High-rate Cycling Stability Research Articles

Construction of 3D Electronic/Ionic Conduction Networks for All-Solid-State Lithium Batteries.

High and balanced electronic and ionic transportation networks with nanoscale distribution in solid-state cathodes are crucial to realize high-performance all-solid-state lithium batteries. Using Cu2 SnS3 as a model active material, such a kind of solid-state Cu2 SnS3 @graphene-Li7 P3 S11 nanocomposite cathodes are synthesized, where 5-10 nm Cu2 SnS3 nanoparticles homogenously anchor on the graphene nanosheets, while the Li7 P3 S11 electrolytes uniformly coat on the surface of Cu2 SnS3 @graphene composite forming nanoscaled electron/ion transportation networks. The large amount of nanoscaled triple-phase boundary in cathode ensures high power density due to high ionic/electronic conductions and long cycle life due to uniform and reduced volume change of nano-Cu2 SnS3. The Cu2 SnS3 @graphene-Li7 P3 S11 cathode layer with 2.0 mg cm-2 loading in all-solid-state lithium batteries demonstrates a high reversible discharge specific capacity of 813.2 mAh g-1 at 100 mA g-1 and retains 732.0 mAh g-1 after 60 cycles, corresponding to a high energy density of 410.4 Wh kg-1 based on the total mass of Cu2 SnS3 @graphene-Li7 P3 S11 composite based cathode. Moreover, it exhibits excellent rate capability and high-rate cycling stability, showing reversible capacity of 363.5 mAh g-1 at 500 mA g-1 after 200 cycles. The study provides a new insight into constructing both electronic and ionic conduction networks for all-solid-state lithium batteries.

From rational construction to theoretical study: Li3V2(PO4)3 nanoplates with exposed {100} facets for achieving highly stable lithium storage

The polyanionic cathodes with high safety and appropriate redox potential, attract tremendous attention for Li-ion batteries. However, their high-rate cycling stability and poor industrial feasibility still remain great challenges. Herein, Li3V2(PO4)3 nanoplates with dominate {100} exposed facets embedded in a N-doped carbon matrix are successfully constructed. The in-situ dispersion-chelating approach benefits from reductive hydrogen peroxide and polyacrylamide, which acts as a strong ligand that coordinates the precursors to the polymer chains, resulting in a desirable construction of a highly porous structure (surface area: 69.667 m2 g−1) with homogeneous carbon coating, and thus facilitating structural stability. Therefore, the designed Li3V2(PO4)3/C composite displays competitive capacities with outstanding cycle stabilities (95.8% retention after 500 cycles at 1C rate and 89.1% after 2000 cycles at 20C rate) under both two and three electron exchange conditions. Moreover, theoretical studies are applied to explore the origin of enhanced kinetics. The molecular dynamics simulations demonstrate an anisotropic Li+ diffusion with a fast [100]-oriented diffusion channel. The first-principles calculations reveal that the architecture induced by defect carbon can provide better interfacial stability and electronic conductive medium. This developed strategy combined with mechanism study provides an exciting perspective and avenue for establishing more-efficient electrode materials.

Bimetallic metal-organic framework derived Sn-based nanocomposites for high-performance lithium storage

