Mineral filler
solutions for
E-Mobility
Nabaltec
oe
Mineral Fillers used for E-Mobility
Thermal Oil Specific
D50* D90* BET conduc- Mohs Product absorption gravity [μm] [μm] [m2/g] tivity hardness [ml/100 g] [g/cm³] [W/mk]
APYRAL® HC – optimized aluminium hydroxide for thermal conductivity
APYRAL® HC 500 30 110 1.2 11
APYRAL® HC 600 20 66 1.5 12
~20 2.4 3
APYRAL® HC 700 20 55 1.8 13
APYRAL® HC 800 5 23 2.5 16
APYRAL® HC – surface coated grades
APYRAL® HC 501P 30 110 0.5 –
APYRAL® HC 502H 30 110 1.2 – ~20 2.4 3
APYRAL® HC 503H 30 110 1.5 10
ACTILOX® HTB – ACTILOX® for high temperature barrier
ACTILOX® HTB PA under development
ACTILOX® HTB PP under development
ACTILOX® HTB UP under development
APYRAL® AOH / ACTILOX® – boehmite for LIBS & electrode edge coating
APYRAL® AOH 30 2.2 4 3.2 28
APYRAL® AOH 60 0.7 1.4 5 30
n. d.** 3 3 - 4
APYRAL® AOH 70 0.5 0.8 7.5 31
ACTILOX® 200 SM 0.3 0.6 18 36
*Laser diffraction, Microtrac S3500
**not defined
2
Content
04 01 PREAMBEL ........................................
02 Inside cell
LIB separator coating ...................................... 06
LIB electrode coating ....................................... 10
03 Inside battery
Thermal conductive components ....................... 12
04 Battery casing
Flame retardancy ............................................ 25
Heat barrier ................................................... 27
02 04
03
Flame retardants for Metal hydrates Metal hydrates
engineering plastics for thermosets for cables
ACTILOX®, APYRAL®, APYRAL®,
ACTILOX® B APYRAL® AOH ACTILOX® B
3
Preamble
The storage of electrical energy is Nabaltec AG supports these developments
a major challenge when it comes to in the battery industry with the aluminium
implementing national and international hydroxide (APYRAL®), aluminium
energy policy goals. Without effective oxides (NABALOX®) and boehmite
storage technology, the energy transition APYRAL® AOH product family. Thanks
toward carbon neutrality would not be to the close cooperation between
realizable. The Lithium ion battery (LIB) Nabaltec and key customers, a large
has a prominent position in this context number of innovative products tailored
due to its power and energy density. LIB to the respective application have
technology is of central importance for been developed. By increasing product
the growth of electromobility and the safety while reducing overall costs at
progressive development of stationary the same time, Nabaltec is making an
storage for renewable energies worldwide. active contribution to the breakthrough
of Lithium ion battery technology in
safety-relevant application areas.
Thermal Runaway – a most discussed safety issue
Thermal runaway is the uncontrolled battery often leads to a total failure of
generation of heat within the battery. battery with devastating consequences,
Thermal runaway specifically in Li-ion an overview is shown in figure 1.
Fire
Explosion
Contamination Smoke
Mechanical Electrical
Abuse Abuse Thermal
Abuse
Thermal
Runaway
Crush Penetration Overcharge Overdischarge Overheat
Deformation Dendrite Growth Exterme Temp
Separator Tearing Separator Piercing Separator Collapsing
Internal short circuit No Thermal Runaway
Figure 1: Abuse conditions leading to thermal runaway.
After: Feng, X.; Ouyang, M.; Liu, X.; Lu, L.; Xia, Y.; He, X. Thermal runaway mechanism of lithium
ion battery for electric vehicles: A review. Energy Storage Mater. 2018,10, 246–267. [CrossRef].
4
The most common cause of a thermal conducting heat out of the battery packs.
runaway is failure of the separator. In this Nabaltec’s product portfolio for LIB
brochure we will show how Nabaltec’s safety is completed by designated
products enable longevity and safety of functional filler blends preventing heat
LIB, by strengthening the separator against propagation on LIB pack level.
failure, protecting the electrodes, and by
Inside cell
APYRAL® AOH, ACTILOX®
• Boehmite for LIB separator coating
• Boehmite for LIB electrode coating
Prevention of short circuit
Inside battery pack
APYRAL® HC
• Aluminium hydrates for high thermal
conductive gap filler/ adhesive and sealant
Prevention of thermal overload
Battery casing
ACTILOX® HTB
• High temperature barrier functional
fillers in battery covers
Prevention of fire propagation
5
Inside cell
LIB separator coating
• General explanation of the polypropylene (PP), or polyethylene
LIB separator coating (PE) based separator without protection
coating will shrink due to the sudden heat
Each battery cell is built up in several development. At some points the direct
different layers. The energy source is hidden contact between the cathode and the anode
in these layers. A porous separator acts will happen. This results in an internal
as an electrically isolating layer between short circuit and continuous in a thermal
the positively charged cathode and its runaway in the battery. The entire system
negative counterpart the anode but allows starts to burn or may even explode.
the free move of Lithium ions (s. figure 2).
Such failure can be prevented by an
However, in case of overcharging or inorganic ceramic coating applied on the
overdischarging, thermal stress in general separator. Boehmite has become the
or an external short circuit, the plain preferred material for such coatings.
