Conversion-type Anode Materials Research Articles

Carbon nanoparticle-entrapped macroporous Mn3O4 microsphere anodes with improved cycling stability for Li-ion batteries

Manganese oxide (Mn3O4) has garnered substantial attention as a low-cost, environment-friendly anode material. It undergoes a conversion reaction involving the formation of Li2O and metallic Mn to provide high-energy Li-ion batteries. However, its low electrical conductivity and significant volume change reduce its capacity during the initial lithiation/delithiation, hindering its practical application. To improve the cycle performance, we propose a new composite structure wherein we entrap carbon nanoparticles in macroporous Mn3O4 microspheres with a unique maze-like porous interior. We fabricate the Mn3O4/C composites using a scalable two-step process involving the thermal decomposition of MnCO3 in water vapor and mixing in a carbon-dispersed solution. The fabricated Mn3O4/C composites with varying carbon contents exhibit a high maximum discharge capacity retention of 86% after 50 cycles, compared to the 18% given by bare Mn3O4. The entrapped carbon nanoparticles improve the cycle performance both electrochemically and physically. The microstructure of the composite particles and the fabrication process developed in this study will help improve the performance of other conversion-type anode materials that suffer from cycle degradation, including inexpensive transition metal oxides and sulfides.

Electrochemical Performance of Electrophoretically Deposited Nickel/ Cobalt Antimony Oxide-Carbon Black Negative Electrodes for Alkali-Ion Batteries

In recent years, the requirement for portable power has increased due to the miniaturization of electronic devices. Developing rechargeable lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), with high power and energy density, long cycle life is the need of the hour. In this present work, nickel antimony oxide (NiSb2O6; NSO) and cobalt antimony oxide (CoSb2O6; CSO), two relatively new conversion-type anode materials have been explored as negative electrodes for both LIB and SIB. Conversion-type anode materials offer many advantages like ease of synthesis, requires inexpensive and abundantly available precursors and exhibit high specific capacities. Besides, relatively higher redox potentials of such anodes minimize the chance of lithium dendrites formation. A simple co-precipitation followed by calcination at 1000◦C leads to formation of tri-rutile phase NSO and CSO powder. The microstructural analysis using scanning electron microscopy of NSO and CSO powder confirms the formation of asymmetric particles having size in the range of 50-100nm. FTIR and Raman results of the calcined NSO and CSO powder indicate the presence of Sb2O6 2- units along with Ni+2/Co+2. The NSO-CB and CSO-CB electrodes are fabricated by facile and reproducible electrophoretic deposition (EPD) technique. EPD is a facile colloidal technique which can be adopted to fabricate different types of materials like conversion, insertion and alloying anode on any complex shaped substrate. Besides being an economical and ecofriendly process, EPD offers excellent reproducibility and control over the deposited film thickness. At a deposition parameter of 100V for 3minutes, well-adhered and uniform coating of NSO-CB and CSO-CB are obtained on the copper current collector. The SEM micrographs of the EPD grown electrodes substantiate the formation of a porous film with uniform distribution of active materials and carbon black (CB). Detailed ex-situ XRD analysis has been carried out to find out the lithium storage mechanism of NiSb2O6 material. It is observed that the NiSb2O6 breaks into NiO and Sb2O5 in the first lithiation step. These oxides further participate in reversible lithiation and de-lithiation reactions in the subsequent cycles. When used as a lithium-ion anode, the NSO-CB and CSO-CB electrode deliver a stable reversible capacity of 594mAhg-1 and 612mAhg-1, respectively, at a specific current of 0.5Ag-1 after 100 cycles (Fig 1(a)). Both the anode material exhibits excellent rate performance delivering a specific capacity of 397mAhg-1 and 510mAhg-1, respectively, at a high specific current of 4Ag-1. On the other hand, as a sodium-ion anode, the NSO-CB and CSO-CB electrodes are able deliver a stable reversible capacity of 255mAhg-1 and 150mAhg-1, respectively, at a specific current of 0.1Ag-1 after 50 cycles (shown in Fig 1(b)). Cyclic voltametric study at different scan rates reveals that the electrochemical reactions of NSO and CSO are mainly dominated by diffusion-controlled behavior. Therefore, both NSO and CSO can be a potential anode material for alkali-ion batteries.Fig 1: Cyclability performance of NSO-CB and CSO-CB electrodes as (a) lithium-ion battery anode, cycled at 0.5mAg-1 specific current and (b) sodium-ion battery anode, cycled at 0.1mAg-1 specific current in the voltage range of 0.01-2.5V. Figure 1