Sn-based materials as potential anode materials have triggered significant research interests for lithium storage owing to their high theoretical capacity and low cost. However, the practical applications of Sn-based materials are hindered by low capacity release and fast capacity fading due to large volume expansion and structural pulverization of the electrodes during cycling. Herein, we demonstrate an efficient strategy to alleviate/resolve the above issues by introducing highly conductive inactive metal to alloy with Sn and then loading the Sn-based alloy particles onto two-dimensional (2D) graphene matrix. The graphene supported Fe–Sn nanoalloy composites (FeSn2/FeSn/Fe-rGO) are synthesized via a facile bimetallic metal-organic framework precursor route, in which Sn3[Fe(CN)6]4 nanocubes are grown in-situ on reduced graphene oxide (rGO) sheets, followed by thermal decomposition of the Sn3[Fe(CN)6]4/rGO precursor in an Ar/H2 atmosphere. As a result, the lithium-ion batteries based on FeSn2/FeSn/Fe-rGO composites exhibit outstanding lithium storage performance with a remarkable reversible capacity of 1274 mAh g−1 at 0.2 A g−1 after 200 cycles, a great rate capability of 665 mAh g−1 at 5.0 A g−1, and excellent high-rate cycling stability with a capacity decay of only 0.025% per cycle within 1200 cycles at 2.0 A g−1. The excellent electrochemical performance of FeSn2/FeSn/Fe-rGO can be ascribed to its unique three-order buffer structures: the Fe atoms in FeSn2 and FeSn acting as tough buffer, metal Fe as framework buffer for cubic nanoparticles, and rGO as 2D elastic matrix buffer, which effectively alleviate the volume expansion and structural pulverization of the electrode during lithiation, synergistically enhance the lithium storage performance.

An Ultra-Fast and Ultra-Stable All-Graphene Lithium Ion Capacitor

Lithium ion capacitors (LICs) are considered as next generation of capacitive energy storage systems , due to their 3~5 times higher energy density than traditional electrochemical double-layer capacitors. However, the battery-type anode inevitably leads to scarified power density and cycling life, due to imbalanced electrochemical performance of two electrodes, which means achieving competitive power density and cycling life simultaneously is an extreme challenge involving in the whole system. We rationally design an ultra-fast and ultra-stable all-graphene LICs, for which various graphene electrode constructions are synthesized orienting in the distinct energy storage principles of two electrodes, and a novel match approach for two electrodes is proposed and applied. Mesoporous graphene (MP-G) cathode is capable to deliver much better high-rate properties and cycling stability, edge carboxyl graphene (G-COOH) anode with expanded graphitic layer spaces enable fast pseudocapacitive and insertion capacity, as well as durability, and an optimal reaction profiles range of G-COOH are systematically determined by a novel quasi-in-situ electrochemical impedance spectroscopy (EIS) to match with MP-G. Thereby, an ultra-fast and ultra-stable LIC system (MP-G//G-COOH) is fabricated and operated in the voltage range of 1.0 ~ 4.2V. As expectedly, MP-G//G-COOH is capable to deliver an ultra-high-power density of 53550 W kg-1and an unprecedented cycling stability of 98.9% retention after 50000 cycles. This result is promising in terms of pushing ultra-fast and ultra-stable LIC system by combining ideal electrode constructions and matching approaches.

MnO2 Modified Reduced Graphene Oxide for Lithium–Sulfur Batteries with Improved High-Rate Cycling Stability

MnO₂ Modified Reduced Graphene Oxide for Lithium–Sulfur Batteries with Improved High-Rate Cycling Stability

Enhanced sodium storage characteristics of P2-Na2/3Mn3/4Co1/4O2 cathode co-modified by La2O3 and TiO2 oxide

A sodium-rich P2-Na2/3Mn3/4Co1/4O2 cathode is co-modified by La2O3 and TiO2 oxide through a solid-state method. Rietveld refinement confirms that a few La3+ and Ti4+ ions have substituted the Na sites and the TM sites in the crystal lattice of P2-Na2/3Mn3/4Co1/4O2, respectively, which leads to the enlargement of Na–O bond length and Na+ migration channels, and the shrinkage of TM–O and O–O bonds. Surface co-modification has reduced Na+ migration resistance, increased Na+ diffusion coefficient and stabilized crystal structure, which can significantly enhance its rate capability and especially cycle stability. The modified layers have been formed on the surface of the Na2/3Mn3/4Co1/4O2, which is capable of preventing the Na2/3Mn3/4Co1/4O2 oxide from exfoliation caused by the surface reactions in the electrode/electrolyte interfaces. It will help to stabilize the layered structure, alleviate Jahn–Teller distortion and form a thinner interface film among the electrode/electrolyte. The optimum modified cathode oxide is prepared using 1 wt% composite oxide in which the mass ratio of La2O3 and TiO2 is 1:1. In the voltage range of 1.8–4 V, the optimum modified cathode delivers a maximum areal capacity of 164.3 mAh g−1 cm−2 at 0.1 C with the capacity retention of 89.5% at 50th cycle and 81.7% after 100 cycles. When cycling at 10 C, it can retain 90.1% of its maximum 79.9 mAh g−1 cm−2 at 240th cycle, and its capacity retention is up to 80.2% even after 400 cycles. The excellent cycle stability, especially superior high-rate cycle stability, can still be traced back to the dual effects of the surface modification and the substitution of La3+ or Ti4+ ions. The high-performance cathode material co-modified by the La2O3 and the TiO2 oxide will give impetus to the development and research of cathode layered oxides for SIBs.

