Tobias Janoschka

Powering up the Future: Radical Polymers for Battery Applications

Our societys dependency on portable electric energy, i.e., rechargeable batteries, which permit power consumption at any place and in any time, will eventually culminate in resource wars on limited commodities like lithium, cobalt, and rare earth metals. The substitution of conventional metals as means of electric charge storage by organic and polymeric materials, which may ultimately be derived from renewable resources, appears to be the only feasible way out. In this context, the novel class of organic radical batteries (ORBs) excelling in rate capability (i.e., charging speed) and cycling stability (>1000 cycles) sets new standards in battery research. This review examines stable nitroxide radical bearing polymers, their processing to battery systems, and their promising performance.

An aqueous, polymer-based redox-flow battery using non-corrosive, safe, and low-cost materials.

For renewable energy sources such as solar, wind, and hydroelectric to be effectively used in the grid of the future, flexible and scalable energy-storage solutions are necessary to mitigate output fluctuations. Redox-flow batteries (RFBs) were first built in the 1940s and are considered a promising large-scale energy-storage technology. A limited number of redox-active materials—mainly metal salts, corrosive halogens, and low-molar-mass organic compounds—have been investigated as active materials, and only a few membrane materials, such as Nafion, have been considered for RFBs. However, for systems that are intended for both domestic and large-scale use, safety and cost must be taken into account as well as energy density and capacity, particularly regarding long-term access to metal resources, which places limits on the lithium-ion-based and vanadium-based RFB development. Here we describe an affordable, safe, and scalable battery system, which uses organic polymers as the charge-storage material in combination with inexpensive dialysis membranes, which separate the anode and the cathode by the retention of the non-metallic, active (macro-molecular) species, and an aqueous sodium chloride solution as the electrolyte. This water- and polymer-based RFB has an energy density of 10 watt hours per litre, current densities of up to 100 milliamperes per square centimetre, and stable long-term cycling capability. The polymer-based RFB we present uses an environmentally benign sodium chloride solution and cheap, commercially available filter membranes instead of highly corrosive acid electrolytes and expensive membrane materials.

Polymer-Based Organic Batteries

The storage of electric energy is of ever growing importance for our modern, technology-based society, and novel battery systems are in the focus of research. The substitution of conventional metals as redox-active material by organic materials offers a promising alternative for the next generation of rechargeable batteries since these organic batteries are excelling in charging speed and cycling stability. This review provides a comprehensive overview of these systems and discusses the numerous classes of organic, polymer-based active materials as well as auxiliary components of the battery, like additives or electrolytes. Moreover, a definition of important cell characteristics and an introduction to selected characterization techniques is provided, completed by the discussion of potential socio-economic impacts.

Redox‐Flow Batteries: From Metals to Organic Redox‐Active Materials

Abstract Research on redox‐flow batteries (RFBs) is currently experiencing a significant upturn, stimulated by the growing need to store increasing quantities of sustainably generated electrical energy. RFBs are promising candidates for the creation of smart grids, particularly when combined with photovoltaics and wind farms. To achieve the goal of “green”, safe, and cost‐efficient energy storage, research has shifted from metal‐based materials to organic active materials in recent years. This Review presents an overview of various flow‐battery systems. Relevant studies concerning their history are discussed as well as their development over the last few years from the classical inorganic, to organic/inorganic, to RFBs with organic redox‐active cathode and anode materials. Available technologies are analyzed in terms of their technical, economic, and environmental aspects; the advantages and limitations of these systems are also discussed. Further technological challenges and prospective research possibilities are highlighted.

