N -Heterocycles Extended π-Conjugation Enables Ultrahigh Capacity, Long-Lived, and Fast-Charging Organic Cathodes for Aqueous Zinc Batteries

Open AccessCCS ChemistryRESEARCH ARTICLES6 Oct 2022N-Heterocycles Extended π-Conjugation Enables Ultrahigh Capacity, Long-Lived, and Fast-Charging Organic Cathodes for Aqueous Zinc Batteries Huiling Peng, Jin Xiao, Zhonghan Wu, Lei Zhang, Yaheng Geng, Wenli Xin, Junwei Li, Zichao Yan, Kai Zhang and Zhiqiang Zhu Huiling Peng State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Jin Xiao School of Science, Hunan University of Technology, Zhuzhou 412007 , Zhonghan Wu Frontiers Science Center for New Organic Matter, Renewable Energy Conversion and Storage Center (RECAST), Key Laboratory of Advanced Energy Materials Chemistry, Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071 , Lei Zhang State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Yaheng Geng State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Wenli Xin State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Junwei Li State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Zichao Yan State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 , Kai Zhang Frontiers Science Center for New Organic Matter, Renewable Energy Conversion and Storage Center (RECAST), Key Laboratory of Advanced Energy Materials Chemistry, Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071 and Zhiqiang Zhu *Corresponding author: E-mail Address: [email protected] State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 https://doi.org/10.31635/ccschem.022.202202276 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The aqueous zinc-organic battery is a promising candidate for large-scale energy storage. However, the rational design of advanced organic cathodes with high capacity, long lifespan, and high rate capability remains a big challenge. Herein, we propose that extending the π-conjugation by N-heterocycles can provide more active sites, lead to insolubility, and facilitate charge transfer, thus boosting the overall electrochemical performance of organic electrodes. Based on this concept, a novel organic compound, dipyrido[3ʹ,2ʹ:5,6;2″,3″:7,8]quinoxalino[2,3-i]dipyrido[3,2-a:2ʹ,3ʹ-c]phenazine-10,21-dione (DQDPD), has been rationally designed and evaluated as the cathode for aqueous zinc batteries. Excitingly, DQDPD shows a record high capacity (509 mAh g−1 at 0.1 A g−1, corresponding to a record-breaking energy density of 348 Wh kg−1), excellent cycling stability (92% capacity retention after 7500 cycles at 10 A g−1), and fast-charging capability (161 mAh g−1 at 20 A g−1). Our work offers new ideas in the molecular engineering of organic electrodes for high-performance rechargeable batteries. Download figure Download PowerPoint Introduction Rechargeable aqueous batteries (ABs) employing low-cost, safe, and eco-friendly aqueous electrolytes have attracted increasing research interest for large-scale energy storage applications.1–5 Among various AB systems, aqueous zinc batteries (AZBs) stand out since the zinc metal anode has the characteristics of high theoretical specific capacity (820 mAh g−1), low redox potential (−0.76 V vs standard hydrogen electrode), resource abundance, and good compatibility with water.6–11 Currently, the cathodes for AZBs mainly rely on inorganic compounds, such as transition-metal oxides/sulfides and Prussian blue analogs, most of which suffer from poor cyclability and slow kinetics due to the irreversible structural distortion and dissolution of active materials.12–14 In addition, these inorganic cathodes usually contain nonrenewable resources and environmentally hazardous elements, making them unsuitable for green and sustainable development.15–17 Compared to inorganic materials, organic materials with the merits of resource renewability, environmental benignity, and synthetic availability are more in line with the requirements for sustainable development.18–22 Moreover, the