R.J. Latham

The effect of plasticiser on zinc polymer electrolytes

Abstract The compounds Eu x ZrSe 1.95 have been prepared by reaction of the zirconium diselenide and europium metal using the liquid ammonia technique. The 1T structural type of pristine ZrSe 1.95 is apparently retained for x lying in the range 0–0.40 (+/− 0.02). For x>0.40, Eu amide is formed. No significant change in the cell parameter values related to size effects is observed as x increases. From magnetic susceptibility measurements together with Mossbauer spectroscopy, discrete Eu 2+ and Eu 3+ valence states are evidenced. The question whether these compounds are real intercalation compounds is discussed.

Novel solid state polymeric batteries

Abstract AC conductivity measurements have been performed on a number of polymeric electrolytes containing Mg, Ca, Sr and Zn perchlorates and Mg and Ca thiocyanates. The electrolytes were characterised using DSC. Results are reported of preliminary tests of cells incorporating anodes of the above metals.

EXAFS and related studies of mixed ion polymer electrolytes

Abstract EXAFS studies on polymer electrolyte systems have provided a unique means of addressing local structure-conductivity relationships. Most polymer electrolytes are anion as well as cation conductors, but it is often desirable to enhance the cation contribution. Conductivity can be enhanced by plasticizers or alternatively by incorporation of two inorganic salts, rather than one, in the polymer matrix. Results are described for the following: (i) PEO 12 : (0.5 ZnBr 2 ), (0.5 CaBr 2 ); (ii) PEO 15 : (0.5 ZnI 2 ), (0.5 CaI 2 ); (iii) (PEO 8 : ZnCl 2 ), (0.7 ethylene carbonate); (iv) PEO 12 : (0.5 ZnBr 2 ), (0.5 ZnI 2 ).

EXAFS and thermal studies on zinc polymeric electrolytes

Abstract(PEO)n:ZnX2 (X = I, Br) complexes were formed at room temperature with values ofn ranging from 8 to 30. Differential scanning calorimetry (DSC) results indicate that none of them contained any crystalline phases that can be associated with the formation of a complex (i.e. it can be assumed that all the salt is in the amorphous phase). EXAFS studies carried out on these samples suggest that the zinc cation is co-ordinated to two of the halide ions and, in addition, to 4 oxygen atoms whereX = I and 6 oxygen atoms whereX = Br. The DSC results confirm that the zinc cation is in an environment independent of overall stoichiometry, as the glass transition temperatures of the samples were found to be similar throughout. By comparing these with those of annealed samples (made by heating the above samples to 150°C and cooling to −80°C at 320°C min−1) it was found that the stoichiometry of the amorphous phase was roughly 6∶1 forX=I and 8∶1 forX = Br.

EXAFS studies of divalent polymeric electrolytes: An investigation of PEO4:CaI2 at room temperature

Abstract The first EXAFS study of a divalent polymeric electrolyte film is reported. The samples were prepared and handled under conditions which do not exclude water. The results indicate an absence of ion pairing within the first two neighbour shells of the cation, and the probable presence of a cation hydration shell. The Ca 2+ ions are surrounded by 10 oxygen atoms as nearest neighbours.

Structure-conductivity relationships in divalent polymer electrolytes

Abstract The potential influence of averaging caused by spherulite morphology on local structures deduced from EXAFS studies of crystallisable films is discussed. Evidence is presented to show that only high-melting, polymer-salt complexes interfere significantly with studies of the ionic environment within the amorphous conducting region. The possible modifications to the amorphous matrix that could result from the proximity of spherulites are considered. Results are presented for EXAFS studies of the local environment surrounding Zn in PEO n ·ZnBr 2 ( n =4, 8) prepared by three different drying procedures, at room temperature, -20°C and -70°C. Structural differences between amorphous and glassy forms were observed. The results suggest the presence of neutral ZnBr 2 entities.

Local structure studies of PEO-based NiBr2 electrolytes

Abstract The local atomic arrangements surrounding Ni(II) and Br(-I) in a high molecular weight PEO (mol.wt = 5 × 10 6 ) electrolyte of composition, NiBr 2 (PEO) 8 , were determined using K -edge EXAFS [Ni(II)] and AXS techniques [Br(-I)]. The results show that the first nearest neighbors of Ni(II) include, on average, four oxygens and two bromides, at distances from Ni(II) of 2.09 and 2.48 A, respectively. Around Br(-1) are, on average, one Ni(II) ion and four carbons at distances of 2.48 and 2.58 A, respectively. The two techniques yield consistent results and clearly show that ion pairing occurs in the electrolyte. The results indicate that Br(-I) ions are bonded more weakly in their local environments and thus likely to be more mobile than Ni(II) ions.

Self-discharge in solid state cells

Abstract The contribution of self discharge processes to solid state battery behaviour is often assessed using the Wagner polarisation technique, which yields a value for electronic conductivity. The validity of this procedure, is, in principle, suspect because of the different natures of the Wagner cell and the working battery. Results are presented for room temperature silver and copper solid state batteries, for which it appears that, in fact, results for Wagner cells can yield useful data pertinent to self discharge.

Room temperature magnesium-iodine solid state cells

Abstract Results are presented for solid state cells involving room temperature silver or copper solid electrolytes in conjunction with iodine cathodes and a variety of metal anodes. It is suggested that these electrolytes can act as conductors of divalent ions such as Ni2+ and Mg2+, in addition to the expected monovalent Ag+ or Cu+ species. The Mg cells produce above 1.2 and up to 120 μA can be drawn for sustained periods.

Mixed Divalent Polymer Electrolytes

Some features of interest for divalent polymer electrolytes are described. Attention is focussed on two contrasting roles for cations: providing chemical cross-links within the polymer matrix and offering a source of mobile charge carriers. The possible merits of using mixtures of two types of cation, one type for each role, is discussed. Alternative mixed salt systems containing two anions with a common cation are considered. Another class of mixed polymer electrolyte systems involving two divalent cations in conjunction with two monovalent anions is also examined in the context of illustrating competitive anion-cation interactions within the polymer matrix by EXAFS local structure techniques. Results for the systems PE0 15 :ZnI 2 /Mg(CIO 4 ) 2 , PEO 15 :ZnI 2 /Mg(CF 3 SO 3 ) 2 , PEO 15 :CaI 2 /ZnI 2 and PEO 15 :CaI 2 /CaBr 2 are discussed.