Electron Conduction Path Research Articles

Chlorosulfonic Acid Stretched Carbon Nanotube Sheet for Flexible and Low-Voltage Heating Applications.

The carbon nanotube (CNT) is celebrated for its electrothermal property, which indicates the capability of a material to transform electrical energy into heat due to the Joule effect. The CNT nanostructure itself, as a one-dimensional material, limits the electron conduction path, thereby creating a unique heating phenomenon. In this work, we explore the possible correlation between CNT alignment in sheets and heating performance. The alignment of carbon nanotubes is induced by immersion and stretching in chlorosulfonic acid (CSA) solution. The developed CSA-stretched CNT sheet demonstrated excellent heating performance with a fast response rate of 6.5 °C/s and reached 180 °C in less than 30 s under a low voltage of 2.5 V. The heating profile of the stretched CNT sheet remained stable after bending and twisting movements, making it a suitable heating material for wearable devices, heatable smart windows, and in de-icing or defogging applications. The specific strength and specific conductance of the CSA-stretched CNT sheet also increased five- and two-fold, respectively, in comparison to the pristine CNT sheet.

Carbon decorated dendritic nickel sulfide coordinating with situ growth enabling hybrid supercapacitors with high specific energy and rate performance

Three-dimensional (3D) carbon nanospheres and two-dimensional (2D) carbon layer co-decorated dendritic nickel sulfide (Ni3S2) is fabricated on a nickel foam via a two-step hydrothermal process. The carbon nanospheres with the diameters ranging from 150 to 200 nm embellished on the “treetop” and the carbon layer coated uniformly on the “trunk”, which enhance the capacitive performance of the composite electrode. Herein, the amorphous carbon can further provide more efficient electron conduction path for the electrodes. With its unique superstructure, the as-fabricated carbon decorated Ni3S2 electrode exhibits a high specific capacity of 297.2 mAh g−1 at 5 mA cm−2, remarkable cycling stability (84.1% of the initial capacity) for 10,000 cycles at 10 mA cm−1. The hybrid supercapacitor fabricates by carbon decorated Ni3S2 and active carbon, which achieves a high specific energy of 62.5 Wh kg−1 at a specific power of 241.5 W kg−1. The encouraging results of the electrode make it as a potential candidate for energy storage.

Effect of Electronic Conductivity on the Polarization Behavior of Li[Li1/3Ti5/3]O4 Electrodes

Along with structural factors such as thickness and porosity, the conductive additive in lithium insertion electrodes in lithium-ion batteries influences the rate capability. The addition of a conductive additive improves the electronic conductivity of the electrodes, necessitating the optimization of such additives. However, the relationship of conductive additives to the electronic conductivity and rate capability of an electrode cannot be explained using classical electrochemical theory. The effect of the electronic conductivity of electrodes on polarization was investigated using Li[Li1/3Ti5/3]O4−pellet electrodes, whose electronic conductivity can be modified using a graphite conductive additive during an oxidation/reduction reaction. Consequently, the polarization behavior of the Li[Li1/3Ti5/3]O4−pellet electrodes without the conductive additive is asymmetric during the reduction and oxidation reactions, while it is symmetrical in the electrodes with the conductive additive. Furthermore, the polarization voltage is significantly lower in the electrodes with the conductive additive. Herein, we propose a rational explanation for the observed relationship between the electronic conductivity and polarization of electrodes using the formation and disappearance of electron conduction paths. This explanation would help us understand the enhancement of the rate capabilities of electrodes with poor electronic conductivity using conductive additives by the construction of the electron conduction paths.

Confined Magnetic-Dielectric Balance Boosted Electromagnetic Wave Absorption.