Active materials
Separator
Active materials
Anode
APYRAL® AOH,
ACTILOX®
Cathode
Figure 2: Three-dimensional structure illustration of a Lithium ion battery cell.
6
untreated separators already shrink at
around 90 °C. Additionally, the coated
separator is reinforced against dangerous
dendrites which may be formed during
charge-discharge cycles and pierce the
non-coated separator resulting in a short
circuit due to the contact of the electrodes.
The heat stable coating with
APYRAL® AOH, ACTILOX® makes
the battery much safer and more
resistant to short-circuit reactions and
Figure 3: A gravure roller coating sytem in prevents possible fires and explosion.
which the boehmite dispersion is applied on
a separator. • Advantage of boehmite over
high purity alumina (HPA) and
Boehmite is produced by hydrothermal low soda aluminium oxide
conversion of aluminium hydroxide (ATH).
Nabaltec’s boehmite products with the trade Due to the further increasing energy
names APYRAL® AOH and ACTILOX® density of Lithium ion batteries, the use
are extremely pure crystalline boehmites of safe separators with ceramic coatings
with a very low ATH and electrolyte residue is becoming more and more important.
(purity min. 99 %). This guarantees an
extraordinary high temperature stability High purity alumina (HPA) was developed
up to 340 °C. Additionally, boehmites as a first-generation commercial solution
have a very good chemical resistance. at the beginning of the 2010 decade.
However, prices of HPA did not allow ceramic
To coat the boehmite on the separator, the coating technology to leave the status
white powder is processed into a so called of a niche product. HPA was therefore
slurry, using the boehmite, water (or an quickly replaced by the second generation
organic solvent like acetone), a dispersant based on low soda aluminium oxide.
and a binder system. This dispersion can
then be applied on one or both sides of As a new coating material for the third
the plain separator, e.g. by the use of a generation, boehmite has the strongest
gravure roller coating or slot die system. growth rate. Technically boehmite is
A basic formulation is given on page 9. characterized by the following advantages:
• high chemical purity
The separator coated in this way gains heat-
• narrow particle size distribution
resistance and prevents shrinkage of the
• uniform morphologypolymer membrane. It is crucial that the
coating is still permeable and has a high • good dispersibility
porosity. Thanks to this ceramic coating the • low moisture content and uptake
separator can withstand a temperature of
• low hardness compared to aluminaup to 250 °C, depending on the substrate as
well as the used additives. In comparison, • moderate physical density
7
Comparison of powder parameters of boehmite (APYRAL® AOH) and low soda
aluminium oxide.
Mohs Density BET Na2Ototal Na2OH2O-soluble Materials hardness [g/m²] [m²/g] [%] [%]
α-Al2O3
typical commercial 9 3.9 6.3 0.037 0.036
grade
APYRAL® AOH 60 3 - 4 3.0 5 0.020 0.002
reduced abrasion and
reduced moisture uptake
total weight
In comparison to aluminium oxide, the Lower Density
use of boehmite results in the following Furthermore, the lower density of
benefits of the LIB-Separator coating: APYRAL® AOH enables ceramic coated
separators with lower specific weight
Reduced abrasion and cells with higher energy density.
Aluminium oxide is one of the hardest
materials with a value of around 9 on the Tailor-made particle size
Mohs hardness scale. In contrast, boehmite distribution (PSD)
with a Mohs hardness of 3 - 4 is a rather soft
Last but not least, the most important
mineral. This difference is clearly noticeable
parameter in powder production and
in the abrasiveness of the slurry during
application is the tailor-made PSD. Less
preparation and coating process. Finally, the
coarse particles and an excellent Top Cut
ceramic separators itself are less abrasive,
serves not only a perfect appearance
making coiling and further processing easier.
of coating layer but also avoids defect
structure or inconsistent thickness of
Reduced moisture uptake coating layer. Special matched PSD offered
Because of its moderate surface area the best performance in different coating
according to BET when comparing with formulation in particular in terms of
alumina of similar fineness, and it’s very low anti-heat shrinkage and ion permability.
level of water-soluble soda, boehmite shows On the following page, application data
low water uptake. Consequently, separators based on APYRAL® AOH 70 is given.
coated with APYRAL® AOH have a very low
moisture uptake what is crucial in a LIB.
8
18
APYRAL® AOH 70 [%]
Water based test 16
formulation calculat-
14 ed on active content:
92 – 97 % boehmite 12 Distribution 0.2 – 2 % dispersant*
0.5 – 1 % wetting agent 10
3 – 5 % binder system competitive product
8
*depending on fineness of the 6
used boehmite
4
2
0
0.100 1.000 10.000
Particle size [µm]
Easy dispersion of APYRAL® AOH 70 In water dispersed APYRAL® AOH 70 using a standard
no milling necessary. lab stirrer.
Uncoated Doubleside coated
150 °C / 30 min 150 °C / 30 min
Result of oven shrinkage test of coated / uncoated separator.