electrochemical performance of organic electrodes, such as theoretical capacity, cycle stability, and rate capability, can be subtly tailored via molecular design,23–29 which offers great opportunities for developing high-performance AZBs. Nevertheless, most organic electrodes, especially small molecules, suffer from limited cycle stability and rate capability, mainly due to their relatively high solubility in the electrolytes and low electrical conductivity.30–32 Although these issues can be partially resolved by molecular engineering and electrolyte modification,33–37 the rational design of high capacity, fast-charging, and long-lasting organic electrodes is still a challenging but ultimately rewarding pursuit. Extending the π-conjugation of organic electrodes represents one promising strategy to improve their electrochemical performance.38–41 Theoretically, the enlarged π-conjugation can enhance the intermolecular interactions and promote the orderly arrangement of organic molecules, which would not only facilitate the charge transfer but also reduce the solubility, thus simultaneously improving the rate capability and cycle stability.42–44 However, the reported extended π-conjugated systems always involve numerous inactive constituents, such as benzene, naphthalene, and other rigid structures, which inevitably reduce the theoretical capacity.38,39 For instance, benzoquinone (BQ), the smallest quinone molecule, with a high theoretical capacity of 496 mAh g−1 cannot be directly used as electrode material due to the sublimation/dissolution issue. In this case, various larger conjugated analogs, such as 1,4-naphthoquinone (1,4-NQ), 9,10-anthraquinone (AQ), and 5,7,12,14-pentacenetetrone (PT), have been designed to gain improved cycle stability and rate performance, but all of which come at the expense of decreased theoretical capacity (Figure 1a).45,46 Therefore, designing novel extended π-conjugated building units that could simultaneously enhance the capacity, cycle stability, and rate capability should be of great importance for exploiting high-performance organic electrodes. Figure 1 | Molecular design of high-performance organic cathodes. (a) Extending the π-conjugation from BQ to NQ, AQ and PT decrease the theoretical capacity. (b) Extending the π-conjugation of BQ by N-heterocycles gives TAPQ and DQDPD, both of which feature higher theoretical capacity than that of BQ. (c) HOMO/LUMO energy levels and energy gaps (ΔEH–L) of BQ, TAPQ, and DQDPD. Download figure Download PowerPoint Here, we proposed that extending the π-conjugation of the organic electrode with redox-active N-heterocycles provides more active sites, facilitates charge transport, and decrease solubility, thus simultaneously enhancing capacity, accelerating reaction kinetics, and prolonging cycle life. As a proof of concept, a novel BQ derivative with extended N-heterocyclic-conjugated structure, dipyrido[3ʹ,2ʹ:5,6;2″,3″:7,8]quinoxalino[2,3-i]dipyrido[3,2-a:2ʹ,3ʹ-c]phenazine-10,21-dione (DQDPD), was rationally designed (Figure 1b), which holds an extremely high theoretical capacity of 519 mAh g−1, even higher than that of BQ. Moreover, the N-heterocycle-extended π-conjugation endows DQDPD with layer-by-layer stacking mode, rodlike morphology, insolubility in water, and relatively high electrical/ionic conductivity, which enable it to deliver unprecedented electrochemical performance as the cathode for AZBs, including an ultrahigh reversible capacity (509 mAh g−1 at 0.1 A g−1), superior rate performance (161 mAh g−1 at 20 A g−1), and outstanding cycle stability (92% capacity retention after 7500 cycles at 10 A g−1). Particularly, both the capacity (509 mAh g−1) and energy density (348 Wh kg−1) of DQDPD set new records for organic cathodes in AZBs. Moreover, the DQDPD cathode also demonstrated excellent performance in the soft-package cell, showing great potential for practical applications. The H+/Zn2+ co(de)insertion mechanism of DQDPD has also