The electrochemical reaction of lithium with ␣-LiFeO 2 , ␤-Li 5 FeO 4 , and CoO is studied by in situ X-ray diffraction and in situ Mo ¨ssbauer measurements. The results of the measurements show that these metal oxides are immediately decomposed during discharge to form lithia and the reduced metal. This reaction proceeds through a single intermediate or surface phase. The reaction products are nanometer-sized, but are not amorphous as was suggested previously. During charge the metal displaces the lithium in lithium oxide to form a metal oxide and lithium. In the case of CoO, the original lithium oxide oxygen lattice is preserved and the reaction resembles an ion exchange process. This also appears to be the case for the iron oxides. Upon discharge, the reverse occurs and the lithium replaces the metal in the metal oxide, once again forming lithium oxide and reduced metal on the bottom of discharge. Further cycling proceeds via oxidation/reduction of the metal by these displacement reactions with lithium.

Nanostructured thin film catalysts (NSTF) with widely varying compositions of Pt x M y and Pt x M y N z (M, N ¼ Ni, Co, Zr, Hf, Fe, Mn) have been evaluated for 0 x, y, z < 1. The catalysts' activity for oxygen reduction (ORR) was measured in 50 cm 2 fuel cell membrane electrode assemblies. Pt 1-x Ni x was found to be unique in showing an extraordinarily sharp peak in ORR activity as a function of the as-made composition around x ¼ 0.69 6 0.02 determined gravimetrically. This composition gave a corresponding fcc lattice parameter of 3.71 Angstroms and a grain size of 7.5 nm. Both surface area and specific activity increases contribute to the increased mass activity of the resultant dealloyed films. The ORR mass activity of the Pt 3 Ni 7 is 60% higher than for the NSTF standard Pt 68 Co 29 Mn 3 alloy. Rotating disk electrode measurements of a Pt 1-x Ni x series on NSTF coated glassy carbon disks show a similar large and sharp peak in activity. In contrast, PtCo shows a diminished but still sharply peaked mass activity in 50 cm 2 tests near x ¼ 0.62 by electron microprobe over the 0 < x < 0.7 range examined.

Thin films of Si 1−x O x were produced using combinatorial sputtering methods. X-ray diffraction studies of these films show that they are amorphous or nanostructured. The effect of oxygen content on the electrochemical performance of these materials was studied. The reversible specific capacity (between 0.005 and 0.9 V) agrees with the assumption that Si 1−x O x is made up of amorphous silicon, which can react to form Li 3.75 Si , and amorphous SiO 2 , which reacts to form Li 4 SiO 4 . The irreversible capacity increases with oxygen content when measured to a potential limit of 0.9 V vs Li/Li + but further Li can be extracted from sites presumably near oxygen up to a potential of 2.0 V vs Li/Li + . However, such potentials for the negative electrode would not be reached in a full Li-ion cell. This work shows that the oxygen content in Si 1−x O x should be optimized to produce materials with a reasonable active/inactive ratio in order to have electrodes with the desired specific capacity, an appropriate irreversible capacity and an appropriate amount of inactive phase to buffer volume expansion.

The reaction of lithium with amorphous Si was studied by 119 Sn Mössbauer effect spectroscopy using small amounts of Sn as probe atoms. Two powder samples, amorphous-Si 87 Sn 13 and amorphous-Si 93 Sn 7 , were prepared by magnetron sputtering and investigated using in situ and ex situ Mössbauer spectroscopy. There are two gently sloping plateaus in the voltage vs capacity of Li/Si cells whose origin has never been explained. There is a clear step between these plateaus at ϳ2.3 Li atoms per Si atom, or Li 2.3 Si. The step between the plateaus is found to correlate with dramatic changes in the Mössbauer effect spectra with x in Li x Si at x Ϸ 2.3, which suggest the step occurs at the point when each Si atom is surrounded only by Li atom first neighbors. The changes in the Mössbauer spectra during the delithiation of the Li/Si-Sn cells also give clues about electrode failure mechanisms.The search for next-generation negative electrode materials for Li-ion batteries has focused on Si-and Sn-based alloy materials that offer a considerably larger specific and volumetric capacity than conventional carbonaceous materials. Obtaining excellent capacity retention of such alloy materials during repeated cycling, however, is challenging due to the large volume changes during lithiation and delithiation. Amorphous or nanostructured alloys show better charge-discharge cycle life because the inhomogeneous expansion, which occurs in two-phase regions in bulk materials and which leads to particle cracking and pulverization, can be eliminated. 1 Possibly suitable alloys include amorphous Si 1−x Sn x , 2 Si/graphite nanocomposites, 3 tin oxide nanocomposites, 4 Sn 2 Fe/SnFe 3 C nanocomposites, 5 "amorphous" or nanostructured Sn-Co-C, 6,7 and so on. Crystalline silicon is also of interest because it becomes amorphous during the first lithiation. 8,9 Studies of the fundamentals of these materials are important yet sometimes difficult because materials that appear amorphous usually have short-range crystalline order that cannot be effectively studied by commonly-used X-ray diffraction ͑XRD͒. Mössbauer spectroscopy ͑MS͒ is a very useful tool to study Sn-based materials because it can characterize the local atomic structure using the 119 Sn probe. For example, Todd et al. 6 studied sputtered ͑Sn 0.63 Co 0.37 ͒ 1−y C y materials with 0 Ͻ y Ͻ 0.40 using MS in conjunction with XRD and proposed a nanostructure consisting of small grains of amorphous or nanostructured Sn 0.63 Co 0.37 in a disordered carbon matrix with Co-C interactions at the interface. Courtney et al. 10 investigated the reaction of Li with SnO and with tin oxide composites by identifying different oxidation states and phases at various lithiation stages as probed by in situ MS. Details of more applications of MS to electrode materials for Li-ion batteries can be found in several review articles. 11, 12 MS has not been used to study Si-based materials for lithium-ion battery applications because Si, unlike Sn or Fe, has no isotopes with suitable Mössbauer transitions. At pre...

A review of recent literature on Si:C composite and nanocomposite electrode materials is first presented emphasizing that most authors do not compare the experimental specific capacity of the composite with that expected based on the phases present. We provide such a comparison and suggest that much of the apparent confusion in the literature, when taken as a whole, can be understood if nanocomposites prepared by "aggressive" methods like high energy milling and high temperature heat-treatment contain significant amounts of amorphous or nanocrystalline SiC. In order to help resolve the confusion, samples of Si 1−x C x were prepared by high-energy mechanical milling for 0.25 Ͻ x Ͻ 0.5 and by combinatorial co-sputtering for 0 Ͻ x Ͻ 0.8. X-ray diffraction shows the mechanically milled samples to be a mixture of nanocrystalline SiC and Si. Electrochemical studies of the mechanically milled samples show that the attained specific capacity can be described accurately assuming that the Si is active and can reversibly react with 3.75 Li atoms per Si atom ͑Li 15 Si 4 ͒, while the SiC is inactive. The co-sputtered samples are amorphous or extremely nanostructured for all x. For 0 Ͻ x Ͻ 0.5, the specific capacity decreases with increasing x, from about 3580 mAh/g at x = 0, to about 1000 mAh/g at x = 0.5, presumably due to the formation of inactive regions of a-SiC. The capacity of the co-sputtered samples does not reach small values at x = 0.5, unlike the ballmilled samples, because there are presumably some regions of a-Si and a-C among the inactive a-SiC regions due to the high quenching rate of the sputtering process. Commercially relevant compositions are identified.