Can and Casing

Can and Casing

Lithium-ion batteries are very sensitive to atmospheric effects like the presence of moisture and interaction with oxygen. Moisture and oxygen render the electrolyte useless and may also induce effects (like increasing flammability) which are unwanted. Also, the battery has to maintain a pressure which will prevent its collapse in environmental conditions.

Aluminium was used in batteries initially due to its high resistance to environmental factors of moisture and air. With time polymers, such as polypropylene, have replaced Aluminium as the material of choice for casings due to the easy moldability of polymers into various shapes along with excellent chemical resistance. The shapes in which batteries are produced are not restricted, although cuboidal (in mobile phones and hybrid vehicles) and cylindrical shapes are very common. In addition to the outer casing polymeric foams are used to prevent damage to the cell from accidental shock.

Ni-coated steels are used as a casing material for lithium ion batteries due to the excellent chemical resistance and corrosion protection provided by nickel to the steel. There is a development of a material (Supernickel) which apart from providing the properties of Nickel coated steel, also provides galvanic resistance.

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The cylindrical cell continues to be one of the most widely used packaging styles for primary and secondary batteries. The advantages are ease of manufacture and good mechanical stability. The tubular cylinder can withstand high internal pressures without deforming.Typical applications for the cylindrical cell are power tools, medical instruments, laptops and e-bikes. To allow variations within a given size, manufacturers use partial cell lengths, such as half and three-quarter formats. The most popular design, the 18650 Li-ion, is used in power tools, medical devices, laptops and e-bikes. The 3Ah 18650 delivers 248Ah/kg.

There are other cylindrical Li-ion formats with dimensions of 20700, 21700 and 22700. While the 18650 has a volume of 66cm3 with a capacity of around 3000mAh, the 97cm3 volume of the 21700 is said to produce a capacity of up to 6000mAh, essentially doubling the capacity with a 50% increase in volume.

The larger 26650 cell with a diameter of 26mm does not enjoy the same popularity as the 18650. The 26650 is commonly used in load-leveling systems. A thicker cell is said to be harder to build than a thinner one. Making the cell longer is preferred.The 32650 cell has a capacity of 6000mA and the dimensions are 32mm in diameter and 65mm in height but weighs about 370g.

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