Na-storage Capacity Research Articles

Graphene supported ultrafine tin oxide nanoparticles enable conversion reaction dominated mechanism for sodium-ion batteries

Na-ion batteries are considered as promising alternatives for Li-ion batteries in electrochemical energy-storage. However, the lack of high performance anode materials severely plagues their practical application. In this work, we synthesized the SnO2@graphene (SnO2@G) nanocomposites through one-pot hydrothermal method, in which the ultrafine SnO2 nanoparticles (∼4 nm) evenly distributed on the graphene sheets surface. The synthesized SnO2@G delivered a Na storage capacity of 343 mAh g−1 at 100 mA g−1 after 100 cycles, with excellent capacity retention. Even at a low temperature of −20 °C, SnO2@G still maintains a specific capacity of 97 mAh g−1 after 100 cycles, making it both available for ambient and low temperature environment. The detailed Na-storage mechanism for SnO2@G is revealed. It is found that both conversion and alloying reaction contribute to sodium storage. The dominating contribution from conversion reaction is attributed to the ultrafine nanoparticles, which triggers the activity of conversion reaction of SnO2 with sodium. The study provides new insights for using SnO2 as the anode materials for Na-ion batteries.

High-Capacity Hard Carbon Pyrolyzed from Subbituminous Coal as Anode for Sodium-Ion Batteries

A pyrolyzed subbituminous carbon is synthesized through a simple one-step carbonization process as low-cost and high-capacity anode for sodium-ion batteries (SIB). The pyrolyzed subbituminous carbon, SHC-1300 anode shows high Na storage capacity of 291 mA h g–1 at 20 mA g–1 and high initial Coulombic efficiency of 79.5%, as well as stable cycling performance, exhibiting a promising alternative anode for affordable and high-performance SIB. Furthermore, according to the investigation of the electrochemical performance and structural characterizations, the SHC-1300 pyrolyzed from subbituminous coal with flexible structure demonstrates a better electrochemical performance compared with the BHC-1300 pyrolyzed from bituminous coal with rigid structure. The sodium storage mechanism and structural evolution reported in this work may give a new prospect for the selection of pyrolyzed carbon materials for high-performance sodium-ion batteries.

The effect of carbonization temperature of waste cigarette butts on Na-storage capacity of N-doped hard carbon anode

It has always been a widespread concern that countless waste cigarette butts cause resource waste and environmental pollution, so it is necessary to explore their recovery and reutilization. For this purpose, waste cigarette butts were recycled via pyrolysis carbonization at 700 °C and 800 °C for sodium ion battery (SIB) anode, respectively. The results suggested that the micro-structure and electrochemical Na-storage performances of N-doped waste cigarette butts hard carbon (NWHC) were affected by the carbonization temperature. For example, NWHC carbonized at 700 °C (NWHC-700) possessed lower degree of graphitization, higher content of N element and larger interlayer spacing than NWHC at 800 °C (NWHC-800). And also, NWHC-700 anode delivered the reversible discharge capacities of 300 mAh g−1 at 25 mA g−1 for 200 cycles and 135 mAh g−1 even at 1500 mA g−1 for 2000 cycles, higher than 241 mAh g−1 and 105 mAh g−1 of NWHC-800 anode, respectively. More disordered micro-structure, lower degree of graphitization, larger interlayer spacing and higher content of N element of NWHC-700 anode may be jointly responsible for higher electrochemical Na-storage performances, which would delay the afflux of the waste cigarette butts into the waste streams.

Facile synthesis of uniform yolk–shell structured FeS@mesoporous carbon spheres for high-performance sodium-ion batteries

The uniform yolk–shell structured FeS@meso-C spheres synthesized by a facile one-pot coating method deliver high Na-storage capacity.

Ultrafast Sodium Full Batteries Derived from XFe (X = Co, Ni, Mn) Prussian Blue Analogs.

