Angular-Shaped Boron Nitride Nanosheets with a High Aspect Ratio to Improve the Out-of-Plane Thermal Conductivity of Polyimide Composite Films.

Polyimide/boron nitride nanosheet (PI/BNNS) composite films have potential applications in the field of electrical devices due to the superior thermal conductivity and outstanding insulating properties of the boron nitride nanosheet. In this study, the boron nitride nanosheet (BNNS-t) was prepared by the template method using sodium chloride as the template, and B2O3 and flowing ammonia as the boron and nitrogen sources, respectively. Then, the PI/BNNS-t composite films were investigated with different loading of BNNS-t as thermally conductive fillers. The results show that BNNS-t has a high aspect ratio and a uniform lateral dimension, with a large dimension and a thin thickness, and there are a few nanosheets with angular shapes in the as-obtained BNNS-t. The synergistic effect of the above characteristics for BNNS-t is beneficial to constructing the three-dimensional heat conduction network of the PI/BNNS-t composite films, which can significantly improve the out-of-plane thermal conduction properties. And then, the out-of-plane thermal conductivity of the PI/BNNS-t composite film achieves 0.67 W m-1 K-1 at 40% loading, which is nearly 3.5 times that of the PI film.

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge-discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g-1 at 50 mA g-1, and the value of the specific capacity remained at 206 mA h g-1 after 500 cycles at a high current density of 1 A g-1. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.