Superior coulombic efficiency of lithium anodes for rechargeable batteries utilizing high-concentration ether electrolytes

This study adopts high-concentration ether electrolytes to improve high-rate capability, cycling stability, and Coulombic efficiency (CE) for lithium ion batteries with lithium anode. A series of ether-based electrolytes including lithium bis(fluorosulfonyl)imide (LiFSI)-glyme/ethylene carbonate (EC), LiFSI-glyme/EC, LiFSI-diglyme/EC, LiFSI-triglyme/EC, LiFSI-tetraglyme (G4)/EC, and LiFSI-1,3-dioxolane (DOL)/EC, along with commonly used LiPF6-DEC/EC were prepared to delineate the influences of concentration, chain length, molecular structure (linear or ring ether), and EC additive on the electrochemical performance of Li anodes. An optimum composition for ether-based electrolyte was determined resulting in significant improvement in anti-flammability as well as CE at both low and high rates. At ultra-high current density operation (e.g. 6 mA cm−2), the CE was 95.5 and 97.1% with 3 M LiFSI-G4/EC and 3 M LiFSI-DOL/EC, respectively. Using 1 M LiPF6 carbonate-based electrolyte tend to grow a needle-like dendritic structure when depositing lithium metal on Cu foils, whereas high-concentration ether electrolyte promotes a knot-like and rounded Li metal microstructure. High concentration EC-based electrolytes, are capable of facilitating Li+ almost in tandem with solvent molecules, thereby reducing the number of free molecules, reducing the chance of side reaction with Li metal, and subsequently inhibiting the formation of dendritic Li structures.

Nb5+-doped P2-type Mn-based layered oxide cathode with an excellent high-rate cycling stability for sodium-ion batteries

P2-Na0.67Co0.25Mn0.75-xNbxO2 (x = 0, 0.015, 0.030, 0.045) cathode materials were obtained by a simple solid-state method. The Nb5+-doped effects on ameliorating the structural and electrochemical properties of the Na0.67Co0.25Mn0.75O2 parent material for sodium-ion batteries have been investigated. XRD measurements confirm a hexagonal main phase (P63/mmc) and some trace of orthorhombic NaNbO3 (P21ma). Rietveld refinements exhibit the higher lattice parameters and the bigger c/a values due to Nb5+ doping into the parent Na0.67Co0.25Mn0.75O2. The optimized 3.0 at.% Nb5+-doped P2-Na0.67Co0.25Mn0.75O2 sample delivers the initial discharge capacity of 126.7 mAh g−1 at 0.1 C in the voltage range of 1.8–4.0 V, and its capacity retention is 75.3% after 100 cycles, which is 63.7% higher than that of the pristine. Whereas at 10 C rate, the optimized sample presents the maximal discharge capacity of 72.8 mAh g−1 with an excellent high-rate cycling stability of 91.6% retention after 100 cycles, correspondingly the pristine shows 61.4 mAh g−1 and 73.1% retention. These excellent electrochemical performances are ascribed to better structural stability, and lower charge transfer resistance and higher Na+ diffusion coefficient after Nb5+ doping. Therefore, the Nb5+-doped P2-type cathode materials can be deemed as a beneficial improvement for researches on sodium-ion batteries.