Design and synthesis of cellulose nanofiber-derived CoO/Co/C two-dimensional nanosheet toward enhanced and stable lithium storage

Nano-sized two-dimensional carbonaceous materials have been widely used as the matrix for alloying-type and conversion-type anode materials for Li-ion batteries (LIBs) to improve structural stability and rate performance. However, relevant synthesis usually requires rigorous conditions and chronic reaction processes. Herein, we have designed a simple solvothermal reaction and heat treatment to prepare a novel CoO/Co/C two-dimensional nanosheet (CoO/Co/C 2DNS) by adopting cellulose nanofibers (CNFs) as the precursor. The unique characteristics of CNFs facilitate the uniform distribution of active materials on the surface and the construction of two-dimensional nanostructure via self-assembly. It is worth noting that CoO/Co/C 2DNS exhibits a striking synergistic effect since the porous 2D carbon framework offers additional pseudo-capacitance and enhances the electronic conductivity, while the ultrafine active materials encapsulated inside shorten the Li-ions diffusion pathways and relieve the volume change. Benefit from the unique structure, the composite anode delivered outstanding rate performance (∼500 mAh g−1 at 10 A g−1) and superior long-range cycling performance up to 800 cycles even at 2 A g−1. This work provides a new strategy for the synthesis of nano-sized 2D composite, offering a promising route to construct high performance conversion-type anodes for next-generation LIBs.

Ta2O5-Rgo Nanocomposite As Emerging Anode Material for Sodium Ion Storage Via Extrinsic Pseudo-Capacitive Red-Ox Process

Ta2O5 nanoparticles (NPs) are an emerging conversion type anode material which store sodium ion via extrinsic pseudo-capacitance behaviour. Ionic liquid supported hydrothermal synthesis method was adopted to synthesise pure Ta2O5 NPs followed by hydrothermal route to prepare Ta2O5–reduced graphene oxide (Ta2O5-rGO) nanocomposite. Ta2O5–rGO composite possesses specific discharge capacity of 19 mAhg-1 after 500 cycles at a current rate of 0.1 C compared to bare Ta2O5 NPs where it shows 18 mAhg-1 @ 150 cycles. The stable electro-chemical performance of Ta2O5–rGO composite could be accessible by 2-D net work structure of graphene with excellent surface area and very low electrical resistivity enhances the electron and ion migration rate. Finally, the present study urges electrochemist to design and fabricate advance Ta2O5-rGO composites for sodium- ion battery applications.

Enhancing the mechanical stability of composite electrodes by regulating the volume of active material using a prelithiation strategy

Significant volume variations in alloy-type and conversion-type anode materials during lithiation/delithiation cycling increase the challenge of assembling a composite electrode with high mechanical stability. This paper theoretically investigated the possibility of applying a prelithiation strategy to the assembly of a composite electrode to improve the mechanical stability of the composite electrode by controlling the pre-volume expansion of the active material. A chemo-mechanical coupled model containing an internal variable describing the irreversible volume dilation is developed to analyze a microunit of the composite electrode. Simulation results indicate that whereas a marginal prelithiation cannot effectively alleviate the high stress, and an excessive prelithiation increases the risk of damage. The optimal prelithiation range mainly depends on the irreversible volume dilation of the active material during cycling. For Si electrodes with the irreversible volume dilation of ~40%, the preferred prelithiation stoichiometric number is 0.3–0.6, the theoretical predictions are consistent with previous experimental results. The theoretical model and findings provide deeper insights on the prelithiation strategy based on the mechanical aspects.

