Anode Material For Na-ion Batteries Research Articles

Carbon/two-dimensional MoTe2 core/shell-structured microspheres as an anode material for Na-ion batteries.

Unique-structured composite microspheres of carbon and MoTe2 were prepared by a two-step process. Precursor C-MoOx composite microspheres were prepared by spray pyrolysis, and then the precursor was transformed into C-MoTe2 composite microspheres by a tellurization process. C-MoTe2 composites with a uniform distribution of MoTe2 nanocrystals (C/MoTe2) and core-shell-structured C-MoTe2 composites (C@MoTe2) were synthesized at tellurization temperatures of 450 and 600 °C, respectively. At a higher tellurization temperature of 600 °C, all of the MoTe2 nanocrystals moved to the surface of the microsphere because of the Ostwald ripening process. The initial discharge capacities of the C/MoTe2, C@MoTe2, and bare MoTe2 (i.e., containing no carbonaceous materials) powders for Na-ion storage at a current density of 1.0 A g-1 were 328, 388, and 341 mA h g-1, respectively. The discharge capacities of the C/MoTe2, C@MoTe2, and bare MoTe2 powders for the 200th cycle were 241, 286, and 104 mA h g-1, respectively, and the corresponding capacity retentions, which were measured from the second cycle were 100%, 99%, and 37%, respectively. The high structural stability and well-developed two-dimensional layer of MoTe2 of the C@MoTe2 microspheres provide superior Na-ion storage properties compared to those of the C/MoTe2 microspheres and bare MoTe2 powder.

Achieving ultralong life sodium storage in amorphous cobalt–tin binary sulfide nanoboxes sheathed in N-doped carbon

Amorphous CoSnSx nanoboxes sheathed in N-doped carbon (CoSnSx@NC) are fabricated as ultra-long life anode materials in Na-ion batteries.

Synergic effect of Bi, Sb and Te for the increased stability of bulk alloying anodes for sodium-ion batteries

A 12.5 at% replacement of Sb with Bi in Sb2Te3leads to a Na-ion battery anode material with enhanced resistance to mechanical degradation when used as micron-sized powder and not as a nanostructured carbon composite.

Enhanced sodium ion batteries performance by the phase transition from hierarchical Fe2O3 to Fe3O4 hollow nanostructures

Hierarchical Fe3O4 hollow nanostructures are synthesized from the phase transition of Fe2O3 hollow nanostructures, which are prepared through a dissolution-recrystallization process. The hierarchical Fe3O4 hollow nanostructures, applied as an anode material for Na-ion batteries, display good rate capability and cycling stability. The reversible capacity of 150mAh/g at 100mA/g after 50 cycles can be maintained for Fe3O4 anode. The superior Na-ion storage properties of hierarchical Fe3O4 could be largely ascribed to the stable electrode structure during Na-ion insertion and extraction process. On the contrary, Fe2O3 anode exhibits a high initial discharge capacity (686mAh/g), but it suffers from poor cycling stability due to the remarkable pulverization of the electrode.

Improving the sodiation performance of Na2Ti3O7 through Nb-doping

Na2Ti3O7 has attracted increasing attention as a promising anode material for Na-ion batteries. However, the low electronic conductivity of Na2Ti3O7 brings about kinetic problems for sodiation. In this study, we report Nb-doped Na2Ti3O7 synthesized from a facile sol-gel method. The obtained Na2Ti2.97Nb0.03O7 has increased unit cell volume and lowered band gap compared to the pristine Na2Ti3O7. The Na2Ti2.97Nb0.03O7 shows a high reversible capacity of 189.7mAhg−1 at 0.2C, a great high-rate performance of 89.4mAhg−1 at 5C, and great cyclability of 78.5% after 500 cycles. Specifically, the rate capability of Na2Ti2.97Nb0.03O7 is considerably superior to that of the pristine Na2Ti3O7. The improved sodiation performance suggests Nb-doping is an effective modification for Na2Ti3O7 anode materials.

Surfactant-Free Aqueous Synthesis of Pure Single-Crystalline SnSe Nanosheet Clusters as Anode for High Energy- and Power-Density Sodium-Ion Batteries.

