Nan Chen

Carbon-coated Na3V2(PO4)2F3 nanoparticles embedded in a mesoporous carbon matrix as a potential cathode material for sodium-ion batteries with superior rate capability and long-term cycle life

A carbon-coated Na3V2(PO4)2F3 nanocomposite (NVPF@C) is successfully realized by a facile sol–gel method. Carbon-coated NVPF nanoparticles are dispersed inside the mesoporous carbon matrix, which can not only improve the electron/ion transfer among different nanoparticles, but also benefit the electrolyte wetting during cycling. As a result, the NVPF@C cathode demonstrates remarkable Na+ storage performance: a high reversible capacity of nearly 130 mA h g−1 over 50 cycles between 4.3 and 2.0 V; superior rate capability with specific capacities of nearly 74 and 57 mA h g−1 at high current densities of 15C (1.92 A g−1) and 30C (3.84 A g−1), respectively; long-term cycle life with capacity retentions of 70% and 50% over 1000 and 3000 cycles at 10C and 30C rates. Thanks to the manifested high energy and power densities, the NVPF@C nanocomposite is suggested as a promising cathode material for grid energy storage.

Na3V2(PO4)3/C composite as the intercalation-type anode material for sodium-ion batteries with superior rate capability and long-cycle life

A Na3V2(PO4)3/C (NVP/C) composite is successfully synthesized by the sol–gel method and examined as the anode material for sodium-ion batteries (SIBs) by means of galvanostatic charge–discharge profiles, cyclic voltammograms, rate performance and cyclic voltammetry comprehensively. The NVP/C electrode delivers a reversible capacity of about 170 mA h g−1 between 3.0 and 0.01 V at a current density of 20 mA g−1 corresponding to three sodium ions insertion/extraction processes. Besides the voltage plateau at 1.57 V, another novel working platform at around 0.28 V is found for the first time in both charging and discharging profiles, possibly owing to the further reduction of vanadium. NVP/C exhibits an excellent rate capability and long-cycle stability with a capacity retention of 62% after 3000 cycles at a high charge rate of 10 C (2 A g−1). Moreover, the intercalation-type Na-ions storage mechanism is proposed on the basis of ex situ X-ray diffraction and high-resolution transmission electron microscopy. Our findings reveal that the NVP/C sample is a promising anode material for SIBs due to its superior rate capability and long cycle life.

Assembly of SnSe Nanoparticles Confined in Graphene for Enhanced Sodium-Ion Storage Performance

Sodium-ion batteries (SIBs) have attracted much interest as a low-cost and environmentally benign energy storage system, but more attention is justifiably required to address the major technical issues relating to the anode materials to deliver high reversible capacity, superior rate capability, and stable cyclability. A SnSe/reduced graphene oxide (RGO) nanocomposite has been prepared by a facile ball-milling method, and its structural, morphological, and electrochemical properties have been characterized and compared with those of the bare SnSe material. Although the redox behavior of SnSe remains nearly unchanged upon the incorporation of RGO, its electrochemical performance is significantly enhanced, as reflected by a high specific capacity of 590 mA h g(-1) at 0.050 A g(-1) , a rate capability of 260 mA h g(-1) at 10 A g(-1) , and long-term stability over 120 cycles. This improvement may be attributed to the high electronic conductivity of RGO, which also serves as a matrix to buffer changes in volume and maintain the mechanical integrity of the electrode during (de)sodiation processes. In view of its excellent Na(+) storage performance, this SnSe/RGO nanocomposite has potential as an anode material for SIBs.

Electrochemical properties and lithium-ion storage mechanism of LiCuVO4 as an intercalation anode material for lithium-ion batteries

LiCuVO4 with distorted inverse spinel structure is prepared by solid-state reaction and comprehensively examined as an intercalation anode material by means of cyclic voltammograms (CV), galvanostatic charge–discharge profiles, rate performance, and electrochemical impedance spectroscopy (EIS). LiCuVO4 shows a stable capacity of 447 mA h g−1 under 3–0.01 V at the current density of 200 mA g−1, and the capacity retention reaches 91% after 50 cycles. At high cutoff voltage, between 3 and 0.2 V, LiCuVO4 also delivers an average reversible capacity of 200 mA h g−1 at a current density of 2000 mA g−1, higher than the performance of the newly reported Li3VO4. Moreover, the lithium ion storage mechanism for LiCuVO4 is also explained on the basis of the ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) at different insertion/extraction depths. While being discharged to 0.01 V, LiCuVO4 decomposes into Li3VO4, whose surface is coated by Cu nanoparticles spontaneously. Interestingly, Li ions are suggested to be inserted into Li3VO4 in the subsequent cycles due to the intercalation mechanism, and Cu nanoparticles would not contribute to the reversible capacity. Our findings provide a strong supplemental insight into the electrochemical mechanism of the anode for lithium-ion batteries. In addition, LiCuVO4 is expected to be a potential anode material because of its low cost, simple preparation procedure, good electrochemical performance and safety discharge voltage.