Facile preparation of α-Ni(OH)2/graphene nanosheet composite as a cathode material for alkaline secondary batteries

α-Ni(OH)2 has attracted great attention as a cathode material for alkaline secondary batteries (ASBs) because of its high theoretical capacity and small volume change during charge/discharge cycles. However, poor cycling stability and low electronic conductivity of α-Ni(OH)2 severely hinder its development and practical applications in ASBs. In this work, α-Ni(OH)2/graphene nanosheet composite was successfully fabricated by a facile homogeneous precipitation method. The nanocomposite is composed of α-Ni(OH)2 nanoflowers decorated homogeneously on the surfaces of graphene nanosheets. When evaluated as cathode material for ASBs, this α-Ni(OH)2/graphene nanocomposite exhibits much enhanced high-rate capability and cycling stability compared to the pure α-Ni(OH)2 due to the improved electrochemical reaction kinetic, enhanced electronic conductivity, and hierarchical nanostructure. For example, the α-Ni(OH)2/graphene nanocomposite presents a rate retention of 74.8% as the current density increasing from 250 to 5000 mA g−1, much higher than that (49.0%) of pure α-Ni(OH)2; moreover, at a current density of 2000 mA g−1, the α-Ni(OH)2/graphene nanocomposite still maintains a reversible capacity of 177 mA h g−1 after 200 cycles, which is four times higher than that (41 mA h g−1) of the pure α-Ni(OH)2. The attractive electrochemical performances and facile synthesis route made the prepared α-Ni(OH)2/graphene nanocomposite become a promising electrode material for ASBs.

High-rate performance of a three-dimensional LiFePO4/graphene composite as cathode material for Li-ion batteries

Based on the graphene sheet stacking via van der Waals and π-π interactions during the solvothermal treatment, a 3D structure, with the carbon-decorated LiFePO4 particles embedded in interconnected graphene aerogels, is established. As the graphene and the carbon-decorated LiFePO4 particles contact adequately and efficiently, the rate performance of the LiFePO4-based cathode material is enhanced significantly. Thus, the 3D carbon-decorated LiFePO4/graphene composite cathode shows high reversible capacities of 112.4 and 96.7 mAh g−1 at extremely high rates of 30C and 50C, respectively. Moreover, good high-rate cycling stability is achieved with a capacity retention of 96.3% after 300 cycles at 30C. The excellent high-rate performance can be ascribed to the 3D conductive framework constructed by graphene, which facilitates fast electron and lithium ion transport. These results not only demonstrate the superiority of the 3D graphene framework in electrode material design, but also offer a promising candidate for high-rate cathode material in high-power Li-ion batteries.

Uniform distribution of siloxane-grafted SiOx nanoparticles in micron hard-carbon matrix for high-rate composite anode in Li-ion batteries

Uniform distribution of siloxane-grafted SiO0.26 hydrophobic nanoparticles in porous micron hard-carbon matrix was in situ made by a simple mixing in the organic medium of N-methylpyrrolidinone during the slurry preparation of composite anode for a fast-charge of lithium-ion batteries, whose characteristics are advantageous for a good electronic conductivity and the accommodation of volume change of silicon during charge-discharge cycling. The composite anode enables fast charge in 6 min at the rate of 10 C and high cycling stability, delivering the discharge capacities of 648–538 mAh g−1, coulombic efficiencies of 99%, and high capacity retention of 98% at the 100th cycle. Surface and structural analysis results reveal that the formation of relatively thinner solid electrolyte interphase (SEI) layer at 10 C and higher structural maintenance than at low rate (0.2 C) are correlated to lowered interfacial resistances at 10 C and a good high-rate cycling stability. The data give an insight into material design principles and the SEI property of anode for high-rate lithium-ion batteries.

