Study On The Preparation And Performance Of ZIF-8 Modified Polyolefin Separator For Li-ion Batteries

With the increasingly environmental and energy problems,the use of new energy vehicles instead of internal combustion engine vehicles to solve the problem of global warming caused by carbon dioxide,at the same time,reducing energy pressure has become the primary problem of global concern.As an important part of lithium-ion batteries,battery separators limit the safety performance and electrochemical performance of the battery.At present,the most widely used polyolefin separators in commerce has problems such as low melting point,poor thermal stability,and poor wettability.There are not only potential safety hazards,but also difficult to meet the high-power charging and discharging of the battery.In this paper,a composite separator was prepared by modifying the polyolefin separator and growing ZIF-8 in situ on it to obtain excellent performance.The main research contents are as follows:First,the polyolefin battery separator was modified by using polyethyleneimine（PEI）-hydraulic（Noria）,and then the P-N-ZIF-8 composite separator was prepared by the in-situ growth method,and it was combined with the commercial polyolefin separator.Compared with commercial polyolefin separator,the P-N-ZIF-8 composite separator exhibits better lyophilicity and wettability,and has a higher retention rate for electrolyte.At the same time,the composite separator has high porosity（60%）and liquid absorption rate（123%）,and the ion conductivity is 0.76m S·cm^-1 at room temperature.Through the test of the P-N-ZIF-8 composite separator assembly battery,it is proved that the composite separator has a higher specific discharge capacity than the commercial polyolefin separator.The discharge specific capacity is maintained at a current density of 1 C for 100 cycles.130 m Ah·g^-1,and good cycle performance.In order to further improve the heat resistance of the battery separator to ensure its safety and stability,polydopamine（PDA）was used to modify the surface of the polyolefin separator,and then the PDA-ZIF-8 composite separator was prepared by the in-situ growth method.Compared with the P-N-ZIF-8 composite separator,the PDA-ZIF-8 battery separator exhibits better lyophilicity and wettability,and has a higher retention rate for electrolyte.In addition,the thermal stability of the PDA-ZIF-8 composite separator is better than that of the P-N-ZIF-8 composite separator,and the decomposition temperature reaches 180o C.At the same time,the PDA-ZIF-8 battery separator exhibits higher lithium-ion migration number（0.8009）,porosity（84%）,liquid absorption rate（154%）and ion conductivity(0.824 m S·cm^-1).The discharge specific capacity remains at 132 m Ah·g^-1 after 100 cycles at a current density of 1 C and the cycle performance is good.At different current densities,the battery specific capacity of the PDA-ZIF-8 battery separator is higher than that of the P-N-ZIF-8 composite separator,and it has excellent electrochemical performance.This research will provide an important research foundation for the industrial application of modified polyolefin lithium-ion battery separators.