Electrochemical properties of VPO4/C nanosheets and microspheres as anode materials for lithium-ion batteries

An advanced BiPO4/super P anode material for high-performance potassium-ion batteries

Dispersed BiPO₄ nanoparticles loaded on the surface of a super P conducting network (BiPO₄/SP) were fabricated and investigated as a novel anode for PIBs. The BiPO₄/SP electrode demonstrates high rate capability (97.1 mA h g^-1 at 500 mA g^-1) and good long-term cycling performance (116 mA h g^-1 at 200 mA g^-1 over 100 cycles).

Controlled Synthesis of Ultrafine β-Mo2C Nanoparticles Encapsulated in N-Doped Porous Carbon for Boosting Lithium Storage Kinetics

Rational construction of anode material architecture to afford excellent cycling stability, fast rate capacity, and large specific capacity is essential to promote further development of lithium-ion batteries in commercial applications. In this work, we propose a facile strategy to anchor ultrafine β-Mo2C nanoparticles in N-doped porous carbon skeleton (β-Mo2C@NC) using a scalable salt-template method. The well-defined and abundant hierarchical porous structure of β-Mo2C@NC can not only significantly enhance the electron/ion transfer but also markedly increase the specific surface area to effectively expose the electrochemically accessible active sites. Besides, the N-doped carbon matrix can turn the d-orbital electrons of the Mo to boost the electron transportation as well as distribute active sites to buffer the volume change of Mo2C and provide conductive pathways during discharge/charge cycles. As a result, the as-prepared β-Mo2C@NC displays excellent lithium storage performance in terms of 1701.6 mA h g-1 at 0.1 A g-1 after 100 cycles and a large capacity of 816.47 mA h g-1 at 2.0 A g-1 after 500 cycles. The above results distinctly demonstrate that the β-Mo2C@NC composite has potential application as anode materials in high-performance energy storage devices.

α-TiPO4 as a Negative Electrode Material for Lithium-Ion Batteries

To realize high-power performance, lithium-ion batteries require stable, environmentally benign, and economically viable noncarbonaceous anode materials capable of operating at high rates with low strain during charge-discharge. In this paper, we report the synthesis, crystal structure, and electrochemical properties of a new titanium-based member of the MPO₄ phosphate series adopting the α-CrPO₄ structure type. α-TiPO₄ has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH₄TiPO₄F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO₄ is refined from powder X-ray diffraction data using a Rietveld method and verified by electron diffraction and high-resolution scanning transmission electron microscopy, whereas the chemical composition is confirmed by IR, energy-dispersive X-ray, electron paramagnetic resonance, and electron energy loss spectroscopies. Carbon-coated α-TiPO₄/C demonstrates reversible electrochemical activity ascribed to the Ti³⁺/Ti²⁺ redox transition delivering 125 mAh g^-1 specific capacity at C/10 in the 1.0-3.1 V versus Li⁺/Li potential range with an average potential of ∼1.5 V, exhibiting good rate capability and stable cycling with volume variation not exceeding 0.5%. Below 0.8 V, the material undergoes a conversion reaction, further revealing capacitive reversible electrochemical behavior with an average specific capacity of 270 mAh g^-1 at 1C in the 0.7-2.9 V versus Li⁺/Li potential range. This work suggests a new synthesis route to metastable titanium-containing phosphates holding prospective to be used as negative electrode materials for metal-ion batteries.

Cr2P2O7 as a Novel Anode Material for Sodium and Lithium Storage

The development of new appropriate anode material with low cost is still main issue for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). Here, Cr2P2O7 with an in-situ formed carbon layer has been fabricated through a facile solid-state method and its storage performance in SIBs and LIBs has been reported first. The Cr2P2O7@C delivers 238 mA h g-1 and 717 mA h g-1 at 0.05 A g-1 in SIBs and LIBs, respectively. A capacity of 194 mA h g-1 is achieved in SIBs after 300 cycles at 0.1 A g-1 with a high capacity retention of 92.4%. When tested in LIBs, 351 mA h g-1 is maintained after 600 cycles at 0.1 A g-1. The carbon coating layer improves the conductivity and reduces the side reaction during the electrochemical process, and hence improves the rate performance and enhances the cyclic stability.

