The fabrication of Li3VO4/Ni composite material and its electrochemical performance as anode for Li-ion battery

In/Ce Co-doped Li3VO4 and Nitrogen-modified Carbon Nanofiber Composites as Advanced Anode Materials for Lithium-ion Batteries

Li₃VO₄ (LVO) is considered as a novel alternative anode material for lithium-ion batteries (LIBs) due to its high capacity and good safety. However, the inferior electronic conductivity impedes its further application. Here, nanofibers (nLICVO/NC) with In/Ce co-doped Li₃VO₄ strengthened by nitrogen-modified carbon are prepared. Density functional theory calculations demonstrate that In/Ce co-doping can substantially reduce the LVO band gap and achieve orders of magnitude increase (from 2.79 × 10^-4 to 1.38 × 10^-2 S cm^-1) in the electronic conductivity of LVO. Moreover, the carbon-based nanofibers incorporated with 5LICVO nanoparticles can not only buffer the structural strain but also form a good framework for electron transport. This 5LICVO/NC material delivers high reversible capacities of 386.3 and 277.9 mA h g^-1 at 0.1 and 5 A g^-1, respectively. Furthermore, high discharge capacities of 335 and 259.5 mA h g^-1 can be retained after 1200 and 4000 cycles at 0.5 and 1.6 A g^-1, respectively (with the corresponding capacity retention of 98.4 and 78.7%, respectively). When the 5LICVO/NC anode assembles with commercial LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) into a full cell, a high discharge capacity of 191.9 mA h g^-1 can be retained after 600 cycles at 1 A g^-1, implying an inspiring potential for practical application in high-efficiency LIBs.

Novel Li3 VO4 Nanostructures Grown in Highly Efficient Microwave Irradiation Strategy and Their In-Situ Lithium Storage Mechanism

The investigation of novel growth mechanisms for electrodes and the understanding of their in situ energy storage mechanisms remains major challenges in rechargeable lithium-ion batteries. Herein, a novel mechanism for the growth of high-purity diversified Li3 VO4 nanostructures (including hollow nanospheres, uniform nanoflowers, dispersed hollow nanocubes, and ultrafine nanowires) has been developed via a microwave irradiation strategy. In situ synchrotron X-ray diffraction and in situ transmission electron microscope observations are applied to gain deep insight into the intermediate Li3+ x VO4 and Li3+ y VO4 phases during the lithiation/delithiation mechanism. The first-principle calculations show that lithium ions migrate into the nanosphere wall rapidly along the (100) plane. Furthermore, the Li3 VO4 hollow nanospheres deliver an outstanding reversible capacity (299.6 mAh g-1 after 100 cycles) and excellent cycling stability (a capacity retention of 99.0% after 500 cycles) at 200 mA g-1 . The unique nanostructure offers a high specific surface area and short diffusion path, leading to fast thermal/kinetic reaction behavior, and preventing undesirable volume expansion during long-term cycling.

Embedding amorphous lithium vanadate into carbon nanofibers by electrospinning as a high-performance anode material for lithium-ion batteries

We design and fabricate a novel hybrid with amorphous lithium vanadate (LiV₃O_x, LVO for short) uniformly encapsulated into carbon nanofibers (denoted as LVO@CNFs) via an easy electrospinning strategy followed by proper postannealing. When examined for use as anode materials for lithium-ion batteries (LIBs), the optimized LVO@CNFs present a high discharge capacity of 603 mAh g^-1 with a capacity retention as high as 90% after 200 cycles at 0.5 A g^-1 and a high rate capacity of 326 mAh g^-1 after 400 cycles even at a high rate of 5 A g^-1. The superior electrochemical performance with excellent cycling stability and rate capability is attributed to the full encapsulation of the amorphous LVO into the conductive carbon nanofibers, which hold enlarged electrochemically active sites for lithium storage, facilitate the charge transfer, and efficiently alleviate the volume changes upon lithium insertion/extraction. More importantly, the current synthesis can be a general strategy to fabricate various alkaline earth metal vanadates, which is promising for developing advanced electrochemical energy storage devices.