SnSe with 3D hierarchical nanostructure composed of interconnected single-crystal SnSe nanosheets is synthesized via a fast and effective strategy. Unexpectedly, when used as the anode material for Na-ion batteries (NIBs), the SnSe exhibits a high capacity (738 mA h g-1 ), superior rate capability (40 A g-1 ), and high energy density in a full cell. These results provide the possibility of SnSe use as NIBs anodes.

New Carbon Materials with Large Closed Pore Volume for the Anode of High Energy Na-Ion Batteries

Recently the demand for rechargeable batteries with high capacity, high power, long life, high reliability, and low cost has been increasing. While Li-ion batteries offer the highest energy density among present battery technologies, the higher cost and insufficient resources of lithium is a bottleneck to enabling their wider use. Na-ion batteries, where sodium acts as the current carrier, are attractive alternatives to Li-ion batteries because of the lower cost and abundance of sodium. However, the energy density of Na-ion batteries is still lower than that of Li-ion batteries, therefore the development of the active materials achieving a higher energy density is eagerly anticipated. For anode materials in Na-ion batteries, a non-graphitized carbon, such as hard carbon, is well-studied in contrast to Li-ion batteries, where graphite is usually used as the anode material. The capacity of non-graphitized carbon in Na-ion batteries is reported to be 200 - 300 mAh/g [1,2]. In Na-ion insertion process, it is proposed that Na-ions are inserted between stacked graphenes in the higher potential above ca. 0.2 V vs. Na+/Na, and then nano-pores are filled during electrochemical reaction in the lower potential region [1,2]. In our previous research, we focused on the effect of the pore structure of carbons, and found a linear relationship between the reversible capacity in the range of 0.2 - 0 V vs. Na+/Na and the closed pore volume of non-graphitized carbons. This result suggests that Na-ion could be inserted reversibly into the closed pore of non-graphitized carbons, and thus the non-graphitized carbon with large closed pore volume is a promising anode material for higher capacity Na-ion batteries [3]. In this study, we synthesized a new carbon material with a large closed pore volume using the carbon sources including a pore-forming agent as the starting material. It has the closed pore volume of 0.49 cc/g and its discharge capacity reached 438mAh/g. [1] D. A. Stevens et al, J. Electrochem. Soc., 148 (2001) A803 [2] S.Komaba et al, ACS Appl. Mater. Interfaces, 3 (2011) 4165 [3] A. Kano et al, 228th ECS meetings, (2015) 221

Synthesis, Electrochemical Properties of 3D Structured Red P-Carbon As an Anode Material for Na-Ion Battery

Li ion batteries have become widely accepted as an effective device for storing electric energy in recent decades. In practice, it can play an important role in present energy industries for offering the highest energy density. However, there are still problems to be solved such as limit in remote, cost, and safety. To date, Na ion batteries has been considerably interested in the field of large energy storage system (ESS) because of needs to go beyond the limits of Li ion batteries. Extensive investigations on alloying reactions of various transition metal (Sn, Sb, Ge, Si etc) as anode materials have been carried out because of their high theoretical capacity. Inspired by this point, phosphorus is one of the most promising candidate with a high theoretical specific capacity (2596 mA h g-1) at the discharge potential range of 0.4-1.2 V. In this paper, we have synthesized 3D structured red P-Carbon composite by facile templating method. For this process, we anticipated a lot of merits such as suppressing the large volume expansion (~300%), offering large reaction site, and minimizing the unnecessity like binders and additives. The phase and morphology of 3D structured red P-Carbon has been investigated by XRD, SEM, and TEM, respectively. The electrochemical performance of red P-CNT composites were tested in sodium non-aqueous electrolytes. It could maintain the reversible capacity in high C-rate because of their structural advantage. In addition, differences of structural phase differences and conductivity during the alloying reactions in sodium system will be discussed.

