All about battery aluminum foil

What is battery aluminum foil?

Battery aluminum foil is an important part of the battery. It is a hot stamping material that is directly rolled into a thin sheet of metal aluminum. Compared with traditional aluminum foil, battery aluminum foil has higher requirements on various aspects of performance, and ultra-thin and high-strength are the future trends.

With the improvement of battery energy density requirements, the requirements for the thickness uniformity, bonding performance, conductivity, surface tension, elongation and other indicators of aluminum foil tend to be higher.

The importance of battery aluminum foil

Battery aluminum foil is the anode current collector material for lithium-ion batteries. Lithium ion battery is the core component of energy storage system, which is a mobile energy source composed of cathode, anode and electrolyte.

The current collector is one of the important components of the power battery and should have good electrical conductivity and physical and chemical properties. The current collector refers to the structural parts that collect current.

Its function is mainly to gather the current generated by the active materials of the battery so as to form a larger current output, and it will fully contact the active materials in the working environment. Therefore, the current collector has performance requirements such as high conductivity, strong corrosion resistance, good toughness, certain rigidity, and easy processing and molding.

Reasons for using aluminum foil as battery anode current collector:

1.The surface of the aluminum foil has a dense oxide layer, which can prevent the current collector from being oxidized and corroded by the electrolyte

2.The anode potential of lithium-ion batteries is high, and copper will undergo lithium intercalation reaction at high potential, while aluminum has a high oxidation potential and is suitable for use as an anode current collector.

3.Aluminum foil is easy to form aluminum-lithium alloy at the low potential of the cathode, so copper foil is usually used as the cathode current collector.

4.The use of aluminum foil as a current collector can greatly reduce the contact resistance between the anode/cathode material and the current collector, and improve the adhesion between the two, thereby significantly improving the capacity and performance of the battery.

In addition to being used for anode current collectors, aluminum foil can also be used in batteries for aluminum-plastic film for battery packaging and aluminum foil for tabs.

Production process of battery aluminum foil

According to the production characteristics, the performance of  aluminum foil has very strict requirements:

Melt quality

During the metal smelting process, there will be a certain amount of gas, metal and scrap metal inclusions in the melt, which will cause excessive pinholes and holes in the finished product, which is also an important reason for affecting the quality of the final aluminum foil.

The key to melt purification lies in the process of degassing, slag removal and filtration. Generally, the hydrogen content index is controlled to be ≤0.1ml/100gAL.

Shape control

Plate shape, also known as tension, mainly reflects the straightness of aluminum foil. The aluminum processing industry uses an online shape meter to control. The principle is to use the shape meter to feel the force per unit area in the transverse direction of the aluminum foil and feedback the tightness of the aluminum foil.

Top 10 lithium energy storage battery manufacturers usually use an offline shape detector to detect the shape. The principle is to use the corresponding tension to flatten the aluminum foil, and detect the difference between the horizontal position and the sagging amount of the product edge, which is called the sagging amount.

Thickness control

Generally, the thickness of aluminum foil for batteries is required to be within ±4%, and the aluminum foil rolling mill is mainly controlled by an online thickness control system. Some downstream battery manufacturers hope to control the thickness tolerance of aluminum foil within ±2%.

But most of the equipment currently on the market cannot achieve such control accuracy. Factors affecting thickness tolerance include alloy composition, hydraulic system, roll roundness, bearing precision, etc.

Surface quality

Aluminum foil has very strict requirements on the surface quality of aluminum foil, requiring uniform color, no serious streaks and color differences, no bumps and drum lines. In order to meet the quality requirements, the finished aluminum foil should be tested for pinholes and surface defects.

Mechanical properties

The tensile strength and elongation of aluminum foil for batteries are the mechanical performance indicators that need to be paid attention to. The higher the tensile strength, the better, and the higher the elongation is within 5%, the better.

Surface wetting tension

This indicator is described by the mechanical unit “dyne value” (ie dyn). Generally, users require a surface wetting tension of 30-32dyn, and some sensitive materials have higher requirements for the dyne value.

End face quality

The cutting quality of the edge of the aluminum foil, there should be no defects such as V-shaped notches, burrs, and aluminum wires on the edge.

Battery aluminum foil market

Demand scale of battery aluminum foil

In the future, the demand for lithium batteries will remain strong. It is estimated that the global sales of electric vehicles will reach 42.61 million in 2029, and the demand for power batteries will be 3196GWh.Due to the rapid development of the energy storage industry, the global demand for energy storage batteries is expected to be 827GWh in 2029.

The demand for consumer batteries is relatively stable, and the global demand for consumer batteries in 2029 is expected to be 179GWh. The global demand for lithium batteries is booming and there is a huge space, and aluminum foil, which is the upstream of lithium batteries, will also have a bright future. It is estimated that its demand will reach 1.8973 million tons in 2029.

Demand structure of battery aluminum foil

At present, batteries used in electric vehicles and other power terminals are the main source of battery aluminum foil, accounting for about 57.55%.

The proportion of demand for lithium batteries on the consumer electronics side also remained at a relatively high level, accounting for about 27.75%. Energy storage batteries currently account for a relatively low proportion, about 14.71%, because they are still in the initial development stage.

With the continued advancement of power batteries and energy storage batteries, the need for power batteries will continue to be the main driver of battery aluminum foil demand in the future. Demand for energy storage batteries will exceed consumer electronics to become the second largest source of demand for battery aluminum foil.

Currently top 10 energy storage battery manufacturers in the world are also paying attention to the new research and development of battery aluminum foil.