Dry vs Wet Separator Technology

A look at dry vs wet separator technology and a look at the next developments in the roadmap.

Author: Paul Wen from ZIMT

The separator is a porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes.

The dry vs wet differentiation is essentially the difference in the way they are produced in the factory. From PolyPropylene (PP) or PolyEthylene (PE) particles that are used to produce the film:

  • PP Dry Separator: the separator is produced without solvents being used in the process
  • PE Wet Separator: the separator is produced using solvents.
Raw materialPEPPPE raw material is ~50% more expensive than PP
Raw material melting Point135°C165°CHigher safety buffer for dry separator
Thickness7μm to 9μm12μm to 16μmWet separator is thinner and hence enables higher energy density at cell level.
Puncture strengthhigherlowerWet separator is easier to pass nail penetration test.
Solvent useyesnoDry separator is more environment friendly.
Production costhigherlowerWet is ~50% more expensive

China produces around 80% of the world’s separators. Out of these, 70% are wet process separators and 30% are process separators. As NMC battery are targeting higher energy density, manufacturers are mostly using wet separators. This is due to wet separators are 30%-40% thinner than dry separators, it can save more space for other components. As for LFP batteries, both wet and dry separators are used by cell manufacturers. Although in the beginning wet separators was more common in LFP, the demand for more affordable cells has become the key factor that driving manufacturers to opt for dry separators. BYD is one of the biggest and well-known manufacturers that began to use dry separators since 2016 and now they are using dry separators in their blade battery.

ZIMT battery separator

One last comment to add is that there are more differences in characteristics between dry and wet separators, and some characteristics can be modified through adjustments in the production process and through various functional coating options. For example, once a customer asked us to deliver high porosity separators to enable better performance in charging/discharging. It took us some time modifying the process and testing samples with the customer, and now we have this solution ready in our portfolio.

What is coming next in separator technology?

  1. Becoming thinner and thinner, to achieve higher energy density. Wet separator is heading 5μm thickness. Dry separator is heading 10μm. ZIMT is testing 10μm product with customers, expect mass shipping in 2024.
  2. Enhancing puncture strength by optimizing production process and material used.
  3. Designing additional functional coatings to improve performance in heat shrinkage, interface stability, and wettability to meet various customer requirements.
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Established in 2012. It is a national high-tech enterprise under Zhongxing New Group specializing in the research and development, production and sales of lithium-ion battery separators.

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