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Review

Enhancing the Performance of Aluminum Anodes in Aqueous Batteries: A Review on Alloying, Microstructure, and Corrosion Inhibition Strategies

by
Peiqiang Chen
1,2,
Jinmao Chen
2,
Qun Zheng
1,
Yujuan Yin
2,
Xing Su
2,
Man Ruan
2,* and
Long Huang
2,*
1
College of Power and Energy Engineering, Harbin Engineering University, Harbin 150001, China
2
Institute of Systems Engineering, Academy of Military Sciences, Beijing 102300, China
*
Authors to whom correspondence should be addressed.
Sustainability 2025, 17(20), 9220; https://doi.org/10.3390/su17209220
Submission received: 4 September 2025 / Revised: 9 October 2025 / Accepted: 16 October 2025 / Published: 17 October 2025
(This article belongs to the Topic Advances in Green Energy and Energy Derivatives)
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Abstract

Aluminum-based seawater activated batteries (Al-SWBs) are highly cost-effective energy storage systems, with aluminum exhibiting a theoretical specific capacity of 2.98 Ah/g, second only to lithium, making it a promising candidate for next-generation sustainable energy storage and conversion technologies. However, severe hydrogen evolution and self-corrosion side reactions hinder the practical application of Al-SWBs, leading to unsatisfactory utilization of aluminum anodes. This review systematically summarizes the fundamental principles and strategies for enhancing the utilization efficiency of aluminum anodes from the perspectives of influencing factors and improvement approaches. In terms of alloying element doping, attention should be paid not only to elements that enhance performance but also to the impact of harmful impurities. Microstructure control can be achieved through advanced preparation techniques and subsequent annealing processes. Furthermore, the addition of corrosion inhibitors to the electrolyte can form a protective layer on the electrode surface, effectively suppressing self-corrosion behavior. This review aims to provide valuable insights and guidance for the development of sustainable and high-performance Al-SWBs, contributing to the advancement of green energy technologies.

1. Introduction

The aluminum based seawater activated cell is a new type of fuel cell, originally designed by a laboratory in the United States during World War II and developed by the General Electric Company. Because this battery does not require carrying electrolyte, it has high energy density, long storage time, and good safety, and it has been widely used in underwater equipment [1,2,3,4,5]. The battery uses active metal Al as the negative electrode, and the positive electrode material is usually AgO. The aqueous AgO–Al battery’s schematic diagram has been shown in Figure 1 [6]. The battery relies on the activation and dissolution of the Al-negative electrode in seawater to provide current: the active metal in the negative electrode dissolves in seawater and generates negative current, while when reduction occurs, the AgO positive electrode provides positive current to the battery. Natural seawater is used as an electrolyte to ensure the directional movement of ions in electrode reactions and form a continuous and stable current. During the discharge process of Al-SWBs, the negative electrode undergoes dissolution of Al metal [7,8,9], consuming OH- and generating a large amount of aluminate (AlO2−). The positive electrode AgO will be reduced to Ag, and the basic working principle is as follows:
Anode: 2Al + 8OH− → 2AlO2− + 4H2O + 6e−
Cathode: 3AgO + 3H2O + 6e− → 6OH− + 3Ag
Overall: 2Al + 3AgO + 2OH− → 2AlO2− + 3Ag + H2O
If the electrolyte is in a NaOH strong alkaline environment, the Al electrode will also undergo corrosion side reactions to produce hydrogen gas as follows:
2Al + 2H2O + 2NaOH → 2NaAlO2 + 3H2
If this side reaction is not suppressed, it will have a significant impact on the internal air pressure of the battery, endangering the safety of the battery system and the entire device [10].
Al-negative electrode material is one of the most important components in Al-SWBs and is also one of the main factors affecting the performance of seawater activated batteries. The standard electrode potential of aluminum in neutral and acidic media is −1.66 V (vs. SHE), and it is −2.31 V (vs. SHE) in alkaline media; the theoretical specific capacity is 2.98 Ah/g, second only to lithium; and its volumetric capacity is 8.05 Ah/cm3, higher than all other metals, making it an ideal negative electrode material [11,12,13,14]. In metal-based batteries, Al-SWBs are one of the most promising energy storage alternatives due to their high specific capacity, low cost, abundant reserves, and light weight. In addition, Al is the most abundant metallic element in the Earth’s crust. Considering the combination of specific capacity and Earth’s reserves, Al is far superior to all other metals, indicating that it is a promising candidate for developing advanced energy storage systems with high energy density and low cost [15]. The positive AgO electrode has a significant impact on the specific capacity of aluminum seawater batteries. Its electrochemical polarization will affect the working voltage and energy output of the battery; its cost and stability are also key considerations in battery design [16]. Therefore, while optimizing the aluminum negative electrode, the performance of the positive electrode and its matching relationship with the negative electrode must be taken into account as a whole.
The primary objective of this review is to systematically summarize and critically evaluate the recent research progress in enhancing the performance of aluminum anodes for aqueous batteries, with a specific focus on alloying design, microstructure control, and corrosion inhibition strategies. While the high theoretical capacity and cost-effectiveness of aluminum anodes are widely recognized, their practical application is severely hampered by parasitic hydrogen evolution and self-corrosion, leading to low utilization efficiency and potential safety hazards. This review is important because it moves beyond a simple compilation of literature. It aims to establish clear structure-property relationships by linking specific strategies (e.g., element doping, heat treatment) to their mechanisms of action (e.g., breaking passivation layers, altering hydrogen overpotential, homogenizing microstructure) in mitigating the key challenges. Furthermore, it provides a comparative perspective on the effectiveness, advantages, and limitations of different approaches. By integrating insights from materials science and electrochemistry, this review seeks to serve as a strategic guide for the rational design of next-generation high-performance aluminum anodes, thereby accelerating the development of reliable and commercially viable Al-SWBs for advanced energy storage and underwater applications.