been comprehensively disclosed by combining experimental characterizations and theoretical calculations. Our work affords new insights for the molecular engineering of organic electrode materials, which should have important implications for advancing the practical application of rechargeable organic batteries. Experimental Methods Materials synthesis Synthesis of tetra(phthalimido)-benzoquinone Tetra(phthalimido)-benzoquinone (TPB) was prepared according to a previous report with slight modifications.47 Under N2 atmosphere, 12.3 g of tetrachloro-p-benzoquinone (Macklin, 98.0%) and 37.2 g of potassium phthalimide (Macklin, 98.0%) were added to 250 mL of acetonitrile (ACN, Heowns) at 80 °C, and then the mixture was stirred for 24 h. After cooling to room temperature, the products were filtered and washed with N,N-Dimethylformamide (Aladdin, 99.5%), and boiling water five times. The obtained samples were suspended in 150 mL of boiled ethanol and then vacuum filtered. After being dried in a vacuum oven at 105 °C for 12 h, 30 g of brown-yellow TPB powder was obtained (yield 80%). Synthesis of tetramino-benzoquinone (TABQ) The synthesized TPB (14.66 g, 20 mmol) was transferred into a 500 mL round bottom flask, into which 200 mL of hydrazine hydrate (Macklin, 80.0 wt %) was added. After being kept at 60 °C for 12 h, purple TABQ was obtained (yield 52%). Synthesis of DQDPD TABQ (84.08 mg, 0.5 mmol) and 1,10-phenanthroline-5,6-dione (PTD, 210 mg, 1 mmol) were added to acetic acid (50 mL) in a three-mouth flask, and then the flask was evacuated and refilled with Ar three times, followed by refluxing for 24 h. After cooling to room temperature, the precipitate was washed with 1-methyl-2-pyrrolidinone (NMP) five times and then dried under vacuum to give a dark brown powder (yield 80%). Synthesis of 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ) TAPQ was synthesized according to a literature report.48 2,5-dihydroxy-1,4-benzoquinone (1.40 g, 10 mmol, Macklin) and o-phenylenediamine (4.33 g, 40 mmol, Macklin) were mixed uniformly using the mortar. The mixture was heated at 180 °C for 5 h in a tube furnace under argon atmosphere. After cooling to room temperature, the mixture was filtered and washed several times successively with deionized water and acetone and then dried at 80 °C in vacuum for 24 h to give deep purple 5,14-dihydroquinoxalino[2,3-b]phenazine (DHTAP) powder (yield 90%). Then, 12 mL H2SO4 (98%) was diluted with 50 mL of deionized water, in which the as-prepared DHTAP (1.00 g, 3.5 mmol) was added. After gradually adding K2Cr2O7 (4.12 g, 14 mmol, Kermel) as an oxidant, the mixture was heated at 80 °C for 4 h and then poured into 100 mL of ice water. The product was then filtered, subsequently washed with deionized water and acetone, and dried at 80 °C in vacuum for 18 h to give brown TAPQ powder (yield 70%). Materials characterizations Fourier transform infrared spectroscopy (FT-IR) was recorded using KBr pellets on a Bruker TENSOR II (FTS6000, Bruker, Germany) in the wavenumber range of 400–4000 cm−1. Raman spectra were recorded using a Raman microscope (Renishaw plc, Gloucestershire, England) with a 532 nm diode laser. The morphologies of the electrodes were investigated using field emission scanning electron microscopy (SEM, TESCAN MIRA3, Tescan, Czech Republic) along with energy-dispersive X-ray spectroscopy (EDX). Transmission electron microscopy (TEM) images were acquired on Talos f200i (Thermo Fisher, Massachusetts, United States) with an electron acceleration energy of 200 kV. X-ray photoelectron spectroscopy (XPS) measurements were conducted on an X-ray photoelectron spectrometer (ESCALAB Xi+; Thermo Fisher, Waltham, United States) under a vacuum of 8 × 10−10 Pa. All of the binding energies were referenced to the C 1s peak at 284.6 eV. X-ray diffraction (XRD) patterns were conducted by the Bruker D8 ADVANCE (Bruker, Germany) with Cu Kα (λ = 0.154 nm) radiation. The 1H and 13C NMR were conducted