Magnetic-dielectric property plays a critical significance for the functional expression toward advanced materials. Within nanoscale, the simultaneous regulation of the electrical and magnetic properties of electromagnetic (EM) wave absorption materials faces huge challenges. Herein, using the metal-organic frameworks (MOF) as templates, highly-dispersed ZnO and Co nanoparticles are uniformly confined inside graphited N-doped carbon skeleton, constructing the balanced EM property in the Co@NC-ZnO absorbers. Meanwhile, a dynamics and symmetrical morphology optimization of MOF-derived Co@NC-ZnO are dependent on the Co/Zn mass ratio and adjusting MOF frameworks, which evolves from the cube, truncated cube, dodecahedron, and to the final microsphere. Simultaneously, both the electronic conduction network and magnetic coupling network are compatible together in the in situ transformed Co@NC-ZnO system. Boosted magnetic responding ability and unique magnetic coupling are verified by the off-axis electronic holography. Plentiful heterojunction interfaces and special electronic conduction paths can be built in this Co-Zn-MOF derivatives, facilitating the dielectric loss behaviors. As expected, MOF-derived Co@NC-ZnO absorber displays outstanding EM wave absorption ability with strongest reflection loss value of -69.6 dB at only 1.9 mm thickness and wideband absorption covering 6.8 GHz at 2.4 mm. Confined EM balance provides new design strategy toward MOF-derived excellent MA materials and functional devices.

Fe3C-inserted “tube plugging into porous network” nanohybrids as advanced sulfur hosts for lithium-sulfur batteries

Commercial applications of lithium-sulfur batteries are hindered by the low electrical conductivity of sulfur cathodes, which can be overcome by the application of suitable sulfur host materials. In this work, a novel and effective method is developed to grow bamboo-like N-doped carbon nanotubes (NCNTs) across three-dimensional N-doped porous carbon network (NPCNs) via chemical vapor deposition, thereby successfully preparing the sulfur-loaded composite carbon material inserted into the porous network. In such structure, carbon nanotubes act as electronic conduction paths, carbon networks as mass transfer channels, as well as the inserted Fe3C nanoparticles can increase the polarity of the carbon matrix. The discharge capacity of the S-NCNT/NPCNs cathode, as high as 1125 mAh g−1 at 0.2 C, retains 43.5% of its value when the current is increased 10-fold to 2 C. A specific capacity of 548.1 mAh g−1 at 1 C remains almost unchanged after 300 cycles, demonstrating better charge and discharge performance and excellent cycling ability of these promising candidate materials for Li-S battery applications. More importantly, the synthesis strategy is universal and can be fully extended to prepare other units, even binary NCNT/NPCNs (for example, NCNT/NPCNs-Co, NCNT/NPCNs-Co-Fe, NCNT/NPCNs-Fe-Ni, and NCNT/NPCNs-Co-Ni). The new strategy provided here may open up new ways for the application of hybrid carbon nanostructures in energy storage systems.

Numerical study of high temperature proton exchange membrane fuel cell (HT-PEMFC) with a focus on rib design

The rib size is a critical engineering design parameter for high temperature proton exchange membrane fuel cell (HT-PEMFC) stack development, yet it hasn't been studied for HT-PEMFC. A three-dimensional, non-isothermal model was developed in this work to investigate the effect of channel to rib width ratios (CRWR) on the performance of HT-PEMFC. The reaction heat caused by entropy change was divided into cathodic half-reaction heat and anodic half-reaction heat. The results show that the ratio value significantly influence the gas diffusion, electron conduction and the distribution of current density in the porous electrodes. Increasing this ratio facilitates gas transport in the porous electrode but causes higher ohmic loss due to longer distance for electron conduction. As a result, an optimal ratio of about 1 is observed, which results in a peak power density of 0.428 W/cm2. High current density is observed under the channel with a small ratio value while a high ratio value would cause high current density to appear under the rib, signifying the rib size effect on electrochemical behavior of HT-PEMFC. Apart from the electrical power output, the CRWR value also greatly influences the fluid flow and temperature distribution inside the cell, which would influence the long-term stability of HT-PEMFC. In the subsequent studies, efforts will be made to develop new stack configurations with more uniform gas distribution, short electron conduction path and low temperature gradient.

Ultralong-Lifespan Magnesium Batteries Enabled by the Synergetic Manipulation of Oxygen Vacancies and Electronic Conduction.