2. The Influencing Factors of Al-Negative Electrode

Al-negative electrode materials have many excellent characteristics, but there are also some problems and defects. Aluminum metal is thermodynamically unstable in alkaline electrolytes because its standard potential is more negative compared to hydrogen (−2.31 V vs. SHE). As a result, the hydrogen evolution reaction (HER) occurs, consuming the Al-negative electrode and producing a large amount of hydrogen gas. At present, the application of Al-negative electrodes in aqueous batteries is mainly limited by hydrogen evolution corrosion and surface passivation [17]. From a thermodynamic perspective, Al has high chemical activity in water and undergoes intense hydrogen evolution corrosion reactions. From a kinetic perspective, the generated reaction products Al2O3, AlOOH, or Al(OH)3 or covering the surface of aluminum will hinder the hydrogen evolution corrosion reaction of aluminum. However, because the surface facial mask is damaged by the grain boundary, impurity particles, and ions in the solution, the hydrogen evolution corrosion reaction will continue at a certain rate. These defects also directly affect the inability of Al-negative electrode materials to exert their high-energy properties [18].
In aqueous electrolytes, the hydrogen evolution corrosion of the Al-negative electrode is mainly caused by the electrochemical corrosion of corrosive microcells, where impurity particles or precipitates serve as cathodic hydrogen evolution sites, and the aluminum matrix serves as the dissolution area of the negative electrode. Hydrogen evolution corrosion consumes metal active substances, reducing the current efficiency of the Al-negative electrode. In addition, the electrode potential exhibited by the Al-negative electrode is a mixed potential after the reaction coupling of Al dissolution and hydrogen precipitation, which seriously deviates from the theoretical potential of the aluminum-negative electrode. The surface passivation of the Al-negative electrode refers to the dense growth of oxides or hydroxides on the electrode surface, which hinders ion conduction and causes high dissolution overpotential, further reducing the electrode potential of aluminum negative electrode. In order to explore the issues of hydrogen evolution, corrosion, and surface passivation of Al-negative electrodes, researchers mainly proposed the study of the effects of microalloying and microstructure on Al-negative electrodes.

