Alan Hooper

The fabrication and performance of all solid state polymer-based rechargeable lithium cells

Abstract All-solid-state lithium cells utilizing a polymeric electrolyte, (PEO) 9 LiF 3 CSO 3 , and a composite cathode based on V 6 O 13 have been continuously cycled at 120°–140°C. Modifications to the cathode microstructure and composition have led to improved performance in terms of achievable current density, material utilization and reproducibility. 100% active cathode utilization is achieved on the first discharge at 0.27 mA cm −2 and 50% utilization at 0.8 mA cm −2 , (140°C). Capacities of approximately 40% theoretical can be maintained over many tens of cycles at current densities up to 1 mA cm −2 . Scale up of cells to 100 cm 2 area has been carried out without loss of performance and series-connected stacks have been cycled successfully.

Linear segmented polyurethane electrolytes—II. conductivity and related properties

Abstract The a.c. and d.c. conductivities of salt-free and LiCF 3 SO 3 -doped linear segmented polyurethanes have been investigated. In all cases, the conductivity depends on the hard segment concentration and on the degree of phase separation exhibited by these materials. A qualitative understanding of the conductivity behaviour of these systems can be obtained from free volume considerations. Increasing the salt concentration in a range from 1.5 to 5 wt% LiCIO 4 produced a maximum in the conductivity at low LiCIO 4 concentrations. A comparison of the salt-doped polyurethanes with similarly doped polyethylene oxides indicated that in some cases comparable conductivities were obtained. A rechargeable cell containing salt-doped polyurethane gave a performance at 389 K similar to a cell utilizing polyethylene oxide electrolyte.

Thermal history and polymer electrolyte structure: Implications for solid-state battery design

Abstract Studies on PEO/LiCF 3 SO 3 polymeric electrolytes using polarising microscopy, SEM/EDX, DSC and complex plane analysis show that thin electrolyte films prepared by slow evaporation from CH 3 CN solution are spherulitic in nature. More than one type of spherulite is present across the composition range and each spherulite type contains both amorphous and crystalline regions. The structural behaviour on heating and cooling is discussed with particular reference to electrolyte films of overall composition PEO 20 :LiCF 3 SO 3 . For these high ratio triflate films, in contrast to similar PEO/LiClO 4 films, high melting salt-rich regions are unexpectedly present in conjunction with low melting, low salt spherulites. No evidence is found for the presence of pure PEO spherulites, but the low melting spherulites may have a crystalline skeleton of pure PEO. Evidence is presented for the dependence of conductivity on thermal history.

Polymer electrolytes based on a dimethylsiloxane-polyethylene oxide copolymer

Abstract Ionic conductivity data are reported for a lithium perchlorate-doped copolymer formed by reaction of dimethyldichlorosilane and poly(ethylene oxide) (PEO) to give a copolymer (DMS-PEO) and also the crosslinked gel formed by reaction of the copolymer (DMS-PEO) with trichloromethylsilane. The data on the copolymer complement an earlier study by Nakaska et al. and confirm that these materials can exhibit high room temperature ionic conductivities. A more efficient method of producing the copolymer is described in this paper. Crosslinking with trichloromethylsilane gives a product with reasonable mechanical properties and adequate ionic conductivity.