As a potential next-generation energy storage system, rechargeable magnesium batteries (RMBs) have been receiving increasing attention due to their excellent safety performance and high energy density. However, the sluggish kinetics of Mg2+ in the cathode has become one of the main bottlenecks restricting the development of RMBs. Here, we introduce oxygen vacancies to spherical NaV6O15 cross-linked with carbon nanotubes (CNTs) (denoted as SNVOX-CNT) as a cathode material to achieve an impressive long-term cycle life of RMBs. The introduction of oxygen vacancies can improve the electrochemical performance of the NaV6O15-X cathode material. Besides, owing to the introduction of CNTs, excellent internal/external electronic conduction paths can be built inside the whole electrode, which further achieves excellent electrochemical performance. Moreover, such a unique structure can efficiently improve the diffusion kinetics of Mg2+ (ranging from 1.28 × 10-12 to 7.21 × 10-12 cm2·s-1). Simulation calculations further prove that oxygen vacancies can cause Mg2+ to be inserted in NaV6O15-X. Our work proposes a strategy for the synergistic effect of oxygen vacancies and CNTs to improve the diffusion coefficient of Mg2+ in NaV6O15 and enhance the electrochemical performance of RMBs.

Mesoporous 3D titanium dioxide embed carbon nanofibers with superior polysulfide adsorption ability for high electrochemical performance Li-S batteries

The rechargeable lithium-sulfur batteries are promising candidate for the energy storage applications due to their low cost and high energy density. However, the lithium-sulfur batteries show poor electrochemical performance, caused by the polysulfide dissolution and low electrical conductivities of the sulfur cathode. Herein, we develop a new strategy to solving these two issues by designing titanium dioxide embed carbon nanofibers/S (CNFs@TO/S) hybrid composites. In this unique hybrid structure, the mesoporous 3D carbon nanofibers could provide fast electron conduction paths and structural stability. The titanium dioxide could act as polysulfide absorber via chemical bond between TiO2 and polysulfide. Owing to these synthetic effect, the as-prepared CNFs@TO/S cathodes exhibit advanced electrochemical performances.

Visualizing Local Electrical Properties of Composite Electrodes in Sulfide All-Solid-State Batteries by Scanning Probe Microscopy

Studies on local conduction paths in composite electrodes are essential to the realization of high-performance sulfide all-solid-state lithium batteries. Here, we directly evaluate the electrical properties of individual LiNi1/3Mn1/3Co1/3O2 (NMC) electrode active material particles in composite positive electrodes by scanning probe microscopy (SPM) techniques. Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM) are combined. The results indicate that all NMC particles exhibit a charged state with increasing potential, but low electronic conduction paths exist at point of contacts of some NMC particles. Furthermore, the I–V characteristics measured by conductive atomic force microscopy (C-AFM) suggest that these specific NMC particles show low charge–discharge reactivity. The results of the SPM techniques indicate that poor conduction locally limits the charge–discharge reactivity of electrode active materials, leading to the degradation of battery performance. Such an SPM combination accelerates the morphological optimization of composite electrodes by facilitating the investigation of the intrinsic electrical properties of the electrodes.

Imaging XAFS Study on Reaction Distribution of Composite Electrode Used As Commercial Lithium-Ion Battery

