.

26. 26
Morphological evolution : scanning electron microscopy
20kV 15,000 1μm
8H (a)
20kV 15,000 1μm
12H (b) 16H (c)
20kV 15,000 1μm
20kV 15,000 1μm
116H (c)
20kV 15,000 1μm
24H (e)
• SEM images of the non
carbonaceous LiFePO4.
• Particle attain a more
compact structure
without any substantial
increase in size .
The particle size reduces slightly with higher ball milling time. There is no
appreciable effect after 12h of ball milling.
8h 12h 16h
20H
24h
20h

27. 27
C
• SEM micrographs of (a) LiFePO4/C RTA method,
(b) LiFe0.97Zn0.3PO4/C and (c) LiFe0.93Zn0.7PO4/C
• This suggests that the carbon binds strongly to
the surface of precursors, thus coating the
particle with carbon restricts further growth of the
particles .
Morphological evolution : scanning electron microscopy
(a)
(b)
(b)
(c)
The grain size reduced with Zn substitution
up to 0.3%; more Zn resulted in
agglomeration

28. 28
J.Of P. Source 178(2008)
•. Transmission electron micrographs of C- LiFePO4 composite
particles calcined at 650°C showing morphological features with
various magnifications
•TEM images shows the synthesized LiFePO4 powder are mainly
fine particle less than <80nm.
•The image shows carbon – like nanometer sized webs wrapped
around and connecting the LiFePO4 particle .
TEM analysis of C/LiFePO4
Schematic diagram illustrating how carbon is distributed and
coated on the LiFePO4 particles

29. 29
Raman Spectroscopy
a) Raman spectra of C-LiFePO4 powder at various stages of charge – discharge process in
frequency range 150 to 1200 cm-1
(b) Raman spectra of C-LiFePO4 powder in the frequency
range 600 to 1800 cm-1
.
 The Raman modes in the range of 900 to 1150 cm-1
(see figure b) are due to the stretching
mode of PO4
3-
unit and involve symmetric and asymmetric of P – O bonds .
 These Raman modes also show a systemic change in Raman intensity with electrochemical
cycling process i.e. Raman intensity of all the PO4
3-
generated optical modes which decreased
during charging process and vive versa.
 The two prominent modes at ~ 1345 and 1587 cm-1
are the fingerprints of amorphous carbon.
The mode at ~ 1587 cm-1
is assigned to sp2
graphite like (G band) and the mode at ~ 1345 cm-1
is assigned to sp3
type amorphous carbonaceous material (D band).

30. 30
 For pure LiFePO4 the anodic/cathodic peaks at scan rate are 3.5/2.9. The separation of
redox peaks ΔV is 0.7 indicating that the electrochemical behavior is controlled by
diffusion step .
 The difference of redox potential peaks was 0.32 V for carbon coated LiFePO4 sample .
 The Li ion diffusion coefficient was ~ 7.13 x 10-14
cm2
s-1
whereas in the case of pure
LiFePO4 it was merely ~ 1.28 ×10-15
cm2
s-1
and 4.67 x 10-14
for LiFe0.97Zn0.3PO4 hence, the
Li ion (de)intercalation was better in C-LiFePO4 and LiFe0.97Zn0.3PO4.
Electrochemical property: Cyclic voltagrams I
ip = 2.69 X 105
n3/2
C0
b
A DLi
1/2
υ1/2
Randles–Sevcik equation
Bull. Korean Chem. Soc. 2011, Vol. 32, No. 3

31. 31
Electrochemical property: Cyclic voltagrams II
2.5 3.0 3.5 4.0 4.5
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Current(mA)
Voltage (V) vs. Li/Li+
Sample S2
Sample S1
2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
-0.0006
-0.0004
-0.0002
0.0000
0.0002
0.0004
0.0006
LF0.93Zn0.07P/C
LF0.97Z0.03P/C
Current(A)
Potential (V)
0.1mV/s
Slow cooling ΔV 0.32> LiFe0.93Zn0.7PO4/C ΔV 0.30>Fast
cooling 0.29> LiFe0.97Zn0.3PO4/C ΔV 0.25
 The difference of redox potential peaks was 0.32 V for
sample S1 (slow cooling rate) and 0.29 V for sample S2 (fast
cooling rates).
 The separation of redox peaks is ΔV is 0.25 , 0.30 for LiFePO4/C ,
LiFe0.97Zn0.3PO4/C and LiFe0.93Zn0.7PO4/C indicates that the
electrochemical behavior is controlled by diffusion step.

