Bio-Based Polyhydroxyanthraquinones as High-Voltage Organic Electrode Materials for Batteries

Organic materials have gained much attention as sustainable electrode materials for batteries. Especially bio-based organic electrode materials (OEMs) are very interesting due to their geographical independency and low environmental impact. However, bio-based OEMs for high-voltage batteries remain scarce. Therefore, in this work, a family of bio-based polyhydroxyanthraquinones (PHAQs)—namely 1,2,3,4,5,6,7,8-octahydroxyanthraquinone (OHAQ), 1,2,3,5,6,7-hexahydroxyanthraquinone (HHAQ), and 2,3,6,7-tetrahydroxyanthraquinone (THAQ)—and their redox polymers were synthesized. These PHAQs were synthesized from plant-based precursors and exhibit both a high-potential polyphenolic redox couple (3.5–4.0 V vs Li/Li+) and an anthraquinone redox moiety (2.2–2.8 V vs Li/Li+), while also showing initial charging capacities of up to 381 mAh g–1. To counteract the rapid fading caused by dissolution into the electrolyte, a facile polymerization method was established to synthesize PHAQ polymers. For this, the polymerization of HHAQ served as a model reaction where formaldehyde, glyoxal, and glutaraldehyde were tested as linkers. The resulting polymers were investigated as cathode materials in lithium metal batteries. PHAQ polymer composites synthesized using formaldehyde as linker and 10 wt % multiwalled carbon nanotubes (MWCNTs), namely poly(THAQ–formaldehyde)–10 wt % MWCNTs and poly(HHAQ–formaldehyde)–10 wt % MWCNTs, exhibited the best cycling performance in the lithium metal cells, displaying a high-voltage discharge starting at 4.0 V (vs Li/Li+) and retaining 81.6 and 77.3 mAh g–1, respectively, after 100 cycles.


SI-I-2 Methods
NMR Spectroscopy 1 H NMR and 13 C NMR spectra were recorded with Bruker Avance DPX 300 or Bruker Avance 400 spectrometers.The NMR chemical shifts were reported as δ in parts per million (ppm) relative to the traces of non-deuterated solvent (e.g.δ = 2.50 ppm for DMSOd 6 or δ = 7.26 for CDCl 3 ).
ATR-FTIR spectroscopy FTIR spectra were obtained using an FTIR spectrophotometer (Nicolet is20, Thermo Scientific Inc.) equipped with the ATR feature with a diamond crystal.Spectra were recorded between 4000 and 500 cm−1 with a spectrum resolution of 4 cm −1 .All spectra were averaged over 16 scans.
Electrochemical characterization: Lithium metal batteries, based on cathodes of THAQ, HHAQ, OHAQ, or the alt-polymers or their MWCNTs composites, were assembled inside an  (1:1, v:v) was used as separator.Cyclic voltammetry (CV) was performed in a three-electrode-cell using a glassy carbon working electrode and lithium metal strips as counter and reference electrode or a lithium metal coin cell.Galvanostatic measurements were performed using a multi-channel Potentiostat (Biologic, VMP3) or a battery cycler (Neware), respectively.The lithium metal coin cells were cycled directly upon assembly.

Computational calculations
The reduction potentials have been calculated using the thermodynamic cycle shown in Figure S1, where the Gibbs free energy of the reduction halfreaction ( ) consists of the free energy change in the gas phase ( ) and the solvation ∆  () ∆  () free energies (in methanol) of the oxidized ( ) and the reduced ( ) ∆ () () ∆ () () species: The relation between the Gibbs energy and the electrode potential (E) of a half-cell is: where F is the Faraday's constant (96485 J•mol -1 •V -1 ) and n is the number of electrons transferred in the half reaction, with the subtraction of the reduction potential of the reference electrode.In this work, we have used the standard hydrogen electrode (E SHE = -4.28V) and the Li/Li + redox couple (E Li/Li+ = -3.04V). [1] Calculation theoretical capacity The theoretical capacity of the PHAQs and their polymer and polymer composite counterparts have been calculated following: Where is the theoretical capacity, is the number of redox (electroactive) chemical species,    is the faradic constant and is the molar mass.Based on initial experiments we assumed a 4   electron process: 2 electrons for the anthraquinone moiety and 2 electrons for the polyphenolic parts, were just one of the two phenolic parts per monomer unit would participate in the redox process..87,152.04, 151.28, 139.04, 124.40, 110.14,  108.51.ATR-FTIR (cm -1 ): 3504, 3457, 3255, 1591, 1327, 1217, 1207, 1117, 1076, 999, 864, 771,  696, 638.S-7

SI-I-3-2 Polymers Syntheses
Table S1.Utilized ratios of conc.H 2 SO 4 and Glacial acetic acid for synthesis of Poly(HHAQ-aldehyde) and its 10wt% MWCNTs composites.Where X and Y are in mL.
Table S2.The systematically altered parameters for the optimization of the synthesis of poly(HHAQ-formaldehyde) from HHAQ and formaldehyde.''

Figure S1 .
Figure S1.Thermodynamic cycle used in the calculation of the redox potentials.

Figure
Figure S18.Solidified reaction mixture of HHAQ polymerization with formaldehyde.

Figure
Figure S19.Solidified reaction mixture of THAQ polymerization with formaldehyde.