Sodiation Process Research Articles

Molecular-level heterostructures assembled from layered black phosphorene and Ti3C2 MXene as superior anodes for high-performance sodium ion batteries

Phosphorus, as one of the most promising anodes for sodium-ion batteries, its electrochemical performance improvement seriously suffers from insulated characteristics and poorly structural stability. Herein, we report an elaborately designed strategy to rationally synthesize molecular-level PDDA-BP/Ti3C2 nanosheet heterostructures taking advantages of high theoretical capacity of black phosphorene (BP) and high electronic conductivity, abundant functional groups of Ti3C2. Due to the face-to-face contact of both components, the parallel 2D interlayer spacing provides effective charge transfer and diffusion channels. DFT calculations show that strong interactions between BP and Ti3C2 could efficiently lower binding energy to facilitate the sodiation process. More importantly, surface functional groups of –F, –O and –OH in Ti3C2 play important roles to immobilize BP and act as more synergistic adsorption sites to accelerate sodiation. The PDDA-BP/Ti3C2 electrode displays extremely structure-stability confining monodispersed BP nanoparticle within Ti3C2 to buffer volume expansion and prevent aggregation of BP, exhibiting an ultrahigh reversible capacity of 1112 mA h g-1 at 500th-cycle at 0.1 A g-1 and ultralong cycling stability of 658 mA h g-1 with only 0.05% degradation per cycle within 2000 cycles at 1.0 A g-1. The related soidation mechanism and effects of functional groups of Ti3C2 on sodiation/desodiation redox reaction are deeply investigated.

In Situ Electron Microscopy Investigation of Sodiation of Titanium Disulfide Nanoflakes.

Two-dimensional (2D) metal sulfides show great promise for their potential applications as electrode materials of sodium ion-batteries because of the weak interlayer van der Waals interactions, which allow the reversible accommodation and extraction of sodium ions. The sodiation of metal sulfides can undergo a distinct process compared to that of lithiation, which is determined by their metal and structural types. However, the structural and morphological evolution during their electrochemical sodiation is still unclear. Here, we studied the sodiation reaction dynamics of TiS2 by employing in situ transmission electron microscopy and first-principles calculations. During the sodium-ion intercalation process, we observed multiple intermediate phases (phase II, phase Ib, and phase Ia), different from its lithiation counterpart, with varied sodium occupation sites and interlayer stacking sequences. Further insertion of Na ions prompted a multistep extrusion reaction, which led to the phase separation of Ti metal from the Na2S matrix, with its 2D morphology expanded to a 3D morphology. In contrast to regular conversion electrodes, TiS2 still maintained a compact structure after a full sodiation. First-principles calculations reveal that the as-identified phases are thermodynamically preferred at corresponding intercalation/extrusion stages compared to other possible phases. The present work provides the fundamental mechanistic understanding of the sodiation process of 2D transition metal sulfides.

Revealing the Simultaneous Effects of Conductivity and Amorphous Nature of Atomic-Layer-Deposited Double-Anion-Based Zinc Oxysulfide as Superior Anodes in Na-Ion Batteries.

Although sodium-ion batteries (SIBs) are considered promising alternatives to their Li counterparts, they still suffer from challenges like slow kinetics of the sodiation process, large volume change, and inferior cycling stability. On the other hand, the presence of additional reversible conversion reactions makes the metal compounds the preferred anode materials over carbon. However, conductivity and crystallinity of such materials often play the pivotal role in this regard. To address these issues, atomic layer deposited double-anion-based ternary zinc oxysulfide (ZnOS) thin films as an anode material in SIBs are reported. Electrochemical studies are carried out with different O/(O+S) ratios, including O-rich and S-rich crystalline ZnOS along with the amorphous phase. Amorphous ZnOS with the O/(O+S) ratio of ≈0.4 delivers the most stable and considerably high specific (and volumetric) capacities of 271.9 (≈1315.6 mAh cm-3 ) and 173.1 mAh g-1 (≈837.7 mAh cm-3 ) at the current densities of 500 and 1000 mA g-1 , respectively. A dominant capacitive-controlled contribution of the amorphous ZnOS anode indicates faster electrochemical reaction kinetics. An electrochemical reaction mechanism is also proposed via X-ray photoelectron spectroscopy analyses. A comparison of the cycling stability further establishes the advantage of this double-anion-based material over pristine ZnO and ZnS anodes.

