High-performance battery: Lithium-ion battery is composed of four main parts: positive electrode material, negative electrode material, separator, and electrolyte. Among them, the separator is a key inner component in lithium-ion batteries. Although it does not directly participate in the electrochemical reaction, it plays a vital role in battery performance. It not only affects the capacity, cycle performance and charge and discharge current density of the battery, but is also related to the safety and life of the battery. The separator maintains proper battery operation and performance by providing ion conduction channels, preventing electrolyte mixing, and providing mechanical support.The ion conductivity of the separator directly affects the charge and discharge speed and efficiency of the battery. Better ion conductivity can improve the power density of the battery. In addition, the electrolyte isolation performance of the separator determines the safety of the battery. Effective isolation of the electrolyte between the positive and negative electrodes can prevent safety issues such as short circuits and overheating. The separator also needs to have good mechanical strength and flexibility to cope with the expansion and contraction of the battery and prevent mechanical damage and internal short circuits. In addition, the separator also needs to maintain structural and functional stability during the battery life to ensure long-term reliable operation of the battery.Although the separator does not directly participate in the electrochemical reaction of the battery, it has an important impact on key properties such as battery capacity, cycle performance, charge and discharge speed, safety and lifespan. Therefore, the development and optimization of separators are of critical significance to the development and application of lithium-ion batteries.
1. The important function of separators in lithium-ion batteries
Separators play a vital role in lithium-ion batteries. It is not only a physical barrier that separates the positive and negative electrodes, but also has the following important functions:1. Ion transmission: The separator must have good ion transmission performance and be able to allow lithium ions to transmit freely between the positive and negative electrodes. At the same time, the separator needs to effectively block the transmission of electrons to prevent short circuits and self-discharge.2. Maintenance of electrolyte: The separator needs to have good resistance to solvent penetration, which can effectively maintain the uniform distribution of electrolyte between the positive and negative electrodes and prevent the loss of electrolyte and concentration changes.3. Mechanical strength: The separator needs to have sufficient mechanical strength to withstand mechanical stress such as compression, expansion and vibration of the battery to ensure the stability and safety of the battery.4. Thermal stability: The separator needs to have good thermal stability to maintain structural stability in high temperature environments and prevent thermal runaway and thermal decomposition.5. Flame retardancy: The separator needs to have good flame retardancy, which can effectively prevent the battery from fire or explosion under abnormal circumstances.In order to meet the above requirements, separators are usually made of polymer materials, such as polypropylene (PP), polyethylene (PE), etc. In addition, parameters such as the thickness, porosity, and pore size of the separator will also affect the performance of the battery. Therefore, in the preparation process of lithium-ion batteries, it is very important to select appropriate separator materials and optimize the structural design of the separator.
2. The main role of separators in lithium batteries:
In lithium-ion batteries, the separator plays a key role and has the following main functions:1. Ion conduction: The separator allows lithium ions to be transported between the positive and negative electrodes. The separator usually has high ionic conductivity, which can promote the rapid and even flow of lithium ions in the battery and achieve efficient charging and discharging of the battery.2. Battery safety: The separator can prevent direct contact and short circuit between the positive and negative electrodes, avoid overcurrent and overheating inside the battery, and provide battery safety.3. Electrolyte isolation: The separator prevents gases, impurities and other substances in the electrolyte in the battery from mixing between the positive and negative electrodes, avoiding unnecessary chemical reactions and losses, and maintaining the stability and cycle life of the battery.4. Mechanical support: The separator plays the role of mechanical support in the battery. It can fix the positions of the positive and negative electrodes and other battery components. It also has a certain degree of flexibility and expansibility to adapt to the expansion and contraction of the battery.Separators play an important role in ion conduction, battery safety, electrolyte isolation and mechanical support in lithium-ion batteries. It can ensure the stable operation and performance of the battery.
3. Types of lithium-ion battery separators
There are many types of lithium-ion battery separators, the common ones include the following:1. Polypropylene (PP) separator: This is currently the most commonly used separator material. Polypropylene separators have excellent chemical resistance, good thermal stability and mechanical strength, while possessing moderate ion selectivity and conductive properties.2. Polyimide (PI) separator: Polyimide separator has high thermal stability and chemical stability, and can maintain stable performance in high temperature environments. Due to its high voltage resistance, polyimide separators are often used in batteries with high energy density and high power requirements.3. Polyethylene (PE) separator: Polyethylene separator has high ion conductivity and good mechanical strength, and is often used in specific types of lithium-ion batteries, such as supercapacitors and lithium-sulfur batteries.4. Composite ceramic diaphragm: Composite ceramic diaphragm is made of ceramic fiber reinforced polymer substrate. It has high mechanical strength and heat resistance and can withstand high temperature and physical damage.5. Nanopore separator: Nanopore separator utilizes the excellent ion conductivity of the nanopore structure, while meeting good mechanical strength and chemical stability. It is expected to be applied in lithium-ion batteries with high power and long life requirements.These separators of different materials and structures can be selected and optimized according to different battery designs and performance requirements.
4. Performance requirements of lithium-ion battery separators
Lithium-ion battery separators are a critical component with the following performance requirements:1. High electrolyte conductivity: The separator must have high electrolyte conductivity to promote ion conduction between the positive and negative electrodes to achieve efficient charging and discharging of the battery.2. Excellent ion selectivity: The separator needs to have good ion selectivity, allowing only the transmission of lithium ions and preventing the penetration or reaction of other substances in the battery.3. Good thermal stability: The separator needs to have good thermal stability and be able to maintain structural stability under extreme conditions such as high temperature or overcharging to prevent thermal runaway or electrolyte evaporation and other problems.4. Excellent mechanical strength and flexibility: The separator needs to have high mechanical strength and flexibility to prevent problems such as edge short circuits or internal damage, and to adapt to the expansion and contraction of the battery.5. Good chemical resistance: The separator needs to have good chemical resistance and be able to resist corrosion or contamination of the separator by electrolytes, gases and impurities in the battery.6. Low resistance and low permeability: The separator should have low resistance and low permeability to reduce resistance loss and electrolyte loss inside the battery.The performance requirements of lithium-ion battery separators are high electrolyte conductivity, excellent ion selectivity, good thermal stability, excellent mechanical strength and flexibility, good chemical resistance, low resistance and low permeability. These performance requirements ensure battery safety, cycle life and energy density.
Post time: Sep-15-2023