Introduction to the development of lithium battery separator
Lithium battery separator, cathode materials, anode materials and electrolyte are the most important materials that make up lithium ion batteries. The interior of the lithium-ion battery adopts a spiral wound structure, which needs to be separated between the cathode and anode with a very fine and highly permeable thin-film separator material.
Table of Contents
Lithium battery separator
Lithium battery separator is one of the four major materials of lithium batteries. As an insulating layer and semi-permeable layer, it is an indispensable core component of lithium batteries. First of all, the lithium battery separator has electronic insulation, which separates the cathode and anode of the lithium battery and prevents the battery from short circuiting. In lithium batteries, the lithium battery separator is to prevent the cathode and anode from contacting and short circuiting.
Secondly, the lithium battery separator must have ionic conductivity to ensure that lithium ions can normally pass through the micropores of the separator during charging and discharging. Lithium battery separator is a thin film with a large number of nano-scale micropores. The size of the micropores must not only hinder electron transmission and prevent short circuits, but also ensure the free passage of lithium ions so that lithium batteries can be charged and discharged normally.
In addition, the manufacture of lithium batteries also requires extremely high uniformity and consistency of the micropore distribution of lithium battery separators. The lithium battery separator also needs to be technically correct, which determines the complexity of the lithium battery separator production process and high technical barriers. High-performance lithium batteries require a separator with uniform thickness, excellent mechanical properties, air permeability and physical and chemical properties. Many performance indicators are often difficult to balance, and research and development are difficult.
Whether the lithium battery separator is excellent or not directly affects the internal resistance, capacity, cycle performance and safety performance of the lithium battery. It is the key inner component with the most technical barriers in the lithium ion battery industry chain. At present, commercial lithium battery separators are mainly polyethylene (PE) separators, polypropylene (PP) separators, and PE and PP composite multilayer microporous membranes.
The production process of lithium battery separator
Lithium battery separator production is divided into two processes: dry process and wet process. Among them, the dry separator production process is divided into two technologies: single-drawing and double-drawing. The dry process separator equipment is mature, the process is relatively simple, and it has high safety because there is almost no heat shrinkage phenomenon. At the same time, the cost is low, and it is suitable for the fields of energy storage, consumer batteries and lithium iron phosphate power batteries.
The cost of the wet separator is higher than that of the dry separator, but the porosity, pore size uniformity and air permeability are better, and a thinner separator can be produced. The “wet base separator + coating layer” separator is considered to be more suitable for the manufacture of power batteries with high energy density. In 2021, the total output of China’s lithium battery separator will be 7.904 billion square meters, and the production capacity of wet-process separator will be greater than that of dry-process diaphragms, continuing to dominate the market.
Market environment of lithium battery separator
Lithium battery separator is widely used in new energy vehicles, energy storage power stations, electric bicycles, power tools, digital electronic products and other fields, and can be divided into three main use scenarios in the fields of power batteries, energy storage and consumer electronics. In recent years, the lithium battery industry has developed rapidly.
In the field of power batteries, under the background of strong policy support and increasing consumer acceptance, the sales of new energy vehicles continue to rise, driving the rapid growth of the power battery market.
In the field of energy storage, new energy power generation has been rapidly developed as a clean power generation technology. However, the contradiction between the volatility of new energy and the security of the power grid is prominent. The development of energy storage has become the key to solving the problem of matching power supply and demand.
In the field of consumer electronics, with the pull of the electronic product market in developing countries and the growth of demand for emerging electronic products, the demand for consumer lithium-ion batteries will remain strong in the future.
The shipments of lithium battery separators have increased significantly, and the market concentration is high. According to statistics, China’s lithium battery separator shipments will reach 7.8 billion square meters in 2021, a year-on-year increase of over 100%. From the perspective of the global market competition pattern, in 2021, 73.8% of the lithium battery separator market share will be concentrated in China, and the global supply of lithium battery separators will be dominated by China, while the remaining separator companies will be dominated by Japanese and Korean companies.
Development trend of lithium battery separator
Wet method and coating is the development trend of lithium battery separator. Polyolefin separators have very obvious disadvantages, such as poor thermal stability. Therefore, coating and modification of polyolefin separators has become a trend. Poor thermal stability, in layman’s terms, is not resistant to high temperature. PE and PP commonly used in lithium battery separator are actually a kind of plastic. When they are close to fire, they will deform or even shrink into a ball. No matter how high the temperature is, they will burn.
Coating, in layman’s terms, is to coat the original diaphragm with a new substance to improve its performance. After coating, the heat resistance and puncture resistance of the film have been significantly improved, thereby alleviating the safety problems of fast charging and heat dissipation of the power battery, and the thermal shrinkage of the separator causing the cathode and anode of the battery to contact, burn, and explode.
The increase in the proportion of wet-process separators is partly due to the fact that coating solves the shortcoming of wet-process in terms of safety. The coating material reduces the thermal shrinkage rate of the separator and greatly improves the puncture resistance of the separator. At the same time, it does not affect the air permeability and ensures the flow of lithium ions.
In addition, the coating material can maintain higher wettability with the electrolyte, thereby reducing the internal resistance of the battery, increasing the discharge power of the battery, and prolonging the cycle life of the battery. Taken together, the wet-coated separator has better pore size uniformity, porosity, and air permeability than the dry-coated separator. Compared with wet-process separators, the puncture strength and thermal stability are significantly improved, making it the best choice for ternary material battery separators.
With the development of thinner separators and the increasing safety requirements of downstream lithium batteries, the shipments of coated separators have risen rapidly. The data shows that in 2021, coated films will account for more than 45% of lithium battery separator shipments (including third-party coatings), and it is expected to exceed 65% in 2022.