High-rate and long-term cycle stability of lithium-ion batteries enabled by boron-doping TiO2 nanofiber anodes

Although the well-known anatase, one of the allotropic forms of natural TiO2, was recently proposed for lithium-ion battery electrodes, the material generally suffers from reduced cyclability and limited power, due to kinetic drawbacks and to its poor charge transport properties. Here, boron (B)-doping anatase TiO2 nanofibers were synthesized via a facile sol-gel method and the electrospinning method for use as anodes. The incorporation of B element not only promotes the crystallization of the building subunits of the microporous TiO2, but also improves the electrochemical performance at higher current rates and longer cycles. A capacity of 147mAhg−1 at a current density as high as 4Ag−1 and an excellent long-term cycling stability with a capacity retention of 167.6mAhg−1 at the current rate of 2Ag−1 over 5000cycles could be achieved when an appropriate amount of B was doped into TiO2 anodes. The reasons for the improvement of rate capability may be attributed to the enhancement of electronic conductivity, lithium ion diffusion kinetics, and the surface storage property for the B-doping anatase TiO2 anodes.

Ion‐ and Electron‐Conductive Buffering Layer‐Modified Si Film for Use as a High‐Rate Long‐Term Lithium‐Ion Battery Anode

The rational design of electrochemically and mechanically stable Si anodes is of great importance for the development of high energy density lithium-ion batteries. In this study, patterned Si-based (Si/ZnO/C) trilayer composite films were synthesized by magnetron sputtering with the assistance of a patterned mask. The electron-conductive C layer at the top of the composite film is deposited to enhance the interfacial stability between active film and electrolyte. The ion- and electron-conductive Li2 O-Zn middle layer can be ingeniously introduced by means of the poor reversed conversion reaction between ZnO and Li+ ions after the first cycle. The resultant Si/Li2 O-Zn/C trilayer composite film delivers a high reversible capacity of 1536 mAh g-1 after 800 cycles at a current density of 1.0 A g-1 and a long high-rate cycling stability (1400 mAh g-1 after 6000 cycles even at a high current density of 10.0 A g-1 ). Excellent rate capability and improved Coulombic efficiency are also achieved. The influences of the patterned structure and each modified layer on the electrochemical properties are analyzed systematically. This work offers a new and promising direction to enhance the lithium-storage properties of Si-based thin-film anodes.

Superior High-Rate and Ultralong-Lifespan Na3V2(PO4)3@C Cathode by Enhancing the Conductivity Both in Bulk and on Surface.

Na3V2(PO4)3 has shown great promise in next-generation cathode materials for sodium-ion batteries owning to its fast Na+ diffusion in the three-dimensional open NASICON framework and high theoretical energy density. However, Na3V2(PO4)3 suffers from undesirable rate performance and unstable cyclability arising from low electronic conductivity. Herein, we propose a facile approach for significantly enhancing the electrochemical properties of Na3V2(PO4)3 by Ti doping at V site and constructing nanoparticle@carbon core-shell nanostructure. This material design provides fast electron conduction network within the whole active particles because of the mixed valence Ti4+/3+ in bulk and highly conductive carbon shell on the surface. Lattice doping and carbon coating reduce the electrode polarization and facilitate the electrode reaction kinetics, while the nanostructure enhances the ionic conduction by shortening the diffusion distance and offers sufficient contact of active particles with organic electrolyte. The multiple synergetic effects enable a superior electrochemical performance. The optimized Na3V1.9Ti0.1(PO4)3@C cathode shows a high specific capacity (116.6 mAh g-1 at 1C), an unprecedented rate performance (93.4 mAh g-1 at 400C), and an exceptional long-term high-rate cycling stability (capacity retention of 69.5% after 14 000 cycles at 100C, corresponding to 0.0002% decay per cycle).

A Hierarchical Silver-Nanowire-Graphene Host Enabling Ultrahigh Rates and Superior Long-Term Cycling of Lithium-Metal Composite Anodes.

