[SMM Aluminum Summit] in the future, the growth rate of production and sales of new energy vehicles or the aluminum foil technology for lithium batteries under the take-off tuyere will become the key!

At the 2021 (16th) China International Aluminum processing Summit jointly held by Shanghai Futures Exchange and SMM, Bian Huijuan, director and deputy general manager of Dingsheng New Materials Group and general manager of Hangzhou Wuxing Aluminum Co., Ltd., introduced the development trend of aluminum foil for current collector of lithium-ion battery.

Overview of Lithium Battery

Current collector: as the name implies, it refers to the structure or part of collecting current, which is one of the indispensable components of lithium battery. Aluminum foil is often used as positive current collector in lithium battery.

Aluminum foil products are used in lithium battery cathode material, electrode ear, aluminum plastic packaging film, aluminum shell and cap.

Lithium battery structure diagram:

Classification of lithium battery products-cylindrical batteries by shape: 18650 and 26650, etc.; square batteries: mostly polymer batteries, because this polymer is malleable and can make a lot of shapes, length, width and height can be adjusted at will; soft package batteries: soft package lithium-ion batteries are just liquid lithium-ion batteries covered with a polymer shell. Aluminum-plastic film packaging is used in the structure, and the soft bag battery will only inflate and crack at most in the case of safety risks.

By use: 3C digital batteries: daily mobile phones, tablets, mobile power sources, etc., these are digital batteries; EV power batteries: new energy electric vehicles, as well as batteries for drones and other products; energy storage batteries: mainly refer to batteries used in solar and wind power generation equipment and renewable energy storage energy.

According to the manufacturing process: the lamination process: the positive and negative electrodes are cut into small pieces, and the diaphragm is superimposed to form a small cell monomer, and then the small cell monomer is superimposed and paralleled to form a large cell. Rely on folding, such as Z-shaped lamination; winding process: according to the negative electrode, diaphragm, positive electrode, diaphragm stacked together, through the winding method directly into, and then placed in the metal shell. Lamination process and winding process, the two are mainly different in the way of pole assembly.

Main process flow chart of lamination process:

Main process flow chart of winding process:

Technical specifications of aluminum foil for lithium battery

Compared with traditional aluminum foil:

Technical requirements and development of aluminum foil for lithium battery

Exploration stage: according to the national standard GB/T31198 standard control; tensile strength ≥ 140Mpa, no elongation requirements; pinholes are controlled according to the ordinary level, 15 μ m pinholes are less than 50 / mm; no surface wetting tension (Din value) requirements; surface end face has no special requirements.

Preparation stage: continuous improvement and improvement of battery foil production process; participation in the formulation of national standards for battery foil in 2016; surface wetting tension requirements of not less than 31 dyne; 13 μ m requirements of no less than 10 pinholes per inch; end burr, aluminum shavings, foreign material requirements began to be quantified.

Preliminary understanding: preliminary understanding of the special requirements of this kind of products, and process design and development. Tensile strength ≥ 180 MPA, elongation ≥ 1.5%; surface wetting tension requires more than 30 dynes; 15 μ m requires no more than 30 pinholes per inch.

Mature stage: Hangzhou Wuxing aluminum factory has formed a perfect battery foil process system; the thinnest thickness is 8 μ m double-sided light; performance strength ≥ 280Mpa, elongation ≥ 4%; special customer factor requirements above 33; surface end quality, surface residual oil and other indicators put forward higher requirements; 13 μ m requires less than 6 pinholes per inch.

Technical requirements of aluminum foil for lithium battery: at present, the thickness of positive current collector aluminum foil for lithium battery is 9 ~ 20 μ m. High conductivity, high strength, high flexibility and ultra-thin current collector are the development trend of current collector in the future.

Thinning: aluminum foil for lithium batteries will be thinner and thinner. 9 μ m double light aluminum foil has been mass produced in 2020 and is in the leading position in the world in thinning technology.

Performance improvement: from 2017 to 2020, the strength increased from 180-200MPA to 260-280MPA. The elongation increased from 1.5-2.5% to 4-5%.

Dyne requirements: 2018 dyn value requirements 30; at this stage dyn value requirements more than 31, special requirements 33 or more.

Other requirements: strict requirements for dimensional accuracy: thickness difference ≤ ±3%; width difference ±0.5 mm; surface end face quality requirements are extremely high; burr, notch length shall not exceed 200um; serious defects such as rimming, bulging, depression or bruising are not allowed. Foreign matter control, surface residual oil and other requirements are very high.

Market Analysis of Lithium Battery

With the rapid development of Xineng automobile market, the production and sales of new energy vehicles in China has increased from 379000 and 331000 in 2015 to 1.366 million and 1.367 million in 2020. Production is expected to reach 4 million and sales of 4 million by 2025, with a growth rate of 193 per cent from 13 per cent in 2021.

With the increase in production and sales of new energy vehicles, the installed capacity of power batteries is also on the rise, reaching 64.1 GWH in 2020. As the epidemic in most countries around the world is gradually brought under control and the industry is able to recover, it is expected that the installed capacity will increase greatly to 150 GWH in 2021, a growth rate of 134%.