Introduction to the development of lithium battery separator
Lithium battery separator, cathode materials, anode materials and electrolyte are the most important materials that make up lithium ion batteries. The interior of the lithium-ion battery adopts a spiral wound structure, which needs to be separated between the cathode and anode with a very fine and highly permeable thin-film separator material.
Lithium battery separator
Lithium battery separator is one of the four major materials of lithium batteries. As an insulating layer and semi-permeable layer, it is an indispensable core component of lithium batteries. First of all, the lithium battery separator has electronic insulation, which separates the cathode and anode of the lithium battery and prevents the battery from short circuiting. In lithium batteries, the lithium battery separator is to prevent the cathode and anode from contacting and short circuiting.
Secondly, the lithium battery separator must have ionic conductivity to ensure that lithium ions can normally pass through the micropores of the separator during charging and discharging. Lithium battery separator is a thin film with a large number of nano-scale micropores. The size of the micropores must not only hinder electron transmission and prevent short circuits, but also ensure the free passage of lithium ions so that lithium batteries can be charged and discharged normally.
In addition, the manufacture of lithium batteries also requires extremely high uniformity and consistency of the micropore distribution of lithium battery separators. The lithium battery separator also needs to be technically correct, which determines the complexity of the lithium battery separator production process and high technical barriers. High-performance lithium batteries require a separator with uniform thickness, excellent mechanical properties, air permeability and physical and chemical properties. Many performance indicators are often difficult to balance, and research and development are difficult.
Whether the lithium battery separator is excellent or not directly affects the internal resistance, capacity, cycle performance and safety performance of the lithium battery. It is the key inner component with the most technical barriers in the lithium ion battery industry chain. At present, commercial lithium battery separators are mainly polyethylene (PE) separators, polypropylene (PP) separators, and PE and PP composite multilayer microporous membranes.
The production process of lithium battery separator
Lithium battery separator production is divided into two processes: dry process and wet process. Among them, the dry separator production process is divided into two technologies: single-drawing and double-drawing. The dry process separator equipment is mature, the process is relatively simple, and it has high safety because there is almost no heat shrinkage phenomenon. At the same time, the cost is low, and it is suitable for the fields of energy storage, consumer batteries and lithium iron phosphate power batteries.
The cost of the wet separator is higher than that of the dry separator, but the porosity, pore size uniformity and air permeability are better, and a thinner separator can be produced. The “wet base separator + coating layer” separator is considered to be more suitable for the manufacture of power batteries with high energy density. In 2021, the total output of China’s lithium battery separator will be 7.904 billion square meters, and the production capacity of wet-process separator will be greater than that of dry-process diaphragms, continuing to dominate the market.
Market environment of lithium battery separator
Lithium battery separator is widely used in new energy vehicles, energy storage power stations, electric bicycles, power tools, digital electronic products and other fields, and can be divided into three main use scenarios in the fields of power batteries, energy storage and consumer electronics. In recent years, the lithium battery industry has developed rapidly.
In the field of power batteries, under the background of strong policy support and increasing consumer acceptance, the sales of new energy vehicles continue to rise, driving the rapid growth of the power battery market.
In the field of energy storage, new energy power generation has been rapidly developed as a clean power generation technology. However, the contradiction between the volatility of new energy and the security of the power grid is prominent. The development of energy storage has become the key to solving the problem of matching power supply and demand.
In the field of consumer electronics, with the pull of the electronic product market in developing countries and the growth of demand for emerging electronic products, the demand for consumer lithium-ion batteries will remain strong in the future.
The shipments of lithium battery separators have increased significantly, and the market concentration is high. According to statistics, China’s lithium battery separator shipments will reach 7.8 billion square meters in 2021, a year-on-year increase of over 100%. From the perspective of the global market competition pattern, in 2021, 73.8% of the lithium battery separator market share will be concentrated in China, and the global supply of lithium battery separators will be dominated by China, while the remaining separator companies will be dominated by Japanese and Korean companies.
Development trend of lithium battery separator
Wet method and coating is the development trend of lithium battery separator. Polyolefin separators have very obvious disadvantages, such as poor thermal stability. Therefore, coating and modification of polyolefin separators has become a trend. Poor thermal stability, in layman’s terms, is not resistant to high temperature. PE and PP commonly used in lithium battery separator are actually a kind of plastic. When they are close to fire, they will deform or even shrink into a ball. No matter how high the temperature is, they will burn.
Coating, in layman’s terms, is to coat the original diaphragm with a new substance to improve its performance. After coating, the heat resistance and puncture resistance of the film have been significantly improved, thereby alleviating the safety problems of fast charging and heat dissipation of the power battery, and the thermal shrinkage of the separator causing the cathode and anode of the battery to contact, burn, and explode.
The increase in the proportion of wet-process separators is partly due to the fact that coating solves the shortcoming of wet-process in terms of safety. The coating material reduces the thermal shrinkage rate of the separator and greatly improves the puncture resistance of the separator. At the same time, it does not affect the air permeability and ensures the flow of lithium ions.
In addition, the coating material can maintain higher wettability with the electrolyte, thereby reducing the internal resistance of the battery, increasing the discharge power of the battery, and prolonging the cycle life of the battery. Taken together, the wet-coated separator has better pore size uniformity, porosity, and air permeability than the dry-coated separator. Compared with wet-process separators, the puncture strength and thermal stability are significantly improved, making it the best choice for ternary material battery separators.
With the development of thinner separators and the increasing safety requirements of downstream lithium batteries, the shipments of coated separators have risen rapidly. The data shows that in 2021, coated films will account for more than 45% of lithium battery separator shipments (including third-party coatings), and it is expected to exceed 65% in 2022.
For more related articles, please refer to Li(NiCoMn)O2 material, top 10 ternary cathode material manufacturer, top 10 lithium battery cathode material manufacturers in China.
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