In Situ Thermal Safety Aspect of the Electrospun Polyimide-Al2O3 Separator Reveals Less Exothermic Heat Energies Than Polypropylene at the Thermal Runaway Event of Lithium-Ion Batteries

Thermal Treatment Induced Crystal Development and Crystal Orientation Change in Electrospun Coaxial Fibers Comprising Dual Crystalline Polymers

This study investigates the crystallization behavior of electrospun coaxial fibers composed of crystalline poly(ethylene oxide) (PEO) in the core and crystalline poly(L-lactide) (PLLA) in the sheath. The influence of cold crystallization temperature and premelting temperature on the crystallization of PEO and PLLA is investigated. At a cold crystallization temperature of ≤60 °C, PLLA remained immobile. PEO crystallization is hard-confined, leading to a low degree of crystallinity. At a cold crystallization temperature of >60 °C, PEO melted, whereas PLLA crystallized. An increase in cold crystallization temperature results in an increase in the crystallite size and crystallinity of PLLA. Furthermore, the melt crystallization behavior of PEO in the coaxial fibers is strongly influenced by its premelting temperature and crystallization temperature. A higher premelting temperature leads to enhanced interdiffusion between PEO and PLLA. This increased confinement results in a decrease in PEO's crystallizability. Additionally, premelting relaxes the PEO chains, causing a shift in crystal orientation from parallel to the fiber axis (observed in as-electrospun fibers) to perpendicular to the fiber axis (observed in melt-crystallized fibers). Moreover, at a low melt crystallization temperature, demixing between PEO and PLLA is observed. This, coupled with a higher degree of supercooling, leads to an increase in PEO's crystallizability.

Scalable Preparation of Polyimide Sandwiched Separator for Durable High-Rate Lithium-Metal Battery

The ever-growing demands for efficient energy storage accelerate the development of high-rate lithium-metal battery (LMB) with desirable energy density, power density, and cycling stability. Nevertheless, the practical application of LMB is critically impeded by internal temperature rise and lithium dendrite growth, especially at high charge/discharge rates. It is highly desired but remains challenging to develop high-performance thermotolerant separators that can provide favorable channels to enable fast Li+ transport for high-rate operation and simultaneously homogenize the lithium deposition for dendrite inhibition. Polyimide-based separators with superior thermal properties are promising candidate alternatives to the commercial polyolefin-based separators, but previous strategies of designing either nanoporous or microporous channels in polyimide-based separators often meet a dilemma. Here, a facile and scalable approach is reported to develop a polyimide fiber/aerogel (denoted as PIFA) separator with the microporous polyimide fiber membrane sandwiched between two nanoporous polyimide aerogel layers, which can enable LMBs with remarkable capacity retention of 97.2% after 1500 cycles at 10 C. The experimental and theoretical studies unravel that the sandwiched structure of PIFA can appreciably enhance the electrolyte adsorption and ionic conductivity; while, the aerogel coating can effectively inhibit dendrite growth to realize durable high-rate LMBs.

Luteolin-loaded biocomposites containing tantalum and polyimide with antibacterial effects for facilitating osteogenic differentiation and bone bonding

Polymer-based composites are considered promising candidates for bone repair as they possess some outstanding advantages over ceramic/metallic/polymeric biomaterials. Tantalum (Ta)/polyimide (PI) biocomposites (PT) containing 20 v% (PT20) and 40 v% (PT40) Ta nanoparticles were fabricated, and luteolin (LU) was loaded on PT40 (LUPT40). Compared with PT20 and PI, PT40 with a high Ta content displayed high surface behaviors (e.g., roughness, surface energy, and hydrophilicity). PT40 remarkably improved cell adhesion and multiplication, and LUPT40 with LU displayed further enhancement in vitro. Moreover, LUPT40 evidently boosted osteoblastic differentiation while suppressing osteoclastic differentiation. Furthermore, LUPT40 exhibited good antibacterial effects because of the slow release of LU. The in vivo results confirmed that PT40 markedly promoted bone formation and LUPT40 further enhanced bone formation/bone bonding. In brief, the incorporation of Ta particles improved the surface behaviors of PT40, which stimulated cell response/bone formation. Moreover, the slow release of LU from LUPT40 not only promoted cell response/bone formation but also enhanced bone bonding. The synergistic effects of Ta and LU release from LUPT40 enhanced bone formation/bone bonding. Therefore, LUPT40 would have great potential for the repair of bear-loading bone.

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.