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Ultrafine antimony (Sb) nanoparticles encapsulated into a carbon microfiber framework as an excellent LIB anode with a superlong life of more than 5000 cycles

Antimony (Sb) anode has attracted increasing attention given its high theoretical capacity and suitable working potential. Nonetheless, its practical application is largely hindered by huge volume changes during the cyclic process, resulting in unsatisfactory long-term cycled stabilities at high current density. In this work, large-scale ultrafine Sb nanoparticles are functionally designed to encapsulate into a 3D carbon microfiber framework (CMF) via a scalable electrospinning approach followed by a thermal treatment process. This fabrication strategy effectively avoids the change in the volume of the Sb anode and provides a fast conductive network to serve as an efficient 3D e/Li⁺ transport pathway. Benefiting from this novel structural design, an ultrafine Sb nanoparticles@carbon microfiber framework (U-Sb-NPs@CMF) composite anode used for lithium-ion batteries (LIBs) delivers a high reversible capacity of 622 mAh g^-1 after 200 cycles at 0.5 A g^-1 and 507 mAh g^-1 after 2000 cycles at 2 Ag^-1 and a high-capacity retention of 350 mAh g^-1 even after 5000 long-term cycles. These outstanding charge-discharge performances suggest that the U-Sb-NPs@CMF composite is a promising candidate for an anode material in the application of LIBs.

Boosting the Deep Discharging/Charging Lithium Storage Performances of Li3VO4 through Double-Carbon Decoration

With high theoretical capacity, good ionic conductivity, and suitable working plateaus, Li₃VO₄ has emerged as an eye-catching intercalation anode material for lithium storage. However, Li₃VO₄ suffers from poor electrical conductivity and 20% volume variation under deep discharging/charging conditions. Herein, we present a "double-carbon decoration" strategy to tackle both issues. Deflated balloon-like Li₃VO₄/C/reduced graphene oxide (LVO/C/rGO) microspheres with continuous electron transport pathways and sufficient free space for volume change accommodation are fabricated through a facile spray-drying method. Under deep discharging/charging conditions (0.02-3.0 V), LVO/C/rGO achieves a high intercalation capacity of 591 mA h g^-1. With high capacity and outstanding stability, LVO/C/rGO outperforms other intercalation anode materials (such as graphite, Li₄Ti₅O₁₂, and TiO₂). In situ X-ray diffraction measurement reveals that the lithium storage is realized through both solid-solution reaction and two-phase reaction mechanisms. A LVO/C/rGO//LiNi_0.8Co_0.15Al_0.05O₂ lithium-ion full cell is also assembled. In such full cell, LVO/C/rGO also demonstrates high specific capacity and excellent cycling stability. The above results manifest that the LVO/C/rGO anode has the potential to be applied in the next-generation high-performance lithium-ion batteries.

Optimization of Rate Capability and Cyclability Performance in Li3 VO4 Anode Material through Ca Doping

A series of Ca-doped lithium vanadates Li_3-x Ca_x VO₄ (x=0, 0.01, 0.03, and 0.05) are synthesized successfully through a simple sol-gel method. XRD patterns and energy-dispersive X-ray spectroscopy (EDS) mappings reveal that the doped Ca²⁺ ions enter into the lattice successfully and are distributed uniformly throughout the Li₃ VO₄ (LVO) grains. XRD spectra and SEM images show that Ca doping can lead to an enlarged lattice and refined Li₃ VO₄ particles. A small quantity of V ions will transfer from V⁵⁺ to V⁴⁺ in the Ca-doped samples, as demonstrated by the X-ray photoelectron spectroscopy (XPS) analysis, which leads to an increase of an order of magnitude in the electronic conductivity. Improved rate capability and cycling stability are observed for the Ca-doped samples, and Li_2.97 Ca_0.03 VO₄ exhibits the best electrochemical performance among the studied materials. The initial charge/discharge capacities at 0.1 C increase from 480/645 to 527/702 mA h g^-1 as x varies from 0 to 0.03. The charge capacity of Li_2.97 Ca_0.03 VO₄ at 1 C retains 95.3 % of its initial value after 180 cycles, whereas the capacity retention is only 40 % for the pristine sample. Moreover, Li_2.97 Ca_0.03 VO₄ maintains a high discharge capacity of 301.7 mA h g^-1 at a high discharge rate (4 C), whereas the corresponding value is only 95.2 mA h g^-1 for the pristine LVO sample. The enhanced cycling and rate performances are ascribed to the increased lithium ion diffusivity and electrical conductivity induced by Ca doping.

