Lithium-iodide cell

The demand for electrically operated tools or devices that can be handled independently of stationary power sources led to a variety of different battery systems which are chosen depending on the field of application. In the case of rare usage, e.g., for household electric torches or for long-term applications with low current consumption, such as watches or heart pacemakers, primary cells (zinc-carbon, alkaline-manganese or lithium-iodide cells) are chosen. For many applications such as starter batteries in cars, only rechargeable battery systems, e.g., lead accumulators, are reasonable with regard to costs and the environment. 

Figure 2.3 Basis of a lithium iodide cell (schematic) (a) electrons are liberated at the lithium metal anode and re-enter the cell via the I2/P2PV cathode (b) lithium ion transport across the electrolyte via Li vacancies, to form Lil at the anode. The number of vacancies (Schottky defects) has been grossly exaggerated.

Fig. 9.7 Mechanism of lithium ion transport by vacancy motion in lithium iodide. Cell discharge is accompanied by the migration of lithium ion vacancies in the direction from cathode to anode. (By permission of John Wiley as Fig, 9,5)...

The cathodic reaction is the reduction of iodine to form lithium iodide at the carbon collector sites as lithium ions diffuse to the reaction site. The anode reaction is lithium ion formation and diffusion through the thin lithium iodide electrolyte layer. If the anode is cormgated and coated with PVP prior to adding the cathode fluid, the impedance of the cell is lower and remains at a low level until late in the discharge. The cell eventually fails because of high resistance, even though the drain rate is low. 

Lithium iodide is the electrolyte in a number of specialist batteries, especially in implanted cardiac pacemakers. In this battery the anode is made of lithium metal. A conducting polymer of iodine and poly-2-vinyl pyridine (P2VP) is employed as cathode because iodine itself is not a good enough electronic conductor (Fig. 2.3a). The cell is fabricated by placing the Li anode in contact with the polyvinyl pyridine-iodine polymer. The lithium, being a reactive metal, immediately combines with the iodine in the polymer to form a thin layer of lithium iodide, Lil, which acts as the electrolyte ... 

In order for the battery to function, the lithium iodide must be able to transfer ions. Lil adopts the sodium chloride structure, and there are no open channels for ions to use. In fact, the cell operation is sustained by the Schottky defect population in the... 

Lithium hydroxide, 15 134, 140-141 Lithium hypochlorite, 4 52 15 141 pool sanitizer, 26 175 Lithium iodide, 3 417 15 140 Lithium-iodine cells, 3 463-464 characteristics, 3 462t speciality for military and medical use, 3 430t... 

Li2S204 being the SEI component at the Li anode and the solid discharge product at the carbon cathode. The Li—SOCI2 and Li—SO2 systems have excellent operational characteristics in a temperature range from —40 to 60 °C (SOCI2) or 80 °C (SO2). Typical applications are military, security, transponder, and car electronics. Primary lithium cells have also various medical uses. The lithium—silver—vanadium oxide system finds application in heart defibrillators. The lithium—iodine system with a lithium iodide solid electrolyte is the preferred pacemaker cell. 

Lithium-iodine cells are produced simply by making direct contact between anode and cathode. On touching, a thin layer of lithium iodide is formed by direct reaction. As soon as the layer becomes complete, the reaction rate decreases sharply, since diffusiou of iodine through lithium iodide is very slow. Thus the cell may be written as... 

The enhancement in conductivity obtained by dispersing A1203 in the lithium iodide has permitted this composite electrolyte to be used in the fabrication of cells in the form of compressed pellets without the creation of prohibitive values of internal resistance at ambient temperatures. An example is given in Fig. 9.14 which shows a schematic cut-away view of the practical cell developed by P.R. Mallory Co (now Duracell International) in the 1970s. 

Lithium batteries are used in many portable consumer electronic devices and are also widely used in industry. The most common type of lithium cell used in consumer applications comprises metallic lithium as the anode and manganese dioxide as the cathode, with a Li salt such as Li perchlorate or Li tetrafluoroborate dissolved in an organic solvent. Lithium batteries find application in many long-life, critical devices such as cardiac pacemakers and other implantable electronic medical devices. These devices use special lithium-iodide batteries designed to last 15 years or more. Lithium batteries can be used in place of ordinary alkaline cells in many devices such as clocks and cameras. Although they are more expensive, lithium cells provide a much longer life, and thereby minimize battery replacement. 

From equation (10) it is evident that if the theory is correct the values of the potential, E, for a given cell should vary directly with the square of the number of revolutions per second, w2, or in other words E/n2 should be a constant. That this is substantially true is shown in Table II which gives the data for a cell containing molal lithium iodide and 0.01 molal iodine. 

The cells of the lithium-iodine system stand somewhat apart. In such cells, the oxidant is not elementary iodine as such, but it is complex with poly-2-vinylpyridine [CH2CH(C5H5N)] (P2VP). Its composition can be expressed as P2VP ml2. The content of iodine in the complex decreases under discharge, and solid lithium iodide is formed ... 

Solid lithium iodide is used in the cells of the lithium-iodine system. Its specific conductivity at the room temperature is several pS/cm. Such cells are characterized by very long-term discharge (years) with very low currents (tens of pA). 

The selective dehydrogenation of short-chain hydrocarbons can be achieved at higher temperatures. Ethane is dehydrogenated at 700 °C at a fuel cell current of 252mAcm" in the presence of oxygen to ethene with 10.6% conversion and 96.9% selectivity . Propane is converted in good yield to propene in a lithium iodide melt at 465 °C at 1-2 A between carbon electrodes and 12 V cell voltage . 

Webber A (1996) Nonaqueous cell having a lithium iodide-ether electrolyte. US Patent 5514491... 

A dry cell is not truly dry, because the electrolyte is an aqueous paste. Solid-state batteries have been developed, however. One of these is a lithium-iodine battery, a voltaic cell in which the anode is lithium metal and the cathode is an I2 complex. These solid-state electrodes are separated by a thin crystalline layer of lithium iodide (Figure 20.11). Current is carried through the crystal by diffusion of Li" ions. Although the cell has high resistance and therefore low current, the battery is very reliable and is used to power heart pacemakers. The battery is implanted within the patient s chest and lasts about ten years before it has to be replaced. 

The anode is lithium metal and the cathode is a complex of iodine, I2 the electrodes are separated by a thin crystalline layer of lithium iodide.The battery consists of two cells enclosed in a titanium shell. 

Lithium cells with solid electrolyte (e.g. lithium iodide). 

The first lithium/iodine cardiac pacemaker battery was implanted in 1972. This type of battery proved to be very successful in this field and for other applications, too. The special features of this solid state battery are explained with its technique, which is limited with its extremely high energy density and reliability, especially for low rate applications. This technique is based firstly on the electrode couple of lithium and iodine with its high energy content - the OCV of the lithium/iodine cell is 2.80 V -and secondly on the favorable fact that the product of the cell reaction, the lithium iodide (LiJ), forms very tight and continuous layers between the active material of the electrodes, which are acceptable ionic conductors with negligible electronic... 

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