PE-Separator (12 µm)
150 °C / 30 min D50 Coated layer Shrinkage of MD & TD Gurley
[nm] [μm] [%] [s/100 ml]
Reference PE – – > 70 140
APYRAL® AOH 70 500 2 + 2 1 - 3 200
9
Flame retardancy Burning test
Furthermore, boehmite coated LIB In LOI (limited oxygen index) test, the test
separator shows effective flame specimen of Al2O3 coated separator burned
resistance in comparison with aluminium through, while the specimen of boehmite
oxide coated LIB separator as shown coated separator self-extinguished.
in the following burning test.
pilot
flame burning
specimen*
N2/O2 supply
Uncoated Al2O3 coated APYRAL® AOH *specimen is an interfolded coated / uncoated LIBS
60 coated
LIB Electrode coating
An additional protection against internal 1. Prevention of cutting burrs caused
short circuit besides separator coating is issues
the electrode coating (e.g. edge coating
via die coating, figure 4). The main The boehmite covered current collector
functions of the electrode coating are: (Al- or Cu-foil) reduces the occurence of
cutting burrs and the risk of such burrs to
puncture through the separator, touching the
counter electrode and causing a short circuit.
2. Isolation to avoid an internal
short circuit caused by possible
deviation of cell assembling.
Other than for separator coating, the
industry chooses boehmite for this
Figure 4: A die coating system in which the application right from the start. The
boehmite dispersion is applied to determining metric to use boehmite is
the cathode edge. the low hardness compared to alumina.
10
Boehmite coating improves the overall Dispersibility of the boehmite powder,
performance of the electrode cutting process sedimentation and agglomeration and
and it avoids a secondary contamination viscosity of the coating slurry are essential
through abrasion of cutting tools. for a successful coating and need a detailed
All these positive effects on processing evaluation. In the following pictures, the
performance and battery cell safety can basic preparation and testing procedure, as
only be deployed when the production it is performed in the Nabaltec application
process from slurry production via slurry lab for an electrode slurry, is shown.
handling and coating is properly designed.
Preparation and testing of an NMP based slurry for cathode coating
Boehmite / APYRAL® AOH, Dispersant / BYK®-ET, PVDF / Kynar® HSV, solvent / NMP
Dispersion PSD Viscosity Coating
• via DISPERMAT® measurement measurement • Via bar coater
Dissolver • Via Grindometer • Via Rheometer
mPas 4000 3500
3000
2500
2000
1500 APYRAL® AOH 60
1000
APYRAL®AOH 30
500
0
10 210 410 610 810 1010
Shear rate [1/s]
Figure 5: Viscosity as a function of shear rate for electrode-
coating slurries. Influence of the fineness of the used boehmite
(APYRAL® AOH 30 vs. APYRAL® AOH 60) is demonstrated using
a solid content of 40 %.
11
Inside battery
Thermal conductive
compounds
Regarding thermal management the major in the electronic industry are used in scale
components which need consideration are of some grams per unit, a modern LIB for
electrical motors, power electronics (e.g. EVs require kilograms of a gap filler. In this
inverter and converters) and last but not regard, easy and fast dispensing plays a
least the Lithium ion batteries (LIBs). critical role to enable short assembly times.
To keep the battery from overheating during Nabaltec AG has developed high
fast charging the heat has to be conducted performance fillers based on aluminium-
out of the battery stacks through the battery tri-hydroxide (ATH) – APYRAL® HC.
enclosure to an external (active) cooling Their optimized particle size distributions
system. Here the adhesive attaching the simultaneously allow high packaging
stacks to the enclosure and especially the densities (resulting in high TC values)
gap filler between the single stacks of the and extremely low viscosity levels.
battery module (s. figure 6) play key roles.
For gap fillers usually a thermal conductivity
(TC) of 2.5 – 3 W/mK is demanded, which
requires filling levels often significantly
above 80 wt.-%. While gap fillers and
classic thermal interface materials (TIM)
Figure 6: Adhesives and gap fillers in a Lithium ion battery.
12
With the help of optimized APYRAL® HC APYRAL® HC 500 d90 = 110 µm
fillers, formulators obtain a toolbox to APYRAL® HC 600 d90 = 66 µm
reach required thermal conductivity APYRAL® HC 700 d90 = 55 µm
levels in an easy way. Depending on the APYRAL® HC 800 d90 = 23 µm
applications the maximum particle size
may be limited. Therefore finer grades are With the fine grades like
offered, as displayed by the d90-value: APYRAL® HC 700 & 800 even
thin applications like conductive
coatings or tapes can be realized.
The highly favorable product finally lead to very attractive
properties of APYRAL® HC compound properties:
grades, like
• extremely low viscosity,
• optimized particle size distribution, • extremely high filler loads,
• unique morphology, • good dispensing properties,
• high packaging density, • high flame retardancy,
• improved sedimentation stability, • good thermal conductivity (isotropic),
• low hardness and abrasion, • good value,
• low cost in comparison to high • very low density & weight.
performance thermal conductive fillers,
• very low density.
13
Parameters influencing thermal conductivity
When trying to improve the TC of a the focus. Naturally the formulator seeks
polymer compound a set of parameters fillers with high intrinsic TC values, like
of the compound ingredients have to boron nitride (BN), aluminium nitride (AlN),
be considered. Figure 7 gives a simple alumina (Al2O3, AO) or magnesia (MgO).
overview on these parameters. First For an overview of selected mineral fillers
and foremost, one usually considers for polymer applications including their
the thermal conductivity of the TC values, please compare table below.
resin and of the mineral filler.
