J. Marzec

Conduction mechanism in operating a LiMn2O4 cathode

Abstract Two series of the Li x Mn 2 O 4 spinel samples were studied at low temperatures (200–300 K) on electrical, thermal (DSC) and structural (X-ray diffraction (XRD)) properties for different lithium contents. Results obtained for deintercalated spinel samples with x ∼1 revealed the existence of a broad (100 K) phase transition that can be attributed to the molecular polaron condensation, leading to the orthorhombic distortion of the initial cubic form. The differential scanning calorimetry (DSC) measurement results enable us to regard the phase transition as a form of order–disorder one. Corresponding thermoelectric power (TEP) and electrical conductivity measurements fall within such description, moreover, indicating clear inconsistency between the measured regular DC conductivity of the spinel sample and that observed for the cathode in the working lithium cell. This discrepancy points to an alternative charge transport mechanism existing in the manganese spinel cathode, and it seems to be essential for the lithium cell performance.

Structural, electrical and electrochemical properties of LiNiO2

Abstract This paper presents structural and electrical properties of LiNiO 2 cathode material. The influence of cation mixing on the structural and electrical properties were determined. It has been found that deintercalation of lithium ions from the LiNiO 2 lattice influences the properties of the compound towards metallic ones. A model of electronic structure of LiNiO 2 has been proposed.

Electrical properties of LiMn2O4−δ at temperatures 220–1100K

Abstract The work presents the results of low-temperature (220–300 K) studies of electrical conductivity and thermoelectric power for manganese spinel obtained by various methods. It has been shown that charge transport takes place through the small polaron mechanism. The results of high-temperature (300–1100 K) studies of electrical conductivity and thermoelectric power carried out in the thermodynamic equilibrium conditions as a function of temperature and oxygen pressure (10 −2 −1 atm) in the whole range of the LiMn 2 O 4− δ phase stability are also presented. It has been shown that an effective reaction related to the deviation from stoichiometry is the reaction Mn +4 +e − ⇔Mn +3 .

Crystallographic and electronic properties of Li1+δMn2−δO4 spinels prepared by HT synthesis

Abstract The aim of this study was to determine an influence of lithium excess in Li 1+ δ Mn 2− δ O 4 spinels (in the 0≤ δ ≤0.32 range) on their transport and structural properties. The additional lithium atoms take Mn positions causing in the lattice parameter diminution and disappearance of the phase transition observed for the stoichiometric Li 1 Mn 2 O 4 manganese spinel. Low-temperature (230–330 K) measurements of electrical conductivity and thermoelectric power indicate rather minor influence of the excess lithium on transport properties in this system.

Electronic structure and reactivity of Li1−xMn2O4 cathode

Abstract The investigations of low temperature electrical and structural properties of the Li 1− x Mn 2 O 4 cathode as a function of lithium concentration are presented. Structure studies of deintercalated spinel revealed the existence of a broad (300–200 K) phase transition from cubic into orthorhombic phase also confirmed by DSC results. Thermoelectric power and electrical conductivity measurements indicate that the manganese spinel undergoes a modification of electronic structure during intercalation process.

Transport properties of the LiNi1−yCoyO2 system

Abstract In this paper results are presented concerning structure, electrical conductivity and thermoelectric power measurements of the LiNi 1− y Co y O 2 system. It has been stated that holes are dominating carriers. It has been also found that cobalt worsens the transport properties of the LiNi 1− y Co y O 2 system.

Electrochemical and chemical deintercalation of LiMn2O4

Abstract This work presents results of measurements of electrical conductivity, thermoelectric power and thermal properties of manganese spinel samples deintercalated in two different ways—an electrochemical and chemical one. It was shown that different methods of lithium extraction lead to striking differences in electrical properties of the obtained Li x Mn 2 O 4 samples what agrees with the observed differences in their structure as seen by XRD.

Electronic and electrochemical properties of LixNi1−yCoyO2 cathode material

Abstract This studies are devoted to structural, electrical and electrochemical investigations of Li x Ni 1− y Co y O 2 system. A modification of electrical properties of the cathode material was observed upon deintercalation. A correlation between electronic properties and effectiveness of lithium deintercalation process was confirmed.

Structural and electrical properties of LiNi1−yCoyO2

Abstract The work presents the results of investigations of electrical properties of the LiNi 1− y Co y O 2 system ( y =0, 0.25, 0.5, 0.85) in a wide temperature range (300–1073 K) and oxygen pressures ranging from 10 −4 to 1 atm. It was found that the replacement of nickel by cobalt in LiNi 1− y Co y O 2 eliminates the presence of a disadvantageous phase transition observed in LiNiO 2 and reduces “cations mixing” phenomenon. However, for cobalt content y ≫0.25 there is a significant deterioration of transport properties related to a drop in the effective carriers concentration.

Charge transport mechanism in LiCoyMn2−yO4 cathode material

Abstract These studies are devoted to electrical and electrochemical investigations of cobalt-doped manganese spinel. The studies of electrical conductivity and thermoelectric power in the wide temperature range (220–1090 K) in relation to oxygen nonstoichiometry together with the behaviour of the material in Li/Li + /Li x Co y Mn 2− y O 4 cell enable to determine electronic defect structure of the LiCo y Mn 2− y O 4 cathode material.