Hydrogel-derived VPO4/porous carbon framework for enhanced lithium and sodium storage

Vanadium phosphate (VPO₄) is attracting extensive attention because of its advantages of low cost, stable structure and high theoretical capacity. However, similar to other phosphates, VPO₄ suffers from low electrical conductivity and large volume expansion, adversely influencing its electrochemical performance and thus limiting its application as an anode in lithium and sodium ion batteries. Herein, we propose a novel, facile strategy based on the organic-inorganic network of a nanostructured hybrid hydrogel for immobilizing VPO₄ in a hierarchically porous carbon framework (3DHP-VPO₄@C). VPO₄ chemically interacts with the carbon framework via a P-C bond, functioning as a buffer layer to maintain structural stability during charge/discharge cycles. The carbon framework offers an efficient pathway for electron and Li⁺/Na⁺ transport to ensure high electronic conductivity of the electrode. The 3DHP-VPO₄@C anode exhibits excellent lithium and sodium storage performances, and notably high capacities of 957 mA h g^-1 at 0.1 A g^-1 and 345.3 mA h g^-1 at 5 A g^-1 for lithium ion batteries. Full cells consisting of a LiFePO₄ cathode and the 3DHP-VPO₄@C anode also prove to have superior cycling stability and rate performance for LIBs.

In situ carbon coated flower-like VPO4 as an anode material for potassium-ion batteries

Here we design a novel carbon coating method for phosphate-based VPO4 with three different morphologies, via the intercalation of isobutanol to layered VOPO4·2H2O combined with thermal reduction. The well-constructed flower-like VPO4 delivers a high reversible capacity of 400 mA h g-1 with a long cycle-life of more than 500 cycles, proving that the special structure is suitable to accommodate the large volume expansion during the electrochemical charge-discharge process.

α-VPO4: A Novel Many Monovalent Ion Intercalation Anode Material for Metal-Ion Batteries

In this paper, we report on a novel α-VPO₄ phosphate adopting the α-CrPO₄ type structure as a promising anode material for rechargeable metal-ion batteries. Obtained by heat treatment of a structurally related hydrothermally prepared KTiOPO₄-type NH₄VOPO₄ precursor under reducing conditions, the α-VPO₄ material appears stable in a wide temperature range and possesses an interesting "sponged" needle-like particle morphology. The electrochemical performance of α-VPO₄ as the anode material was examined in Li-, Na-, and K-based cells. The carbon-coated α-VPO₄/C composite exhibits 185, 110, and 37 mA h/g specific capacities respectively at the first discharge and around 120, 80, and 30 mA h/g at consecutive cycles at a C/10 rate. The considerable capacity drop after the first cycle in Li and Na cells is presumably due to irreversible alkali ion consumption taking place upon alkali-ion de/insertion. The EDX analysis of the recovered electrodes revealed an uptake of ∼23% of Na after the first discharge with significant cell parameter alteration validated by operando XRD measurements. In contrast to the known β-VPO₄ anode materials, both Li and Na de/insertion into the new α-VPO₄ proceed via an intercalation mechanism with the parent structural framework preserved but not via a conversion mechanism. The dimensionality of alkali-ion migration pathways and diffusion energy barriers was analyzed by the BVEL approach. Na-ion diffusion coefficients measured by the potentiostatic intermittent titration technique are in the range of (0.3-1.0)·10^-10 cm²/s, anticipating α-VPO₄ as a prospective high-power anode material for Na-ion batteries.