32. 32
The flats voltage profile of about
3.4 V versus Li/Li+
is
characteristic of olivine structure
Electrochemical property: Charge – Discharge I
0 10 20 30 40 50 60 70 80 90
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Voltage(V)
Capacity mAh/g
16h
12h
20h
24h
Id
=Ic
= 15mA/g
Electrochemical charge/discharge tests
of the cathodes showed a significant
improvement on forming nano sized
material
0 20 40 60 80
2.4
2.8
3.2
3.6
4.0
4.4
Voltage(VvsLi/Li+)
capacity mAh/g
1st ch
1st dis
5th ch
5th dis
15th ch
15th dis
2.5-4.5V
IC=Id= 15mA/g
0 10 20 30 40 50 60 70
2.4
2.8
3.2
3.6
4.0
4.4
Voltage(Li/Li+)(V)
capacity (mAh/g)
8HBM
Volatge 2.5-4.4
C/10
15mA/g
Currentt density

33. 33
Electrochemical property: Charge – Discharge II
-20 0 20 40 60 80 100 120 140 160
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
LF0.93
Zn0.07
P/C
Potential(V)
Capacity mAh/g
Cycled between
2.5- 4.3
Ic=Id=30 mA/g
1st discharge
20th discharge
High current density with moderate
capacity was obtained with
LiFe0.97Z0.3PO4/C compared LiFePO4/C
LiFe0.93Zn0.7PO4/C had inferior specific
capacity and rate-capability compared to
LiFe0.97Z0.3PO4/C and LiFePO4/C
LiFe0.93Zn0.7PO4/C
IC=Id=30mA/g
-20 0 20 40 60 80 100 120 140 160
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
LiFePO4/C
IC=Id=30mA/g
0 20 40 60 80 100 120 140 160
2.4
2.8
3.2
3.6
4.0
4.4
Potential(V)
Capacity, mAh/g
cycled between
with IC
=ID
=30mA/gm
1st ch
20th ch
1st dis
20th dis
LiFe0.97Zn0.03PO4/CLiFe0.97Zn0.3PO4/C

34. 34
0 5 10 15 20 25 30
0
10
20
30
40
CapacitymAh/g
no . of cylcle
15mA/g 30mA/g 45mA/g 120mA/g 15mA/g
0.7C 2.5C 6.6C 12C
0 5 10 15 20 25 30 35
20
25
30
35
40
45
50
55
60
capacitymAh/g
cycle no.
15mA/g 30mA/g
60mA/g
 Nanoparticle LiFePO4
show high rate
capability
8HBM
12HBM
24HBM
0 10 20 30 40 50 60
20
40
60
80
DischargeCapacity(mAh/g)
Cycle number
0.2C 1.3C
4.3C
0.2C
Electrochemical property: Rate Capability and Cyclability-I

35. 35
cycle performance for prepared for
samples LiFePO4 , LiFePO4/C and
0 5 10 15 20 25
10
20
30
40
50
60
DischargecapacitymAh/g
Cycle number
LiFe0.03Zn0.07PO4/C
LiFePO4/C
LiFe0.93Zn0.7PO4/C
0 10 20 30 40
20
40
60
80
100
120
140
160
DischargeCapacity,mAh/g
Cycle number
Id
= 60mA/g
C/2.5
0 10 20 30 40
20
40
60
80
100
120
140
160
DischargeCapacity,mAh/g
Cycle number
Id
= 60mA/g
C/2.5
Electrochemical property: Rate Capability and Cyclability-II
LiFe0.93Zn0.7PO4/C

36. 36
LiFe0.93Zn0.7PO4/C had inferior specific capacity
and rate-capability compared to LiFe0.97Zn0.3PO4/C
and LiFePO4/C
Electrochemical property: Rate Capability and Cyclability-III