2.1. Microalloying

The electrode potential, self-corrosion rate, and hydrogen evolution rate of Al-negative electrode materials are greatly affected by the composition of microalloying elements and microstructure in aluminum alloy materials. Various drawbacks of pure aluminum can be improved through microalloying and microstructure adjustment. Therefore, studying the influence of microalloying elements and microstructure on the discharge performance of aluminum alloys can provide important guiding significance for subsequent research on negative electrode materials. The pure aluminum negative electrode exhibits a higher self-corrosion rate than the designed aluminum alloy negative electrode, resulting in a decrease in the utilization efficiency of the aluminum negative electrode. And alloying elements can improve the electrochemical reaction performance and suppress the occurrence of self-corrosion reactions to a certain extent, so they are also a simple strategy to improve electrode utilization efficiency (As shown in Table 1). There are several main functions of alloying elements as follows [19,20,21,22]:
(1)
Damaging the passivation film on the surface of aluminum, reducing the resistance of the oxide film, increasing the dissolution activity of the alloy, and having a high hydrogen evolution overpotential, can effectively inhibit the corrosion of the alloy due to hydrogen evolution. These elements include In, Ga, Sn, and Mg, etc.;
(2)
A low eutectic mixture with good fluidity can be formed on the surface of aluminum to improve the microstructure of aluminum alloy, destroy the oxide film on the surface of aluminum alloy, and improve the electrochemical performance of aluminum alloy. These elements include In, Ga, Sn, and Bi, etc.;
(3)
Can improve the chemical activity and corrosion resistance of aluminum, such as Pb, Sn, and Hg, etc.;
The effect of adding an appropriate amount of alloying elements on the electrochemical performance of aluminum negative electrode alloys was found, and it was found that the alloy grains were refined, the self-corrosion rate decreased, and the electrochemical performance was not significantly affected. These elements include Mn and rare earth (RE), etc.
The simultaneous doping of different elements can also have different effects on the aluminum negative electrode. The presence of metallic Fe can lead to rapid corrosion of the Al-negative electrode, while increasing the addition of Mn can reduce the harmful effects of Fe in industrial pure aluminum components [23]. The study by Moghanni et al. [24] shows that the Al-Mg-Zn-Bi-In negative electrode has excellent electrochemical performance and a lower self-corrosion rate. As a negative electrode, it can improve the performance of Al-AgO batteries and reduce serious self-corrosion and passivation problems. At a current density of 50 mA·cm−2, the working voltage of an Al-AgO battery with an Al-Mg-Zn-Bi-In negative electrode in a 7 M KOH electrolyte is 2.04 V, and the negative electrode utilization rate is 69.95%. The participation of Mg has a significant promoting effect on improving the performance of aluminum alloy negative electrodes.
Currently, the most popular research is on ternary and above aluminum alloys, where each different alloying element has its own corresponding effect to improve overall performance [25,26,27]. The joint addition of Mg and Sn does not result in better performance improvement, indicating that Mg and Sn have no cumulative effect on the inhibition of self-corrosion. The addition of Mg significantly improves the corrosion resistance of aluminum alloy negative electrodes, while the addition of Sn significantly reduces the membrane resistance, which helps the battery achieve high output voltage at high current densities. Professor Ren et al. [28] studied and evaluated pure aluminum and three types of aluminum alloy negative electrodes. Aluminum alloy negative electrodes showed better corrosion resistance and battery performance than pure aluminum negative electrodes. The self-corrosion rate of aluminum alloy increases in the following order: Al > Al-Sn > Al-Mg-Sn > Al-Mg. The Al-Mg alloy exhibits the minimum self-corrosion rate and maximum capacity. The Al-Mg-Sn alloy has the best electrochemical performance and battery discharge performance. In addition, the positive role of alloy elements in enhancing corrosion and electrochemical performance was revealed through energy calculations.
The influence of alloying elements Sn, Ga, and Mg on the self-corrosion rate and electrochemical performance of negative electrode alloys: Sn and Ga elements are mainly distributed in the form of precipitated phases on the surface of the aluminum negative electrode matrix as active points, reducing the oxide film resistance of the negative electrode alloy. Due to their high hydrogen evolution overpotential, they can effectively reduce the hydrogen evolution self-corrosion of aluminum alloy negative electrode materials and transform the alloy negative electrode from pitting corrosion to uniform corrosion [29]. Sn and Ga elements can significantly enhance the activation ability of the alloy negative electrode, but in the alloy negative electrode without Mg participation, the negative electrode material not only enhances its activation ability but also increases its self-corrosion rate. Scholar Xu et al. [30] conducted a detailed study on the influence of Mg, Sn, and Ga on the electrochemical behavior and anode property of the Al-Sb alloy. The single addition of Mg increases the discharge activity and suppresses the hydrogen evolution corrosion, improving the anode property of the Al-Sb alloy. The Al-0.3Mg-0.05Sb alloy presents a high specific capacity of 2881.8 mAh·g−1, outstanding anode utilization of 96.71%, and energy density of 2356.5 mWh·g−1 at 80 mA·cm−2. Scholar Xia et al. [31] have fabricated an Al/seawater battery using simulated seawater with an appropriate pH and added polyacrylic acid (PAA) as the electrolyte. This electrolyte simultaneously greatly retards self-corrosion of the Al anode by in situ forming a PAA-Al3+ complex film on it and increases the electrocatalytic activity toward the hydrogen evolution reaction by improving the electronic structure of Pt. When utilizing the multielement-doped Al sheet as the anode and nickel foam supported loading-amount-optimized Pt/C catalyst as the cathode and adopting the developed new electrolyte, the obtained Al/H2O battery exhibits an energy density of 2271 Wh·kg−1, and a power density of 20.87 mW·cm−2.
The above discussed the promoting effect of alloy elements on aluminum negative electrodes, and it is also necessary to pay attention to the influence of impurity elements on aluminum alloy negative electrode materials. Alloy elements such as Cu and Fe are harmful elements in aluminum negative electrode materials. When Cu is introduced, aluminum alloys are prone to pitting corrosion, with severe localized corrosion, and the generated corrosion products firmly adhere to the surface of the alloy, making it difficult to detach. This will greatly reduce the negative electrode efficiency of aluminum negative electrode alloys. When the element Fe content in aluminum alloy is high, it is easy to form brittle needle like or flake like FeAl3 cathode phases with poor solubility, which increases the self-corrosion rate of aluminum alloy [32]. When the Si content reaches a certain level, Al6Fe2Si3 with similar properties to FeAl3 will form, and its presence will lead to uneven corrosion and increase the rate of hydrogen evolution corrosion.

