Electrolyte and diaphragm of power lithium-ion battery
Electrolyte (electrolyte) is one of the important components of lithium-ion batteries. During the working process of a lithium ion battery, the electrolyte solution is filled in the space between the positive and negative electrodes and the separator, and plays the role of transmitting lithium ions and communicating the positive and negative electrodes. The electrolyte solution is essential to the safety and service life of the battery. Important.
In the conventional electrolyte (electrolyte) system, the organic solvent is mainly carbonate, and the lithium salt is mainly lithium hexafluorophosphate (LiPF6). Among them, carbonates mainly include cyclic carbonates (such as ethylene carbonate EC, propylene carbonate PC, etc.) and chain carbonates (such as dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, etc.), General electrolyte (electrolyte) contains basic components such as EC and DEC. In addition, in order to improve the stability of the SEI film, VC, VEC and additives containing sulfur and boron are often added to the electrolyte (electrolyte); to prevent overcharging, additives such as biphenyl are often added; to improve safety, phosphate esters are added Class flame retardants and fluorine substitute solvents. According to the function, the electrolyte solution can be divided into high-power type, high-temperature type, low-temperature type, anti-overcharge type and high-capacity type, all of which are realized by adding corresponding additives.
In the main raw materials of lithium-ion batteries, in addition to the positive and negative electrodes and electrolyte solutions, the separator is also a very important component. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the positive and negative electrodes from contacting and short-circuit. In addition, the diaphragm also has the function of allowing electrolyte ions to pass through.
Lithium-ion battery separator materials mainly include polyolefins, polymer materials, and inorganic materials. According to the characteristics of raw materials and different processing methods, lithium-ion battery separators can be divided into polyolefin separators, polymer separators, ceramic separators, and fiber separators.
At present, polyolefin membranes are mainly polyethylene and polypropylene, including single-layer polyethylene (PE), single-layer polypropylene (PP), and three-layer PP/PE/PP composite films. At present, the preparation process of polyolefin membrane has two technical routes: dry method and wet method.
Polymer membranes are currently the most studied membrane. Compared with ordinary polyolefin membranes, polymer membranes have lower production process requirements, better electrochemical performance, abundant polymer raw materials, and low production costs. However, polymer films generally have poor mechanical strength, and their mechanical strength must be enhanced to adapt to mechanical automated production.
SEPARION diaphragm is a ceramic porous membrane composed of PET non-woven fabric as an organic support and a layer of inorganic ceramic oxide coating on its surface. The diaphragm has good thermal stability. Compared with polyolefin membranes, the safety performance is greatly improved, but the puncture strength of the membrane needs to be improved.
Nanofiber diaphragm is prepared by electrostatic spinning method, which is a new type of preparation method and preparation process of diaphragm material. In this method, under the action of a high-voltage electric field, the polymer material solution splits into countless nano jets at the tip of the spinneret and solidifies to form a polymer nanofiber membrane. The diaphragm has good thermal stability, but its industrialization is relatively complicated. Recently, this process is not very mature and has not yet been commercialized.