Demands for large-scale lithium-ion batteries for electric vehicles and grids have increased in order to reduce CO2 emissions in consideration of the global environment. To improve the reliability for practical large-scale batteries, further improvements in safety, rate capability, and cycle life are required. One of the unique behaviors taking place in lithium-ion battery composite electrodes is an inhomogeneous reaction of active materials.1 Since the heterogeneous reaction behavior induces overcharge and degradation of local active materials, the homogeneous charge-discharge reaction should be required. Ouvrard et al. reported that an inhomogeneous electrode reaction was caused during the charge-discharge process in LiFePO4 lithium-ion battery cathode, which was detected by using X-ray absorption spectroscopy.2 The study concluded that the ionic and electronic connectivity influenced by applied pressure is a crucial parameter for reaction distribution in composite electrodes.In this study, we examine the commercially utilized composite electrodes where enough electronic conduction path is formed. We compare the electrochemical characteristics using the commercial electrodes with self-made composite electrodes prepared in the laboratory and then measured the reaction distribution by imaging XAS.Two types of composite electrodes using LiFePO4 as the active material were used, and their thickness and mass loading were almost similar. Two electrode cells were assembled using 1 M LiFP6 in a solvent mixture of ethylene carbonate (EC) and ethyl metal carbonate (EMC) at a volume ratio of 3:7, and lithium counter electrode. Charge-discharge measurements were performed with an upper limit voltage of 3.6 V and a lower limit voltage of 2.0 V at rates of 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, 20, 30, 40 and 50 C. Imaging XAS measurements were performed at beamline BL-4 in Ritsumeikan University SR Center. Fe K-edge XAS was measured in a transmission mode using a two-dimensional detector.As a result of the discharge rate capability test, the capacity retention of 5 C was 92% for the commercial electrode and 5.4% for the self-made electrode, compared with the discharge capacity at 0.1 C, and the self-made electrode showed a remarkable decrease in capacity at high rates. The imaging XAS of the commercial electrodes implies a lack of inhomogeneous reaction after discharging at 5C. The previous reports have shown that the reaction in the planar direction of LiFePO4 proceeds from island-shaped points.3 We assume that the commercial composite electrodes are developed to be improved ionic and electronic connectivity.Reference: J. Liu, M. Kunz, K. Chen, N. Tamura, J. Richardson, J. Phys. Chem. Lett., 1, 2120-2123 (2010).G. Ouvrard, M. Zerrouki, P. Soudan, B. Lestrez, C. Masquelier, M. Morcrette, S. Hamelet, S. Belin, A. M. Flank, F. Baudelet, J. Power Sources, 229, 16-21 (2013).M. Katayama, K. Sumiwaka, R. Miyahara, H. Yamashige, H. Arai, Y. Uchimoto, T. Ohta, Y. Inada, Z. Ogumi, J. Power Sources, 269, 994-999 (2014).

Performance of Lithium Sulfur Batteries Consisting of Li2s/Carbon Composite Cathode

Lithium sulfur (Li-S) battery is a rechargeable battery typically consisting of sulfur as a cathode, Li metal as an anode, and a Li-ion conductive electrolyte. The sulfur has many advantages, such as high gravimetric theoretical capacity, high terrestrial abundance, and low price. Despite this potential, Li-S batteries are facing some challenges. Firstly, sulfur is an electrical insulator, which requires a large amount of conductive additive such as carbon for the formation of the electron conduction path. As a result, the loading amount of sulfur on the cathode is hard to increase. Secondly, lithium polysulfide intermediates dissolve in conventional organic electrolytes, leading to a redox shuttle. Thirdly, the volume expansion/shrinkage of sulfur during lithiation/delithiation is large, resulting in the mechanical degradation of the electron-conduction path in the electrode, which deteriorates the capacity. Finally, Li dendrites grow on Li metal during cycles, which causes a short circuit.Our group has proposed the combination of Li2S/carbon composite cathode, a graphite/Si anode, and a sparingly solvating electrolyte for solving these problems.1-4 Li2S is a reduction product of sulfur and has a high theoretical capacity. Replacing sulfur with Li2S enables us to use a non-Li anode such as graphite/Si,1,2 where the lithium dendrites are not growing. Furthermore, Li2S can improve the mechanical stability of the composite cathode because it starts with shrinkage in the initial charge process. The instability and low processability of Li2S was the problem; however, we recently reported the preparation process by the simple reduction of Li2SO4/carbon mixture, where carbon acts as a reductant, at a high temperature.3 The sparingly solvating electrolyte makes the solubility of polysulfide intermediates significantly low, which can suppress the redox shuttle, and the usage of graphite anode possible.2 Up to now, we used three-dimensional (3D) porous Al as the current collector for Li2S/carbon electrode to increase the loading amount of Li2S.4 However, to enhance the energy density and to simplify fabrication process of the cells, the use of simple Al foil (2D) is desirable. In this study, we prepared Li2S/carbon composite cathodes using the 3D and 2D current collectors and compared the electrochemical performances.Li2S/carbon composite was synthesized by the reduction of Li2SO4/carbon mixture. A slurry was prepared by mixing poly(N-vinyl pyrrolidone) (PVP), N-methyl pyrrolidone (NMP) and Li2S/carbon composite, and was inserted and coated to the 3D and 2D current collector, respectively, followed by drying. The 1:2 mixture of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and sulfolane (SL), [Li(SL)2][TFSA], diluted by 1,1,2,2,-tetrafluoroethyl-2,2,3,3,-tetrafluoropropyl ether (HFE) was employed as the sparingly solvating electrolyte. Charge/discharge tests were performed at C/12.It was rather difficult to make a uniform slurry suitable for the 2D electrodes due the aggregation of carbon-rich Li2S cathode materials. The usage of two different molecular weight PVPs (10,000 and 360,000 Da) as dispersant and binder polymers, respectively, was effective to disperse the carbon-rich materials in NMP. Fig. 1 shows a comparison of the capacity retention with cycling between Li2S cathodes using 3D and 2D current collectors, where the Li2S loading amount was 3.2 mg cm-2 and 1.9 mg cm-2, respectively. For the both cells, the Coulombic efficiency was ca. 98% due to the low solubility of polysulfide intermediates, and cycle characteristic was relatively stable. The discharge capacity of the 2D electrode was a little lower than that of the 3D electrode. The lower apparent electronic conductivity of the electrode could be a reason. Further, the loading amount of Li2S on the 2D electrodes cannot be as high as that on the 3D electrodes. In the presentation, merits and demerits to use 2D and 3D electrode will be discussed.AcknowledgementsThis study was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST). The authors are indebted to Lithium Ion Battery Technology and Evaluation Center (LIBTEC) for the preparation of the 2D cathode.References Zhe Li et al., ACS Appl. Mater. Interfaces, 8, 16053-16062 (2016).Zhe Li et al., Electrochemistry, 84, 887-890 (2016).Zhe Li et al., Nanoscale, 7, 14385-14392 (2015).Taisho Seita et al., ACS Energy Lett, 5, 1-7 (2020) Figure 1

