lithium battery 18650 Factory

　　Important technical progress of lithium battery separator

　　1. Polyolefin surface modification

　　Adding or compounding materials with lyophilic properties and high temperature resistance properties on the single-layer polyolefin diaphragm to obtain a composite diaphragm with better performance is a major research direction for preparing high-performance diaphragms.

　　Currently commonly used processes include coating, dipping, spraying, and compounding. Studies have shown that polyarylate materials are coated on the PE diaphragm to form a composite diaphragm of porous polymer precipitates. Due to the good heat resistance of polyarylate, the melting temperature of the composite diaphragm is increased to greater than 180 °C.

　　Coating dopamine on the PE separator by dip coating method, the obtained modified separator has higher performance of absorbing electrolyte, which effectively improves the high-rate cycle performance of the separator.

　　Using a mixture of PVDF/SiO2 to modify the polyolefin diaphragm, the composite diaphragm has both the electrophilic performance of PVDF and the high temperature resistance of SiO2, and the charge and discharge efficiency of the various Zhong ion batteries can reach 94% at a discharge rate of 2C.

　　2. Polyolefin-ceramic composite diaphragm

　　Polyolefin-based organic separators have good mechanical properties and low cost, but have deficiencies in thermal stability and lyophilicity. Therefore, as battery separators, their safety performance needs to be improved. Therefore, the process of coating inorganic ceramic particles on polyolefin organic separators to prepare composite membranes emerged as the times require.

　　Although the impact of ceramic coating on battery performance still needs more in-depth research and evaluation to draw a final conclusion, this technology has been imitated by many diaphragm companies and battery companies and has been rapidly promoted.

　　In polymer-ceramic composite membranes, polyolefin-based organic microporous membrane materials provide flexibility to meet the needs of battery assembly processes. Inorganic ceramic particles form a rigid framework in the composite membrane to prevent the separator from shrinking or even melting under high temperature conditions, so as to improve the safety performance of the battery. The binder has an important influence on the surface properties, pore structure, mechanical strength and other properties of the ceramic composite membrane.

　　The polymer-ceramic composite membrane improves the thermal stability and electrolyte wettability of the polyolefin separator to a certain extent, but the biggest problem of this composite technology is that the combination of the ceramic phase and the organic phase is weak, and it is easy to appear. Ceramic shedding (powder dropping phenomenon. The process of pre-dispersing inorganic ceramic particles in the film-forming solution by rationally regulating the amount of thinner, using in-situ composite technology, and making a diaphragm through wet biaxial stretching technology or electrospinning method, etc. method can alleviate this phenomenon to a certain extent.

　　The composite diaphragm product based on polyolefin diaphragm mainly maintains the machinability of polyolefin diaphragm, which is easy to stretch and form holes, and at the same time improves the safety, lyophilicity and other characteristics of the diaphragm, and realizes commercialization in the replacement product of the diaphragm Before, it will still occupy an important market share.

　　3. New material system

　　According to the materials used, battery separators are divided into polyolefin modified separators and new material system separators. Among them, the new material system mainly includes fluorine-containing polymer diaphragms, cellulose diaphragms, polyimide (PI) diaphragms, polyester (PET) diaphragms and other polymer ceramic composite diaphragms.

　　(1) Fluoropolymer diaphragm mainly refers to PVDF diaphragm material. From the perspective of materials, it can be divided into three categories: single polymer, multi-polymer and organic-inorganic composite. The most commonly used single polymers include PVDF, P(VDF-HFP) (polyvinylidene fluoride-hexafluoropropylene), and P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene).

　　Compared with polyolefin diaphragm materials, the fluoropolymer diaphragm has stronger polarity and higher dielectric constant, which greatly improves the lyophilicity of the diaphragm and facilitates the ionization of lithium salts.

　　In addition, there are various molding methods for this kind of materials, such as casting method, electrospinning method, hot pressing method, etc., which are beneficial to control the porosity.

　　(2) The battery performance of cellulose separator is comparable to that of polyolefin separator, but its resource is abundant and renewable. At the same time, the initial decomposition temperature of cellulose materials is higher (>270"C), and the thermal stability is significantly better than that of polyolefin materials.

　　The cellulose-based materials used in the early stage have excellent fast charge and discharge performance, but there is a self-discharge phenomenon, the cycle performance is not stable enough, and the voltage resistance is not enough. Some researchers used non-woven cellulose as the substrate and P(VDF-HFP) as the coating to prepare a cellulose/PVDF composite separator. Compared with the traditional PP membrane, the lyophilicity is significantly enhanced and the thermal stability is greatly improved. promote.

　　(3) New process method

　　There are two core contents in the research and development of the diaphragm: one is the new material system, and the other is the process method that can realize industrial production. Without efficient process methods, no matter how good the material is, it cannot become a widely accepted commodity.