Potassium ion batteries (PIBs) with high-volumetric energy densities are promising for next-generation low-cost energy storage devices. Metallic bismuth (Bi) with a structure similar to graphite, is ...a promising anode material for PIBs due to its high theoretical volumetric capacity (3763 mA h cm
−3
) and relatively low working potential (−2.93 V
vs.
standard hydrogen electrode). However, it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium. This study reports a flexible and free-standing Bi nanosheet (BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging. The controlled pore structure improves the electron and ion transport during cycling, and strengthens the structural stability of the electrode during potassiation and depotassiation, leading to excellent electrochemical performance for potassium-ion storage. In particular, it delivers a high reversible volumetric capacity of 451 mA h cm
−3
at the current density of 0.5 A g
−1
, which is much higher than the previously reported commercial graphite material.
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.
A freestanding thin film (Se@MCNFs) with unique multichannel core/shell structure is successfully prepared by electrospinning, followed by encapsulation of selenium process. The unique composite exhibits excellent capacity and long cycle life with coulombic efficiency approaching to 100%, showing that is a promising cathode material for Na–Se batteries.
A flexible and free‐standing porous carbon nanofibers/selenium composite electrode (Se@PCNFs) is prepared by infiltrating Se into mesoporous carbon nanofibers (PCNFs). The porous carbon with ...optimized mesopores for accommodating Se can synergistically suppress the active material dissolution and provide mechanical stability needed for the film. The Se@PCNFs electrode exhibits exceptional electrochemical performance for both Li‐ion and Na‐ion storage. In the case of Li‐ion storage, it delivers a reversible capacity of 516 mAh g−1 after 900 cycles without any capacity loss at 0.5 A g−1. Se@PCNFs still delivers a reversible capacity of 306 mAh g−1 at 4 A g−1. While being used in Na‐Se batteries, the composite electrode maintains a reversible capacity of 520 mAh g−1 after 80 cycles at 0.05 A g−1 and a rate capability of 230 mAh g−1 at 1 A g−1. The high capacity, good cyclability, and rate capability are attributed to synergistic effects of the uniform distribution of Se in PCNFs and the 3D interconnected PCNFs framework, which could alleviate the shuttle reaction of polyselenides intermediates during cycling and maintain the perfect electrical conductivity throughout the electrode. By rational and delicate design, this type of self‐supported electrodes may hold great promise for the development of Li‐Se and Na‐Se batteries with high power and energy densities.
A flexible and free‐standing porous carbon nanofibers/selenium composite electrode (Se@PCNFs) is prepared by infiltrating Se into mesoporous carbon nanofibers (PCNFs). The Se@PCNFs electrode exhibits excellent electrochemical performance for both lithium and sodium storage, which is attributed to synergistic effects of the uniform distribution of Se in PCNFs and the 3D interconnected PCNFs framework.
A one‐step synthesis procedure is developed to prepare flexible S0.6Se0.4@carbon nanofibers (CNFs) electrode by coheating S0.6Se0.4 powder with electrospun polyacrylonitrile nanofiber papers at 600 ...°C. The obtained S0.6Se0.4@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 S0.6Se0.4 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.
A flexible S0.6Se0.4@carbon nanofibers (CNFs) electrode is prepared by coheating S0.6Se0.4 powder with electrospun polyacrylonitrile nanofiber papers. The S0.6Se0.4@CNFs show excellent electrochemical performance for Li–S batteries and room temperature Na–S batteries, which attributes to the chemical bonding between Se and S, the chemical bonding between S0.6Se0.4 and CNFs matrix, and the 3D CNFs network.
Free-standing and binder-free porous carbon nanofibers (P-CNFs) electrodes were prepared by pyrolysis of PAN-F127/DMF nanofibers via an electrospinning process as potential anodes for Na-ion ...batteries (NIB). The P-CNFs delivers a reversible capacity of 266 mA h g(-1) after 100 cycles at 0.2 C, corresponding to ~80% of the initial charge capacity. When cycled at a current density as high as 500 mA g(-1) (2 C), it still delivers a reversible capacity of ~140 mA h g(-1) after 1000 cycles. The improvement of electrochemical performance is attributed to the special design and microstructure of P-CNFs, which conferred a variety of advantages: hierarchical porous channels enabling short transport length for ions and electrons, 3D interconnected structure resulting in low contact resistances, good mechanical properties leading to the excellent morphology stability.
