In-situ TEM examination and exceptional long-term cyclic stability of ultrafine Fe3O4 nanocrystal/carbon nanofiber composite electrodes

Xu, Zheng; Zhang, Biao; Gang, Yang; Cao, Ke; Garakani, Mohammad Akbari; Abouali, Sara; Huang, Jiaqiang; Huang, Jian; Heidari, Elham Kamali; Wang, Hongtao; Kim, Jang Kyo

doi:10.1016/j.ensm.2015.08.002

Cited by 48 publications

(29 citation statements)

References 48 publications

(102 reference statements)

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“…In view of the large volume expansion of over 300% of red P during sodiation, the structural evolution of the HPCNS/P composite electrode during the first sodiation/desodiation process was examined in real time by the in situ TEM experiment ( Figure 5 a–c). Figure S12a (Supporting Information) schematically displays the setup of the constructed nanocell for in situ TEM, similar to that employed in our previous studies . A few TEM images taken during the first sodiation and desodiation cycle are presented in Figure a–c along with the corresponding SAED patterns.…”

Section: Resultsmentioning

confidence: 99%

“…Figure S12a (Supporting Information) schematically displays the setup of the constructed nanocell for in situ TEM, similar to that employed in our previous studies. [36,[70][71][72][73] A few TEM images taken during the first sodiation and desodiation cycle are presented in Figure 5a-c along with the corresponding SAED patterns. Prior to sodiation, the pristine HPCNS/P nanospheres had a perfect spherical shape with an average outer diameter of ≈75 nm.…”

Section: In Situ Tem Examinationmentioning

confidence: 99%

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Rational Assembly of Hollow Microporous Carbon Spheres as P Hosts for Long‐Life Sodium‐Ion Batteries

Yao

Cui

Huang

et al. 2017

Advanced Energy Materials

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have been considered as an alternative to lithium-ion batteries (LIBs) for largescale applications like smart grid energy storage. [1][2][3][4][5][6] Significant progress has been made in developing cathode materials for high-performance SIBs, such as layered transition metal oxides (Na x MeO 2 , Me = 3d transition metals), [7] polyanionic compounds, [8] and miscellaneous Na insertion materials. [9] The progress of designing efficient anode materials, however, has been relatively slow and finding proper ones is exigent because the commercial graphite anode for LIBs cannot be used to host the Na + ions whose diameter is ≈34% larger than Li + ions in the commonly used carbonate-based electrolytes. [10][11][12][13] Further, graphite has negligible capacities of 30-35 mA h g −1 in SIBs. [14,15] Although Si has been considered the most promising anode for LIBs, it holds very limited Na storage capacities at ambient temperature due to the unfavorable kinetics. [16][17][18] In view of the abovementioned reasons, it is crucial to identify anode materials that possess high capacities and long cyclic stability in SIBs. Benefiting from the high theoretical capacity of 2596 mA h g −1[19-23] by forming a highly reactive Na 3 P phase [24] and a safe working potential of ≈0.45 V versus Na/Na + , [25] phosphorus (P) has been considered a promising anode candidate for SIBs among many proposed materials. [26,27] Red P presents better chemical stability at room temperature and is commercially available at lower cost than other phosphorus allotropes, like white P, black P, [28] and violet P. [29] Nevertheless, most electrodes made from red P suffered low rate capacities, severe capacity reduction, and poor electrochemical reversibility, [19,21,30] which hindered the wide application of red P-based anodes. The following unfavorable reaction mechanisms are responsible for the poor electrochemical performance. (i) The extremely large volume expansion over 300% occurring when red P is transformed to Na 3 P phase causes pulverization of the active material and separation of red P from the current collectors, leading to rapid capacity deterioration. [23,[31][32][33] (ii) The electrically insulating amorphous red P whose electrical conductivity is ≈10 −14 S cm −1 results in large polarization and poor utilization of active material, [20,21,23,25,34] limiting the high-rate performance. (iii) The unstable, electronically insulating solid electrolyte This paper reports the rational assembly of novel hollow porous carbon nanospheres (HPCNSs) as the hosts of phosphorous (P) active materials for high-performance sodium-ion batteries (SIBs). The vaporization-condensation process is employed to synthesize P/C composites, which is elucidated by both theories and experiments to achieve optimized designs. The combined molecular dynamics simulations and density functional theory calculations indicate that the morphologies of polymeric P 4 and the P loading in the P/C composites depend mainly on the pore size and surface condition of carbon supports. M...

