Organic redox materials for high performance lithium batteries

The ever-growing global economy implies a steadily increasing demand for more portable energy sources, currently relying mostly on Li-ion technology. In this context, the market is continuously asking for improved performances from Li-ion batteries (LIBs). Furthermore, not only the consumer needs are driving the research toward higher standards but also the global energy demand growth, evermore pressing the need of a cleaner and more sustainable energy supply chain. Yet LIBs are well-optimized devices and going beyond what is the current state-of-the art in the battery field entails to explore new materials and components. The quest for better batteries has shed light on materials and technologies promising improved levels of sustainability, cost-effectiveness, power density and/or energy density. In that respect, significant efforts are devoted to new organic positive electrode materials that could supersede their inorganic counterparts at all levels mentioned beforehand. The goal of this thesis is to develop new concepts to allow a successful implementation of redox organics as positive electrode materials without any trade-off over their current inorganic counterparts. To that end, we explored different strategies based on: (i) the design of hybrid materials with near-ideal dispersion properties thanks to the covalent grafting of our nitroxide-bearing polymers on conductive carbon nanotubes, (ii) the design of a cross-hybrid structure merging the conducting properties of polyaniline with the high specific capacity of quinone redox moieties, (iii) the modulation of electrode potentials driven by changes of electrolyte composition to increase the battery voltage output.(SC - Sciences) -- UCL, 202

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

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. © The Royal Society of Chemistry 2015

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

Negative Redox Potential Shift in Fire-Retardant Electrolytes and Consequences for High-Energy Hybrid Batteries

Fire-retardant electrolyte chemistries have attracted great attention given their potential to solve the grand challenges of alkali-ion batteries: safety, use of metallic anodes, and anodic stability. Whereas extensive analysis and correlations are drawn to explain their unusual electrochemical behavior, one essential property, their effects on redox potentials of battery components (redox potential shift) pervasively lack a strict description and quantification. Here we show that the strong solvation of lithium cations by organic phosphates, the widely used flame-retardant constituents, induces a negative redox potential shift by as much as 500 mV. We demonstrate that the redox potential shift is characteristic of Li-cation (de)solvation processes whereas it is negligible for other processes. This has important consequences for high energy hybrid battery concepts such as high voltage dual-ion graphite or organic batteries. These findings also shine a different light on the enhanced anodic stability of these nonconventional battery electrolyte formulations

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

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)

Li+-solvent interactions in ternary EC-DEC-TMP electrolyte mixtures by NMR measurements

The great importance of Li-ion mobility and the electrode-electrolyte interface interactions for ensuring good performance and high reliability in Li-ion batteries has inspired, in the past few years, the development of a wide range of electrolyte formulations. Accordingly, probing the electrolyte solution structures is now considered pivotal to extend the performance limit of the current Li-ion batteries. However, comprehension of solution structure and ion transport behavior in Li-ion batteries is far from being fully understood. For the above reasons, the development of improved analytical techniques is highly required and NMR is one of the most promising analysis tool in this field. Herein, we report a NMR investigation of the structure and properties of LiPF6-salt solutions based on ternary (ethylene carbonate (EC), diethyl carbonate (DEC) and trimethylphosphate (TMP)) electrolyte solvent mixtures for lithium-ion battery applications. The approach consists of the use of the internally referenced diffusion-ordered spectroscopy (DOSY) method. Solvent coordination ratio, cation valence number as well as self-diffusion coefficients have been thus analyzed upon the different (EC+EDC+TMP) electrolyte formulations and compared with electrochemical measurements