Rational Design and Facial Synthesis of Li3V2(PO4)3@C Nanocomposites Using Carbon with Different Dimensions for Ultrahigh-Rate Lithium-Ion Batteries

Core-shell nanomaterials: Applications in energy storage and conversion

Materials with core-shell structures have attracted increasing attention in recent years due to their unique properties and wide applications in energy storage and conversion systems. Through reasonable adjustments of their shells and cores, various types of core-shell structured materials can be fabricated with favorable properties that play significant roles in energy storage and conversion processes. The core-shell material can provide an effective solution to the current energy crisis. Various synthetic strategies used to fabricate core-shell materials, including the atomic layer deposition, chemical vapor deposition and solvothermal method, are briefly mentioned here. A state-of-the -art review of their applications in energy storage and conversion is summarized. The involved energy storage includes supercapacitors, li-ions batteries and hydrogen storage, and the corresponding energy conversion technologies contain quantum dot solar cells, dye-sensitized solar cells, silicon/organic solar cells and fuel cells. In addition, the correlation between the core-shell structures and their performance in energy storage and conversion is introduced, and this finding can provide guidance in designing original core-shell structures with advanced properties.

Synergetic effect of Na-doping and carbon coating on the electrochemical performances of Li3-x Na x V2(PO4)3/C as cathode for lithium-ion batteries

Carbon coated Li_3-x Na _x V₂(PO₄)₃/C (x = 0.04, 0.06, 0.10, 0.12, 0.18) cathode materials for lithium-ion batteries were synthesized via a simple carbothermal reduction reaction route using methyl orange as the reducing agent, which also acted as the Na and carbon sources. The influence of various Na-doping levels on the structure and electrochemical performance of the Li_3-x Na _x V₂(PO₄)₃/C composites was investigated. The valence state of vanadium, the form of residual carbon and the overall morphology of the Li_2.90Na_0.10V₂(PO₄)₃/C, which showed the highest initial specific discharge capacity of 128 mA h g^-1 at the current density of 0.1C (1C = 132 mA g^-1) among this series of composites, were further examined by X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy, respectively. The results indicated that a well crystallized structure of Na-doped Li_2.90Na_0.10V₂(PO₄)₃ coated by a carbon matrix is obtained. In the further electrochemical measurements, the Li_2.90Na_0.10V₂(PO₄)₃/C cathode material shows superior discharge capacities of 124, 118, 113, 106 and 98 mA h g^-1 at 0.3, 0.5, 1, 2 and 5C, respectively. High capacity retention of 97% was obtained after 1100 cycles in long-term cyclic performance tests at 5C. The reason for such a promising electrochemical performance of the as-prepared Li_2.90Na_0.10V₂(PO₄)₃/C has also been explored, which revealed that the synergetic effect of the Na-doping and carbon coating provide enlarged Li⁺ diffusion channels and the increased electronic conductivity.

Nanostructured Li3 V2 (PO4 )3 Cathodes

To further increase the energy and power densities of lithium-ion batteries (LIBs), monoclinic Li₃ V₂ (PO₄ )₃ attracts much attention. However, the intrinsic low electrical conductivity (2.4 × 10^-7 S cm^-1 ) and sluggish kinetics become major drawbacks that keep Li₃ V₂ (PO₄ )₃ away from meeting its full potential in high rate performance. Recently, significant breakthroughs in electrochemical performance (e.g., rate capability and cycling stability) have been achieved by utilizing advanced nanotechnologies. The nanostructured Li₃ V₂ (PO₄ )₃ hybrid cathodes not only improve the electrical conductivity, but also provide high electrode/electrolyte contact interfaces, favorable electron and Li⁺ transport properties, and good accommodation of strain upon Li⁺ insertion/extraction. In this Review, light is shed on recent developments in the application of 0D (nanoparticles), 1D (nanowires and nanobelts), 2D (nanoplates and nanosheets), and 3D (nanospheres) Li₃ V₂ (PO₄ )₃ for high-performance LIBs, especially highlighting their synthetic strategies and promising electrochemical properties. Finally, the future prospects of nanostructured Li₃ V₂ (PO₄ )₃ cathodes are discussed.