Exploration of CrPO4@N-doped carbon composite as advanced anode material for potassium-ion batteries

Metal phosphates are attracting great attention as anode materials for alkali-ion batteries due to their chemical stability, low working voltage, and high theoretical capacity. However, there are few reports on the application of metal phosphate as potassium-ion batteries (PIBs) anode material, and the potassium storage mechanism remains mysterious. Herein, a core–shell chromium phosphate@N-doped carbon (denoted as CrPO4@NC) composite is newly synthesized and demonstrated as conversion-type anode material for PIBs. The N-doped carbon coating layer effectively relieves the mechanical strain and improves electrical conductivity during repetitive cycling. The formed P–C bonding between CrPO4 core and nitrogen-doped carbon shell can help to maintain structural integrity and accelerate charge transfer. As a consequence, the CrPO4@NC composite exhibits a decent capacity (304.6 mAh g−1 at 50 mA g−1), good rate capability (135.1 mAh g−1 at 500 mA g−1), and superior stability (133.2 mAh g−1 at 200 mA g−1 after 100 cycles). Particularly noteworthy, we also provide experimental evidence that a conversion reaction occurs at CrPO4@NC electrode with metallic Cr and K3PO4 formed during the potassiation process. This work illustrates that CrPO4 may be a kind of anode material for applications in energy storage systems.

Concentration Gradient Induced Delithiation Failure of MoO3 for Li-Ion Batteries.

Electric vehicle manufacturers worldwide are demanding superior lithium-ion batteries, with high energy and power densities, compared to gasoline engines. Although conversion-type metal oxides are promising candidates for high-capacity anodes, low initial Coulombic efficiency (ICE) and poor capacity retention have hindered research on their applications. In this study, the ICE of conversion-type MoO3 is investigated, with a particular focus on the delithiation failure. A computational modeling predicts the concentration gradient of Li+ in MoO3 particles. The highly delithiated outer region of the particle forms a layer with low electronic conductivity, which impedes further delithiation. A comparative study using various sizes of MoO3 particles demonstrated that the electrode failure during delithiation is governed by the concentration gradient and the subsequent formation of a resistive shell. The proposed failure mechanism provides critical guidance for the development of conversion-type anode materials with improved electrochemical reversibility.

Fe2O3/Carbon nanocomposite as anode material for Li-ion cells

To achieve sufficient energy density required for powering electric and hybrid electric automobiles, Li-ion cells using high capacity anode materials should be developed. Transition metal oxides are extensively being investigated as prospective anode materials for developing high capacity Li-ion cells. Depending on the type of energy storage mechanism, anode materials are classified as insertion, conversion and alloying type. Iron oxide is a conversion type anode material that has drawn extreme attention due to high specific capacity (theoretical capacity of Fe2O3 is 1007 mAh/g and that for Fe3O4 is 926 mAh/g), environmental friendliness and the possibility of using simple synthesis routes. Never-ending shuttling of lithium ions during charging and discharging (or lithiation and delithiation) is the mechanism of an ideal Li-ion cell. For efficient cell performance, electrode should retain its structural stability, porosity and conductivity after many cycles of charging and discharging. Present work deals with studies on the influence of pH of hydrothermal solution on the particle size distribution of Fe2O3, with a view to achieve structural stability for iron oxide/carbon nanocomposite, when used as anode active material in Li-ion cells. Cells assembled against lithium metal in half-cell configuration are used for electrochemical studies. Fe2O3/C nanocomposite anode shows initial discharge capacity of 880 mAh/g with a capacity retention of 11.5% after 50 cycles.

Study of the Lithium Diffusion Properties of (Mgconilizn)O High Entropy Oxide as an Anode in Lithium-Ion Battery

High-entropy oxide (HEO) based materials have recently significant attention as a conversion type anode material for lithium-ion batteries (LIBs) due to the high specific capacity, cycling stability and rate capability. However, the diffusion kinetics of HEO based anodes for conversion reactions, which occur during the charge and discharge processes have been not studied deeply in the literature. Therefore, the diffusion properties of lithium in the HEO electrodes need to be studied in detail. In this work, the (MgCoNiLiZn)O HEO anode was synthesized by conventional solid-state method. The obtained HEO sample was characterized structurally by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD analysis show that the HEO sample has been successfully synthesized with a single-phase rock-salt structure. The lithium diffusion properties of HEO sample were investigated by various electrochemical techniques including electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).

