6.2 Lithium Batteries and Lithium-Ion Batteries
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of the electrolyte during repeated charge and discharge. The interface compatibility
between the separator material and the electrode, and the retention of the separator on the electrolyte all have important effects on charge and discharge performance and cycling property of the lithium-ion battery. Lithium-ion battery commonly
used diaphragm materials that include fiber paper or non-woven fabric, synthetic
resin made of porous membrane. The common diaphragms are polypropylene and
polyethylene porous membranes, and the basic requirement for the membrane is a
high stability in the electrolyte. Because polyethylene, polypropylene microporous
membrane has higher porosity, lower resistance, higher tear strength, better resistance to acid and alkali, good elasticity, and retention of aprotic solvents, so the goods
of Lithium-ion battery separator material mainly uses polyethylene, polypropylene
microporous membrane. Polyethylene and polypropylene separators have defects
that have poor affinity for electrolytes. For this, they need to be modified, such as
grafting hydrophilic monomers on the surface of polyethylene, polypropylene microporous membranes, or changing the organic solvents of the electrolytes, etc. Some
studies have found that cellulose composite membrane materials have good lithiumion conductivity and good mechanical strength and serve as lithium-ion battery
separator materials.
Lithium-ion battery separator preparation methods are mainly melt-spinning and
cold-stretching (MSCS), or dry and thermally induced phase separation (TIPS) or
wet method, the two major categories of methods. Because the MSCS method does
not include any phase separation process, the process is relatively simple and there
is no pollution during the production process. At present, most manufacturers in the
world use this method for production, such as Ube, Mitsubishi, Tonen, and Celanese
of the United States. The TIPS process is more complex than the MSCS process
and requires the addition and removal of diluents. Therefore, the production cost is
relatively high and may cause secondary pollution. Currently, the world’s companies
that use this method to produce membranes include Asahi Kasei of Japan, Akzo of
the United States, and 3M. Company, etc.
In lithium batteries, the basic function of the separator is to block electron conduction while conducting ions between the positive and negative electrodes. Polypropylene microporous membranes are commonly used in lithium primary batteries
and separators common to lithium-ion secondary batteries that are polypropylene and polyethylene microporous membranes which have good chemical and
electrochemical stability in secondary batteries.
In summary, the requirements for the separator material for lithium-ion battery
are as follows:
1. Thickness
Lithium-ion batteries commonly use thinner diaphragms (<25 pm); diaphragms
used in electric cars and hybrid cars are thicker (about 40 pm). In general, the
thicker the diaphragm, the greater its mechanical strength and the less likely it
is to puncture the battery during assembly. However, the same type of battery,
such as a cylindrical battery, has less active material that can be added to it;
With less space occupied by thinner diaphragms, more active material is added,
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of the electrolyte during repeated charge and discharge. The interface compatibility
between the separator material and the electrode, and the retention of the separator on the electrolyte all have important effects on charge and discharge performance and cycling property of the lithium-ion battery. Lithium-ion battery commonly
used diaphragm materials that include fiber paper or non-woven fabric, synthetic
resin made of porous membrane. The common diaphragms are polypropylene and
polyethylene porous membranes, and the basic requirement for the membrane is a
high stability in the electrolyte. Because polyethylene, polypropylene microporous
membrane has higher porosity, lower resistance, higher tear strength, better resistance to acid and alkali, good elasticity, and retention of aprotic solvents, so the goods
of Lithium-ion battery separator material mainly uses polyethylene, polypropylene
microporous membrane. Polyethylene and polypropylene separators have defects
that have poor affinity for electrolytes. For this, they need to be modified, such as
grafting hydrophilic monomers on the surface of polyethylene, polypropylene microporous membranes, or changing the organic solvents of the electrolytes, etc. Some
studies have found that cellulose composite membrane materials have good lithiumion conductivity and good mechanical strength and serve as lithium-ion battery
separator materials.
Lithium-ion battery separator preparation methods are mainly melt-spinning and
cold-stretching (MSCS), or dry and thermally induced phase separation (TIPS) or
wet method, the two major categories of methods. Because the MSCS method does
not include any phase separation process, the process is relatively simple and there
is no pollution during the production process. At present, most manufacturers in the
world use this method for production, such as Ube, Mitsubishi, Tonen, and Celanese
of the United States. The TIPS process is more complex than the MSCS process
and requires the addition and removal of diluents. Therefore, the production cost is
relatively high and may cause secondary pollution. Currently, the world’s companies
that use this method to produce membranes include Asahi Kasei of Japan, Akzo of
the United States, and 3M. Company, etc.
In lithium batteries, the basic function of the separator is to block electron conduction while conducting ions between the positive and negative electrodes. Polypropylene microporous membranes are commonly used in lithium primary batteries
and separators common to lithium-ion secondary batteries that are polypropylene and polyethylene microporous membranes which have good chemical and
electrochemical stability in secondary batteries.
In summary, the requirements for the separator material for lithium-ion battery
are as follows:
1. Thickness
Lithium-ion batteries commonly use thinner diaphragms (<25 pm); diaphragms
used in electric cars and hybrid cars are thicker (about 40 pm). In general, the
thicker the diaphragm, the greater its mechanical strength and the less likely it
is to puncture the battery during assembly. However, the same type of battery,
such as a cylindrical battery, has less active material that can be added to it;
With less space occupied by thinner diaphragms, more active material is added,