Graphene/antimonene/graphene heterostructure: A potential anode for sodium-ion batteries

Antimony has been regarded as a promising anode for Na-ion batteries (NIBs) owing to its high specific capacity and electrical conductivity, as well as low potential range. However, its practical application is largely hindered by the poor cyclability due to the acute pulverization. Herein, we propose a trilayer graphene/antimonene/graphene (G/Sb/G) heterostructure as a potential anode material for NIBs. The aim of this anode design is to markedly increase the surface active sites via modifying the two-dimensional morphology and to alleviate volume expansion by introducing the graphene buffer. Based on density functional theory calculations and ab initio molecular dynamics simulations, the structural, electronic, mechanical properties, and the Na storage characteristics of the G/Sb/G heterostructure are systematically investigated. The results indicate that the G/Sb/G heterostructure exhibits superior thermodynamic stability, good electronic conductivity and ultrahigh stiffness. The trilayer G/Sb/G heterostructure can provide strong binding with sodium and low-migration barrier for sodium, endowing the anode with high specific capacity and good rate capability. More importantly, the coupling interaction between graphene and antimonene can greatly suppress the structural destruction of the antimonene layer during the sodiation process, offering excellent cyclability. Our findings suggest that the G/Sb/G heterostructure is a promising anode material for practical NIBs.

Lithium Pre‐cycling Induced Fast Kinetics of Commercial Sb2S3 Anode for Advanced Sodium Storage

Because of the abundant sodium resources and identical fundamental principles, sodium ion batteries (SIBs) are the state‐of‐the‐art alternative for lithium ion batteries. However, the larger ionic radius of Na+ causes sluggish reaction kinetics, which directly results in inferior electrochemical performance. In this work, the sodium storage properties of commercial bulk Sb2S3 (CSS) were improved by a single lithiation/delithiation cycle obtaining the lithium pre‐cycled Sb2S3 (LSS). Quantitative analysis reveals that the sodiation/desodiation kinetics of CSS and LSS is mainly diffusion‐controlled behavior and capacitive process, respectively. Thus, the reaction kinetics of LSS is promising, which exhibits improved initial coulombic efficiency, stable cycling performance, and high rate capability. In addition, a stable Li‐containing solid electrolyte interphase film was formed during the lithiation process, which can prevent continuous consumption of electrolyte during the each sodiation process. These results demonstrate that prelithiation technique should be a potential strategy to promote practical application for SIBs.

Red phosphorus filled biomass carbon as high-capacity and long-life anode for sodium-ion batteries

Red phosphorus is a promising anode material for sodium-ion batteries due to its low cost and superior theoretical capacity of 2596 mAh g−1. However, intrinsically inferior conductivity and huge volume changes during sodiation/desodiation processes hinder its practical application. Herein, we report an integrated red phosphorus/N-doped biomass carbon composite via filling red phosphorus nano-particles into the nano-pores of N-doped carbon derived from a renewable coconut shell biomass. In the rational structural design, N-doped biomass carbon serves as hard template for embedding red phosphorus nano-particles, buffers the volume expansion of red phosphorus during sodiation processes, and enhances the conductivity of composite. The composite delivers a high reversible capacity of 2481 mAh g−1 at 50 mA g−1 with a higher 89% initial coulombic efficiency. When the current density increases by 100 times to 5000 mA g−1, the capacity can remain 855 mAh g−1. Moreover, the composite maintains a reversible capacity of 1857 mAh g−1 at 500 mA g−1 after 100 cycles, and 845 mAh g−1 at 2000 mA g−1 after 500 cycles. This work introduces abundant biomass into application of high performance electrode materials for sodium-ion batteries.

