Bruno Ernould

Grafting of a redox polymer onto carbon nanotubes for high capacity battery materials

In this contribution we disclose an original strategy towards dense grafting of electrochemically active nitroxide-bearing polymer brushes on multi-walled carbon nanotubes (MWCNTs). Our strategy involves the surface initiated polymerization of 2,2,6,6-tetramethylpiperidin-4-yl methacrylate (TMPM) through atom transfer radical polymerization from the high-density initiator functionalized surface of MWCNTs and the oxidation of accordingly obtained PTMPM into poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA), leading to MWCNT-g-PTMA composites. Extended chemical and morphological analysis confirmed the compact core–shell morphology with a high active material mass loading of 60 wt%. The electrodes made out of these MWCNT-g-PTMA composites display good cycling stability (87% of capacity retention after 200 cycles), good rate capabilities and an excellent specific capacity (85% of the theoretical capacity). The success of this strategy offers new opportunities to overcome the issue of PTMA solubilization through an electrolyte and minimal utilization of conductive carbon species.

Exploring the potential of polymer battery cathodes with electrically conductive molecular backbone

Organic redox materials have the potential to radically shift the battery technology landscape. Here, the chemical synthesis of poly(2,5-dihydroxyaniline) with intrinsic electrical conduction and a theoretical energy storage capacity of 443 mA h g−1 is detailed for the first time. The genuine intramolecular cross-hybridization of quinone redox and polyaniline conductor moieties leads to a subtle interplay between redox stability and the lithiation capacity with the underlying processes being discussed. Superior to the conventional electrode materials performances are expected upon further optimization of this novel class of organic redox materials with ion and electron conduction for energy storage.

Melt-polymerization of TEMPO methacrylates with nano carbons enables superior battery materials.

A solvent-free, melt polymerization process of a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) precursor for rechargeable organic radical batteries is proposed. In situ carbon incorporation in the melted monomer phase yields a nanoscale homogenous polymer composite. Superior battery performances including higher power and cycling stability are attained by using the melt-polymerization method.

Synthesis of polymer precursors of electroactive materials by SET-LRP

The synthesis of electroactive polymer precursors by single electron transfer-living radical polymerisation (SET-LRP) is demonstrated here. Standard SET-LRP conditions are employed for the controlled polymerisation of 2,2,6,6-tetramethylpiperidin-4-yl methacrylate (TMPM). The controlled behaviour of the polymerisation under these conditions is demonstrated by kinetic experiments. Moreover, the synthesis of functional block copolymers is investigated with 3-azidopropyl methacrylate (AzPMA). The TMPM containing (co)polymers are oxidised to produce electroactive poly(TEMPO methacrylate) (PTMA). The redox behaviour of the PTMA was furthermore evidenced by cyclic voltamperometry. These polymers are promising in the frame of organic radical batteries.

A one-pot two-step efficient metal-free process for the generation of PEO-b-PCL-b-PLA amphiphilic triblock copolymers

In an effort to reduce hazardous chemicals, a one-pot two-step process with active bases and inactive salts was developed for the synthesis of high molar mass PEO-block-PCL-block-P(L- or D,L-LA) amphiphilic triblock copolymers. A series of poly(e-caprolactone) (PCL)/poly(L- or D,L-lactide) (P(L- or D,L-LA)) di- and triblock copolymers have been prepared in bulk from metal-free catalytic systems and starting from either 1-pyrenemethanol or poly(ethylene oxide) (PEO) macroinitiator. The controlled generation of such structures was obtained after screening and comparing a wide variety of organic activators. Narrower dispersity characterizing each sample prepared from the PEO macroinitiator were elucidated by theoretical modeling. Finally, the ability of those triblock copolymers to self-associate in water was studied by dynamic light scattering and compared to PEO-b-P(CL-co-LA) copolymers.

