Preparation And Properties Studied Polyimide Composite Separator For The Lithium-ion Battery Via Electrospinning

The separator is a critical component of lithium-ion batteries（LIBs）.Although the separator does not contribute to the chemical reactions of the LIBs,it isolates the two electrodes to avoid short circuits and provides a path for the rapid migration of lithium ions.However,the inherent nonpolar characteristics of commercial polyolefin separators lead to poor wettability and low uptake of their electrolytes,which affects the cycling performance of lithium-ion batteries at high power.In addition,the low melting point of polyolefin separators,in the overheating will occur the phenomenon of size shrinkage or even melt,which will cause the internal short circuit of the battery or even a fire.Therefore,in view of the above problems,in this paper,organic montmorillonite（OMMT）and hydrotalcite（LDH）were used as modified materials to prepare a polyimide（PI）composite separator with high thermal stability and good electrolyte wettability.The details are as follows:（1）The PI composite separator containing OMMT was prepared by in situ polymerization,electrospinning technique,and thermal imidization method using organically modified montmorillonite（OMMT）as modified filler.The results show that the prepared PI@OMMT composite separator has a thermal weight loss of 5%up to 568°C under a nitrogen atmosphere and exhibits good flame retardancy;Moreover,the addition of OMMT increases the tensile strength of the PI separator from 8.1 MPa to 14.7 MPa,thus reducing the risk of separator rupture during production and assembly;compared with the commercial Celgard 2500separator,the prepared PI@OMMT composite separator exhibited a wider electrochemical stability window（5.0 V）and higher ionic conductivity(0.77 m S·cm^-1);in the cyclic charge/discharge test of the cells,the Li Fe PO₄/Li half-cells with PI@OMMT separator still have a discharge capacity of 131 m Ah·g^-1 and capacity retention of 97%after 100 cycles at 1C,much higher than that of Celgard 2500 Separator(107 m Ah·g^-1 and 80%).（2）The PI composite separator containing LDH was prepared by in situ polymerization,electrospinning technology,and thermal imidization method using two-dimensional flame retardant material hydrotalcite（LDH）as modified filler.The results show that the porosity of the PI/LDH-3 wt%composite separator is about 70%,and the good porosity makes the electrolyte contact angle 13°,which is much lower than the 47°of the commercial Celgard2500 separator and 3°of PI separator;in addition,the tensile strength and elongation at break of PI/LDH-3 wt%composite separator were as high as 11.0 MPa and 11.2%,respectively;in the cyclic charge/discharge test of the cells,the Li Fe PO₄/Li half-cells with PI/LDH-3 wt%composite separator possess a maximum discharge capacity of 128 m Ah·g^-1 after 90 cycles at1 C,while the cells with Clagard 2500 separator have a discharge capacity of only 115 m Ah·g^-1;furthermore,combustion experiments show:PI/LDH-3 wt%composite separators are significantly better than commercial Celgard 2500 separators in terms of flame retardancy and self-extinguishing properties,which will bring safety to batteries at high temperatures in practical applications.