Facile synthesis and excellent electrochemical performance of LiMn0.6Fe0.4PO4/C with 3D conductive network

In this paper, the LiMn0.6Fe0.4PO4/C with 3D conductive network was synthesized using β-cyclodextrin (β-CD) and carbon nanotubes (CNTs) as complex carbon source by a simple preparation route which include combination of wet ball milling, spray drying, and carbothermal reduction. The unique conductive network result in the composite has sufficient contact with electrolyte and three-dimensional electron conduction path. SEM and TEM images indicate that the active materials were uniformly coated by amorphous carbon and CNTs. The addition of β-CD and CNTs not only restricted growth of active particle but also reduced electron conduction distance. The composite possesses superior electron conductivity (8.8 × 10−2 S cm−1) and Li+ diffusion efficiency (6.1 × 10−13 cm2 s−1) due to unique 3D conductive network. As a result, the prepared sample exhibits distinguished discharge capacity of 160.2 mAh g−1 at 0.2 C and 131.7 mAh g−1 capacity even in 10 C.

Facile formulation and fabrication of the cathode using a self-lithiated carbon for all-solid-state batteries

We propose a innovative concept to boost the electrochemical performance of cathode composite electrodes using surface-modified carbons with hydrophilic moieties to increase their dispersion in a Lithium Nickel Manganese Cobalt Oxide (NMC) cathode and in-situ generate Li-rich carbon surfaces. Using a rapid aqueous process, the hydrophilic carbon is effectively dispersed in NMC particles followed by the conversion of its acid surface groups (e.g. –COOH), which interact with the NMC particles due to their basicity, into grafted Li salt (–COO−Li+). The solid-state batteries prepared using the cathode composites with surface-modified carbon exhibit better electrochemical performance. Such modified carbons led to a better electronic conduction path as well as facilitating Li+ ions transfer at the carbon/NMC interface due to the presence of lithiated carboxylate groups on their surface.

The controlled fabrication of hierarchical CoS2@NiS2 core-shell nanocubes by utilizing prussian blue analogue for enhanced capacitive energy storage performance

