4 research outputs found
Dihexyl-Substituted Poly(3,4-Propylenedioxythiophene) as a Dual Ionic and Electronic Conductive Cathode Binder for Lithium-Ion Batteries
The polymer binders used in most lithium-ion batteries (LIBs) serve only a structural role, but there are exciting opportunities to increase performance by using polymers with combined electronic and ionic conductivity. To this end, here we examine dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx₂) as an electrochemically stable π-conjugated polymer that becomes electrically conductive (up to 0.1 S cm⁻¹) upon electrochemical doping in the potential range of 3.2 to 4.5 V (vs Li/Li⁺). Because this family of polymers is easy to functionalize, can be effectively fabricated into electrodes, and shows mixed electronic and ionic conductivity, PProDOT-Hx₂ shows promise for replacing the insulating polyvinylidene fluoride (PVDF) commonly used in commercial LIBs. A combined experimental and theoretical study is presented here to establish the fundamental mixed ionic and electronic conductivity of PProDOT-Hx₂. Electrochemical kinetics and electron spin resonance are first used to verify that the polymer can be readily electrochemically doped and is chemically stable in a potential range of interest for most cathode materials. A novel impedance method is then used to directly follow the evolution of both the electronic and ionic conductivity as a function of potential. Both values increase with electrochemical doping and stay high across the potential range of interest. A combination of optical ellipsometry and grazing incidence wide angle X-ray scattering is used to characterize both solvent swelling and structural changes that occur during electrochemical doping. These experimental results are used to calibrate molecular dynamics simulations, which show improved ionic conductivity upon solvent swelling. Simulations further attribute the improved ionic conductivity of PProDOT-Hx₂ to its open morphology and the increased solvation is possible because of the oxygen-containing propylenedioxythiophene backbone. Finally, the performance of PProDOT-Hx₂ as a conductive binder for the well-known cathode LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ relative to PVDF is presented. PProDOT-Hx₂-based cells display a fivefold increase in capacity at high rates of discharge compared to PVDF-based electrodes at high rates and also show improved long-term cycling stability. The increased rate capability and cycling stability demonstrate the benefits of using binders such as PProDOT-Hx₂, which show good electronic and ionic conductivity, combined with electrochemical stability over the potential range for standard cathode operation
Simultaneous Measurement of Ionic and Electronic Conductivities of Conductive Polymers as a Function of Electrochemical Doping in Battery Electrolyte
We show that the ionic and electronic conductivity of a wide range of p-type and n-type conducting polymer thin films can be reliably measured as a function of electrochemical doping in relevant battery electrolytes by impedance spectroscopy on interdigitated electrodes by combining two separate electrode geometries. The results demonstrate the broad applicability of the methodology for gaining insights into the electrical conduction in polymers in relevant environments, particularly for batteries and other electrochemical device
DataSheet1_Electrochemical Studies of the Cycloaddition Activity of Bismuth(III) Acetylides Towards Organic Azides Under Copper(I)-Catalyzed Conditions.pdf
Time-dependent monitoring of the reactive intermediates provides valuable information about the mechanism of a synthetic transformation. However, the process frequently involves intermediates with short lifetimes that significantly challenge the accessibility of the desired kinetic data. We report in situ cyclic voltammetry (CV) and nuclear magnetic resonance (NMR) spectroscopy studies of the cycloaddition reaction of organobismuth(III) compounds with organic azides under the copper(I)-catalyzed conditions. A series of bismuth(III) acetylides carrying diphenyl sulfone scaffolds have been synthesized to study the underlying electronic and steric effects of the tethered moieties capable of transannular oxygen O···Bi interactions and para-functionality of the parent phenylacetylene backbones. While belonging to the family of copper-catalyzed azide-alkyne cycloaddition reactions, the reaction yielding 5-bismuth(III)-triazolide is the sole example of a complex catalytic transformation that features activity of bismuth(III) acetylides towards organic azides under copper(I)-catalyzed conditions. Stepwise continuous monitoring of the copper(I)/copper(0) redox activity of the copper(I) catalyst by cyclic voltammetry provided novel insights into the complex catalytic cycle of the bismuth(III)-triazolide formation. From CV-derived kinetic data, reaction rate parameters of the bismuth(III) acetylides coordination to the copper(I) catalyst (KA) and equilibrium concentration of the copper species [cat]eq. are compared with the overall 5-bismuth(III)-triazolide formation rate constant kobs obtained by 1H-NMR kinetic analysis.</p
Evaluating the Impact of Conjugation Break Spacer Incorporation in Poly(3,4-propylenedioxythiophene)-Based Cathode Binders for Lithium-Ion Batteries
The driving force behind the significant advancement of conductive polymer binders for lithium-ion batteries (LIBs) stems from the poor binding strength, limited mechanical properties, and absence of electronic conductivity of the commonly used nonconjugated polymer binder, poly(vinylidene fluoride) (PVDF). With a goal to induce stretchability and deformability to the otherwise brittle conjugated backbone, we report here dihexyl-substituted poly(3,4-propylenedioxythiophene)-based (PProDOT-Hx2-based) conjugated polymers wherein conjugation break spacers (CBS, T-X-T) of varying alkyl spacer lengths (X = 6, 8, and 10) and varying contents (5, 10, and 20%) have been randomly incorporated into the PProDOT backbone, generating a family of nine random PProDOT-CBS copolymers. Electrochemical characterization revealed that three out of the nine PProDOT-CBS polymers (5% T-6-T, 5% T-8-T, and 10% T-6-T) are electrochemically stable over long-term cycling of 100 cycles. The electronic conductivity of the PProDOT-CBS polymers is consistent with previous literature reports on CBS polymers, where a decline in charge carrier mobility is observed with an increase in CBS content and spacer length, although no significant difference in ionic conductivity in these polymers was observed. This is supported by GIWAXS studies indicating a decrease in lamellar peak intensity with increasing CBS content and spacer length. Mechanical properties of the three selected PProDOT-CBS polymers were investigated by using the established “film-on-water” technique and a novel “film-on-solvent” technique that we report here for the first time, where the solvent used is the same as employed in the battery electrolyte. Both techniques showcase a generally lower tensile modulus (E) and higher crack onset strain (COS) of the PProDOT-CBS polymers relative to fully conjugated PProDOT-Hx2. Furthermore, significant enhancement in mechanical properties is observed with the “film-on-solvent” method, suggesting that electrolyte-induced swelling has a plasticizing effect on the polymers, accounting for their increased stretchability and deformability. Finally, cell testing of the PProDOT-CBS polymers with NCA cathodes aligned well with the electrochemical and mechanical studies, where a higher crack onset strain was crucial for higher capacity retention during long-term cycling. On the contrary, rate capability measurements proved that higher electronic conductivity is favored over mechanical properties during high rates of discharge. This work illustrates that the strategic introduction of CBS units into conjugated polymer binders is a viable method for the generation of stretchable conductive polymer binders for emerging high-capacity electrodes in LIBs