However a high intrinsic TC of the filler
The TC of most resins is very low, is not a necessity. A high filler loading
consequently TC of the mineral filler is in can be more important, which the
following chapters shall demonstrate.
Important powder parameters of common thermal conductive fillers.
Tdecomp TC Density Mohs Name, abbreviation Formula [°C] [W/mK] [g/cm³] hardness
APYRAL® HC, aluminium
Al(OH)3 200 20 - 25 2.4 3 hydroxide, ATH
APYRAL® AOH, boehmite, AOH AlOOH 340 n. d.* 3.0 3 - 4
Alumina, AO Al2O3 >> polymer 20 - 40 3.9 9
Magnesium hydroxide, MDH Mg(OH)2 320 10 2.4 3
Magnesia MgO >> polymer 40 - 60 3.6 6
Hexagonal boron nitride BN >> polymer 15 - 400 2.2 1
Aluminium nitride AlN >> polymer 180 - 220 3.2 9
Silica SiO2 >> polymer 1 - 12 2.2 - 2.6 6 - 7
Calcium carbonate CaCO3 >> polymer 4 - 6 2.7 3
Polymers – > 350 0.2 - 0.5 – –
*not determined
14
Dispersion
Size
quality
Thermal Filler
TC of
conductivity VOLUME Viscosity Particle Morphology
Polymer
of compound load
TC of
Density Shape
Mineral
Figure 7: Important parameters to influence the thermal conductivity of a polymer compound.
Filler load
When filling a compound one quickly realizes of the slope changes more slowly. But both
that filler loading level is a very crucial parameters, TC and EC, have in common
parameter. This is understandable as one that a minimum filling level is required
tries to replace as much of the insulating to gain an adequate level of conductivity.
polymer by the better conducting mineral. The percolation threshold explains why
With low loading levels the TC is affected it is better to plot the TC versus volume
only little, while with increasing load the based filling level (vol.-%) rather than filler
incremental increase of TC becomes higher. loading based on weight percent (wt.-%).
Such an effect is well known when trying
to increase the electrical conductivity (EC). Ultimately, the formulator has to gain as
Only when the particles start to touch each high filling levels as possible. These levels
other, the conductivity rises strongly. This may be limited by mechanical properties
point is called the percolation threshold, and processing factors during compounding.
see figure 8 (next page). For EC this point Such an important factor is the viscosity
is very sharp, while for TC the steepness performance of the filler, as a low viscosity
is crucial to gain high filler loadings.
15
EC
TC
Figure 8: Percolation threshold for the electrical (EC) and thermal
conductivity (TC) of a compound.
Viscosity
As indicated above the viscosity effect of Subsequently after dispersion each resin
the filler cannot be underestimated. Actually compound was measured in a rotational
this is the dominating factor to obtain high rheometer. The viscosity value was
filling levels necessary for high TC values. determined at a shear rate of 10-s at 22 °C.
The upper graph in figure 9 shows the The plotted relative viscosity represents
influence of the filler loading to the resulting the quotient of the viscosity of the filled
viscosity increase of an unfilled unsaturated resin to the viscosity of the neat, unfilled
polyester resin (UP) by various mineral resin at same measuring conditions. After
fillers. The fillers have been dispersed by a measuring the viscosity, the compounds
high speed dissolver into the resin, which have been cured and the specimens where
featured a low viscosity of about 0.9 Pa·s polished to obtain a plain surface necessary
only. Step by step the filling level was for measuring the thermal conductivity by
increased until the maximum filling level Hot Disk method at 22 °C, according to
with a visible good dispersion was reached ISO 22007-2. The TC of these cured
(indicated by the sign in figure 9). compounds are plotted in the lower
graph of figure 9.
16
[-] 600
500 Al2O3, 3 µmincrease
visosity 400 Al2O3, 0.9 µm
300
Relative 200 APYRAL® HC 500
APYRAL® HC 600
100 Al2O3, 80 µm
BN, 9 µm
0
0 10 20 30 40 50 60 70
Filler [vol.-%]
[W/mK] 2.5 APYRAL® HC 500
2
Al2O3, 3 µm
1.5conductivity
Al2O3, 80 µm BN, 9 µm
1
APYRAL® HC 600Thermal Al2O3, 0.9 µm
0.5
0
0 10 20 30 40 50 60 70
Filler [vol.-%]
Figure 9: Relative viscosity of APYRAL® HC in comparison to
calcined Al2O3, and BN in UP resin at shear rate 10 s-1 at 22 °C
(above) and the corresponding TC values obtained by
Hot Disk method after curing (below).
Similarly to the conductivity, the viscosity These discrepancies can be explained when
is rising strongly with increasing filler loads. considering the differences in particle size
However, the rheological performance of BN and morphology of the individual minerals,
and alumina is lacking far behind the one of displayed in figure 10 (next page).
optimized APYRAL® HC.
17
A B
25 µm 25 µm
C D
5 µm 10 µm
Figure 10: SEM-images of calcined alumina (80 µm, A),
APYRAL® HC 500 (B), calcined alumina (3 µm, C), and BN (9 µm, D).
