Julien Rolland

Hybrid supercapacitor-battery materials for fast electrochemical charge storage

High energy and high power electrochemical energy storage devices rely on different fundamental working principles - bulk vs. surface ion diffusion and electron conduction. Meeting both characteristics within a single or a pair of materials has been under intense investigations yet, severely hindered by intrinsic materials limitations. Here, we provide a solution to this issue and present an approach to design high energy and high power battery electrodes by hybridizing a nitroxide-polymer redox supercapacitor (PTMA) with a Li-ion battery material (LiFePO4). The PTMA constituent dominates the hybrid battery charge process and postpones the LiFePO4 voltage rise by virtue of its ultra-fast electrochemical response and higher working potential. We detail on a unique sequential charging mechanism in the hybrid electrode: PTMA undergoes oxidation to form high-potential redox species, which subsequently relax and charge the LiFePO4 by an internal charge transfer process. A rate capability equivalent to full battery recharge in less than 5 minutes is demonstrated. As a result of hybrids components synergy, enhanced power and energy density as well as superior cycling stability are obtained, otherwise difficult to achieve from separate constituents.

Tocol modified glycol chitosan for the oral delivery of poorly soluble drugs

The aim of this study was to develop tocol derivatives of chitosan able (i) to self-assemble in the gastrointestinal tract and (ii) to enhance the solubility of poorly soluble drugs. Among the derivatives synthesized, tocopherol succinate glycol chitosan (GC-TOS) conjugates spontaneously formed micelles in aqueous solution with a critical micelle concentration of 2 μg mL(-1). AFM and TEM analysis showed that spherical micelles were formed. The GC-TOS increased water solubility of 2 model class II drugs. GC-TOS loading efficiency was 2.4% (w/w) for ketoconazole and 0.14% (w/w) for itraconazole, respectively. GC-TOS was non-cytotoxic at concentrations up to 10 mg mL(-1). A 3.4-fold increase of the apparent permeation coefficient of ketoconazole across a Caco-2 cell monolayer was demonstrated. Tocol polymer conjugates may be promising vehicles for the oral delivery of poorly soluble drugs.

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.

Chemically anchored liquid-PEO based block copolymer electrolytes for solid-state lithium-ion batteries

Solid-state electrolytes are being considered the keystone element for the development of safer all-solid-state lithium-ion batteries. While poly(ethylene oxide) (PEO) solid-state polymer electrolytes are known to support a Li+ flux, satisfying conductivities are reached only above the melting point of the PEO crystallites (>65 °C) rendering PEO unpractical. Herein, by means of block-copolymer engineering, we design a mechanically clamped liquid-PEO electrolyte that combines the high ionic conductivity of a low molecular mass PEO while retaining the dimensional integrity of a solid material. Attractive ionic conductivities of about 0.01 mS cm−1 are attained at room temperature without compromising mechanical properties. The electrolyte shows a wide electrochemical stability window and help in building a stable interface with lithium metal. Competitive performances are attained when integrating the developed materials into operational/functional prototype batteries highlighting the provided potential.

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 an original fluorinated triethylene glycol methacrylate monomer and its radical copolymerisation with vinylidene fluoride. Its application as a gel polymer electrolyte for Li-ion batteries

The synthesis and characterisation of novel poly[VDF-g-oligo(EO)] graft copolymers (where VDF and EO stand for vinylidene fluoride and ethylene oxide, respectively) are presented. First, 2-trifluoromethyl oligo(EO) acrylate, MAFTEG, was prepared by esterification of triethylene glycol monomethyl ether (TEG) with 2-trifluoromethacrylic acid (MAF) catalyzed by methanesulfonic acid, in 50% yields. Then, various radical copolymerisations of such MAFTEG with VDF from different feeds (VDF ranging from 86 to 95 mol.%) led to random poly[VDF-co-MAFTEG] copolymers that bore oligo(OE) side-chains in satisfactory yields (67%). These original graft copolymers were characterised by 1H, 19F and 13C NMR spectroscopy. Their molar masses reached 7,000 g∙mol-1 and their thermal properties were investigated while their glass transition temperatures ranged between -31 and -19 °C. Their thermogravimetric analyses under air showed decomposition temperatures from 235 to 325 °C with 10 % weight loss (Td,10%). Gel polymer electrolytes were achieved at room temperature by blending ionic liquid electrolyte (RTIL), poly[VDF-g-oligo(EO)] graft copolymers, and silica nanoparticles, the ionic liquid being made of 1-propyl-1-methyl pyrrolidinium bis(fluorosulfonyl)imide (PyrFSI) dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). These novel copolymers are of potential interest as gel polymer electrolytes in lithium ion batteries, showing competitive ambient conductivities of 0.2 mS.cm-1 that increased up to 0.5 mS.cm-1 with the content of silica nanoparticles at 20 wt%. In addition, the electrolyte gel appeared to be electrochemically stable in a wide range of potentials varying from 1.5 V to 4 V vs. Li+/Li, compatible with 4 V class lithium ion batteries.

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.