A. Honders

Bounded diffusion in solid solution electrode powder compacts. Part II. The simultaneous measurement of the chemical diffusion coefficient and the thermodynamic factor in LixTiS2 and LixCoO2

Abstract Two electrochemical methods - involving the application of a long-time galvanostatic current pulse and a small potentiostatic voltage step to a M/M x SSE cell - are presented. From the overvoltage, respectively current response the chemical diffusion coefficient ( D M + ) and the thermodynamic factor (∂ ln a /∂ ln c ) are obtained. The methods have been applied to the cells: Li/1M·LiClO 4 in propylenecarbonate/Li x Ti 1.03 S 2 0.05 x T = 20°C; and Li x CoO 2 0.10 T = 20°C. From the application of the current pulse/voltage decay method it followed: D Li + ( Li x Ti 1.03 S 2 ) = 1−4 × 10 −8 cm 2 s −1 , with a slight tendency to increase with decreasing x ; D Li C ( Li x CoO 2 ) = 2−40 × 10 −9 cm 2 s −1 , decreasing with decreasing x . These values are among the highest found for solid state Li + -ion diffusion, and will be closely evaluated and compared with data reported by other workers. The x -dependence of the thermodynamic factor, determined from kinetic data, for Li x Ti 1.03 S 2 ( x = 0.05-0.95) and Li x CoO 2 ( x = 0.60-1.00) is in accordance with a simple thermodynamic model. Unlike for Li x Ti 1.03 S 2 , the thermodynamic factor for Li x CoO 2 , determined from the EMF- x relation, cannot be accounted for by this model. Furthermore, a fast, but crude method to determine the average chemical diffusion coefficient in Li x Ti 1.03 S 2 and Li x CoO 2 is discussed.

The thermodynamic and thermoelectric properties of LixTiS2 and LixCoO2

Abstract The partial thermodynamic functions Δ H Li and Δ S Li for Li x Ti 1.03 S 2 (0.13 ⩽ x ⩽ 0.97) and Li 0.95 CoO 2 were obtained from EMF-temperature measurements ( T =-30−20° C ). For Li x Ti 1.03 S 2 , the x -dependence of these quantities is discussed in relation to a semiempirical expression for the EMF- x relation. The electronic component of the thermoelectric power in Li x Ti 1.03 S 2 (0 ⩽ × ⩽ 0.97, T = 50−200° C ) and Li x CoO 2 (0.20 ⩽ x ⩽ 1.00, T = 30−400° C ) was determined. From the sign of the (electronic) Seebeck coefficient it followed that Li x Ti 1.03 S 2 is a n -type and Li x CoO 2 a p - type electronic conductor. The influence of the amount of inserted lithium and temperature dependence on the Seebeck coefficient is discussed. A new method to determine the ionic heat of transport directly from the ionic Seebeck co-efficient was developed. This method was applied to Li x Ti 1.03 S 2 (0.61 ⩽ x ⩽ 0.97, T = -30−30° C ). The heat of transport is uch smaller than the activation enthalpy for Li + -conduction, indicating a high ionic polaron binding energy. Thermogravimetric analysis indicates that Li x CoO 2 with x 1 CoO 2 and Co 2 O 3 at temperatures higher than 80°C. This is sustained by the data for the electronic Seebeck coefficient. Also the thermodynamic, thermoelectric and kinetic data of Li x Ti 1.03 S 2 are critically compared with those of Ag x TiS 2 .

Bounded diffusion in solid solution electrode powder compacts. Part I. The interfacial impedance of a solid solution electrode (MxSSE) in contact with a m+-ion conducting electrolyte

Abstract The transient and ac electrical response of electrochemical systems containing a solid solution electrode is derived using Laplace transform methods. First, the operational impedance of the electrolyte/solid solution electrode interface is derived, for both asymmetrical and symmetrical cell systems. From the operational impedance the current, voltage and ac impedance response is calculated. By combination of semi-infinite and bounded diffusive behaviour, both the chemical diffusion coefficient of the inserted ions and the thermodynamic factor (∂ ln a /∂ ln c ) can be obtained from kinetic data only.

Bounded diffusion in solid solution electrode powder compacts. Part III. The kinetic properties of AgxTiS2 and AgxNiPS3

The kinetic properties of AgxTiS2 and AgxNiPS3 have been determined with dc (long-time current pulse) and ac techniques, using symmetrical cells of the type: Ag/AgI/AgxSSE/AgI/Ag AgxTiS2 : 0.07 ⩽ × ⩽0.98, T= 193°C, AgxNiPS3 : 0.05 ⩽ x ⩽ 0.90, T = 300–350°C. Data for the chemical diffusion coefficient (DAg+), the thermodynamic factor (Kt), the ionic (σAg+) and electronic (σe) conductivity, and the activation enthalpy (in the case of Ag0.05NiPS3) for these quantities, are obtained. In AgxTiS2, both DAg+(= 0.8-5 × 10−6cm2s−1) and Kt increase with increasing x; while σe is very high te≅1). In Ag0.05NiPS3, DAg+ has the same order of magnitude as in AgxTiS2, but the electronic conductivity is comparatively low tAg+≅0.10). Kt(Ag0.05NiPS3) is relatively high, and the AgI/Ag0.05NiPS3 interface exhibits an ionic charge transfer resistance. This indicates that Ag0.05NiPS3 is not suitable to incorporate Ag+-ions. Because of 2-phase behaviour of AgxNiPS3 with x > 0.20 for T < 350°C, the experimental data could only be qualitatively analyzed. Furthermore it is shown that carbon does not behave as an inert electrode material for AgxNiPS3.

