Reshaping Inner Helmholtz Layer and Electrolyte Structure via Multifunctional Organic Molecule Enabling Dendrite-Free Zn Metal Anode

The zinc ion concentration dynamically regulated by an ionophore in the outer Helmholtz layer for stable Zn anode

The Zn dendrite limits the practical application of aqueous zinc-ion batteries in the large-scale energy storage systems. To suppress the growth of Zn dendrites, a zinc ionophore of hydroxychloroquine (defined as HCQ) applied in vivo treatment is investigated as the electrolyte additive. HCQ dynamically regulates zinc ion concentration in the outer Helmholtz layer, promoting even Zn plating at the anode/electrolyte interface. This is evidenced by the scanning electron microscopy, which delivers planar Zn plating after cycling. It is further supported by the X-ray diffraction spectroscopy, which reveals the growth of Zn (002) plane. Additionally, the reduced production of H2 during Zn plating/stripping is detected by the in-situ differential electrochemical mass spectrometry (DEMS), which shows the resistance of Zn (002) to hydrogen evolution reaction. The mechanism of dynamic regulation for zinc ion concentration is demonstrated by the in-situ optical microscopy. The hydrated zinc ion can be further plated more rapidly to the uneven location than the case in other regions, which is resulted from the dynamic regulation for zinc ion concentration. Therefore, the uniform Zn plating is formed. A cycling life of 1100 h is exhibited in the Zn||Zn symmetric cell at 1.6 mA cm-2 with the capacity of 1.6 mAh cm-2. The Zn||Cu battery exhibits a cycling life of 200 cycles at 4 mA cm-2 with a capacity of 4 mAh cm-2 and the average Coulombic efficiency is larger than 99 %. The Zn||VO2 battery with HCQ modified electrolyte can operate for 1500 cycles at 4 A g-1 with a capacity retention of 90 %. This strategy in the present work is wished to advance the development of zinc-ion batteries for practical application.

Formulating Self-Repairing Solid Electrolyte Interface via Dynamic Electric Double Layer for Practical Zinc Ion Batteries

Zinc ion batteries (ZIBs) encounter interface issues stemming from the water-rich electrical double layer (EDL) and unstable solid-electrolyte interphase (SEI). Herein, we propose the dynamic EDL and self-repairing hybrid SEI for practical ZIBs via incorporating the horizontally-oriented dual-site additive. The rearrangement of distribution and molecular configuration of additive constructs the robust dynamic EDL under different interface charges. And, a self-repairing organic-inorganic hybrid SEI is constructed via the electrochemical decomposition of additive. The dynamic EDL and self-repairing SEI accelerate interfacial kinetics, regulate deposition and suppress side reactions in the both stripping and plating during long-term cycles, which affords high reversibility for 500 h at 42.7 % depth of discharge or 50 mA ⋅ cm-1. Remarkably, Zn//NVO full cells deliver the impressive cycling stability for 10000 cycles with 100 % capacity retention at 3 A ⋅ g-1 and for over 3000 cycles even at lean electrolyte (7.5 μL ⋅ mAh-1) and high loading (15.26 mg ⋅ cm-2). Moreover, effectiveness of this strategy is further demonstrated in the low-temperature full cell (-30 °C).

Achieving Dendrite-Free and By-Product-Free Aqueous Zn-Ion Battery Anode via Nicotinic Acid Electrolyte Additive with Molecule-Ion Conversion Mechanism

The widespread adoption of aqueous Zn ion batteries is hindered by the instability of the Zn anode. Herein, an elegant strategy is proposed to enhance the stability of Zn anode by incorporating nicotinic acid (NA), an additive with a unique molecule-ion conversion mechanism, to optimize the anode/electrolyte interface and the typical ZnSO4 electrolyte system. Experimental characterization and theoretical calculations demonstrate that the NA additive preferentially replaces H2O in the original solvation shell and adsorbs onto the Zn anode surface upon conversion from molecule to ion in the electrolyte environment, thereby suppressing side reactions arising from activated H2O decomposition and stochastic growth of Zn dendrites. Simultaneously, such a molecule-to-ion conversion mechanism may induce preferential deposition of Zn along the (002) plane. Benefiting from it, the Zn||Zn symmetric battery cycles stably for 2500 h at 1 mA cm-2, 1 mAh cm-2. More encouragingly, the Zn||AC full batteries and the Zn||AC full batteries using NA electrolyte and Zn||VO2 full batteries also exhibit excellent performance improvements. This work emphasizes the role of variation in the form of additives (especially weak acid-based additives) in fine-tuning the solvation structure and the anode/electrolyte interface, hopefully enhancing the performance of various aqueous metal batteries.

Stabilizing Zn anode for high-performance Zn-Ni battery through a complexing agent electrolyte addition

Zn-Ni batteries have garnered considerable attention due to their high specific energy, consistent discharge voltage, favorable performance at low temperatures, and environmentally benign nature. Nevertheless, anode interface issues such as dendrite growth, hydrogen evolution, and interfacial side reactions lead to poor cycling stability of Zn-Ni batteries, significantly limiting their further commercial applications. In this study, we propose a facile electrolyte engineering strategy to optimize the Zn anode interfacial environment and stabilize the Zn anode by introducing tannic acid (TA) into the KOH electrolyte. The incorporated TA complexing agent addition will be used to prevent the direct contact of H2O with the anode surface and promote the desolvation of Zn2+ through complexation, thus suppressing the interfacial corrosion. Consequently, the Zn symmetric battery using TA electrolyte cycles stably for 178 h at 1 mA cm-2. The Zn-Ni full batteries with TA electrolyte maintain 98.08 % capacity retention after 2000 cycles at 20C. This study will be of immediate benefit in commercializing large-scale, practical energy storage applications.