The solid electrolytes MAg(4)I(5), where M may be potassium, rubidium, or ammonium, have an ionic conductivity of 0.2 (ohm cm)(-1) at 20 degrees C. Although pure CsAg(4)I(5) does not form, partial substitution of cesium into the M position was obtained. The high-conducting phases of KAg(4)I(5) and RbAg(4)I(5) may be quenched to low temperatures, where they transform to resistive phases at -136 degrees and -155 degrees C, respectively.

Doped vanadium pentoxides with a doping ratio M/V (M = Ag and Cu) ranging from 0.01 to 0.5 were synthesized. With the successful doping, the electronic conductivity of V2O5 was increased by two to three orders of magnitude. The electrochemical performance of the doped materials is very high. Up to 4 moles of lithium per mole of doped V2O5 were found to be reversibly intercalated. The composite cathodes containing the doped materials also showed very high intercalation rate performance. In addition, copper‐doped V2O5 cathodes showed excellent reversibility upon cycling with no capacity fading after more than 450 cycles. © 1999 The Electrochemical Society. All rights reserved.

Supercritical drying of V205 gels yields amorphous aerogels (ARG) that serve as reversible, high capacity hosts for lithium ion intercalation. We have found that ARG material consists of a highly interconnected solid network that has a surface area up to 450 m2/g and a specific pore volume of 2.3 cm3/g. The material hosts at least 4 Li per mole of V205 (ARG) as determined by both galvanostatic intermittent titration (GITT) and chemical lithiation (CL) techniques. The equilibrium voltage-composition curve is identical for both GITT and CL techniques as well. V205 (ARG) has a specific energy in excess of 1600 Wh/kg, the highest ever reported for any vanadium oxide host. * Electrochemical Society Student Member. * * Electrochemical Society Active Member.

Complexes of amorphous tetraglyme ͑G4͒ and lithium bis͑trifluoromethylsulfonyl͒imide ͑LiTFSI͒ or lithium bis͑perfluoroethyl-sulfonyl͒imide ͑LiBETI͒ were prepared as pol͑yethylene͒ oxide-type electrolytes. Addition of equimolar amounts of LiTFSI and tetraglyme results in a room temperature ionic liquid with the general formula ͓Li͑G4͔͒TFSI. Differential scanning calorimetry analysis of ͓Li͑G4͔͒TFSI reveals that it has a T g ϭ Ϫ61°C, and the complex remains amorphous over a wide temperature range ͑Ϫ100 to 200°C͒, and has a very low vapor pressure for tetraglyme at room temperature. The corresponding BETI complex, ͓Li͑G4͔͒BETI, crystallizes upon cooling and displays a T m ϭ 31°C. Room temperature conductivities ͑25°C͒ of ͓Li͑G4͔͒TFSI and ͓Li͑G4͔͒BETI were 1.13 and 0.63 mS/cm, respectively. Composite polymer electrolytes were prepared by addition of the complexes to polycations possessing TFSI or BETI anions. The composites afforded thin flexible membranes at polymer concentrations у50 mol % polymer with room temperature conductivities greater than 10 Ϫ4 S/cm. In general, increased concentrations of BETI anions in these materials resulted in increased mechanical stability but decreased ionic mobility. The complexes and composite polymer electrolytes displayed excellent anodic stability up to ϩ4.5 V ͑vs. Li ϩ /Li) and exhibited breakdown voltages уϩ5.5 V ͑vs. Li ϩ /Li) on stainless steel electrodes.The development of suitable lithium ion conducting polymer electrolytes is an important goal for use in solid-state lithium batteries with high cell voltages and energy densities. 1,2 The desired properties of these electrolytes include good mechanical strength, high ionic conductivity, and high lithium ion transference numbers. The most widely studied electrolyte system thus far has been the combination of a lithium salt with poly͑ethylene oxide͒ ͑PEO͒. The highest conductivities in this class of electrolytes has been reported for LiX-PEO systems of lithium bis͑trifluoromethylsulfonyl͒imide ͑LiTFSI͒ 3,4 or lithium bis͑perfluoroethylsulfonyl͒imide ͑LiBETI͒ 5 which display conductivities as high as 10 Ϫ4 S/cm at 50°C.Although the conduction mechanism of LiX-PEO systems is still being studied with intense interest, it is generally accepted that amorphous rather than crystalline regions account for the conductivity observed in the materials. 6 For example, the LiPF 6 -PEO system displays a conductivity near 10 Ϫ4 S/cm at 70°C, and falls dramatically to 10 Ϫ8 S/cm at room temperature. 7 This can be directly related to the semicrystalline nature of PEO which displays a melting temperature near 65°C. Although the LiTFSI-PEO system is less prone to crystallization and demonstrates much more favorable room temperature conductivities, it does display a crystalline eutectic as its favored thermodynamic state. 8 One approach to overcome the problem of low conductivity at temperatures below the melting point of the eutectic is to replace semicrystalline PEO with a purely amorphous complexing medium. Low molecular weight oligomers of PE...

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