on a 400 MHz NMR spectrometer (Bruker ADVANCE III HD, Bruker, Billerica, United States). Thermogravimetric analysis (TGA) was carried out on a TGA/DSC3+ (DSC = differential scanning calorimetry) thermal analysis system (STA 700, Hitachi, Tokyo, Japan). Inductively coupled plasma emission spectrometry (ICP-OES) was characterized by the Agilent 5110 (Agilent, New York, United States). Elemental analyses including C, H, O, and N were checked by an elementar vario el III. For the ex situ FT-IR, Raman, XPS, XRD, and SEM measurements, the cells were cycled to a certain state of charge at 0.2 A g−1, and then disassembled to get the used electrode. Before each test, the cycled electrodes were washed with ethanol and vacuum dried at 40 °C. Electrochemical measurements To prepare the DQDPD electrode, DQDPD, conductive carbon, and poly(vinylidene difluoride) binder were mixed in NMP in a weight ratio of 6:3:1. The slurry was cast onto a tantalum foil by using the doctor blade technique, which was then dried under vacuum at 80 °C for 24 h. The electrode plate was 10 mm in diameter and 1–2 mg cm−2 of active load. The electrochemical performance of the DQDPD in different electrolytes (i.e. 1 M ZnSO4 in water, 1 M ZnSO4 + 2 M Na2SO4 in water, 1 M Zn(OTf)2 in ACN) were investigated by using CR2032-type coin cells containing the Zn foil as the anode and a glass fiber membrane as the separator (GF/D Whatman). Galvanostatic charge/discharge (GCD) test was performed on the LAND-CT2001A battery instrument in the voltage range of 0.15–1.5 V. Cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS) were conducted using a Squidstat Plus electrochemical workstation. The EIS was performed in a frequency range of 105–0.1 Hz with an amplitude of 10 mV of alternating current. All the electrochemical tests were conducted at room temperature. For the soft-package cell, the DQDPD cathode and Zn foil were cut to a size of 3 cm × 4 cm, respectively. The mass loading of DQDPD material was about 12∼13 mg. Whatman glass fiber in a size of 3.2 cm × 4.2 cm was used as the separator and 1 M ZnSO4 + 2 M Na2SO4 aqueous solution was used as the electrolyte. For the CV test in 0.05 mM H2SO4 and 1 M ZnSO4 + 2 M Na2SO4 aqueous solution using typical three-electrode systems, the DQDPD cathode was used as the working electrode, Ag/AgCl was used as the reference electrode, and a titanium sheet was used as the counter electrode. Computational method Density functional theory (DFT) calculations were carried out with the Materials Studio dmol3 software package to investigate the reactivity of DQDPD. The geometry optimization and electronic properties were calculated using the first-principles density functional with B3LYP function and double numerical plus polarization basis set.49–51 In all calculations, the spin was unrestricted. The convergence is reached when the residual forces on each atom are less than 0.001 Ha/Å, and the change of total energy was less than 10−6 Ha. The isosurface figures of the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and electrostatic potential (ESP) are shown by Material Studio.49 The isovalue is 0.03 e/Bohr3 for all HOMO and LUMO figures. Result and Discussion To demonstrate the superiority of the N-heterocycles extended π-conjugation in boosting the electrochemical performance of organic electrodes, the smallest quinone, BQ, was chosen as the starting molecule. Two BQ derivatives with an extended N-heterocyclic conjugated system, TAPQ and DQDPD were designed for comparison (Figure 1b). Interestingly, the theoretical capacity increased on the order of BQ (496 mAh g−1) < TAPQ (515 mAh g−1) < DQDPD (519 mAh g−1), which is contrary to the previous strategy that extending the π-conjugation always decreases the theoretical capacity.38,39 This is reasonable since the redox-active C=N group in N-heterocycles could also contribute to the theoretical capacity. Figure 1c displays the LUMO and HOMO of these three molecules. Accordingly, the