Study on the Electrochemical Reaction Mechanism of NiFe2O4 as a High-Performance Anode for Li-Ion Batteries

Nickel ferrite (NiFe₂O₄) has been previously shown to have a promising electrochemical performance for lithium-ion batteries (LIBs) as an anode material. However, associated electrochemical processes, along with structural changes, during conversion reactions are hardly studied. Nanocrystalline NiFe₂O₄ was synthesized with the aid of a simple citric acid assisted sol-gel method and tested as a negative electrode for LIBs. After 100 cycles at a constant current density of 0.5 A g^-1 (about a 0.5 C-rate), the synthesized NiFe₂O₄ electrode provided a stable reversible capacity of 786 mAh g^-1 with a capacity retention greater than 85%. The NiFe₂O₄ electrode achieved a specific capacity of 365 mAh g^-1 when cycled at a current density of 10 A g^-1 (about a 10 C-rate). At such a high current density, this is an outstanding capacity for NiFe₂O₄ nanoparticles as an anode. Ex-situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) were employed at different potential states during the cell operation to elucidate the conversion process of a NiFe₂O₄ anode and the capacity contribution from either Ni or Fe. Investigation reveals that the lithium extraction reaction does not fully agree with the previously reported one and is found to be a hindered oxidation of metallic nickel to nickel oxide in the applied potential window. Our findings suggest that iron is participating in an electrochemical reaction with full reversibility and forms iron oxide in the fully charged state, while nickel is found to be the cause of partial irreversible capacity where it exists in both metallic nickel and nickel oxide phases.

Enhanced Electrochemical Performance of Ultracentrifugation-Derived nc-Li3VO4/MWCNT Composites for Hybrid Supercapacitors

Nanocrystalline Li3VO4 dispersed within multiwalled carbon nanotubes (MWCNTs) was prepared using an ultracentrifugation (uc) process and electrochemically characterized in Li-containing electrolyte. When charged and discharged down to 0.1 V vs Li, the material reached 330 mAh g(-1) (per composite) at an average voltage of about 1.0 V vs Li, with more than 50% capacity retention at a high current density of 20 A g(-1). This current corresponds to a nearly 500C rate (7.2 s) for a porous carbon electrode normally used in electric double-layer capacitor devices (1C = 40 mA g(-1) per activated carbon). The irreversible structure transformation during the first lithiation, assimilated as an activation process, was elucidated by careful investigation of in operando X-ray diffraction and X-ray absorption fine structure measurements. The activation process switches the reaction mechanism from a slow "two-phase" to a fast "solid-solution" in a limited voltage range (2.5-0.76 V vs Li), still keeping the capacity as high as 115 mAh g(-1) (per composite). The uc-Li3VO4 composite operated in this potential range after the activation process allows fast Li(+) intercalation/deintercalation with a small voltage hysteresis, leading to higher energy efficiency. It offers a promising alternative to replace high-rate Li4Ti5O12 electrodes in hybrid supercapacitor applications.

Facile synthesis of a nickel vanadate/Ni composite and its electrochemical performance as an anode for lithium ion batteries

Ni₃V₂O₈/Ni composites are synthesized by a simple hydrothermal route, and show high-rate capability and outstanding long-life cycling stability as a new anode material for Li-ion batteries.

Surface-Amorphous and Oxygen-Deficient Li3VO4-δ as a Promising Anode Material for Lithium-Ion Batteries

Surface-amorphous and oxygen-deficient Li₃VO_4-δsynthesized by simple annealing of Li₃VO₄ powders in a vacuum shows great enhancements in both reversible capacity and coulombic efficiency for the first discharge/charge without delicate size control and carbon coating. The results are associated with the improved charge-transfer kinetics caused by the amorphous surface of Li₃VO_4-δ .