Exploring high-rate electrode materials with excellent kinetic properties is imperative for advanced sodium-storage systems. Herein, novel cubic-like XFe (X = Co, Ni, Mn) Prussian blue analogs (PBAs), as cathodes materials, are obtained through as-tuned ionic bonding, delivering improved crystallinity and homogeneous particles size. As expected, Ni-Fe PBAs show a capacity of 81 mAh g-1 at 1.0 A g-1 , mainly resulting from their physical-chemical stability, fast kinetics, and "zero-strain" insertion characteristics. Considering that the combination of elements incorporated with carbon may increase the rate of ion transfer and improve the lifetime of cycling stability, they are expected to derive binary metal-selenide/nitrogen-doped carbon as anodes. Among them, binary Ni0.67 Fe0.33 Se2 coming from Ni-Fe PBAs shows obvious core-shell structure in a dual-carbon matrix, leading to enhanced electron interactions, electrochemical activity, and "metal-like" conductivity, which could retain an ultralong-term stability of 375 mAh g-1 after 10 000 loops even at 10.0 A g-1 . The corresponding full-cell Ni-Fe PBAs versus Ni0.67 Fe0.33 Se2 deliver a remarkable Na-storage capacity of 302.2 mAh g-1 at 1.0 A g-1 . The rational strategy is anticipated to offer more possibilities for designing advanced electrode materials used in high-performance sodium-ion batteries.

Flexible sodium-ion battery anodes using indium sulfide-based nanohybrid paper electrodes

Flexible nanohybrid paper electrode (termed as C-I) consisting of multi-walled carbon nanotubes (MWCNTs) and indium sulfide (In2S3) nanoplates is formed via a simple vacuum-assisted assembly and used as an anode for sodium-ion batteries (SIBs). In2S3 nanoplates which are well distributed on and bound to the MWCNTs provide a high Na storage capacity of the nanohybrid electrode as high as 410 mAh g−1 at a specific current of 50 mA g−1 over 100 charge/discharge cycles and ∼97% of rate-retention capability over the specific currents of 50 mA g−1 to 1 A g−1 for at least 50 charge/discharge cycles. Particularly, when In2S3 in the form of nanoplates was added to MWCNTs, the electrochemical performances are considerable as compared to those of bulk In2S3 or MWCNTs film electrodes. This highlights the importance of nanohybrid approach in overcoming the intrinsic complication of In2S3, i.e., the agglomeration of In2S3 into bulk form during assembly, followed by annealing. For C-I nanohybrid electrode, capacitive contribution (∼95%) rather than insertion contribution (∼5%) is predominant during charge/discharge process. The nanohybrid paper electrode is robust and thus retains capacity even under repeated mechanical deformation (flat-bent-flat cycles), demonstrating the potential of the electrode being used for flexible and wearable energy storage.

Effects of heteroatom doping on the performance of graphene in sodium-ion batteries: A density functional theory investigation

Heteroatom doped-graphene is a potential candidate as an anode material in sodium-ion batteries (SIBs). However, one of the major issues holding back its development is that a complete understanding of the doping effects accounting for the Na-ion storage of heteroatom-doped graphene has remained elusive. In this work, first principles calculations have been conducted to systematically investigate the electronic and geometric effects in various heteroatom-doped graphene. Graphene doping with pyridinic-N, pyrrolic-N, F and B improves the electrochemical Na storage due to the electronic effect which originates from electron deficient sites (i.e. defects or electron deficient atoms). On the other hand, P doping improves the Na storage ability of graphene due to the geometric effect caused by bond length mismatch. In contrast, the introduction of graphitic-N and S into graphene is inefficient for Na storage because of their inability to accept electrons from Na. Interestingly, the diffusion energy barriers obtained for Na on doped graphene are lower than that for the pristine graphene. Furthermore, co-doping strategy is predicted to achieve even better Na storage capacity due to the synergistic effect.

High-temperature treatment induced carbon anode with ultrahigh Na storage capacity at low-voltage plateau

Sodium-ion batteries (NIBs) show great prospect on the energy storage applications benefiting from their low cost and the abundant Na resources despite the expected lower energy density compared with lithium-ion batteries (LIBs). To further enhance the competitive advantage, especially in energy density, developing the high-capacity carbon anode materials can be one of the effective approaches to realize this goal. Herein, we report a novel carbon anode made from charcoal with a high capacity of ∼400 mAh g−1, wherein about 85% (>330 mAh g−1) of its total capacity is derived from the long plateau region below ∼0.1 V, which differs from those of typical hard carbon materials (∼300 mAh g−1) in NIBs but is similar to the graphite anode in LIBs. When coupled with air-stable Na0.9Cu0.22Fe0.30Mn0.48O2 oxide cathode, a high-energy density of ∼240 Wh kg−1 is achieved with good rate capability and cycling stability. The discovery of this promising carbon anode is expected to further improve the energy density of NIBs towards large-scale electrical energy storage.