Unusual Na Storage Behavior of Ordered Mesoporous Carbon on Ether-Based Electrolyte System

The Li-ion battery (LIB) market increases rapidly due to the development of portable electronic devices and energy storage systems (ESSs). By increasing the demand for commercialization of scale-up LIB, large amounts of accumulated lithium resources will be consumed in the near future. Recently, Na-ion battery (NIB) system is considered as an alternative to LIB system because sodium resources are abundant and distributed around the world as well as sodium storage mechanism is similar to that of lithium. In contrast to LIB, graphite is not suitable for NIB anode material due to the small interlayer for large ionic radius of Na+ ion. Therefore, previous studies have investigated that non-graphitic carbon materials can deliver reversible Na+ ion insertion and extraction with initial capacity up to 300mAh g-1, however, the cycle stability of non-graphitic carbon materials is very poor.Ordered mesoporous carbon (OMC) has the advantage of large surface area due to the development of nano-sized pores inside a micron-sized particle, which results in large electrode/electrolyte interface, easy penetration of electrolyte, and fast diffusion of Li+/Na+ ion. The ordered hexagonal structure of the OMC was formed as an inverse replica of a mesoporous silica SBA-15 structure and started from phenanthrene as a carbon source. In carbonate-based electrolyte system, the first and second discharge capacities of the OMC were 800 mAh g-1 and 350 mAh g-1 at a current density of 100 mA g-1, respectively, which means a large irreversible capacity loss, whereas in ether-based electrolyte system, the first irreversible capacity decreased considerably, implying an enhanced reaction reversibility. Even though the first discharge capacity in the ether-based electrolyte was about 200 mAh g-1, the capacity in the ether-based electrolyte increased during repeated cycling and achieved 350 mAh g-1 after 100 cycles. In contrast, the cycle retention in carbonate-based electrolyte degraded down to 200mAh g-1 consistently during 100 cycles.To elucidate the electrolyte system-dependent Na+ storage of the OMC, various electrochemical analyses and synchrotron X-ray based techniques were performed using two-type electrolytes of 1 M NaPF6 in EC/DMC=1/1 and 1 M NaPF6 in DEG/DME.

Two-Dimensional Y2C Electride: A Promising Anode Material for Na-Ion Batteries

By means of first-principles computations, we explored the potential of using Y2C monolayer as anode material for rechargeable Na-ion batteries (NIBs). As a two-dimensional electride material, Y2C monolayer is metallic and has a strong in-plane stiffness. Significant interactions between Y2C monolayer and Na atom ensure its high theoretical specific capacity of 564 mA·h/g. The Y2C monolayer also has high Na mobility and rather small average open-circuit voltages. All these characteristics suggest that the Y2C monolayer could be a promising anode material for NIBs.

Iron Telluride-Decorated Reduced Graphene Oxide Hybrid Microspheres as Anode Materials with Improved Na-Ion Storage Properties.

Transition-metal telluride materials are studied as the anode materials for Na-ion batteries (NIBs). The FeTe2-reduced graphene oxide (rGO) hybrid powders (first target material) are prepared via spray pyrolysis and subsequent tellurization. The H2Te gas treatment transforms the Fe3O4-rGO powders to FeTe2-rGO hybrid powders with FeTe2 nanocrystals (various sizes <100 nm) embedded within the rGO. The FeTe2-rGO hybrid powders contain 5 wt % rGO. The Na-ion storage mechanism for FeTe2 in NIBs is described by FeTe2 + 4Na(+) + 4e(-)↔Fe + 2Na2Te. The FeTe2-rGO hybrid discharge process forms metallic Fe nanocrystals and Na2Te by a conversion reaction of FeTe2 with Na ions. The discharge capacities of the FeTe2-rGO hybrid powders for the first and 80th cycles are 493 and 293 mA h g(-1), respectively. The discharge capacities of the bare FeTe2 powders for the first and 80th cycles are 462 and 83 mA h g(-1), respectively. The FeTe2-rGO hybrid powders have superior Na-ion storage properties compared to bare FeTe2 powders owing to their high structural stability and electrical conductivity.

