Mario Wachtler

Structured Silicon Anodes for Lithium Battery Applications

Pillar arrays fabricated on silicon substrates have been tested as potential anodes for lithium batteries. Electrodes of array characteristics, diameter 580 ′ 150 nm: fractional surface coverage 0.34: height 810 nm are reported here. Cyclic voltammetry (CV) and cyclic galvanostatic tests of alloying/dealloying of electrochemically produced lithium with silicon were carried out, and results correlated with SEM studies. Aerial current densities in the low and fractional mA cm - 2 , and voltage 25 mV to 2 V (vs. L/Li + ) were used. CV features correspond to various Zintl phase compounds (ZPCs). Structured electrodes of Si pillars maintained their structural integrity throughout cycling; planar Si electrodes showed cracks (2 μm features) after 50 cycles. A model is advanced in which lithium diffuses through a layer of ZPC to react with Si: growing ZPCs plastically deforms where necessary. Upon lithium dealloying vacancies coalesce to form voids at the ZPC/Si interface, Si rejoins the substrate. or precipitates out as a nanocrystalline material, and the voids appear as a fine pattern of cracks, looking like dried mud. The extra surface area that a pillar structure can confer on Si electrodes is essential and makes it practical to consider the possible eventual use of such anodes in integrated battery structure;.

Sub‐Microcrystalline Sn and Sn ‐ SnSb Powders as Lithium Storage Materials for Lithium‐Ion Batteries

The cycling behaviors of and powders, which were synthesized by chemical reduction and combined with a binder and a conductive additive to produce composite electrodes, are presented. The cycling stability of the electrode increased with decreasing particle size, and was higher for the multiphase material than for the single‐phase material of comparable particle size. The higher cycling stability of is explained by the subsequent reaction of the constituent phases and the mechanism of the reaction of with , and is discussed with respect to other multiphase materials which have been reported in the literature. The best‐performing material was of particle size , yielding about 200 cycles for galvanostatic, charge‐limited cycling. ©1999 The Electrochemical Society

Electron microscopical characterization of Sn/SnSb composite electrodes for lithium-ion batteries

Abstract Lithium storage alloys such as Sn/SnSb are promising new anode materials for Li-ion batteries. Due to a proper design of the active Sn/SnSb material as well as the composite electrode, capacities exceeding 500 mAh g −1 have been achieved with this system for more than 30 cycles. The observation of micro- and nano-structural changes in the composite electrode during charge/discharge cycling is of immense importance for a further improvement of the cycling performance. Electron microscopy (SEM and TEM) in combination with analytical techniques (EFTEM, EDXS and EELS) has been used for the characterization of Sn/SnSb raw powder as well as the Sn/SnSb composite electrodes. The pristine morphology and the changes of morphology during cycling of the electrode material have been studied. Furthermore, the chemical composition and particularly compositional fluctuations within the composite material have been investigated using EFTEM and EDXS. The electron microscopy results indicate that parts of the active material get finer during the initial cycles. Moreover, amorphous regions are detected in the cycled material. The experimental results are discussed with regard to the reaction mechanism of SnSb with Li.

Optical spectroscopy of lanthanide ions in ZnO–TeO2 glasses

Zinc tellurite glasses of compositions 19ZnO-80TeO2-1Ln2O3 with Ln = Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f-->f transitions the Judd-Ofelt parameters ohm(lambda) were obtained. The values of the ohm(lambda) parameters are in the range usually observed for oxide glasses. For Nd3+ and Er3+, luminescence spectra in the near infrared were measured and the stimulated emission cross sections sigma(p) were evaluated for some laser transitions. The high values of sigma(p), especially for Nd3+, make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu3+ doped glass were measured at 20 K, and the energies of the Stark components of the 7F1 and 7F2 states were obtained. A crystal field analysis was carried out assuming a C2v site symmetry. The behaviour of the crystal field ratios B22/B20 and B44/B40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu3+ sites appears to be very low compared to other oxide glasses.

A Safe, Low-Cost, and Sustainable Lithium-Ion Polymer Battery

A polymer lithium-ion battery, formed by a Li 4/3 Ti 5/3 O 4 -LiFePO 4 electrode combination and a poly(vinylidene fluoride) (PVdF)-based gel electrolyte, is presented and discussed. The electrochemical characterization demonstrates that this battery is capable of delivering appreciable capacity values at rates ranging from C/32 (160 mAh g -1 ) to 0.75C (130 mAh g -1 ), this being accompanied by a remarkable cycle life. In addition, because the two electrodes are based on common and nontoxic materials and operate within the stability window of the electrolyte, the battery is expected to be safe, inexpensive, and compatible with the environment. All these properties make the battery of prospective interest for application in the hybrid and electric vehicle field.

