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Nowadays, lithium-ion batteries (LIBs) have become an indispensable part of human life, and researchers around the world are dedicated to improving their specific capacity and service life. Since their commercialization, LIBs have been widely used in portable electronic products such as mobile phones, laptops, and electric vehicles. These devices are in close contact with users, so safety is of great importance. As the core component, the battery also needs to have high safety. Conventional polymer - based separators are prone to shrinkage at high temperatures, resulting in internal short - circuits and increasing the risk of battery explosion. Developing polymer - free membranes is the key to solving the high - temperature problems of separators. Although solid - state electrolytes are safe, they have compatibility issues with existing flexible separator production lines. Therefore, a polymer - free flexible separator with high - temperature tolerance is an ideal choice for high - safety LIBs.
This paper reports for the first time the synthesis of a fully silica membrane by electrospinning machine -assisted polymer - free electrospinning. Eliminating the carrier polymer in the electrospinning process enables the preparation of a polymer - free separator without the need for an additional high - temperature calcination step to remove the polymer. Temperature tests reveal its extremely high temperature resistance, providing high safety at elevated temperatures. The obtained separator has a good porosity of 89%, a high ionic conductivity of 3.59 mS/cm, and an ultra - high electrolyte uptake of 1566%, showing significant improvements compared with similar works. In addition, a lithium - ion battery half - cell with an LFP cathode has been assembled. At a rate of 1C, the synthesized PSN separator shows a specific capacity of 90 mAh/g in the rate performance test, which is 28% higher than that of the PP separator. The preparation process is simple, cost - effective, and scalable. Using this flexible polymer - free membrane as a separator for advanced high - safety LIBs offers high performance.
In the experiments of this paper, a unique polymer - free electrospinning process was adopted. As can be clearly seen from the SEM images in Figure 1, the PSN separator exhibits a uniformly interwoven nanowire structure without defects such as beads caused by polymer residues. The direct presentation of this ideal microstructure strongly demonstrates that the use of carrier polymers was successfully avoided during the electrospinning process, eliminating the need for subsequent high - temperature calcination to remove the polymer and enabling the smooth synthesis of a fully silica membrane. This technological innovation lays a solid microstructural foundation for the PSN separator to exhibit excellent performance later. The electrospinning device played a crucial role in this process, ensuring the precise formation of the separator's structure.
Figure 1 (a) Schematic representation of the PSN separator synthesis process. (b, c) Surface SEM images of the PSN separator. (d) Cross - sectional SEM image of the PSN separator. (e) Histogram of the diameter of PSN separator fibers obtained from the SEM image. (f) Optical image of the PSN separator in a bent position to show its flexibility. (g) Contact angle test for PP and PSN separators.
The PSN separator was found to have extremely high temperature resistance through temperature - testing experiments. The combustion test in Figure 2a visually shows that the PP separator burns completely quickly when exposed to a flame, while the PSN separator shows excellent flame tolerance. Figure 2b further indicates that under different high - temperature environments, the weight change of the PSN separator is extremely small, and its shape remains unchanged. Especially below 400 °C, its diameter shrinkage rate is less than 4%. These results fully demonstrate that the PSN separator can effectively prevent high - temperature short - circuits and provide reliable high - safety protection for batteries in high - temperature environments.
Figure 2 (a) Combustion tests of two PP and PSN separators at five different time intervals. (b) Temperature stability of the PSN separator at four different temperatures. Weight loss and diameter shrinkage related to room temperature are shown. (c) Normalized Fourier - transform infrared spectroscopy (FTIR) absorption spectra of the heated separator at two temperatures of 200 °C and 300 °C.
The paper calculated that the PSN separator has a porosity as high as 89%, an ionic conductivity of 3.59 mS/cm, and an electrolyte uptake of 1566% through relevant formulas. In Table 1, when comparing these properties of the PSN separator with those of the PP separator, the advantages of the PSN separator are obvious. The high porosity provides more channels for ion transport, and the ultra - high electrolyte uptake enables the electrolyte to fully infiltrate the separator. The synergy of these two factors greatly promotes the achievement of high ionic conductivity.
Table 1 Separator parameters of SNF and PP
In the experiment, a lithium - ion battery half - cell with an LFP cathode was assembled and subjected to a rate performance test. As can be clearly seen from Figure 4d, at different rates such as 0.05C, 0.1C, 0.2C, 0.5C, and 1C, the specific capacity of the battery with the PSN separator is significantly higher than that of the battery with the PP separator. Specifically, at a rate of 1C, the specific capacity of the synthesized PSN separator reaches 90 mAh/g, which is 28% higher than that of the PP separator. This data comparison fully demonstrates that the PSN separator has obvious advantages in enhancing the rate performance of batteries, providing strong support for the efficient and stable operation of batteries under different charge - discharge rates.
Figure 4 (a) Electrochemical impedance spectroscopy (EIS) data for the SS/separator/SS structure of PP and PSN separators. (b) Cycle stability at 0.1C for PP and PSN separators with an electrospun LFP cathode. (c) Voltage profiles of the PSN separator with an electrospun LFP cathode at the 2nd, 50th, and 90th cycles. (d) Rate capabilities of PP and PSN separators.
This paper successfully proposes a method for synthesizing a polymer - free silica - based separator. The synthesis process does not involve a high - temperature annealing step, which facilitates the realization of an "all - electrospun battery". Due to the lack of a polymer - free separator with the specific specifications described in the introduction, the fabrication of all - electrospun batteries has not been feasible. However, this goal has been achieved in this paper.
The overall experimental process of this paper details the simplicity of the PSN separator preparation process. In terms of cost, it avoids complex and costly steps such as high - temperature calcination and does not require expensive carrier polymers, reflecting high cost - effectiveness. At the same time, the electrospinning machine - based electrospinning process itself has good scalability, facilitating large - scale production. The results of various performance tests in the paper, such as the charts and analyses corresponding to the above points, comprehensively demonstrate the superiority of the PSN separator's performance brought about by this preparation process. Using this flexible polymer - free membrane as a separator has great potential for high - performance applications in advanced high - safety LIBs, providing strong support for its wide - scale promotion in the field of practical battery applications.
Electrospinning Nanofibers Article Source: https://doi.org/10.1016/j.jpowsour.2025.236237