Morphology Controlled Synthesis of SnS2-Based Nanoflowers, and Nanoplates and Their Comparative Na Storage Properties

Different morphological structures of tin sulfide (SnS2) were prepared by a solvothermal process using the thioacetamide as a sulphuring agent, are explored as anode material for Na-ion battery. All of the as-prepared SnS2 show much higher Na storage capacity and better cyclability along with good rate capability. Particularly, the flowerlike SnS2 (F-SnS2) demonstrates the highest reversible discharge capacity of 430 mAh g–1 at 50 mA g–1 and better cyclability with 97.8 % coulombic efficiency (CE) after 50 cycles. This behaviour is mainly attributed to the unique hierarchical structure and high porosity, which can provide enough space to buffer the volume expansions during the cyclic processes, increase the contact area between the electrode and electrolyte, and reduce the transport lengths of both sodium ions and electrons. The high capacity at high current rate and long cycling makes this porous F-SnS2 a promising anode material for Na-ion batteries.

Design of nanoconfined MWNTs@NaTi2(PO4)3 coaxial cables with superior rate capability and long-cycle life for Na-ion batteries

NASCION-type NaTi2(PO4)3 (denoted as NTP) has been established well as a promising anode material for Na-ion batteries (NIBs) in view of striking structure advantages. Unfortunately, the excellent rate capability of NTP is seriously limited by its intrinsic modest electrical conductivity. In this work, an efficient solvothermal strategy combined with following calcination is purposefully developed to synthesize morphology-controlled one-dimensional (1D) coaxial nanocables consisting of highly conducting multi-walled carbon nanotubes (MWNTs) cores and well-crystalline NTP sheath (afterwards designed as MWNTs@NTP). When evaluated as an anode for non-aqueous NIBs, the unique MWNTs@NTP coaxial nanocables exhibit excellent Na-storage performance with high charge–discharge capacities, rate performance and long cycle life, much better than those for MWNTs/NTP mixture, originating from the optimum design and synergetic effect of rapid electron delivery, convenient Na+ transport and large electrode/electrolyte contacting sur-/interfaces provided by the three-dimensional entangling coaxial nanonetworks.

Advantages of Ge anode for Na-ion batteries: Ge vs. Si and Sn

The sodiation properties of alloy-type anode materials (Si, Ge, and Sn) have been evaluated in terms of electrochemical energy storage using first-principles molecular dynamics calculations. We report that Ge can deliver reasonably good performance in all aspects of sodium storage capability, mechanical stability, and ion conductivity, when compared with Si and Sn. The Ge anode: (1) has a strong thermodynamic driving force for sodiation that is comparable to that of Sn and much stronger than that of Si, (2) exhibits moderate volume expansion and bulk modulus upon sodiation that are superior to those of Sn, and (3) allows fast Na ion conductivity that is comparable to that of Sn and is faster by three orders of magnitude than that of Si. Our study suggests that among the group 14 elements, Ge is fairly promising as an anode material for Na-ion batteries.

Investigation of the Charge Storage Mechanism of Mxenes As Anode Materials for Na-Ion Batteries

Two dimensional (2D) materials such as graphene have attracted tremendous interest and have shown promising potential in various applications due to their unique physical structure and properties. Another new class of 2D materials, a group of early transition metal carbides and/or carbonitrides, called MXene, have been studied and reported recently. MXenes are chemically derived from layered Mn+1AXn or MAX phases, where M is early transition metal, A is an A-group element (mainly groups 13 and 14), X is C and/or N, and n=1,2, and 3. Since discovery of the first MXene (Ti3C2) in 2011, more than 10 new MXenes have been synthesized and demonstrated its interesting and unique properties in many applications. It has been shown that MXenes have promising potential in electrochemical energy storage applications such as lithium ion batteries (LIBs) and electrochemical capacitors (ECs), due to their high electrical conductivity, good structural/chemical stability, and large surface areas. Recently, MXene application studies are expanding to other battery systems such as Na-ion batteries (NIBs). The growing concerns on the cost and resource limit of lithium for large scale applications have triggered the development of NIBs as an alternative battery system to LIBs for large scale energy storage applications due to their potentially low-cost and natural abundance. Moreover, the accumulated knowledge and technology of LIBs enables fast-advancements of NIBs research since the operating principles of the NIBs are similar to that of “rocking-chair” mechanism in LIBs. Although many concepts can be adopted from LIB in NIB research, the electrochemistry of NIBs turns out to be different in many aspects requiring new design of electrode materials and electrolyte for improving and/or optimizing performance of NIBs. In particular, Na+ has a larger radius than Li+, which directly affects the mass transport and storage in the electrochemical reaction. This makes many of current LIB anode materials, such as graphite, unsuitable for NIBs. In this regards, the laminar nature of MXenes bonded by weak van der walls forces and its inherent interlayer spacing are very attractive as anode materials for NIBs. However, most of studies on the electrochemical behavior of MXenes as anode materials for NIBs are just at the theoretical estimation only without much experimental support. In this study, we present a systematic study on the electrochemical properties and their charge storage mechanisms of V2C and Nb2C MXenes as anode materials for NIBs. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) were used in both ex situ and in situ way to look at the structural changes during electrochemical cycling. By utilizing such combined X-ray techniques, we are able to get better understanding of structural/electronic structure changes of MXenes and their related charge storage behavior during sodiation/desodiation process. A systematic comparison of electrochemical properties and charge storage mechanism for MXenes between NIBs and LIBs as well as the approaches to improve them will also be discussed. Acknowledgement The work done at Brookhaven National Lab was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, under Contract Number DE-SC0012704. The work performed at Drexel University was supported by the Office of Electricity Delivery and Energy Reliability, Energy Storage Systems Program, through Sandia National Laboratories. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Structural Recognition of Some Layer-Structured Materials for Na-Ion Batteries

