Research and progress of lithium-ion battery separator materials -Lithium - Ion Battery Equipment
Lithium-ion battery is a kind of secondary battery, which mainly relies on lithium ions to move between positive and negative electrodes to work. Lithium-ion batteries are composed of the following five parts: positive electrode material, negative electrode material, organic electrolyte, separator and battery case. Among them, the diaphragm is one of the key components of lithium-ion batteries, and has two crucial uses:
1. It serves as electronic insulation between the positive and negative electrodes: the separator with good insulation provides a good safety guarantee for the battery, and the good puncture strength and tensile strength can prevent the separator from being broken by burrs and dendrites. cause a short circuit inside the battery. In addition, the thickness and thermal stability of the separator are also important factors affecting the safety of lithium-ion batteries.
2. Supply migrating microporous channels for lithium ions, which determines the charge-discharge and cycle performance of the battery. Therefore, the separator must have a high porosity and a uniform distribution of micropores.
1. Research Status of Lithium-ion Battery Separators
According to different physical and chemical properties, lithium-ion battery separator materials can be divided into the following types: microporous diaphragm, modified microporous diaphragm, non-woven diaphragm, composite membrane and electrolyte membrane. Microporous membranes can be divided into single-layer and multi-layer microporous membranes, depending on the number of layers. The modified microporous membrane is obtained by modifying the surface of the traditional microporous membrane, and the commonly used modification methods are plasma and radiation-induced grafting or coating a layer of different polymers on the surface. The non-woven separator is composed of entangled fibers combined to form a network structure. It is prepared by melt blown method, wet laying method and electrospinning technology. Due to its small fiber diameter, the non-woven separator has a high porosity compared to other separators. . Composite separators are prepared by coating microporous membranes or nonwoven membranes or filling them with inorganic materials, so they have excellent thermal stability and wettability.(Lithium - Ion Battery Equipment)
1. Microporous membrane
Research on microporous diaphragms mainly focuses on PE, PP single-layer diaphragms and multi-layer composite diaphragms such as PE/PP and PP/PE/PP. The reason why these polyolefin microporous separators are widely used is that they can provide good mechanical properties and chemical stability. However, due to the generally low melting point of this type of polymer (PE melts at about 130°C), when the temperature of the battery rises due to long-term operation, the microporous polyolefin separator is prone to heat shrinkage, resulting in a large area of positive and negative contact. A short circuit can cause the battery to catch fire and explode. In addition, the poor electrolyte wettability of the polyolefin microporous separator makes it impossible to further improve the electrochemical performance of the battery.
In view of the characteristics of this type of material, the researchers improved the comprehensive performance of the microporous diaphragm from the perspective of improving the preparation process. Generally speaking, there are two methods for the preparation of microporous separators, namely dry method (melt extrusion stretching method, MSCS) and wet method (thermally induced phase separation method, TIPS). The dry process is simple and has high production efficiency, and no pollutants will appear, but the pore size and porosity of the separator cannot be precisely controlled. The microporous diaphragm prepared by the wet process has a small and uniform pore size, but the process is complicated and the cost is high, and it is difficult to realize industrial production.
In recent years, the research and development of ultra-high molecular weight polyethylene separator (UHMWPE) has received great attention. The following advantages make the safety of the battery greatly improved:
①Excellent resistance to external force puncture reduces the short circuit rate of the battery;
② Good heat resistance improves the closed cell temperature and membrane rupture temperature;
③Dimensional stability and corrosion resistance under high temperature environment.
2. Modified Microporous Separator
Currently, separators widely used in Li-ion batteries are made of polyolefins, especially microporous PE and PP films. However, the thermal stability and wettability of polyolefin separators are poor. In order to improve these properties, a series of modification methods are needed to change the structure of microporous polyolefin separators.
1. It serves as electronic insulation between the positive and negative electrodes: the separator with good insulation provides a good safety guarantee for the battery, and the good puncture strength and tensile strength can prevent the separator from being broken by burrs and dendrites. cause a short circuit inside the battery. In addition, the thickness and thermal stability of the separator are also important factors affecting the safety of lithium-ion batteries.
2. Supply migrating microporous channels for lithium ions, which determines the charge-discharge and cycle performance of the battery. Therefore, the separator must have a high porosity and a uniform distribution of micropores.
1. Research Status of Lithium-ion Battery Separators
According to different physical and chemical properties, lithium-ion battery separator materials can be divided into the following types: microporous diaphragm, modified microporous diaphragm, non-woven diaphragm, composite membrane and electrolyte membrane. Microporous membranes can be divided into single-layer and multi-layer microporous membranes, depending on the number of layers. The modified microporous membrane is obtained by modifying the surface of the traditional microporous membrane, and the commonly used modification methods are plasma and radiation-induced grafting or coating a layer of different polymers on the surface. The non-woven separator is composed of entangled fibers combined to form a network structure. It is prepared by melt blown method, wet laying method and electrospinning technology. Due to its small fiber diameter, the non-woven separator has a high porosity compared to other separators. . Composite separators are prepared by coating microporous membranes or nonwoven membranes or filling them with inorganic materials, so they have excellent thermal stability and wettability.(Lithium - Ion Battery Equipment)
1. Microporous membrane
Research on microporous diaphragms mainly focuses on PE, PP single-layer diaphragms and multi-layer composite diaphragms such as PE/PP and PP/PE/PP. The reason why these polyolefin microporous separators are widely used is that they can provide good mechanical properties and chemical stability. However, due to the generally low melting point of this type of polymer (PE melts at about 130°C), when the temperature of the battery rises due to long-term operation, the microporous polyolefin separator is prone to heat shrinkage, resulting in a large area of positive and negative contact. A short circuit can cause the battery to catch fire and explode. In addition, the poor electrolyte wettability of the polyolefin microporous separator makes it impossible to further improve the electrochemical performance of the battery.
In view of the characteristics of this type of material, the researchers improved the comprehensive performance of the microporous diaphragm from the perspective of improving the preparation process. Generally speaking, there are two methods for the preparation of microporous separators, namely dry method (melt extrusion stretching method, MSCS) and wet method (thermally induced phase separation method, TIPS). The dry process is simple and has high production efficiency, and no pollutants will appear, but the pore size and porosity of the separator cannot be precisely controlled. The microporous diaphragm prepared by the wet process has a small and uniform pore size, but the process is complicated and the cost is high, and it is difficult to realize industrial production.
In recent years, the research and development of ultra-high molecular weight polyethylene separator (UHMWPE) has received great attention. The following advantages make the safety of the battery greatly improved:
①Excellent resistance to external force puncture reduces the short circuit rate of the battery;
② Good heat resistance improves the closed cell temperature and membrane rupture temperature;
③Dimensional stability and corrosion resistance under high temperature environment.
2. Modified Microporous Separator
Currently, separators widely used in Li-ion batteries are made of polyolefins, especially microporous PE and PP films. However, the thermal stability and wettability of polyolefin separators are poor. In order to improve these properties, a series of modification methods are needed to change the structure of microporous polyolefin separators.