Na3V2(PO4)3 (denoted as NVP) has been considered as a promising cathode material for room temperature sodium ion batteries. Nevertheless, NVP suffers from poor rate capability resulting from the low ...electronic conductivity. Here, the feasibility to approach high rate capability by designing carbon‐coated NVP nanoparticles confined into highly ordered mesoporous carbon CMK‐3 matrix (NVP@C@CMK‐3) is reported. The NVP@C@CMK‐3 is prepared by a simple nanocasting technique. The electrode exhibits superior rate capability and ultralong cyclability (78 mA h g−1 at 5 C after 2000 cycles) compared to carbon‐coated NVP and pure NVP cathode. The improved electrochemical performance is attributed to double carbon coating design that combines a variety of advantages: very short diffusion length of Na+/e− in NVP, easy access of electrolyte, and short transport path of Na+ through carbon toward the NVP nanoparticle, high conductivity transport of electrons through the 3D interconnected channels of carbon host. The optimum design of the core–shell nanostructures with double carbon coating permits fast kinetics for both transported Na+ ions and electrons, enabling high‐power performance.
Nanoconfined carbon‐coated Na3V2(PO4)3 particles in mesoporous carbon are prepared using a simple nanocasting technique. The optimum design of the core–shell nanostructures with double carbon coating permits fast kinetics for both transported Na+ ions and electrons, enabling excellent rate capability of the Na3V2(PO4)3 electrode.
Sodium-ion hybrid capacitors (SIHCs) are an emerging energy storage device with various potential applications due to their combined merits of batteries and supercapacitors. However, this device ...still suffers from the slow kinetics of the anode, which severely restricts the rate performance. Herein, we demonstrate that the rate performance of a carbon-nanofiber-based anode can be remarkably enhanced by coating a thin layer of oxygen-vacancy-rich TiO2. The as-prepared material (TiO2@PBC) is used as an anode in a sodium-ion battery, which delivers a reversible capacity of 180.2 mA h g−1 at 10 A g−1 with a capacity retention of 110.7% after 20,000 cycles, outperforming those without TiO2 coating. Furthermore, the TiO2@PBC is assembled into a SIHC with activated carbon as the cathode, which shows an energy density of 91.0 W h kg−1 at a power density of 165 W kg−1 and retaining an energy density of 43.4 W h kg−1 at an ultra-high power density of 13 kW kg−1. The excellent sodium storage performance of TiO2@PBC is attributed to the three-dimensionally cross-linked conductive network, the open ion-transportation channels, and more importantly, the TiO2 coating with high content of oxygen vacancies which expands the lattice and thus enables fast ion transport.
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•P-doped carbon nanofiber is coated with TiO2 by magnetron sputtering.•The TiO2 coating is rich in oxygen vacancy.•The oxygen vacancy in TiO2 enhances the sodium storage performance significantly.•The composite enables a power density of 13 kW kg−1 in a sodium ion capacitor.
A facile strategy is developed to synthesis selenium/carbon composites (Se@CNFs-CNT) by co-heating Se powder and electrospun Polyacrylonitrile (PAN)-CNT nanofibers at 600°Cin a sealed vessel. The Se ...molecules are chemically bonded and physical encapsulated by carbonized PAN-CNT composite (CNFs-CNT), which leads to prevent the dissolution of polyselenide intermediates in carbonate based electrolyte. When directly used as flexible free-standing cathode material for Li–Se batteries in low cost carbonate-based electrolyte, the Se@CNFs-CNT electrode exhibits improved cyclability (517 mAh g−1 after 500 cycles at 0.5 A g−1) and rate capability (485 mAh g−1 at 1 A g−1). Moreover, when tested as sodium batteries, it maintains a reversible capacity of 410 mAh g−1 after 240 cycles at 0.5 A g−1. The superior electrochemical performance (especially at high rates) of Se@CNFs-CNT is attributed to synergistic effect of the additive of CNT, the well confine of Se in the CNFs-CNT matrix through chemical bonding and the 3D interconnected carbon nanofibers (CNFs). This simple yet efficient process thus provides a promising route towards fabrication of a variety of high performance flexible Li–Se and Na–Se batteries.
•Se/CNFs-CNT composite were prepared by heating Se with carbon nanofibers-CNT.•The Se/CNFs-CNT can be used as a flexible free-standing electrode for Li–Se and Na–Se batteries.•The composite shows high specific capacity and stable capacity retention.
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.
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 m
2
/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.
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