(Keynote) Comparison of the Electrode Materials for Li and Na Ion Batteries

Secondary battery is becoming the key enabling technology for 3C products, electric vehicles (EVs) and energy storage system (ESS). Lithium-ion batteries (LIBs) with high energy density are widely used for mobile electronics, EVs and energy storage. Due to the abundant of resources, sodium-ion batteries (SIBs) have been considered as the promising candidate for large-scale energy storage system owing to the economic efficiency. LIBs and SIBs share similar concept and many materials. This presentation will summarize and compare their anode and cathode materials. Carbonaceous materials are commonly used for both of them as anode materials. However, well crystallized graphite is a good anode material for LIBs but not for SIBs. We have made hard carbon from sugar and anthracite for Li+ and Na+ storage. Sn, Sb, Si etc., which can alloy with Li and Na, show higher Na storage capacity. The rate capability of battery electrodes is highly dependent on the grain size, texture, and morphology of the electrode materials. An ordered, high surface area structure of electrochemically active materials on the nano scale can yield enhanced charge/discharge characteristics. Using nano materials as electrodes presents new opportunities for energy density, exceptionally high rate of charge and discharge, high cyclability, and low cost. The spinel Li4Ti5O12, well-known as a ‘zero-strain’ anode for lithium-ion batteries, can also store sodium, displaying an average storage voltage of 0.91 V and a reversible capacity of 155 mAh g1 and presents the best cyclability among all reported oxide-based anode materials. A three-phase separation mechanism, 2Li4Ti5O12 + 6Na+ + 6e- → 2Li7Ti5O12 + Na6LiTi5O12, has been confirmed. Furthermore, we also proposed many organic anode materials for SIBs including: Na2C8H4O4, Na2C6H2O4, Na2C14H6O4. In particular, we resolved the crystal structure of Na2C6H2O4 and found that it consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation. The experiment and calculation results reveal the Na-O inorganic layer provides both Na+ ion transport pathway and storage site, while the benzene organic layer provides electron transport pathway and redox centre. A large variety of cathode materials have been proposed based on the abundant knowledge developed on LIBs. They include layer- and spinel-structured transition metal oxides, and poly-anionic-type compounds. While layer-structured oxides with Co show high capacity for LIBs, the poly-anionic-compounds，spinel-type oxides and organic cathode materials are more promising for wide range of applications. Spinel-type oxides are used for LIBs only and certain nano-layered materials protected their surface and improve their cycling performance even at elevated-temperatures. High-voltage spinel LiNi0.5Mn1.5O4 cathode material has specific energy (~640 Wh/kg) due to the high operation voltage of ~4.7 V. The relatively inexpensive Ni and Mn in LiNi0.5Mn1.5O4 make this cathode material particularly desirable for large-scale applications. The surface regions (~ 2nm) show an irreversible migration of TM ions into lithium tetrahedral sites to form a Mn3O4-like structure. When the surface LiNi0.5Mn1.5O4 was modified by coating and superficial doping, the cycling performance of the material at elevated temperatures has been much improved and the Coulombic efficiency of discharge/charge is also obviously increased. Theoretical calculations analyses reveal that the stability of O at surface layer is enhanced by those surface modifications. Many layered oxide cathode materials with a general formula of NaxMO2 (M = Ni, Co, Mn, Fe, Cr, etc.) have attracted great attention for SIBs. We discovered that a novel Cu2+/Cu3+ redox couple is electroactive in Na containing layered oxides. On the basis of this important finding, we designed a new layered oxide, O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2, showing unexpectedly superior stability against moisture and excellent electrochemical cycling stability. The material delivers a reversible capacity of 100 mAh/g with an average voltage of 3.2 V and stable cycling. A prototype sodium-ion pouch cell using our Cu based cathode and anthracite derived carbon anode is demonstrated to have an energy density of 117 Wh/kg and good cycling as well as high safety. The perspective of future practical application will be discussed based the comparison of materials.

