S. Atlung

Lithium insertion in different TiO2 modifications

Abstract The insertion of Li into the three titanium dioxide modifications, anatase, rutile, and TiO2(B), is studied primarily by electrochemical techniques. At 25°C at potentials above 1.4 V versus Li/LiAsF6,PC the maximal Li uptake is 0.5 Li/Ti in anatase and TiO2(B), while rutile does not insert Li. At 120°C utilizing LiCF3SO3/PEO electrolyte an amount of 0.8, 0.5, and 0.5 Li/Ti, respectively, is inserted above 1.3 V. The different behaviour of the chemically identical, but structurally non-equivalent oxides, is discussed.

Modeling of Porous Insertion Electrodes with Liquid Electrolyte

The dynamics of porous insertion electrodes during charge or discharge is described by a simplified mathematical model, accounting for the coupled transport in electrode and electrolyte phases. A numerical method to evaluate the response of this model to either controlled potential or controlled current is outlined, and numerical results for the discharge of a porous TiS/sub 2/ electrode in an idealized organic electrolyte are presented. It is demonstrated how electrolyte depletion is the principal limiting factor in the capacity obtained during discharge of this electrode system. This depletion is a consequence of the mobility of the ions not inserted, therefore the performance or this type of electrode is optimized by choosing electrolytes with transport number as close to unity as possible for the inserted ion. 23 refs.

V6O13 As cathode material for lithium cells

Abstract The e.m.f. vs. composition relationship of Li/LixV6O13 has been studied at 25 °C and 155 °C by cyclic voltammetry using organic and polymeric electrolytes, respectively. At both temperatures the lithium insertion reaction is found to be reversible in the composition interval: 0 ⩽, x ⩽ 8. a.c.- impedance measurements on single crystals (25 °C) show that Li+ diffusion in LixV6O13 is one dimensional and proceeds along the channels in the b axis direction. Cycling of Li/LixV6O13 cells with organic and polymer electrolyte shows that high materials utilization and good cycling performance can be achieved with both systems. It is demonstrated that LixV6O13 is sensitive to discharge below 1 V vs. Li.

Determination of the differential capacity of intercalation electrode materials by slow potential scans

Abstract The differential capacity of an insertion electrode material and an estimate of the time constant for transport can be obtained directly from the linear sweep voltammograms at sufficiently low sweep-rates. A simple method of conducting sweep experiments at sweep-rates below 10 μV s −1 is outlined, and the use of this method as a tool in assessing the properties of intercalation electrode materials is demonstrated with results from the cell: Li/LiClO 4 in propylene carbonate/Li x TiS 2 .

On the ac-impedance of electroactive powders. γ-manganese dioxide

Abstract A method has been developed for studying electrochemical kinetic parameters of substances in powdered or dispersed form. The method is based on the frequency dependence of the ac -impedance of the powder dispersed in a suitable electrolyte. This communication presents an introductory study of γ-manganese dioxide. The material was chosen in particular because of its practical importance to the dry battery industry and the numerous number of studies on its properties. The requirements to be met in investigations of the electro-chemical properties of this material are discussed, and a number of the methods hitherto employed for these studies are critically reviewed and compared with the techniques used in this work. The emphasis is placed on the application of ac -impedance techniques. Based on our experimental results for a typical battery-active manganese dioxide an electrical equivalent network for the dispersion is developed. It is shown that in this case information about the interfacial impedance—reflecting diffusion in the solid phase—and the electronic resistance can be extracted from impedance data. The agreement between the results obtained in this way and by other methods is not considered satisfactory. The method used in this work has principal advantages, but the results obtained depend on the correctness of several assumptions. Therefore it is concluded that a broader range of experiments and a refinement of the electrical network used is needed. Such investigations are in progress and will be reported in a subsequent paper.

