Solid LiAsF

The recent example of the ab initio structure determination of the polymer electrolyte Poly (ethylene oxide)6 LiAsFe by Bruce et is a notable example of the complex structures that can be determined from powder diffraction on a pulsed neutron source. Polymer electrolytes consist of salts dissolved in solid high molecular weight polymers, and represent a unique class of solid coordination compounds. Their importance lies in their potential in the development of truly all-solid-state rechargeable batteries. The structure of the 6 1 complex is particularly important, as it is a region where the conductivity increases markedly. The structure of the complex is distinct from all known crystal structures of PEO salt complexes (see Figure 7). The Li-i- cations are arranged in rows, with each row located inside a cylindrical surface formed by two PEO chains, with the PEO chains adopting a previously unobserved conformation. Furthermore the anions are located outside the PEO cylinders and are not coordinated with the cations. 

FIGURE 10.7 EIS of a LiMn2O4 electrode in 1 M LiAsF /Cethylcnc carbonate + dimethyl carbonate) at 20°C. (From Sinha and Munichandraiah, 2008. J. Solid State Electrochem. 12, 1619-1627, with permission from Springer.)... 

Figure 12 PTIR spectra obtained from Li surfaces freshly prepared and stored in EC solutions (external reflectance, at a grazing angle, protected with KBr windows). (a,b) EC-PC 4 1 mixture (c,d) EC-LiAsF solution. Solid lines (a,c) 2 h of storage dashed lines (b,d) 2 days of storage [175]. (With copyrights from The Electrochemical Society Inc., 1998.)... 

Figure 10 Typical modeling of experimental results (Li electrode in PC-1.5 M LiAsF solution after 24 h) by equivalent circuit of five RC circuits in series. Both the Nyquist and the Bode plots are shown. Dashed line, experimental results. Solid line, calculated response. Reprinted with copyright from The Electrochemical Society Inc. (See [72].)...

Figure 23 XPS spectra measured from Li electrodes prepared and stored in solutions for 3 days (a) EC-DMC 1 1/ 1 M LiAsF,. (b) EC-DMC 1 1/ 1 M liPF,. (c) DN 1 M/ liCfSO CFjlj. Solid lines, before sputtering dashed lines, after removal of 30-50 A of surface layer. The relevant elements are marked in each spectmm. Reprinted with copyright from ACS. (See [104].)...

As lithium bromide appeared to initiate the reactions causing electrolyte instabilities, Honeywell investigated other lithium salts for use in reserve battery electrolytes and concluded that lithium hexafluoro-arsenate (LiAsFe) combined with acetonitrile and sulphur dioxide was a suitable electrolyte, which did not exhibit discoloration or deposition of solids during storage. Table 24.1 compares the performance of batteries made up using the lithium bromide- and lithium hexafluoroarsenate-based electrolytes. Clearly, the 0.5 molal lithium hexafluoroarsenate electrolyte is functionally equivalent or superior to the lithium bromide electrolyte. 

The ionic conductivity of lithium-based solid polymer films, prepared from PEO and lithium hexafluoarsenate (LiAsFe) with varying compositions of plasticizers like dibutyl sebacate (DBS) and ethylene carbonate (EC), was measured by the AC impedance method. The addition of DBS increased the ionic conductivity from 5.98 x 10 S/cm to 10 S/cm. 

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