2.2. Microstructure

In addition to incorporating alloying elements, the microstructure of the material is another important factor affecting the electrochemical performance of aluminum alloy negative electrodes [33]. Most of the alloying elements added in microalloying of aluminum alloy negative electrode materials are low melting point and high specific gravity metals. While forming low melting point mixtures to improve activity, they are also prone to aggregation at grain boundaries, forming grain boundary segregation. The uneven composition caused by segregation will increase the point and rate of galvanic corrosion, thereby intensifying the self-corrosion of the negative electrode material and precipitating a large amount of hydrogen gas. In response to these issues, aluminum alloy negative electrode materials need to be controlled by microstructure to ensure that the added microalloyed elements are evenly distributed within the alloy microstructure. At the same time, the number, size, and distribution of related second phases in the aluminum alloy need to be controlled and improved to ensure that the second phase is uniformly distributed within the microstructure and has a small size. This can reduce or eliminate the enrichment of alloy elements at grain boundaries or the formation of second phase particles, thereby reducing the rate of self-corrosion hydrogen evolution in aluminum alloy negative electrode materials. Therefore, the microstructure of suitable aluminum alloy negative electrode materials can effectively optimize the comprehensive performance of aluminum alloy negative electrode materials, especially the electrical and corrosion properties [34].
The annealing treatment after rolling can refine the grain size of the aluminum negative electrode. The fine grains reduce the internal potential difference in the aluminum negative electrode and improve its corrosion resistance. After annealing, the aluminum negative electrode with significant morphological changes has a more uniform microstructure, which improves the corrosion resistance of the aluminum negative electrode. Zheng et al. [35] proved this point. In addition, the surface of the aluminum negative electrode with lower morphology has Bi and Pb precipitates, leading to pitting corrosion. As the morphology increases, the element distribution becomes uniform, and the precipitated phase dissolves in the aluminum matrix, resulting in improved corrosion performance. Meanwhile, compared with low form aluminum negative electrodes, the energy density and specific capacity of high form aluminum negative electrodes have increased by 584.35 Wh·kg−1 and 579.61 mAh·g−1, respectively, and the negative electrode efficiency has also increased by 19.45%. After annealing, the negative electrode efficiency of the high variant sample increased by 10.74%. At a constant current density, fine-grained aluminum anodes exhibit higher discharge voltage and electrochemical performance than coarse-grained aluminum anodes.
Due to the fact that most of the alloying elements added to the aluminum alloy negative electrode are high specific gravity, low melting point metals, and are immiscible with aluminum, it is easy to form component segregation, dendritic segregation, and specific gravity segregation. These factors can cause uneven corrosion or even perforation of the aluminum alloy negative electrode, and some grain boundary precipitates relative to the aluminum melt form a negative electrode phase, leading to micro primary cell corrosion and reducing the utilization rate of the aluminum electrode, which poses great harm to the performance of the finished aluminum alloy negative electrode and battery.
Heat treatment has a significant impact on the corrosion rate and electrochemical performance of aluminum alloy negative electrode materials [36]. Annealing treatment can effectively reduce the segregation of alloy components, make the material composition more uniform, reduce precipitates at alloy grain boundaries, and reduce intergranular corrosion of the alloy. At the same time, the distribution state of the added elements was changed, making the second phase distribution of the aluminum alloy negative electrode more uniform and smaller in size, thereby changing the activation performance of the material surface in the electrolyte, which can uniformly destroy the passivation film structure of the aluminum alloy material, making the electrode potential of the aluminum alloy negative electrode material more negative. It can also reduce the number of micro primary cells inside the material, reduce the self-corrosion rate caused by the micro primary cell effect inside the material, and improve the utilization rate of the negative electrode material [37].

3. Negative Electrode Improvement Measures

At present, there are still some problems and defects in the aluminum negative electrode studied [38,39,40], such as surface passivation, polarization phenomenon, and corrosion problems, which directly affect the inability of aluminum negative electrode materials to exert their high-energy characteristics. (1) The reaction process is easily hindered, and the electrical performance decreases. Although aluminum alloy negative electrode materials have high electrochemical activity, polarization often occurs on the surface of the aluminum alloy during discharge. The non-conductive layer formed by polarization will prevent the metal aluminum plate from directly contacting the electrolyte, hindering the electrode reaction process. (2) The current efficiency is not high during the discharge reaction. When discharging aluminum negative electrode materials, with the increase in discharge current, polarization causes the potential to shift forward. On the contrary, there will be an increase in the “self-corrosion current density” of the electrode, an acceleration of the hydrogen evolution rate, and a decrease in utilization rate. This phenomenon is known as the “negative difference effect”. The negative difference effect is the main reason for the decrease in discharge current efficiency when aluminum alloys are used as negative electrodes in chemical power sources. (3) The problem of self-corrosion hydrogen evolution is severe. The self-corrosion of aluminum negative electrodes is a significant problem. In chemical power sources, aluminum negative electrode materials undergo electrochemical oxidation reactions and discharge in the electrolyte, often accompanied by self-corrosion hydrogen evolution reactions. This accompanying side reaction leads to reactive power consumption of the aluminum negative electrode material, reducing the utilization efficiency of the electrode [41]. At the same time, the production of hydrogen gas makes the structure of the battery complex.
In response to the above-mentioned issues and influencing factors of Al-negative electrode materials, combined with the demand for seawater activated batteries, the main ways to solve the problems of aluminum negative plate materials currently include material nanomaterialization and microalloying. The role and effectiveness of each method will also vary:
(1)
Material nano materialization involves powder pressing or sintering of materials to obtain particle structures with different nanosizes and morphologies, effectively increasing the alloy surface area and reducing the polarization effect per unit area;
(2)
Obtaining high-purity aluminum-based materials through special refining processes reduces the influence of impurities on the open circuit potential, reduces the tendency of self-corrosion, and thus reduces the surface polarization effect caused by self-corrosion products.;
(3)
The addition of microalloyed elements can effectively suppress hydrogen evolution, reduce losses caused by self-corrosion of the alloy matrix, improve current efficiency, and improve the microstructure and electrochemical performance of aluminum alloy negative electrode materials.
Researchers often do not only use one optimization method to improve the physical and chemical properties of aluminum anodes, but also combine different optimization methods to jointly improve the performance. At present, the urgent problems of aluminum negative electrodes include low discharge voltage, severe hydrogen evolution reaction, and high self-corrosion rate. Based on the improvement effects of different optimization methods, the existing problems of aluminum negative electrodes should be solved.
To provide a clear overview, the main strategies for improving aluminum anodes are summarized in Table 2, comparing their key methods, mechanisms, advantages, and limitations.

