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Characterization Novel nanocrystalline anodes for Lithium Ion Batteries Tan Yan Yuh 1 , M.V. Reddy 2,3 1 SRP student, Hwa Chong Institution, 661 Bukit Timah Road, Singapore 269735 2 Department of Physics, Energy Lab, National University of Singapore, Singapore 117542 3 Departments of Materials Science & Engineering, National University of Singapore, Singapore 117546 • Lithium ion batteries are widely used as an energy source all over the globe, especially in the fields of communication and consumer electronics. Introduction : Lithium ion batteries Advantages: High energy density No memory effect Longer cycle life Disadvantages: High production costs Performance sensitive to high temperatures Risk of short-circuit at high charge rate • Utilizes LiCoO 2 as cathode, graphite as anode and gel polymer as electrolyte • Commercial graphite anode has a low theoretical capacity (372 mAhg -1 ) • Metal alloys ( Sn, Zn, Sb, Al, Si) have high theoretical capacities when alloyed with Lithium metal and have potential to replace graphite anodes + - Power Source + - Load Charging: Discharging: Aims of our Project 1. To successfully synthesise nanocrystalline Li 2 ZnSn 3 O 8 and Li 2 Zn(VSbSn)O 8 using the sol-gel method. 2. To investigate and compare the physical and electrochemical properties of the compounds with respect to the commercial graphite anode. Methodology : Preparation of Li 2 ZnSn 3 O 8 and Li 2 Zn(VSbSn)O 8 Li 2 ZnSn 3 O 8 Li 2 Zn(VSbSn)O 8 2CH 3 CO 2 Li + Zn(C 2 H 3 O 2 ) 2 .H 2 O + 3SnCl 2 .2H 2 O Li 2 ZnSn 3 O 8 4CH 3 CO 2 Li + 2Zn(C 2 H 3 O 2 ) 2 .H 2 O + 2SnCl 2 .2H 2 O + NH 4 VO 3 + 2Sb 2 S 3 Li 2 Zn(VSbSn)O 8 Procedure: 1. Addition of citric acid as a complexing agent to form gel 2. Addition of ethylene glycol to facilitate polyesterification 3. Drying and decomposition of gel 4. Calcination to obtain phase Characterization Techniques Li 2 ZnSn 3 O 8 (BET area: 9.28 m 2 g -1 ) Li 2 Zn(VSbSn)O 8 (BET area: 0.92 m 2 g -1 ) Scanning Electron Microscopy (SEM): To verify that particles are of nano-size via electron micrograph X-ray Diffraction (XRD): To check the purity of the compounds and obtain info about its crystalline structure, crystalline size and other data. Deductions: • Prepared samples are of single phase, with minimal traces of impurities. • Ordered double hexagonal type structure (a=18.7385 Å and c=10.2908 Å). 2Theta (Degrees) 75 70 65 60 55 50 45 40 35 30 25 20 15 10 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Intensity (a.u.) 2Theta (Degrees) Anode & Battery Fabrication 1) Weigh out the prepared salt , Super P Carbon, and PVDF binder then mix in a grinder. Add NMP as solvent to form slurry. 2) To a separate sample of Li 2 ZnSn 3 O 8 , add 10% in mass of graphene oxide before making slurry. 