Conducting polymers, such as polyacetylene, polyaniline, and polypyrrole (PPy), have been studied as electrode materials for rechargeable batteries because they are electrochemically active and permit penetration of the electrolyte into the polymer mass. These polymers can be charged and discharged by a redox reaction involving lithium ions or counter anions of the electrolyte.[ /3dn + 1 pair of a first-row transition element. The operating voltage of the lithium-ion rechargeable battery should then reflect the energy level of the redox couple over the capacity range of the attached couple, which is expected to flatten the charge-discharge curves over this capacity range and add this capacity to that of the polymer.As an example of the chemical bonding of a redox couple to the polymer, we have covalently anchored ferrocene groups to the PPy backbone. Previous work on ferrocene tethered to PPy was mostly focused on membrane materials. [3] In this study, [(ferrocenyl) amidopropyl]pyrrole is used in conjunction with pure pyrrole to make the copolymer chains (Fig. 1).To examine the physical binding of redox couples to the polymer, we have incorporated the oxide LiFePO 4 into PPy; this oxide exhibits a flat V OC value of 3.4 V versus Li + /Li 0 and has a theoretical specific capacity of 170 mA h g -1 .[4] Although LiFePO 4 is inexpensive, thermally safe, and environmentally friendly, it is plagued by a low conductivity because of a subtle first-order phase change that distinguishes it from FePO 4 .[4]This phase change is responsible for the desirable flat V OC behavior, but has made it difficult to realize the theoretical capacity, particularly at high charge-discharge rates. Previous work has shown that the conductivity problems can be somewhat alleviated by a partial surface coating of carbon on the LiFePO 4 particles. [5] By physically incorporating fine carbon-coated LiFePO 4 particles into PPy, we have fabricated a cathode that is sufficiently porous to allow good penetration of the electrolyte to the surfaces of the oxide particles; the conducting polymer eliminates the need for carbon-black and polymer binder additives while providing additional capacity. In these proofof-concept experiments, no attempts have been made to optimize the polymer/oxide ratio of the composite cathodes. PPy/ferrocene polymer films with a uniform thickness have been electrodeposited onto a stainless-steel mesh (Fig. 2a). These films show an uneven surface morphology, which is typical of nucleation events, causing uneven current distribution. COMMUNICATION 848

No carbon added: Using the intrinsic oxidative power of LiFePO4/FePO4 combined with the reinsertion of lithium ions, the formation of the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) at the solid surface is demonstrated (see picture). The resulting composites have very promising electrochemical properties in rechargeable lithium batteries; in particular, they allow for the elimination of carbon additives.

Conducting polymers have been widely explored as coating materials for metal electrodes to improve neural signal recording and stimulation because of their mixed electronic–ionic conduction and biocompatibility. In particular, the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) is one of the best candidates for biomedical applications due to its high conductivity and good electrochemical stability. Coating metal electrodes with PEDOT has shown to enhance the electrode’s performance by decreasing the impedance and increasing the charge storage capacity. However, PEDOT-coated metal electrodes often have issues with delamination and stability, resulting in decreased device performance and lifetime. In this work, we were able to electropolymerize PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability. Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile, and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization, and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking, and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in rats and stimulated daily, for 7 and 15 days. The electrochemical properties monitored in vivo demonstrated that the stimulation procedure for both coated and uncoated electrodes decreased the impedance.

No abstract

A cathode material (see figure) is shown to give a performance and cycle life comparable to that obtained with the LiCoO2 cathode now used in cellular phones and laptop computers. These performance features have been accomplished without the use of the expensive and toxic element cobalt and without compromising the volume energy density desired for hand‐held devices.