A Rechargeable Cell Based on a Conductive Polymer/Metal Alloy Composite Electrode

Abstract

A composite electrode composed of a conductive polymer and an alkali-metal alloy has been investigated as the negative electrode for a nonaqueous rechargeable cell. A sodium-alloy based composite electrode composed of Na3.7~Pb, poly(p-phenylene), and binder achieved a capacity of 234 mAh/g or 450 mAh/cm 3. This electrode also exhibited excellent cycle life and rate capability without dendrite formation. The composite electrode exhibited kinetic behavior similar to that of pure sodium metal. A balanced cell was constructed by combining the above sodium-ion-inserting composite negative electrode with a sodium-ion-inserting positive electrode, Na=CoO2, of approximately equal capacity. The cell exhibited excellent cycle life (>250 cycles). The semiempirical energy density of the NaxCoO2/composite electrode system is comparable to alternative lithium metal based cell such as TiS2/Li assuming that excess Li is needed in the latter case.One of the primary concerns in the development of secondary lithium batteries is the rechargeability of the Li electrode. Among the various approaches, the selection of particular combinations of salt and solvent (or mixed solvents) have previously seemed the most successful (1-2) in addressing the rechargeability problem. Recently, Jow et al. (3) presented a novel approach which utilizes the special attributes of conductive polymers to construct composite negative electrodes which offer excellent rechargeability. In these composite electrodes the conductive polymer provides a matrix which offers special electrical, electrochemical, and mechanical attributes. Conductive polymers function as mixed conductors which conduct both electrons and ions. Conductive polymers also offer reversible electroactivity over a wide potential range which depends on the polymer and the electrolyte employed (3-5). For polyacetylene (PA) in LiPFJ2-methyltetrahydrofuran (2-MTHF) solution, the lithium-doped polymer is stable and electrochemically active between 0.1 and 1.5V vs. Li/Li +. For sodium-doped polyphenylene (PPP) in NaPF6/dimethoxyethane (DME) solution, the electroactive range extends between 0 and 0.8V vs. Na/Na § These wide potential ranges encompass the range of electroactivity of most alkali-metal alloys.When conductive polymers with such attributes are combined with alkali-metal alloys, the resulting composite electrodes have good rate capability and cyclability because the polymer matrix can efficiently transport and exchange ions and electrons between current collector, electrolyte, and alloy. The long life and high rate capability largely derive from the unique mechanical characteristics of conductive polymers. They possess a degree of elasticity which allows the matrix to accommodate volume changes in the alloy, and they swell in the electrolyte to provide a matrix which offers a particularly high effective diffusivity for ions, ca. 10 6 cm2/s (6).All solid-state composite electrodes composed of a mixture of alloys have als0 been previously suggested as an alternative for the lithium...

Electrochemically Active Polymers for Rechargeable Batteries

“…Composite PPP−metal alloy electrodes have been prepared by mechanical blending of PPP powder, PE binder, and alkali−lead alloys and pressing into screens. ,− Formation cycles proved to be beneficial for all electrodes involving PPP powder of chemical origin. ,, …”

“…For the PPP−metal alloy composite electrodes, the electrode potential varies by about 0.5 V due to changes in alloy stoichiometry involving phase changes during charge and discharge. − Complete cells with PPP−alloy composite negatives and oxide positives exhibit a potential variation of distinctly more than 1 V with some rather pronounced steps.…”

“…222 Composite PPP-metal alloy electrodes have been prepared by mechanical blending of PPP powder, PE binder, and alkali-lead alloys and pressing into screens. 59,[223][224][225][226] Formation cycles proved to be beneficial for all electrodes involving PPP powder of chemical origin. 39,216,225 Early attempts at an electrochemical polymerization of benzene failed to give PPP films of good quality, 227 until Japanese workers added cupric chloride to the usual salt-organic solvent system.…”

Development of a novel isotype organic heterojunction diode consisting of poly{7-spiro(9-fluorenyl)cyclopentadithiophene} and poly(3-octylthiophene)

“…In recent years research impetus has been devoted in search of novel electroactive polymers with appropriate band gaps suitable for various applications like light emitting diodes, [1][2][3][4][5] electrochromic devices, [6][7][8] rechargeable batteries [9][10][11] and others. More recently much attention has been drawn towards polymeric semiconductor devices in view of their potential applications requiring low cost processing over large areas.…”

Conducting Polymers: Past, Present and Future…

“…Somewhat similar industrial prototype rechargeable batteries involving polypyrrole have also been announced [36,37]. Rechargeable, completely packaged batteries using a polyacetylene or polyparaphenylene/ alkali metal cathode have also been developed [38]. These have approximately twice the energy density of nickel/cadmium batteries.…”