Metallic lithium (Li) is a promising anode for next-generation high-energy-density batteries, but its applications are still hampered due to the limited charging/discharging rate and poor cycling performance. Here, a hierarchical 3D porous architecture is designed with a binary network of continuous silver nanowires assembled on an interconnected 3D graphene skeleton as the host for Li-metal composite anodes, which offers a significant boost in both charging/discharging rates and long-term cycling performance for Li-metal batteries. This unique hierarchical binary network structure in conjunction with optimized material combination provides ultrafast, continuous, and smooth electron transportation channel and non-nucleation barrier sites to direct and confine Li deposition. It also offers outstanding mechanical strength and toughness to support massive Li deposition and buffer the internal stress fluctuations during long-term repeated Li stripping/plating thereby minimizing fundamental issues of dendrite formation and volume change even under ultrafast charging/discharging rates. As a result, the composite anode using this hierarchical host can work smoothly at an unprecedented high current density of 40 mA cm-2 over 1000 plating/stripping cycles with low overpotential (<120 mV) in symmetric cells. The as-constructed full cell, paired with LiNi0.5 Co0.2 Mn0.3 O2 cathode, also exhibits excellent rate capability and high-rate cycling stability.

Fe2O3@C core@shell nanotubes: Porous Fe2O3 nanotubes derived from MIL-88A as cores and carbon as shells for high power lithium ion batteries

To pursue Fe2O3-based electrode with high-rate and long-life lithium storage capacity, we have developed a porous Fe2O3@C core@shell nanotube synthesized by a facile thermal treatment combining with hydrothermal method. As an advanced anode for lithium ion batteries, the Fe2O3@C core@shell nanotubes deliver high initial coulombic efficiency of 80.3% at 0.1 C with the first charge/discharge capacity of 1097.7/1366.9 mAh g−1, and excellent high-rate and long cycling stability with reversible capacity of 811.3 mAh g−1 after 1000 cycles at 1 C. The greatly improved performance is ascribed to the 1D porous nanotube and carbon shell: the 1D porous nanotube can not only effectively increase the contact area between active materials and electrolyte, but also shorten the migration path for Li+ ions and electrons. The carbon shell works as buffer to accommodate volume changes of Fe2O3 during cycling and as conductive support to improve the electrical conductivity of Fe2O3.

In Situ Chelating Synthesis of Hierarchical LiNi1/3 Co1/3 Mn1/3 O2 Polyhedron Assemblies with Ultralong Cycle Life for Li-Ion Batteries.

Layered lithium transition-metal oxides, with large capacity and high discharge platform, are promising cathode materials for Li-ion batteries. However, their high-rate cycling stability still remains a large challenge. Herein, hierarchical LiNi1/3 Co1/3 Mn1/3 O2 polyhedron assemblies are obtained through in situ chelation of transition metal ions (Ni2+ , Co2+ , and Mn2+ ) with amide groups uniformly distributed along the backbone of modified polyacrylonitrile chains to achieve intimate mixing at the atomic level. The assemblies exhibit outstanding electrochemical performances: superior rate capability, high volumetric energy density, and especially ultralong high-rate cyclability, due to the superiority of unique hierarchical structures. The polyhedrons with exposed active crystal facets provide more channels for Li+ diffusion, and meso/macropores serve as access shortcuts for fast migration of electrolytes, Li+ and electrons. The strategy proposed in this work can be extended to fabricate other mixed transition metal-based materials for advanced batteries.

Synthesis Method for Long Cycle Life Lithium-Ion Cathode Material: Nickel-Rich Core-Shell LiNi0.8Co0.1Mn0.1O2.