The case for fluoride-ion batteries

<h2>Summary</h2> Fluoride-ion batteries (FIBs) have recently emerged as a candidate for the next generation of electrochemical energy storage technologies. On paper, FIBs have the potential to match or even surpass lithium-metal chemistries in terms of energy density, while further eliminating the dependence on strained resources, such as lithium and cobalt. Research into FIBs has accelerated since its inception in 2011. In this perspective, we examine the case for fluoride-ion batteries, considering electrode and electrolytes from the literature and beyond, to outline the potential pathways to a competitive energy storage technology. We present the most promising, feasible conversion-type cathode and anode materials in terms of capacity, electrode potential, volume change, crystal structure, and cost/abundance. The capabilities of current and future fluoride intercalation electrodes are also examined. Using a subset of these materials, we conduct a techno-economic analysis comparing the energy density and cost of conversion and intercalation-type FIBs with state-of-the-art lithium-ion batteries and high-energy-density lithium-metal-based chemistries. This investigation highlights the potential commercial value of conversion-type, liquid-cell FIB, with energy densities as high as 588 Whkg⁻¹ (1,393 WhL⁻¹) and costs as low as 20 US$ kWh⁻¹ at the stack level. This perspective highlights the major obstacles hindering the development of FIBs, drawing relevant lessons from the lithium-ion literature. In order to practically advance FIBs into a viable technology, further research must be focused on safe liquid fluoride electrolytes and solid electrolyte interphase formation; mechanistic study and theoretical modeling of electrode materials; and stable non-active battery components and reference electrodes. We conclude by prescribing several critical research fronts in these areas.

Elucidation of Operating Mechanism of BiFeO3 As a Negative Electrode for Na-Ion Batteries Using in Operando XAS Investigation

Sodium-ion batteries (SIBs) are gaining much attention in the global market of rechargeable batteries especially in the field of large-scale electrical energy storage systems. Considering the increasing demand for the efficient energy storage systems, it is necessary to design new electrode materials, which are capable to deliver higher reversible capacity. A wide spectra of positive electrode materials were employed in sodium ion batteries, whereas more development is required in the field of negative electrodes. Anode materials of sodium-ion batteries were mainly classified under insertion, conversion and alloying type materials1. Among the conversion type materials, Perovskite materials have gained significant attention as conversion type anode materials in sodium-ion batteries, owing to the high theoretical capacity possessed by these materials2,3.BiFeO3 is one such perovskite which possess the potential to deliver higher reversible capacity through conversion and alloying reactions4.In the present work, BiFeO3 was synthesized using a sol-gel method. Structural and morphological characterizations were done with X-ray diffraction and Field emission scanning electron microscopy techniques. Further, electrochemical studies were carried out in a sodium half-cell in the voltage range 0.01-3.00 V vs. Na+/Na. In the cyclic voltammogram, pronounced difference is observed between the first and subsequent cycles and to understand the reason behind this, elucidation of operating mechanism is required. In situ/ex situ XRD techniques are usually not sufficient to get information regarding the operating mechanism of conversion type electrode materials as these converts into metallic nanoclusters (without a long-range order) distributed in Na2O matrix during the insertion of Na+ ions. Hence, in this work, element specific X-ray absorption spectroscopic (XAS) technique was applied to elucidate the oxidation state and coordination environment changes of BiFeO3 during cycling in a sodium half-cell. Evidences for the electrochemical activity of Bi through conversion reaction (Bi3+ - Bi0) and alloying reaction (with metallic Na) during first discharge was obtained from XAS results. Further, involvement of Fe in the charge storage mechanism through conversion of its oxidized (Fe3+) form to metallic Fe was also observed, which is absent in previous literature reports. In the subsequent charging, reversible dealloying and subsequent oxidation of Bi and oxidation of Fe were noted. The Bi LIII edge and Fe K edge XAS results during second discharge reveals that similar conversion and alloying reactions occur as in the case of first discharge by reduction of Bi and Fe oxides. However, Fe and Bi oxides exists in different oxidation states at the end of first charge than in pristine BiFeO3.In addition to the elucidation of operating mechanism, the electrochemical performance of BiFeO3 was optimized by varying binder and electrolyte compositions. The best electrochemical performance was obtained when Fluoroethylene carbonate was used as an electrolyte additive. Acknowledgement A. Bhaskar gratefully acknowledge financial support from “DST-IISc Energy Storage Platform on Supercapacitors and Power Dense Devices” through the MECSP-2K17 program under grant no. DST/TMD/MECSP/2K17/20”. D. Dixon acknowledges the financial support from funding agency, Science and Engineering Board (SERB), New Delhi, India through Ramanujan Fellowship, under the grant number SB/S2/ RJN-162/2017. A. Surendran is grateful to UGC New Delhi (Ref. no.:63/CSIR-UGC NET DEC. 2017) for the UGC SRF grant and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India. A.T acknowledges the Council of Scientific and Industrial Research (CSIR) for a senior research fellowship and Innovative Research (AcSIR), Ghaziabad- 201002. DESY, Hamburg, Germany is acknowledged for the beamtime allocation at the P65 beamline at PETRA III and we acknowledge the beamline scientist Dr. Edmund Welter for the support. The CIF, CSIR-CECRI is acknowledged for technical support with material characterization. Reference [1] Wu, C., Dou, S. X. & Yu, Y. The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage. Small 14, 1–20 (2018).[2] M. Nakayama, H. Ikuta, Y. Uchimoto, M. Wakihara, Changes in local structure during electrochemical Li insertion into A-site deficient perovskite oxides, La1/3NbO3, J. Phys. Chem. B,107(2003)10715-10721[3] M. Kong, K. Liu, J. Ning, J. Zhou, H. Songa, Perovskite framework NH4FeF3/carbon composite nanosheets as a potential anode material for Li and Na ions storage, J. Mater. Chem. A, 5(2017)19280-19288[4] X. Dinga, Y.Liub, Hollow bismuth ferrite combined graphene as advanced anode material for sodium-ion batteries, 30(2020)153-159