Transport Limitations of Sodium-Ions in Type-II Clathrates

The development of material for room temperature sodium ion batteries with high cycling stability is of great significance. Clathrates are potential sodium ion conductors with the properties of cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. In this paper, we evaluated the type II clathrate performance in sodium ion batteries. Slightly elevated testing temperature (45 oC) can improve the cell capacity and rate performance due to the improved ionic conductivity. Side reactions on the solid electrolyte interface and loss of active materials during the first sodiation process contribute to the low Coulombic efficiency of the first cycle. Electrode morphology and elemental mapping analysis for clathrate electrodes at different states corroborate the above analysis.

Unique Double-Interstitialcy Mechanism and Interfacial Storage Mechanism in the Graphene/Metal Oxide as the Anode for Sodium-Ion Batteries.

Graphene/metal oxides (G/MO) composite materials have attracted much attention as the anode of sodium ion batteries (SIBs), because of the high theoretical capacity. However, most metal oxides operate based on the conversion mechanism and the alloying mechanism has changed to Na2O after the first cycle. The influence of G/Na2O (G/N) on the subsequent sodiation process has never been clearly elucidated. In this work, we report a systematic investigation on the G/N interface from both aspects of theoretical simulation and experiment characterization. By applied first-principles simulations, we find that the sluggish kinetics in the G/MO materials is mainly caused by the high diffusion barrier (0.51 eV) inside the Na2O bulk, while the G/N interface shows a much faster transport kinetics (0.25 eV) via unique double-interstitialcy mechanism. G/N interface possesses an interfacial storage of Na atom through the charge separation mechanism. The experimental evidence confirms that high interfacial ratio structure of G/N greatly improves the rate performance and endows G/MO materials the interfacial storage. Furthermore, the experimental investigation finds that the high interfacial ratio structure of G/N also benefits from the reversible reaction between SnO2 and Sn during cycling. Lastly, the effects of (N, O, S) doping in graphene systems at the G/N interface were also explored. This work provides a fundamental comprehension on the G/MO interface structure during the sodiation process, which is helpful to design energy storage materials with high rate performance and large capacity.

Hierarchically Interconnected Ni3S2 Nanofibers as Binder-Free Electrodes for High-Performance Sodium-Ion Energy-Storage Devices

Direct growth of hierarchically interconnected Ni3S2 nanofibers as binder-free electrodes for high-performance sodium (Na+)-ion batteries was demonstrated by a facile one-step hydrothermal method on a nickel (Ni) foam. The hierarchically interconnected Ni3S2 nanofibers can effectively relieve volume expansion of Ni3S2 and shorten diffusion paths of Na+ ions that can enhance the high electronic conductivity during the electrochemical reaction, yielding high specific capacitance, excellent cycling stability, and outstanding rate capability. As a result, a high discharge specific capacity of 584.2 mAh g–1 at a current density of 0.2 A g–1 in the first sodiation process with a capacity retention of 91.9% after 100 cycles (retains 536.9 mAh g–1) can be achieved. The asymmetric Na+-ion capacitor based on the hierarchically interconnected Ni3S2 nanofibers as binder-free anode materials and the activated carbon as a cathode material exhibits high energy and power density. Interestingly, the conversion reaction me...

Pseudocapacitive Graphene‐Wrapped Porous VO2 Microspheres for Ultrastable and Ultrahigh‐Rate Sodium‐Ion Storage

