Deng-Tswen Shieh

Electrochemical Characterizations on Si and C-Coated Si Particle Electrodes for Lithium-Ion Batteries

The understanding of cycling and electrochemical characteristics of Si particle anodes for Li-ion batteries has previously been hindered by very fast capacity fading. Optimizing the electrode architecture to significantlyimprove its stability up to the 1000 mAh/g charge-discharge level has made it possible to investigate these properties to a greater depth than before. The capacity fading and lithiation mechanisms of Si and C-coated Si particles have been studied in this paper by cycling test and electrochemical impedance spectroscopy (EIS) analysis. The capacity vs cycle number plot exhibits two regions of different fading rates, including an initial region of slow fading followed by accelerated decay. The latter may be associated with large-scale failure of the electrode structure. EIS revealed a core-shell lithiation mechanism of Si. C-coating not only exerts remarkable favorable effects against capacity fading, but also serves as a conduit for Li ions to the reaction with Si particles.

Synthesis and Characterization of Nanoporous NiSi-Si Composite Anode for Lithium-Ion Batteries

Porous NiSi-Si composite particles having homogeneously distributed intraparticle pores with the size distribution peaked at 200 nm and a porosity of ∼40% have been synthesized by a novel method, which comprises steps of ballmilling induced reaction to form Ni/NiSi/Si preform particles and subsequent dissolution of unreacted Ni. Upon lithiation/delithiation cycling, the composite particle electrode exhibits much reduced thickness expansion and capacity fading rate, as compared with the pure Si particle electrode. The improvements have been attributed to the success in introducing the preset voids to partially accommodate volume expansion arising from Si lithiation. In situ synchrotron XRD further indicates that NiSi of the composite is active toward Li alloying, and it undergoes reversible transformation to/from Ni 2 Si and Li y Si. The reversible transformation between the silicides involves volume change in opposite to lithiation of Si, and is beneficial to stabilizing the composite electrode upon charge/ discharge cycling.

Enhanced High-Temperature Cycle Life of LiFePO4-Based Li-Ion Batteries by Vinylene Carbonate as Electrolyte Additive

Addition of vinylene carbonate (VC) in electrolyte solution has been found to greatly improve the high-temperature (55°C) cycling performance of LiFePO 4 -based Li-ion batteries. It has been established that the VC additive remarkably suppresses Fe dissolution from LiFePO 4 cathode and hence, subsequent Fe deposition on the anode side. Furthermore, the VC additive also significantly reduces formation of solid-electrolyte interface layers on both LiFePO 4 cathodes and mesocarbon microbead (MCMB) anodes. With VC addition, a 18650-type LiFePO 4 /MCMB cell has been shown to retain ∼80% capacity after 980 cycles at 55°C under 1-3 C charge-discharge rates. This is in contrast with more than 25% capacity loss after merely 100 cycles when no VC is added.

Electrochemical Performances of Cu Nanodots Modified Amorphous Si Thin Films for Lithium–Ion Batteries

Amorphous Si thin films have been prepared using radio-frequency magnetron sputtering. Cu nanodots of 2-10 nm in diameter were sputter deposited on the surface of Si films. The Si films modified with Cu nanodots (n-Cu/Si) were used as anodes for lithium-ion batteries. The performances of the n-Cu/Si anodes with different thickness of Si films, 120 and 1000 nm, were characterized and compared. The Cu nanodots can greatly improve the cycling stability. The amount of capacity fading was 66% after 150 cycles for the thinner Si films (120 nm), and was over 90% after 50 cycles for thicker films (1000 nm). For the n-Cu/Si films, the amount of capacity fading was 33% for thin films and 45% for thicker films.

Anode-Shielded, Sputter-Deposited Nanocrystalline Sn Thin-Film Anodes for Lithium-Ion Batteries

Sn thin-film anodes have been prepared using radio frequency driven magnetron sputtering. With appropriate anode shielding on the sputter gun during deposition, film crystallinity and surface morphology can be well controlled. The anode shielding changed the plasma ion density, resulting in lower ion flux available on the substrate. Sn thin-film anodes deposited with anode shielding can develop fine and smooth morphology composed of ultrasmall particles (5-10 nm) uniformly dispersed on the surface. Grazing-angle X-ray diffraction and field-emission scanning electron microscopy were used to characterize the film crystallinity and surface morphology. The electrochemical properties of the thin-film anodes deposited under various conditions were measured and compared. High reversible capacity with low first-cycle capacity loss can be obtained. During the first 15-20 cycles significant capacity loss was observed, but at the next cycles capacity became more stable. The cycling properties of the Sn thin-film anodes were improved significantly.

The significant role of solid oxide interphase in enhancement of cycling performance of sn thin-film anodes

Sn thin-film anodes have been prepared by radio-frequency magnetron sputtering with additional anode shielding on the sputter gun. The anode shielding effectively reduced kinetic energy of the adatoms during deposition, and the deposited thin films were X-ray amorphous and exhibited fine and smooth morphology with nanoparticles (5-10 nm) uniformly dispersed on the surface. By changing the charge-discharge scheme and deliberately depositing a SnO 2 surface coating, the properties of the solid electrolyte interphase of these anodes can be modulated. The cycling properties of the Sn thin films with deliberate SnO 2 surface coating are sienificantlv improved.