摘要:

Electrochemical discharge/charge curves vs Lithium of coin cells using as cathodes various transition-metal oxide hosts for lithium insertion/extraction reactions provide information on the operative redox energies of the transition-metal atoms. The relative positions of the redox energies were found to vary little, but their absolute positions by as much as 1 eV, with changes in structure or, for an isostructural series, with changes in counter cation. Use of polyanions to obtain a more open framework with a larger free volume for Li+-ion motion was found to be more important for high-power applications than the loss in electronic mobility, but a larger free volume for ionic motion reduces the capacity per unit volume. It was shown that introduction of a second phase with a higher redox energy provides a buffer against over discharge. A reversible decrease in capacity with increasing current density was identified and its origin discussed. Substitution of the polyanions (PO4)3−or (SO4)2−for oxide ions brings the V4+/V3+and Fe3+/Fe2+redox energies to levels of interest for cathodes in a lithium-ion battery.

ISSN:1058-725X    

DOI:10.1080/10587259808042359

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The paper presents the results of electrical and electrochemical measurements of intercalation compounds (LixCoO2, LixVO2, LixWO3). A close correlation has been shown between the electronic structure of transition metal compounds and the reactivity in relation to lithium.

ISSN:1058-725X    

DOI:10.1080/10587259808042360

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Electrochemical insertion of lithium into perovskite structure NbO2F has been investigated. Lithium insertion leads to a structural transformation from the initial cubic unit cell to the LiNbO3-type structure which presents a hexagonal symmetry. The maximum lithium uptake is 1.2 Li/Nb at room temperature. It corresponds to 60% of the expected maximum. Insertion has been followed by discharge experiments associated with impedance spectroscopy. The experimental results show that the electrochemical process can be characterized by an electrode reaction - layer formation - diffusion sequence. An equivalent circuit model which includes charge transfer reaction, layer formation, constant phase elements and diffusion impedance is proposed. The mechanism of insertion is discussed on the basis of the crystallographic structure of the perovskite. The layer may be viewed as a shell of a high inserted compound surrounding a relatively unaffected nucleus which is formed as insertion proceeds.

ISSN:1058-725X    

DOI:10.1080/10587259808042361

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A large amount of 16 lithium ions reacts with the phase Bi4V2O11between 3 and 1 Volts. From the structural characterisation of inserted compounds LixBi4V2O11(0<x<12) we can infer that the insertion mechanism does not involve the reduction of (VO3.5)2−layers, and that lithium ions locate around the Bi+3lone pair Electrostatics interactions Bi+36s2-Li+may originate the observed irreversibility of the insertion reaction.

ISSN:1058-725X    

DOI:10.1080/10587259808042362

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A thorough study concerning the formation of LiNiO2by a low temperature exchange reaction under hydrothermal conditions has been made. LiNiO2with low degree of cationic mixing and good electrochemical performances was prepared from NiOOH. LiCoO2is obtained from CoOOH using the same procedure. The synthesized products (LT-LiNiO2) present electrochemical properties similar to those of LiNiO2prepared by conventional powder synthesis (HT-LiNiO2) in spite of the difference in BET surface area: 20 m2/g for LT-LiNiO2and 0.7 m2/g for HT-LiNiO2. We found the thermal and moisture stability of our LT-LiNiO2prepared material to be much lower than that of HT made material. Furthermore, this instability was found to be 1) intrinsic to the material and not due to the synthetic method 2) enhanced by decreasing the LiNiO2particle size, and 3) much lower than that of LiCoO2. A complete mechanism is proposed to describe the correlation between the stability of the Ni based lithiated oxides in reducing conditions and their stability over moisture. Finally, in view of electrochemical applications, cobalt substituted products should be used in order to ensure the stability both against reduction-delithiation and hydrolysis.

ISSN:1058-725X    

DOI:10.1080/10587259808042363

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The electrochemical behavior of the lithium / V2(SO4)3system has been studied with XRD observation of the intercalation/deintercalation induced structural changes. Experiments have been performed on the NASICON type rhombohedral form. The use of very slow staircase potentiodynamic cycling made able to show that the first reduction occurs in two steps very close in energy and that the system experiences an irreversible structural change if this reduction is driven to the second step, below 2.59V vs Li0-Li+. Then, after a specific first oxidation step at 2.8 V, the system can be cycled reversibly through two redox levels at 2.63 V and 2.59 V.

ISSN:1058-725X    

DOI:10.1080/10587259808042364

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The layered titanate CsxTi2-x/4O4has been synthesized in the range of 0.68 ≤ × ≤ 0.88 at 700°C. Lithium has been intercalated into the titanate Cs0.68Ti1.83O4(x = 0.68 in CsxTi2-x/4O4) chemically and electrochemically. The increase of the electrical conductivity on the intercalation is estimated at a factor of 105at room temperature. The saturated intercalation compound of Li0.48Cs0.68Ti1.83O4shows the broad optical absorption spectrum around 1050 nm due to the intervalence transition in the same manner as mixed-valence oxide such as HXWO3. The titanate exhibits electrochromism on the intercalation-deintercalation of lithium.

ISSN:1058-725X    

DOI:10.1080/10587259808042365

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The usual preparation route of lithiated Rancieite-type Manganese Oxide (Li-RMO) includes three steps: reduction of KMnO4in acidic medium (1), followed by a further acidic treatment which ensures a complete K+/H+exchange (2) and subsequent Li+/H+ion-exchange reaction (3). The surface area of the as prepared Li-RMO is always several tens of m2g−1. Its initial capacity with respect to electrochemical Li intercalation is 220 mAh/g with an average voltage of 2.85V (vs Li). However, a rapid capacity fading is observed upon cycling, due to a dissolution of the material likely related to its large surface area. A new synthetic route is proposed leading to a material with a surface area less than 10 m2g−1. As expected, the cycling behavior of this new material is greatly improved.

ISSN:1058-725X    

DOI:10.1080/10587259808042366

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

OCV measurements, cyclic voltammetry and chrono-amperometric measurements have been performed to provide information on the type of mechanism of Li insertion into Li4Ti5O12spinel material. Step-wise potentiodynamic electrochemical techniques allow us to distinguish between a single-phase versus two-phase reaction and to conclude on the type of growing mechanism (nucleation-and-growth or homogeneous growth) and the evolution upon cycling.

ISSN:1058-725X    

DOI:10.1080/10587259808042367

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this study, sulfide based spinel materials of tin and titanium were synthesized (Cu2FeTi3S8and Cu2FeSn3S8). A topotactic substitution of tin by titanium atoms was performed in order to obtain electrode materials with high specific capacity associated to a good conductivity. According to the first electrochemical tests the Cu2FeTi3S8spinel appears as a possible anodic material for the Rocking-Chair batteries.

ISSN:1058-725X    

DOI:10.1080/10587259808042368

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor