Tailoring the Stability and Kinetics of Zn Anodes through Trace Organic Polymer Additives in Dilute Aqueous Electrolyte

Abstract

High electrochemical stability and reaction kinetics of Zn anodes are crucial for rechargeable aqueous zinc batteries. Developing low-cost aqueous electrolytes is highly required. In this work, the fundamental principles to improve Zn anodes are systematically revealed in low-cost 1 M ZnSO 4 -based aqueous electrolytes using trace polymer additives with different polarities. The functional polymer additive could rearrange the "Zn 2+ −H 2 O−SO 4 2− −polymer" bonding network accordingly and reconstruct the space charge region of Zn anodes, resulting in distinctive cycling stability and reaction kinetics. Polymers with moderate polarity, such as polyacrylamide, exhibit synergic enhancement as the "smoother" and "thruster" for Zn 2+ toward Zn anodes, with which Zn anodes run over 1300 h with Coulombic efficiency >99.65% under 2 mA cm −2 , 2 mAh cm −2 , showing uniform Zn deposition with minimal impact on reaction kinetics. This work provides useful insights on designing low-cost and high-performance aqueous electrolytes through functional electrolyte additives.

A Universal Additive Strategy to Reshape Electrolyte Solvation Structure toward Reversible Zn Storage

“…[ 29 ] As such, investigations now are focusing on developing electrolyte additives on Zn 2+ ‐solvation structure in dilute solutions, such as methanol, [ 30 ] polyhydric alcohols, [ 31,32 ] dimethyl sulfoxide, [ 33,34 ] and polyacrylamide. [ 35 ] Although the Zn deposition behavior is optimized, many organic additives are still plagued by limited alleviation of side reactions. [ 10 ] Meanwhile, most of them hugely increase the polarization voltage while improving the cycling stability, leading to inferior electrochemical performance under practical conditions with high current density and areal capacity.…”

Advanced Buffering Acidic Aqueous Electrolytes for Ultra‐Long Life Aqueous Zinc‐Ion Batteries

“…[7][8][9] Due to the lack of pH buffering effect in the mild acidic electrolytes, the local OH − concentration could vary significantly along with the release of H 2 from H 2 O, which correspondingly leads to the formation of Zn salt hydroxide compounds and passivates the Zn electrodes. [9][10][11][12] The parasitic reactions on Zn electrodes contribute to low coulombic efficiency (CE) and short cycle life of aqueous Zn batteries.…”

“…To inhibit parasitic reactions, considerable strategies are developed to improve the reversibility of Zn anodes, including optimized design of Zn electrodes, [13,14] artificial functional coating layer, [15][16][17][18] electrolyte engineering, [7][8][9][10][11][19][20][21][22][23][24] etc. Among them, electrolyte engineering is a fundamental approach to stabilize Zn anodes.…”

Highly reversible zinc metal anodes enabled by protonated melamine

“…[14][15][16] Therefore, many researchers have attempted to improve Zn anodes' stability from the aspect of electrolyte additives that may interact with the Zn surface for regulating the electrical double layer (EDL) structure or coordinate with Zn 2+ cations for adjusting the solvation sheath. [17][18][19][20][21][22][23] For example, Wang et al introduced a Zn(NO 3 ) 2 additive into an aqueous electrolyte to improve the stability of the Zn anode. 14 The experimental results conrm that NO 3 À can participate in the Zn 2+ solvation sheath due to its high electron-donating ability, and this unique solvation sheath structure endows the Zn anode with a stable solid electrolyte interphase, enhancing the reversibility of the Zn anode.…”