Pouch cell
The pouch cell ( English pouch , German pouch), also pouch bag cell or coffee bag cell is a widespread type of lithium-ion battery .
General
The “pouch cell” design says nothing about the electrical properties of the cell, nor about the manufacturer. The English term pouch ( German pouch or bag) only describes the technical structure of the cells. Cells with a wide variety of cell chemistries can be produced as pouch cells.
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In the widespread cylindrical cells with mostly solid metallic outer shells, the active layers are wrapped around the inner electrode. In contrast to this, in pouch cells, the stacked or folded active layers are enclosed by a flexible, mostly aluminum- based outer film. The open sides of the outer bags are usually thermally welded . Several individual electrical cells can be stacked inside to increase the electrical voltage in series and the capacity and current carrying capacity in parallel . The film outer cover is at the end of the production vacuumed , whereby the cell layers pressed and fixed; however, they usually remain flexible.
Only the outer connection electrodes leave the bag-shaped cell envelope. Copper is mostly used at the negative pole . Aluminum is usually used as a conductor for the positive electrode, often based on graphite .
Advantages of the pouch cells
Due to the lack of an outer housing, pouch cells can be manufactured with low thicknesses, low weight and application-specific sizes. Thanks to their flat outer shape, they have good opportunities for heat dissipation.
Disadvantages of the pouch cells
In contrast to the cylindrical designs, which can withstand greater internal pressure without mechanical deformation due to the housing structure, the cells of pouch cells expand slightly even during regular operation due to aging and without technical defects. This fact must be taken into account when designing the enclosing housing, for example the housing of a cell phone. Incorrect treatment, such as an electrical short circuit or mechanical damage to the cell, can lead to the release of gases and significant expansion or bursting of the cells. Without a massive outer shell, not only the cell but also surrounding parts can be mechanically stressed and destroyed. Due to the thin outer foil, the cells are generally sensitive to mechanical damage and are therefore combined in massive outer housings, e.g. for traction batteries . Part of the weight gain is lost again.
Another disadvantage is the difficulty that pouch cells are manufactured in a wide variety of shapes and, contrary to the cylindrical cells, there are no standardized dimensions. This complicates the exchange in the consumer good as well as the cost-reducing mass production .
The welded sides of the outer bag hold the risk that components of the electrolyte diffuse to the outside or that oxygen gets inside the cells. Both would shorten the life of the cell and must be avoided through careful manufacturing technology.
Web links
Method for characterization and modeling of lithium-ion cells (PDF) , Jan Philipp Schmidt, KIT 2013, ISSN 1868-1603 / ISBN 978-3-7315-0115-2
Individual evidence
- ↑ Springer Professional, December 18, 2014: The battery cell also draws its power from its shape , accessed April 6, 2017
- ↑ a b c d Center for Fuel Cell Technology ZBT, March 3, 2016: Final report on lithium-ion cells for small commercial vehicles , PDF, April 6, 2017
- ^ LG Chem: 'Lamination & Stacking' procedure , accessed on April 6, 2017
- ^ TU Munich, Chair for Electrical Energy Storage Technology: Structure of a Lithium-Ion Battery , accessed on April 6, 2017
- ↑ AJ Louli et al .: Volume, Pressure and Thickness Evolution of Li-Ion Cells with Silicon Pouch composite Negative Electrodes . In: Journal of The Electrochemical Society . tape 164 , no. 12 , 2017, doi : 10.1149 / 2.1691712jes .
- ↑ Dr. Jochen Mähliß, Batteryuniversity, August 2012: Structure, functionality, risk potential ... , PDF, accessed April 6, 2017