High Performance and Structural Stability of K and Cl Co-Doped LiNi0.5Co0.2Mn0.3O2 Cathode Materials in 4.6 Voltage

The high energy density lithium ion batteries are being pursued because of their extensive application in electric vehicles with a large mileage and storage energy station with a long life. So, increasing the charge voltage becomes a strategy to improve the energy density. But it brings some harmful to the structural stability. In order to find the equilibrium between capacity and structure stability, the K and Cl co-doped LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) cathode materials are designed based on defect theory, and prepared by solid state reaction. The structure is investigated by means of X-ray diffraction (XRD), rietveld refinements, scanning electron microscope (SEM), XPS, EDS mapping and transmission electron microscope (TEM). Electrochemical properties are measured through electrochemical impedance spectroscopy (EIS), cyclic voltammogram curves (CV), charge/discharge tests. The results of XRD, EDS mapping, and XPS show that K and Cl are successfully incorporated into the lattice of NCM cathode materials. Rietveld refinements along with TEM analysis manifest K and Cl co-doping can effectively reduce cation mixing and make the layered structure more complete. After 100 cycles at 1 C, the K and Cl co-doped NCM retains a more integrated layered structure compared to the pristine NCM. It indicates the co-doping can effectively strengthen the layer structure and suppress the phase transition to some degree during repeated charge and discharge process. Through CV curves, it can be found that K and Cl co-doping can weaken the electrode polarization and improve the electrochemical performance. Electrochemical tests show that the discharge capacity of Li_0.99K_0.01(Ni_0.5Co_0.3Mn_0.2)O_1.99Cl_0.01 (KCl-NCM) are far higher than NCM at 5 C, and capacity retention reaches 78.1% after 100 cycles at 1 C. EIS measurement indicates that doping K and Cl contributes to the better lithium ion diffusion and the lower charge transfer resistance.

Exploration of VPO4 as a new anode material for sodium-ion batteries

Carbon-coated VPO₄ nanoparticles embedded into a porous carbon matrix were synthesized via a facile sol-gel approach and investigated as a novel polyanion anode material for sodium-ion batteries. The VPO₄@carbon anode demonstrates excellent rate capability and superior cyclic stability (245.3 mA h g^-1 at 1000 mA g^-1 after 200 cycles).

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.

Rational Construction of Multivoids-Assembled Hybrid Nanospheres Based on VPO4 Encapsulated in Porous Carbon with Superior Lithium Storage Performance

The design of a new nanostructured anode material with high tap density while still keeping the common advantages of the hollow structure is a great challenge for future lithium-ion batteries (LIBs). Here, multivoids-assembled hierarchically meso-macroporous nanospheres based on VPO₄ encapsulated in porous carbon (MVHP-VPO₄@C NSs) were designed and fabricated. This unique structure can evidently decrease the excessive interior space in hollow spheres or multishelled hollow spheres to gain high volumetric energy density and at the same time can alleviate the large mechanical strain during the cycling process. As expected, MVHP-VPO₄@C NSs show good lithium storage behavior with gravimetric discharge capacity of 628 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1. Furthermore, the full cell (LiFePO₄ cathode//MVHP-VPO₄@C NSs anode) also exhibits outstanding lithium storage performance. The insight obtained from this structure may provide guidance for the design of other electrode materials experiencing large volume variation during the lithiation-delithiation process.

Electrochemical detection of PCR amplicons of Escherichia coli genome based on DNA nanostructural probes and polyHRP enzyme

Fast, portable and sensitive analysis ofE. coliis becoming an important challenge in many critical fields (e.g., food safety, environmental monitoring and clinical diagnosis).

Facile Synthesis of Na0.33V2O5 Nanosheet-Graphene Hybrids as Ultrahigh Performance Cathode Materials for Lithium Ion Batteries

Na0.33V2O5 nanosheet-graphene hybrids were successfully fabricated for the first time via a two-step route involving a novel hydrothermal method and a freeze-drying technique. Uniform Na0.33V2O5 nanosheets with a thickness of about 30 nm are well-dispersed between graphene layers. The special sandwich-like nanostructures endow the hybrids with high discharge capacity, good cycling stability, and superior rate performance as cathodes for lithium storage. Desirable discharge capacities of 313, 232, 159, and 108 mA·h·g(-1) can be delivered at 0.3, 3, 6, and 9 A·g(-1), respectively. Moreover, the Na0.33V2O5-graphene hybrids can maintain a high discharge capacity of 199 mA·h·g(-1) after 400 cycles even at an extremely high current density of 4.5 A·g(-1), with an average fading rate of 0.03% per cycle.