Key Takeaways & Executive Findings
- •• Introduction of low-cost Na+ into Zn(ClO4)2 electrolyte suppresses Zn2+ aggregation via preferential adsorption and electrostatic repulsion, enabling homogeneous Zn deposition and enhanced low-temperature reversibility. • Na+ with low ionic potential spontaneously adsorbs at the anode–electrolyte interface, reducing solvated water molecules and suppressing parasitic reactions, significantly improving Coulombic efficiency at low temperatures. • At −40 °C, Zn||Zn cells maintained stable cycling for over 2500 h, and Zn||PANI full cells exhibited over 8000 cycles with >90% capacity retention. • The organic-free antifreeze electrolyte offers a cost-effective and practical strategy for long-term operational stability of aqueous zinc metal batteries in subzero environments.
Abstract
Aqueous zinc metal batteries (AZMBs) are promising candidates for renewable energy storage, yet their practical deployment in subzero environments remains challenging due to electrolyte freezing and dendritic growth. Although organic additives can enhance the antifreeze properties of electrolytes, their weak polarity diminishes ionic conductivity, and their flammability poses safety concerns, undermining the inherent advantages of aqueous systems. Herein, we present a cost-effective and highly stable Na2SO4 additive introduced into a Zn(ClO4)2-based electrolyte to create an organic-free antifreeze electrolyte. Through Raman spectroscopy, in situ optical microscopy, density functional theory computations, and molecular dynamics simulations, we demonstrate that Na+ ions improve low-temperature electrolyte performance and mitigate dendrite formation by regulating uniform Zn2+ deposition through preferential adsorption and electrostatic interactions. As a result, the Zn||Zn cells using this electrolyte achieve a remarkable cycling life of 360 h at −40 °C with 61% depth of discharge, and the Zn||PANI cells retained an ultrahigh capacity retention of 91% even after 8000 charge/discharge cycles at −40 °C. This work proposes a cost-effective and practical approach for enhancing the long-term operational stability of AZMBs in low-temperature environments.
1. Introduction
Aqueous zinc metal batteries (AZMBs) have emerged as highly promising next-generation energy storage systems for renewable energy applications, owing to their exceptional safety and high theoretical capacity [1]. The zinc metal anode offers abundant reserves and outstanding theoretical energy density (820 mAh g−1 and 5855 mAh cm−3), along with a favorable redox potential (−0.76 V vs. SHE) [2]. Additionally, aqueous electrolytes exhibit high ionic conductivity, low volatility, and non-flammability [3]. These advantages make AZMBs become popular subject of research. However, AZMBs still face a series of challenges during low-temperature operation, including electrolyte freezing, uneven zinc deposition and dendrite growth due to slow ion transport, as well as hydrogen evolution reaction (HER) [4–8]. These issues can severely impair the low-temperature performance of aqueous batteries and restrict their application scenarios and commercialization process [9–12].
Enhancing the low-temperature performance of AZMBs relies on improving the resistance of aqueous electrolytes to freezing. Organic additives like DMSO, EG, and SL can lower freezing points, but their weak polarity reduces ionic conductivity, increases viscosity, and impairs ion transport at low temperatures (Fig. 1a) [13–16]. To address these limitations, increasing the salt concentration has emerged as an alternative to avoid the drawbacks of organic additives. Organic-free electrolytes with strong antifreezing properties include 7.5 m ZnCl2 and 5 m Zn(ClO4)2, hereafter referred to as 5 ZClO [17–19]. The high-concentration ClO4− in 5 ZClO has a strong electronegativity, which can effectively disrupt the water–water hydrogen bond network in the electrolyte [20–24]. This enables 5 ZClO to exhibit exceptional low-temperature resistance and high ionic conductivity as an aqueous electrolyte. While these electrolytes effectively enhance the freezing resistance of aqueous electrolytes, they overlook the critical challenge of dendrite growth and parasitic reactions at the anode interface, which are exacerbated at low temperatures.
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Guanchong Mao, Pan Xu, Xin Liu, Xingyu Zhao, Zexiang Shen, Dongliang Chao, Minghua Chen (2026). Prioritized Na+ Adsorption-Driven Cationic Electrostatic Repulsion Enables Highly Reversible Zinc Anodes at Low Temperatures. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01889-9
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Frequently Asked Questions
What is the main challenge for aqueous zinc metal batteries at low temperatures?
At low temperatures, aqueous zinc metal batteries suffer from electrolyte freezing, slow ion transport, uneven zinc deposition, dendrite growth, and hydrogen evolution reaction, which severely impair their performance and practical deployment.
How does the Na2SO4 additive improve low-temperature performance?
The Na+ ions preferentially adsorb at the anode–electrolyte interface and create electrostatic repulsion among cations, which suppresses Zn2+ aggregation, promotes uniform zinc deposition, and reduces parasitic reactions, thereby enhancing reversibility and cycling stability at low temperatures.
What are the key performance metrics achieved with the proposed electrolyte?
At −40 °C, Zn||Zn cells achieved over 2500 hours of stable cycling, and Zn||PANI full cells retained over 90% capacity after 8000 charge–discharge cycles, demonstrating excellent low-temperature performance.
Why is the organic-free electrolyte advantageous over organic additives?
Organic additives often reduce ionic conductivity and increase flammability, whereas the organic-free Na2SO4 additive maintains high ionic conductivity and safety, making it a cost-effective and practical solution for low-temperature aqueous batteries.
What methods were used to investigate the mechanism?
The study employed Raman spectroscopy, in situ optical microscopy, density functional theory (DFT) computations, and molecular dynamics simulations to demonstrate the preferential adsorption and electrostatic interactions of Na+ ions.
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