Ian D. Raistrick

Behavior of Some Binary Lithium Alloys as Negative Electrodes in Organic Solvent‐Based Electrolytes

In an attempt to overcome problems associated with the reversible lithium electrode in organic solvent-based electrolytes, the electrochemical characteristics of a number of binary and ternary lithium alloys in propylene carbonate have been studied. Thermodynamic and kinetic results for the Li-Sn, Li-Sb, and Li-Bi systems are reported here. In each of these systems, one or more two-phase regions with apparently rapid transformation kinetics at ambient temperature have been identified. Lithium chemical potentials and partial molar entropies for the alloys have been determined. Constant current charge-discharge characteristics and diffusion coefficient data have also been obtained.

Ionic conductivity of lithium phosphate-doped lithium orthosilicate

Abstract The ionic conductivities of samples of lithium orthosilicate containing up to 50 mole % of lithium phosphate have been measured by both a c and d c techniques. Results indicate a large enhancement in lithium ion conduction due to the presence of the phosphate, making these materials attractive candidates for use as solid electrolytes in applications such as battery systems.

Steady‐State D‐C Polarization Characteristics of the O 2, Pt/Stabilized Zirconia Interface

Four‐probe d‐c polarization studies were carried out on the Pt/stabilized zirconia interface between 600° and 900°C in the presence of 10−6–1 atm of oxygen partial pressure. Three types of polarization effects were observed. At high currents, the oxygen flux density is limited by diffusion of molecular oxygen in the gas phase through a boundary layer near the interface. At intermediate currents, porous Pt electrodes are almost completely non‐blocking to oxygen, and the primary impedance present is due to ionic resistivity in the electrolyte. At low overvoltages, a limiting current plateau is observed at 600° and 700°C, which disappeared completely at 800°C and above. Two alternative mechanisms involving slow diffusion of either atomic oxygen or an electronic species are proposed to account for the observed behavior.

Relationships among Electrochemical, Thermodynamic, and Oxygen Potential Quantities in Lithium‐Transition Metal‐Oxygen Molten Salt Cells

The interdependence of thermodynamic parameters, phase equilibria, and electrochemical measurements can be used as a powerful tool in the development of high specific energy cells. These principles were used in the analysis of electrochemical experiments performed on ternary lithium-transition metal-oxide (M = Mn, Fe, and Co) positive electrodes. The free energies of formation of LiMnO/sub 2/, Li/sub 5/FeO/sub 4/, LiFeO/sub 2/, and LiCoO/sub 2/ were found to be -178.21, -399.88, -154.18, and 131.62 kcal/mol at 400/sup 0/C. The electrochemical displacement reactions were found to be reversible in LiCl/KCl molten salt cells over a range of 0.0-3.0 Li equivalents per mol at current densities of 5-15 mA/cm/sup 2/. The equilibrium potential vs. Li was found to be a logarithmic function of the calculated oxygen partial pressure for any tie triangle in which Li/sub 2/O is present, or for any tie triangle containing ternary oxide phases Li /SUB x/ MO /SUB y/ which are only marginally stable with respec to Li/sub 2/O and the relevant binary oxides MO /SUB y/ . Compounds with oxygen partial pressures above 10/sup -25/ atm were found to be unstable in LiCl/KCl electrolyte at 400/sup 0/C.

Thermodynamic investigations of ternary lithium-transition metal-oxygen cathode materials

Abstract The reaction of lithium with three transition metal oxides (MnO, LiFeO 2 , and LiCoO 2 ) has been investigated by an equilibrium electrochemical technique in cells of the type: (−) Al, Li 0.9 Al/LiClKcl (l) /[Li x MO y ] (+) Each system exhibits long constant voltage plateaus characterized by three-phase equilibria. The compositional range of reaction of lithium with MnO is 2.0 equivalents, whereas 3.0 equivalents may be reacted with the compounds LiFeO 2 and LiCoO 2 . The ternary iron and cobalt oxide systems have been found to be kinetically fast (10–15 mA/cm 2 ) and reversible at 400°C. The free energies of formation ΔG f o of Li 5 FeO 4 , LiFeO 2 , and LiCoO 2 were calculated and found to be −399.88, −154.18, and −131.62 kcal/mole, respectively. Replacement of sulfide with oxide cathode materials might reduce the high temperature lithium battery corrosion problems currently associated with sulfur-containing cells.

Lithium ion conduction in Li5A104, Li5GaO4 and Li6ZnO4

Abstract Polycrystalline samples of Li5Al04, Li5Ga04, and Li6Zn04 have been synthesized, and their ionic conductivity measured over a range of temperature. These materials, which have the antifluorite structure with large concentrations of intrinsic cation vacancies, have Arrhenius-like conductivities at low temperatures, with a steep rise in the range 385–450°C, reaching very high values, with a very small temperature dependence, thereafter. Materials of this type, which exhibit the highest values of lithium ion conductivity yet found, may have important practical applications in devices such as elevated temperature batteries.

An electrochemical study of the mixed beta-vanadium bronzes LiyNaxV2O5 and LiyKxV2O5

It has been found that lithium may be rapidly inserted into ..beta..-phase sodium and potassium vanadium bronzes to yield phases of composition Li /SUB y/ Na /SUB x/ V/sub 2/O/sub 5/ and Li /SUB y/ K /SUB x/ V/sub 2/O/sub 5/. For (x + y) values less than about 2/3, a single phase region is found. For higher lithium contents two additional narrow phases are formed; the maximum alkali metal content appears to correspond to a vanadium oxidation state of 4. The reversibility of the insertion reactions and x-ray powder diffraction indicate that the structures of the higher lithium content phases are closely related to the ..beta..-phase. Thermodynamic data have been derived from the electrochemical results.

The transient electrical response of electrochemical systems containing insertion reaction electrodes

Abstract The transient electrical response of electrochemical systems containing an insertion reaction solid-solution electrode is derived using Laplace transform methods. An electrode impedance is first calculated which allows the response of the system to any input signal to be calculated, either for the electrode alone, or in combination with other circuit elements. Effects of finite length are included and steady-state ac response is also derived. The results are illustrated by calculation of the effect of a series resistance on the rate of charge accumulation in an electrode under voltage control.

Thermodynamics and kinetics of the electrochemical insertion of lithium into tungsten bronzes

Abstract The electrical insertion of lithium into cubic and hexagonal tungsten bronzes has been investigated using equilibrium and transient galvanic cell measurements. The thermodynamic properties (chemical potential and partial molar entropy) of the mixed bronzes have been determined. Lithium may be readily inserted into the cubic phase as long as the sodium concentration is less than about 2 3 . The chemical diffusion coefficient of lithium is very high in both the structures, being approximately 10−7cm2/s for low lithium concentrations. The shape of the coulometric titration curves for the cubic case is due to the contribution to the chemical potential from a degenerate electron gas and the configurational entropy of the ions.

Thermodynamic and structural considerations of insertion reactions in lithium vanadium bronze structures

Abstract Lithium vanadium bronze structures show promise for use as positive electrode materials in advanced lithium batteries. Many studies indicate that the insertion of lithium in these structures is reversible and at high rates. However, the electrochemical behaviors among these phases are quite different and also deviate from that predicted by the high temperature phase diagram. In this paper, a rationalization based on the thermodynamic and structural considerations is proposed. Strikingly, metastable reactions are found during the insertion and metastable allotropes are produced. We call these types of reactions “allotropic insertions” to distinguish from the conventional isomorphic insertion and displacement reactions.