New Technology InsightsHeat-Resistant Coating Binder PNVATM GE191 Series

Separator is one of key components in Li-ion battery(LIB). It isolates the cathode and anode, and plays an important role in the safety of LIB.
SDK offers Poly N-vinylacetamide (PNVATM) GE191 series, an original water-soluble polymer as binder for separator coatings.
PNVATM exhibits excellent thermal stability and high coating property. Separator coated with ceramic particles and PNVATM contributes to enhancing safety and energy density of LIB.

What is PNVATM

What is PNVA™?

PNVATM is the water-soluble polymer produced by polymerization of N-vinylacetamide. SDK only succeeded in the commercial production.

SDK has started sales of PNVATM in 1997, and it has been used for the application such as flocculants, poultice bases, water absorption rubber and so on.

PNVATM GE191 Series is suitable for the binders of the ceramic heat resistance layers for LIB separator and electrode. Owing to higher number of hydrogen bond structure, it enables more uniform dispersion of metal oxide particles and thinner coating layer. These characteristics contribute to increasing energy density and reducing production cost.

Because PNVATM enhances heat resistance of coating layer, it improves safety and durability of LIBs, PNVATM GE191 series has already been employed for LIB of xEVs.

metal oxide particles

PNVATM GE191 series well coat the metal oxide particles such as alumina and boehmite by hydrogen bond.

Please see below for the grade information.

https://www.sdk.co.jp/english/products/126/132/13830.html

Basic properties

High heat resistance of the ceramic heat resistance layer

Generally, LIB separators are composed of films of polyethylene or polypropylene, which contain crystals with a melting point of around 130-150 degrees Celsius. When the temperature keeps increasing, the crystals of the separator completely fuse below 200 degrees and the separator film contracts. Then, this may causes ignition triggered by the contact of the electrode materials and consequential short-circuits. The addition of the PNVATM GE 191 series prevents contact of anode/cathode and contributes to safety enhancement. The shape of the heat-resistant layer of separators is maintained by adding PNVATM GE191 series, which enables to avoid possible short-circuit and ignition while adding PVP or CMC-Na does not contribute to such result.

Heat Resistance Test

Heat resistant shrinkage rate(average of M direction and T direction)
 PVPCMC-NaPNVATM
GE191 series
Before Heating Before Heating PVP Before Heating CMC-Na Before Heating PNVA™ GE191 series
150℃ After Heating,15min 7.0%
150℃ After Heating,15min PVP
34.4%
150℃ After Heating,15min CMC-Na
1.3%
150℃ After Heating,15min PNVA™ GE191 series
200℃ After Heating,15min 30%
200℃ After Heating,15min PVP
Fuse
200℃ After Heating,15min CMC-Na
0.7%
200℃ After Heating,15min PNVA™ GE191 series

The data shown above are representative figures. They are not guaranteed values.

Test
condition

Comparison of coated separators with different additives in different temperatures.

Ceramic layer:Almina based paint
Separator:polypropylene

Cost reduction and high energy density with uniform thin coating

PNVATM GE191 series shows high hydrophilicity. In aqueous solution, the molecular chains spread and viscosity of the water solution largely increases. Also, it is possible to form homogeneous dispersion of ceramic particle and it has a good thixotropy. Hence, the viscosity is well reduced in accordance with shear rate.

Homogeneity of the dispersion is kept for long period of time. Hence, it is able to reduce material loss and prepare thin and smooth ceramic coating layer at high rate. Due to these characteristics, PNVATM GE191 is able to contribute to process cost reduction and energy density increase.

Coating properties

Because viscosity of coating material with PNVATM decreases under higher share rate condition, it is possible to prepare homogeneous coating layer even at a high speed.

Correlation between viscosity and share rate

Correlation between viscosity and share rate
The data shown above are representative figures. They are not guaranteed values.

Effects of coating speed on surface roughness

Effects of coating speed on surface roughness
The data shown above are representative figures. They are not guaranteed values.

Comparison of uniform coating
(200mm/sec)

Comparison of uniform coating (200mm/sec)
Test
condition

Comparison of coated separators with different additives in different coating speed.

Ceramic layer:Almina based paint
Separator:polypropylene