Amidst the accelerating global energy transition, flow batteries, with their long lifespan, high safety, and flexible power/capacity configurations, have become a core solution for large-scale renewable energy storage. As a key component of flow batteries, the choice of casing material directly impacts the battery's corrosion resistance, sealing, and overall cost. This article will delve into the advantages of aluminum in flow battery casings and, drawing on cutting-edge industry case studies, provide a technical selection guide for the global energy storage market.

I. Core Requirements for Flow Battery Casing Materials

Flow batteries charge and discharge through electrolyte circulation, and their casings must meet the following stringent requirements:

Chemical corrosion resistance: They must withstand long-term corrosion from strong acids (such as the sulfuric acid system in all-vanadium flow batteries) or strong alkaline electrolytes;

Mechanical strength: They must withstand the pressure and vibration generated by battery stacking;

Sealing: They must prevent electrolyte leakage from causing system failure or environmental pollution;

Lightweighting and cost reduction: They must reduce transportation costs and increase system energy density while controlling material and processing costs.

Traditional materials such as graphite, while offering excellent conductivity, carry the risk of brittle fracture; and plastics, while low-cost, lack temperature resistance. Against this backdrop, aluminum, with its comprehensive performance advantages, is becoming an innovative choice for flow battery casings.

II. Technical Advantages of Aluminum in Flow Battery Casings

1. Corrosion Resistance: Surface Treatment Technology Breaks Through Industry Bottlenecks

Aluminum is susceptible to corrosion in acidic environments. However, through anodizing, micro-arc oxidation, or coating techniques (such as epoxy resin or polytetrafluoroethylene spraying), a dense oxide film can be formed, significantly improving corrosion resistance. For example, in an all-vanadium flow battery, the corrosion rate of a micro-arc-oxidized 6061 aluminum alloy casing is less than 0.01 mm/year after immersion in a 5% sulfuric acid solution for 1000 hours, meeting the requirements of long-term operation.

2. Lightweight and High Strength: Improving System Energy Density

Aluminum alloy has a density only one-third that of steel, but through T6 heat treatment or the addition of elements such as magnesium and silicon, its tensile strength can reach 300-500 MPa. A German energy storage company uses a flow battery system with a 7075 aluminum alloy casing, achieving a 40% weight reduction compared to traditional steel-cased solutions. Finite element analysis has also optimized the structural design, ensuring no deformation under a 1.5 MPa pressure test, ensuring safe operation of the battery stack.

3. Thermal Conductivity: Optimizing Thermal Management Efficiency

Aluminum's thermal conductivity (237 W/m·K) is significantly higher than that of plastic (0.2-0.3 W/m·K), enabling rapid heat dissipation from the battery's interior. A flow battery with an aluminum alloy casing, developed by a Chinese manufacturer, operates at an ambient temperature of 40°C, achieving a 15°C reduction in surface temperature compared to a plastic-cased solution. This effectively slows electrolyte decomposition and extends the battery life to over 20 years.

4. Processability and Cost-Effectiveness: Advantages of Large-Scale Production

Aluminum alloys can be used through processes such as extrusion and die-casting to achieve integrated molding of complex structures, reducing welding steps and sealing risks. For example, using a 20-foot containerized energy storage system, an aluminum alloy casing reduces costs by 30% compared to a graphite-based solution and shortens production cycles by 50%. Furthermore, the aluminum recycling rate exceeds 95%, in line with the global trend toward carbon neutrality.

III. Industry Application Cases and Market Prospects

1. All-Vanadium Flow Battery: Commercialization of the Aluminum Shell Solution

In the world's first 100-megawatt-scale all-vanadium flow battery project, Dalian Rongke Energy Storage Technology Development Co., Ltd. uses an aluminum alloy shell instead of the traditional graphite bipolar plate + plastic shell combination, reducing system costs by 18%. Furthermore, the IP67-rated design ensures zero electrolyte leakage. By 2025, its aluminum shell flow batteries had been exported to renewable energy-rich regions such as Australia and Chile, with a cumulative installed capacity exceeding 1.2 GWh.

2. Zinc-Based Flow Battery: Aluminum Enables Low-Cost Energy Storage

The zinc-iron flow battery developed by Form Energy in the United States utilizes an aluminum alloy frame and a corrosion-resistant coated shell, reducing system costs to $20/kWh, approaching the level of lithium-ion batteries. Its core innovation lies in leveraging aluminum's lightweight properties to reduce the weight of electrolyte storage tanks. Micro-arc oxidation technology also addresses corrosion caused by zinc deposition, promoting the commercialization of long-duration energy storage (over 100 hours).

3. Market Forecast: Aluminum Demand Continues to Grow

According to the China Machinery Industry Research Institute's "2025-2030 Global Flow Battery Market Report," as the proportion of renewable energy increases, the flow battery market is expected to grow at an average annual rate of 35%, with global installed capacity expected to exceed 100GWh by 2030. Aluminum alloy casing solutions, due to their cost-effectiveness, are expected to capture over 40% of the market share by 2027, primarily driven by large-scale energy storage projects in China, the United States, and Europe.

IV. Selection Recommendations: How to Choose an Aluminum Supplier?

Material Certification: Prioritize manufacturers certified to international standards such as ASTM B209 (aluminum alloy plates) and ISO 9227 (salt spray testing).

Surface Treatment Capabilities: Examine the uniformity and adhesion of processes such as micro-arc oxidation and coating spraying.

Structural Design and Simulation: Select suppliers with CAE analysis capabilities and the ability to provide coupled thermal-mechanical simulation optimization solutions.

Global Supply Chain: Ensure that aluminum complies with target market environmental regulations (such as EU REACH and US TSCA) and possesses localized processing capabilities to reduce logistics costs.

Conclusion

The use of aluminum in flow battery casings is not only a breakthrough in materials technology but also a key driver in the evolution of the renewable energy storage industry towards high efficiency, low cost, and sustainability. With continued innovation in surface treatment processes and structural design, aluminum alloy casings will further consolidate their core position in long-duration energy storage, providing solid support for the global energy transition.