Preparation process of power lithium iron battery separator: dry method and
wet method. Anyone who is familiar with the structural principles of power iron
lithium batteries knows that the separator in the lithium battery plays a vital
role in the performance. However, there are many and very complex production
processes for lithium battery separators, including dry and wet manufacturing. ,
which process is more mature? The editor of this article will talk about it in
detail.
Preparation process of power lithium iron battery separator: dry method and
wet method
The production process of power lithium iron battery separators is divided
into two categories: dry production process and wet production process. The dry
production process is further subdivided into one-way stretching process and
two-way stretching process. The many characteristics that lithium-ion battery
separators need to possess put forward special requirements for its production
process, which includes raw material formula and rapid formula adjustment,
micropore preparation technology, and independent design of complete sets of
equipment.
Lithium iron battery separator dry process
The dry method can be subdivided into one-way stretching process and
two-way stretching process. The dry uniaxial stretching process is a method of
producing hard elastic fibers to prepare highly oriented polypropylene or
polyethylene films with low crystallinity. During the high-temperature annealing
process, a film with high crystallinity is obtained. This film is first
stretched at low temperatures to form micro-defects, and then at high
temperatures the defects are pulled apart to form micropores.
The dry biaxial stretching process adds a beta crystal modifier with a
nucleating effect to polypropylene and utilizes the density difference between
different phases of polypropylene to transform the polypropylene from its
crystal form into micro-forms during the stretching process. hole. At present,
more than one-third of China's production capacity uses the dry double drawing
process, and its products occupy a large proportion of the mid- to low-end
market. Application scope: large lithium-ion power batteries (electric vehicles,
electric motorcycles, power tools, large energy storage equipment, special large
batteries)
Wet production process of lithium iron battery separator
Wet production process, also known as phase separation method or thermal
phase separation method, wet process mixes liquid hydrocarbons or some small
molecular substances with polyolefin resin. After heating and melting, a uniform
mixture is formed, and then the temperature is cooled for phase separation and
pressing. The membrane is obtained, and then the membrane is heated to a
temperature close to the melting point, biaxially stretched to orient the
molecular chains, and finally kept warm for a certain period of time. The
residual solvent is eluted with volatile substances to prepare interconnected
microporous membrane materials.
The wet production process can not only prepare interconnected microporous
membrane materials, but also produce power lithium iron battery separators with
high longitudinal and transverse strength. At present, the wet production
process is mainly used to produce single-layer lithium battery separators.
Application scope: high-performance lithium-ion batteries, etc.
In terms of physical and mechanical properties, the separator produced by
the dry uniaxial stretching process has more advantages. However, lithium
battery separators produced by wet production processes have high porosity and
good air permeability, which can meet the high current charging and discharging
requirements of power batteries. On the contrary, since the wet production
process uses polyethylene material, the melting point of the polyethylene
material is only 140°C. Therefore, compared with the lithium battery separator
produced by the dry production process, the lithium battery separator produced
by the wet production process is Thermal stability is poor.
Can the wet process of lithium battery separators replace the dry
process?
As one of the four core components of lithium batteries, separators account
for 10%-14% of the cost of lithium batteries, with gross profit margins as high
as 50%-60%. The performance of the separator greatly affects the interface
structure and internal resistance of lithium batteries, which in turn affects
key characteristics such as battery capacity, charge and discharge current
density, and cycle performance.
At present, the separator production process can be divided into dry method
and wet method according to the difference in micropore formation mechanism, and
the two have different characteristics. The dry stretching process is simple,
environmentally friendly, and highly productive but has low capacity retention,
safety and reliability. The wet process produces small and uniform micropores
with better mechanical properties and product uniformity. It is suitable for
high-capacity batteries, but it is not environmentally friendly. The output of
wet process separators is growing rapidly, and industry experts believe that dry
processes will coexist with wet processes for a long time.
Judging from the progress of process technology, currently, my country's
lithium-ion battery separators have made major breakthroughs in the dry process
and have achieved world-class manufacturing levels. The wet separator process
technology has also been continuously improved, and production capacity and
output have increased steadily in recent years. With the continuous development
of wet process technology, the competitive landscape of my country's lithium
battery separator industry has also undergone some changes.
Judging from the current market applications and the choices of global
lithium battery companies, dry separators and wet separators coexist.
Lithium-iron battery separator technology is now mature, and battery separators
manufactured by either dry or wet methods can well meet the needs of products in
different fields.
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