Electroactive polymer/carbon nanotube hybrid materials for energy storage synthesized via a “grafting to” approach

This paper describes the synthesis and characterization of a new hybrid material based on poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) for lithium battery applications. Our strategy relies on the anchoring of nitroxide-embedding polymer chains onto multi-walled carbon nanotubes (MWCNTs). The resulting hybrid material (MWCNT-g-PTMA) not only prevents the solubilization of the PTMA active material but also benefits from its structural design aspects. The MWCNT-g-PTMA structure confers high performances thanks to the precise distribution of the PTMA redox material with respect to the MWCNT conductive network, as confirmed by molecular modeling simulations of the polymer/MWCNT interface. Physicochemical characterizations are evidence of the success of MWCNT-g-PTMA synthesis with a polymer loading up to 30 wt%. Electrochemical analysis shows the potential of MWCNT-g-PTMA as a battery material, with a capacity reaching 85% of the theoretical value, a good cyclability (retention > 80% after 150 cycles) and excellent power performances (capacity at 60C exceeding 65% of the nominal value).

One-pot synthesis of electro-active polymer gels via Cu(0)-mediated radical polymerization and click chemistry

Recently, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) has attracted intensive attention for energy storage applications. Organic radical batteries built with this polymer display high power performance. However, the solubility of PTMA in commercial electrolytes shortens the lifespan and the overall performance of the battery. To circumvent this issue, we propose to immobilize PTMA in a three-dimensional network. Indeed, an electrolyte swollen network (gel) enables a good ionic diffusion and brings good mechanical properties to the cathodic material. Here we report on the synthesis of PTMA gels by a combination of Cu(0)-mediated reversible-deactivation radical polymerization and copper-catalyzed azide–alkyne cycloaddition (CuAAC). The structure of the accordingly obtained gels is characterized by NMR, SEC and FTIR and the mechanical properties of these materials are studied by rheology. Finally, their electrochemical performances are studied in the context of organic radical batteries.

Polymeric Janus nanoparticles templated by block copolymer thin films

We report a novel approach to synthesize well-defined polymeric Janus nanoparticles by combining the self-assembly of block copolymers in thin films and surface modification by polymer grafting.

Mechanochemical Synthesis of PEDOT:PSS Hydrogels for Aqueous Formulation of Li-Ion Battery Electrodes

Water-soluble binders can enable greener and cost-effective Li-ion battery manufacturing by eliminating the standard fluorine-based formulations and associated organic solvents. The issue with water-based dispersions, however, remains the difficulty in stabilizing them, requiring additional processing complexity. Herein, we show that mechanochemical conversion of a regular poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) water-based dispersion produces a hydrogel that meets all the requirements as binder for lithium-ion battery electrode manufacture. We particularly highlight the suitable slurry rheology, improved adhesion, intrinsic electrical conductivity, large potential stability window and limited corrosion of metal current collectors and active electrode materials, compared to standard binder or regular PEDOT:PSS solution-based processing. When incorporating the active materials, conductive carbon and additives with PEDOT:PSS, the mechanochemical processing induces simultaneous binder gelation and fine mixing of the components. The formed slurries are stable, show no phase segregation when stored for months, and produce highly uniform thin (25 μm) to very thick (500 μm) films in a single coating step, with no material segregation even upon slow drying. In conjunction with PEDOT:PSS hydrogels, technologically relevant materials including silicon, tin, and graphite negative electrodes as well as LiCoO2, LiMn2O4, LiFePO4, and carbon-sulfur positive electrodes show superior cycling stability and power-rate performances compared to standard binder formulation, while significantly simplifying the aqueous-based electrode assembly.

On the improved electrochemistry of hybrid conducting-redox polymer electrodes

The electrochemistry of poly(2,5-dihydroxyaniline) (PDHA), a novel hybrid molecular configuration with redox active sites and electrical charge conduction along the polymer chain, has been recently reported. The theoretical capacity of this material is estimated at 443 mAh g−1, with high power performances being proposed given the intrinsic electrical conductivity. However, the initial results were below the expectations: only half the theoretical capacity attained, poor cycling stability and modest power behavior calling for further investigations on improving these performances. Herein we detail the optimized chemical synthesis and electrode formulation for poly(2,5-dihydroxyaniline) resulting in improved cycling stability, power performances and defined electrochemical response. We also detail the alternative electrochemical synthesis and activation route for PDHA and compare the results with the chemical approach.