Multidimensional synergistic architecture of Ti3C2 MXene/CoS2@N-doped carbon for sodium-ion batteries with ultralong cycle lifespan

Sodium-ion batteries (SIBs) based on conversion-type anode materials exhibit great prospect in the field of large-scale energy storage because of their superior sodiation capacities and low costs. However, poor charge transfer kinetics and short cycle life induced by huge volume change remain two great challenges. Herein, a multidimensional synergistic structure of few-layered Ti3C2 MXene/CoS2@N-doped porous carbon (f-Ti3C2/CoS2@NPC) is rationally designed as SIBs anodes, where N-doped porous carbon matrix-encapsulated ultrafine CoS2 nanoparticles are anchored on few-layered Ti3C2 MXene via TiOC bonds. The synergistic effects among each component greatly inhibit the aggregation of CoS2 nanoparticles (CoS2 NPs), readily build a long-range electron/Na+ conductive network and effectively provide a dual protection effect on CoS2 NPs during sodiation/desodiation process. Consequently, the f-Ti3C2/CoS2@NPC anode delivers a high-rate performance (282.6 mAh g−1 at 10 A g−1) and superior cyclability (200.6 mAh g−1 at 2 A g−1 after 1500 cycles). Furthermore, Na3V2(PO4)3//f-Ti3C2/CoS2@NPC full cells can release a high reversible capacity and good cyclability (325.8 mAh g−1 at 200 mA g−1 after 50 cycles), demonstrating great potential in practical application. This work further broadens the scope of multidimensional synergistic architectures and may inspires more research on MXene-based multidimensional structure for high-performance SIBs.

Areca-inspired core-shell structured MnO@C composite towards enhanced lithium-ion storage

MnO based composites are regarded as advanced conversion-type anode materials for lithium-ion batteries (LIBs) due to the low cost and high theoretical specific capacities (∼756 mA h g−1). Nevertheless, the undesirable structural stability and sluggish electrochemical reaction kinetics of the electrode materials lead to poor lithium storage performance. Herein, inspired by the structure of areca, the areca-like core-shell MnO@C composites containing of the MnO core and N-doped porous carbon shell are prepared via a biomass-assisted strategy. The formation mechanism of the MnO@C composites with well-defined core-shell structure are successfully clarified through heterogeneous contraction and carbon pyrolysis processes. As anodes for LIBs, the MnO@C composite delivers superior specific capacities of 915.9 and 218.1 mA h g−1 at 0.1 and 5.0 A g−1, respectively, and maintains outstanding cycling performance over 900 cycles at 1.0 A g−1. More importantly, electrochemical kinetics tests further confirm that the improved LIBs capacity mainly originated from the unique areca-like core-shell structure and self-N doped porous carbon shell.

