Electrical communication between the flavin adenine dinucleotlde redox centers of glucose oxidase and a conventional carbon paste electrode has been achieved by using electron-transfer relay systems based on polyslloxanes. Six materials for amperometric biosensors are described In which ferrocene and dlmethylferrocene electron relays are covalently attached to Insoluble slloxane polymers. Sensors containing these polymeric relay systems and glucose oxidase respond rapidly to glucose, with steady-state current responses achieved In less than 10 s. The response to glucose under N2 saturation shows apparent Michaells-Menten constants, *VPP, In the range 16-71 mM and limiting current densities, ymax, of 29-275 µ /cm2. The dependence of the sensor response on the nature of the slloxane polymer and the type of polymer-bound relay Is discussed.
The electrochemical stability of the boron anion receptor, tris͑pentafluorophenyl͒ borane ͑TPFPB͒, on a carbonaceous mesocarbon microbeads ͑MCMB͒ electrode and its compatibility with the passivated solid electrolyte interphase ͑SEI͒ layer on the carbon anode were investigated. Comparison of the irreversible capacity loss of the MCMB electrode during initial galvanostatic cycling using electrolyte with and without the TPFPB additive indicates excellent electrochemical stability of TPFPB on the carbonaceous electrode. Cyclic voltammetry studies show that the SEI layer on the surface of the carbon electrode can be formed through the decomposition of ethylene carbonate in the presence of TPFPB. Prolonged cycling test verifies the long-term stability of the SEI layer on carbon in the presence of the TPFPB additive. The SEI layer is not dissolved by TPFPB even after heat-treatment under conditions which dissolve LiF salt. This suggested a cross-linked structure for the SEI layer on carbon electrode. A Li-ion cell using an electrolyte containing TPFPB displays better cycling performance than a cell without TPFPB under the same conditions. © 2003 The Electrochemical Society. ͓DOI: 10.1149/1.1536475͔ All rights reserved. The low conductivity of nonaqueous electrolyte for lithium batteries is mainly due to ion pairing or low solubility of the lithium salts in organic solvents. Development of neutral ligands as additives is a very effective way to break down ion pairing and enhance the ionic conductivity.1-5 Anion coordination ligands are much more favorable than cation coordination ligands for a lithium battery electrolyte, because they increase both ionic conductivity and lithium transference number which are necessary to achieve high power density and good rechargeablity for lithium batteries.6 Anion receptors are a very active field of research with most of the work aimed at molecular recognition to mimic how ion-binding protons control ion transport in biological membranes. Most anion receptors are based either on positively charged sites, hydrogen bonding, or Lewis acid metal centers. None of these are suitable for use in nonaqueous electrolytes. A new family of boron-based anion complexing agents has been synthesized and reported by our group recently. These compounds are based on electron deficient borate or borane compounds with various fluorinated aryl or alkyl groups.7-10 Some of these boron anion receptors can dramatically promote the dissolution and conductivity of various lithium salts in organic solvents. Even LiF, which is normally insoluble in organic solvents, can be dissolved in several organic solvents with the assistance of these anion receptors. The additives increase the solubility of LiF from Ͻ10 Ϫ5 to Ͼ1.0 M and conductivities of ϳ10 Ϫ3 S/cm can be achieved in carbonate solvents. Most of these boron-based anion acceptors have a high solubility in conventional nonaqueous solvents. Several of these compounds have exceptional chemical, electrochemical, and thermal stability. Composite electrolytes mad...
Using in situ X-ray diffraction, the capacity fading mechanism of LiMn 2 O 4 under various conditions has been studied. The capacity fading can be monitored by the structural changes during cycling. At the beginning of cycling, the structural changes closely follow the charge-discharge curve: the main structure starts in cubic I, transfers to cubic II, and ends as cubic III during charge, and reverses the course during discharge. These phase transitions track the charging and discharging curves with small hysteresis. However, with an increased amount of capacity fading during cycling, the structural changes deviate from the chargedischarge curve: Bragg peaks representing cubic I and II remain present at the end of charge, when the whole cathode should have been transferred to cubic III. Similarly, the residues of cubic II and III were observed at the end of discharge. The amount of residues increases with increasing capacity fading by cycling at 55°C, overcharging to 5.2 V, or after multiple cycling at normal condition. Adding a tris͑pentafluorophenyl͒ borane ͑TPFPB͒ compound in electrolyte can reduce the residues and washing the cathode with solvent can partially restore the lost capacity in the subsequent cycling, showing the important role of electrolyte decomposition in capacity fading.
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