Sn and SnBi Foil as Anode Materials for Secondary Lithium Battery
- PDF / 1,081,988 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 298 Views
EE8.4.1
Sn and SnBi Foil as Anode Materials for Secondary Lithium Battery Shoufeng Yang, Peter Y. Zavalij and M. Stanley Whittingham Institute for Materials Research, SUNY-Binghamton University, Binghamton, NY 13902 ABSTRACT: In order to better understand the cycling mechanism of metal alloy anodes, and to mitigate the capacity fade observed in lithium battery use a study of simple systems was initiated. Tin foil and tin-bismuth mixtures were chosen because there is no need for conductive diluents or binders so that the intrinsic behavior could be observed. A pure tin foil was found to react rapidly with lithium, ≥ 3 mA/cm2, and with no capacity fade for over 10 cycles. This is better than tin powder or electrodeposited tin. After the first cycle, the foil reacts with Li following a stepwise formation of different alloys as dictated by the thermodynamics. Incorporation of bismuth into the foil increased the capacity fade after the first few cycles, with the eutectic composition Sn0.57Bi0.43 having better capacity retention than the Sn0.5Bi0.5 composition. XRD and SEM-EDS shows that bismuth is rejected from the tin rich phase during lithium insertion and is not reincorporated on lithium removal, just as expected from the phase diagram. INTRODUCTION The use of Li-Ion batteries is very popular due to their small size and high capacity, but new electronics demand even more capacity at affordable price. The current graphite anode cannot meet the higher demand because its capacity is only 372 mAh/g [1], and higher capacity carbons can lead to unsafe lithium formation. Sn based materials have received much attention in the past 30 years due to their high capacity and energy density, 2.7 and 9 times of graphite, respectively. [2-5] However, pure Sn has not performed very well due to the large volume changes during reaction with lithium, so previous studies mainly dealt with near nano-sized Sn or Sn intermetallic powder in order to mitigate the capacity fading. [6-8] Alternatively the Sn phase may be evenly dispersed into an electronically conductive matrix system [9,10], which system can buffer the large volume changes resulting in better performance [11-13]. We have undertaken a study to better understand the reactions occurring on lithiation, so as to find a means to mitigate the capacity fading found in electrode performance. Our initial studies used pure tin foil, without any conductive additives or binder to complicate the data interpretation. We also report here the effect of control of particle size by addition of a second phase, in particular bismuth which is also electrochemically active. Tin and bismuth form a eutectic composition at Sn0.57Bi0.43. Throughout the paper, discharge refers to the lithiation of the foil and recharge refers to the delithiation process. EXPERIMENTAL DETAILS Sn foil (average thickness: 25-30 µm) was purchased from Aldrich, Sn-Bi binary alloys were prepared by arc-melting a mixture of Sn (Aldrich) and Bi shots (Alfa Aesar) at 600oC in a water-cooled copper hearth under an argon atmosphere
Data Loading...
