High-Rate and Long-Cycle Stability with a Dendrite-Free Zinc Anode in an Aqueous Zn-Ion Battery Using Concentrated Electrolytes

Abstract

Recently, metallic zinc (Zn) is becoming a promising ideal anode material for rechargeable aqueous batteries by providing high theoretical capacity (820 mA h/g) with divalent reaction, environmental friendliness, earthy abundance, low cost, low toxicity, higher water compatibility, and low electrochemical potential (−0.762 V vs SHE). However, intensive growth of zinc dendrites while plating/stripping lowers its coulombic efficiency and shortens the cycle life of the rechargeable devices. Here, we report a concentrated aqueous electrolyte (4.2 M ZnSO4 + 0.1 M MnSO4) with improved cycling stability of zinc metal anode achieving an average coulombic efficiency (ACE) ∼99.21% cycling for more than 1000 h at 0.2 mA/cm2 current density using a Zn||Cu cell. However, a frequently used diluted electrolyte (2 M ZnSO4 + 0.1 M MnSO4) only produces ACE ≈ 97.54% with a relatively short life cycle. The developed concentrated electrolyte with strongly aggregated ion pairs shows the synergetic effects of the enhanced solvation/desolvation process, electrostatic shielding, and Le Chatelier’s principle. Consequently, the additives simultaneously suppress Zn dendrites and dissolution of Mn2+ ions from the MnO2 cathode. A highly stable and reversible Zn||MnO2 cell retaining about 88.37% retention capacity was obtained after cycling for more than 1200 cycles at 938 mA/g current density.

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

“…The observed differences in Zn plating/stripping behavior from the two electrolytes could be attributed to the association of Zn 2+ cations with the different counteranions: singly charged and bulky TFSI − anions (vs SO 4 2− with double charge) and the concurrent solvation effects. [ 36–38,42,48 ] In order to corroborate that, we first explored the interaction between the water molecules and the different salts by using Raman spectroscopy ( Figure 2 a). A broad Raman band that observed in 2900–3700 cm −1 range consisting of several components of the OHH stretching vibration for a typical strongly hydrogen‐bonded pure liquid water was considerably narrowed ZnSO 4 < Zn(TFSI) 2 order, signifying the stronger interaction of the water molecules with the TFSI − than with the SO 4 2− anion.…”

“…As already well‐proven systems, the formation of passivation layer of Zn 4 SO 4 (OH)6·3H 2 O in ZnSO 4 and ZnO in KOH and various by‐products (such as Zn(OH) 2 , x ZnCO 3 ⋅ y Zn(OH) 2 ⋅ z H 2 O, and ZnO) was evidenced from XRD pattern (Figure S8, Supporting Information). [ 48 ] Whereas, XRD of Zn after immersion in 4 m Zn(TFSI) 2 was almost similar to that of bare Zn without/or minimal formation of such corrosion by‐products.…”

“…The selection of 4 m concentrated aqueous electrolytes is based on previous reports that revealed enhanced stability and reversibility of Zn in near‐saturated electrolyte solutions. [ 36,46–48 ] As shown in Figure S1 (Supporting Information), both the electrolyte solutions are homogenous and transparent liquids even after standing for months at ambient temperature.…”

“…The XRD was then applied to the cycled Zn anode to analyze the nature of by‐products (Figure S23, Supporting Information). The peak intensity corresponding to the Zn hydroxides and zincates by‐products in the range of 2θ = 10°–20°, [ 49,48 ] was found to be relatively high in ZnSO 4 compared to that in Zn(TFSI) 2 , once again suggesting better chemical and/or electrochemical compatibility of Zn metal anode in the latter electrolyte.…”

High‐Voltage Rechargeable Aqueous Zinc‐Based Batteries: Latest Progress and Future Perspectives

“…For example, the coordination number of Zn 2+ with H 2 O would decrease and the interaction between Zn 2+ and would be reinforced by increasing the concentration of a ZnSO 4 electrolyte. [ 18 ] In other words, the hydration number and hydrated cation radius are reduced in lower water surroundings, which is conducive to the rapid and reversible intercalation/deintercalation of hydrated Zn 2+ ions into the cathode materials, thus enhancing the electrochemical performance of the battery. Therefore, the “water‐in‐salt” concept has been proposed in AZB systems.…”