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XRD (a) and Rietveld refinement results of LFP/C (b) and LFP·LVP/C (c), partial zoom of XRD diagrams (d).
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Nano-sized LiFePO4·Li3V2(PO4)3/C was synthesized via a sol-gel route combining with freeze-drying. X-ray diffraction results show that this composite mainly consists of olivine LiFePO4 and monoclinic Li3V2(PO4)3 phases with small amounts of V-doped LiFePO4 and Fe-doped Li3V2(PO4)3. The magnetic properties of LiFePO4·Li3V2(PO4)3/C are significantly...
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... XRD and Rietveld refinement results of LFP/C and LFP·LVP/C are illustrated in Fig. 1. From Fig. 1a, it can be seen that all diffraction peaks of LFP/C are indexed as an olivine phase with orthorhombic structure (ICSD #72545). While the LFP·LVP/C composite consists of both olivine LiFePO 4 (ICSD #72545) and monoclinic Li 3 -V 2 (PO 4 ) 3 (ICSD #161335) phases without any other impurity. The Rietveld refinement results ...
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... XRD and Rietveld refinement results of LFP/C and LFP·LVP/C are illustrated in Fig. 1. From Fig. 1a, it can be seen that all diffraction peaks of LFP/C are indexed as an olivine phase with orthorhombic structure (ICSD #72545). While the LFP·LVP/C composite consists of both olivine LiFePO 4 (ICSD #72545) and monoclinic Li 3 -V 2 (PO 4 ) 3 (ICSD #161335) phases without any other impurity. ...
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... in Fig. 1. From Fig. 1a, it can be seen that all diffraction peaks of LFP/C are indexed as an olivine phase with orthorhombic structure (ICSD #72545). While the LFP·LVP/C composite consists of both olivine LiFePO 4 (ICSD #72545) and monoclinic Li 3 -V 2 (PO 4 ) 3 (ICSD #161335) phases without any other impurity. The Rietveld refinement results (Fig. 1b, c) further confirm that these samples are well crystallized. The weight fractions of LFP and LVP in LFP·LVP/C are 28.8 (0.3)% and 71.2 (0.5)%, respectively, basically agreeing with theoretical values. Fig. 1d shows that diffraction peaks (for example (011) and (400) lattice planes) of LFP in LFP·LVP/C shift to low diffraction angles in ...
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... 4 (ICSD #72545) and monoclinic Li 3 -V 2 (PO 4 ) 3 (ICSD #161335) phases without any other impurity. The Rietveld refinement results (Fig. 1b, c) further confirm that these samples are well crystallized. The weight fractions of LFP and LVP in LFP·LVP/C are 28.8 (0.3)% and 71.2 (0.5)%, respectively, basically agreeing with theoretical values. Fig. 1d shows that diffraction peaks (for example (011) and (400) lattice planes) of LFP in LFP·LVP/C shift to low diffraction angles in comparison with those of pristine LFP/C, indicating the enlarged cell volume. The unit cell lattice parameters are calculated and listed in Table 1. The lattices of LFP in LFP·LVP/C are expanded in all ...
Citations
... To address this problem, researchers have applied surface coatings composed of conductive materials to enhance the electronic conductivity of these active materials, used doping elements to enhance the intrinsic electronic conductivity as well as lithium ion diffusion, and prepare alternative nanostructures to enhance the electrochemical reaction area and shorten the lithium-ion diffusion pathway [15][16][17][18]. Many synthesis techniques have been developed and investigated to realize these objectives, including solid-state reaction [19,20], the sol-gel method [21,22], the hydrothermal or solvothermal methods [23,24], the micro emulsion method [25,26], the freeze-drying method [27,28], and spray pyrolysis [29,30]. Among these methods, the sol-gel method has been widely used at industrial scales to prepare nano-characteristic cathode materials having good rate performance and cycle life [31][32][33]. ...
Lithium-ion batteries have emerged as the primary source of power for use in hybrid electric vehicles and electric vehicles in recent years. Monoclinic-phase Li3V2(PO4)3 (LVP) is a potential cathode material for the next generation of lithium-ion batteries owing to its high operating voltage and low cost because of the use of inexpensive elements. Single-phase LVP nano-crystallites coated with carbon were synthesized using the citric-acid gel process. The effects of the amount of carbon coating on the material characteristics and electrochemical performance of LVP are investigated in this study. HR-TEM images indicated that the synthesized LVP crystallites had high crystallinity, and that 5–15-nm-thick amorphous carbon films were coated uniformly on the surfaces of the LVP crystallites. The 11.9% and 14.7% carbon-coated LVP samples exhibited good electrochemical performance with respect to capacity rates, cycle stability, and Coulombic efficiency at charge-discharge voltages of 3.0–4.3 V. For practical applications, we propose the use of 11.9% carbon-coated LVP; it had a high capacity of 114.3 mAh g⁻¹ (0.1 C) and excellent cycle stability with 97% capacity retention after 100 cycles.
