Polyacetylene and Polyphenylene as Anode Materials for Nonaqueous Secondary Batteries

Abstract

The conjugated polymers polyacetylene (PA) and poly(p-phenylene) (PPP) have been examined for their possible use as negative electrode materials in nonaqueous secondary batteries. Cathodically stable electrolytes have been identified which allow high reduction levels for these polymers, and charge-storage capacities of 0.34 Ah/g for PA and 0.15 Ah/g for PPP have been demonstrated. Structural evolution of these polymers during cation insertion and extraction has been shown to have a significant influence on their electrochemical behavior. Several new stoichiometric phases have been identified.Polyacetylene (PA) (1) and poly(p-phenylene) (PPP) (2, 3) are crystalline conjugated polymers which can be either partially oxidized or reduced electrochemically. This process results in the formation of a highly conducting complex between the reduced or oxidized polymer and the appropriate counterion from the electrolyte. The electrochemical reaction which occurs in a cell containing PA or PPP electrodes involves the removal or addition of electrons through the external circuit and the insertion of ions from the electrolyte into the polymer lattice.Polyacetylene (1), polyphenylene (2, 3), and other conjugated polymers have been considered for application to nonaqueous-electrolyte secondary batteries, where they may function as either anode or cathode. Recently, the prospects for a particular cell employing polyacetylene as a cathode have been reviewed (4). In this paper, we will discuss the characteristics of polyacetylene and polyphenylene as they relate to the potential use of these polymers as anodes. In this case, we will only be concerned with partially reduced polymers for which the ioninsertion reaction may be represented by-xy e where P denotes the polymer compositional repeat unit, C ~ the inserted cation, y the fractional charge per repeat unit (frequently called the doping level), and x the degree of polymerization. In this paper, P denotes --CH--for PA and --C6H4--for PPP. Two of the most important considerations relating to use in batteries concern the charge storage capacity (maximum value of y) and the operating voltage of the polymer. To date, there has been a discrepancy in the reported values of y obtainable with Li + for polyacetylene by chemical means (5) (y = 0.3) and by electrochemical means (6) (y = 0.08). We have been able to resolve this discrepancy by performing electrochemical reductions in more cathodically stable electrolytes.Having found a stable electrochemical system, we have been able to study the intrinsic properties of polyacetylene and polyphenylene at varying degrees of reduction. ExperimentalAs we will detail in the following sections, we have found that a variety of organoborate salts offer superior stability to the reduced polymers. Some of these salts, lithium tetraphenyl borate (LiBPh4), lithium tetrabutyl borate (LiBBu4), and sodium tetraethyl borate (NaBEt4), were purchased from Atfa Products. Others, which included lithium tetramethyl borate (LiBMe4) and potassium tributyl(N-pyrro...

Electrochemical Intercalation of Lithium Ions into Polyparaphenylene in LiClO4-Carbonates Electrolytes

“…The values are similar to those previously reported for intercalation of Li> into PPP in liquid electrolytes such as lithium tetraphenylborate/ tetrahydrofuran (THF) (9).…”

Aromatic porous-honeycomb electrodes for a sodium-organic energy storage device

“…5). Another even more effective approach to improving affordability is to replace the current metal-based electrodes with organic materials [19][20][21][22][23][24][25][26][27] that are more abundant in nature. Since the advent of conductive polymers 28 and reversible redox polymers 22 , a large number of p-, n-and bipolar organic electrodes have been investigated for energy storage devices due to their low-cost and possible applications in flexible plastic batteries 21 .…”

“…Since the advent of conductive polymers 28 and reversible redox polymers 22 , a large number of p-, n-and bipolar organic electrodes have been investigated for energy storage devices due to their low-cost and possible applications in flexible plastic batteries 21 . Although there is a long history of research in sodium-based energy storage devices, there have been only a few reports of organic materials applied to rechargeable sodium batteries, for example, polyparaphenylene and sodium terephthalate 23,24,27 , and often they are only suitable as the anode. Finding a new, suitable group of organic materials for use as cathodes in sodium batteries could stimulate the development of sodium-based energy storage devices and meet the requirement of next-generation batteries, namely high-specific energy and power, and most importantly, affordability.…”

Perspectives on Electrochemical Insertion of Lithium in Carbon Nanotubes

“…With regard to the change in resistance, as occurred during the doping and dedoping processes, use of an electrolyte that is known to not to interfere-1M LiPF 6 in THF-helped to decisively substantiate charge transfer processes between Li and C. 11 Here, a nearly 20-fold resistivity decrease was observed upon doping.…”