3) Magnetic stirring for 12 h for thorough mixing 4) Using the Doctor Blade technique, coat the slurry on a Copper foil. 5) Cut the coated foil into circles (d= 16mm) Upper Lid Plastic Ring Steel Spring Lithium Metal Separator Coin Cell Cap Cyclic Voltammetry Studies • Electrochemical charge-discharge mechanism in batteries is caused by the alloying/de-alloying reactions as shown below. xLi Zn/Sn Oxidation (Forward)/ Reduction (Backward): 3Sn + 13.2 Li + + 14 e - ↔ 3Sn + Zn + 8Li 2 O Zn + Li + + e - ↔ LiZn • Cycled between 0.005-3.0V at a scan rate of 0.1mV/s • New peaks of Li 2 Zn(VSbSn)O 8 correspond to the oxidation of Sn, Sb and V • Good reversibility of Li 2 ZnSn 3 O 8 compounds • Sharper peaks for Li 2 ZnSn 3 O 8 + GO indicate better electron conductivity Impedance Studies • Impedance plotted on complex plane (Z’ against Z”) • Nyquist plot was fitted to a theoretical equivalent electrical circuit. Figure 3a: Nyquist plot (left) Figure 3b: Fitted equivalent circuit model* (top) for Li 2 ZnSn 3 O 8 *R1: electrolyte resistance, Rct: charge transfer resistance, W1: Warburg impedance, Ci: intercalation capacitance. Acknowledgements Special thanks to: • Mentor, Dr. M.V. Reddy • Dr. K.P. Abhilash • Dr Erkan Polatdemir, HCI • Faculty of Science, NUS References 1. B. Scrosati, J. Garche, J. Power Sources 195 (2010) 2419-2430. 2.A.N. Dey, J. Electrochem. Soc. 118 (1971) 1547-1549 3.Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276 (1997) 1395-1397. 4.I.A. Courtney, J.R. Dahn, J. Electrochem. Soc. 144 (1997) 2045-2052. 5.H. Li, X. Huang, L. Chen, Solid State Ionics 123 (1999) 189-197. 6.S. Machill,T. Shodai, Y. Sakurai, J. Yamaki, J. Power Sources 73 (1998) 216-223. 7.K. Wan, S. F.Y.Li,Z. Gao, K. S. Siow, J. Power Sources 75 (1998) 9-12. * All graphs and images are self-plotted and self-taken by author. (b) (c) Figure 2: Cyclic Voltammograms (Current vs. Voltage plots) (a) Li 2 ZnSn 3 O 8 , (b) Li 2 ZnSn 3 O 8 + GO, (c) Li 2 Zn(VSbSn)O 8 , cycled from 0.005-3.0V Summary & Conclusion • Successfully synthesised nanocrystalline Li 2 ZnSn 3 O 8 and Li 2 Zn(VSbSn)O 8 using the sol-gel method and analysed their physical and electrochemical properties. • Superior capacity compared to graphite despite low preparation temperature • Li 2 ZnSn 3 O 8 +Graphene Oxide and Li 2 Zn(VSbSn)O 8 showed reduced capacity fading • Good potential as future anode material Sol-gel method (SG) Temperature/time : 60 o C / 2h 90 o C / 1h 300 o C / 3h 700 o C / 3h Figure 1a: Capacity vs cycle number plots of (i) Li 2 ZnSn 3 O 8 (ii) Li 2 ZnSn 3 O 8 +GO (iii) Li 2 Zn(VSbSn)O 8 Voltage range: 0.005-1.20V Results & Discussion : Galvanostatic Cycling Studies Figure 1b: Capacity-Voltage Profile of Li 2 ZnSn 3 O 8 , Integers labeled on graph indicate cycle number. • Li 2 ZnSn 3 O 8 started with a capacity of ~550 mAhg -1 and had 65.0% capacity retention over 35 cycles. • Li 2 Zn(VSbSn)O 8 started at a lower capacity of ~290 mAhg -1 but exhibited excellent capacity retention of 87% over 35 cycles. • Li 2 ZnSn 3 O 8 + GO proves that the addition of graphene oxide significantly improved the electrochemical performance of Li 2 ZnSn 3 O 8 as it started with a high capacity of ~900 mAhg -1 and had only 91.8 % capacity retention after 12 cycles. • In comparison, Commercial graphite ~ 370 mAhg -1 experiences low capacity retention at only 28% over 50 cycles (Reddy, 2012) (ii) (iii) (i) 30, 20, 10, 5, 2 30, 20, 10, 5, 2 X-ray photoelectron spectroscopy (XPS): To verify composition of elements in compound ON: Sn (+4), Zn (+2), Li (+1) • Li 2 ZnSn 3 O 8 is in the correct composition
