Jean-Bernard Leriche

Effect of Particle Size on Lithium Intercalation into α ­ Fe2 O 3

The electrochemical reaction of lithium with crystallized -Fe2O3 (hematite) has been studied by means of in situ X-ray diffraction. When reacting large particles (~0.5 µm), we observed the well-known transformation of the close-packed anionic array from hexagonal (hc) to cubic (ccp) stacking. At the early stage of the reduction, a very small amount of lithium (xc<0.1 Li/Fe2O3) can be inserted before this structural transformation occurs. Nanosize -Fe2O3 made of fine monolithic particles (200 A) behaves very different, since up to one Li per formula unit (-Li1Fe2O3,xc = 1) can be inserted in the corundum structure without phase transformation. To our knowledge, this is the first time this phase is maintained for such large xc values. This cationic insertion was found to come with a small cell volume expansion evaluated to 1%. Unsuccessful attempts to increase the xc values on large particles by decreasing the applied discharge current density suggest that the particle size is the only parameter involved. The better structural reversibility of this monophasic process compared to the biphasic one was confirmed by electrochemical cycling tests conducted with hematite samples of various particle sizes. Therefore, by using nanosize particles, we can drastically increase the critical Li concentration required to observe the hcccp transition. This work demonstrates that a careful control of the texture/particle size of electrochemically active oxide particles is likely an important variable that has been largely disregarded for such properties. ©2002 The Electrochemical Society. All rights reserved.

Toward Understanding of Electrical Limitations (Electronic, Ionic) in LiMPO4 (M = Fe , Mn) Electrode Materials

To better understand the factors responsible for the poor electrochemical performances of the olivine-type LiMnPO 4 , various experiments such as chemical delithiation, galvanostatic charge and discharge, cyclic voltamperometry, and impedance conductivity, were carried out on both LiFePO 4 and LiMnPO 4 . Chemical delithiation experiments confirmed a topotactic two-phase electrochemical mechanism between LiMnPO 4 and the fully delithiated phase MnPO 4 (a = 5.909(5) A, b = 9.64(1) A, and c = 4.768(6) A). We conclude that the limiting factor in the MnPO 4 /LiMnPO 4 electrochemical reaction is nested mostly in the ionic and/or electronic transport within the LiMnPO 4 particles themselves rather than in charge transfer kinetics or structural instability of the MnPO 4 phase. For instance, the electrical conductivity of LiMnPO 4 (σ ∼ 3.10 - 9 S cm - 1 at 573 K, ΔE ∼ 1.1 eV) was found to be several orders of magnitude lower than that of LiFePO 4 (σ ∼ 10 - 9 S cm - 1 at 298 K, ΔE ∼ 0.6 eV).

An Electrochemical Cell for Operando Study of Lithium Batteries Using Synchrotron Radiation

A new electrochemical cell has been specially designed for operando experiments at synchrotron facilities both for X-ray diffraction and X-ray absorption. It allows the investigation of insertion materials under high current densities (up to 5C rate) and hence to study complex phenomena of structural and electronic changes out of equilibrium. The LiFePO 4 -FePO 4 system has been chosen as a case study to validate this cell, and tricky phenomena, with apparent delays in phase formation compared with the number of electrons exchanged, have been spotted.

In situ X-ray diffraction techniques as a powerful tool to study battery electrode materials

The performances of rechargeable Li-based batteries depend on many factors amongst which is the structural evolution of the electrode materials upon cycling. To address these issues, efforts have been devoted towards reliable, rapid, and facile ways to perform in situ measurements. We show how recent advances in both cell design (e.g. the emergence of plastic cells) and instrumentation have boosted the implementation of in situ X-ray characterisation methods to the field of energy storage. The benefits of such measurements are discussed and commented through descriptive examples of a new insertion electrode material (PNb9O25) and an existing one of commercial interest LiCoO2. The link between the fundamental findings and their relevance to practical applications is highlighted. The rapidly growing field of in situ characterisation techniques in the field of battery materials extending beyond X-rays and involving XANES, Mossbauer, Raman, RMN and microscopy measurements, is also commented on.

Understanding the Second Electron Discharge Plateau in MnO2-Based Alkaline Cells

We present a study of the MnOOH → Mn(OH) 2 reduction process leading to the second electron plateau occasionally occurring during the electrochemical discharge of MnO 2 -based alkaline cells. The origin of the second plateau is nested in a dissolution-reduction-precipitation mechanism, and its onset potential is governed by Mn +3 /Mn +2 solution species through the Nernst law. Also, the appearance of this second plateau in MnO 2 -based alkaline cells is a strong function of the nature of the counter electrode, and is, for instance, rarely observed when Zn slurries are used as the counter electrode. Direct experimental evidence, by means of in situ XRD, SEM, and EDX analyses, is given for the formation of the spinel ZnMn 2 O 4 during the first electron reduction of MnO 2 , An ion exchange reaction is proposed to account for the formation of this phase. Based on these findings, we show that the likelihood of raising the second potential through chemical approaches, thereby using the second electron capacity in MnO 2 -based alkaline cells, is low.