3.1. Increase Discharge Voltage

Adding ion additives to the electrolyte can promote the dissolution of the passivation film, which has a significant promoting effect on increasing the discharge voltage of the battery. Gu et al. [42] found that adding Ga3+ to an electrolyte containing NaCl can shift the surface charge of Al towards the activation direction, induce Cl− enrichment, and generate more active sites, thereby promoting the dissolution of the passivation film. As shown in Figure 2, when the concentration of Ga3+ added is greater than or equal to 0.1 M, Ga3+ reacts with Al at specific activation sites, decomposing the oxide film to generate gallium metal and activating the Al-negative electrode. Through microstructure observation and electrochemical energy spectrum analysis, the influence of the activation mechanism of Ga3+ on the discharge behavior of industrial pure Al was elucidated. Due to the formation of gallium aluminum amalgam, aluminum batteries have the best discharge characteristics in electrolytes containing 0.2 M Ga3+, with a discharge voltage of 0.9734 V, which is significantly higher than that of NaCl solution (0.4228 V). Therefore, in aluminum batteries containing NaCl solution, Ga3+ additive can significantly increase the discharge voltage of the battery.

3.2. Reduce Hydrogen Evolution Rate

Commercial aluminum alloys can be divided into 2xxx (Al-Cu), 3xxx (Al-Mn), 4xxx (Al-Si), 5xxx (Al-Mg), 6xxx (Al-Mg-Si), and 7xxx (Al-Zn), etc. The elemental composition of commercial aluminum alloys has a significant impact on the electrochemical performance of aluminum anodes. According to reports, magnesium is beneficial for the electrochemical performance of aluminum negative electrodes in alloy elements. As representative magnesium rich aluminum alloys, commercial 5052 and 6061 aluminum alloys (A5052, A6061) have a wide range of industrial applications and exhibit excellent corrosion resistance. The utilization rate of aluminum has also been greatly improved. For example, the Mg contained in 6061 alloy can not only refine the grain size and improve the microstructure, but also increase the hydrogen evolution overpotential of the alloy, thus exhibiting better corrosion resistance and electrode activity. Wang et al. [19] investigated the low hydrogen evolution rate and excellent electrochemical performance of 6061 aluminum alloy (A6061), and found that increasing current density can suppress hydrogen evolution reaction. Figure 3 shows that as the discharge current density increases, the voltage decreases while the power density increases, indicating a decrease in the self-corrosion rate. The negative electrode efficiency of A6061 is as high as 89.28%, with a specific capacity of 2660.69 mAh·g−1. The energy density at a current density of 80 mA·cm−2 is 2119.09 Wh·kg−1. Its excellent performance is attributed to its crystal orientation, which facilitates the dissolution of aluminum and promotes electrochemical activity. This study can provide a better understanding of commercial aluminum alloy negative electrodes and contribute to optimizing the structure of aluminum alloy negative electrodes.
In addition to A5052 and A6061 aluminum alloys, Yu et al. [43] also studied the lower self-corrosion rate and better electrochemical performance of 7075 alloy in 4 M NaOH. In addition, as the discharge current density increases, HER is suppressed, and the 7075 based aluminum battery has a high specific capacity of 2508.04 mAh·g−1 and a high specific capacity of 2020.64 Wh·kg−2 at 75 mA·cm−2. However, when the alkaline concentration is 4 M, although the activation of the negative electrode alloy increases with the increase in solution temperature, the hydrogen evolution rate significantly increases.
In addition, researchers introduced micrometer sized AlSb precipitates into selected commercial aluminum alloys as negative electrode materials for alkaline aluminum batteries. Zhang et al. [44] found that the addition of Sb can coexist harmoniously with other alloying elements already added to aluminum alloys, and further improve the microstructure and electrochemical performance of aluminum anodes. Under the condition of 10 mA·cm−2, the energy density of 1080 alloy with added Sb (1544 Wh·kg−1) is 30.9% higher than that without added Sb. The electrochemical impedance spectroscopy (EIS) after adding Sb shows that as the thickness of the passivation film on the negative electrode surface decreases, the diffusion resistance (RC) and inductance (L) decrease, while the discharge voltage increases. The improvement and refinement of microstructure can also suppress hydrogen evolution in aluminum based negative electrodes. This is of great help in designing and manufacturing high-performance aluminum alloys made from low-cost commercial alloys.