Layer-structured materials have been widely used in various applications due to their distinctive structures and physical/ chemical properties. As the electrode materials for sodium (Na)-ion batteries (NIB), their intercalation mechanisms remain unclear and their electrochemical performances are unsatisfied with low storage capacity and poor cycling stability. Therefore, it is essential to find new layered materials, explore their intercalation mechanisms and improve their electrochemical performance. In these regards, this thesis focuses on four layered materials in terms of atomic structural characterization, phase transition and intercalation mechanism, and improvement of their electrochemical performance, including anti-P2 Na0.5NbO2, Mxene Ti3C2X and transition-metal dichalcogenides MoS2. Most of the layered AxMO2 (A=alkali ions, M= transition metals) are composed of edge-shared MO6 octahedrons, wherein A ions occupy in the interlayers with varied coordination polyhedron such as octahedrons (O), tetrahedrons (T) or trigonal prisms (P). We synthesized a new layered oxide material anti-P2 Na0.5NbO2 with negative strain effect. Its structure is composed of NbO6 trigonal prisms and NaO6 octahedrons. Analysis by X-ray absorption spectroscopy(XAS) and density functional theory (DFT) calculations indicates that the negative volume change is mainly a result of the enhanced interlayer (Na-O) interaction and the weakened Nb-Nb and Nb-O bonding in the O-Nb-O slab upon Na intercalation. As an anode material for NIB, Na0.5NbO2 exhibits high structural stability, long cycle life and prominent rate performance for NIB. Thanks to its negative stain effect, Na0.5NbO2 can be used as a “volume buffer” for the positive-strain electrode materials to construct long-term batteries with high energy density. MXenes represent a large family of functionalized two-dimensional (2D) transition-metal carbides and carbonitrides. However, most of the understandings on their unique structures and applications are stopped at the theoretical suggestion. We clarified the surface structure and intercalation chemistry of Ti3C2X at the atomic scale by aberration-corrected scanning transmission electron microscope (STEM) and DFT calculations. The STEM studies show that the functional groups (e.g. OH-, F-, O-) and the intercalated sodium (Na) ions prefer to stay on the top sites of the centro-Ti atoms and the C atoms of the Ti3C2 monolayer, respectively. Double Na-atomic layers are found within the Ti3C2X interlayer upon extensive Na intercalation via two-phase transition and solid-solution reactions. In addition, aluminum (Al)-ion intercalation leads to horizontal sliding of the Ti3C2X monolayer. Based on these observations, the previous monolayer surface model of Ti3C2X is modified. DFT calculations using the new modeling help to understand more about their physical and chemical properties. Meanwhile, the Ti3C2X exhibits prominent rate performance and long-term cycling stability as an anode material for NIB. The distinctive electronic and chemical properties of transition-metal dichalcogenides are closely related to their structure and intercalation chemistry. By means of STEM, we clarified the phase transition from semiconductive 2H-MoS2 to metallic 1T-MoS2 and occupancy of the intercalated Na at the atomic scale. It is shown that x = 1.5 in NaxMoS2 is a critical point for the reversibility of the structural evolution. If light of the understanding of the phase transitions and intercalation chemistry of the MoS2, the cycling stability and rate performance of MoS2 are improved by controlling its reaction depth, optimizing the binder and nano-treatment. Figure 1

