Conducting Polymer-Inorganic Nanoparticle (CPIN) Nanoarrays for Battery Applications - Final Technical Report

Our objective was to develop new, self-assembling conducting polymer-inorganic nanoparticle nanoarrays (CPIN nanoarrays) comprised of nanoparticles of inorganic Li+ insertion compounds that are “wired” together with oligomeric chains of derivatives of polythiophene. Using these nanoarrays, we developed an understanding of the relationship between structure and electrochemical function for nanostructured materials. Such nanoarrays are expected to have extremely high specific energy and specific power for battery applications due to the unique structural characteristics that derive from the nanoarray. Under this award we developed several synthetic approaches to producing manganese dioxide nanoparticles (NPs). We also developed a layer-by-layer approach for immobilizing these NPs so they could be examined electrochemically. We also developed new synthetic procedures for encapsulating manganese dioxide nanoparticles within spheres of polyethylenedioxythiophene (PEDOT), a conducting polymer with excellent charge-discharge stability. These have a unique manganese dioxide core-PEDOT shell structure. We examined the structures of these systems using transmission electron microscopy, various scanning probe microscopies, and electrochemical measurements. Various technical reports have been submitted that describe the work, including conference presentations, publications and patent applications. These reports are available through http://www.osti.gov, the DOE Energy Link System

Redox Active Layer-by-Layer Structures containing MnO2 Nanoparticles

Nanoscale materials provide unique properties that will enable new technologies and enhance older ones. One area of intense activity in which nanoscale materials are being used is in the development of new functional materials for battery applications. This effort promises superior materials with properties that circumvent many of the problems associated with traditional battery materials. Previously we have worked on several approaches for using nanoscale materials for application as cathode materials in rechargeable Li batteries. Our recent work has focused on synthesizing MnO2 nanoparticles and using these in layer-by-layer (LbL) structures to probe the redox properties of the nanoparticles. We show that the aqueous colloidal nanoparticles produced by butanol reduction of tetramethylammonium permanganate can be trapped in thin films using a layer-by-layer deposition approach, and that these films are both redox active and exhibit kinetically facile electrochemical responses. We show cyclic voltammetry of MnO2 colloidal nanoparticles entrapped in a LbL thin film at an ITO electrode surface using poly(diallyldimethylammonium chloride) (PDDA). CV experiments demonstrate that Li+ insertion accompanies Mn(IV) reduction in LiClO4 supporting electrolytes, and that reduction is hindered in supporting electrolytes containing only tetrabutylammonium cations. We also show that electron propagation through multilayer films is facile, suggesting that electrons percolate through the films via electron exchange between nanoparticles

Use of Conducting Polymers for Electronic Communication with Redox Active Nanoparticles

Nanoscale materials provide unique properties that will enable new technologies and enhance older ones. One area of intense activity in which nanoscale materials are being used is in the development of new functional materials for battery applications.1-4 This effort promises superior materials with properties that circumvent many of the problems associated with traditional battery materials. Previously we have worked on several approaches for using nanoscale materials for application as cathode materials in rechargeable Li batteries.5-11 Our recent work has focused on synthesizing MnO2 nanoparticles and using conducting polymers to electronically address these particles in nanoparticle assemblies. This presentation will focus on those efforts. MnO2 nanoparticles that are encapsulated with poly(3,4-ethylenedioxythiophene) (PEDOT) are prepared using 3,4-ethylenedioxythiophene (EDOT) as a chemical reductant for permanganate anion. This non-aqueous preparation is based on a recent report of a similar method for preparation of PEDOT-encapsulated Au nanoparticles.12 We also describe the synthesis of MnO2 colloidal nanoparticles prepared using an aqueous route involving reduction of permanganate anion with butanol using a previously described route.13 We report the synthesis and characterization of the PEDOT material, and the aqueous colloidal material. We show that the aqueous colloidal nanoparticles can be trapped in thin films using a layer-by-layer deposition approach, and that these films are both redox active and exhibit kinetically facile electrochemical responses. This is illustrated in Figure 1 below, which shows cyclic voltammetry of MnO2 colloidal nanoparticles entrapped in a thin film at an ITO electrode surface using poly(diallyldimethylammonium chloride (PDDA). Finally, we report on the use of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) to characterize the oxidation state and coordination environment around Mn in these materials

Study of charge compensation during the redox process of self-doped polyaniline in aqueous media

One of the most important problems associated with use of polyaniline as a cathode material in rechargeable lithium batteries is related to energy density degradation due to the predomination of anion participation in the charge compensation process. This work describes the synthesis of a self-doped polyaniline, poly-(aniline-co-N-propanesulfonic acid-aniline), and evaluates its properties in aqueous acid solutions, with special attention to the increase of proton participation in the electroneutralization mechanism. The characterization was carried out using elemental analysis, FTIR and UV-vis spectroscopies. Electrochemical properties were investigated with the electrochemical quartz crystal microbalance and cyclic voltammetry. The results obtained show that proton participation was increased for the redox process of poly-(aniline-co- N-propanesulfonic-acid-aniline) in relation to polyaniline

Size-Dependent Underpotential Deposition of Copper on Palladium Nanoparticles

The underpotential deposition (UPD) of copper on palladium nanoparticles (NPs) with sizes in the range 1.6–98 nm is described. A dependence of the UPD shift on size of the nanoparticle is observed, with the UPD shift decreasing as the particle size decreases. This size dependence is consistent with the known dependence of UPD shift on work function difference between the substrate metal (Pd) and the depositing metal (Cu). The shift suggests the work function of the NPs decreases with decreasing size as expected (i.e., the smaller nanoparticles are more easily oxidized and therefore have lower work functions than larger NPs). For the smallest nanoparticles, the UPD shift does not follow the expected trend based solely on predictions of work function changes with size. On the basis of preliminary competitive anion adsorption experiments, it is speculated that strong chloride absorption on the smallest nanoparticles may be responsible for this deviation