Quinone Based Materials as Renewable High Energy Density Cathode Materials for Rechargeable Magnesium Batteries

Organic cathode materials are promising cathode materials for multivalent batteries. Among organic cathodes, anthraquinone (AQ) has already been applied to various metal‒organic systems. In this work, we compare electrochemical performance and redox potential of AQ with 1,4-naphthoquinone (NQ) and 1,4-benzoquinone (BQ), both of which offer significantly higher theoretical energy density than AQ and are tested in two different Mg electrolytes. In Mg(TFSI)2-2MgCl2 electrolyte, NQ and BQ exhibit 0.2 and 0.5 V higher potential than AQ, respectively. Furthermore, an upshift of potential for 200 mV in MgCl2-AlCl3 electrolyte versus Mg(TFSI)2-2MgCl2 was confirmed for all used organic compounds. While lower molecular weights of NQ and BQ increase their specific capacity, they also affect the solubility in used electrolytes. Increased solubility lowers long-term capacity retention, confirming the need for the synthesis of NQ and BQ based polymers. Finally, we examine the electrochemical mechanism through ex situ attenuated total reflectance infrared spectroscopy (ATR-IR) and comparison of ex situ cathode spectra with spectra of individual electrode components. For the first time, magnesium anthracene-9,10-bis(olate), a discharged form of AQ moiety, is synthesized, which allows us to confirm the electrochemical mechanism of AQ cathode in Mg battery system

Design of organic cathode material based on quinone and pyrazine motifs for rechargeable lithium and zinc batteries

Despite the rapid expansion of the organic cathode materials field, we still face a shortage of materials obtained through simple synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of a small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox-active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAh g$^{−1}$ with an average voltage of 2.63 V vs Li/Li$^+$ in the Li-ion battery. That corresponds to an energy density of 860 Wh kg$^{−1}$ on the OTQC material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82% after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in aqueous Zn−organic battery, reaching the specific capacity of 326 mAh g$^{−1}$ with an average voltage of 0.86 V vs Zn/Zn$^{2+}$. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading

Design of organic cathode material based on quinone and pyrazine motifs for rechargeable lithium and zinc batteries

Despite the rapid expansion of the organic cathode materials field, there is still a lack of materials obtained through facile synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAhg-1 with an average voltage of 2.63 V vs. Li/Li+ in the Li-ion battery. That corresponds to an energy density of 860 Whkg-1 on the material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82 % after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in Zn-organic battery using aqueous electrolyte, reaching the specific capacity of 326 mAhg-1 with an average voltage of 0.86 V vs. Zn/Zn2+. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading

Synthesis of Redox Polymer Nanoparticles Based on Poly(vinylcatechols) and Their Electroactivity

Organic materials are being investigated as an alternative to inorganic cathodes in lithium batteries with the promise of higher sustainability as well as increased theoretical capacity. Among organic materials, redox polymers based on poly(vinyl catechol) presenting the catechol/o-benzoquinone redox pair show high energy storage potential. Our main motivation in this work was to prepare polymer nanoparticles of different sizes and study their redox properties. As linear polymers are usually soluble/mechanically unstable, we prepared cross-linked polymers to maintain the size of the nanoparticles in different electrolytes. (Mini)emulsion polymerization of two dimethoxy monomers was used to synthesize spherical polymer nanoparticles cross-linked with divinylbenzene (DVB) where the size was controlled by changing the concentration of the surfactant. Deprotection yielded poly(4-vinyl catechol) and poly(3-vinyl catechol) redox active nanoparticles (RPNs) of sizes ranging between 40 and 330 nm as characterized by scanning electron microscopy. The electrochemical properties of the RPN were tested in aqueous- and acetonitrile-based electrolytes using cyclic voltammetry. First the effect of the nanoparticle size and the cross-linker content in the electrochemical properties was investigated. Particle size did not have a crucial effect on the electrochemistry and only the biggest 330 nm RPN showed slightly diminished electrochemical properties. The cross-linker had a negative effect on the maximum reduction current (iC) but improved cycling stability. Based on these results we decided to use the smallest 40 nm nanoparticles with the lowest (1% DVB) cross-linker content for further electrochemical testing. Both RPN isomers showed reversible behavior in aqueous acidic-, neutral-, as well as in acetonitrile-based electrolyte. Poly(4-vinyl catechol)-based RPN had slightly higher reduction potential at 0.45 V versus Ag/AgCl (0.1 M HClO4) compared to another isomer with 0.40 V versus Ag/AgCl. When switching from an acidic aqueous electrolyte to neutral, the redox potential was shifted 440-475 mV to lower values. Because of their high reduction potential and theoretical capacity at 394 mA h/g these synthetic RPNs show promising properties to be used as cathodes in a variety of batteries. However, exact capacity determination, long term cycling, testing in nonaqueous electrolytes, and redox flow batteries needs to be performed in the future.This work was financially supported by the European Research Council by Starting Grant Innovative Polymers for Energy Storage (iPes) 30625 and Slovenian research agency (ARRS): research project J2-8167 and public call MS-ERC-FS/2017-002. N.B. acknowledges the financial support obtained through the Post-Doctoral fellowship Juan de la Cierva-Incorporacion (IJCI-2016-28442), from the Ministry of Economy and Competitiveness of Spain. L.P. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no 797295