Particle size
Very often formulators seek for fillers with Thus, only one, low filling level could be
big particle size as they expect to gain not obtained no higher filling was possible,
only lower viscosity enabling higher filling limiting the obtainable TC (s. figure 9).
level, but also higher TC levels in comparison
to small particles. In theory this is truly In case of calcined alumina the optimum
the case when one compares particles of viscosity is gained when the primary
the same chemistry and morphology which particles (figure 10 C) are set free by gentle
feature low porosity. However, this is not grinding without further destroying them.
easy to obtain in every kind of mineral. This is usually the case at mean particle
sizes between 1 and 10 µm, depending
For example, APYRAL® HC and the coarse on the calcination state. When grinding
calcined alumina have similar particle is enforced to smaller particle sizes, then
size, but their viscosity is very different. the primary particles are destroyed and
APYRAL® HC (figure 10 B) consists of more micropores generated which leads
single grown, compact crystals, while the to high oil absorption and viscosity
coarse alumina (figure 10 A) is revealed (s. Al2O3, 0.9 µm in figure 9). However,
as a hard agglomerate of small primary even alumina in ideal primary crystals state
crystals with many internal macro pores. do not feature the viscosity performance
This raises oil absorption and viscosity. of the unique crystals of APYRAL® HC.
18
Particle shape
The distinct platy nature of the BN than through plane. Thus, BN has a strong
crystals (figure 10 D) lead to very intrinsic anisotropy in its particles. However,
strong shear thinning effect in fluids. due to the rheological properties plates often
align into the same direction during flow,
In the reported experiments a filler load of e.g. during injection molding. Therefore in
20 vol.-% BN could be generated only, a lot of applications where BN is utilized
leading to a low TC level. When trying to as a filler, a strong anisotropy of TC in the
disperse a higher loading of 27 vol.-%, final component needs to be considered.
the BN could not be dispersed. During
addition of the filler the compound was To check for anisotropy a simple
clogging at the wall of the container, experiment was made. The two specimens
(s. figure. 11), a region of low shear from the viscosity/TC-experiment
where the viscosity is several orders of described above were cut into stripes,
magnitude higher than in the near of the each stripe turned by 90 degrees and
dispersion blade (high shear region). glued together with same uncured resin
compound. The TC of these specimens
This makes the dispersion of platy BN very was measured again after hardening and
difficult and leads to low to moderate filling polishing of the former cut stripes.
levels only. The high intrinsic TC level of
this mineral could not be fully utilized as Although the original specimen have been
the rheology was limiting the filler loading. prepared by a simple casting, which should
not evoke a high degree of alignment of
Another aspect influenced by the particle the BN particles, a significant higher in-
shape is the 3-dimensional flux of the plane-TC could be determined for the BN
conducted heat. Ideally the heat shall compound (s. figure 12 , next page) in
be conducted in equal measure in all contrast absolutely no difference of TC,
dimensions (isotropy) and not directed was observed for APYRAL® HC whether
in one direction only (anisotropy). measured in plane or through plane.
This is confirming the expected isotropy
The graphite-like molecular structure of of ATH, demonstrating that parts made
BN does not only lead to a platy shape, by APYRAL® HC filled resins are free
but also to the fact that within the plates from geometrical design restrictions.
the heat is conducted much faster in plane
Figure 11: Aborted experiment trying to
disperse 27 vol.-% of BN in UP-resin. All
material clogs to the wall while the dissolver
blade (not shown) is mixing only air.
19
[W/mK] 1.82
1.6
HC HC
BN conductivity 500 500
1.4 vol.-%
1.2 Thermal APYRAL® 20 APYRAL® BN
1 vol.-% vol.-% vol.-%
61 61 20
0.8
through-plane in-plane
Figure 12: Thermal conductivity of an UP resin filled with BN or
APYRAL® 500 HC, measured in- (right) and through-plane (left).
Density (specific gravity)
Considering the model of touching particles Again one can see the strong effect of the
to generate a high TC it is better to plot low density of APYRAL® HC: The alumina
the TC versus volume based filling level with best viscosity features (3 µm) can be
rather than filler loading based on weight filled up to 76 wt.-% but results in a lower
percent. Therefore the density (specific TC than APYRAL® HC 600 which reaches
gravity) of the filler plays an important role. only 75 wt.-% loading. The higher TC
Low density fillers will gain a higher volume value can only be explained when taking
loading at the same loading level by weight. the volume based filling level into account,
displayed as green bars. When utilizing
APYRAL® HC exhibits a very low density APYRAL® HC 500 with its outstanding
(2.4 g/ml). This is a very important point viscosity performance an even
when calculating the mass based formulation higher volume loading and a TC
cost versus the volume based application of 2 W/mK can be obtained.
cost, where a certain volume has to be filled.
The unique properties of APYRAL® HC 500
Finally, using APYRAL® HC with its unique were demonstrated in several resins with
rheological properties allows highest filler varying viscosity and intrinsic TC levels. The
loadings resulting in even higher TC levels in results are displayed in figure 14. Depending
comparison to calcined alumina or even BN. on the viscosity level and the mechanical
properties (e.g. cross linking degree) of the
The obtained TC of the maximum filling resin, different loadings and TC levels close
levels of the UP compounds are plotted to 3 W/mK can be gained. This makes
in figure 13 in two ways, by volume APYRAL® HC 500 and 600 ideal
fraction (vol.-%) and weight fraction candidates for modern TIM and
(wt.-%) of the same compound. especially gap fillers for EV batteries.
