The three manufacturing methods of lithium battery separators, dry single
drawing, dry double drawing, and wet method, have different pore sizes under the
microscope and have their own characteristics. Which one is better? Let’s look
at the article for breakdown.
In recent years, as the power battery market has heated up, wet-coated
separators have become increasingly popular in China. Even some in the industry
believe that wet-coated separators will dominate the future power battery
separator market. On the contrary, those who support the dry method believe that
domestic companies are just following the trend of Japan and South Korea. In
fact, wet-coated separators have some weaknesses, which can easily lead to power
battery safety hazards after long-term use. Dry-coated separators are the best.
Suitable choice.
Judging from market trends and the new investment in production lines by
separator companies, wet-coated separators currently have the upper hand. It is
reported that there is a qualitative difference between dry double drawing and
dry single drawing, and there are not many companies with dry double drawing
technology. The market demand for dry double drawing coated separators is also
increasing rapidly.
As one of the key materials of power batteries, separators will have a
vital impact on power battery products and the company itself.
Do you want to look at market choices?
In the face of controversy, the direct approach is: let the market make its
own choice. Whoever has the last laugh will naturally be able to verify right
and wrong. But what needs to be noted is, will this make the market pay a lot of
unnecessary "trial and error" costs? Or in the end, different technical routes
will have their own paths suitable for survival?
According to relevant data, in the first quarter of 2016, Chinese lithium
battery separator manufacturers shipped 107.2 million square meters of
dry-process separators, a year-on-year increase of 65%; wet-process separators
shipped 78 million square meters, a year-on-year increase of 132.8%. In the
second quarter, domestic dry-process separators produced 125 million square
meters, a year-on-year increase of 41.24%, and a month-on-month increase of
16.7%; wet-process separators shipped 95.5 million square meters, a year-on-year
increase of 77.5%, and a month-on-month increase of 22.43%.
The growth in dry-process separator shipments was mainly due to dry-process
single-drawn separators, while the growth in wet-process separator shipments was
driven by the power market, high-end digital market, import substitution and
exports. Overall, the growth rate of wet separator shipments is significantly
higher than that of dry separators.
The favorable market situation for diaphragms has driven the growth of
investment
In order to fully guarantee the supply of separators, the alliance between
downstream power battery companies and separator companies is increasing. For
example, Lishen and Huianhui (Tianjin) New Energy Technology Co., Ltd. signed a
strategic cooperation framework agreement, and the two parties will cooperate in
the field of power lithium battery separators; Xing Source Materials and Guoxuan
jointly established a company with a total investment of 3 billion to build a
power battery separator production base; Cangzhou Mingzhu and AVIC Lithium
Battery established a joint venture to jointly build a wet separator project
with an annual output of 100 million square meters. Judging from the above
investment projects, most of them are wet separator projects.
The first phase of the cooperation project between Guoxuan and Xingyuan
Materials will be put into production in August 2016. The main products are wet
separators and coated separators for power lithium batteries; Suzhou Jieli, a
subsidiary of Shengli Precision, currently has 2 wet separator production lines
, with an annual production capacity of 70 million to 80 million square meters.
It is expected that 4 new wet production lines will be added this year, with the
new annual production capacity reaching 150 million square meters. It is
reported that if there is no advance layout planning, the wet separators in
enterprise production will be in short supply.
Of course, dry separators have not been ignored. In January this year, Del
Future planned to acquire 14.6154% of Henan Yiteng, which has a large shipment
volume of dry-process double-drawn separators, through equity transfer and
capital increase.
Newmi Technology has both wet and dry production lines. He Yuan, sales
director of Newmi Technology, revealed: "After process transformation and
equipment deployment, the company's wet production line has doubled the original
wet production capacity to 60 million square meters. The dry production line is
in Yunnan, with a designed production capacity of 30 million square meter, is a
dry-process double-drawn three-layer composite lithium-ion battery separator
with independent intellectual property rights, and has been recognized and
promoted by large power battery companies."
