Linchao Zeng

Carbon‐Coated Germanium Nanowires on Carbon Nanofibers as Self‐Supported Electrodes for Flexible Lithium‐Ion Batteries

A hybrid structure with carbon-coated germanium nanowires grown on the surface of carbon nanofibers is fabricated using an in situ vapor-liquid-solid process. It is used as a self-supported and flexible anode for Li-ion batteries.

N-doped porous hollow carbon nanofibers fabricated using electrospun polymer templates and their sodium storage properties

N-doped hollow porous carbon nanofibers (P-HCNFs) were prepared through pyrolyzation of hollow polypyrrole (PPy) nanofibers fabricated using electrospun polycaprolactone (PCL) nanofibers as a sacrificial template. When used as anode material for NIBs, P-HCNFs exhibit a reversible capacity of 160 mA h g−1 after 100 cycles at a current density of 0.05 A g−1. An improved rate capability is also obtained at even higher charge–discharge rates. When cycled at a current density of 2 A g−1, the electrode can still show a reversible capacity of 80 mA h g−1. The N-doped sites, one-dimensional nanotube structure, and functionalized surface of P-HCNFs are capable of rapidly and reversibly accommodating sodium ions through surface adsorption and redox reactions. Therefore, P-HCNF is a promising anode material for next-generation NIBs.

Highly Reversible and Ultrafast Sodium Storage in NaTi2(PO4)3 Nanoparticles Embedded in Nanocarbon Networks

Sodium ion batteries (NIBs) have been considered as an alternative for Li ion batteries (LIBs). NaTi2(PO4)3 (denoted as NTP) is a superior anode material for NIBs. However, the poor electrochemical performance of NTP resulting from the low electronic conductivity prevents its application. Here, NTP nanoparticles embedded in carbon network (denoted as NTP/C) were fabricated using a simple soft-template method. This anode material exhibits superior electrochemical performance when used as anode electrodes for NIBs, including highly reversible capacity (108 mAh g(-1) at 100 C) for excellent rate performance and long cycle life (83 mAh g(-1) at 50 C after 6000 cycles). The excellent sodium storage property can be resulted from the synergistic effects of nanosized NTP, thinner carbon shell and the interconnected carbon network, leading to the low charge transfer resistance, the large surface area for electrolyte to soak in and enough void to buffer the volume variation during the repeated cycle.

Binding S0.6Se0.4 in 1D Carbon Nanofiber with CS Bonding for High-Performance Flexible Li-S Batteries and Na-S Batteries

A one-step synthesis procedure is developed to prepare flexible S0.6 Se0.4 @carbon nanofibers (CNFs) electrode by coheating S0.6 Se0.4 powder with electrospun polyacrylonitrile nanofiber papers at 600 °C. The obtained S0.6 Se0.4 @CNFs film can be used as cathode material for high-performance Li-S batteries and room temperature (RT) Na-S batteries directly. The superior lithium/sodium storage performance derives from its rational structure design, such as the chemical bonding between Se and S, the chemical bonding between S0.6 Se0.4 and CNFs matrix, and the 3D CNFs network. This easy one-step synthesis procedure provides a feasible route to prepare electrode materials for high-performance Li-S and RT Na-S batteries.

Recent progress in Li–S and Li–Se batteries

Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high (several times higher than that of traditional Li-ion batteries). Besides, Li–S and Li–Se batteries are low cost and environmental benign. However, the commercial applications of Li–S and Li–Se batteries are hindered by the dissolution and shuttle phenomena of polysulfide (polyselenium), the low conductivity of S (Se), etc. To overcome these drawbacks, scientists have come up with various methods, such as optimizing the electrolyte, synthesizing composite electrode of S/polymer, S/carbon, S/metal organic framework (MOF) and constructing novelty structure of battery. In this review, we present a systematic introduction about the recent progress of Li–S and Li–Se batteries, especially in the area of electrode materials, both of cathode material and anode material for Li–S and Li–Se batteries. In addition, other methods to lead a high-performance Li–S and Li–Se batteries are also briefly summarized, such as constructing novelty battery structure, adopting proper charge–discharge conditions, heteroatom doping into sulfur molecules, using different kinds of electrolytes and binders. In the end of the review, the developed directions of Li–S and Li–Se batteries are also pointed out. We believe that combining proper porous carbon matrix and heteroatom doping may further improve the electrochemical performance of Li–S and Li–Se batteries. We also believe that Li–S and Li–Se batteries will get more exciting results and have promising future by the effort of battery community.

A Freestanding and Long-Life Sodium-Selenium Cathode by Encapsulation of Selenium into Microporous Multichannel Carbon Nanofibers

Selenium cathode has attracted more and more attention because of its comparable volumetric capacity but much higher electrical conductivity than sulfur cathode. Compared to Li-Se batteries, Na-Se batteries show many advantages, including the low cost of sodium resources and high volumetric capacity. However, Na-Se batteries still suffer from the shuttle effect of polyselenides and high volumetric expansion, resulting in the poor electrochemical performance. Herein, Se is impregnated into microporous multichannel carbon nanofibers (Se@MCNFs) thin film with high flexibility as a binder-free cathode material for Na-Se batteries. The fibrous unique structure of the Se@MCNFs is beneficial to alleviate the volume change of Se during cycling, improve the utilization of active material, and suppress the dissolution of polyselenides into electrolyte. The freestanding Se@MCNF thin-film electrode exhibits high discharge capacity (596 mA h g-1 at the 100th cycle at 0.1 A g-1 ) and excellent rate capability (379 mA h g-1 at 2 A g-1 ) for Na-Se batteries. In addition, it also shows long cycle life with a negligible capacity decay of 0.067% per cycle over 300 cycles at 0.5 A g-1 . This work demonstrates the possibility to develop high performance Na-Se batteries and flexible energy storage devices.

Enhanced sodium storage performance in flexible free-standing multichannel carbon nanofibers with enlarged interlayer spacing

A flexible and free-standing multichannel carbon nanofiber (MCNF) film electrode was fabricated through electrospinning and carbonization. After high-temperature treatment of MCNFs in vacuum, the obtained fibers (MCNFs-V) had a dilated interlayer spacing of graphene sheets (0.398 nm) and an ultra-low specific surface area (15.3 m2/g). When used as an anode for sodium-ion batteries, the MCNFs-V showed a discharge plateau below 0.1 V, and sodium was intercalated into the stacked graphene sheets layers during the sodiation process. The MCNFs-V exhibited a reversible and high specific capacity of 222 mAh/g at a current density of 0.1 A/g after 100 cycles and excellent long-term cycling stability, which was superior to that of MCNFs. The improved sodium storage performance was attributed to the unique microstructure of the MCNFs-V with an enlarged interlayer spacing of graphene sheets for sodium intercalation. The MCNFs-V electrode holds great promise as an anode material for commercial sodium-ion batteries.