Robust polyetherimide fibrous membrane with crosslinked topographies fabricated via in-situ micro-melting and its application as superior Lithium-ion battery separator with shutdown function

Class of Boehmite/Polyacrylonitrile Membranes with Different Thermal Shutdown Temperatures for High-Performance Lithium-Ion Batteries

Nowadays, lithium-ion batteries are required to have a higher energy density and safety because of their wide applications. Current commercial separators have poor wettability and thermal stability, which significantly impact the performance and safety of batteries. In this study, a class of boehmite particles with different grain sizes was synthesized by adjusting hydrothermal temperatures and used to fabricate boehmite/polyacrylonitrile (BM/PAN) membranes. All of these BM/PAN membranes can not only maintain excellent thermal dimensional stability above 200 °C but also have good electrolyte wettability and high porosity. More interestingly, the BM/PAN membranes' thermal shutdown temperature can be adjusted by changing the grain size of boehmite particles. The lithium-ion batteries assembled with BM/PAN separators exhibit different thermal stability phenomena at 150 °C and have excellent rate performance and cycle stability at room temperature. After 120 cycles at 1C, the LiFePO₄ half-cell assembled by the best BM/PAN separator has almost unchanged discharge capacity, whereas the capacity retention of Celgard 2325 is only about 85%. Meanwhile, the NCM523 half-cell assembled with the best BM/PAN separator shows superb cycle stability after 500 cycles at 8C, with a capacity retention of 79% compared with 56% for Celgard 2325.

Polyimide-Based Materials for Lithium-Ion Battery Separator Applications: A Bibliometric Study

Polyimide (PI) has excellent thermal stability, high porosity, and better high-temperature resistance. It has the potential to become a more high-end separator material, which has attracted the attention of the majority of researchers. This review is aimed at identifying the research progress and development trends of the PI-based material for separator application. We searched the published papers (2012–2021) from the WOS core collection database for analysis and analyzed their research progress and development trend based on CiteSpace text mining and visualization software. The analysis shows that the PI-based composite separator material is a research hotspot in the future and the combination of nanofiber and cellulose materials with PI is also an important research direction in the future.

Preparation and application of a high-temperature–resistant EVOH-SO3Li/PI fiber membrane with self-closing pores

A lithium ethylene-vinyl alcohol copolymer sulfate (EVOH-SO3Li)/polyimide (PI) composite fiber membrane prepared via high-voltage electrospinning and impregnation was used as a lithium-ion battery separator for research purposes. The polyamic acid spinning solution was synthesized from 3,3′′,4,4′′-benzophenone tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether. The PI fiber membrane was prepared via high-voltage electrospinning and thermal imidization, and EVOH-SO3Li was then coated on the surface of the PI fiber to prepare an EVOH-SO3Li/PI composite fiber membrane material (t-EVOH-SO3Li/PI). Overall, the EVOH-SO3Li/PI membrane exhibits excellent basic physical properties, given the clear three-dimensional network microstructure. When compared with EVOH-SO3Li/PI composite fiber membrane prepared via the cospinning method (s-EVOH-SO3Li/PI), its electrolyte uptake and tensile strength can increase to 739% and 17.56 MPa, respectively. Additionally, the EVOH-SO3Li/PI composite fiber membrane prepared via high-voltage electrospinning and impregnation exhibits better heat shrinkage stability, electrochemical performance, and high-temperature self-closing pores function. The electrochemical stability window, electrochemical impedance, and ionic conductivity correspond to 5.8 V, 310 Ω, and 3.753 × 10−3 S cm−1, respectively. Specifically, at 200°C, the internal pores can close effectively, and this is extremely important for the safety of lithium-ion batteries.

A Janus nanofiber-based separator for trapping polysulfides and facilitating ion-transport in lithium-sulfur batteries

Endowing separators with the polysulfide-blocking function is urgently needed for high-performance lithium-sulfur (Li-S) batteries. Thus far, most of the reported research has focused on modifying conventional polyolefin separators but with poor thermal stability and low ionic conductivity. To address these issues, herein we report a Janus separator based on a thermally stable polymeric nanofabric designed with abilities to trap polysulfides and facilitate the transport of Li+ simultaneously. This Janus separator possesses a configuration of a carbon nanofiber (CNF) layer toward the sulfur cathode and the polyimide (PI) nanofabric toward the Li metal anode. It is demonstrated that the conductive CNF layer can effectively anchor and convert the polysulfides; meanwhile, the excellent wettability with liquid electrolytes and the highly porous structure of the PI nanofiber layer significantly promote the Li+-transport. In addition, the Janus separator presents notable advantages in thermal dimensional stability benefiting from the PI nanofabric. As a result, the Li-S battery armed with the Janus separator shows a high initial capacity (1393 mA h g-1 at 0.1 A g-1), stable cycling performance (822 mA h g-1 at 1 A g-1) and high coulombic efficiency of 99.6%.

Robust polyimide nanofibrous membrane with porous-layer-coated morphology by in situ self-bonding and micro-crosslinking for lithium-ion battery separator

Herein, we demonstrate a strategy to improve the tensile strength, thermal safety issues, and electrochemical performance of an as-synthesized polyimide separator. By spraying the solution of a specific chemical constituent on both sides of a poly(amic acid) non-woven membrane followed by thermal treatment, a novel polyimide nanofibrous membrane with porous-layer-coated morphology was successfully fabricated by in situ self-bonding and micro-crosslinking technique. The self-bonding and micro-crosslinking techniques improve the tensile strength of the nanofiber membranes from 5 MPa to 28 MPa by forming a crosslinked network structure, thereby reducing the risk of nanofiber disassembly during long-term operation. The rigid structure and aromatic groups in the polyimide chain enable the separator to have outstanding thermal dimensional stability at temperatures as high as 300 °C and thermal stability (5% weight loss at about 528 °C). Additionally, the unique flame retarding capability of polyimide ensures high security of the battery as well. Notably, the lithium-ion battery using porous-layer-coated polyimide separator exhibits a much higher capability (129.9 mA h g^-1, 5C) than that using a Celgard-2400 separator (95.2 mA h g^-1, 5C) and could work steadily at 120 °C, thus implying promising application in next generation high-safety and high-performance lithium-ion batteries.