A Rechargeable All‐Solid‐State Sodium Cell with Polymer Electrolyte

INTRODUCTION sodium with thicknesses between 50 ;~m and 100 ~m were obtained. Secondary lithium cells with intercalation or insertion materials as positive Polymer electrolyte sheets (-~30 ~m) electrodes are now an extensively stuWere prepared by evaporation of acetodied subject. However, only few papers nitrile solutions of poly-(ethylene covering the corresponding sodium sysoxide) (PEO) and the proper amount of terns have yet appeared. Ostensibly this Nal, recrystallized from acetonitrile is due to the lack of reversible sodium and vacuumdried at l~0~ The PEO (WSR /electrolyte half-cells functioning be301 Polyox, MW = 4.I0 ~, BDH) was used low 200~ higher temperatures most as received. The films were prepared electrode materials will react via and handled in an argon filled dry box. displacement reactions, which generally The Nal concentration in the films used have lower electrode potentials and do corresponded to a Na/O ratio of 1:10. not possess the inherent reversibility With this electrolyte, the operating of intercalation reactions, temperature of the cell is confined to the interval between 98~ (melting of Liquid organic electrolytes consisting sodium) and 65~ as the electrolyte of NaI dissolved in propylene carbonate conductivity decreases rapidly below have been used for electrochemical prethis temperature. paration of sodium intercalated TiS 2 (1,2). The Exxon group has cycled both Composite MoS 3 electrode films (-~50 ~m) Na/TiS~ and Na/MoS 3 using sodium triewith the overall composition: 72 w/o thyl [N-pyrrol) b~orate dissolved in MoS3, 20 w/o PEO, and 8 w/o Nal were 1.3-dioxolane as electrolyte (3,4). Most other groups have chosen to use two-electrolyte systems with an ionic conducting ceramic membrane. This membrane separates molten sodium from the liquid electrolyte forming contact to the active material in the positive electrode (5).

The potential of battery active manganese dioxide

Abstract The development and background for the “homogeneous reduction” hypothesis is reviewed and discussed. It is concluded that the potential calculated from this hypothesis cannot account for the experimentally observed values. It is proposed to treat the manganese dioxide as an insertion electrode for protons. A thermodynamic treatment indicates that an electronic term, μ e in the dioxide, can be important. Including this, and using a statistical mechanical treatment, based on the concept of a concentration dependent number of accessible sites for the proton, a very good agreement is obtained between calculated and observed potentials over the entire discharge range. This procedure is supported by crystallographic evidence about the structure in the range near MnOOH.

Failure mode of the negative plate in recombinant lead/acid batteries

Abstract Experimental recombinant valve-regulated lead/acid batteries failed after 250 to 350 deep cycles. The failure was attributed to the negative electrode which showed loss of capacity. When the cells were converted to operation in the flooded mode, they delivered up to 1400 deep cycles. The failure mechanism is assumed to be sulfation due to insufficient recharge. A simple model for the partial currents during recharge is used to analyse the role of recombination and hydrogen and oxygen evolution in the failure mechanism. It is concluded that, at high recombination efficiencies, hydrogen evolution prevents the complete recharge of the negative plate, thus limiting the cycle life.

Electrostatic interactions during the intercalation of Li in Lix TiS2

Abstract A model for the electrostatic interactions between the Li + ions and the conducting electrons in the layered compound Li x TiS 2 is developed. Li x TiS 2 is considered as a sandwich structure consisting of layers of a homogeneous dielectric separated by conducting planes. The Li + ions intercalated in the van der Waal gaps are treated as point charges in the dielectric and their charges are screened by the conducting planes. By image technique the interaction energy can be calculated as the Madelung energy of an ionic crystal. Assuming an effective dielectric constant of 30 good agreement between the calculated and the experimental emf-x reaction is obtained. On this basis it is concluded that the strong deviations from ideality observed during intercalation of Li + in Li x TiS 2 are due to electrostatic forces screened by the conduction electrons.

On the zinc-chloride complex formation

Abstract The complex formation between zinc and chloride ions has been investigated by emf measurements on the cell Ag,AgCl¦x M NaCl + y M NaClO4 + 0.025 M ZnCl2¦Zn(Hg),Pt. The total concentration was varied between 1 and 4.6 mol·1−1. Three mononuclear complexes with 1,3 and 4 chloride ligands were found to be present. The complex constants based on the concentrations of the unhydrated species −βn(c)− showed a pronounced increase with decreasing water activity. A set of concentration independent constants is obtained when the solution is treated as an ideal mixture of hydrated ions and free water. The number of water molecules in the hydration shell replaced by one chloride ligand was estimated to four and the complex constants to: Where Σci is the total concentration of hydrated ions and free water, and xH2O is the mole fraction of free water.