Materials Research Activities

Whittingham 1968-1984

Michael Stanley Whittingham 1968-1984: Stanford University and Exxon Research, New Jersey


Stanley Whittingham grew up in the British Midlands and graduated from Oxford University in 1968 with a D.Phil. in solid-state chemistry. It was quite common for British chemists aspiring to an academic or industrial job to sojourn in the United States, so after completing his doctorate, Whittingham went to Stanford University. There he met up with Robert Huggins.

First love: Beta alumina

At Stanford, Whittingham began to work on the measurement of the conductivity of beta alumina. These materials were being investigated because they promised to serve as the electrolyte in a new form of battery, turning the conventional type on its head. The conventional battery consists of a liquid electrolyte and two solid electrodes. In 1967, researchers at Ford Motor Company introduced a battery with a solid electrolyte (beta alumina) and liquid electrodes. Beta alumina were special because they allowed for ions to diffuse through them at much greater speed than any other known solid, thus yielding a high ionic conductivity (as opposed to the conductivity due to electrons). For the next few years, beta alumina were all the rage within battery research, until other materials were found to possess even more promising characteristics. (Incidentally, some of the impetus for all this research came from a connection between superconductivity and the high ionic conductivity.)

Whittingham and Huggins published a series of papers (see Whittingham's list of publications) in the early 1970s on the use of beta alumina for battery purposes, one of which at the National Bureau of Standards in 1971. They reported on the utility of sodium tungsten bronzes as cathodes in conjunction with beta alumina, especially in that this material avoids problems of polarization. The sodium ions insert themselves in the interstitial spaces of the bronzes (this process was later to be termed intercalation, see below). These useful qualities of the sodium tungsten bronzes were found to apply for a wide range of temperatures at low oxygen partial pressures. With this electrode material the ionic conductivity of beta alumina could be determined; it was found to contribute almost all the conductivity (almost none contributed by the electrons) under all conditions, precisely what one would want from an electrolyte. Whittingham and Huggins also examined the production of tungsten bronzes and they related their transport properties to their structure. Their octahedral units of the so-called perovskite structure were found to arrange themselves in such a way as to form large channels running through the structure, presumably constituting the path by which the ions moved. They pioneered the use of nuclear magnetic resonance to investigate such structures.

After 1973, Whittingham no longer published on beta alumina. Most researchers in the field turned to other candidate materials for the electrolyte, as it gradually transpired that high ionic conductivity was a property of many materials, and that consequently beta alumina were not particularly special and indeed could not compete with other candidates. In addition, Whittingham was drawn towards research on suitable materials for cathodes, and on intercalation more generally.

Titanium disulfide

The structure-property relation guided the search for other suitable materials, and by 1974, Whittingham published on titanium disulfide and its chemical relatives: the disulfides of transition metals in groups IVB, VB, and VIB. All were found to be amenable to the intercalation (Whittingham employed this term from 1974 onwards) because they formed layers held together only by weak Van der Waals forces.

In 1975 and 1976, Whittingham gradually honed in on titanium disulfide, the promise of which for battery construction began to stand out. He did continue research on other compounds, such as graphite and tungsten bronzes, but rather with the aim of learning more about the mechanisms of intercalation; not because the latter were serious contenders as electrode materials. In the following years up until 1981 he examined molybdenum disulfide along with other bronzes and trisulfides, all of which theoretically offered advantages over titanium disulfide but which in practice all proved inferior. Much of this comparative work was enabled by the discovery of an effective general cathode screening agent: n-Butyllithium. Whittingham argued that this chemical agent mimics the half-cell reaction under consideration.

Titanium disulfide showed the viability of such battery systems, but its voltage is ultimately proved insufficient when combined with a lithium alloy or carbon anode even for the 1990s generation of 2-V electronic devices. This drove the search for alternative materials.

Elaboration of the concept of intercalation


in this case of lithium ions into a titanium disulfide host lattice.

By permission of McGraw Hill. Source: McGraw-Hill Encyclopedia of Science and Technology, entry on Intercalation.

In this same period (1976-1982) Whittingham also elaborated more general or theoretical statements, beginning with this: "The electrochemical reaction of layered titanium disulfide with lithium giving the intercalation compound lithium titanium disulfide is the basis of a new battery system. This reaction occurs very rapidly and in a highly reversible manner at ambient temperatures as a result of structural retention." (Quote taken from a 1976 article in Science entitled "Electrical energy storage and intercalation chemistry".) The utility of the materials that he had examined as electrode materials could thus be explained by guest ions not breaking up the structure of the host material but merely lodging themselves temporarily in the layers held together by weak Van der Waals forces. The distance between layers were thus continually increased and decreased with intercalation and de-intercalation, basically leaving the host structure intact, allowing for many cycles of charging and de-charging (high reversibility). The generality of expression culminated in something like a paradigm expressed in an introduction to an overview monograph: "The essential feature of the intercalation reaction, and that which makes it so exciting and profitable, is that guest and host experience some degree, along a spectrum from subtle to extreme, of perturbation in their geometric, chemical, optical, and electronic properties. There is considerable latitude available to the worker for controlling many of the parameters in order to tailor the behavior desired." This statement illustrates perfectly the idiom of materials science.

This page was written and last updated on 16-Feb-2001 by Arne Hessenbruch.