LiFe(MoO4)2 as a Novel Anode Material for Lithium-Ion Batteries

Polycrystalline LiFe(MoO4)2 is successfully synthesized by solid-state reaction and examined as anode material for lithium-ion batteries in terms of galvanostatic charge-discharge cycling, cyclic voltammograms (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). The LiFe(MoO4)2 electrode delivers a high capacity of 1034 mAh g(-1) at a current density of 56 mA g(-1) between 3 and 0.01 V, indicating that nearly 15 Li(+) ions are involved in the electrochemical cycling. LiFe(MoO4)2 also exhibits a stable capacity of 580 mAh g(-1) after experiencing irreversible capacity loss in the first several cycles. Moreover, the Li-ion storage mechanism for LiFe(MoO4)2 is suggested on the basis of the ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) at different insertion/extraction depths. A successive structural transition from triclinic structure to cubic structure is observed, and the tetrahedral coordination of Mo by oxygen in LiFe(MoO4)2 changes to octahedral coordination in Li2MoO3, correspondingly. When being discharged to 0.01 V, the active electrode is likely to be composed of Fe and Mo metal particles and amorphous Li2O due to the multielectron conversion reaction. The insights obtained from this study will benefit the design of new anode materials for lithium-ion batteries.

Brannerite-Type Vanadium–Molybdenum Oxide LiVMoO6 as a Promising Anode Material for Lithium-Ion Batteries with High Capacity and Rate Capability

Brannerite-type vanadium-molybdenum oxide LiVMoO6 is prepared by a facile liquid-phase method, and its electrochemical properties as anode of lithium-ion batteries are comprehensively studied by means of galvanostatic charge-discharge profiles, rate performance, and cyclic voltammetry. In the working voltage between 3.0 and 0.01 V, LiVMoO6 delivers a high reversible capacity of more than 900 mAh g(-1) at the current density of 100 mA g(-1) and a superior rate capability with discharge capacity of ca. 584 and 285 mAh g(-1) under the high current densities of 2 and 5 A g(-1), respectively. Moreover, ex situ X-ray diffraction and X-ray photoelectron spectroscopy are utilized to examine the phase evolution and valence changes during the first lithiated process. A small amount of inserted Li(+) induces a decomposition of LiVMoO6 into Li2Mo2O7 and V2O5, which play the host during further lithiated processes. When being discharged to 0.01 V, most V(5+) change into V(3+)/V(2+), suggesting intercalation/deintercalation processes, whereas Mo(6+) are reduced into a metallic state on the basis of the conversion reaction. The insights obtained from this study will benefit the design of novel anode materials for lithium-ion batteries.

Preparation and Electrochemical Properties of Tin-Iron-Carbon Nanocomposite as the Anode of Lithium-Ion Batteries.

Tin-iron-carbon nanocomposite is successfully prepared by a sol-gel method followed by a chemical vapor deposition (CVD) process with acetylene gas as the carbon source. The structural properties, morphology, and electrochemical performances of the nanocomposite are comprehensively studied in comparison with those properties of tin-carbon and iron-carbon nanocomposites. Sheet-like carbon architecture and different carbon contents are induced thanks to the catalytic effect of iron during CVD. Among three nanocomposites, tin-iron-carbon demonstrates the highest reversible capacity of 800 mA h g(-1) with 96.9% capacity retention after 50 cycles. It also exhibits the best rate capability with a discharge capacity of 420 mA h g(-1) at a current density of 1000 mA g(-1). This enhanced performance is strongly related to the carbon morphology and content, which can not only accommodate the large volume change, but also improve the electronic conductivity of the nanocomposite. Hence, the tin-iron-carbon nanocomposite is expected to be a promising anode for lithium-ion batteries.

High Rate Capability and Enhanced Cyclability of Na3V2(PO4)2F3 Cathode by In Situ Coating of Carbon Nanofibers for Sodium-Ion Battery Applications

A facile chemical vapor deposition method is developed for the preparation of carbon nanofiber (CNF) composite Na3 V2 (PO4 )2 F3 @C as cathodes for sodium-ion batteries. In all materials under investigation, the optimized composite content, denoted as NVPF@C@CNF-5, shows excellent sodium storage performance (86.3 % capacity retention over 5000 cycles at 20 C rate) and high rate capability (84.3 mA h g-1 at 50 C). The superior sodium storage performance benefits from the enhanced electrical conductivity of the working electrode after formation of a composite with CNF. Furthermore, the full cell using NVPF@C@CNF-5 and hard carbon as the cathode and anode, respectively, demonstrates an impressive electrochemical performance, realizing an ultrahigh rate charge/discharge at a current rate of 30 C and long-term stability over 1000 cycles. This approach is facile and effective, and could be extended to other materials for energy-storage applications.

Electrochemical Performance and Storage Mechanism of Ag2Mo2O7 Micro‐rods as the Anode Material for Lithium‐Ion Batteries

Ag2 Mo2 O7 micro-rods are prepared by one-step hydrothermal method and their lithium electrochemical properties, as the anode for lithium-ion batteries, are comprehensively studied in terms of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. The electrode delivers a high reversible capacity of 825 mAh g-1 at a current density of 100 mA g-1 and a superior rate capability with a discharge capacity of 263 mAh g-1 under the high current density of 2 Ag-1 . The structural transition and phase evolution of Ag2 Mo2 O7 were investigated by using ex situ XRD and TEM. The Ag2 Mo2 O7 electrode is likely to be decomposed into amorphous molybdenum, Li2 O, and metallic silver based on the conversion reaction. Silver nanoparticles are not involved in the subsequent electrochemical cycles to form a homogeneous conducting network. Such in situ decomposition behavior provides an insight into the mechanism of the electrochemical reaction for the anode materials and would contribute to the design of new electrode materials in future.