POLYMER ELECTROLYTE

Polymer electrolytes are the newest area of solid ionics for applications in electrochemical device such as batteries and electrochromic windows. Electrochromic windows are windows that can be darkened or lightened electronically. A small voltage applied to the windows will cause them to darken; reversing the voltage causes them to lighten. 

Two general types of polymer electrolytes have been investigated intensively:

1. Polymer salt-complexes

2. Polyelectrolytes

A polymer-salt complex consist of a coordinating polymer in which salt is dissolved. Both anion and cation can be mobile in this type. 

Figure 1. a polymer electrolyte containing a salt MX

Polyelectrolytes contain of charged groups, either cations or anions, covalently attached to the polymer, so only the

counter ion is mobile.

Figure 2. polyelectrolyte in which the anion is attached to the polymer

Polymer Salt Complexes

Poly(ethylene oxide) (PEO) has been the most intensively studied host polymer for polymer electrolytes. 

Figure 3. The structure of crystalline poly(ethylene oxide) showing the contents of one salt

The conductivity collected over the wide temperature range on amorphous polymer-salt complexes is more

accurately represented by a Vogel-Tamman-Fulcher (VTF) equation than a simple Arrhenius function as described

in equation (1).

       (1)

VTF equation can be derived on the assumption that the ions are transported by the semirandom motion of a 

short polymer segments. 

The polymer motions are:

- Crank-shaft torsional motion around C-C or C-O bonds

- C-C and C-H stretching vibrations

- The segmental motion could promote ION MOTION by making and breaking  the coordination sphere of the solvated ions and by providing space (free volume)  into which the ion may diffuse under the influence of the electrical field.

Figure 4. Scheme of ion motions in a polymer electrolyte

FORMATION OF POLYMER ELECTROLYTE

Salt crystal may be directly diffused in a polymer to produce a polymer-salt complex. Usually prepared in 

nonaqueous solutions of dried polymer and dry salt in a dry nitrogen atmospheres.

Analysis:

- XRD and Electron microscope

Structure:

The structures of crystalline polymer-salt complexes provide insight into the structure of the more conducting

amorphous materials.

Figure 5. The crystal structure of (PEO)3:NaI complex

There are some host polymers usually applied in polymer electrolyte, those are:

1. Poly propylene oxide, the structure is described in Figure 6.

Figure 6. Molecular structure of poly(propylene oxide)

2. Methoxy linked Poly(ethylene oxide). The structures is figured in Figure 7.

Figure 7. The molecular structure of Methoxy linked poly(ethylene oxide)

You may find the ppt file in this link

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