bandgap decreases in the order of BQ (3.904 eV) > TAPQ (3.637 eV) > DQDPD (3.613 eV), which means that extending the π-conjugation can also increase the conductivity.38,42 Moreover, the extension of the π-conjugated system is expected to decrease the solubility and facilitate the charge transfer, which is beneficial to improving the cycle stability and rate capability (discussed later).42–44 Based on the above analysis, DQDPD with the larger N-heterocyclic conjugated system should provide much better performance compared to BQ and TAPQ. In fact, BQ is not suitable for use as an electrode in AZBs due to serious sublimation and dissolution. TAPQ is much more stable and has recently been explored as the cathode material for AZBs.48 However, it only achieved a capacity of 443 mAh g−1 (86% of its theoretical capacity) at 0.05 A g−1 in the voltage range of 0.15–1.5 V versus Zn2+/Zn, and the capacity dropped quickly during cycling. Therefore, DQDPD was selected as a model in this study. Synthesis and characterizations DQDPD was synthesized by a one-step solvothermal condensation reaction of TABQ with PTD in acetic acid at 120 °C for 24 h (Figure 2a), which gives a high yield of ∼80% (see Supporting Information Figures S1–S3). The successful synthesis of DQDPD was confirmed by FT-IR (see Supporting Information Figure S4a,b), NMR (see Supporting Information Figure S4c–f), and mass spectrum (see Supporting Information Figure S5). Elemental analysis (see Supporting Information Table S1) manifested that the accurate composition of the as-prepared DQDPD should be C30H12O2N8·H2O, suggesting the presence of crystal or/and adsorbed water. This is consistent with the thermogravimetric analysis (see Supporting Information Figure S6) showing that DQDPD experienced ∼4% weight loss below 350 °C. Nevertheless, the degradation of DQDPD mainly occurs at above 550 °C, implying its outstanding thermal stability. Figure 2 | Synthesis and characterizations of DQDPD. (a) Schematic of the synthetic route for DQDPD, (b) XRD pattern, (c) SEM image, (d) TEM image, (e–f) EDS elemental mapping, and (g) HRTEM image of DQDPD. Download figure Download PowerPoint The structure and morphology of the as-prepared DQDPD were also studied. The XRD result indicates that the obtained DQDPD shows high crystallinity, which originates from its large π-conjugation that induces a layer-by-layer molecular arrangement.38 Accordingly, the peak of 28.11° should correspond to the π–π stacking construction with a d-spacing of 3.21 Å (Figure 2b).52 The SEM analysis reveals that DQDPD shows rodlike morphology assembled by various nanosheets (Figure 2c), consistent with the TEM image (Figure 2d). The EDX elemental mapping images reveal the uniform distribution of C, N, and O elements (Figure 2e–g). In addition, clear lattice fringes with a diameter of 0.33 nm were observed in the high-resolution TEM (HRTEM) image (Figure 2h), which agrees well with the XRD results. The π–π stacking mode could provide a convenient ion channel while the rodlike structure could shorten the ion diffusion path, which could endow DQDPD with fast-charging capability.53 Next, the solubility and electrical conductivity of DQDPD were investigated. The results of the other two smaller conjugated analogs, BQ (purchased from Macklin) and TAPQ (see Supporting Information Figures S7 and S8) are also shown for comparison. Excitingly, DQDPD is insoluble in water and most common organic solvents except CHCl3 and CF3COOH (see Supporting Information Figure S9), which might be benefited from the strong π–π intermolecular interactions and hydrogen bonds between adjacent molecules.52,54 In sharp contrast, BQ is easily dissolved in water while TAPQ is slightly soluble in water but freely soluble in most common organic solvents, which confirms the efficacy of the enlarged π-conjugation in reducing the solubility. Moreover, the electrical conductivity increases in the order of BQ (1.21 × 10−11 S