Technical discussion and comparison
The three manufacturing methods of lithium battery separators, dry single
drawing, dry double drawing, and wet method, have different pore sizes under the
microscope and have their own characteristics.
"Dry single-drawing is the earliest separator product. The mechanical
properties in one direction are enhanced, but the mechanical properties are
worse in the other direction. The dry double-drawing method will have much
better uniformity in both directions. At the same time, The thickness uniformity
and consistency will also be much better than that of single-drawn films." Dr.
Yang Feng from the Polymer Research Institute of Sichuan University said that
most single-drawn films are not easy to be coated, while double-drawn films are
easy to be coated.
In fact, the coating materials of dry double-draw coating and wet coating
are basically the same, and the equipment used is also the same, but the base
film is different. The difference in base film causes the two products to
perform differently in key indicators. The two schools of thought have fierce
disputes over their respective performance indicators. For the time being, the
supporters of dry double-draw coating will be referred to as dry, and the
supporters of wet coating will be referred to as wet.
basement membranepk
Qian: "If the wet PE base film is directly used in the battery, it cannot
be used or is difficult to use because the thermal temperature of the base film
is too low. In order to improve the thermal stability, the surface of the base
film must be coated to compensate for the Those 50% defects. But will it be
improved through different coating technologies? Being disabled since birth, the
body is very weak, and it doesn’t matter how much armor is worn outside.”
Wet: "In the field of power batteries, many manufacturers are switching to
wet coating, and wet single-layer coatings are also used. The wet separators
have uniform pore sizes, while the dry separators are incomparable. The pore
sizes of the dry base membranes are uneven, and the coating What’s the use of
covering it up?”
Breathabilitypk
Dry: "The pore size of the dry-processed double pull-based membrane only
needs to be uniform enough. There will be no problem charging and discharging
the battery, there will be no short circuit, and the overall safety is good, so
it does not need to be as uniform as the wet-processed membrane. The pore size
of the wet-processed membrane Although it is more uniform, the pore size is too
small, and with coating, how can we ensure high air permeability?"
Wet: “Wet separators can be made with high or low air permeability
according to the needs of the battery.”
Strengthpk
Qian: "The dry-process double-stretch coated separators and wet-process
coated separators were dissected in the same way, and the puncture and tensile
strength were compared. The wet-process coated separators dropped much more.
This is verified by data. There is no problem with wet-coating separators for
mobile phone lithium batteries. Mobile phones are usually replaced every two
years, but can electric vehicles be replaced after one or two years? The
strength of power battery separators decreases, which can easily cause short
circuits and increase the probability of accidents."
Wet: “When it comes to anti-corrosion properties, these two separators are
both polymer materials. Polypropylene has it, and polyethylene will also have
it.”
melting point pk
Dry: "The materials of dry separators and wet separators are quite
different, and the melting point difference is more than 40 degrees. At 120
degrees, 70%-80% of the wet separators will close up; at 150 degrees, the dry
separators can still maintain In relatively good condition.”
Wet: “A lower melting point is the biggest difference between the two
separators. This is determined by the characteristics of the material itself,
but as long as it meets the battery usage requirements.”
Thinness pk
Qian: "Currently, lithium batteries have a trend of high energy and
lightweight development. Wet process separators have obvious advantages in this
aspect. The wet process can achieve 5μ or 7μ, and the coating is not much
thicker, but the dry process alone is the thickest. The thinnest one is 20μ, the
thinnest one by dry double drawing is 12μ, and with coating it becomes even
thicker.”
Wet: "We don't dare to use too thin separators for power batteries. We
haven't seen 5μ or 7μ wet separators used in power batteries. If they are too
thin, the puncture strength will be greatly reduced. The thinnest wet separators
are '12+' 4' is used for power batteries, and dry double-pull '12+4' is
enough."
Cost pk
Dry: "The price of wet separators is more than twice as expensive as that
of dry separators. When the performance in batteries is equivalent, it is
obvious that dry double-draw coating is more cost-effective for power
batteries."
Wet: "As long as the quantity of wet separators is sufficient and produced
according to stable specifications, the cost will not be high."
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