Porous carbon matrix-encapsulated MnO in situ derived from metal-organic frameworks as advanced anode materials for Li-ion capacitors

Conversion-type anode materials hold great potential for Li+ storage applications owing to their high specific capacity, while large volume expansion and poor electrical conductivity limit their rate and cycling performances. Herein, a bimetal ZnMn-based metal-organic framework (ZnMn-MOF) is engineered for in situ conversion of MnO-encapsulated porous carbon (MnO/PC) composite. The templating and activation effects of coordinated Zn endow the converted PC matrix with a highly porous structure. This enhances the compatibility of PC matrix with MnO particles, resulting in the full encapsulation of MnO particles in the PC matrix. More significantly, the PC matrix provides enough void space to buffer the volume change, which fully wraps the MnO without crack or fracture during repeated cycling. As a result, MnO/PC shows high charge storage capability, extraordinary rate performance, and long-term cycling stability at the same time. Thus MnO/PC exhibits high delithiation capacities of 768 mA h g−1 at 0.1 A g−1 and 487 mA h g−1 at a high rate of 0.7 A g−1, combined with an unattenuated cycling performance after 500 cycles at 0.3 A g−1. More significantly, MnO/PC demonstrates a well-matched performance with the capacitive activated carbon electrode in a Li-ion capacitor (LIC) full cell. LIC demonstrates a high specific energy of 153.6 W h kg−1 at 210 W kg−1, combined with a specific energy of 71.8 W h kg−1 at a high specific power of 63.0 kW kg−1.

Electrophoretically deposited NiSb2O6-carbon black composite film as a potential anode for sodium-ion battery

In this manuscript, we propose nickel antimony oxide (NiSb 2 O 6 , NSO), crystallized in the tri-rutile form, as a high capacity conversion-type anode material for the sodium-ion batteries. The material is synthesized via co-precipitation method followed by calcination at high temperatures. X-ray diffraction studies confirm the formation of a phase pure tri-rutile NSO powder after calcination at 1000 °C for 5 h. The as-prepared powder is then electrophoretically deposited on a copper foil along with carbon black as conductive additive to develop uniform, porous, and adherent NSO‑carbon black films. The deposited film is then tested as an anode for sodium-ion battery, which delivers a specific capacity of 255mAhg −1 after 50 cycles at a specific current of 100mAg −1 , with a coulombic efficiency of ~98%. The deposited film also exhibits good cycling stability as well as rate capability. Furthermore, the film delivers a specific capacity of 140mAhg −1 after 100 cycles, when cycled at a higher specific current (750mAg −1 ). • NiSb 2 O 6 , a new Na-ion battery anode material is developed. • Electrophoretic deposition method is used to fabricate NiSb 2 O 6 ‑carbon black anode. • EPD grown electrodes exhibit good electrochemical properties.

Realizing the enhanced cyclability of a cactus-like NiCo2O4 nanocrystal anode fabricated by molecular layer deposition.

Lithium-ion batteries with conversion-type anode electrodes have attracted increasing interest in providing higher energy storage density than those with commercial intercalation-type electrodes. However, conversion-type materials exhibit severe structural instability and capacity fade during cycling. In this work, a molecular layer deposition (MLD)-derived conductive Al2O3/carbon layer was employed to stabilize the structure of the cactus-like NiCo2O4 nanocrystal (NC) anode. The conductive Al2O3/carbon network and cactus-like NiCo2O4 NCs are beneficial for fast Li+/e- transport. Moreover, the Al2O3/carbon buffer-layer can prevent the NiCo2O4 NCs from agglomeration and form a steady solid electrolyte interphase (SEI), thus hampering the penetration of the electrolyte. Owing to these advantages, the assembled NiCo2O4@Al2O3/carbon half battery shows a high reversible capacity (931.2 mA h g-1 at 2 A g-1) and long-term stability of 290 mA h g-1 at 5 A g-1 over 500 cycles. Quantitative analyses further reveal the fast kinetics and the capacitance-battery dual model mechanism in the 3D core-shell structures. The design and introduction of MLD-derived hybrid coating may open a new way to conversion-type and alloy-type anode materials beyond NiCo2O4 to achieve high cyclability.