Organic-phase synthesis of Li3V2(PO4)3@Carbon nanocrystals and their lithium storage properties

Decreasing particle size is an efficient strategy for improving the lithium storage properties of Li₃V₂(PO₄)₃ (LVP) due to a shorter transport distances of lithium ion and electrons. However, designing and synthesizing LVP nanocrystals (NCs) with sizes smaller than 30 nm remains a challenge. In this work, we developed a facile approach for the fabrication of the monodisperse LVP NCs through a robust high-temperature organic-phase method. The thermodynamics of the synthesis and the possible reaction mechanism were investigated. The results indicate that the organic-phase environment (at 320 °C) may not thermodynamically allow the crystallization of LVP. Nevertheless, oleic acid (OA) and oleylamine (OAm) are essential as capping agents to hinder the agglomeration and growth of the particles. Based on the thermodynamic need, calcination is essential to prepare LVP. The surface electronic conductivity of the LVP NCs was enhanced through a subsequent carbon-coating treatment. The optimum combination of reduction and carbon coating is very favorable for the kinetics of electron transfer and lithium ion diffusion. Therefore, the fabricated LVP@C NCs exhibit superior lithium storage properties with excellent rate capability (84 mA h g⁻¹ at a rate of 20C) and perfect cyclic stability (96.2% capacity retention after 200 cycles at 5C), demonstrating their potential application in high-performance lithium-ion batteries.

Li₃V₂(PO₄)₃@Carbon nanocrystals exhibit superior lithium storage properties due to the shortened lithium-ion diffusion length and the enhanced surface electronic conductivity.

Tuning the morphologies of fluorine-doped tin oxides in the three-dimensional architecture of graphene for high-performance lithium-ion batteries

The morphology of electrode materials plays an important role in determining the performance of lithium-ion batteries (LIBs). However, studies on determining the most favorable morphology for high-performance LIBs have rarely been reported. In this study, a series of F-doped SnO _x (F-SnO₂ and F-SnO) materials with various morphologies was synthesized using ethylenediamine as a structure-directing agent in a facile hydrothermal process. During the hydrothermal process, the F-SnO _x was embedded in situ into the three-dimensional (3D) architecture of reduced graphene oxide (RGO) to form F-SnO _x @RGO composites. The morphologies and nanostructures of F-SnO _x , i.e., F-SnO₂ nanocrystals, F-SnO nanosheets, and F-SnO₂ aggregated particles, were fully characterized using electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Electrochemical characterization indicated that the F-SnO₂ nanocrystals uniformly distributed in the 3D RGO architecture exhibited higher specific capacity, better rate performance, and longer cycling stability than the F-SnO _x with other morphologies. These excellent electrochemical performances were attributed to the uniform distribution of the F-SnO₂ nanocrystals, which significantly alleviated the volume changes of the electrode material and shortened the Li ion diffusion path during lithiation/delithiation processes. The F-SnO₂@RGO composite composed of uniformly distributed F-SnO₂ nanocrystals also exhibited excellent rate performance, as the specific capacities were measured to be 1158 and 648 mA h g^-1 at current densities of 0.1 and 5 A g^-1, respectively.

Carbon Nanofibers Heavy Laden with Li3V2(PO4)3 Particles Featuring Superb Kinetics for High-Power Lithium Ion Battery

Fast lithium ion and electron transport inside electrode materials are essential to realize its superb electrochemical performances for lithium rechargeable batteries. Herein, a distinctive structure of cathode material is proposed, which can simultaneously satisfy these requirements. Nanosized Li3V2(PO4)3 (LVP) particles can be successfully grown up on the carbon nanofiber via electrospinning method followed by a controlled heat-treatment. Herein, LVP particles are anchored onto the surface of carbon nanofiber, and with this growing process, the size of LVP particles as well as the thickness of carbon nanofiber can be regulated together. The morphological features of this composite structure enable not only direct contact between electrolytes and LVP particles that can enhance lithium ion diffusivity, but also fast electron transport through 1D carbon network along nanofibers simultaneously. Finally, it is demonstrated that this unique structure is an ideal one to realize high electron transport and ion diffusivity together, which are essential for enhancing the electrochemical performances of electrode materials.

