Transcript PowerPoint 프레젠테이션

Sn based anodes for lithium rechargeable
microbatteries
Heon-Young Leea, Seung-Joo Leeb, Sung-Man Leea
aDepartment
of Advanced Material Science and Engineering
Kangwon National University
bMicrosystem Research Center, Korea Institute of Science &
Technology (KIST)
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Thin Film Microbattery as a Micro Power Source
Battery composed of
- Thin film electrodes (Negative & Positive)
- Thin film electrolyte
+
Incorporated into Devices
+
Li ion
IC card
Current collector
Negative electrode
Electrolyte
Discharge
~ 10mm
Positive electrode
Current collector
Charge
Substrate
TFB
Negative
electrode
Electrolyte
IC
Positive
electrode
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Microbattery-based technology in the 21st century
Micro
Battery
MEMS
Power Implantable Device
Electronics
• Smart card
• Hazard card
• On-chip appl.
• Micro PDA
• Medical
• Military
• Aerospace
• Micro mechanics
MEMS Electronics
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Introduction
Thin Film anode electrodes
Lithium metal
low melting point (181℃) & high reactivity with air
limit the application area
Li-alloys ( Si, Sn, Al)
: Large capacity active phase
significant volume change during cycling
drastic capacity fade
Active / inactive alloys (SnM)
buffering inactive elements
enhanced cyclability (?)
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Background & Approach
H Sn-Zr  H Sn-Li
• Sn-Zr (active / inactive composites)
Formation enthalpy(△Hf) of M-Sn system
• Suppress agglomeration of Sn
• strong affinity between Sn and M limits
the Sn alloying with Li and forms a
buffering phase
• Sn-Zr-Ag (ternary system)
¡â H f(KJ/mol.atom)
25
0
-50
-75
-100
• Buffering effect
• Fine and uniform distribution of the Sn
Li-Sn
-25
Zr-Sn
0
M
20
40
60
Atomic Percent Tin
80
100
Sn
• excellent stability
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Objective
To Investigate the possibility of Sn, Sn-Zr thin-film as
anode for microbatteries
Fabrication of Sn-Zr-(Ag) thin films
Evaluation of Electrochemical characteristics of
Sn-Zr-(Ag) thin films
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Experimental Procedure : Negative Electrode
Thin Film Fabrication
Substrate : Cu disc (12 mm dia.)
Substrate cooling : Cooling or without cooling
Sputtering Targets : Co-sputtering or Co-deposition by e-beam (Sn & Zr or Si & Zr & Ag)
Deposition Conditions :
- Base P. : 2  10-6 Torr
- Atmosphere : 5  10-3 Torr Ar ambient
- Negative DC bias : 0 – 100V was applied for some samples
Film Characterization
Composition
- RBS
Thickness
- Profilometer
Morphology
- SEM
Structure
- XRD
Electrochemical Test : Discharge & Charge
Cell construction : 2016 coin type cell
Counter & Reference electrode : Li foil
Electrolyte : 1M LiPF6 in EC/DEC
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
First charge-discharge curves for pure Sn thin film electrode
+
Voltage (V vs. Li/Li )
2.0
1.5
low irreversible capacity
1.0
The plateau at 0.69, 0.53 and 0.43 V
are associated with the Sn, Li2Sn5
and LiSn phases
0.5
0.0
0
20
40
60
80
100
Capacity (mAh)
film thickness : 700 Å
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Normalised capacity vs. cycle number for Sn thin films of vatious thickness
Normalized capacity (%)
120
100
The discharge capacity is normalised
80
against the first discharge capacity
60
a
40
The cycling performance is little
improved by a decrease in film
thickness
b
20
c
0
0
10
20
30
40
50
Cycle number
(a) 300 Å
(b) 700 Å
(c) 1200 Å
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Surface morphology of Sn thin-film Anodes after cycles
a
(a) before cycling
As a result of large volumetric change
with lithium insertion
the formation of large cracks and the
delamination of active material from
the substrate
b
6cyc
(b) after 6 cycles
c
loss of electronic contact between the
active materials as well as between
the active material and the current
collector
poor cyclelability
(c) after 20 cycles
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
The capacity vs. cycle number for Sn-Zr-Ag thin films
Cycle Performance
3
Capacity(mAh/cm )
3000
The cycling performances of the Ag-
2500
2000
(c)
1500
(b)
1000
(a)
containing Sn-Zr films are better than
that of the Sn-Zr sample
The 10 at.% Ag containing electrode
(Sn57Zr33Ag10) exhibits a stable
500
0
capacity retention for long cycles
0
100
200
Cycle No.
(a) Sn62Zr38
(b) Sn64Zr34Ag2
(c) Sn57Zr33Ag10
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Structure of Sn-Zr-Ag thin-film Anodes
XRD
S
: Sn
S
Intensity(a. u.)
(c)
(b)
Ag-doped samples, even for the film
containing 2 at. % Ag, the diffraction
lines of Sn cannot be distinguished
(a)
25
30
35
40
45
50
55
60
may be attributed to the existence of
very finely dispersed Sn within the
matirix
2¥È
2Θ
(a) Sn62Zr38
(b) Sn64Zr34Ag2
(c) Sn57Zr33Ag10.
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Surface morphology of Sn-Zr-Ag thin-film Anodes
FESEM
(a) Sn62Zr38
The Ag-doped films show a fine and
uniform distribution of the Sn
aggregated particles compared with
that of the undoped sample
(b) Sn64Zr34Ag2
(c) Sn57Zr33Ag10
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.
Conclusion
The cyclability of Sn-Zr thin films is improved with the addition of
Zr although the capacity decreases
The cycling stability of Sn-Zr thin film electrodes appear to be
significantly increased by doping Ag into the film
Thin Film & Battery Materials Lab.
National Research Lab.
Kangwon Nat’l Univ.