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Author

Lei Ma

Bio: Lei Ma is an academic researcher. The author has contributed to research in topics: Materials science & Polyimide. The author has an hindex of 2, co-authored 8 publications receiving 11 citations.

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Journal ArticleDOI
TL;DR: In this article , a flexible carbon nanofiber membrane with a three-dimensional network structure was fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies.
Abstract: 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.

6 citations

Journal ArticleDOI
28 Aug 2022-Polymers
TL;DR: In this article , a triple crosslinking strategy, including pre-rolling, solvent and chemical imidization cross-linking, was proposed to solve the problem of low electrical conductivity of carbon nanofiber membranes.
Abstract: In order to solve the problem of low electrical conductivity of carbon nanofiber membranes, a novel triple crosslinking strategy, including pre-rolling, solvent and chemical imidization crosslinking, was proposed to prepare carbon nanofiber membranes with a chemical crosslinking structure (CNMs-CC) derived from electrospinning polyimide nanofiber membranes. The physical-chemical characteristics of CNMs-CC as freestanding anodes for lithium-ion batteries were investigated in detail, along with carbon nanofiber membranes without a crosslinking structure (CNMs) and carbon nanofiber membranes with a physical crosslinking structure (CNMs-PC) as references. Further investigation demonstrates that CNMs-CC exhibits excellent rate performance and long cycle stability, compared with CNMs and CNMs-PC. At 50 mA g−1, CNMs-CC delivers a reversible specific capacity of 495 mAh g−1. In particular, the specific capacity of CNMs-CC is still as high as 290.87 mAh g−1 and maintains 201.38 mAh g−1 after 1000 cycles at a high current density of 1 A g−1. The excellent electrochemical performance of the CNMs-CC is attributed to the unique crosslinking structure derived from the novel triple crosslinking strategy, which imparts fast electron transfer and ion diffusion kinetics, as well as a stable structure that withstands repeated impacts of ions during charging and discharging process. Therefore, CNMs-CC shows great potential to be the freestanding electrodes applied in the field of flexible lithium-ion batteries and supercapacitors owing to the optimized structure strategy and improved properties.

2 citations

Journal ArticleDOI
TL;DR: In this paper , 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 borsheets and nitrogen sources, respectively.
Abstract: 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.

1 citations

Journal ArticleDOI
TL;DR: In this article , the complex magnetic transition, MCE, refrigerant capacity, and magnetic phase diagram of single-phase TbDyHoEr HEA were studied, and the results showed that due to complex magnet transition and an ideal table-like MCE with large magnetocaloric effect (MCE), the RC improved from 883.19 to 1049.22 J kg−1 by melt-spun treatment.
Abstract: Rare‐earth‐based high‐entropy alloys (HEAs) with large magnetocaloric effect (MCE) have been recently recognized as good candidates for magnetic refrigeration. Herein, the complex magnetic transition, MCE, refrigerant capacity (RC), and magnetic‐phase diagram of single‐phase TbDyHoEr HEA are studied. It is showed in the results that due to complex magnetic transition and an ideal table‐like MCE, the RC of TbDyHoEr is significantly improved from 883.19 to 1049.22 J kg−1 by melt‐spun treatment. In terms of RC value and hysteresis performance, the melt‐spun treatment significantly improves the application potential of TbDyHoEr HEA as a high‐efficient magnetic refrigeration material, and the ideal table‐like MCE in a large temperature range enables this material to meet the requirements of both cryogenic refrigeration and mesothermal refrigeration for an Ericsson cycle.