Graphical abstract
... The commonly methods for cathode materials' modification include synthesis method, surface modification, and elemental doping [15][16][17][18][19]. Among these modifications, the introduction of metal cations can change the intercrystal spacing of the cathode material, alleviate the crystal deformation, and improve the conductivity and ion diffusion rate [20][21][22][23]. ...
Li3V2-xMnx(PO4)3 (x = 0, 0.02, 0.04, 0.06 and 0.1) cathode materials for aqueous zinc-ion hybrid batteries (AZHBs) have been synthesized by freeze-drying-assisted sol–gel method. The effects of Mn²⁺ dopping content on the structure, morphology, and electrochemical performance of the samples were investigated. XRD results indicated that the Li3V2-xMnx(PO4)3 products belong to the Li3V2(PO4)3 structure (P21/n). XPS results indicate that Mn2p1/2 and Mn2p2/3 are located at 653.94 eV and 642.46 eV, respectively, with trace amounts of Mn doping in the material. SEM images show that Li3V1.94Mn0.06(PO4)3 sample has more dispersed and smaller particle size in morphology, and the uniform distribution of elements of Li3V1.94Mn0.06(PO4)3 sample (V, Mn, P, O) in the precursor composites was confirmed by EDAX. The Zn// Li3V1.94Mn0.06(PO4)3 battery delivers a superior initial capacity of 106.5 mAh g⁻¹ at the current density of 2 C (200 mA g⁻¹), remarkable cycle stability (98% capacity retention for 50th cycles) and superior rate capability (when current density reaches up to 20 C, the reversible capacities are 98mAh g⁻¹). The results of CV indicated that the diffusion coefficient of zinc ion in Li3V1.94Mn0.06(PO4)3 electrode is 1.30 × 10–12 cm² s⁻¹, which is larger than the other four electrodes. The result of EIS demonstrated that the Rct value.
of Li3V1.94Mn0.06(PO4)3 is the lowest (243.5 Ω), which is in good agreement with rate capability and cyclic results. ex situ XRD results demonstrate that Li⁺ ion can be inserted or de-inserted reversibly during charge and discharge.
In this paper, fast ion and electron delivery inside electrode materials, which is very crucial to the aqueous zinc-ion hybrid batteries (AZHBs), has been studied in order to achieve the excellent electrochemical performance. The Li3V2(PO4)3@C ([email protected]) composites were successfully fabricated by freeze-drying assisted sol-gel method, and the effects of carbon content on the structure, morphology and electrochemical performance of [email protected] composites were investigated. XRD results suggested that the products were made up of an ideal monoclinic structure of LVP, and the structural changes of Li⁺ intercalation and de-intercalation during charge-discharge process were verified. Particularly, the [email protected] sample exhibits excellent crystallinity. SEM images presented that with the increase of carbon content, the size of particles is smaller, and the distribution of particles is more uniform and dispersed. Especially, the [email protected] sample has the smallest and the most uniform dispersed particles. The charging-discharging results indicated that the [email protected] sample delivers the highest initial capacity of 95mAh g⁻¹ at the current density of 2C, and the capacity retention after 50th cycles is 91%. Even at 20C current density, the [email protected] also shows an attractive
discharge capacity as high as 67mAh g⁻¹. CV results presented that the ionic diffusion coefficient of the [email protected] sample is the highest (2.59×10⁻¹² cm² s⁻¹), compared to the value of [email protected], [email protected], [email protected] sample. Besides, EIS and Nyquist plots fitting results indicated that the Rct of [email protected] sample is the lowest (189.5Ω), showing a lower charge transfer resistance and increasing the kinetics of the reaction.
Co-doped ZnO/C composites derived from Co-doped MOF-5 were applied as the anode materials for Li-ion batteries (LIBs), which showed advanced capacity and rate performance. Their good electrochemical properties were attributed to the Co-doping and C complex which greatly enhance ZnO electrical conductivity, and the microporous and macroporous structure which augments the contact area between electrolyte and electrode shortening the diffusion path of Li ions as well as releasing the intense heat caused by Li alloying.
