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.

High-performance electrolytes are at the heart of magnesium battery development. Long-term stability along with the low potential difference between plating and stripping processes are needed to consider them for next-generation battery devices. Within this work, we perform an in-depth characterization of the novel Mg[Al(hfip) 4 ] 2 salt in different glyme-based electrolytes. Specific importance is given to the influence of water content and the role of additives in the electrolyte. Mg[Al(hfip) 4 ] 2 -based electrolytes exemplify high tolerance to water presence and the beneficial effect of additives under aggravated cycling conditions. Finally, electrolyte compatibility is tested with three different types of Mg cathodes, spanning different types of electrochemical mechanisms (Chevrel phase, organic cathode, sulfur). Benchmarking with an electrolyte containing a state-of-the-art Mg[B(hfip) 4 ] 2 salt exemplifies an improved performance of electrolytes comprising the Mg[Al(hfip) 4 ] 2 salt and establishes Mg[Al(hfip) 4 ] 2 as a new standard salt for the future Mg battery research.

Mg batteries are a promising energy storage system due to the high capacity of the Mg metal anode. However, until recently Mg battery practical application seemed very distant due to corrosive nature of Mg electrolytes and the lack of suitable cathode materials. In this work, we bridge this gap by combining novel chloride‐free Mg electrolyte, Mg perfluorinated pinacolato borate (MgFPB), with quinone based organic cathode. ATR‐IR spectroscopy and complementary energy dispersive X‐ray spectroscopy (EDS) of ex situ cathodes confirm reduction of carbonyl group during discharge an its preferred coordination with Mg2+ cations, although monovalent not fully dissociated MgFPB+cation pairs are detected as well. Mediocre capacity retention of PAQS/CNTs is improved through the use of phenanthrenequinone based polymer (PFQ/rGO). The study demonstrates the promising performance of organic compounds in chloride‐free electrolytes and points towards future steps on the path towards practical Mg metal organic batteries.