Preparation and Characterization of Si-based Anode Materials for Lithium-Ion Batteries
Date Issued
2006
Date
2006
Author(s)
Liu, Wei-Ren
DOI
en-US
Abstract
Silicon is a very promising candidate to replace graphite as an anode material in Li-ion batteries because of its high theoretical capacity. However, the main obstacles to commercialization are dramatic volume changes for lithium insertion/extraction and intrinsically poor conductivity of bare silicon, bring mechanical instability and poor rechargeability during cycling.
From the view point of stabilizing electrode structure, the effects of Si particle size and the content of conductive additives (CA) on the performance of the Si anode are investigated. It is found that CA content has a profound effect on the cycle life of the electrode, which increases with increasing CA content. Reducing Si particle size, on the other hand, effectively facilitates the charging/discharging kinetics. A cycle life, for instance, exceeding 50 cycles with >96% capacity retention at the charge capacity of 600 mAh/g-Si has been demonstrated by adopting the combination of 30 wt. % of CA and 3-um Si particles.
In addition, the choice of binder is also very crucial issue. The cycle-life of the particulate electrode of Si, either with or without carbon coating, has significantly been improved by using a modified elastomeric binder containing Styrene-Butadiene-Rubber (SBR) and Sodium-Carboxyl-Methyl- cellulose (SCMC). Compared with poly-vinylidene-fluoride (PVdF), the (SBR+SCMC) mixture binder shows smaller moduli, a larger maximum elongation, stronger adhesion strength on Cu current collector, and much smaller solvent-absorption in organic carbonate. There are demonstrated cycle lives of > 50 cycles for bare Si at 600 mAh/g or carbon-coated Si at 1000 mAh/g, as contrast to < 8 cycles for PVdF-bound electrode in all cases.
The capacity fading and lithiation mechanisms of Si and C-coated Si particulate have also been studied in this study by cycling tests and electrochemical impedance spectroscopy (EIS) analyses, respectively. The capacity versus cycle number plot was found to serve as a useful guide to elucidating two fading modes, including a local mode arising from loss of electronic contact between individual particles and the conductive network of the electrode and a global mode that results from failure of the entire electrode structure. EIS revealed a core-shell lithiation mechanism of Si. C-coating not only exerts remarkable favorite effects against both fading modes, but also serves as a conduit for Li ions to the reaction with Si particles.
Porous NiSi/Si particles having a pore size distribution peaked at 200 nm and an intra-particle porosity of nearly 40% have been synthesized by high-energy ball milling of mixture of Ni and Si and subsequent dissolution of un-reacted Ni, and the material has been characterized for its microstructures and electrochemical properties for Li ion battery application. The preset intra-particle voids have been shown to help to accommodate volume expansion arising from alloying of the Si component. As a result, upon charge/discharge cycling, the composite electrode exhibits much reduced thickness expansion, as compared with pure Si electrode, and hence significantly reduced capacity fading rate. In-situ synchrotron XRD further indicates that the NiSi component of the composite is active toward Li alloying, and it undergoes reversible transformation to Ni2Si during charge/discharge cycling.
Apart from Si, Si/C, and NiSi/Si composites, the fundamental studies and preliminary electrochemical tests of other active materials, such as Si/ZrO2, Si/TiO2/C, Nano-Si/TiO2/C, SiO, SiO/C, and Nano-SiO/ZrO2/C composite are providing in chapter 6. It is believed that these novel anode composites potentially have opportunities to be promising candidates as anode materials for Li-ion batteries in the future.
Subjects
鋰離子二次電池
矽
流體化床
化學氣相沈積
溶膠凝膠法
鎳矽合金
Lithium-ion batteries
silicon
fluidized-bed
chemical vapor deposition
sol-gel process
high energy ball milling
nickel silicide
SDGs
Type
thesis
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