AbstractThe exploration of anode materials with enhanced electronic/ionic conductivity and structural stability is beneficial for the development of sodium‐ion batteries. Herein, a simple solution‐derived method is demonstrated to fabricate porous VO2 microsphere composite with a graphene‐wrapped structure (VO2/G). When used as the anode material for sodium‐ion batteries, the VO2/G electrode delivers a high reversible specific capacity (373.0 mAh g−1), great rate capability (138.8 mA h g−1 at 24.0 A g−1, ≈21 s per charge/discharge), and excellent long‐cycling performance (95.9 % capacity retention for 3600 cycles at 2.0 A g−1). The outstanding electrochemical property of VO2/G is mainly attributed to its unique graphene‐wrapped porous structure and the pseudocapacitive‐dominated feature. In addition, the sodium‐ion storage mechanism of VO2/G is investigated by various ex‐situ characterization techniques. During the first sodiation process, the sodium‐ion appears to partially reduce VO2/G and form metallic vanadium, sodium oxide, and amorphous sodium vanadium. This work provides new fundamental information for the design and application of vanadium oxides for energy storage system.

Revealing sodium ion storage mechanism in hard carbon

Although many studies have demonstrated the excellent potential of hard carbon as an anode in sodium ion batteries, the contribution of its active sites to the capacities of the sloping and plateau voltage regions is not yet clear. Herein, systematical investigation of the relationship between the active sites and sodium ion (Na+) storage in the sloping and plateau voltage regions was presented. In light of the physicochemical properties of the lignin-derived hard carbon (graphitization degree, interlayer spacing, micropore size distribution, and specific surface area), the results of Na+ ion diffusivity, and the change in these properties during Na+ ion insertion/extraction (as characterized by ex situ techniques), new mechanistic insights into Na+ ion storage were proposed. At the beginning of the sodiation process, Na+ ions were adsorbed on defect/edge sites; then partial micropore filling occurred in the sloping region above 0.1 V. In the plateau region below 0.1 V, Na+ ions were intercalated in the graphitic layers, and further adsorption in the micropores occurred near the cutoff potential. Furthermore, sodium clustering occurred below 0.1 V owing to the high concentration of Na+ ions in the micropores.

Electrochemical Properties and Challenges of Type II Silicon Clathrate Anode in Sodium Ion Batteries

The development of advanced anodes for low-cost room temperature sodium-ion batteries (SIBs) with high cycling stability is of great significance. Silicon clathrates are promising intercalation anodes due to their cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. However, the complicated surface structure and chemical reactions make it challenging to understand the electrochemical performance of clathrate anodes in SIBs. In this paper, we evaluated the performance of type II clathrate anodes in SIBs. A slightly elevated testing temperature (45°C) is shown to improve the cell capacity and rate performance due to the improved ionic conductivity. However, side reactions on the solid electrolyte interface (SEI) and loss of active material during the first sodiation process contribute to the low Coulombic efficiency during the first cycle. Analysis is supported by electrode morphology, elemental mapping, and X-ray photoelectron spectroscopy (XPS) on the clathrate electrodes at different electrochemical states. Na+ ion transport behavior between clathrate cages and surface in terms of migration barriers was also computed to explain the positive effect of higher cell testing temperature, and the low Coulombic efficiency of the first cycle.

States of thermochemically or electrochemically synthesized NaxPy compounds analyzed by solid state 23Na and 31P nuclear magnetic resonance with theoretical calculation

Phosphorus is a promising material for the electrode in sodium ion batteries (NIBs). In this study, the states of NaxPy compounds synthesized by thermochemical reaction and electrochemical sodiation were compared using solid state 23Na magic angle spinning (MAS) NMR, 23Na multiple quantum (MQ) MAS NMR, and 31P MAS NMR. The NMR signals in thermochemically synthesized NaxPy compounds (Na3P, NaP, Na3P7, Na3P11, NaP7) are assigned in reference to theoretical chemical shifts, based on first-principles calculations. Furthermore, the NMR signals in electrochemically prepared NaxPy compounds after two sodiation/desodiation cycles are ascribed to Na3P compounds and three amorphous compositions. The amorphous compounds ascribed to Na1−αP (0 < α < 1), Na2−βP (0 < β < 1), and Na3−γP (0 < γ < 1) are formed below 0.58 V in the charge and discharge process. These Na3P and the amorphous phases overlapped in the range from 0.20 V (sodiation process) to 0.58 V (desodiation process). 23Na and 31P NMR spectra reveal reversible sodiation and desodiation processes in the third cycle.

