Electrodes composed of silicon nanoparticles (SiNP) were prepared by slurry casting and then electrochemically tested in a fluoroethylene carbonate (FEC)-based electrolyte. The capacity retention after cycling was significantly improved compared to electrodes cycled in a traditional ethylene carbonate (EC)-based electrolyte.

Hydrothermally synthesized single-crystalline hematite (α-Fe 2 O 3 ) nanorods were investigated as an anode material for Li-ion batteries. Electrodes prepared with this material exhibited initial reversible capacities of 908 mAh g À1 at 0.2 C rate and 837 mAh g À1 at 0.5 C rate, and these capacities were completely retained after numerous cycles. The α-Fe 2 O 3 nanorods average ∼40 nm in diameter and ∼400 nm in length providing a short path for lithium-ion diffusion and effective accommodation of the strain generated from volume expansion during the lithiation/delithiation process.

Silicon and partially oxidized silicon thin films with nanocolumnar morphology were synthesized by evaporative deposition at a glancing angle, and their performance as lithium-ion battery anodes was evaluated. The incorporated oxygen concentration was controlled by varying the partial pressure of water during the deposition and monitored by quartz crystal microbalance, X-ray photoelectron spectroscopy. In addition to bulk oxygen content, surface oxidation and annealing at low temperature affected the cycling stability and lithium-storage capacity of the films. By simultaneously optimizing all three, films of ~2200 mAh/g capacity were synthesized. Coin cells made with the optimized films were reversibly cycled for ~120 cycles with virtually no capacity fade. After 300 cycles, 80% of the initial reversible capacity was retained.

Sn0.9Cu0.1 nanoparticles were synthesized via a surfactant-assisted wet chemistry method, which were then investigated as an anode material for ambient temperature rechargeable sodium ion batteries. The Sn0.9Cu0.1 nanoparticle-based electrodes exhibited a stable capacity of greater than 420 mA h g(-1) at 0.2 C rate, retaining 97% of their maximum observed capacity after 100 cycles of sodium insertion/deinsertion. Their performance is considerably superior to electrodes made with either Sn nanoparticles or Sn microparticles.

Amorphous GeO2 nanoparticles were prepared via a surfactant-assisted hydrothermal process. The effect of the reaction temperature and the surfactant concentration on the morphology of GeO2 particles were investigated. Particles of less than 300 nm were obtained when using 1,2-diaminopropane surfactant in a synthesis carried out at 180(◦)C. The synthesized germanium oxide nanoparticles were evaluated for their utility as the active anode material in Li-ion batteries. The electrode prepared with this material exhibited a stable capacity ∼600 mAh g(-1) at 0.2 C rate for up to 150 cycles in a conventional electrolyte containing ethylene carbonate (EC). The cyclability of the GeO2 nanoparticle electrode was further improved by using a fluorinated ethylene carbonate (FEC) based electrolyte, which showed capacities greater than 600 mAh g(-1) and retained more than 96% of their capacity after 500 cycles at 0.2 C rate. The effect of different electrolyte systems was studied by using electrochemical impedance spectroscopy and electron microscopy.

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The effect of a sol-gel derived amorphous zirconium oxide surface coating on the high charge-discharge ͑CD͒ 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 ͑delithiation͒. The enhancement in the high-rate cycling stability has been attributed to the combination of these favorable effects.Cubic spinel LiMn 2 O 4 is of great interest for the replacement of LiCoO 2 in Li-ion batteries due to its high voltage, natural abundance, low cost, and environmental benignity. 1-3 Particular enthusiasm has been shown to use this material in electric vehicle application owing to its superior safety properties to LiCoO 2 . 4,5 For this application, however, high-rate cycling stability will be one major issue. The discharge ͑lithiation͒ potential signatures in Li x Mn 2 O 4 ͑x ഛ 1͒ include two large plateaus near 4.1 and 4.0 V ͑all the potentials referred to herein are referenced to Li/Li + ͒, 6 which have been suggested 7 to involve transitions among three cubic phases. Insertion of Li for x Ͼ 1 results in another plateau near 2.8 V, corresponding to the transition from cubic LiMn 2 O 4 to tetragonal Li 2 Mn 2 O 4 . The phase transition involves Jahn-Teller distortions, associated with Mn 3+ Jahn-Teller ions. 8 The spinel exhibits faster capacity fading upon charge-discharge ͑CD͒ cycling than LiCoO 2 , and the cubic-tetragonal ͑CT͒ transition, which involves a large ͑ϳ10%͒ unit cell volume variation, has been considered as one important cause to the fading at room temperature ͑RT͒. 9 When a LiMn 2 O 4 electrode is discharged in the practical full-cell operation, the Li concentration gradient is expected to develop throughout the particle, and the Li stoichiometry, x in Li x Mn 2 O 4 , at particle surface may be well above 1.0, even when the average stoichiometry is less than 1.0. This was evidenced by microscopy analysis, which showed the presence of the tetragonal surface layer. 10 The higher the discharge rate is, the more pronounced this surface transition effect is expected to be. Accordingly, the fading rate of the spinel is expected to increase appreciably with CD rate. Capacity fading of the spinel is also increasingly serious with increasing temperature, and it has in part been attributed to the degradation of the spinel by dissolution of Mn ions into the acidic electrolyte. 11,12 Some studies ͑e.g., Ref. 13 and 14͒ showed the substitution of Mn at the 16d sites with ions with a valence ഛ+3 to give doped spinels Li x M y Mn 2−y O 4 ͑M = Ti, Fe, Ni, Co, Zn, Al, and Mg͒, which could enhance the cycling stability at RT. Although this approach has improved the structural stability, it seriously reduces initial capacity. As ...

ible Ta 2 O 5 thin film electrodes were made instead by e-beam evaporating tantalum in a chamber containing 10 À6 torr O 2 onto copper foils. [5] The resultant film morphologies were controlled by the angle of deposition. Dense, non-porous films were obtained at normal incidence (i.e. 08), while nanostructured films are obtained when the e-beam-evaporated tantalum impinged on the substrate at a glancing angle of 708. When the substrate was held at or below ambient temperature, the deposition was ballistic, that is, "hit-and-stick": there was little or no surface migration of the adatoms. In the absence of migration, self-shadowing of the deposit resulted in highly porous nanocolumnar films. The method, known as reactive ballistic deposition, (RBD), [6] has been previously employed to grow nanostructured thin films of a-Fe 2 O 3 , [7] Ti-and Sn-doped a-Fe 2 O 3 , [8] BiVO 4 , [9] W-and Mo-doped BiVO 4 , [10] Cr/TiO 2 , [4] CdSe-TiO 2 , [11] Ta 3 N 5 , [12] TiO 2 , [13] SiO x , [14] Si (1Àx) Ge x , [15] and Si. [5c, 16] Flaherty et al. [17] recently reviewed studies of RBD films for energy-conversion-and storage-related research.