20
80
70vol.-%]
or 60
50[wt.-%
Loading 4030 W/mk
1.1
20
W/mk W/mk W/mk W/mk W/mk 10
1.0 1.4 1.0 1.6 2.0
0
BN, 9 µm Al2O3, 0.9 µm Al2O3, 3 µm Al2O3, 80 µm APYRAL® HC 600 APYRAL® HC 500
max. possible load [vol.-%] max. possible load [wt.-%]
Figure 13: TC of APYRAL® HC in comparison to calcined alumina, and BN in UP-resin at 22 °C
(Hot Disk method).
3.0
APYRAL® HC 500 – TC @ max. possible load[W/mK] 2.5
2.0conductive
Thermal 1.51.0
0.5 wt.-% wt.-% wt.-% wt.-% wt.-%
80 83 83 78 87
0.0
UP, UP, ultra PUR, PUR, EP, ultra
low viscosity low viscosity hard soft low viscosity
Figure 14: Thermal conductivity of selected resins of various
chemistry and cross linking density filled with APYRAL® 500 HC
to the maximum possible load in each resin.
21
Abrasion
Thermal conductive compounds used in it is not a good idea to use big alumina
EV parts, especially gap fillers for LIB particles at high loadings. Materials with
packs and modules, are to be consumed low Mohs hardness and low abrasion, like
in big volumes so far not known from APYRAL® HC (Mohs 3) are to be preferred.
TIM in classical electronic applications. In
large scale industrial applications abrasion In figure 15 the color of a PU resin
and wear of tools during production and compound filled with APYRAL® HC 500,
dispensing of HC compounds becomes an a fine ground alumina and a coarse
extremely important quality and cost factor. spherical alumina is shown. The differences
of abrasion from a common high speed
Because of Mohs hardness 9 (only diamond dissolver disk during a 10 minute
is harder) Al2O3 particles are excellent dispersion are very obvious. Practically
abrasive materials – and it is known that no abrasion occurs when utilizing
abrasiveness increases strongly with APYRAL® HC, while alumina will always
particle size. This is another reason why cause additional cost due to abrasion.
Spherical
APYRAL® HC Al2O3 3 μm
Al2O3, 75 μm
Figure 15: Color change of a PUR compound due to abrasion from dissolver disk when utilizing Al2O3.
22
Battery casing
Flame retardancy &
Heat barrier
Flame retardancy
Likewise other electric components, LIBs Exemplarily, figure 16 (next page) shows
belong to the safety sensitive components the results of the cone calorimetry
of an EV. Such components need to fulfil measurement of PUR, unfilled as well as with
fire safety requirements. While final high filler loading of APYRAL® HC 500.
standardization is still in progress, materials It can be easily seen that the addition of
in use are commonly requested to fulfill APYRAL® HC 500 leads to a significant
flame retardancy classification according reduction of the peak heat release rate
the UL 94 V0 (similar to E&E applications). which means in effect a considerably
Even when using BN or alumina at high improved flame retardancy.
filling levels which fulfil the required
3 W/mK, an UL94 V0 classification is not Such highly filled glass fiber reinforced
easy to achieve. Therefore additional flame plastics (e.g. SMC / BMC) are already
retardants have to be used, which lead to in use, when such severe flame
higher cost and even higher viscosity. retardancy classifications are required.
This makes APYRAL® HC grades
This is not the case with APYRAL® HC as also an ideal solution for glass fiber
it is based solely on ATH, a well-known reinforced battery housings in an EV.
mineral flame retardant. In many resins a
UL94 V0 classification is already achieved Hence APYRAL® HC is not only a filler
with filler loadings of 60 – 65 wt.-%. enabling required thermal conductivity
When it is used at loadings enabling but features also excellently as flame
2.5 - 3 W/mK reported above, often very retardant and smoke suppressor, enabling
stringent flame retardancy classifications additional value and performance for
like e.g. lined out in EN 45545 (European a broad use in EV applications.
railway standard) or CPR can be achieved.
23
[kW/m2] 12001000
PUR reference (unfilled)
HRR
800
600
46.7 vol.-% standard Al2O3 in PUR
400
46.7 vol.-% APYRAL® HC 500 in PUR
200
61.4 vol.-% APYRAL® HC 500 in PUR
0
0 200 400 600 800 1000 1200 1400 1600 1800
Time [s]
Figure 16: Cone measurement of PUR. Heat release rate of unfilled PUR in comparison with
APYRAL® HC 500 and standard Al2O3 filled PUR.
