Dany Carlier

Multiple phases in the ε-VPO4O–LiVPO4O–Li2VPO4O system: a combined solid state electrochemistry and diffraction structural study

Polyanionic materials attract great interest in the field of Li-ion battery research thanks to the wide range of possible available compositions, resulting in a great amount of different properties. Tavorite type compositions offer a very rich crystal chemistry, among which LiVPO4F delivers the highest theoretical energy density. In this work we focus our interest on the homeotypic composition LiVPO4O. This oxy-phosphate shows the ability to exploit two redox couples, V5+/V4+ at 3.95 V vs. Li+/Li0 and V4+/V3+ at an average potential of 2.3 V vs. Li+/Li0 upon Li+ extraction and insertion, respectively. The two domains show marked differences both in the electrochemical signature and in the phase diagram. Here we address for the first time both topics with a combination of electrochemical techniques and ex situ/in situ X-ray and neutron diffraction and support of density functional theory (DFT) calculations, to get a deep understanding of the behavior of Li1±xVPO4O. In the low voltage region, in particular, the formation of intermediate phases and the crystal structure of the end member Li2VPO4O are reported for the first time.

Structural Study of the Li0.5Na0.5MnFe2(PO4)3 and Li0.75Na0.25MnFe2(PO4)3 Alluaudite Phases and Their Electrochemical Properties As Positive Electrodes in Lithium Batteries

The alluaudite lithiated phases Li(0.5)Na(0.5)MnFe(2)(PO(4))(3) and Li(0.75)Na(0.25)MnFe(2)(PO(4))(3) were prepared via a sol-gel synthesis, leading to powders with spongy characteristics. The Rietveld refinement of the X-ray and neutron diffraction data coupled with ab initio calculations allowed us for the first time to accurately localize the lithium ions in the alluaudite structure. Actually, the lithium ions are localized in the A(1) and A(1) sites of the tunnel. Mössbauer measurements showed the presence of some Fe(2+) that decreased with increasing Li content. Neutron diffraction revealed the presence of a partial Mn/Fe exchange between the two transition metal sites that shows clearly that the oxidation state of the element is fixed by the type of occupied site. The electrochemical properties of the two phases were studied as positive electrodes in lithium batteries in the 4.5-1.5 V potential window, but they exhibit smaller electrochemical reversible capacity compared with the non-lithiated NaMnFe(2)(PO(4))(3). The possibility of Na(+)/Li(+) ion deintercalation from (Na,Li)MnFe(2)(PO(4))(3) was also investigated by DFT+U calculations.

Structure and properties of alkali cobalt double oxides A(0.6)CoO(2) (A = Li, Na, and K).

Lamellar A(x)CoO(2) cobalt double oxides with A = Li, Na, and K (x approximately 0.6) have been synthesized and their chemical (alkali content, oxidation state, and structure) and physical (resistivity, thermopower, magnetization, and specific heat) properties have been studied. All the three materials exhibit strong electron correlation emphasized by their behavior ranging from Fermi liquid to spin-polarized system. Our results show that both the dimensionality of the interactions and the nature of the alkali play a determining role on the properties.

Iron(III) phosphates obtained by thermal treatment of the Tavorite-type FePO4·H2O material: structures and electrochemical properties in lithium batteries.

Thermal treatment of the Tavorite-type material FePO(4)·H(2)O leads to the formation of two crystallized iron phosphates, very similar in structure. Their structural description is proposed taking into account results obtained from complementary characterization tools (thermal analyses, diffraction, and spectroscopy). These structures are similar to that of the pristine material FePO(4)·H(2)O: iron atoms are distributed between the chains of corner-sharing FeO(6) octahedra observed in FePO(4)·H(2)O and the octahedra from the tunnels previously empty, in good agreement with the formation of a Fe(4/3)PO(4)(OH)-type phase. The formation of an extra disordered phase was also proposed. These samples obtained by thermal-treatment of FePO(4)·H(2)O also intercalate lithium ions through the reduction of Fe(3+) to Fe(2+) at an average voltage of ~2.6 V (vs Li(+)/Li), with a good cyclability and a reversible capacity around 120 mA h g(-1) (>160 mA h g(-1) during the first discharge).

Reinvestigation of the OP4-(Li/Na)CoO2-layered system and first evidence of the (Li/Na/Na)CoO2 phase with OPP9 oxygen stacking.