The effect of the binder morphology on the cycling stability of Li–alloy composite electrodes

Abstract It is demonstrated that the design of the composite electrode, or more precisely the morphology and distribution of the binder poly(vinylidine fluoride) (PVdF) within the composite electrode, has a significant impact on the cycling performance of Li storage alloy (Sn/SnSb) electrodes. Different binder morphologies and distributions have been obtained by using different solvents for the slurry preparation, such as 1-methyl-2-pyrrolidinone (NMP), in which PVdF is dissolved, yielding electrodes with a homogeneously and finely distributed binder, or decane, in which PVdF is only dispersed, yielding electrodes in which the original particle morphology of the binder powder is preserved. In constant current cycling tests carried out in an excess of electrolyte, the electrodes with the ‘dispersed’ binder show far better cycling capacities and stabilities than those with the ‘dissolved’ binder. This is explained by the different binding strengths, swelling behaviour in the electrolyte, electrode porosities, and possible ‘buffer’ effects of the compact and the finely distributed binders.

Phonon sidebands and vibrational properties of Eu3+ doped lead germanate glasses

Abstract The phonon sideband spectra of the 7 F 0 → 5 D 0 and 7 F 0 → 5 D 2 electronic transitions of Eu 3+ are reported and assigned on the basis of the vibrational Raman spectra for a series of lead garmanate glasses of molar compositions ( x − 1)PbO · (100 − x )GeO 2 · 1Eu 2 O 3 with x = 30, 40 and 50 mol%. The samples were prepared by melting the appropriate amount of the oxides at 1100°C for 2 h, and quenching and annealing at temperatures from 320 to 380°C for 15 h. The electron-phonon coupling strength of the GeO stretching modes coupled to the 7 F 0 → 5 D 2 transition was evaluated by determining the ratio of the intensity of the phonon sideband to the intensity of the zero phonon line. With increasing lead content, the coupling strength appears to increase (within the experimental uncertainties) from 0.010 ( x = 30 mol%) to 0.012 ( x = 50 mol%).

Studies on the Anode/Electrolyte Interface in Lithium Ion Batteries

Rechargeable lithium ion cells operate at voltages of 3.5–4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and anode corrosion has to be anticipated, leading to irreversible loss of electroactive material and electrolyte and thus strongly deteriorating cell performance. To minimize these reactions, anode and electrolyte components have to be combined that induce the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface, which hinders further electrolyte decomposition reactions, but acts as membrane for the lithium cations, i.e. behaving as a solid electrolyte interphase (SEI). This paper focuses on important aspects of the SEI. By using key examples, the effects of film forming electrolyte additives and the change of the active anode material from carbons to lithium storage alloys are highlighted.

Sn-Sb and Sn-Bi alloys as anode materials for lithium-ion batteries

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH4 and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH4 yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g−1, ∼ 350 – 400 mAh g−1, and ∼ 500 mAh g−1 were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation.

Site-selective spectroscopy of Eu3+ doped lead germanate glasses

Abstract A series of lead germanate glasses of molar compositions (x−1)PbO–(100−x)GeO2–1Eu2O3 with x=30, 40 and 50 were prepared and studied by laser-induced fluorescence line narrowing (FLN) techniques. The energies of the Stark levels of the 7 F 1 and 7 F 2 multiplets were obtained from experimental FLN spectra and a crystal field (CF) analysis was carried out for each excitation energy. The dependence of the CF Bkq parameters on the excitation energy is qualitatively similar to the behaviour observed for Eu3+ in other oxide glasses. The CF calculated ratios B22/B20 and B44/B40 agree reasonably well with the trend predicted by the Brecher and Riseberg geometric model. The CF strength parameter S decreases with increasing lead content in the glass host. This behaviour is explained on the basis of the tendency of lead to form strongly directional Pb–O bonds. On the basis of the present CF analysis, we find no evidence of changes of the local structure at the Eu3+ sites on increasing the amount of lead and also of 6-fold co-ordinated germanium.