Investigation of electrochemical reaction mechanism for antimony selenide nanocomposite for sodium-ion battery electrodes

Antimony selenide and its carbon composite were synthesized through a mechanochemical process and investigated as anode materials for sodium-ion secondary batteries. X-ray diffraction (XRD) with rietveld refinement and transmission electron microscopy (TEM) analyses confirm that Sb2Se3 were composed of agglomerated highly crystalline nanocrystallites and the Sb2Se3/C composite consisted of nanocrystalline Sb2Se3 dispersed homogeneously throughout an amorphized carbon matrix. The initial Coulombic efficiency, rate capability, and cycle performance of the Sb2Se3/C composite were superior to those of Sb, or Sb2Se3. The Sb2Se3/C composite, in particular, showed excellent cycle stability, with 98.2% of initial capacity at 200 mA g−1 after 200 cycles. Based on the reaction potentials, ex situ XRD patterns and ex situ HR-TEM analysis of the Sb2Se3/C composite electrode revealed the structural changes which occurred reversibly within the Sb2Se3/C composite by conversion and recombination reaction during sodiation and desodiation process. Furthermore, XPS analysis study was carried out for identifying the surface films formed on both the electrodes and their effects on the performances.

Scalable Fabrication of Core-Shell Sb@Co(OH)2 Nanosheet Anodes for Advanced Sodium-Ion Batteries via Magnetron Sputtering.

Antimony (Sb) has captured extensive attention as a promising anode for sodium-ion batteries (SIBs) due to its high theoretical capacity and moderate sodiated potential but is held back from practical applications owing to its pulverization induced by dramatic volumetric variations during the (de)sodiation process. Herein, we report a core-shell Sb@Co(OH)2 nanosheet anode fabricated via magnetron sputtering Sb onto the mass-productive Co(OH)2 substrate anchored on stainless-steel mesh, which is scalable and suitable for flow-line production. In SIBs, the Sb@Co(OH)2 anode displays superior rate performance (383.5 mAh/g at 30 A/g), high discharge capacity, and excellent stability. Compared with the sputtered Sb film electrode, the improved performance of the core-shell Sb@Co(OH)2 nanosheet anode can be attributed to the open framework of the Co(OH)2 substrate, not only accelerating the ion and electron transfer but also serving as the buffer for alleviating the volumetric variation and the supporting scaffold for prohibiting the aggregation. More importantly, the (de)sodiation mechanism of the Sb@Co(OH)2 anode was explored by operando ( in situ) X-ray diffraction, and the similar alloying-dealloying processes (Sb ↔ Na xSb ↔ Na3Sb) for the 1st, 13th, and 30th cycles illustrate the excellent stability of the electrode.

Reduced Graphene Oxide-Anchored Manganese Hexacyanoferrate with Low Interstitial H2O for Superior Sodium-Ion Batteries.

Low-cost manganese hexacyanoferrate (NMHCF) possesses many favorable advantages including high theoretical capacity, ease of preparation, and robust open channels that enable faster Na+ diffusion kinetics. However, high lattice water and low electronic conductivity are the main bottlenecks to their pragmatic realization. Here, we present a strategy by anchoring NMHCF on reduced graphene oxide (RGO) to alleviate these problems, featuring a specific discharge capacity of 161/121 mA h g-1 at a current density of 20/200 mA g-1. Moreover, the sodiation process is well revealed by ex situ X-ray diffraction, EIS and Car-Parrinello molecular dynamics simulations. At a rate of 20 mA g-1, the hard carbon//NMHCF/RGO full cell affords a stable discharge capacity of 84 mA h g-1 (based on the weights of cathode mass) over 50 cycles, thus highlighting NMHCF/RGO an alternative cathode for sodium-ion batteries.