3.3. Inhibiting Self-Corrosion Reactions

Researchers have conducted extensive research on self-corrosion hydrogen evolution, with widely used methods including adding corrosion inhibitors and improving material preparation techniques. Indole-2-carboxylic acid (ICA) is a cathodic inhibitor. According to surface bonding analysis and DFT simulation, ICA molecules mainly exist in deprotonated form under alkaline conditions. In this case, aluminum atoms form coordination bonds with oxygen atoms in the -COO- group, which is conducive to the formation of a surface protective film. Zheng et al. [45] studied the effect of it on the self-corrosion of aluminum alloy and the enhancement of aluminum battery function at different concentrations. When the inhibitor concentration was 0.07 M, the inhibition efficiency was 54.0%, the negative electrode utilization rate increased from 40.2% to 79.9%, the capacity density increased from 1197.6 to 2380.9 mAh·g−1, and the energy density increased from 1469.9 to 2951.8 Wh·kg−1. In addition, theoretical calculations were conducted to support the experimental results. The capacity density increased from 1197.6 to 2380.9 mAh·g−1, and the energy density increased from 1469.9 to 2951.8 Wh·kg−1. It can be seen that ICA is an effective corrosion inhibitor in alkaline solutions, and its impact increases with the increase in concentration.
Rare earth element salts can reduce the redox reaction of aluminum alloys. Adding rare earth element (cerium) inhibitors with self-healing properties to the electrolyte is beneficial for reducing the self-corrosion behavior of aluminum alloys. Cerium coating (CeC) can self-repair, mainly depending on the presence of Ce metastable particles at the substrate coating interface. These particles can react with Al3+ in the first step of corrosion and form a Ce-Al-O phase through the redox reaction of Ce (III)/Ce (IV). Harchegani et al. [46] investigated the effect of adding 0.5 to 1.5 wt% cerium chloride to a 4 mol·L−1 KOH electrolyte on the self-corrosion of pure aluminum negative electrodes through electrochemical experiments, as shown in Figure 4. The results indicate that adding cerium chloride to the electrolyte can reduce the self-corrosion of the aluminum negative electrode, and the impact on the negative electrode activity can be ignored. Cerium chloride forms cerium hydroxide (Ce(OH)3) in alkaline electrolytes and adsorbs on the surface of Al. Therefore, as the corrosion potential increases, the self-corrosion current density decreases. With the increase of cerium chloride concentration, the aluminum negative electrode efficiency increased from 43.8% to 76.1%, and the capacity density increased from 1294 to 2244 mAh·g−1. In addition, increasing the immersion time of aluminum negative electrodes in electrolytes containing cerium chloride improves the self-corrosion resistance of the negative electrode and provides self-healing performance for the negative electrode.
In addition, Peirow Asfia also suppressed the occurrence of the self-corrosion reaction of aluminum anode by adding thiourea [47] and CdO nanoparticles [48]. By adding corrosion inhibitors, the initial corrosion rate of the aluminum is reduced, and the generation and expansion of pitting corrosion are controlled by forming a protective layer on the surface. As the soaking time increases, the surface inhibitor provides uniform corrosion for the aluminum negative electrode, providing the electrons and capacity required for better performance of the battery.
In addition to adding corrosion inhibitors, researchers will also improve the preparation technology of aluminum alloys to reduce the occurrence of self-corrosion reactions of aluminum alloys from a material perspective. Ren et al. [49] studied the use of spray forming technology and subsequent heat treatment to produce commercial 7050 aluminum alloy as the negative electrode of aluminum batteries, which greatly suppressed self-corrosion. The microstructure of the prepared aluminum alloy negative electrode was characterized and compared with the cast 7050 aluminum alloy negative electrode. The aluminum negative electrode formed by spray forming has finer grains, a lower volume fraction, and discontinuous second phase distribution, resulting in a smaller self-corrosion rate. After deformation and heat treatment, the spray formed Al alloy shows a further decrease in the volume fraction of the second phase and a high fraction of low angle grain boundaries. Therefore, the prepared Al battery exhibits a larger specific capacity and higher operating voltage. This study indicates that commercial aluminum alloys prepared by combining spray molding and appropriate heat treatment are an ideal material for negative electrodes in aluminum batteries.