The composition and synthesis conditions of the (Li/Na)CoO(2) phase with an ordered 1:1 Li/Na stacking alternating with CoO(2) slabs were determined from a careful study of the P2-Na(∼0.7)CoO(2)-O3-LiCoO(2) system. An in situ X-ray diffraction (XRD) thermal study emphasizes the metastable character of this phase that can be stabilized only by very fast quenching. Its composition, (Li(0.42)Na(0.37))CoO(2), is significantly different from the ideally expected one, (Li(0.50)Na(0.35))CoO(2), and its structure, confirmed by Rietveld refinement of the XRD pattern, presents an ideal alternate ordering of lithium, cobalt, and sodium layers within OP4-type oxygen packing. The presence of vacancies in both alkali-ion layers was confirmed by electrochemical intercalation of lithium and sodium. For the first time, a new type of layered oxide exhibiting OPP9-type oxygen packing was evidenced. Between the CoO(2) slabs, alkali ions are intercalated in the following order: Li(octa)-Na(prism)-Na(prism). This material crystallizes in the R3m space group with a(hex) = 2.828 Å and c(hex) = 46.85 Å cell parameters.

Structural and electrochemical studies of a new Tavorite composition: LiVPO4OH

Polyanionic materials attract strong interest in the field of Li-ion battery research thanks to the wide range of compositions, structures and electrochemical properties they offer. Tavorite-type compositions offer a very rich crystal chemistry, among which LiVPO4F has the highest theoretical energy density (i.e. 655 W h kg−1). A new Tavorite-type LiVPO4OH composition was synthesized by a hydrothermal route from three different vanadium-containing precursors. The crystal structure of this new phase was fully determined thanks to synchrotron X-ray and neutron diffraction. 1H, 7Li, and 31P magic angle spinning nuclear magnetic resonance spectroscopy as well as diffuse reflectance infra-red spectroscopy were performed in order to support further the nature of the phases formed. Galvanostatic intermittent titration technique experiments in lithium batteries and ex situ X-ray diffraction analyses revealed that during oxidation the concomitant extraction of Li+ and H+ occurs at the same equilibrium potential (3.95 V vs. Li+/Li) and leads to the formation of the Tavorite phase VPO4O at the end of the charge. LiVPO4OH is also electrochemically active in the low voltage region, upon Li+ insertion. The reversible insertion/extraction of lithium at 1.35 V vs. Li+/Li leads to the formation of Li2VPO4OH at the end of discharge.

Vanadyl-type defects in Tavorite-like NaVPO4F: from the average long range structure to local environments

Tavorite-type compositions offer rich crystal chemistry for positive electrodes in rechargeable batteries, among which LiVIIIPO4F has the highest theoretical energy density (i.e. 655 Wh kg−1). In this article, we report for the first time the synthesis of the related Na-based phase crystallizing in the Tavorite-like structure. Its in-depth structural and electronic characterization was conducted by a combination of several techniques, spanning electron and X-ray powder diffraction as well as infrared and X-ray absorption spectroscopy. The magnetic susceptibility measurement reveals an average oxidation state for vanadium slightly higher than V3+. This slight oxidation is supported by infrared and X-ray absorption spectroscopies which highlight the presence of V4+[double bond, length as m-dash]O vanadyl-type defects leading to an approximated NaVIII0.85(VIVO)0.15(PO4)F0.85 composition. In this material, the profile of the diffraction lines is governed by a strong strain anisotropic broadening arising from the competitive formation between the ionic V3+–F and the covalent V4+[double bond, length as m-dash]O bonds. This material shows a limited extraction of sodium, close to 15% of the theoretical capacity. Indeed, its electrochemical properties are strongly inhibited by the intrinsic low sodium mobility in the Tavorite framework.

Influence of the Initial Li/Co Ratio in LiCoO2 on the High-Voltage Phase-Transitions Mechanisms

The influence of the initial Li/Co stoichiometry in LiCoO2 (LCO) (1.00xa0≤ Li/Co ≤ 1.05) on the phase-transition mechanisms occurring at high voltage during lithium deintercalation ( V > 4.5 vs Li+/Li) was investigated by in situ X-ray diffraction. Even if the excess Li+ in Li1.024Co0.976O1.976 does not hinder the formation of the H1-3 and O1 phases, the latter are obtained at higher voltages and exhibit larger c parameters compared with their analogues formed from Li1.00CoO2. We also showed that for the stoichiometric Li1.00CoO2 the deintercalation process is more complex than already reported, with the formation of an intermediate structure between H1-3 and O1.