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Section: Resultsmentioning

confidence: 99%

Section: In Situ Tem Examinationmentioning

confidence: 99%

Rational Assembly of Hollow Microporous Carbon Spheres as P Hosts for Long‐Life Sodium‐Ion Batteries

Yao

Cui

Huang

et al. 2017

Advanced Energy Materials

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“…Figure 6 a presents a schematic of the experimental setup where a potential of −2 V versus Li/Li + was applied to drive lithiation when a physical contact was confirmed between the Li/Li 2 O reference electrode and the porous CNF/S working electrode . The gradual volume expansion due to lithiation of the PCNF/A550/S electrode was recorded in Movie S1 (Supporting Information), from which the captured images taken of the initial and fully lithiated stages are shown in Figure b–d.…”

Section: Resultsmentioning

confidence: 99%

In Situ TEM Study of Volume Expansion in Porous Carbon Nanofiber/Sulfur Cathodes with Exceptional High‐Rate Performance

Huang

Chong

et al. 2017

Advanced Energy Materials

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100

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Although lithium sulfur batteries (LSBs) have attracted much interest owing to their high energy densities, synthesis of high-rate cathodes and understanding their volume expansion behavior still remain challenging. Herein, electrospinning is used to prepare porous carbon nanofiber (PCNF) hosts, where both the pore volume and surface area are tailored by optimizing the sacrificial agent content and the activation temperature. Benefiting from the ameliorating functional features of high electrical conductivity, large pore volume, and Li ion permselective micropores, the PCNF/A550/S electrode activated at 550 °C exhibits a high sulfur loading of 71 wt%, a high capacity of 945 mA h g −1 at 1 C, and excellent high-rate capability. The in situ transmission electron microscope examination reveals that the lithiation product, Li 2 S, is contained within the electrode with only ≈35% volume expansion and the carbon host remains intact without fracture. In contrast, the PCNF/A750/S electrode with damaged carbon spheres exhibits sulfur sublimation, a larger volume expansion of over 61%, and overflowing of Li 2 S, a testament to its poor cyclic stability. These findings provide, for the first time, a new insight into the correlation between volume expansion and electrochemical performance of the electrode, offering a potential design strategy to synthesize high-rate and stable LSB cathodes.

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“…The in-situ electrochemical experiments were carried out on a JEOL 2100F TEM equipped with a Nanofactory® scanning tunneling microscope (STM)/TEM holder [24]. The uncoated Si or Si/C particles were dispersed on a gold rod of 200 μm in diameter as one electrode while a tungsten wire covered with Li metal was used as the counter electrode.…”

Section: In-situ Tem Examinationmentioning

confidence: 99%

“…Although there exist many studies on carbon coating as a means to improve the electrochemical performance, few efforts have been made to explore the roles of carbon coating during electrochemical reactions and the structural evolution of Si particles upon reaction. The in-situ transmission electron microscopy (TEM) has emerged as an indispensable tool to probe in realtime the lithiation/delithiation process of electrodes on an atomic scale [24][25]. Following the recent in-situ TEM characterization of nanostructured Si and Si composites, like Si nanoparticles (NPs) [26][27], alucone/Si NPs [28], graphene/Si NPs [29], carbon nanofiber (CNF)/Si NPs [30] and Si/C yolk/shell structure [31], this paper is dedicated to identifying the reaction mechanisms and morphological changes in Si/C NP electrodes in real-time.…”

Section: Introductionmentioning

confidence: 99%

Study of lithiation mechanisms of high performance carbon-coated Si anodes by in-situ microscopy

Cao

Abouali

et al. 2016

Energy Storage Materials

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Carbon coated Si (Si/C) composites with a high Si content of 81 wt.% are synthesized by one-pot carbonization of the mixture containing commercial Si particles and polyvinylidene fluoride (PVDF) at an optimized temperature. The Si/C electrodes deliver a high cyclic capacity of 2003 mAh g-1 at 0.5 A g-1 after 50 cycles and an enhanced rate capability of ~750 mAh g-1 at 4 A g-1 for over 200 cycles. The effect of ultrathin carbon coating on lithiation mechanisms of Si particles is evaluated using the in-situ transmission electron microscopy (TEM). It is revealed that the carboncoated Si particles undergo an isotropic to anisotropic transition during the initial lithiation, whereas such transition is not observed for the uncoated Si particle. The lithiation rate of Si/C is 3 to 4.5 times faster than that of uncoated Si with the same diameter, a testament to high rate capacities of Si/C in real batteries. The flexible, amorphous carbon coating favorably alters the damage mode of Si particles from pulverization by multiple cracking to fracture by a single crack. The above findings offer fundamental understanding and practical guideline for designing carbon coatings of Si-based electrodes with much enhanced electrochemical performance.

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In-situ TEM examination and exceptional long-term cyclic stability of ultrafine Fe3O4 nanocrystal/carbon nanofiber composite electrodes

Cited by 48 publications

References 48 publications

Rational Assembly of Hollow Microporous Carbon Spheres as P Hosts for Long‐Life Sodium‐Ion Batteries

Rational Assembly of Hollow Microporous Carbon Spheres as P Hosts for Long‐Life Sodium‐Ion Batteries

In Situ TEM Study of Volume Expansion in Porous Carbon Nanofiber/Sulfur Cathodes with Exceptional High‐Rate Performance

Study of lithiation mechanisms of high performance carbon-coated Si anodes by in-situ microscopy

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