Tantalum pentoxide-reduced graphene oxide nanocomposite as a new conversion type anode material having extrinsic pseudocapacitance for electrochemical lithium storage

Ta2O5 nanoparticles could be an exemplary conversion type anode material for electrochemical lithium ion storage which possesses promising extrinsic pseudocapacitance property. Ionic liquid assisted hydrothermal method have been employed to synthesize Ta2O5 nanoparticles followed by hydrothermal method to synthesize Ta2O5–reduced graphene oxide (Ta2O5-rGO) nanocomposite. The Ta2O5–rGO nanocomposite delivered enhanced specific capacity of 175 mAh g−1 after 200 cycles at 0.1C current rate compared to the pure Ta2O5 nanoparticles. The outstanding electrochemical performance of Ta2O5–rGO nanocomposite could be offered by two-dimensional reduced graphene oxide possessing high surface area, better mechanical stability and high electrical conductivity enhances the electron and ion transfer rate and also avoiding agglomeration of Ta2O5 NPs. Finally, the present investigation urges contemporary researchers to design advance Ta2O5-rGO nanocomposites for lithium ion battery applications.

Tunable Surface Selenization on MoO2 -Based Carbon Substrate for Notably Enhanced Sodium-Ion Storage Properties.

Transition metal chalcogenides with high theoretical capacity are promising conversion-type anode materials for sodium ion batteries (SIBs), but often suffer from unsatisfied cycling stability (hundreds of cycles) caused by structural collapse and agglomerate. Herein, a rational strategy of tunable surface selenization on highly crystalline MoO2 -based carbon substrate is designed, where the sheet-like MoSe2 can be coated on the surface of bundle-like N-doped carbon/granular MoO2 substrate, realizing partial transformation from MoO2 to MoSe2 , and creating b-NC/g-MoO2 @s-MoSe2 -10 with robust hierarchical MoO2 @MoSe2 heterostructures and strong chemical couplings (MoC and MoN). Such well-designed architecture can provide signally improved reaction kinetics and reinforced structural integrity for fast and stable sodium-ion storage, as confirmed by the ex situ results and kinetic analyses as well as the density functional theory calculations. As expected, the b-NC/g-MoO2 @s-MoSe2 -10 delivers splendid rate capability and ultralong cycling stability (254.2mAh g-1 reversible capacity at 5.0 A g-1 after 6000 cycles with ≈89.0% capacity retention). Therefore, the tunable surface strategy can provide new insights for designing and constructing heterostructures of transition metal chalcogenides toward high-performance SIBs.

Decoding of Oxygen Network Distortion in a Layered High-Rate Anode by In Situ Investigation of a Single Microelectrode.

Sluggish conversion reactions severely impair the rate capability for lithium storage, which is the main disadvantage of the conversion-type anode materials. Here, the microplatform based on a single microelectrode is designed and utilized for the fundamental understanding of the conversion reaction. The kinetic-favorable layered structure of the anode material is on-site synthesized in the microplatform. The in situ characterization reveals that introducing an oxygen network distortion in the layered oxide anode effectively circumvents the severe passivation of the electrode material by lithium oxide, thus leading to highly reversible conversion reactions. As a result, the high-rate capability of the conversion-type anode materials is realized. The on-site synthesis strategy is further applied in the large-scale synthesis of nanomaterials for lithium-ion batteries. As such, oxide nanorods with the layered structure are synthesized by a facile chemical strategy, showing high rate performance (574 mAh g-1 at 10 A g-1). This work unveils the beneficial effect of oxygen network distortion in the layered anode for conversion reactions over cycling, thus providing an alternative strategy to enhance the rate capability of conversion-type anodes for lithium storage.

Highly durable Li-ion battery anode from Fe3O4 nanoparticles embedded in nitrogen-doped porous carbon with improved rate capabilities

For next generation, lithium-ion batteries (LIBs) developing high capacity anode materials are crucial with increasing demand of large-scale application. Conversion-type anode materials are promising if stable cycling behavior could be achieved. In this work, a nitrogen-doped porous carbon-Fe3O4 (NPC-Fe3O4) nanocomposite is synthesized via a simple and scalable approach. Composite is prepared by pyrolysis of polymer silica hybrid PolyHIPE (high internal phase emulsion) into NPC, and Fe3O4 nanoparticles (NPs) are anchored on its surface via hydrothermal synthesis. As-prepared NPC-Fe3O4 nanocomposite delivers high reversible capacity of around 1001 mAhg−1 at 0.1 Ag−1 current density and rate capabilities and displays excellent cycling stability as high as 95% capacity retention even after 400 cycles. Superior electrochemical performance of NPC-Fe3O4 is attributed to the hierarchical porous structure and nitrogen doping of carbon which shorten the diffusion path of Li+ and provide ample space to prevent aggregation of Fe3O4 nanoparticles.