3.4. Heat Treatment Improves Material Defects

Heat treatment is an important technique for improving the microstructure and properties of metals and alloys. Some defects in alloys during the preparation process, such as uneven grain size and segregation, can be reduced or eliminated through heat treatment technology [50,51,52]. Aluminum alloy negative electrode materials are required to react from the surface to the inside during the reaction. After the outermost layer of reaction is completed and detached, the next layer of fresh metal aluminum participates in the reaction. If the grain size deviation of the alloy is too large, or some other defects (such as segregation, pores, etc.) occur inside the alloy, it will cause different reaction rates and corrosion rates of the negative electrode material at different positions, seriously affecting the stability performance of the aluminum alloy negative electrode material during discharge.
Heat treatment regulation technology is one of the key technologies that affects the comprehensive performance of aluminum alloy negative electrode materials and even the overall performance of seawater activated batteries. Cui et al. [53] controlled the microstructure of Al-0.5Mg-0.1Sn alloy through rolling deformation and subsequent annealing processes. As the annealing temperature increased, the self-corrosion rate of the alloy first decreased and then increased. At low temperature annealing (≤300 °C), the grain boundaries in the alloy were mainly small angle grain boundaries (LAGBs), which was beneficial for improving its corrosion resistance. The corrosion resistance and discharge performance of the Al-0.5Mg-0.1Sn alloy are related to the grain structure and Sn rich phase, with differences in grain size and grain boundary orientation playing a dominant role. Low temperature annealed (≤300 °C) alloys have more Sn rich phases than high temperature annealed (≥400 °C) alloys, and their corrosion resistance and discharge performance are better. The alloy annealed at 200 °C achieved the best discharge performance, with a peak energy density increased by 15.71% compared to the cast state at 20 mA·cm−2; at 40 mA·cm−2, the negative electrode efficiency of the annealed alloy at 200 °C is as high as 98.69%, corresponding to a specific capacity of approximately 2941 mAh·g−1.
By using appropriate heat treatment control techniques, internal defects such as segregation and processing stress can be eliminated, while improving the distribution of alloy elements and the second phase within the microstructure, making the composition and second phase distribution of aluminum alloy negative electrode materials more uniform, effectively controlling and optimizing the performance of aluminum negative electrodes.

4. Summary and Outlook

Although Al-SWBs have practical application potential due to their high specific capacity and power density, the severe self-corrosion and low utilization rate of aluminum anodes limit their large-scale development. This review analyzes many factors that affect Al-negative electrodes and summarizes improvement strategies for improving negative electrode utilization in recent years, including aluminum Al-negative electrode modification and electrolyte regulation. For the negative electrode, high-purity aluminum and aluminum alloys doped with alloying elements have been widely studied, and currently, the most popular research is on ternary and above aluminum alloy materials. In addition, the grain size and crystal orientation of the Al-negative electrode can also affect the electrochemical performance, and the microstructure of the material can be controlled by adjusting the preparation technology and heat treatment. As for electrolytes, a protective layer can be formed on the electrode surface by adding corrosion inhibitors to suppress self-corrosion, thereby improving the actual efficiency of Al-SWBs.
Overall, current Al-SWBs have received more attention due to their excellent energy and capacity characteristics, which is of great significance for future research on seawater activated batteries. Future research topics should focus on improving negative electrode performance by manipulating the microstructure. For example, (1) exploring high-performance negative electrode materials by combining crystal chemistry and alloy materials; (2) developing new negative electrode materials with lower self-corrosion rates; and (3) by using high-temperature calcination and annealing technology to regulate commercial pure aluminum materials, they can achieve the performance required for aluminum negative electrodes. In the near future, high specific energy, high power, and high safety Al-SWBs are likely to become a hot research direction for researchers.