In this project, for the first time we successfully develop an approach to fabricate a novel core-shell structure of CoPBA@Ni(OH)2, in which Ni(OH)2 nano-sheets covered on the surface of CoPBA nanocubes through in-situ etching and growing processes, furthermore, being sulfurized into its hierarchical porous structure of CoS2@NiS2. The CoS2@NiS2 composite as a high-performance surpercapacitor electrode has been demonstrated. It exhibits very high specific capacitance value of 1731.2 F g−1 at 1 A g−1, excellent rate performance of 83.5% retention at 10 A g−1 and cycle performance with 87.1% retention after 5000 cycles together with distinguished coulombic efficiency of around 100%. Kinetic analysis and electrochemical impedance spectroscopy (EIS) results reveal the related mechanism. Herein, prussian blue analogue (PBA) as central core with cubic skeleton displays some great advantages, (1) it can provide more efficient electron conduction path to reduce the resistance of composite, (2) it can effectively prevent the agglomeration of electroactive Ni(OH)2 as well as sulfurized CoS2@NiS2 composite, (3) it can reduce ion diffusion pathway with mesoporous structure and enlarged surface area, greatly improving cycle stability. Such synthetic strategy opens up a new avenue for the effective construction of core-shell structure based on PBA basement for promising supercapacitor application.

Highly aligned carbon nanotubes and their sensor applications.

Flexible electronics comprising carbon nanotube (CNT) membranes and polymer composites are used in diverse applications, including health monitoring. Devices prepared using such electronics need to exhibit acceptable sensitivity at high strains, with the advantage of negligible hysteresis. Herein, we report a simple, physically robust method to fabricate a highly sensitive and stretchable sensor that enables the detection of pressure, strain, and human activity with facial expressions based on the highly aligned carbon nanotubes embedded in polydimethylsiloxane (PDMS). The aligned CNT network in PDMS modulates the electron conduction path in a unidirectional manner and provides multimodal mechanical sensing ability with a wide sensing range and high sensitivity. The highly aligned CNT sensor demonstrates high-pressure sensitivity (1.29 kPa-1), excellent stability and repeatability (over 10 000 cycles) with negligible hysteresis, and a good strain sensitivity over a wide range (up to 65%) with a good linear response. We confirmed the applicability of the sensor to detect small signals, such as heartbeat and pulse rate, expressions, and voice recognition, and that it could distinguish between various human motions with a very short recovery time of approximately 50 ms.

Effect of Nitrogen Doping on Oxygen Reduction Activity of TiO2 in Acidic Media

In order to develop low-cost nonprecious metal cathodes that have both high activity of oxygen reduction reaction (ORR) and high durability as alternatives to Pt-based electrocatalysts for practical fuel cell vehicle application, we have focused on group 4 and 5 oxide-based compounds because they are insoluble in acidic media and are much less expensive than platinum. We already demonstrated that titanium and zirconium oxide-based compounds prepared from these oxy-phthalocyanines showed definite ORR activities [1,2]. However, these types of the catalysts used multi-walled carbon nano-tubes as a support and deposited carbon derived from phthalocyanine as a local electron conduction path. Carbons are fundamentally oxidized at high potential and temperature. Therefore, carbon-free nonprecious ORR catalysts are required for fuel cell vehicle application. An arc-plasma deposition method is useful to control the oxidation state of the oxides without heat-treatment. We prepared zirconium oxide-based cathode using tin-oxide based electroconductive support by arc-plasma deposition as a carbon-free nonprecious metal cathode. Fig. 1 shows the potential-ORR current density curves of the ZrOx/SnO2-based support prepared by arc-plasma deposition method, the SnO2-based support, and the TixNbyOz+Ti4O7 [3] in 0.1 M H2SO4 at 30 oC. The ZrOx/SnO2-based support had superior ORR activity. Fig. 2 shows comparison of the onset potential of the ZrOx/SnO2-based support and the TixNbyOz+Ti4O7 in 0.1 M H2SO4 at 30 oC. Both onset potentials are above 1.1 V vs. RHE, indicating that these active sites are superior in quality. Figs. 1 and 2 suggested the great potential of carbon-free nonprecious metal oxide-based cathodes. Acknowledgment The authors thank the New Energy and Industrial Technology Development Organization (NEDO) for financial support. This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

Characterization of Sn4P3-Carbon Composite Films for Lithium-Ion Battery Anode Fabricated by Aerosol Deposition.