cm−1) < TAPQ (8.21 × 10−11 S cm−1) < DQDPD (6.74 × 10−9 S cm−1) (see Supporting Information Figure S10), agreeing well with the trends predicted by the bandgap calculations. As a result, in addition to its high theoretical capacity, DQDPD also features layer-by-layer stacking mode, rodlike morphology, insolubility in water, and relativity high electrical conductivity, all of which render it a promising organic electrode for AZBs. Electrochemical performance The electrochemical performance of DQDPD was evaluated by using a 2032 coin-type cell with a zinc metal as the counter electrode. Unless otherwise stated, the electrolyte used in this work was 1 M ZnSO4 + 2 M Na2SO4 in water. The usage of Na2SO4 aims to stabilize the Zn anode (see Supporting Information Figure S11), and the added Na+ ions will not participate in the redox reaction of DQDPD (see Supporting Information Figure S12).55,56 The redox behavior of the DQDPD electrode in 1 M ZnSO4 + 2 M Na2SO4 was first investigated by CV test.57 Figure 3a shows the initial three CV curves of the DQDPD cathode at a scan rate of 0.1 mV s−1, which display three reduction peaks (1.28, 0.78, and 0.32 V) and three oxidization peaks (0.43, 0.94, and 1.36 V), suggesting the multistep reaction processes.40 The following two cycles are slightly different from the first cycle, which is generally considered to be the activation process of the electrode material.58 Figure 3b shows the GCD curves of DQDPD in the voltage range of 0.15–1.5 V at 0.1 A g−1. The first discharging and charging capacity were 500 and 498 mAh g−1, respectively, giving a high Coulombic efficiency of 99%. Notably, the discharging capacity reached 509 mAh g−1 in the second cycle (97% of its theoretical specific capacity), giving an unprecedented energy density of 348 Wh kg−1 (based on the mass of active materials). Both the capacity and energy density of DQDPD surpass those of all reported organic cathodes in AZBs (Figure 3c),31,32,35,42,45,48,52,53,59 which owe a good deal to the extended N-heterocyclic conjugated system that offers rich redox-active C=N groups. Figure 3 | Electrochemical performance of the DQDPD cathode in AZBs. (a) CV curves of DQDPD at a scan rate of 0.1 mV s−1. (b) GCD profiles of DQDPD for the first five cycles at 0.1 A g−1 in the voltage range of 0.15–1.5 V. (c) Ragone plots of DQDPD cathode with previously reported organic cathodes in AZBs. (d) Cyclability of BQ, TAPQ, and DQDPD electrodes at 0.1 A g−1. (e) Rate performance of TAPQ and DQDPD at different current densities. (f) Comparison of the rate performance of DQDPD with reported organic cathodes for AZBs. (g) Long cycling stability of DQDPD at 10 A g−1. (h) Charge transfer impedance of TAPQ and DQDPD (inset: equivalent circuit). (i) GCD profiles of the Zn-DQDPD soft-package cell at 0.1 A g−1. (j) Cycle stability of the soft-package cell at 2 A g−1. Inset shows the optical photograph of the soft-package cell supporting the normal operation of the electronic meter. (k) Rate performance of soft-package cell in the current range of 0.1–5 A g−1. Download figure Download PowerPoint As mentioned before, the large π-conjugation of DQDPQ also leads to insolubility in water, which ensures long-term cycling. As shown in Figure 3d, a capacity of 453 mAh g−1 was maintained after cycling at 0.1 A g−1 for 100 cycles, corresponding to a capacity retention of 91%. When cycled at 0.5 A g−1, it rendered an initial capacity of ∼380 mAh g−1 with 92% capacity retention after 500 cycles (see Supporting Information Figure S13). It should be pointed out that in previous literature, the good cycle performance of aqueous Zn-organic batteries was generally realized under high current densities (>3 A g−1), which undoubtedly sacrificed the energy density.15,48 Therefore, the excellent cycle stability of DQDPD obtained at such low current densities is highly desirable for practical applications. As control experiments, the cycle stability of BQ and TAPQ in 