Cone Calorimeter
24
Heat barrier
As the number of EVs is increasing strongly, OEMs to evaluate thermal propagation
fire safety of the battery casings becomes in case of a thermal runaway scenario.
more and more important. Herein, the Nabaltec AG has developed innovative filler
trend goes far beyond the well-known systems called ACTILOX® HTB to meet
UL 94 V0 classification but towards a this new and demanding requirement.
real heat barrier which can enclose the ACTILOX® HTB are mineral based flame
thermal runaway of a battery for a certain retardant filler blends, which together
time. Since first of January 2021 China with the polymer matrix form hard
as pioneer in electromobility has already ceramic-like layers during torch testing.
defined a new standard (GB 38031- 2020) These ceramic like residues guarantee
which demands a thermal propagation physical strength and a strong
test. It is described that after the thermal heat barrier for battery casings
runaway of an individual cell, there in a thermal runway event.
must be at least 5 minutes until thermal
propagation leads to battery ignition or
explosion. This requirement shall allow
passengers to have enough time to escape
the EV. It is expected that new standards
all around the world will be implemented
to tackle this thermal propagation
issue of the battery module in EVs.
Lightweight materials like aluminum or
fiber reinforced composites are preferred
for the construction of battery casings.
These materials per se do not withstand
torch flame tests which are requested by Figure 17: Torch Flame Test
25
Coating of Aluminum sheets
As a non-corrosive light metal, aluminum More preferred are heat barrier coatings
is a well-established automotive material applied on the inner side of the Al-sheet.
and therefore also broadly used for the With an ACTILOX® HTB blend optimized for
construction of battery enclosures. But an epoxy-resin coating, a stable ceramic-
its low melting temperature of 660°C like ash crust is formed during the torch
hinders the use of pure Aluminum. flame test (see figure 18). The Al-sheet
Mica-sheets are used as additional heat keeps faultless on the backside, and the
barriers applied on battery modules. But backside temperature stays below 140 °C
this requires an extra assembly step. for the 20 min test duration (see figure 19).
Figure 18: Al-sheet coated with EP-resin with 300 phr ACTILOX® HTB after torch flame test.
Left: exposed (coated) side showing ceramic like residue, right: backside showing intact Al.
Temperature backside
600 °C
in
T 500
AI-Plate pure
400
300
200
1,3 mm Coating
3,5 mm Coating 2,0 mm Coating
100
2,5 mm Coating
5,0 mm Coating
0
1 3 5 7 9 11 13 15 17 19 21
t in minutes
Figure 19: Temperature on backside during 20 min torch-flame test procedure. Upper curve:
pure Al-Plate (no coating). All other Al-Plate specimens are coated with EP, containing 300 phr
ACTILOX® HTB at different thicknesses. While non-coated reference reaches > 500 °C on
backside, even the thinnest coated specimen (1.3 mm) stays < 140 °C.
26
SMC (Sheet Moulding Compounds)
A B
Figure 20: UP-laminate (15 wt.-% GF) after torch test: A) 300 phr APYRAL® HC 500
and B) 200 phr ACTILOX® HTB.
Glass-fiber reinforced thermosets like UP- One specimen is highly filled with pure ATH
resins highly filled with ATH APYRAL® HC APYRAL® HC 500 at 300 phr (specimen
are already used for battery covers A), left). The other one (specimen B), right)
made of SMC. But to fulfil the heat is filled with 200 phr ACTILOX® HTB.
barrier requirements against thermal Both specimens keep intact after the torch
runaway scenario, mica sheets must be flame test, but the specimen filled only with
glued onto the inner side of the SMC ATH is relative fragile. Figure 21 compares
battery lid in addition. Again, this is a the cross-section of specimens A) and B).
non-favored extra assembly step. While the ATH filled laminate A) results in a
soft ash with loose fibers (area exposed to
When using ACTILOX® HTB as specialty the torch), the ACTILOX® HTB containing
mineral flame-retardant filler during SMC laminate builds a very strong ceramic like
production, this additional assembly step residue. This residue builds an excellent
is no longer needed. ACTILOX® HTB can heat barrier proven by the temperature
easily be mixed into the reactive resin recording shown in figure 22. The
blend with standard process equipment. temperature difference between torch-
The two specimens shown in figure 20 are flame exposed front side and backside
hand laminates based on UP-resin and does not undercut 600°C and backside
15 wt.-% glass fiber matts after 30 min temperature does not exceed 400°C.
exposure to the torch flame.
A B
Figure 21: cross-section of specimen A) = 300 phr APYRAL® HC 500 on left side and specimen
B) = 200 phr ACTILOX® HTB on right side.
27
Temperature front/back
°C 1200
in 1000
T front
800
600
400
back
200
0
0 5 10 15 20 25 30
t in minutes
Figure 22: Temperature recording over 30 min torch-test on
ACTILOX® HTB containing laminate B) for front side (light blue,
exposed to flame) and back side (dark blue).
GFRP (Glass Fiber Reinforced Plastic)
GFRP based on PP or engineering plastification are the glass fiber content,
plastics like e.g. PA6, PA6.6, are further the composition of the flame-retardant
light-weight material options under blend and its addition level. The flame-
investigation for battery covers. Other retardant composition as such is the key
than crosslinked thermosets used for for the formation of a stable crust.
SMC, thermoplastics soften and start to Figure 23 shows three examples based on
flow when exposed to heat. This effect PA6. For the specimen on top, the
is lessened with GF reinforcement, flame retardant – boehmite
but it is still existent. Crosslinking is APYRAL® AOH 30 – did not form a
doable, but non-desirable, because then stable char during torch-flame test.
