The Preparation And Performance Study Of Polyimide Lithium-ion Battery Separator

The increasing development of lithium ion batteries(LIBs) and their expanded applications in electric vehicles, aerospace industry, energy storage, and other electric devices and instruments demand a comprehensive improvement of the battery performance. Batteries assembled with traditional polyolefin separators gradually present some week points like poor high-temperature safety performance and poor high-rate discharge performance, which is mainly caused by the poor thermal stability and low porosity of polyolefin separators. Thus, the separator is considered to be one of the key points that restrict the development and application of LIBs.In respective of the reality above, a research aiming at preparing a kind of separator with good high temperature stability is conducted, to solve the security issues lying in batteries assembled with traditional polyolefin separators. Meanwhile, the study tries to apply new materials and preparation methods to break though the shortcomings of the most commonly used polyolefin separators, bringing an improvement for the battery performance.Based on the above consideration, a new type of polyimide(PI) lithium ion battery separator is successfully prepared via an electrospinning method in this paper, to meet the demands of high-temperature safety and high-rate discharge performance of LIBs used in power equipment. The main contents and results of this paper are as follows:A new type of PI lithium ion battery separator is successfully prepared via an electrospinning method, and the effects of process parameters like concentration of the precursor solution, spinning voltage, injection rate, receiving distance and spinning time on the morphology and properties of the PI separator are studied. The experimental results determine the optimum concentration of the precursor solution, spinning voltage, injection rate, receiving distance and spinning time to be 25%, 18 KV, 0.6m L/h, 20 cm and 5~8min, respectively.An overall performance test of the PI separator is conducted, and the results are as follows: the separator presents relatively high porosity(>90%), good electrolyte affinity and retention performance; Moreover, the separator shows no obvious shrinkage at 500℃, presenting excellent high-temperature stability, which is much superior to traditional polyethylene(PE) separator that shows about 20% shrinkage at 150℃; Along with the increase of the imidization temperature within the temperature range of 240~450℃, the tensile strength of the PI separator tends to increase when the temperature is below 300℃ and then decreases gradually, reaching a peak as 10.99 MPa at 300℃.The power lithium ion batteries assembled with PI separators(PI-LIBs) present better electrochemical performance than those with PE separators(PE-LIBs): during the process of high-rate discharge, the capacity of PI-LIBs remains 33.6% at 28.8C rate, while that of PE-LIBs decreases to only 8.84% at 16 C rate. Meanwhile, PI-LIBs present excellent storage performance, and after stored at room temperature for 28 days and 60℃ for 7 days, the PI-LIBs show good cycle performance.