Conductors using lithium ions

A second type of soHd ionic conductors based around polyether compounds such as poly(ethylene oxide) [25322-68-3] (PEO) has been discovered (24) and characterized. These materials foUow equations 23—31 as opposed to the electronically conducting polyacetylene [26571-64-2] and polyaniline type materials. The polyethers can complex and stabilize lithium ions in organic media. They also dissolve salts such as LiClO to produce conducting soHd solutions. The use of these materials in rechargeable lithium batteries has been proposed (25). 

In practice, for a ternary system, the decomposition voltage of the solid electrolyte may be readily measured with the help of a galvanic cell which makes use of the solid electrolyte under investigation and the adjacent equilibrium phase in the phase diagram as an electrode. A convenient technique is the formation of these phases electrochemically by decomposition of the electrolyte. The sample is polarized between a reversible electrode and an inert electrode such as Pt or Mo in the case of a lithium ion conductor, in the same direction as in polarization experiments. The... 

Instrumentation. Traditional methods of alpha and beta spectrometry instrumentation have changed little over the past decade. Alpha spectrometric methods typically rely on semi-conductor or lithium-drifted silicon detectors (Si(Li)), or more historically gridded ion chambers, and these detection systems are still widely used in various types of uranium-series nuclide measurement for health, environmental, and... 

For using lithium batteries (which generally have high energy densities) under extreme conditions, more durable and better conducting electrolytes are necessary. Salt-in-polymer electrolytes discovered by Angell et al. (1993) seem to provide the answer. Polypropylene oxide or polyethylene oxide is dissolved in low melting point mixtures of lithium salts to obtain rubbery materials which are excellent lithium-ion conductors at ambient temperatures. 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

The solid state synthesis process has also been used to study many other variations of doped lithium titanium phosphate solid ionic conductors. The ionic conductivities and compositions of the most promising lithium-ion ceramic electrolytes are shown in Table 26.2. 

Lithium carbonate can be used more directly as the auxiliary electrode with a lithium ion conductor, since the in situ formation of another carbonate phase is not required. Lithium ion conductors used with Li2CO3 include LISICON [163] and other Li3PO4-based electrolytes [164—173]. As with sodium ion conductors, Li2CO3-containing carbonates are used with lithium ion conductors [174, 175], The outputs of some examples of these lithium ion-conducting electrolyte-based sensors are shown in Figure 13.11 [163, 172-174]. 

The last few years have witnessed a high level of activity pertaining to the research and development of all-solid, thin-film polymer electrolyte batteries most of these use lithium as the active anode material, polymer-based matrices as solid electrolytes, and insertion compounds as active cathode materials. High-performance prototypes of such batteries stand currently under research, whose trends are expected to include the development of amorphous polymers with very low glass-transition temperatures, mixed polymer electrolytes, and fast-ion conductors in which the cationic transport number approaches unity. 

Initial measurements carried out on PEO-alkali metal salt complexes indicated that the observed conductivities were mostly ionic with little contribution from electrons. It should be noted that the ideal electrolyte for lithium rechargeable batteries is a purely ionic conductor and, furthermore, should only conduct lithium ions. Contributions to the conductivity from electrons reduces the battery performance and causes self-discharge on storage. Salts with large bulky anions are used in order to reduce ion mobility, since contributions to the conductivity from anions produces a concentration gradient that adds an additional component to the resistance of the electrolyte. 

The activation energy AU has been calculated for lithium fast ion conductors using this formalism , and a modified form of this equation was used by Colomban Lucazeau in a study of in-plane cation translatory modes in P-alumina . 

The development of organic or inorganic lithium-ion conductor such as lithium super-ion conducting glass (LISICON). lithium iodide (Lit), solid polymer electrolytes(SPE) were activated with progress of a lithium battery. In these electrolytes, the technology of solid electrolyte is useful to improve the performance of batteries. 

Laminated ECDs using poly-AMPS electrolytes and WO3 glasses have been effectively realized [33]. These ECDs are efficient and simple to use since the polymer electrolyte is an easily handled proton conductor which, in addition to practicality, assures faster kinetics (protons are more mobile than lithium ions) and thus short response times. 

Polymer electrolytes (e.g., poly(ethylene oxide), poly(propylene oxide)) have attracted considerable attention for batteries in recent years. These polymers form complexes with a variety of alkali metal salts to produce ionic conductors that serve as solid electrolytes. Its use in batteries is still limited due to poor electrode/ electrolyte interface and poor room temperature ionic conductivity. Due to its rigid structure it can also serve as the separator. Polymer electrolytes are discussed briefly in the section Separators for Lithium-Ion Batteries. 

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