0.15–1.5 V at 0.1 A g−1 was also tested (Figure 3d, see Supporting Information Figure S14). Notably, TAPQ offered much better cycle stability compared to BQ, but its capacity also kept decreasing during cycling (from 405 to 196 mAh g−1 after 100 cycles), which is consistent with the previous report.48 This is reasonable because TAPQ and its discharging product are still soluble in water (see Supporting Information Figure S15). Comparison among BQ, TAPQ, and DQDPD corroborates the effectiveness of extending the π-conjugation of organic electrodes in enhancing the cycling performance. Figure 3e compares the rate performance of TAPQ and DQDPD at various current densities. BQ was not studied here since its cycle stability is too poor. Remarkably, the specific capacities of DQDPD reached 507, 476, 411, 365, 321, 280, and 216 mAh g−1 at the current densities of 0.1, 0.2, 0.5, 1, 2, 5, and 10 A g−1, respectively, much higher than that of TAPQ obtained at the same current. Even at an ultrahigh current of 20 A g−1 (ca. 29 s for a full charge), DQDPD could also release a reversible capacity of 161 mAh g−1 (see Supporting Information Figure S16). Moreover, the capacity was restored to 486 mAh g−1 when the current density to returned 0.1 A g−1, implying the excellent ability of DQDPD to survive under extremely fast charging/discharging conditions. Such supreme rate capability of the DQDPD cathode compares favorably with previously reported aqueous Zn-organic batteries (Figure 3f).32,33,42,45,48,52,59–61 Furthermore, DQDPD realized long-term cycling at 5 A g−1, preserving 91% of its initial capacity after 5000 cycles (see Supporting Information Figure S17). Even at a high current density of 10 A g−1, a capacity retention of 92% was achieved after 7500 cycles, which is propitious to high-power applications (Figure 3g). The fast-charging capability of DQDPD should be attributed to its layer-by-layer molecular arrangement, rodlike morphology, and relatively high electrical conductivity, which guarantees fast electron and ionic transportation. To further estimate the effects of the N-heterocycle extended π-conjugation on reaction kinetics, EIS and galvanostatic intermittence titration measurements were carried out. As displayed in Figure 3h, DQDPD shows a lower charge transfer impedance (43.2 Ω) than that of TAPQ (119.7 Ω), which should be ascribed to the higher electronic conductivity of DQDPD. In addition, the diffusion coefficient of DQDPD during the whole discharging and charging is in the range of 10−10∼10−9 cm2 s−1, one order of magnitude larger than those of TAPQ (10−11∼10−10 cm2 s−1) (see Supporting Information Figure S18). In fact, the diffusion coefficient of DQDPD is comparable or even better compared to most of the reported electrode materials for AZBs (see Supporting Information Table S2).15,16,37,52,59 These results again evidence that the extension of π-conjugation facilitates both electron and ion transportation, which is highly effective for developing high-rate organic cathodes. The remarkable electrochemical properties of DQDPD prompted us to further assess its practicability in soft-package cells. Excitingly, the soft-package cell also exhibited an ultrahigh capacity of 485 mAh g−1 at 0.1 A g−1, up to 93% of its theoretical capacity (Figure 3i). When the current density increased to 2 A g−1, a capacity of 281 mAh g−1 was still achieved, along with a capacity retention of 86% after 1000 cycles (Figure 3j). As a demonstration, the soft-package could well support the operation of an electronic meter (inset of Figure 3j). The rate performance of this soft-package cell was also impressive, delivering reversible capacities of 486, 452, 427, 381, 330, 297, 284, and 255 mAh g−1 at 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5 A g−1, respectively (Figure 3k, see Supporting Information Figure S19). To sum up, the DQDPD electrode displayed unprecedented electrochemical performance in both coin-type and soft-p