Several electrochemical methods for the simultaneous measurement of thermodynamic activity and effective kinetic properties of inserted ions in solid solution electrodes

Three electrochemical methods for thesimultaneous measurement of thermodynamic activity and the effective kinetic properties of inserted ions Solid Solution Electrode powder compacts are presented. The theoretical substructure of these methods, and the practical application on the systemsAg/AgxTiS2/Ag(0<x<1, T=193°C),Li/LixCoO2(0.96<x<1, T=20°C), resulting in values for both the chemical diffusion coefficient and the Darken factor of the inserted ions, are discussed.

The thermoelectric power in solid solution electrodes: A disregarded phenomenon?

The aim of this paper is to demostrate the usefulness of thermoelectric power measurements for the determination of some important physical properties of insertion compounds. The electronic component of the thermoelectric power was measured for AgxTiS2 and LixTi1.03S2 (0<x<1, 50 °C<T<200 °C). From the data for the Seebeck-coefficient, together with estimations of the partial entropy of electrons, the free electron density in these materials is calculated. The influence of temperature and the amount of inserted metal (Ag, Li) on the electron density is discussed. The ionic component of the thermoelectric power was measured for AgxTiS2 (150 °C<T<200 °C) and AgxNiPS3 (150 °C<T<350 °C) for 0<x<1. From the data of the ionic Seebeckcoefficient the kinetically important heat of transport of silver ions is obtained. The heat of transport is much smaller than the activation enthalpy for Ag+-conduction, suggesting a high ionic polaron binding energy in these materials.

The thermoelectric power in AgxTiS2. part I. The electronic component of the thermoelectric power

Abstract The electronic component of the thermoelectric power, Δ E /Δ T of the cell: Pt/Ag x TiS 2 /Pt (argon atmosphere) ( T ) ( T +Δ T ) has been measured as a function of x (0 x E ) it is concluded that electrons are the majority electronic charge carriers. The electron density in these materials is determined from the measured Seebeck coefficients and calculated values for S 0 e . The electron density increases linearly with the amount of inserted silver up to x ≈ 0.70. For higher values of x the electron density remains constant, probably due to a lower degree of ionization of the inserted silver.

Thermogalvanic measurement of low partial pressures of oxygen with oxygen ion conductors: a disregarded possibility?

The thermogalvanic e.m.f. of O2− conducting solid oxide cells can be used to detect small electronic contributions to the oxide conductivity, as a function of the ambient O2 partial pressure. When this contribution is negligible, the thermocell can serve as an ‘oxygen gauge’. Gas-tightness of the oxide specimen is not required, in contrast to more conventional (concentration cell) techniques.

The thermoelectric power in AgxTiS2 and AgxNiPS3. Part II. The ionic component of the thermoelectric power

The EMF of the isothermal cells: Ag/AgI/AgxTiS2: 0<x<1, T=150–200°C/AgxNiPS3: 0<x<3, T=150–350°C has been measured. From the EMF-x curves the existence ranges of the 2-phase (stage I and II) regions −0.16<x<0.32 for the Ag/AgxTiS2 system at 190°C; 0.20 < x < 0.50 and 1 < x < 2 for the Ag/AgxNiPS3 system at 400°C - have been determined. The results are sustained by X-ray diffraction and electrical conductivity measurements. From the EMF-T curves the partial enthalpy (ΔHAg) and entropy (ΔSAg) of dissolution of silver in the AgxSSE (solid solution electrode) materials were obtained. In the case of AgxTiS2, ΔHAg has a low absolute value, while ΔSAg is distinctly positive. The EMF of the Ag/AgxNiPS3 system also has a positive temperature coefficient. Furthermore, the ionic component of the thermoelectric power, ΔE/ΔT, of the thermogalvanic cells: Ag/AgI/AgxSSE/AgI/Ag AgxTiS2: 0 < x < 1, T = 150–200°C( T ) (T+ΔT) AgxNiPS3: 0 < x < 1, T= 150–350°C has been measured. The kinetically important heat of transport of silver ions in the AgxSSE materials has been determined in two ways: first from the dependence of the ionic Seebeck coefficient (ϵAg+) on reciprocal temperature; and second from direct calculation, using the data for ϵAg+ and ΔSAg. The heat of transport is much smaller than the activation enthalpy for Ag+-conduction, indicating a high ionic polaron binding energy in these materials.

Thermogalvanic power and fast ion conduction in δ-Bi2O3 and δ-(Bi2O3)1−x(R2O3)x with R = Y, TbLu

Abstract The thermogalvanic power ∈ (Seebeck coefficient) of O2- conducting δ-Bi2O3 and δ-(Bi2O3)1−x(Y2O3)x has been measured directly as a function of temperature and partial oxygen pressure in N2O2 mixtures. The ∈ of δ-(Bi2O3)0.75(R2O3)0.25 with R = TbLu was indirectly determined using an isothermal concentration cell technique. Except for pure δ-Bi2O3, the heat of transport is much smaller than the activation energy for O2- conduction for all materials. The vibrational freedom of O2− ions in all δ-stabilized materials is reflected in their IR spectra at room temperature. Two prototypes of a thermogalvanic PO2 meter were tested.