Rechargeable Zn-based batteries (RZBs) have attracted much attention and been regarded as one of the most promising candidates for next-generation energy storage featured with high safety, low costs, environmental friendliness, and satisfactory energy density. The aqueous electrolyte system exhibits great potential to power future wearable electronics. Apart from the achievements of high-capacity cathode and stable electrolyte, the anode suffers from problems of dendrite growth, hydrogen evolution and passivation with limited attention. Enormous effort has been devoted to suppressing the dendrites growth which greatly restricts the life span of Zinc (Zn) anode. However, the commercialization of a battery system requires a comprehensive understanding which emphasizes not only dendrites but the forms of the anode, operation conditions, test methods and so on. Therefore, it’s imperative to conduct muti-dimensional studies for the Zn anode to better understand its electrochemical behaviours.

Apart from Zn foil as a potential candidate as a commercial anode, Zn powder (Zn-P) is also a practical choice for processing and controlling but has rarely been studied in past research. Herein, we first quantitatively study corrosion of the Zn-P@Coppoer (Cu) anode-induced swelling after aging and cycling. During the aging process of Zn-P@Cu electrode, 10.1 μmol cm-2 hydrogen generates on the surface of Cu, the Zn-P dissolves and morphology changes and further contact between the substrate after 120 h and Zn-P layer has deteriorated. By dissecting the electron pathway and quantitative measurement, those phenomena can be ascribed to galvanic corrosion. To address this issue, tin (Sn) with higher overpotential for hydrogen generation is proposed to be plating in the Cu surface, the corresponding phenomena are then ameliorated. The hydrogen amount during cycling has been reduced to 12.5% (7.9 μmol•cm^-2) of the number of Zn-P@Cu (57 μmol•cm^-2). With a low NP ratio (mass) of 10:7, much better storage and cycling performance for Zn-P@Cu||MnO₂ are achieved.

Next, considering one promising application of RZBs is to power flexible electronics, we conduct Zn anode evaluation in flexible working conditions to understand the challenges of anode part. The phenomenon of Zn accumulation on the folded line and curve areas is revealed. The correlation between the bending radius and the lifespan of symmetric cells is proposed. Interface contact of hydrogel electrolytes when working in a bending mode is another key factor affecting cell lifespan. After detailed analysis, the ideal cell configuration is to apply hydrogel electrolytes with suitable chemistry, satisfactory mechanical properties, and high adhesivity. Based on the criteria, a water-in-salt (WIS) hydrogel is proposed to satisfy those criteria and demonstrate highly stable cell performance. This work has provided a brand-new perspective toward Zn anode research and is a good starting point to propel the development of flexible energy storage devices (FESDs).

Another dimension of study is the morphological evolution starting from the initial process. Different electrochemical protocols lead to different zinc metal electrode surface morphologies. By coupling electrochemical and optical microscopy measurements, we demonstrate that an initial zinc deposition on the metal electrode allows homogeneous stripping and plating processes during prolonged cycling in symmetric Zn||Zn cell. Interestingly, when an initially plated zinc metal electrode is tested in combination with a manganese dioxide (MnO₂)-based positive electrode and a two molar zinc sulfate aqueous electrolyte solution in coin cell configuration, a specific discharge capacity of about 90 mAh g^-1 can be delivered after 2000 cycles at around 5.6 mA cm^-2.

The test methodology is also of exceptional significance. Based on symmetric cells, exceptional strides have been increasingly reported to address the bottlenecking dendrite issues of Zn anodes. However, substantial discrepancies exist between symmetric cells and full cells in terms of their applied current densities and accumulative stripping/plating capacities, indicating a possible hidden mechanism in symmetric cells that induces the misjudgement of Zn stability and obscures the development of reliable research. This part studies the often-overlooked soft short phenomenon in symmetric cells and exemplifies how its dynamic nature convolutes the evaluation of Zn anode stability. Accordingly, we propose two pertinent test protocols that can be combined with the typical galvanostatic cycling test to assess symmetric cells and characterize the genuine stability of Zn anodes. We expect this timely perspective will be a fresh and pertinent impetus to help rationalizing future endeavours toward the Zn anode and accelerate the development of reliable RZBs.

In summary, studies on Zn metal anode have been studied from multidimensions in this thesis. The mechanisms behind have been investigated throughout and further improvement methods have been proposed and validated. It’s believed that the studies in this thesis are significant in moving the commercialization of RZBs forward.