An Ultrahigh Performance Zinc‐Organic Battery using Poly(catechol) Cathode in Zn(TFSI)₂‐Based Concentrated Aqueous Electrolytes

Abstract

are limited by high cost, safety issues, poor recycling infrastructure, and growing concerns of resource scarcity. [4,5] Therefore, in the quest of finding alternative sustainable energy storage solutions, systems based on multivalent chemistries, such as Ca 2+ , Mg 2+ , Zn 2+ , Al 3+ , etc., should provide ample opportunities owing to their greater abundance, lower costs, superior safety features, in addition to their significantly higher volumetric energy densities. [6][7][8][9][10][11] In particular, zinc metal batteries (ZMBs) are highly intriguing because Zn anode shows high specific capacity (820 mAh g −1 ), high volumetric capacity of 5851 mAh cm −3 , nontoxicity, nonflammability, cost-effectiveness, large production, and easy processing. [12][13][14][15][16][17] Moreover, differently from other multivalent chemistries (Ca 2+ , Mg 2+ , Al 3+ ), the relatively higher redox potential of Zn (−0.76 V vs standard hydrogen electrode) makes it the only feasible choice as reversible anode for aqueous electrolytes. Certainly, taking advantage of the potentially large voltage window (>2 V) and high ionic conductivity of aqueous electrolytes, aqueous zinc metal batteries (AZMBs) might present an excellent high energy/power trade-off which is triggering the growing interest of this technology in the last years. [18,19] To date, AZMBs are mainly based on inorganic intercalation/ conversion cathode materials such as metal oxides (manganese, vanadium, etc.), transition metal dichalcogenides, polyanionic olivine-based phosphates, and Prussian blue analogs. [12,13,18,19] However, these cathode materials resulted in poor cell performances, exhibiting slow kinetics, low round-trip efficiency, and unstable cycling. This is due to the large cation size which hinders interfacial charge transfer and provokes strong electrostatic interactions between the highly charged Zn 2+ and the host inorganic framework causing destabilization of the crystal lattice and significant volume changes upon intercalation/deintercalation. [6][7][8][9][10][11] It is also important to highlight that most of these multivalent cathodes still involve toxic and/or environmentally unfriendly elements (except widely used MnO 2 ), which make further steps critical toward accomplishment of large-scale, sustainable energy storage systems. Therefore, the main challenge Aqueous zinc-metal batteries (AZMBs) are predicted to be an attractive solutions for viable, high-performance, and large-scale energy storage applications, but their advancement is greatly hindered by the lack of adequate aqueous electrolytes and sustainable cathodes. Herein, an ultra-robust Zn-polymer AZMB is demonstrated using poly(catechol) redox copolymer (P(4VC 86 -stat-SS 14 )) as the cathode and concentrated Zn(TFSI) 2 aqueous solution as stable electrolyte. The Zn(TFSI) 2 electrolyte shows enhanced iontransport properties and confers improved (electro)chemical compatibility with superior cell performance compared to traditional ZnSO 4 . The assembled Zn||P(4VC 86 -stat-SS 14 ) (2.5 mg cm ...

Macromolecular Engineering of Poly(catechol) Cathodes towards High-Performance Aqueous Zinc-Polymer Batteries

“…Figure 1b shows CV of Zn anodic semi-reaction and CVs of P(4VC) 100 and P(4VC 86stat-SS 14 ) cathode materials using 4 m Zn(TFSI) 2 as the aqueous electrolyte. As previously demonstrated, a facile and highly reversible Zn plating/stripping process with onset potentials of initial −0.06/+0.01 V (vs. Zn/Zn 2+ ) in 4 m Zn(TFSI) 2 can be observed [51]. Both the homopolymer and copolymers featured well-defined oxidation/reduction peaks at 1.3 and 1.27 V/1.14 and 1.20 V (vs. Zn/Zn 2+ ), respectively.…”

“…Both the homopolymer and copolymers featured well-defined oxidation/reduction peaks at 1.3 and 1.27 V/1.14 and 1.20 V (vs. Zn/Zn 2+ ), respectively. As previously demonstrated, these redox processes are associated to the conversion of catecholates to ortho-quinones during the oxidation step and reverse reaction happens during the cathodic sweep reducing ortho-quinones to catecholates with concomitant Zn 2+ coordination (See Figure 1a for the simplified redox reaction scheme) [39,40,46,48,51]. Taking advantage of poly(catechol)'s high redox potential, Zn||polymer battery with an anticipated voltage output of~1.2 V can be potentially constructed by combining Zn anode and poly(catechol) cathode in the aqueous electrolyte (Figure 1b).…”

“…First, the comparative rate capability studies between Zn||P(4VC) 100 and Zn||P(4VC 86stat-SS 14 ) full-cells revealed superior dynamic performance in the case of copolymer not only at the room temperature, but also at lower temperatures (up to −35 • C). Thanks to the low meting temperature of 4 m Zn(TFSI) 2 (i.e., −38 • C), we successfully achieved the low-temperature operativity for both the polymers even way below the freezing point of water [51]. Note that most of the conventional low-to-moderately concentrated zinc based aqueous electrolytes generally will not offer such a low melting temperature window.…”

“…Polymers 2021, 13, x 12 of 16 freezing point of water [51]. Note that most of the conventional low-to-moderately concentrated zinc based aqueous electrolytes generally will not offer such a low melting temperature window.…”

“…In contrast, p-type RAPs delivered high voltage output (as high as 1.58 V) and good cycle performance but demonstrated low specific capacities (typically, <150 mAh g −1 ). In our most recent work, we pushed the limits of AZPBs to a new level for n-type organics by employing high performance poly(catechol) copolymer, P(4VC 86 -stat-SS 14 ) cathode in a novel 4 m Zn(TFSI) 2 aqueous electrolyte [51]. This battery simultaneously achieved high gravimetric capacity (324 mAh g −1 ), high voltage output (1.1 V), remarkable rate capability (98 mAh g −1 at 450 C) and extremely high cyclability with 83% capacity retention of over an extended 48,000 cycles.…”