As one of the important parts of lithium ion batteries, the diaphragm can avoid the positive and negative electrode contact and promote the shuttle of lithium ions between the two electrodes. It does not participate in the electrochemical reaction, but determines the performance and safety of the battery. Inorganic ultrafine powder coating or composite modified polymer is one of the effective methods to improve the thermal stability of the diaphragm. Using inorganic powder with high heat resistance and mechanical strength as a modifier can improve the mechanical strength of the separator and reduce the thermal shrinkage of the separator. In addition, the mixed inorganic ultrafine powder material has a good affinity with the electrolyte, which can enhance the absorption rate of the electrolyte, thereby helping to achieve a uniform distribution of lithium ions. The ultrafine powder can also increase the stability of the slurry and ensure the uniformity of the coating on the diaphragm. The ultrafine powder can also improve the compatibility when compounding with the diaphragm.

1. Al2O3 composite diaphragm

Alumina is abundant in nature and has excellent chemical inertness, thermal stability and mechanical properties. As a lithium battery separator ceramic coating, it has the following advantages:
1) The alumina coating has high temperature resistance and can maintain the complete shape of the diaphragm at 180°C;
2) Alumina coating can neutralize free HF in the electrolyte and improve the acid resistance and safety performance of the battery;
3) Nano-alumina can form a solid solution in lithium batteries to improve rate and cycle performance;
4) Nano alumina powder has good wettability, and has certain liquid absorption and liquid retention capabilities;
5) Alumina coating can increase the tortuosity of the micropores, and the self-discharge is lower than that of ordinary diaphragms.
The method of aluminum oxide modified lithium battery separator usually involves coating aluminum oxide particles on the surface of the polyolefin separator with the assistance of a polymer binder to improve the thermal stability, mechanical strength and wettability of the separator. Studies have found that the thickness of the Al2O3 coating has an effect on its thermal stability, physical properties and electrochemical performance. As the thickness of the Al2O3 coating increases, the absorption rate of the separator to the liquid electrolyte becomes higher and the thermal shrinkage rate decreases. Compared with pure PE separators, soft-pack batteries using Al2O3 coated separators show better cycle stability.

2. AlOOH modified diaphragm

Compared with high-purity alumina, AlOOH as a ceramic coating for lithium battery separators has the following advantages:
1) The hardness is low, and the wear on the machine is small during the cutting and coating process, which can reduce the risk of equipment wear and foreign objects;
2) High heat-resistant temperature and good compatibility with organics;
3) The density is small, and AlOOH of the same quality coats 25% more area than high-purity Al2O3;
4) The coating has high flatness and low internal resistance;
5) Low energy consumption, and the production process is more environmentally friendly;
6) The preparation process is simpler and the production cost is low.
The production of AlOOH is easier than that of α-Al2O3. In industry, boehmite slurry is obtained by gibbsite hydrothermal method, and then filtered, dried, pulverized and classified to obtain AlOOH ultrafine powder. In addition, the microscopic morphology of AlOOH is easier to control. Nanosheets, submicron blocks, nanobelts and other different sizes can be synthesized by hard template method, water/solvothermal method, sol-gel method, electrochemical method, and microemulsion method. And the morphology of AlOOH, which will give it rich macroscopic properties.

3. TiO2 modified diaphragm

Titanium dioxide (TiO2) has the advantages of non-toxic, stable performance, and easy to control preparation. It can improve the thermal stability of the diaphragm and the wettability of the electrolyte, and can absorb some impurity electrolytes, which helps to reduce the interface impedance between the diaphragm and the electrode. . At the same time, TiO2 has good compatibility with the electrolyte, which can promote the transportation of lithium ions and increase the ionic conductivity of the diaphragm. It is an ideal organic polymer diaphragm modified material. In addition, the introduction of TiO2 in the separator can reduce the inter-particle stress and improve the internal stability of the battery.

TiO2 is easy to control the composition, morphology, size and surface and interface structure. It is easy to prepare micro-nano-scale TiO2 with different microscopic shapes through hydrothermal method, microemulsion method, precipitation method, and sol-gel method, and then continue to develop TiO2 Modified diaphragm.

4. SiO2 modified diaphragm

Silica (SiO2) is a common thermally stable inorganic powder filler, which is widely used in the filling and modification of polymers. Because of its large specific surface area and easy to produce a large amount of silanol (Si-OH), it can improve the electrolyte wettability of the diaphragm while improving the hydrophilicity of the diaphragm, thereby improving the lithium ion transmission performance and improving the electrochemical performance of the battery. At the same time, SiO2 particles can be used as an inorganic material to enhance the mechanical strength of the separator, and can prevent the continuous growth and puncture of the negative electrode lithium dendrites, thereby avoiding thermal short circuits in the battery.

Compared with Al2O3, AlOOH and TiO2, the microscopic morphology of SiO2 is easier to control. SiO2 nanospheres, SiO2 submicron spheres, and SiO2 nano-coating are easy to obtain and realize.

In order to solve the problem of uneven distribution of SiO2 particles in the diaphragm coating, the researchers modified the surface of the SiO2 particles, such as grafting functional groups on the surface of the SiO2 particles or coating the SiO2 particles with polymers.

SAT NANO is one of the best supplier of al2o3, AlOOH, TiO2, SiO2 powder with nano particle and micron particle, if you have any enquiry, please feel free to contact us at admin@satnano.com