PowerPoint Kangwon Nat’l Univ.
aDepartment of Advanced Material Science and Engineering
Kangwon National University
Sn based anodes for lithium rechargeable
microbatteries
My presentation subject is Sn based anodes for lithium rechargeable
microbatteries.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
Battery composed of
Thin film electrolyte
Incorporated into Devices
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I want to introduce the concept of micro battery. this figure shows
typical diagram of bulk battery system. As you see, battery
composed of electrodes(negative and positive)
And electrolyte. Like this, thin film microbattery has same
structure, but the thickness is usually less than
10micrometer.
these batteries can be fabricated in a variety of shapes and
to any required size, large or small, on virtually any type of
substrate. They can, for example, be added to integrated circuits
or
To individual circuit components. Because of their high energy and
power per unit of volume and mass and because they are
rechargeable, thin-film micro batteries have potentially many
applications as small power supplies for electronic devices.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
Micro
Battery
And also, it is possible to applicated in MEMS(medical, military,
aerospace, micro mechanics) or Electronics(like smart card, hazard
card, so on..)
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
Thin Film anode electrodes
limit the application area
: Large capacity active phase
drastic capacity fade
buffering inactive elements
Lithium metal
This chart shows the thin film anode electrodes. Lithium metal has
commonly been used or proposed as anodes for rechargeable thin-film
microbatteries which can be employed as power sources for
microdevices. However, lithium metal has some problems for the
application due to its low melting point, high reactivity with air,
and tendency to form dendrites. Hence, there is currently a
significant interest in finding new anode materials.
Alloy-based materials containing such lithium storage metals as Al,
Si and Sn have been extensively studied as anodes for lithium ion
batteries. However, these alloy systems undergo large volume
changes during Li insertion/extraction cycling. This limits the
mechanical stability and cycle life of the electrode.
Recently, intermetallic compounds or alloys have been widely
studied. The performance of alloy electrodes can be improved
significantly when the active alloying element are finely dispersed
with an inactive component in a composite matrix.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
Sn-Zr (active / inactive composites)
Suppress agglomeration of Sn
strong affinity between Sn and M limits the Sn alloying with Li and
forms a buffering phase
H Sn-Zr H Sn-Li
excellent stability
Background & Approach
This shows the comparison between the values of the enthalpy of
formation for lithium-tin and tin-zirconium. A large negative value
for formation enthalpy implies a large affinity between atoms in a
phase. As you see, as this formation enthalpy of tin-zirconium much
less than that of lithium-tin, the alloying of with zirconium may
limit lithium alloying with tin form LixSn alloys and suppress
agglomeration of tin during cycling due to the strong affinity
between tin and zirconium atoms.
Ag is chosen as a doping element. First, Ag is ductile to relieve
the stress due to the volume expansion of Sn. Second, Ag is mixed
conducting material for Li ion and electron. Last, Ag is immiscible
with Sn, which leads to large reversible capacity and electrode
stability.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
anode for microbatteries
Sn-Zr-(Ag) thin films
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
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 :
- Atmosphere : 5 10-3 Torr Ar ambient
- Negative DC bias : 0 – 100V was applied for some samples
Film Characterization
Counter & Reference electrode : Li foil
Electrolyte : 1M LiPF6 in EC/DEC
Thickness
- Profilometer
Morphology
- SEM
Structure
- XRD
Experimental Procedure : Negative Electrode
Thin film anode was fabricated by co-sputtering or co-deposition by
e-beam.
And the film characterized by RBS, profilometer, SEM, XRD. Then
electrochemical test carried out using this condition.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
film thickness : 700
low irreversible capacity
The plateau at 0.69, 0.53 and 0.43 V are associated with the Sn,
Li2Sn5 and LiSn phases
First charge-discharge curves for pure Sn thin film electrode
This figure shows first charge-discharge curves for pure Sn thin
film electrode.
It has low irreversible capacity. The plateau at 0.69, 0.53 and
0.43 V are associated with the Sn, Li2Sn5 and LiSn phases.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
The discharge capacity is normalised
against the first discharge capacity
The cycling performance is little improved by a decrease in film
thickness
Normalised capacity vs. cycle number for Sn thin films of vatious
thickness
This figure shows normalised capacity vs. cycle number for Sn thin
films of vatious thickness. The discharge capacity is
normalised
against the first discharge capacity. The cycling performance is
little improved by a decrease in film thickness.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
As a result of large volumetric change with lithium insertion
the formation of large cracks and the delamination of active
material from the substrate
loss of electronic contact between the active materials as well as
between the active material and the current collector
poor cyclelability
Surface morphology of Sn thin-film Anodes after cycles
This SEM picture shows Surface morphology of Sn thin-film Anodes
after cycles. In case of figure a, there was no crack. In the early
stage of cycling, as a result of large volumetric change with
lithium insertion during cycling, the formation of large cracks and
the delamination of active material from the substrate take place.
This leads to a loss of electronic contact between the active
materials as well as between the active material and the current
collector. Together, these features results in a loss of capacity
and poor cyclelability.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
that of the Sn-Zr sample
The 10 at.% Ag containing electrode
(Sn57Zr33Ag10) exhibits a stable
Cycle Performance
The capacity vs. cycle number for Sn-Zr-Ag thin films
This figure shows the capacity vs. cycle number for Sn-Zr-Ag thin
films. As you see, the cycling performances of the Ag-containing
Sn-Zr films are better than that of the Sn-Zr sample. In
particular, The 10 at.% Ag containing electrode (Sn57Zr33Ag10)
exhibits a stable capacity retention for long cycles. It seems
likely that the excellent stability of the Ag-doped electrode may
be attributed to the existence of very finely dispersed Sn within
the matrix.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
XRD
2Θ
Ag-doped samples, even for the film containing 2 at. % Ag, the
diffraction lines of Sn cannot be distinguished
may be attributed to the existence of very finely dispersed Sn
within the matirix
Structure of Sn-Zr-Ag thin-film Anodes
The XRD patterns of Ag-containing Sn-Zr films are shown.
For Ag-doped samples, even for the film containing 2 at. % Ag, the
diffraction lines of Sn cannot be distinguished. It may be
attributed to the existence of very finely dispersed Sn within the
matirix.
Thin Film & Battery Materials Lab. National Research Lab.
Kangwon Nat’l Univ.
(b) Sn64Zr34Ag2
(a) Sn62Zr38
The Ag-doped films show a fine and uniform distribution of the Sn
aggregated particles compared with that of the undoped sample
Surface morphology of Sn-Zr-Ag thin-film Anodes
SEM indicates that the morphology of the Sn-Zr film has been
substantially modified by Ag-doping. The Ag-doped films show a fine
and uniform distribution of the Sn aggregated particles compared
with that of the undoped sample.
These results are well matched as I mentioned before. Such as cycle
data and XRD data.
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
In conclusion, the cyclability of Sn-Zr thin films is improved with
the addition of Zr although the capacity decreases. And the cycling
stability of Sn-Zr thin film electrodes appear to be significantly
increased by doping Ag into the film.
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