Mo-Hua Yang

Enhanced Cycle Life of Si Anode for Li-Ion Batteries by Using Modified Elastomeric Binder

Department of Chemical Engineering, Tung Hai University, Taichung, Taiwan 407Cycle-life of the particulate electrode of Si, either with or without carbon coating, for Li-ion battery has significantly beenimproved 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 1 SCMC) mixture binder shows smaller moduli,a larger maximum elongation, a stronger adhesion strength on Cu current collector, and much smaller solvent-absorption inorganic carbonate. There were demonstrated cycle lives of .50 cycles for bare Si at 600 mAh/g or carbon-coated Si at 1000mAh/g, as contrast to <8 cycles for PVdF-bound electrode in all cases.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1847685# All rights reserved.Manuscript submitted July 28, 2004; revised manuscript received September 27, 2004. Available electronically December 16,2004.

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.

Enhanced High-Rate Cycling Stability of LiMn2O4 Cathode by ZrO2 Coating for Li-Ion Battery

The effect of a sol-gel derived amorphous zirconium oxide surface coating on the high charge-discharge (CD) rate performance of LiMn 2 O 4 was studied. When cycled between 4.5 and 2.9 V (vs. Li/Li + ) at room temperature, the coated spinel electrode, containing 5 wt %-ZrO 2 , shows tremendous enhancement in cycling stability at CD rates up to 10 C. Concurrently, the coated spinel electrode exhibits a lower cubic-tetragonal transition potential, a smaller charge-transfer impedance by 4-5-fold, and it profoundly reduces, by 66%, lattice contraction upon charge (delithiation). The enhancement in the high-rate cycling stability has been attributed to the combination of these favorable effects.

Local structure transformation of nano-sized Al-doped LiMn2O4 sintered at different temperatures

LiMn2O4 and LiAl0.15Mn1.85O4 were synthesized via the sol–gel process using citric acid as the chelating agent, followed by sintering at various temperatures. The electronic and atomic structures of LiMn2O4 and LiAl0.15Mn1.85O4 powders were probed by means of Mn K-edge X-ray absorption spectroscopy (XAS). Al-doping was found to promote the sintering of spinel LiMn2O4 so that the degree of structural disorder around Mn atoms in LiAl0.15Mn1.85O4 becomes lower than that of LiMn2O4, leading to an excellent capacity retention of this cathode material for lithium battery in charge–discharge cycle. # 2003 Published by Elsevier Science B.V.

Structure Effect of Si-Based Powder on Cycle Performance of Lithium Ion Battery

In this study, an inactive material (Ni) is introduced into Si for buffering the volume change causing by the lithium insertion and de-insertion. A porous structure is designed for further reducing of the volume change. The surface-porous structure SiNi powder is prepared by gas atomization method and wet-etching in an acidic solution, which shows positive effects on cycle performance, high capacity and the efficiency at the first cycle. Coated a carbon layer onto SiNi powders by CVD process can further improve the cycle performance by preventing structure collapse.