Designing composite structure of active materials is critical for the high-performance Lithium-ion batteries, which determines the reversibility of lithium-ion insertion and extraction of the electrodes. The V2O3 anode has high specific capacity, while presents poor cycling stability due to large volume change. Herein, a novel [email protected] composite with ultra-stable cycling stability is constructed. In this composite structure, the interconnected ultra-small V2O3 and Li4Ti5O12 nanoparticles (5-10 nm) construct robust interfaces in the carbon matrix. The Li4Ti5O12 nanoparticles with excellent cycling stability and minor volume change act as fixtures, which effectively restrict the volume change of V2O3 nanoparticles and improve the cycling stability of [email protected] composite. The [email protected] composite maintains no degradation during 500 cycles under the current density of 100 mA g-1. The results demonstrate that constructing a highly stable interface between the active nanoparticles with smaller and larger volume change is of great significance to suppress their pulverization and achieve high reversibility. This work contributes to a new strategy to design structure of long cycling anode materials for high stable Lithium-ion batteries.
The applications of solid polymer electrolytes in all-solid-state Li-ion batteries are restricted by their low ion conductivities at room temperature and poor mechanical and thermal stabilities. Herein, Li1.4Al0.4Ti1.6(PO4)3 (LATP) electrolyte nanoparticles were used as active fillers to improve the properties of polyethylene oxide (PEO)-based electrolytes. The ion conductivity of the composite electrolyte with 1 wt% LATP increased to 1.2 × 10⁻⁵ S/cm at room temperature, because of the effective inhibition of the PEO matrix crystallization by the high-conductivity LATP nanofillers. The electrochemical, mechanical and thermal stabilities were also enhanced by the LATP nanofillers. The LATP-filled composite electrolytes can effectively block Li dendrites in symmetric Li/electrolyte/Li cells during repeated Li stripping/plating with a current density of 0.10 mA/cm² for 600 h at 30 °C. Furthermore, the LATP-based all-solid-state LiFePO4/Li cells exhibited higher reversible capacity (152 mAh/g at 0.10 C), cycling stability (84% after 20 cycles at 50 °C) and rate capability than the LATP-free cells.
The development of high-performance nonprecious electrocatalysts for both H2 and O2 evolution reaction (HER and OER activities) and for overall water splitting is a highly desirable but remains a grand challenge. Herein, we report a facile method to synthesize ultrathin, amorphous, porous, oxygen and defect enriched NiCoFe phosphate nanosheets (NSs). Owing to their microporous confinement on 2D orientation that can reduce the ion transport resistance during electrochemical process, defect enriched structure with higher electrochemically active surface area, this NiCoFe phosphate porous nanosheets supported on Nickel Foam (NiCoFe phosphate NSs/NF) facilitate the diffusion of gaseous product (H2 and O2) and exhibited remarkable catalytic performance and outstanding stability for both HER, OER and also for overall water spilliting in alkaline electrolyte (1.0 M KOH). For the OER electrocatalyst, 2D NiCoFe phosphate NSs/NF was oxidized to NiCoFe oxides/hydroxide on the catalyst surface and exhibited remarkable OER activity with a low overpotential of only 240 mV to reach a current density of 10 mAcm-2. For the HER, 2D NiCoFe phosphate NSs/NF afforded a current density of 10 mAcm-2 at a low overpotential of only -231 mV. Furthermore, 2D NiCoFe phosphate NSs/NF was employed as the electrocatalyst for both anode and cathode, a water splitting electrolyzer was able to reach 10 mAcm-2 at a cell voltage of 1.52 V with robust durability. Various characterization techniques indicated that the long term stability and the activity for overall water splitting are due to porosity, electrochemically active constitutes, and synergetic effect. This work can be inspiring in the design of earth abundant and highly efficient electrocatalyst for overall water splitting, especially for OER.
Two-dimensional nanomaterials, particularly multimetallic nanosheets with single or few atoms thickness, are attracting extensive research attention because they display remarkable advantages over their bulk counterparts, including high electron mobility, unsaturated surface coordination, a high aspect ratio, and distinctive physical, chemical, and electronic properties. In particular, their ultrathin thickness endows them with ultrahigh specific surface areas and a relatively high surface energy, making them highly favorable for surface active applications; for example, they have great potential for a broad range of fuel cell applications. First, the state-of-the-art research on the synthesis of nanosheets with a controlled size, thickness, shape, and composition is described and special emphasis is placed on the rational design of multimetallic nanosheets. Then, a correlation is performed with the performance of multimetallic nanosheets with modified and improved electrochemical properties and high stability, including for the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), formic acid oxidation (FAO), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and methanol tolerance are outlined. Finally, some perspectives and advantages offered by this class of materials are highlighted for the development of highly efficient fuel cell electrocatalysts, featuring low cost, enhanced performance, and high stability, which are the key factors for accelerating the commercialization of future promising fuel cells.