Synthesis and characterization of TEMPO- and viologen-polymers for water-based redox-flow batteries

Redox-flow batteries that employ redox-active polymers (pRFB) represent a novel energy storage technology requiring innovative materials. Polymers bearing a viologen unit (N,N′-dialkyl-4,4′-bipyridines) or a TEMPO radical are synthesized. Acrylamide, poly(ethyleneglycol) methyl acrylates, di(ethylene glycol) methacrylate and 2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride are studied as water-solubility-enhancing comonomers. The rheological and electrochemical properties of these polymers in aqueous solutions are evaluated, revealing poly(1-methyl-1′-(4-vinylbenzyl)-[4,4′-bipyridine]-1,1′-diium dichloride) (P2a) and poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl-co-2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride) (P4e) to be most suited as anode and cathode materials, respectively, for a pRFB.

Polymer/zinc hybrid-flow battery using block copolymer micelles featuring a TEMPO corona as catholyte

A well-defined block copolymer was applied in a semi-organic polymer hybrid-flow battery (pHFB). A 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) containing polymer was utilised as cathode active material. Micellar structures of the active material were achieved by utilising a diblock copolymer composed of a polar poly(TEMPO methacrylate) (PTMA) and an unpolar poly(styrene) (PS) block, which enables the formation of core-corona micelles in organic carbonates. The synthesised PTMA-b-PS was electrochemically investigated and subsequently utilised as catholyte in polymer/Zn pHFBs. The constructed flow batteries feature an excellent cycling stability of 1000 consecutive charge/discharge cycles with 95% retention of initial discharge capacity and a stable voltage range of 2 V. Further, the charging process leads to slight changes in the micellar structure combined with an increased solubility.

Polymers based on stable phenoxyl radicals for the use in organic radical batteries.

Polymers with pendant phenoxyl radicals are synthesized and the electrochemical properties are investigated in detail. The monomers are polymerized using ring-opening metathesis polymerization (ROMP) or free-radical polymerization methods. The monomers and polymers, respectively, are oxidized to the radical either before or after the polymerization. These phenoxyl radicals containing polymers reveal a reversible redox behavior at a potential of -0.6 V (vs Ag/AgCl). Such materials can be used as anode-active material in organic radical batteries (ORBs).

Poly(exTTF): A Novel Redox‐Active Polymer as Active Material for Li‐Organic Batteries

The first polymer bearing exTTF units intended for the use in electrical charge storage is presented. The polymer undergoes a redox reaction involving two electrons at -0.20 V vs Fc/Fc(+) and is applied as active cathode material in a Li-organic battery. The received coin cells feature a theoretical capacity of 132 mAh g(-1) , a cell potential of 3.5 V, and a lifetime exceeding more than 250 cycles.

PolyTCAQ in organic batteries: enhanced capacity at constant cell potential using two-electron-redox-reactions

The application of polymers bearing tetracyano-9,10-anthraquinonedimethane (TCAQ) units as electrode materials in organic batteries enables one narrow charge discharge plateau due to the one two-electron-redox-reaction of the TCAQ core. Li-organic batteries manufactured with this polymer display repeatable charge–discharge characteristics associated with a capacity of 156 mA h g−1 and a material activity of 97%.

Nanostructured organic radical cathodes from self-assembled nitroxide-containing block copolymer thin films

This contribution describes the formation of nanostructured thin film organic radical cathodes. First, the self-assembly of poly(styrene)-block-poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA-b-PS) diblock copolymers is detailed. In order to improve the nano-morphology of the immiscible PTMA and PS domains, the effect of thermal and solvent annealing is investigated. The formation of thin films with different morphologies such as cylindrical or lamellar nanostructures is observed depending on the processing conditions. The electrochemical properties of the nanostructured films are further investigated to assess the redox activity of the PTMA domains. Cyclic voltammetry of PTMA-b-PS diblock copolymers, either in dissolved or thin film supported configuration, confirms the reversible redox behavior of the nitroxide radical. Galvanostatic cycling of the thin film nanostructured cathodes reveals good capacity retention with fast charge/discharge response resulting from efficient charge and ion transfer as well as structural integrity. Such nanostructured organic radical cathodes provide opportunities for the fabrication of new generation nanostructured organic radical battery architectures.