20100520-jcp-SI

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Supporting Information
Lithium Transport at Silicon Thin Film:
Barrier for High-rate Capability Anode
Bo Peng, Fangyi Cheng, Zhanliang Tao, and Jun Chen*
Institute of New Energy Material Chemistry and Key Laboratory of Advanced
Micro/Nanomaterials and Batteries/Cells (Ministry of Education), Chemistry College,
Nankai University, Tianjin 300071, P.R. China
* To whom correspondence should be addressed. E-mail: [email protected]
This material contains Figure S1 , Figure S2, and Table S1.
Figure S1. (a) Cutoff energy test of Si bulk; (b) Lattice constant predicted by GGA
vs. experimental value (error < 1%); (c–e) k-points test of Si unit cell (c), 3×3×3 Si
supercell (d), and c(4×4) Si (100) (e).
Figure S2. Full Li transport path profile in B-doped case.
Table S1. Possible species that may exist at the surface of silicon anode and their
properties during the electrochemical process.
Species
-Si-O
Property
SiO2,
-Si-O-Si-,
-Si-OH
React with the organic solvent, lithium salt, organic additive
or impurities, which is one of the major reasons of initial
irreversible capacity loss.1
-Si-OCH2CH2OCO2Li
Less dense , decomposable, through which the electrolyte
can penetrate and break Si-Si network (cracking).2
-Si-F
With large bond energy (565 kJ mol-1) but high reactivity
due to a kinetics-driven surface chemistry,3 thus the
existence of Si-F at the surface is doubted.
-Si-C
Experimentally, to avoid these undesirable species, some
additives (e.g. carbon) are introduced to result in stable
solid-electrolyte-interface (SEI). For example, coating
Si-anode with carbon layer helps to enhance the electronic
conductivity and to keep the anode remaining integrated
after cycling.4 However, for a carbon-coated Si-anode with
the thickness of carbon layer less than the XPS penetration
depth (~10 nm), no obvious signal of interfacial Si-C bond
could either be observed from Si(2p3/2) or from C(1s) X-ray
photoelectron spectroscopy (XPS).4,5 Thus, Si-C is Less
possibly located on the surface of nanostructured silicon.
According to Ref. 4 and 6, Si-C exists with the form of
siloxane (C-Si-O), which may be soluble in the electrolyte
and subsequently diffuse through the SEI layer to deposit on
the top of carbon layer.
-Si-H
Reactive and can chemically reduce the electrolyte
References
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fluoroethylene carbonate additive on interfacial properties of silicon thin-film
electrode ”J. Power Sources 2006, 161, 1254-1259.
[3] Ren, B.; Liu, F. M.; Xie, J.; Mao, B. W.; Zu, Y. B.; Tian, Z. Q. “In situ monitoring
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solutions” Appl. Phys. Lett. 1998, 72, 933.
[4] Yen, Y.-C.; Chao, S.-C. ; Wu, H.-C. ; Wu, N.-L. “Study on
solid-electrolyte-interphase of Si and C-coated Si electrodes in lithium cells” J.
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[5] Kim, H.; Han, B.; Choo, J.; Cho, J. Angew. Chem. Int. Ed. 2008, 47,
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of the solid electrolyte interphase on silicon nanowire lithium-ion battery anodes” J.
Power Sources 2009, 189, 1132-1140.
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