Author Contributions

Conceptualization, L.H.; validation, Q.Z.; formal analysis, Y.Y.; investigation, P.C.; resources, M.R.; data curation, X.S.; writing—original draft preparation, P.C.; writing—review and editing, L.H.; visualization, J.C.; supervision, L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This study received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors express sincere gratitude to the supervisors and academic advisors for their guidance and invaluable insights. Acknowledgement is also due to the Harbin Engineering University (College of Power and Energy Engineering) and Academy of Military Sciences (Institute of Systems Engineering) for financial support towards the successful completion of this study. The authors would like to sincerely thank the editor who took his/her time to read this manuscript and provided us with their invaluable feedback to improve the quality and scientific soundness of this paper.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic diagram of aqueous AgO–Al battery [6].
Figure 1. Schematic diagram of aqueous AgO–Al battery [6].
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Figure 2. (a) Potentiodynamic polarization, (b) Linear potentiodynamic scan curves of Al in 2 M NaCl electrolytes without and with different additives [42].
Figure 2. (a) Potentiodynamic polarization, (b) Linear potentiodynamic scan curves of Al in 2 M NaCl electrolytes without and with different additives [42].
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Figure 3. (a–f) Galvanostatic discharge curves at different current densities. (g) Voltage and power density, (h) specific capacity, and (i) energy density [19].
Figure 3. (a–f) Galvanostatic discharge curves at different current densities. (g) Voltage and power density, (h) specific capacity, and (i) energy density [19].
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Figure 4. Constant current discharge curve of aluminum anode in a 4 mol·L−1 KOH solution containing cerium chloride with a current density of 20 mA·cm−2 [46].
Figure 4. Constant current discharge curve of aluminum anode in a 4 mol·L−1 KOH solution containing cerium chloride with a current density of 20 mA·cm−2 [46].
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Table 1. Different effects of different elements on aluminum negative electrodes.
Table 1. Different effects of different elements on aluminum negative electrodes.
NumberElemental CompositionImpact on Discharge Performance
1Beneficial elements such as Mg, Hg, Ga, In, etc.Low melting point and high density can cause a significant negative shift in the negative electrode potential of aluminum alloy, resulting in a decrease in negative electrode polarization
2Beneficial elements such as Zn, Sn, Pb, Bi, etc.High resolution hydrogen overpotential elements have an inhibitory effect on hydrogen evolution in aluminum alloy negative electrodes, which can improve their current efficiency and utilization efficiency of aluminum alloy electrodes
3Harmful elements such as Cu and FeEasy to cause pitting corrosion, severe local corrosion, increased hydrogen evolution corrosion rate, greatly reducing the negative electrode efficiency of aluminum negative electrode alloy
Table 2. Summary of improvement strategies for aluminum anodes in aqueous batteries.
Table 2. Summary of improvement strategies for aluminum anodes in aqueous batteries.
StrategyKey MethodsMechanism of ActionAdvantagesLimitations/Challenges
AlloyingDoping with elements like Mg, Sn, Ga, In, etc.Disrupts the continuous passive oxide film.
Increases hydrogen evolution overpotential.
Promotes uniform dissolution.		Significantly reduces self-corrosion.
Enhances activation and discharge voltage.
Mature and scalable fabrication process.		Complex interplay between multiple elements.
Risk of promoting galvanic corrosion if elements are improperly selected.
May increase material cost.
Microstructure ControlThermo-mechanical processing (e.g., rolling, annealing).
Spray forming.		Refines grain size and reduces segregation.
Promotes uniform distribution of alloying elements and second phases.		Reduces internal potential differences and intergranular corrosion.
Improves overall corrosion resistance and discharge stability.
Synergizes effectively with alloying.		Requires precise control of process parameters (temperature, time, deformation).
Adds complexity and cost to manufacturing.
NanostructuringFabricating nano-sized powders or porous structures.Dramatically increases specific surface area.
Reduces current density per unit area, mitigating polarization.		Enhances electrochemical activity and rate capability.
Can lead to very high utilization rates.		High fabrication cost.
Severe self-corrosion due to large surface area.
Challenges in electrode fabrication and long-term stability.
High-Purity MaterialsUsing high-purity aluminum or removing harmful impurities (Fe, Cu).Eliminates cathodic sites for hydrogen evolution.
Reduces micro-galvanic cell formation.		Effectively lowers the intrinsic self-corrosion rate.
Simple conceptual approach.		High cost of purification.
Does not address the issue of surface passivation.
Limited improvement in activation.
Corrosion InhibitorsAdding organic (e.g., ICA, thiourea) or inorganic (e.g., Ce3+) compounds to the electrolyte.Adsorbs and forms a protective film on the anode surface.
Blocks active corrosion sites.		Directly suppresses self-corrosion without modifying the anode.
Can be combined with other strategies.
Some inhibitors (e.g., Ce3+) offer self-healing properties.		Consumption over time requires replenishment in a closed system.
May increase electrolyte resistance or cause unwanted side reactions.
Optimization of concentration is critical.
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Chen, P.; Chen, J.; Zheng, Q.; Yin, Y.; Su, X.; Ruan, M.; Huang, L. Enhancing the Performance of Aluminum Anodes in Aqueous Batteries: A Review on Alloying, Microstructure, and Corrosion Inhibition Strategies. Sustainability 2025, 17, 9220. https://doi.org/10.3390/su17209220

AMA Style

Chen P, Chen J, Zheng Q, Yin Y, Su X, Ruan M, Huang L. Enhancing the Performance of Aluminum Anodes in Aqueous Batteries: A Review on Alloying, Microstructure, and Corrosion Inhibition Strategies. Sustainability. 2025; 17(20):9220. https://doi.org/10.3390/su17209220

Chicago/Turabian Style

Chen, Peiqiang, Jinmao Chen, Qun Zheng, Yujuan Yin, Xing Su, Man Ruan, and Long Huang. 2025. "Enhancing the Performance of Aluminum Anodes in Aqueous Batteries: A Review on Alloying, Microstructure, and Corrosion Inhibition Strategies" Sustainability 17, no. 20: 9220. https://doi.org/10.3390/su17209220

APA Style

Chen, P., Chen, J., Zheng, Q., Yin, Y., Su, X., Ruan, M., & Huang, L. (2025). Enhancing the Performance of Aluminum Anodes in Aqueous Batteries: A Review on Alloying, Microstructure, and Corrosion Inhibition Strategies. Sustainability, 17(20), 9220. https://doi.org/10.3390/su17209220

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