High-nickel materials with core-shell structures, whose bulk is rich in nickel content and the outer shell is rich in manganese content, have been demonstrated to improve cycle stability. The high-nickel cathode material LiNi0.8Co0.1Mn0.1O2 is a very promising material for lithium-ion batteries; however, its low rate performance and especially cycle performance currently hamper further commercialization. This study presents a new synthesis method to prepare this core-shell material (LiNi0.8Co0.1Mn0.1O2@ x[Li-Mn-O], x = 0.01, 0.03, 0.06). Electrochemical data show that LiNi0.8Co0.1Mn0.1O2@ x[Li-Mn-O] ( x = 0.03, CS-0.03) exhibits the best high-rate performance, cycle stability, and thermal stability. The initial discharge capacity of the core-shell sample CS-0.03 is 118 mAh g-1, which is almost the same as the discharge capacity of pristine LiNi0.8Mn0.1Co0.1O2 (117 mAh g-1) at the rate of 10 C in the voltage range of 3.0-4.3 V. Notably the capacity decay of CS-0.03 is 18.4% after 200 cycles compared to 27% decay in capacity of the pristine sample. Furthermore, CS-0.03 exhibits better thermal cycling stability. The capacity retention of the CS-0.03 sample reached 65.1% which is over 1.3 times than that of the pristine one, whose capacity retention is 49.2% after 105 cycles (55 °C). Evidently, the core-shell structured CS-0.03 sample has excellent cycle stability and this synthesis method can be applied to other cathode materials.

High-Rate and Long-Term Cycle Stability of Li-S Batteries Enabled by Li2S/TiO2-Impregnated Hollow Carbon Nanofiber Cathodes.

The high theoretical energy density of lithium-sulfur (Li-S) batteries makes them an alternative battery technology to lithium ion batteries. However, Li-S batteries suffer from low sulfur loading, poor charge transport, and dissolution of lithium polysulfide. In our study, we use the lithiated S, Li2S, as the cathode material, coupled with electrospun TiO2-impregnated hollow carbon nanofibers (TiO2-HCFs), which serve as the conductive agent and protective barrier for Li2S in Li-S batteries. TiO2-HCFs provide much improved electron/ionic conductivity and serve as a physical barrier, which prevents the dissolution of lithium polysulfides. The Li2S/TiO2-HCF composite delivers a discharge capacity of 851 mA h gLi2S-1 at 0.1C and the bilayer TiO2-HCFs/Li2S/TiO2-HCF composite delivers a high specific capacity of 400 mA h gLi2S-1 at 5C.

Binding MoSe2 with carbon constrained in carbonous nanosphere towards high-capacity and ultrafast Li/Na-ion storage

Most of the reported MoSe2 electrode materials are suffered from tended stacking, large volume expansion and relatively low capacity. As shown the experiences of Li/Na-Se batteries, the encapsulating of the exfoliated MoSe2 into carbon nanospheres are successfully constructed with the introduction of C-O-Mo bonds and larger layer distance (0.89 nm). Interestingly, the C-O-Mo bonds stayed on the surface of the Se-O insulation layer can improve the rate of ions transfer and also promote the reversible conversion of MoSe2. The first-principles calculations demonstrated that the frontier molecular orbitals of C-O-Mo interface structure are mainly localized on the MoSe2 sheet fragment with an appropriate HOMO-LUMO gap (<4 eV), proving that its conductivity is being greatly enhanced with higher stability. Utilized as an anode for LIBs, it delivers Li-storage capacities of 1208 mAh g−1 after 150 cycles at 1.0 A g−1 and 519 mAh g−1 after 200 cycles at 4.0 A g−1. Also note that the Na-storage capacities are found to be 543, 491 mAh g−1 after 120 cycles at 0.1, 1.0 A g−1, respectively. Through the analysis of CV, the reduced particles might improve the capacitive behaviors, further leading to the higher rate performances. Ex-situ techniques showed that the emerging Se during the electrochemical process was constrained uniformly in the carbon matrix. More greatly, the controlling of by-product Se plays key roles in achieving high-rate capability and cycling stability, which would open up a potential avenue for these metal-selenide anodes designs of battery storage systems.