We fabricated tin phosphide–carbon (Sn4P3/C) composite film by aerosol deposition (AD) and investigated its electrochemical performance for a lithium-ion battery anode. Sn4P3/C composite powders prepared by a ball milling was used as raw material and deposited onto a stainless steel substrate to form the composite film via impact consolidation. The Sn4P3/C composite film fabricated by AD showed much better electrochemical performance than the Sn4P3 film without complexing carbon. Although both films showed initial discharge (Li+ extraction) capacities of approximately 1000 mAh g−1, Sn4P3/C films retained higher reversible capacity above 700 mAh g−1 after 100 cycles of charge and discharge processes while the capacity of Sn4P3 film rapidly degraded with cycling. In addition, by controlling the potential window in galvanostatic testing, Sn4P3/C composite film retained the reversible capacity of 380 mAh g−1 even after 400 cycles. The complexed carbon works not only as a buffer to suppress the collapse of electrodes by large volume change of Sn4P3 in charge and discharge reactions but also as an electronic conduction path among the atomized active material particles in the film.

Binder‐free carbon‐coated nanocotton transition metal oxides integrated anodes by laser surface ablation for lithium‐ion batteries

In this paper, an efficient laser surface ablation strategy for producing binder‐free carbon‐coated nanocotton CoO‐Co integrated anode is reported. The fabrication process introduces in‐situ growing nanocotton‐like CoO on the surface of Co foil via ablating with a nanosecond laser. After that, coated with dopamine as carbon source, the CoO‐Co composite foil is heated in Argon atmosphere to form a CoO@C‐Co foil as an anode of LIB. The laser surface ablation exhibits high fabrication speed (~10 minutes) and significantly reduces the processing time. The obtained binder‐free CoO@C‐Co integrated anode shows a unique cotton‐like villous structure with large specific surface area and an active material/current collector integrated architecture, which provides a stabilized rapid electronic conduction path. When tested as an anode for LIBs, the CoO@C‐Co integrated anode possesses superior performance: First discharge capacity of 1301.5 mAh g−1 is achieved at a current density of 0.1 A g−1. Also at a high current density of 1.5 A g−1, the second discharge capacity of 791.7 mAh g−1 is achieved. After 800 cycles, reversible capacities of 799.8 mAh g−1 can still be achieved with an average coulombic efficiency of nearly 100%. In addition, this strategy is suitable for the production of other carbon coated transition metal oxides integrated anodes, such as NiO@C‐Ni, Fe2O3/Fe3O4@C‐Fe, and CuO/Cu2O@C‐Cu integrated anodes.

Rate capability of carbon-free lithium titanium oxide electrodes related to formation of electronic conduction paths observed by color change

Lithium titanium oxide prepared by the hydrogen reduction synthesis of Li[Li1/3Ti5/3]O4 (LTO) exhibits electronic conductivity. The product demonstrated a superior rate capability than pristine LTO upon the examination of a pellet electrode in the absence of conductive additives. The rate capability of the pristine LTO pellet electrode is poor during the oxidation reaction due to low electronic conductivity of the electrode originated from insufficiently developed electronic conduction paths. In contrast, the rate capability during the reduction reaction is improved due to the formation of electronic conduction paths resulting from transformation to the electronic conductor LTO during the reduction process. Visual inspection indicated that the formation and loss of electronic conduction paths in the electrode are key to determining the rate capability of the LTO pellet electrode in the absence of a conductive additive. Our results confirmed that this LTO exhibiting an electronic conductivity maintains an electronic conduction path in the pellet electrode in the absence of a conductive additive during the redox reaction, thereby resulting in an improved rate capability in both the oxidation and reduction reactions.

Hierarchical MoS2-Based Onion-Flower-like Nanostructures with and without Seedpods via Hydrothermal Route Exhibiting Low Turn-on Field Emission

Herein, we report facile hydrothermal synthesis of hierarchical MoS2 -based nanomorphs (displaying onion-flower-like features) with the primary focus on field-emitter applications. The synthesized nanostructures were characterized physicochemically to understand their basic structural and morphological features. Interesting nanoscale morphological evolution of onion-flower-like MoS2—from plain nanoflowers to those containing seedpods—is observed with the change in hydrothermal reaction time from 9 h to 21 h. Peculiarly, MoS2 nanomorphs with only onion-flower-like morphology displayed lower turn-on field value of 3.7 V/μm as compared to 4.2 V/μm for the nanoflowers containing seedpod-like particles. This might be attributed to the possibility of an easy electron conduction path available for the petals in plain nanoflowers, which may be impeded by the seedpod-like particles in the latter case.