Fluorosulfate Positive Electrodes for Li-Ion Batteries Made via a Solid-State Dry Process.

Ionothermal synthesis has recently been used to prepare a fluorosulfate (LiFeSO 4 F) capable of reversibly intercalating Li at 3.6 V vs Li, making this material a serious contender to LiFePO 4 for HEV and electric vehicle applications. Although fluorosulfates are made from low cost and abundant starting materials, their synthesis is costly because of the use of ionic liquids as synthetic medium. Herein, we report a solid-state process by which LiFeSO 4 F can be synthesized without the use of ionic liquids but at the expense of both longer reaction time and weakly contaminated samples. Additionally, we show how powerful Mossbauer spectroscopy can be in the optimization of the various stages of electrode preparation as shown through the synthesis of LiFeSO 4 F and its implementation into an electrode. The importance of having Fe 3+ -free hydrated precursors to routinely obtain pure LiFeSO 4 F samples is shown together with the need to optimize ballmilling conditions to preserve Fe 3+ -free LiFeSO 4 F composites. Samples prepared via this low temperature solid-state process show battery performances approaching those of samples prepared using ionic liquids as synthetic medium. Furthermore, this process can be extended to the synthesis of the other members of the fluorosulfates AMSO 4 F family with A = Li, Na and M = Fe, Co, and Ni.

Bismuth‐Enhanced Electrochemical Stability of Cobalt Hydroxide Used as an Additive in Ni/Cd and Ni/Metal Hydride Batteries

For performance purposes, the electrochemically active positive electrode in Ni-based rechargeable alkaline batteries consists of Ni(OH) 2 particles coated with CoOOH. The positive attributes of the CoOOH coating, however, vanish upon cycling because it transforms into Co 3 O 4 or even Co(OH) 2 through dissolution-crystallization processes, The benefit of adding Bi-based salts or bismuth oxide to prevent these phase transformations is presented. From chemical and electrochemical studies, coupled with potentiometric titration and ultraviolet-visible spectroscopy, we demonstrate that the positive effect of Bi additives is twofold. First, Bi adsorption onto the Co surface modifies the CoOOH chemical reactivity and thereby its dissolution. Second, since bismuth forms Bi-Co-oxohydroxo complexes in solution, as experimentally proved, it delays precipitation of the Co 3 O 4 and Co(OH ) 2 phases during cycling. Finally, an implementation of these findings toward the most efficient use of nickel positive electrodes containing Co-based additives is shown.

On the electrochromic properties of antimony-tin oxide thin films deposited by pulsed laser deposition

Antimony–tin oxide (ATO) thin films were deposited using pulsed laser deposition. From a wide survey of deposition conditions (deposition atmosphere and substrate temperature), we deduced that the optimum experimental parameters to obtain electrochromic active films were a deposition temperature of 200 j Ca t a1 0 � 2 mbar oxygen pressure followed by an annealing at 550 jC, the latter being critical. Through potentiostatic tests, we showed that depending on the composition, which influences film morphology, the Sn–Sb–O films could present either a faradic or a capacitive-like behavior, associated to a color or a neutral switching over a wide range of potentials, respectively. In addition, a relationship between the film annealing temperature and its structure as well as its electrochromic properties was evidenced by means of complementary electrochemical, X-ray diffraction and electron microscopy techniques. Finally, the electrical and optical properties of the ATO films were discussed in terms of the energy band theory. D 2003 Elsevier Science B.V. All rights reserved.

Spinel materials for Li-ion batteries: new insights obtained by operando neutron and synchrotron X-ray diffraction

In the last few decades Li-ion batteries changed the way we store energy, becoming a key element of our everyday life. Their continuous improvement is tightly bound to the understanding of lithium (de)intercalation phenomena in electrode materials. Here we address the use of operando diffraction techniques to understand these mechanisms. We focus on powerful probes such as neutrons and synchrotron X-ray radiation, which have become increasingly familiar to the electrochemical community. After discussing the general benefits (and drawbacks) of these characterization techniques and the work of customization required to adapt standard electrochemical cells to an operando diffraction experiment, we highlight several very recent results. We concentrate on important electrode materials such as the spinels Li1 + xMn2 - xO4 (0 ≤ x ≤ 0.10) and LiNi0.4Mn1.6O4. Thorough investigations led by operando neutron powder diffraction demonstrated that neutrons are highly sensitive to structural parameters that cannot be captured by other means (for example, atomic Debye-Waller factors and lithium site occupancy). Synchrotron radiation X-ray powder diffraction reveals how LiMn2O4 is subject to irreversibility upon the first electrochemical cycle, resulting in severe Bragg peak broadening. Even more interestingly, we show for the first time an ordering scheme of the elusive composition Li0.5Mn2O4, through the coexistence of Mn(3+):Mn(4+) 1:3 cation ordering and lithium/vacancy ordering. More accurately written as Li0.5Mn(3+)0.5Mn(4+)1.5O4, this intermediate phase loses the Fd\overline 3m symmetry, to be correctly described in the P213 space group.