Facile synthesis of free-standing, flexible hard carbon anode for high-performance sodium ion batteries using graphene as a multi-functional binder

The use of reduced graphene oxide (rGO) as an environmentally friendly, multi-functional conductive binder is proposed as a novel strategy for manufacturing free-standing, flexible, high-performance hard carbon anodes for sodium ion batteries (NIBs). Compared with the conventional electrodes fabricated with insulating, fluorine-containing polymer binder (PVDF), the unique two-dimensional structure enable rGO can act as a strong binder and flexible backbone, resulting in free-standing, flexible hard carbon film, which can be directly used as anode for sodium ion batteries without any current collector. What's more, rGO also acts as active material, providing Na-storage capacity, as well as conductive addition to construct 3D conductive network, improving the rate performance of hard carbon. The obtained rGO-bonded hard carbon film with excellent flexibility can deliver a high reversible electrode capacity up to 372.4 mA h g−1. After 200 charging/discharging cycles, the capacity loss is only 9%. The good electrochemical performance and excellent flexibility, combined with its facile fabrication approach make it to be a promising electrode candidate for developing next-generation flexible and environmentally friendly energy storage devices.

Three-Dimensional Hierarchical Framework Assembled by Cobblestone-Like CoSe2@C Nanospheres for Ultrastable Sodium-Ion Storage.

Sodium-ion batteries (SIBs), as the promising commercial energy system, are restricted by their sluggish kinetics and low sodium-ion storage. Metal selenide possesses good conductivity and capacity but still suffers from the stacked problem and volume expansion. Significantly, CoSe2/C is successfully prepared with the assistance of citric acid as both a chelating agent and carbon precursor, displaying that cobblestone-like nanospheres with the radii (<25 nm) distribute uniformly in the carbon matrix. It is expected that the established Co-O-C bonds enhance the stability of the structure with faster ion shuttling. With the available electrolyte (NaCF3SO3/diethylene glycol dimethyl ether) in a potential window range from 0.5 to 3.0 V, the as-obtained sample shows the ultralong lifespan at 4.5 A g-1, retaining a capacity of 345 mA h g-1 after 10 000 cycles. From the detailed kinetic analysis, it is clear that the surface-controlled electrochemical behavior mainly contributes to the excellent large-current cycling stability and Na storage capacity. The ex situ results support that the crystal and morphological structure remains stable. This work is anticipated to enhance the in-depth understanding of the CoSe2/C anode and supply a facile manner to obtain electrode materials for SIBs.

In Situ Encapsulating α-MnS into N,S-Codoped Nanotube-Like Carbon as Advanced Anode Material: α → β Phase Transition Promoted Cycling Stability and Superior Li/Na-Storage Performance in Half/Full Cells.

Incorporation of N,S-codoped nanotube-like carbon (N,S-NTC) can endow electrode materials with superior electrochemical properties owing to the unique nanoarchitecture and improved kinetics. Herein, α-MnS nanoparticles (NPs) are in situ encapsulated into N,S-NTC, preparing an advanced anode material (α-MnS@N,S-NTC) for lithium-ion/sodium-ion batteries (LIBs/SIBs). It is for the first time revealed that electrochemical α → β phase transition of MnS NPs during the 1st cycle effectively promotes Li-storage properties, which is deduced by the studies of ex situ X-ray diffraction/high-resolution transmission electron microscopy and electrode kinetics. As a result, the optimized α-MnS@N,S-NTC electrode delivers a high Li-storage capacity (1415 mA h g-1 at 50 mA g-1 ), excellent rate capability (430 mA h g-1 at 10 A g-1 ), and long-term cycling stability (no obvious capacity decay over 5000 cycles at 1 A g-1 ) with retained morphology. In addition, the N,S-NTC-based encapsulation plays the key roles on enhancing the electrochemical properties due to its high conductivity and unique 1D nanoarchitecture with excellent protective effects to active MnS NPs. Furthermore, α-MnS@N,S-NTC also delivers high Na-storage capacity (536 mA h g-1 at 50 mA g-1 ) without the occurrence of such α → β phase transition and excellent full-cell performances as coupling with commercial LiFePO4 and LiNi0.6 Co0.2 Mn0.2 O2 cathodes in LIBs as well as Na3 V2 (PO4 )2 O2 F cathode in SIBs.

A Scalable Strategy To Develop Advanced Anode for Sodium-Ion Batteries: Commercial Fe3O4-Derived Fe3O4@FeS with Superior Full-Cell Performance.

