Phase formation in alloy-type lithium storage anode materials with C, Si and Sn

Transcription

1 JP09: Phase stability of alloy-type lithium storage anode materials Phase formation in alloy-type lithium storage anode materials with C, Si and Sn M. Drüe 1, A. Kozlov 2, M. Seyring 1, X. Song 3, R. Schmid-Fetzer 2, M. Rettenmayr 1 1 Otto-Schott-Institut für Materialforschung, Friedrich-Schiller-Universität Jena 2 Institut für Metallurgie, Technische Universität Clausthal 3 School of Materials Science and Engineering, Beijing University of Technology

2 Motivation: Lithium Ion Battery electrode materials must be able to take up lithium anode: graphite LiC 6 improvement of capacity, charging time etc. needed M. Winter et al., Adv. Mat. 10 (1998) 2

3 Anode Materials: Alternatives JP 09: Li Sn Si C M.N. Obrovac et al., J. Eletrochem. Soc. 154 (2007) Si and Sn can take up much more Li, different Li insertion mechanism volume expansion up to 300% still graphite used battery-related properties strongly depend on thermodynamic data phase diagram 3

4 Anode Materials: Alternatives JP 09: Li Sn Si C M. Drüe et al., J. All. Comp. 575 (2013) combined approach of DSC, long-term annealing and XRD Li 2 C 2 is the only stable phase in the Li-C phase diagram, LiC 6 decomposes during annealing re-assessment of the Li-C phase diagram (TUC) 4

5 Binary phase diagrams Si-C Li-C Li-Si Li 17 Si 4 S. Kawanishi et al. Mat. Trans. 50 (2009) A. Kozlov et al. Int. J. Mat Res. 101 (2013) P. Wang et al. Intermetallics 42 (2013) good assessment of binary systems investigation of the ternary phase diagram needed 5

6 Selection of alloy compositions 25 C SiC Li 2 C 2 Li 12 Si 7 Li 17 Si 4 Li 13 Si 4 +SiC+Li 2 C 2 two key compositions chosen, according to preliminary calculations 1: LiSiC 2: Li 68 Si 25 C 7 DSC and long-term annealing experiments adjustment of compositions is complicated starting materials: binary compounds Li 13 Si 4 +SiC 6

7 Synthesis and characterization of Li-alloys Ar-filled Glovebox (O 2, H 2 O<2ppm) compressing of pure elements to pellets, subsequent annealing Li+C or Li+Si Li 2 C 2, Li 12 Si 7, Li 17 Si 4 XRD analysis air-tight capsule 7

8 Synthesis and characterization of Li-alloys binary pre-alloys for adjustment of ternary compositions: Li 2 C 2, Li 12 Si 7, Li 17 Si 4 mixed in the chosen compositions for DSC and compressed to pellets for long-term annealing subsequent XRD analysis 8

9 Composition 1: LiSiC α-sic + Li 12 Si 7 + Li 2 C 2 Li 13 Si 4 +SiC+Li 2 C 2? DSC measurements Li 7 Si 3? 9

10 Composition 1: LiSiC α-sic + Li 12 Si 7 + Li 2 C 2 Li 13 Si 4 +SiC+Li 2 C 2? α-sic + Li 17 Si 4 + Li 2 C 2 fabrication of pellets annealing: 650 C, 96h annealing: 630 C, 96h Li 7 Si 3, Li 2 C 2 and SiC can be identified no Li 13 Si 4? 10

11 Composition 2: Li 68 Si 25 C 7 Li 2 C 2 + Li 12 Si 7 + Li 17 Si 4 Li 13 Si 4 +SiC? DSC measurements Li 7 Si 3 11

12 Composition 2: Li 68 Si 25 C 7 Li 2 C 2 + Li 12 Si 7 + Li 17 Si 4 Li 13 Si 4 +SiC? fabrication of pellets annealing: 630 C, 96h phases identified: Li 7 Si 3, Li 2 C 2, little SiC (?) no Li 13 Si 4! 12

13 Conclusion first approach to investigate ternary system Li-Si-C no ternary phases three-phase equilibrium identified Li 7 Si 3 has formed during all experiments equilibrium at the studied compositions contains Li 7 Si 3 instead of Li 13 Si 4 25 C Li 13 Si 4 +SiC+Li 2 C 2? Li 7 Si 3 +SiC+Li 2 C 2 13

14 Joint project JP 09 information about phase stabilities insufficient TU Clausthal FSU Jena alloy fabrication C Li Si Sn Beijing UT thermodynamic data (DSC) nanostructuring (SPS) phase diagrams (CALPHAD) microstructure characterization (XRD, LM, SEM, TEM) annealing experiments modeling of nc-li-alloys sensitive Li-alloys have to be handled under protective gas (no H 2 O, O 2, N 2 )

15 Synthesis and phase diagram: Li-C Li-C: pure samples of LiC 6 and Li 2 C 2, DSC (TUC) and long-term annealing Li 2 C 2 is the only stable phase in the Li-C phase diagram, LiC 6 decomposes during annealing re-assessment of the Li-C phase diagram (TUC) TU Clausthal [Okamoto1989] FSU Jena Beijing UT [Kozlov2013]