Electrode Materials for Na-Ion Batteries Studied By Atmc in Situ NMR Spectroscopy

Due to the high abundance, low costs and very suitable redox potential, Na-ion batteries (NIBs) should open new avenues of research and engineering as complementary alternatives to Li-ion batteries (LIBs).[1] This shift has to be accompanied with a deeper understanding of the chemical reactions involving the multiple cell components. The application of a non-invasive analysis tool that can follow the reactions in operando is therefore highly desired. A fundamental technique for this approach is in situ solid-state nuclear magnetic resonance (NMR) due to its high chemical specificity and sensitivity to crystalline, amorphous as well as metastable/short-lived phases.[2] However, in situ NMR on LIBs/NIBs does not come without its challenges, e.g., significantly different shifts of the multi-component samples, changing sample conditions (such as the magnetic susceptibility and conductivity) during cycling, signal broadening due to paramagnetism as well as interferences between the NMR and external cycler circuit that might impair the real-time monitoring of the electrochemical processes.[2–4] In this matter, we are developing and exploring the use of a new Automatic Tuning Matching Cycler (ATMC) in situ NMR probe system that addresses many of these issues (Figure 1a).[4] We applied the new in situ NMR methodology to paramagnetic Na3V2(PO4)2F3 cathodes as well as Na—Na cells and Sn anodes to study local atomic changes and the formation of new/intermediate phases, respectively, during cycling of these materials while being used in electrochemical cells. 31P in situ NMR on Na3V2(PO4)2F3 as a cathode in a NIB enabled the detection of different P signals within a huge frequency range of 4000 ppm (Figure 1b).[4] Thereby, two NMR carrier frequencies with 4000 and 5900 ppm offset were applied and re-calibrated “on-the-fly” during the in situ NMR experiment (Figure 1b). The data shows a significant shift and changes in the number as well as intensities of 31P signals during desodiation of the cathode. Furthermore, the in situ experiments reveal changes of local P environments that in part have not been seen in ex situ NMR investigations.[5] Furthermore, we applied ATMC 23Na in situ NMR on symmetrical Na—Na cells during galvanostatic plating. An automatic adjustment of the NMR carrier frequency during the in situ experiment ensured on-resonance conditions for the Na metal and electrolyte peak, respectively. Thus, interleaved measurements with different optimal NMR set-ups for the metal and electrolyte, respectively, became possible. This allowed the formation of different Na metal species as well as a quantification of electrolyte consumption during the electrochemical experiment to be monitored.[4,6] The use of Sn metal as an anode material for NIBs was investigated by 23Na in situ NMR to study the formation of both crystalline and amorphous NaxSn phases during sodiation.[7] The new approach is likely to benefit a further understanding of Na-ion battery chemistries.

In Situ TEM Investigation of Structural Evolution of Black Phosphorous Anode for Sodium Ion Batteries

Na-ion batteries have attracted enormous interest due to its low cost and the abundance of sodium in the earth, holding the potential to become the technology of choice for large-scale electrochemical energy storage. However, the investigation of suitable anode materials for Na-ion batteries is still in its infancy and few electrode materials meet the performance requirement for practical applications. Black phosphorous (BP), which possesses layered structure, is a promising anode material for sodium ion batteries due to its extremely high theoretical capacity (2596 mAh/g) and good conductivity. However, there are few studies on the electrochemical reaction between BP and sodium.1,2 Here, we explored the structural evolution of BP during the sodiation reaction by employing a state-of-the art in situ (scanning) transmission electron microscopy electrochemical testing technique.3,4 Our in situ TEM study indicates that the sodium ion transport pathway is highly orientation dependent inside the BP. An anisotropic expansion and multiple phase transitions are also observed during the sodiation process. [1] Park, C. M.; Sohn, H. J. Adv. Mater. 2007, 19, 2465-2468 [2] Sun, J.; Lee, H.-W.; Pasta, M.; Yuan, H.; Zheng, G.; Sun, Y.; Li, Y.; Cui, Y. Nat. Nanotechnol. 2015, 10, 980-985. [3] Nie, A.; Cheng, Y. C.; Zhu, Y. H.; Asayesh-Ardakani, H.; Tao, R. Z.; Mashayek, F.; Han, Y.; Schwingenschlogl, U.; Klie, R. F.; Vaddiraju, S. Nano Lett. 2014, 14, 5301-5307. [4] Nie, A.; Cheng, Y.; Zhu, Y.; Asayesh-Ardakani, H.; Tao, R.; Mashayek, F.; Han, Y.; Schwingenschlögl, U.; Klie, R. F.; Vaddiraju, S.; Shahbazian-Yassar, Reza. Nano let. 2014, 14, 5301-5307