A novel core-shell Fe3O4@FeS composed of Fe3O4 core and FeS shell with the morphology of regular octahedra has been prepared via a facile and scalable strategy via employing commercial Fe3O4 as the precursor. When used as anode material for sodium-ion batteries (SIBs), the prepared Fe3O4@FeS combines the merits of FeS and Fe3O4 with high Na-storage capacity and superior cycling stability, respectively. The optimized Fe3O4@FeS electrode shows ultralong cycle life and outstanding rate capability. For instance, it remains a capacity retention of 90.8% with a reversible capacity of 169 mAh g-1 after 750 cycles at 0.2 A g-1 and 151 mAh g-1 at a high current density of 2 A g-1, which is about 7.5 times in comparison to the Na-storage capacity of commercial Fe3O4. More importantly, the prepared Fe3O4@FeS also exhibits excellent full-cell performance. The assembled Fe3O4@FeS//Na3V2(PO4)2O2F sodium-ion full battery gives a reversible capacity of 157 mAh g-1 after 50 cycles at 0.5 A g-1 with a capacity retention of 92.3% and the Coulombic efficiency of around 100%, demonstrating its applicability for sodium-ion full batteries as a promising anode. Furthermore, it is also disclosed that such superior electrochemical properties can be attributed to the pseudocapacitive behavior of FeS shell as demonstrated by the kinetics studies as well as the core-shell structure. In view of the large-scale availability of commercial precursor and ease of preparation, this study provide a scalable strategy to develop advanced anode materials for SIBs.

Graphdiyne for Electrochemical Energy Storage Devices

Electrochemical energy storage devices are becoming increasingly important in modern society for efficient energy storage. The use of these devices is mainly dependent on the electrode materials. As a newly discovered carbon allotrope, graphdiyne (GDY) is a two-dimensional full-carbon material. Its wide interlayer distance (0.365 nm), large specific surface area, special three-dimensional porous structure (18-C hexagon pores), and high conductivity make it a potential electrode material in energy storage devices. In this paper, based on the facile synthesis method and the unique porous structure of GDY, the applications of GDY in energy storage devices have been discussed in detail from the aspects of both theoretical predictions and recent experimental developments. The Li/Na migration and storage in mono-layered and bulk GDY indicate that GDY-based batteries have excellent theoretical Li/Na storage capacity. The maximal Li storage capacity in mono-layered GDY is LiC3 (744 mAh.g(-1)). The experimental Li storage capacity of GDY is similar to theoretical predictions. The experimental Li storage capacity of a thick GDY film is close to that of mono-layered GDY' (744 mAh.g(-1)). A thin GDY film with double-side storage model has two-times the Li storage capacity (1480 mAh.g(-1)) of mono-layered GDY. Powder GDY has lower Li storage capacity than GDY film. The maximal Na storage capacity in GDY corresponds to NaC5.14 (316 mAh.g(-1)), and mono-layered GDY possesses higher theoretical Na storage capacity (NaC2.57). The experimental Na storage capacity (261 mAh.g(-1)) is similar to its theoretical value. Besides, GDY as electrode material, applied in metal-sulfur batteries, presents excellent electrochemical performance (in Li-S battery: 0.1C, 949.2 mAh.g(-1); in Mg-S battery: 50 mA.g(-1), 458.9 mAh.g(-1)). This ingenious design presents a new way for the preparation of carbon-loaded sulfur. GDY electrode material is also successfully used in supercapacitors, including the traditional supercapacitor, Li-ion capacitors, and Na-ion capacitors. The traditional supercapacitor with GDY as the electrode material shows good double layer capacitance and pseudo-capacitance. Both Li-ion capacitor (100.3 W.kg(-1), 110.7 Wh.kg(-1)) and Na-ion capacitor (300 W.kg(-1), 182.3 Wh.kg(-1)) possess high power and energy densities. Moreover, the effects of synthesis of GDY nanostructure, heat treatment of GDY, and atom-doping in GDY on the performance of electrochemical energy storage will be introduced and discussed. The results indicate that GDY has great potential for application in different energy storage devices as an efficient electrode material.

