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Heon-Young Lee a , Seung-Joo Lee b , Sung-Man Lee a

Sn based anodes for lithium rechargeable microbatteries. Heon-Young Lee a , Seung-Joo Lee b , Sung-Man Lee a a Department of Advanced Material Science and Engineering Kangwon National University b Microsystem Research Center, Korea Institute of Science & Technology (KIST). -. +. +. Li.

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Heon-Young Lee a , Seung-Joo Lee b , Sung-Man Lee a

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  1. 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)

  2. - + + Li ion Discharge Charge Thin Film Microbattery as a Micro Power Source • Battery composed of • Thin film electrodes (Negative & Positive) • Thin film electrolyte Incorporated into Devices IC card Current collector Negative electrode ~ Electrolyte 10mm Positive electrode Current collector Substrate IC TFB Negative electrode Positive electrode Electrolyte

  3. Micro Battery Microbattery-based technology in the 21st century Power Implantable Device MEMS Electronics • Smart card • Hazard card • On-chip appl. • Micro PDA • Medical • Military • Aerospace • Micro mechanics MEMS Electronics

  4. 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 (?)

  5. Background & Approach H Sn-Zr  H Sn-Li Formation enthalpy(△Hf) of M-Sn system • 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 • Sn-Zr-Ag(ternary system) • Buffering effect • Fine and uniform distribution of the Sn • excellent stability

  6. 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

  7. 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

  8. First charge-discharge curves for pure Sn thin film electrode low irreversible capacity The plateau at 0.69, 0.53 and 0.43 V are associated with the Sn, Li2Sn5 and LiSn phases film thickness : 700 Å

  9. 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 (a) 300 Å (b) 700 Å (c) 1200 Å

  10. Surface morphology of Sn thin-film Anodes after cycles a b c 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 (a) before cycling (b) after 6 cycles (c) after 20 cycles

  11. The capacity vs. cycle number for Sn-Zr-Ag thin films Cycle Performance The cycling performances of the Ag- containing Sn-Zr films are better than that of the Sn-Zr sample The 10 at.% Ag containing electrode (Sn57Zr33Ag10) exhibits a stable capacity retention for long cycles (a) Sn62Zr38 (b) Sn64Zr34Ag2 (c) Sn57Zr33Ag10

  12. Structure of Sn-Zr-Ag thin-film Anodes XRD 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 2Θ (a) Sn62Zr38 (b) Sn64Zr34Ag2 (c) Sn57Zr33Ag10.

  13. 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

  14. 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

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