GFRP materials lose their benefit of A hole was burnt into the plate within
being recyclable by thermo-forming. 4 min, the test failed. The specimen in
the middle shows a composite containing
To make a thermoplastic GFRP pass the an ACTILOX® HTB variant (-a) which
torch test, compound melt flow should not formed a stable, ceramic like crust. But
be too high and solidification kinetic of burnt the non-burned compound plasticized too
compound needs to fit to the melt flow in the quickly. The solidified crust broke out of
areas surrounding the spot exposed to the the test plate after 15 min and test failed.
torch flame. In other words, the composite The specimen on bottom passed the test
needs to be balanced between ceramification in all criteria. One reason is the glass fiber
reaction of flame-retardant component content, which was increased up to
with polymer / glass fiber matrix – which 20 wt.-%. An optimized ACTILOX® HTB
is induced by the direct contact of the variant (-b) was used at 40 wt.-%. Backside
torch flame – and the plastification of the temperature stays below 400 °C for the
composite under the influence of the heat. 20 min test duration and the residue is a
Parameters influencing melt flow and very solid and mechanically integer plate.
28
Figure 23: PA6-plates with varying glass fib-
er (GF) and flame-retardant contents
(all values in wt.-%) after torch-flame test.
Top: pure boehmite APYARAL® AOH 30
Middle: non-optimized flame-retardant
ACTILOX® HTB (-a) blend
Bottom: GF-content increase to 20 %
and 40 wt.-% of an optimized
ACTILOX® HTB (-b)
PA6_5%GF_50% APYRAL® AOH 30 4 min
until sample burns through
PA6_5%GF_50% ACTILOX® HTB -a 15 min
until solid, ceramic like residue breaks out
PA6_20%GF_40% ACTILOX® HTB -b
No burn through within 20 min; very solid,
ceramic like residue; backside
temperature < 400 °C
29
Our know-how
for your safety
31
Annex
Abbreviation Meaning
α-Al2O3 Alpha-alumina
AlN Aluminium nitride
AO Aluminium oxide
AOH Aluminium oxide hydroxide
ATH Aluminium trihydroxide (aluminium hydroxide)
BET Specific surface area according to Brunauer, Emmett, Teller
BN Boron nitride
BMC Bulk moulding compound
d50 Median particle diameter/size
d90 90 % of particles have a smaller particle diameter/size
BYK®-ET Dispersant from BYK-Chemie GmbH, Wesel, Germany
E&E Electrical and electronics
EC Electrical conductivity
EV Electric vehicle
EP Epoxy
GFRP GLASS FIBER REINFORCED PLASTIC
HC Heat / thermal conductivity
HPA High purity alumina
Kynar® HSV PVDF from ARKEMA
HTB High temperature barrier
LIB Lithium ion battery
LOI Limiting oxygen index
MD Machine direction
MDH Magnesium dihydroxide (magnesium hydroxide)
MgO Magnesia, magnesium oxide
NMP N-Methyl-2-pyrrolidone
PE Polyethylene
PP Polypropylene
PSD Particle size distribution
PUR Polyurethane
PVDF Polyvinyliden fluoride
SEM Scanning electron microscope
SMC Sheet moulding compound
TC Thermal conductivity
Tdecomp Decomposition temperature
TD Transverse direction
TIM Thermal interface material
UP Unsaturated polyester resin
GB 38031-2020 Electric vehicles traction battery safety requirements
Class H NEMA insulation classes for motors (180 °C)
CPR Contruction product regulation (July 1, 2017)
EN 45545 European railway standard
Plastics – Determination of thermal conductivity and thermal diffusivity – ISO 22007-2 Part 2: … Transient plane heat source (hot disc) method…
UL 94 Vertical burning test according to UL 94 (Underwriter Laboratory)
32
Nabaltec
product portfolio
ACTILOX® GRANALOX®
Boehmite, as flame retardant Ceramic bodies, for
filler and catalyst carrier the production of
engineering ceramics
APYRAL® AOH NABALOX®
Boehmite, as flame retardant Aluminium oxides, for the
filler and functional filler production of ceramic, refractory
and polishing products
APYRAL®
Aluminium hydroxides, as flame
retardant and functional filler
33
Nabaltec
worldwide
Visit us at our website www.nabaltec.de where you will find the latest company updates and
recent versions of all available certificates free for download as PDF-documents.
Naprotec LLC
Chattanooga, TN, USA
Nabaltec AG
Schwandorf, Germany
Nabaltec USA Corporation
Corpus Christi, TX, USA
Nashtec LLC
Corpus Christi, TX, USA
Nab
Shan
Locations Agencies
34
Further information:
Nabaltec AG
P.O. Box 1860 · 92409 Schwandorf
Phone +49 9431 53-0
www.nabaltec.de
info@nabaltec.de
Customer Service
Phone +49 9431 53 910
sales@nabaltec.de
altec (Shanghai) Trading Co., Ltd.
nghai, China Technical Service
Phone +49 9431 53 920
tec-service@nabaltec.de
35
Nabaltec AG
P.O. Box 1860 · 92409 Schwandorf
Tel +49 9431 53-0
Fax +49 9431 61 557
www.nabaltec.de
info@nabaltec.de
All data listed in this brochure are reference values
and subject to production tolerance. These values
are exclusive to the product description and no
guarantee is placed on the properties.
It remains the responsibility of the users to test
the suitability of the product for their application. 02 / 2025