Theoretical predication of a two-dimensional structure of non-layered ScC as an excellent electrode material for rechargeable Na-ion battery

Non-layered two-dimensional structures with the atomic thickness recently attract much attention. In this work, we predicated a two-dimensional structure of non-layered ScC, denoted as ScC sheet, and evaluated its potential as the electrode material of Na-ion battery. The stability of ScC sheet is determined by the cohesive energy, phonon spectrum and potential energy curve calculations. Interestingly, the proposed ScC sheet can exhibit many unexpected electrochemical properties. It is found that ScC sheet can possess strong Na adsorption capability. Both pristine and Na-interacted ScC sheets represent good electronic conductivity due to the metallic nature. The structural degradation of the ScC during the sodiation and desodiation processes will not be anticipated. Besides, our results reveal that the ScC sheet has a minimal diffusion barrier of 9 meV and the calculated theoretical capacity of ScC sheet can reach to 940 mAh·g−1 on the basic of the second layer adsorption. Thus, benefiting from these features, ScC sheet is expectable to be served as a promising electrode material for the Na-ion battery.

Synthesis of Graphene Nanosheets through Spontaneous Sodiation Process

Graphene is one of the emerging materials in the nanotechnology industry due to its potential applications in diverse areas. We report the fabrication of graphene nanosheets by spontaneous electrochemical reaction using solvated ion intercalation into graphite. The current literature focuses on the fabrication of graphene using lithium metal. Our procedure uses sodium metal, which results in a reduction of costs. Using various characterization techniques, we confirmed the fabrication of graphene nanosheets. We obtained an intensity ratio (ID/IG) of 0.32 using Raman spectroscopy, interlayer spacing of 0.39 nm and our XPS results indicate that our fabricated compound is relatively oxidation free.

Necklace-Like Structures Composed of Fe3 N@C Yolk-Shell Particles as an Advanced Anode for Sodium-Ion Batteries.

It is of great importance to develop cost-effective electrode materials for large-scale use of Na-ion batteries. Here, a binder-free electrode based on necklace-like structures composed of Fe3 N@C yolk-shell particles as an advanced anode for Na-ion batteries is reported. In this electrode, every Fe3 N@C unit has a novel yolk-shell structure, which can accommodate the volumetric changes of Fe3 N during the (de)sodiation processes for superior structural integrity. Moreover, all reaction units are threaded along the carbon fibers, guaranteeing excellent kinetics for the electrochemical reactions. As a result, when evaluated as an anode material for Na-ion batteries, the Fe3 N@C nano-necklace electrode delivers a prolonged cycle life over 300 cycles, and achieves a high C-rate capacity of 248 mAh g-1 at 2 A g-1 .

Achieving Ultrafast and Stable Na-Ion Storage in FeSe2 Nanorods/Graphene Anodes by Controlling the Surface Oxide.

Designing transitional metal selenides (TMSes) with superior rate and cyclic performance for sodium-ion storage remains great challenges. To achieve this task, the influence of surface oxides on Na-ion storage behavior of FeSe2 is investigated by designing FeSe2 with varying oxide content. It is found that surface oxide has an inhibitory effect on the activity of FeSe2. Small-sized FeSe2 on graphene with higher surface oxide content exhibits obviously inferior performance compared to large-sized FeSe2 with lower oxide content. By controlling oxide content, the prepared FeSe2 nanorods/graphene exhibits a high capacity of 459 mAh/g at 0.1 A/g and superior rate performance. Only 10% capacity decrease occurs with the increase in current density from 0.1 to 5 A/g. Even at 25 A/g (∼50 C), it delivers a capacity of 227 mAh/g with almost no decay after 800 cycles. The influence mechanism of surface oxide is investigated. The oxide can be converted to a sodiated shell with high mechanical strength and poor conductivity, which generates phase-transition resistance to suppress the sodiation of FeSe2 core, blocks the transfer of Na-ions and electrons in subsequent sodiation processes. Understanding the effect of surface oxide on Na-ion storage will be helpful in designing TMSes and other active materials.