Anthraquinone‐Based Polymer as Cathode in Rechargeable Magnesium Batteries

Abstract

Mg batteries are a promising battery technology that could lead to safer and significantly less expensive non-aqueous batteries with energy densities comparable or even better than state-of-the-art Li-ion batteries. Although the first prototype Mg battery using stable Mo6S8 as cathode was introduced over fifteen years ago, major challenges remain to be solved. In particular, the design of high energy cathode materials and the development of non-corrosive electrolytes with high oxidative stability are issues that need to be tackled. Herein, we present a new, general, and robust approach towards achieving stable cycling of Mg batteries. The core of our approach is the use of stable polymer cathode and Mg powder anode coupled with non-nucleophilic electrolytes. Our systems exhibit an excellent rate capability and significant improvement in electrochemical stability.

Fervent Hype behind Magnesium Batteries: An Open Call to Synthetic Chemists—Electrolytes and Cathodes Needed

“…Thew ell-known electrochemical redox properties of quinones have also been evaluated within the context of Mg battery cathode chemistry.P an et al [110] studied the charge/ discharge properties of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) in electrolytes capable of reversible Mg electrochemistry,0 .5 m Mg(TFSI) 2 /2MgCl 2 in dimethoxyethane (DME) and 0.5 m Mg(TFSI) 2 in diglyme.D MBQ was chosen for evaluation based on its low solubility in many organic solvents and high theoretical capacity (319 mAh g À1 ). Initial discharge in the DME electrolyte showed ar elatively flat voltage plateau at 2.0 Vv s. Mg/Mg 2+ up to about 100 mAh g À1 ,a nd sloping discharge thereafter with at otal capacity at low discharge rate of 226 mAh g À1 .However, rapid capacity fade was observed with at otal capacity of only 74 mAh g À1 after 30 cycles.T he authors speculated that the charge cut-off voltage of 2.8 Vw as insufficient to fully recharge the DMBQ cathode material, and that even the limited solubility of DMBQ in the electrolyte was still sufficient to contribute to capacity loss.P erformance in the diglyme electrolyte was worse,w ith discharge voltages only around 0.5 Vand initial capacity of 100 mAh g À1 declining to 20 mAh g À1 after 30 cycles.F ormation of apassivating surface layer was also speculated as contributing to the low cell voltage in this electrolyte.P ossible strategies to combat the problems encountered with DMBQ include the use of quinone-based polymers and non-nucleophilic electrolytes, which was the approach taken by Bitenc et al [111] Poly(anthraquinoyl) sulfide (PAQS; theoretical capacity 225 mAh g À1 )w as used as the cathode material in this work, along with an electrolyte consisting of [Mg 2 Cl 3 ·6 THF] [HMDS-AlCl 3 ]i nT HF.T he initial discharge capacity was only about 100 mAh g À1 but did decline slower than the capacity of DMBQ ( % 90 mAh g À1 after 30 cycles and 60 mAh g À1 after 80 cycles). Thed ischarge voltage was primarily between 2.0 and 1.5 Vv s. Mg/Mg 2+ .S ubstitution of Mg powder for Mg sheet at the anode increased discharge potential by about 0.3-0.4 V, indicating that polarization of the Mg anode contributed to total cell voltage loss.E limination of AlCl 3 from the electrolyte by using an electrolyte consisting of 0.37 m MgCl 2 /0.15 m Mg(TFSI) 2 /THF/glyme did yield nearly theoretical first cycle capacity while maintaining good discharge rate capability,a lthough extended cycling performance was not reported when using this electrolyte.…”

First-Principle Insights Into Molecular Design for High-Voltage Organic Electrode Materials for Mg Based Batteries

“…Few multivalent organic electrode materials with sufficiently high voltage for a cathode were reported, that are, e.g., quinones such as anthraquinones providing voltages of ca. 2 V as Mg ion battery cathodes (Sano et al, 2012;Zhao-Karger et al, 2013;Bitenc et al, 2015Bitenc et al, , 2016Pan et al, 2016a,b). The low voltage is a key problem in multivalent batteries and is a direct consequence of multivalence: the average voltage V to achieve a given state of charge is…”

Recent Progress in Multivalent Metal (Mg, Zn, Ca, and Al) and Metal‐Ion Rechargeable Batteries with Organic Materials as Promising Electrodes

“…To overcome the dissolution behavior of carbonyl‐containing compounds from the aspect of molecular tuning, the common method is the polymerization of small carbonyl molecules to obtain polymers with some limited solubility . In particular, quinones and anhydrides in their polymer forms show significantly enhanced capacity storage and cycling stability as compared with their small‐molecule forms .…”