Ultra-High-Capacity and Dendrite-Free Zinc–Sulfur Conversion Batteries Based on a Low-Cost Deep Eutectic Solvent

Abstract

Traditional cathodes for aqueous Zn-ion batteries are afflicted by a limited specific capacity and fearful Zn dendrites. Herein, these troubles are disposed of with a conversion-type Zn–S battery and low-cost deep eutectic solvent (DES). By utilizing the optimized electrolyte, the symmetrical Zn battery can stably cycle over 3920 h, which also confers on the Zn–S battery an ultrahigh specific capacity of ∼846 mA h gS –1 and energy density of 259 W h kg–1 at 0.5 A g–1. Importantly, the conversion chemistry of S and ZnS is responsible for the superior anti-self-discharge behavior (capacity retention: 94.58 and 68.58% after standing for 72 and 288 h versus Zn//VO2 battery: 76.82 and 47.80% after resting for 24 and 72 h versus Zn//MnO2 battery: 95.96 and 91.57% after resting for 24 and 72 h, respectively). This work is the first authentication of Zn–S batteries based on a newly developed low-cost DES-based electrolyte, which meanwhile settles the deep-rooted low specific capacity and infamous Zn dendrite issues in conventional (de)­intercalation Zn-ion batteries.

Zn-Based Deep Eutectic Solvent as the Stabilizing Electrolyte for Zn Metal Anode in Rechargeable Aqueous Batteries

“…Figure 6A shows that a relatively substantial initial overpotential is required to trigger the Zn plating/stripping reaction (shown by the red arrow), but the overpotential is reduced during consecutive cycles. Furthermore, the maximum voltages did not increase during cycling, demonstrating that no passivation layer was formed on the Zn surface (Cui et al, 2021). The excellent performance of the Zn metal anode was further validated by long-term cycling at different current densities, as shown in Figure 7A.…”

Eutectic Electrolytes Chemistry for Rechargeable Zn Batteries

“…[ 40 ] In addition, eutectic electrolytes without water contents possibly prevent problems caused by Zn dendrite growth and side reactions. [ 86 ] Analogous, some research related to Zn anodes protection and modification promotes the nonaqueous eutectic electrolytes for ZIBs, [ 44,87 ] Zn–S batteries, [ 65 ] Zn–I 2 batteries, [ 88 ] and Zn–Fe flow batteries. [ 8b ]…”

“…[40] In addition, eutectic electrolytes without water contents possibly prevent problems caused by Zn dendrite growth and side reactions. [86] Analogous, some research related to Zn anodes protection and modification promotes the nonaqueous eutectic electrolytes for ZIBs, [44,87] Zn-S batteries, [65] Zn-I 2 batteries, [88] and Zn-Fe flow batteries. [8b] Zn-based eutectic electrolytes, constitute mixing anhydrous/ hydrated Zn metal with quaternary ammonium salts (e.g., ChCl) or HBDs (e.g., urea, acetamide, and ethylene glycol).…”

“…The resulting eutectic electrolytes optimize the solvation structures of Zn ions in the electrolyte and allow dendrite-free Zn stripping/plating over 3920 h for Zn-S batteries. [65] Coincidentally, Cao et al prepared a novel eutectic liquid composed of ChCl and ethylene glycol (EG) with Cerium chloride (CeCl 3 ) and ZnCl 2 as the active materials for positive and negative electrolytes, respectively, working for high-energy and low-cost Zn-Ce redox flow batteries. [53] Small 2022, 18,2200550 Table 1.…”

“…Nonaqueous eutectic electrolytes 5 m ZnCl 2 -aceramide Carbon ≈1.00 1.30 90 A h L −1 (-) -Wang et al [42] ChCl-urea (Molar ratio 1:2) δ-MnO 2 -2.54 170 [50 mA g −1 ] ≈50% [0.1 A g −1 , 150 cycles] Kao-ian et al [64] Zn(TFSI) 2 -acetamide (Molar ratio 1:7) V 2 O 5 0.31 2.40 186 [100 mA g −1 ] 92.8% [0.6 A g −1 , 800 cycles] Qiu et al [44] 0.5 m ZnCl 2 + 0.5 m LiCl in 5 vol% AN/ChClurea (Molar ratio 1:2) Sulfur 4.66 4.65 846 [0.5 A g −1 ] ≈27.8% [2 A g −1 , 500 cycles] Cui et al [65] 1 m CeCl 3 in ChCl-EG (Molar ratio 1:2) Graphite 1.32 b) 2.20 0.1 mA h [0.5 mA cm −2 ] ≈79% [0.5 mA cm −2 , 50 cycles] Cao et al [53] Aqueous Zhao et al [66] 7.…”