Transcript Development of superior Graphite anodes for Li

High Capacity Graphite Anodes for
Li-Ion battery applications
using Tin microencapsulation
Basker Veeraraghavan, Anand Durairajan, Bala Haran
Ralph White and Branko Popov
University of South Carolina, Columbia, SC 29208
and
Ronald Guidotti
Sandia National Laboratories
Albuquerque, NM 87185-0614
Introduction
Graphite has good cycle life but low
theoretical capacity (372 mAh/g)
Tin has high theoretical capacity (991
mAh/g)
Tin based anodes have poor cycling
characteristics due to density changes of Tin
Reducing the Sn particle size may mitigate
the problem
Objectives
 To obtain an anode material with high specific
capacity, better rate capability and good cycle
life
 To use electroless deposition for preparing Sn-C
composites and to optimize the deposition
conditions
 To optimize the Sn loading on graphite based on
discharge characteristics
 To study the effect of Sn loading on the
electrochemical performance of the composite
Experimental
Preparation of Sn/Graphite composites
Electroless
deposition
of
Sn
hypophosphite bath
pH-10 (using NaOH) and T-50C
using
Cell Preparation for testing
1/2” T-cells used for electrochemical testing
Electrodes prepared by cold rolling using
PTFE binder (10wt%)
Whatman fiber used as separator and Li-foil
used as counter and reference electrode
1M LiPF6 in EC/DMC (1:1 v/v) used as
electrolyte
Experimental (Cont’d.)
Electrochemical characterization
Charge-discharge and cycling behavior
Cycling was performed between 2V and 5 mV at C/15
rate (0.1mA/cm2)
Electrochemical Impedance Spectroscopy (EIS)
100kHz to 1mHz with 5mV sinusoidal signal
Cyclic Voltammetry
CVs were performed in the potential range 1.6V to
0.01V at 0.05 mV/s
Physical characterization
SEM, EDAX and XRD
SEM images of bare and 15% sn-coated SFG10 samples
Bare
10 m
15% Sn
EDAX studies of bare and 15% sn-coated SFG10 samples
Bare
15% Sn
XRD analysis of 15% sn-coated SFG10 samples as a
function of heat treatment temperature
1000
B a re
100 o C
200 o C
300 o C
400 o C
Inte ns ity
750
500
250
0
40
41
42
43
44
45
46
47
48
49
50
2
XRD pa t t e rns of SFG10 wi t h 15% Sn he a t t re a t e d a t di ffe re nt t e m pe ra t ure s.
Charge discharge studies of 15% sn-coated SFG10
samples as a function of heat treatment temperature
2 .2
o
100 C
o
200 C
o
300 C
o
400 C
2 .0
Po ten tial (V v s L i/L i + )
1 .8
(3 3 2
(4 0 0
(3 4 3
(3 3 7
mA h / g )
mA h / g )
mA h / g )
mA h / g )
1 .6
1 .4
1 .2
1 .0
0 .8
0 .6
0 .4
0 .2
0 .0
-1 0 0
100
300
500
700
Sp ecific Cap acity (mA h /g )
Sp ecific Cap acities o f SFG 1 0 co ated w ith 1 5 % Sn as a fu n ctio n o f temp eratu re o f d ry in g
Comparison of charge-discharge curves of bare and 15
wt% sn-coated graphite.
4 .0
P o ten tial ( V v s L i/L i+ )
3 .0
2 .0
Bar e
1 5 % Sn
1 .0
0 .0
0
1000
2000
3000
S p ecif ic cap acity ( m A h /g )
4000
5000
Charge-Discharge curves of bare and sn-coated SFG10 samples
10%
5 % Sn
1 .8
Po ten tial (V v s L i/L i + )
20%
15%
Bare
1 .3
0 .8
0 .3
-0 .2
100
300
500
700
Sp ecific Cap acity (mA h /g )
Sp ecific Cap acity as a fu n ctio n o f Sn lo ad in g at C/1 5 rate
Percentage increase in reversible capacity as a function of
composition of sn
Pe rc e nta ge inc re a s e in re ve rs ible c a pa c ity (% )
70
60
50
40
30
20
10
0
0
5
10
15
20
C ompos ition of Sn (%)
Pe rc e nta ge inc re a s e in re ve rs ible c a pa c ity a s func tion of Sn c ompos ition
25
Utilization of sn in the coated samples as a function of the
composition of tin
Sample
Reversible
Capacity
(mAh/g)
Capacity
due to Sn
(mAh/g)
Utilization
of Sn1 (%)
Specific
Surface
area
(m2/g)
Volumetric
Surface
area
(m2/cm3)
Volumetric
Capacity
(mAh/cm3)
Bare
284.6
-
-
9.84
21.65
626.1
5% Sn
327.8
57.4
55.0
8.52
20.49
788.4
10% Sn
374.6
118.5
53.8
8.30
21.66
977.7
15% Sn
433.2
191.3
54.7
7.61
21.42
1219.5
20% Sn
381.7
154.0
31.1
7.12
21.50
1152.7
1Utilization
of tin = (Capacity due to tin/weight of tin in the composite)/Theoretical
capacity of tin (991 mAh/g)*100
Impedance plots for the bare and sn-coated SFG10
samples at fully discharged state
2
.
0
ImaginryZ( g
1
.
5
1
5
%
S
n
1
0
%
S
n
B
a
r
e
1
.
0
0
.
5
5
%
S
n
0
.
0
2
0
%
S
n
0 1 2 3 4
R
e
a
l
Z
(

g
)
I
m
p
e
d
a
n
c
e
p
l
o
t
o
f
S
F
G
1
0
s
a
m
p
l
e
s
Cyclic Voltammograms of bare and 15% sn coated SFG10
samples for the reversible cycle
1 5 % Sn
Bare
Sp ecific Cu rren t (m A /g )
300
100
-1 0 0
-3 0 0
0 .0
0 .4
0 .8
1 .2
+
P o ten tial (V v s L i/L i )
1 .6
2 .0
Cycle life studies of bare and 15% sn coated SFG10
samples at C/15 rate
Sp ecific Cap acity (m A h /g )
500
400
1 5 % Sn
300
200
Bare
100
0
5
10
15
20
Cy cle n u mb er
25
30
35
Rate Capability studies of bare and 15% sn coated SFG10
samples
500
C /15
B a re
15% Sn
Spe c ific C a pa c ity (mA h/g)
400
C /6
300
C /3
200
C
2C
100
0
0.0
0.5
1.0
1.5
D is c ha rge c urre nt de ns ity in mA /c m
2.0
2
Conclusions
 Tin encapsulation on SFG10 graphite results in high
performance anodes for use in Li-ion batteries
Reversible capacities are improved upto 15% Sn, relative to
bare graphite
Cycle life of the bare graphite is improved on Sn-encapsulation
 The optimum heat treatment temperature was found to
be 200 C
Crystallinity increases with temperature
 Sn-C based anodes show better conductivity and lower
polarization resistance compared to virgin carbon
 Addition of Polypyrrole reduces irreversible capacity
and further studies need to be done to optimize the
amount of polypyrrole
Acknowledgements
This work was funded by the Dept. of Energy
division of Chemical Science, Office of Basic
Energy Sciences and, in part, by Sandia
National Laboratories
(Sandia National Laboratories is a multiprogram laboratory operated by Sandia corp.,
a Lockheed Martin Company, for the U.S.
Dept. of Energy under Contract DE-AC0494AL85000.)