37. 37
Electrochemical impedance spectroscopy in Li-Ion Batteries
RS
Rct1 Rct2
CPE1 CPE2
The equivalent circuit of the Li-ion battery
This curve can be used to
determine the cell capacity, effect
of the discharge-charge rate,
temperature and information on
the state of health of the battery.
(-X)
(1/wc)
R
Ohmic
ACTIVATION
PROCESSES
f Increasing
DIFFUSION
(WARBURG BEHAVIOR)
Voltage
Discharge
OCV
IR drop
Activization
Polarization
Ohmic
polarization
High rate discharge
End of life
(concentration polarization)

38. 38
Electrochemical impedance spectroscopy(EIS)
Fitted RC model for various EIS
spectra where R1 electrolyte
resistance, R2 surface layer resistance
,R3- charge transfer resistance , CPE-
double layer capacitance and w-
Warburg impedance.
100 150 200 250 300 350 400 450
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
Voltage(V)
Charge transfer Rct
0 100 200 300 400 500
0
100
200
300
400
OCV3.45
0CV3.460
OCV3.47
OCV3.59
OCV3.92
OCV4.03
-Z(Img)[ohm]
Z(Re) [ohm]
Charging applied voltage
-10 0 10 20 30 40 50 60 70 80
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Voltage
Charge
IR drop
Activation Polarization
diffusion

39. 39
Electrochemical impedance spectroscopy(EIS)
0 50 100 150 200 250 300 350 400
0
50
100
150
200
250
300
OCV3.63
OCV3.432
OCV3.387
OCV3.206
OCV2.78
-Z(Img)[ohm]
Z(Rel)[ohm]
Dischrge-apply Voltage
120 140 160 180 200 220 240 260 280 300
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
Voltage(V)
Charge transfer resistance
B
The charge transfer resistance increases
with the relaxation time accompanied by a
drop in the measured OCV as indicated in
the legend. This linear increase in charge
transfer resistance implies a change in the
electrode-electrolyte interface at the
charged cathode with increasing relaxation
time.

40. 40
Charge applied Voltage
R1 (ohm.cm2
) R2 (ohm.cm2
) CPE(ohm.cm-2
) n W
3.45 405.9 2.27E-05 0.716 2.53E-07
3.464 355.1 2.36E-05 0.715 3.10E-07
3.92 272.7 1.95E-06 0.749 1.05E-07
4.03 117.6 9.56E-06 0.796 3.56E-06
Discharging applied voltage
R1 R2 CPE n W
4.133 146 1.17E-05 0.793 3.88E-05
4.034 150 1.20E-05 0.787 8.50E-06
4.034 210 1.24E-05 0.785 80.99-06
4.129 280 1.00E-05 0.798 4.49E-09
4.108 290 1.01E-05 0.795 3.70E-09
EIS data

41. 41
 IntroductionIntroduction
Some basics!Some basics!
Emergence of Li-(ion) rechargeable batteriesEmergence of Li-(ion) rechargeable batteries
Current status of cathode materialsCurrent status of cathode materials
 MotivationMotivation
 ExperimentExperimental detailsal details
 Results and discussionsResults and discussions
 Summary
Outline

42. 42
Summary and conclusion
 Pure and composite LiFePO4 material with olivine phase was successfully synthesized
using a solid state method
+Good reproducibility, high product yield , and short heat treatment.
+No evidences of additional crystalline
 Residual carbon coating on the LiFePO4 particles ensured composite LiFePO4/C in a
reducing atmosphere and which enhanced the inter-particle electronic conductivity
and electrochemical properties.
+result in reduction to Fe2+
which help to improve the electrical conductivity
 CV analysis revealed an approximately 3.8 fold increase in diffusion constant when
the bare LiFePO4 was coated with carbon.
 The results from CV & in situ EIS suggested that the carbon coating reduced the
electrical resistance (Rct) at the particle surface during the charge-discharge cycles
which led to enhance Li ion diffusion and electrochemical performances.
 CV analysis revealed an approximately 1.8 fold increase in diffusion constant was
achieved by complementary Zn doping.
 Electrochemical charge/discharge and rate capability tests of the composite cathodes
with LiFe0.97 Z0.3 PO4/C with 3% ZnO showed high rate capability and capacity
compared to 7% ZnO and 10% carbon coating.
The results indicate that the Zinc atoms prevent the collapse of the LiFePO4 lattice

43. 43
Thank you
Sincere thanks to
Dr Reji Thomas
Dr. Naba Karan
Dr. Jose Savadara