Unusual Na Storage Behavior of Ordered Mesoporous Carbon on Ether-Based Electrolyte System

The Li-ion battery (LIB) market increases rapidly due to the development of portable electronic devices and energy storage systems (ESSs). By increasing the demand for commercialization of scale-up LIB, large amounts of accumulated lithium resources will be consumed in the near future. Recently, Na-ion battery (NIB) system is considered as an alternative to LIB system because sodium resources are abundant and distributed around the world as well as sodium storage mechanism is similar to that of lithium. In contrast to LIB, graphite is not suitable for NIB anode material due to the small interlayer for large ionic radius of Na+ ion. Therefore, previous studies have investigated that non-graphitic carbon materials can deliver reversible Na+ ion insertion and extraction with initial capacity up to 300mAh g-1, however, the cycle stability of non-graphitic carbon materials is very poor. Ordered mesoporous carbon (OMC) has the advantage of large surface area due to the development of nano-sized pores inside a micron-sized particle, which results in large electrode/electrolyte interface, easy penetration of electrolyte, and fast diffusion of Li+/Na+ ion. The ordered hexagonal structure of the OMC was formed as an inverse replica of a mesoporous silica SBA-15 structure and started from phenanthrene as a carbon source. In carbonate-based electrolyte system, the first and second discharge capacities of the OMC were 800 mAh g-1 and 350 mAh g-1 at a current density of 100 mA g-1, respectively, which means a large irreversible capacity loss, whereas in ether-based electrolyte system, the first irreversible capacity decreased considerably, implying an enhanced reaction reversibility. Even though the first discharge capacity in the ether-based electrolyte was about 200 mAh g-1, the capacity in the ether-based electrolyte increased during repeated cycling and achieved 350 mAh g-1 after 100 cycles. In contrast, the cycle retention in carbonate-based electrolyte degraded down to 200mAh g-1 consistently during 100 cycles. To elucidate the electrolyte system-dependent Na+ storage of the OMC, various electrochemical analyses and synchrotron X-ray based techniques were performed using two-type electrolytes of 1 M NaPF6 in EC/DMC=1/1 and 1 M NaPF6 in DEG/DME.

NaV3(PO4)3/C nanocomposite as novel anode material for Na-ion batteries with high stability

Anode materials with long cycling life and rate capability have remained a great challenge for sodium-ion batteries. Herein, a vanadium-based orthophosphate, NaV3(PO4)3/C nanocomposite has been investigated as a novel anode material for Na-ion batteries. The electrochemical performance of NaV3(PO4)3/C nanocomposite is evaluated in Na-half cell, which delivers a reversible capacity of 146mAhg−1 at the charging/discharging rate of 1C, and remarkable rate capability. EIS, XPS and in-situ XRD are performed to give the insight into interfacial property of electrode and structural evolution of material during cycling. The excellent cycling stability could be attributed to stable interface at higher cutoff voltage and slight change of structure with intercalation/deintercalation of Na+. Moreover, we achieve a Na-ion full battery with long term cycle life based on NaV3(PO4)3/C anode and Na3V2(PO4)3/C cathode, retaining 80% of initial capacity after 1000 cycles at charging/discharging rate of 5C, suggesting the feasibility of the as-obtained materials applied as a promising candidate for anode of Na-ion batteries.