Layer-stacked Sb@graphene micro/nanocomposite with decent Na-storage, full-cell and low-temperature performances

Resolving the large volume changes and achieving the ultrafast charge-discharge capability for the alloy anode of sodium-ion batteries (SIBs) are needed urgently. Rational design of unique structure is an effective strategy to solve these problems. Herein, we reported a facile route to synthesize a layer-stacked Sb@graphene (LS-Sb@G) micro/nanocomposite via solvothermal method by using a mild reducing agent. In the LS-Sb@G, the Sb nanosheets are uniformly pasted on the graphene matrix and embedded into the interlayers, which leading to the formation of tight layer-by-layer micro/nanostructure. When employed as anode materials for SIBs, the unique structural characteristics offer the LS-Sb@G micro/nanocomposite with impressive Na-storage properties, such as high Na-storage capacity of 495.2 mAh/g after 100 cycles at 125 mA/g and decent rate capabilities up to 6 A/g. In addition, the LS-Sb@G electrode achieves superior electrochemical performance with a high reversible capacity of 116.5 mAh/g at 0.1 C (1 C = 120 mA/g) for sodium-ion full cells. Moreover, we firstly studied the low-temperature Na-storage performance of Sb-based composite at −20 °C. The LS-Sb@G composite demonstrated good low-temperature properties (e.g., 506.6 and 472.5 mAh/g at 25 and 50 mA/g at −20 °C, respectively) for SIBs, which endow great promise as an anode material for the normal operation of electric vehicles under low temperature condition.

Delineating Adsorption-Insertion Mechanism in Hard Carbon Materials for Sodium Ion Storage

Na ion batteries (NIBs) have attracted much attention in the field of electrochemical energy storage, due to the natural abundance of Na resources. The practical applicability of NIBs relies on the development of electrode materials with high performance and low cost. Presently the need for high performing anode materials is the main bottleneck in the full cell performance. Due to the large ionic radius (1.02 Å for Na compared to 0.76 Å for Li) and relatively high ionization potential (5.139 eV), Na ions cannot intercalate into graphite regions (interlayer spacing of 0.335 nm) in carbonate electrolyte. This limitation is partially lifted in nongraphitizable hard carbon, which is currently the most promising anode material available showing specific capacity over 300 mAh g-1 and average potential of 0.15 V vs. Na/Na+. Hard carbon has a “house of cards” structure containing graphite-like microcrystallites and amorphous region. The microcrystallites consist of few approximately parallel graphene sheets stacked together with large d-spacing (0.36-0.4 nm). Besides, these materials have numerous active sites such as edges, defects and functional groups containing O, N, P, S, etc. Three different Na storage environments and three corresponding modes have been reported in the literature for Na interactions with hard carbon: adsorption on the surface active sites; nanopore filling analogous to adsorption and intercalation between the graphene layers with suitable d-spacing. Experimentally two distinct voltage regions have been observed: a slope above 0.1 V and a plateau below 0.1 V. Although a number of studies have been conducted aiming to elucidate Na interactions with hard carbon, the assignment of Na storage mechanisms to different voltage regions is still debated. In order to resolve some of the differences in the literature data and develop a comprehensive understanding of Na storage, we synthesized a series of nanostructured hard carbon materials with controlled architectures. Using a combination of in-situ XRD mapping, ex-situ NMR, EPR, electrochemical techniques and simulations, an “adsorption-intercalation” (A-I) mechanism is established for Na ion storage. During the initial stages of Na insertion, Na ions adsorb on the defect sites of hard carbon with a wide adsorption energy distribution, producing a sloping voltage profile. In the second stage, Na ions intercalate into graphitic layers with suitable spacing to form NaCx compounds similar to the Li ion intercalation process in graphite, producing a flat low voltage plateau as illustrated in Scheme 1.[1-3] The clarification of Na storage mechanism provides new insights critical for knowledge-based design and synthesis of carbonaceous materials with improved Na ion storage capacity and reduced coulombic efficiency, that is, design of highly ordered layered structures with suitable layer spacing (0.37~0.38 nm) to improve Na storage capacity in the low potential plateau region, and low defective carbon to improve coulombic efficiency to a great extend to meet the practical application. Scheme 1. Schematic illustration of the mechanisms for Na-ion storage in hard carbon. “adsorption-intercalation” mechanism. 1. Y. Cao, L. Xiao, M. L. Sushko, W. Wang, B. Schwenzer, J. Xiao, Z. Nie, L. V. Saraf, Z. Yang, J. Liu, Nano Lett., 2012, 12, 3783。 2. L. Xiao, Y. Cao, W. A. Henderson, M. L. Sushko, Y. Shao, J. Xiao, W. Wang, M. H. Engelhard, Z. Nie, J. Liu, Nano Energy, 2016, 19, 279. 3. Shen Qiu, Lifen Xiao, Maria L. Sushko, Kee Sung Han, Yuyan Shao, Mengyu Yan, Xinmiao Liang, Liqiang Mai, Jiwen Feng, Yuliang Cao, Xinping Ai, Hanxi Yang and Jun Liu, Advanced Energy Materials, Accepted. Figure 1

