Ceramic polymer electrolytes

Abstract In this chapter a brief review on solid polymeric electrolytes is given, followed by the discussion of challenges and requirements to fulfil in order to commerciahse them. Among various ways of polymeric electrolyte modification, composites with ceramic phases are discussed in detail here. Special attention is paid to electrolytes for lithium cells, based on polyethers. The main achievements, theories developed and precautions for future researchers willing to work in this area are discussed. 

Key words composite polymer electrolyte, lithium battery, all solid state battery, surface treatment, ceramic filler, polymer-in-ceramic composite. 

Ever since electrochemical cells became objects of interest not only to researchers but also to consumers, their development sped up a lot and forced significant changes in the materials and geometries used. The size, weight, resistance to mechanical and thermal shocks, flexibility of the operating conditions, price, lifetime, and safety to the user and the environment of cells (more commonly, but not very correctly, called batteries ), started to rule this business very quickly. Apart from optimisation of electrode materials, which is not discussed here, a lot of effort was devoted to the development of electrolyte systems, tailored to the speciflc electrochemical system. 

In most cases the third function of the electrolyte is not required (or very limited), therefore from the point of view of the cell mass balance, the electrolyte is considered as a dead mass which should be cut down to the indispensable minimum. Taking into account simple Zn-Mn02 cells, the change that took place between the first and commercial design is more than clear when looking at the geometry evolution which allowed the amount of the electrolyte to be decreased dramatically (Fig. 2.1). 

The advantages of using solid polymer electrolytes in commercial lithium cells (up-to-date systems of choice for mobile applications) could be numerous (Tarascon and Armand 2001). They could offer  

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Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Figure 1 shows the temperature variation of the ionic conductivities for several polymer-electrolyte systems. At room temperature they are typically 100 to 1000 times less than those exhibited by a liquid or the best ceramic- or glass-based electrolytes [6,8], Although higher conductivities are preferable, 100-fold or 1000-fold... 

Addition of both ion-conducting and inert ceramics enhances the conductivity of a polymer electrolyte. This increase is attributed to an increase in volume fraction of the amorphous phase [133-136]. No... 

The equivalent series resistance (ESR) and equivalent series inductance (ESL) of the output capacitor substantially control the output ripple. Use an output capacitor with low ESR and ESL. Surface mount Tantalums, surface mount polymer electrolytic and polymer electrolytic and polymer Tantalum, Sanyo OS-CON, or multilayer ceramic capacitors are recommended. Electrolytic capacitors are not... 

A polymer electrolyte with acceptable conductivity, mechanical properties and electrochemical stability has yet to be developed and commercialized on a large scale. The main issues which are still to be resolved for a completely successful operation of these materials are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70 °C. Croce et al. found an effective approach for reaching both of these goals by dispersing low particle size ceramic powders in the polymer electrolyte bulk. They claimed that this new nanocomposite polymer electrolytes had a very stable lithium electrode interface and an enhanced ionic conductivity at low temperature. combined with good mechanical properties. Fan et al. has also developed a new type of composite electrolyte by dispersing fumed silica into low to moderate molecular weight PEO. 

There are two classes of materials which may be used as electrolytes in all-solid-state cells polymer electrolytes, materials in which metal salts are dissolved in high molar mass coordinating macromolecules or are incorporated in a polymer gel, and ceramic crystalline or vitreous phases which have an electrical conductance wholly due to ionic motion within a lattice structure. The former were described in Chapter 7 in this... 

Figure 30 Schematic of the UHV/antechamber/transfer chamber system for electrochemical measurements involving solid polymer electrolytes. Insert A provides an exploded view of the HOPG(bp) sample holder and Li[C/R]/PE0(LiC104) stainless steel holder (SSH) arrangement attached to both magnetically coupled manipulators. Insert B shows in detail the assembled H0PG(bp)/PE0(LiC104) cell in the UHV chamber. MCM = magnetically coupled manipulator GV = gate valve N = nipple CN = ceramic nipple SSH = stainless steel holder TMP = turbomolecular pump. (From Ref. 6.)...

Polymer electrolytes have been shown to stabilize the lithium/electrolyte interface, yielding stable and low interface resistance, especially when ceramic additives such as y-LiA102 are used. Furthermore, the 7-LiA102 ceramic additive has been shown to stabilize the polymer amorphous phase and to slow down the recrystallization process [99-103]. Thus, the unique electrochemical performance of lithium metal can be applied in practical devices by substitution of the liquid electrolyte with a solid one whose conductivity and stability can be enhanced with ceramic additives. 

Table 1.3 Comparison of the three capacitor types, polymer foil, ceramic and electrolyte capacitor, with some examples of typical applications [263],...

Polymer foil capacitors Ceramic capacitors Electrolyte capacitors ... 

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