1 citations


Cited by
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Journal ArticleDOI
28 Aug 2022-Polymers
TL;DR: In this article , a triple crosslinking strategy, including pre-rolling, solvent and chemical imidization cross-linking, was proposed to solve the problem of low electrical conductivity of carbon nanofiber membranes.
Abstract: In order to solve the problem of low electrical conductivity of carbon nanofiber membranes, a novel triple crosslinking strategy, including pre-rolling, solvent and chemical imidization crosslinking, was proposed to prepare carbon nanofiber membranes with a chemical crosslinking structure (CNMs-CC) derived from electrospinning polyimide nanofiber membranes. The physical-chemical characteristics of CNMs-CC as freestanding anodes for lithium-ion batteries were investigated in detail, along with carbon nanofiber membranes without a crosslinking structure (CNMs) and carbon nanofiber membranes with a physical crosslinking structure (CNMs-PC) as references. Further investigation demonstrates that CNMs-CC exhibits excellent rate performance and long cycle stability, compared with CNMs and CNMs-PC. At 50 mA g−1, CNMs-CC delivers a reversible specific capacity of 495 mAh g−1. In particular, the specific capacity of CNMs-CC is still as high as 290.87 mAh g−1 and maintains 201.38 mAh g−1 after 1000 cycles at a high current density of 1 A g−1. The excellent electrochemical performance of the CNMs-CC is attributed to the unique crosslinking structure derived from the novel triple crosslinking strategy, which imparts fast electron transfer and ion diffusion kinetics, as well as a stable structure that withstands repeated impacts of ions during charging and discharging process. Therefore, CNMs-CC shows great potential to be the freestanding electrodes applied in the field of flexible lithium-ion batteries and supercapacitors owing to the optimized structure strategy and improved properties.

2 citations

Journal ArticleDOI
TL;DR: In this article , a composite polyimide (PI) nanofiber membrane with a core-shell structure that anchors γ-Al2O3 nanoparticles was developed as an separator for high-safety lithium-ion batteries.
Abstract: Owing to its excellent thermal stability, polyimide (PI) is regarded as one of the most promising alternatives among separators for high-safety lithium-ion batteries (LIBs). Unfortunately, the wettability of the PI separator to electrolytes is still undesirable. The complexation–hydrolyzation method was used to develop a composite membrane with a core–shell structure that anchors γ-Al2O3 nanoparticles on PI nanofiber (PI@γ-Al2O3) as an LIB separator. The effects of surface treatment on the physicochemical and electrochemical properties of PI composite membranes are studied in detail, using the pristine PI nanofiber membrane as a reference. The results show that the PI@γ-Al2O3 nanofiber membrane exhibits better physicochemical properties and electrochemical performances. Specifically, the wettability property of the PI@γ-Al2O3 nanofiber membrane is improved with an almost zero contact angle, which significantly meets the requirements of high-performance LIBs. Furthermore, the electrochemical performance of the PI@γ-Al2O3 nanofiber membrane also shows excellent comprehensive properties with the ionic conductivity improving from 0.81 to 1.74 mS cm–1. Besides, the PI@γ-Al2O3 nanofiber membrane maintains a long charge–discharge process with a capacity retention rate of 98% at 0.5 C after 100 cycles. Consequently, the aforementioned excellent performances illustrate that core–shell PI@γ-Al2O3 nanofiber membranes have a promising future for the safety and stability of LIBs.

1 citations

Journal ArticleDOI
TL;DR: In this article , Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber (N-PCNF) electrodes were successfully synthesized via combining centrifugal spinning, chemical polymerization of pyrrole and a two-step heat treatment.
Abstract: Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber electrodes were successfully synthesized via combining centrifugal spinning, chemical polymerization of pyrrole and a two-step heat treatment. Nanoparticle-on-nanofiber morphology with highly porous carbon nanotube like channels were observed from SEM and TEM images. Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber (N-PCNF) electrodes exhibited excellent cycling and C-rate performance with a high reversible capacity of around 280 mA h g−1 in sodium ion batteries. Moreover, at 1000 mA g−1, a high reversible capacity of 172 mA h g−1 was observed after 300 cycles. The superior electrochemical properties were attributed to a highly porous structure with enlarged d-spacings, enriched defects and active sites due to nitrogen doping. The electrochemical results prove that N-PCNF electrodes are promising electrode materials for high performance sodium ion batteries.

1 citations