Layered hybrid phase Li2NaV2(PO4)3/carbon dot nanocomposite cathodes for Li+/Na+ mixed-ion batteries

Hybrid phase Li₂NaV₂(PO₄)₃ (H-LNVP) is one of the most promising cathode materials for Li⁺/Na⁺ mixed-ion batteries.

Advanced High Energy Density Secondary Batteries with Multi-Electron Reaction Materials

Secondary batteries have become important for smart grid and electric vehicle applications, and massive effort has been dedicated to optimizing the current generation and improving their energy density. Multi-electron chemistry has paved a new path for the breaking of the barriers that exist in traditional battery research and applications, and provided new ideas for developing new battery systems that meet energy density requirements. An in-depth understanding of multi-electron chemistries in terms of the charge transfer mechanisms occuring during their electrochemical processes is necessary and urgent for the modification of secondary battery materials and development of secondary battery systems. In this Review, multi-electron chemistry for high energy density electrode materials and the corresponding secondary battery systems are discussed. Specifically, four battery systems based on multi-electron reactions are classified in this review: lithium- and sodium-ion batteries based on monovalent cations; rechargeable batteries based on the insertion of polyvalent cations beyond those of alkali metals; metal-air batteries, and Li-S batteries. It is noted that challenges still exist in the development of multi-electron chemistries that must be overcome to meet the energy density requirements of different battery systems, and much effort has more effort to be devoted to this.

Superior rate performance of Li3V2(PO4)3 co-modified by Fe-doping and rGO-incorporation

Reduced graphene oxide (rGO) incorporated Li₃V_1.94Fe_0.06(PO₄)₃/C cathode materials were successfully prepared by a sol–gel method.

A novel synthesis of gadolinium-doped Li3V2(PO4)3/C with excellent rate capacity and cyclability

We report here the synthesis of gadolinium (Gd)-doped Li₃V_2−xGd_x(PO₄)₃/C (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials using a rheological phase method.

Bicontinuous Structure of Li₃V₂(PO₄)₃ Clustered via Carbon Nanofiber as High-Performance Cathode Material of Li-Ion Batteries

In this work, the composite structure of Li3V2(PO4)3 (LVP) nanoparticles with carbon nanofibers (CNF) is designed. The size and location of LVP particles, and the degree of graphitization and diameter of carbon nanofibers, are optimized by electrospinning and heat treatment. The bicontinuous morphologies of LVP/CNF are dependent on the carbonization of PVP and simultaneous growing of LVP, with the fibers shrunk and the LVP crystals grown toward the outside. LVP nanocystals clustered via carbon nanofibers guarantee improving the diffusion ability of Li(+), and the carbon fiber simultaneously guarantees the effective electron conductivity. Compared with the simple carbon-coated LVP and pure LVP, the particle-clustered structure guarantees high rate capability and long-life cycling stability of NF-LVP as cathode for LIBs. At 20 C rate in the range 3.0-4.3 V, NF-LVP delivers the initial capacity of 122.6 mAh g(-1) close to the theoretical value of 133 mAh g(-1), and maintains 97% of the initial capacity at the 1000th cycle. The bead-like structure of cathode material clustered via carbon nanofibers via electrospinning will be further applied to high-performance LIBs.

A study of the electrochemical behavior at low temperature of the Li3V2(PO4)3 cathode material for Li-ion batteries

CNT coatings combined with an optimized electrolyte are introduced to improve the low temperature performances of Li₃V₂(PO₄)₃.