18650 lithium battery 3000mah.What is the progress of the important technology of lithium-ion battery separators?

Main technical progress of lithium battery separators 1. Polyolefin surface modification. Adding or compounding materials with lyophilic properties, high temperature resistance and other characteristics to a single-layer polyolefin separator to obtain a composite separator with better performance, which is the best way to prepare high-performance separators. A major research direction. Currently commonly used processes include coating, dip coating,

Important technological progress in lithium battery separators

1. Polyolefin surface modification

Adding or compounding materials with lyophilic properties, high temperature resistance and other properties to a single-layer polyolefin separator to obtain a composite separator with better performance is a major research direction in preparing high-performance separators.

Currently commonly used processes include coating, dipping, spraying, compounding, etc. Studies have shown that polyarylate materials are coated on PE separators to form composite separators with porous polymer precipitates. Because polyarylate has good heat resistance, the melting temperature of the composite separator increases to greater than 180°C.

Dopamine is coated on the PE separator by the dip coating method, and the modified separator obtained has higher electrolyte adsorption performance, which effectively improves the high-rate cycle performance of the separator.

Using a mixture of PVDF/SiO2 to modify the polyolefin separator, the composite separator has both the electrolyte properties of PVDF and the high-temperature resistance of SiO2. The resulting Zhong-ion battery has a charge-discharge efficiency of 94% at a 2C discharge rate.

2. Polyolefin-ceramic composite diaphragm

Polyolefin organic separators have good mechanical properties and low cost, but they 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 at the historic moment.

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

Among polymer ceramic composite membranes, polyolefin organic microporous membrane materials provide flexibility to meet the needs of the battery assembly process. Inorganic ceramic particles form a rigid skeleton in the composite film to prevent the separator from shrinking or even melting under high temperature conditions to improve battery safety performance. Binders have an important impact on the surface properties, pore structure, mechanical strength and other properties of ceramic composite membranes.

The polymer-ceramic composite membrane improves the thermal stability and electrolyte wettability of the polyolefin separator to a certain extent. However, the biggest problem with this composite technology is that the binding force between the ceramic phase and the organic phase is weak and prone to occurrence. Ceramic shedding (powder falling off phenomenon). Through reasonable control of the amount of dilute mixture, inorganic ceramic particles are pre-dispersed in the film-forming solution using in-situ composite technology, and the process of making a separator through wet biaxial stretching technology or electrospinning, etc. Methods can alleviate this phenomenon to a certain extent.

Composite separator products based on polyolefin separators mainly maintain the processability of polyolefin separators that are easy to stretch into holes, and at the same time improve the safety, lyophilicity and other characteristics of the separators, and achieve commercialization in the replacement of separators. Before that, 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, new material systems mainly include fluoropolymer separators, cellulose separators, polyimide (PI) separators, polyester (PET) separators and other polymer ceramic composite separators.

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

Compared with polyolefin separator materials, fluoropolymer material separators have stronger polarity and higher dielectric constant, which greatly improves the lyophilicity of the separator and contributes to the ionization of lithium salts.

In addition, there are various molding methods for this type of material, such as casting, electrospinning, hot pressing, etc., which are conducive to controlling porosity.

(2) The battery performance of cellulose separators is equivalent to that of polyolefin separators, but it is resource-rich and renewable. At the same time, cellulose materials have a higher initial decomposition temperature (>270"C), and their thermal stability is significantly better than polyolefin materials.

The cellulose materials used in the early days had excellent rapid charge and discharge properties, but they had self-discharge phenomena, unstable cycle performance, and insufficient voltage resistance. Some researchers used non-woven cellulose as the base material 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 methods

There are two core contents in the research and development of separators: 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 product.