Cobalt phosphide nanoparticles embedded in nitrogen-doped carbon nanosheets: Promising anode material with high rate capability and long cycle life for sodium-ion batteries

Cobalt phosphide (CoP) nanoparticles which were uniformly embedded in N-doped C nanosheets (CNSs) were fabricated via the simple one-step calcination of a Co-based metal–organic framework (MOF) and red P and exhibited a high capacity, fast kinetics, and a long cycle life. This CoP/CNS composite contained small CoP particles (approximately 11.3 nm) and P–C bonds. When its electrochemical properties were evaluated by testing CoP/Na coin cells, the composite delivered a Na-storage capacity of 598 mAh·g−1 at 0.1 A·g−1 according to the total mass of the composite, which means that the capacity of pure CoP reached 831 mAh·g−1. The composite also exhibited a high rate capability and long-term cyclability (174 mAh·g−1 at 20 A·g−1 and 98.5% capacity retention after 900 cycles at 1 A·g−1), which are commonly attributed to robust P–C bonding and highly conductive CNSs. When the reaction mechanism of the CoP/CNS composite was investigated, a conversion reaction expressed as CoP + 3Na+ + 3e− ↔ Co + Na3P was observed. The outstanding Na-storage properties of the CoP/CNS composite may suggest a new strategy for developing high-performance anode materials for Na-ion batteries.

Graphene oxide templated nitrogen-doped carbon nanosheets with superior rate capability for sodium ion batteries

Doping of N atoms into the carbonacous materials can generate extrinsic defects and more active sites, improve electrode wettability and also broaden the interlayer distance of carbon, hence promote Na storage capacity and high rate capability. Herein, we report the nitrogen-doped carbon nanosheets materials (PPyCs) obtained from pyrolysis of Polypyrrole coated graphene oxides. The pyrolysis temperature plays an important role on the electrochemical performance of PPyCs. With thermal treatment at 400, 600 and 800 °C, PPyCs have different content of N doping, and the doped N shows different existential forms. The PPyCs thermal treated at 600 °C (PPyC-600) exhibit a reversible capacity of 388.8 mA h g−1 at a current density of 100 mA g−1, and even at a high current density of 10 A g−1, high capacity of 198.6 mA h g−1 is maintained after 10,000 cycles, demonstrating outstanding cyclic stability, and high-rate capability. Furthermore, the assembled NVP/PPyC-600 full-cell demonstrates a high capacity of 122.2 mA h g−1 at a current density of 100 mA g−1 after 100 cycles, indicating the practical application of PPyCs nanosheets anode in sodium ion batteries.

Nanostructured layered vanadium oxide as cathode for high-performance sodium-ion batteries: a perspective

Abstract

Unexpected elastic isotropy in a black phosphorene/TiC2 van der Waals heterostructure with flexible Li-ion battery anode applications

Recently, flexible electrodes with biaxial/omnidirectional stretchability have attracted significant attention. However, most existing pliable electrode materials can be only stretched in one direction. In this work, an unexpected isotropic van der Waals (vdW) heterostructure is proposed, based on the assembly of two-dimensional crystals of anisotropic black phosphorene (BP) and transition metal carbide (TiC2). Using vdW-corrected density functional theory calculations, the BP/TiC2 vdW heterostructure was predicted to have excellent structural and mechanical stability, superior electrical conductivity, omnidirectional flexibility, and a high Li storage capacity. We have unraveled the physical origin of the excellent stability, as well as the Li adsorption preferences of the lithiated heterostructure, based on a three-step analysis of the stability of the Li-adsorption processes. In addition, the BP/TiC2 vdW heterostructure can also be applied as the anode material for flexible Na-ion batteries because of its high Na storage capacity and strong Na binding. However, compared with Na adsorption, the capacity is higher, and the adsorption energy is more negative for Li adsorption. Our findings provide valuable insights into the exploration of a rich variety of vdW heterostructures for next-generation flexible energy storage devices.