Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Heon-Young Lee a,...

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.
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 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.
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.
anode for microbatteries
Sn-Zr-(Ag) thin films
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.
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.
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.
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.
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.
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.
(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.
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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Date post:	11-Jan-2016
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Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Heon-Young Lee a,...

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