Improving electrochemical performance of LiMnPO<Subscript>4</Subscript> by Zn doping using a facile solid state method

Olivine structure LiMnPO₄/C as cathode materials for Li-ion batteries were synthesized via a simple solidstate reaction. Improvement of the electrochemical performance of LiMnPO₄/C cathode material was realized significantly by the method of doping Zn. The obtained LiMn_0.95Zn_0.05PO₄/C electrode material was studied by the measurements of X-ray diffraction pattern, scanning electronic microscopy, electrochemical impedance spectroscopy and electrochemical performance. The results indicate that the LiMn_0.95Zn_0.05PO₄/C materials exhibit discharge specific capacity of 140.2 mA h g⁻¹ at 0.02 C rate and better rate capability. These excellent results are elucidated by EIS test, which showed that there was the decrease of charge transfer resistance and faster lithium-ion diffusion in LiMnPO₄/C cathode materials after Zn doping.     

Synthesis and characterization of sulfur-doped carbon decorated LiFePO4 nanocomposite as high performance cathode material for lithium-ion batteries

This is the first report where crystalline sulfur-doped carbon decorated LiFePO₄ nanocomposite are employed as cathode material for lithium-ion batteries. The electrode has been synthesized via a sol–gel route, in which benzyl disulfide and oxalic acid are used as the sulfur and carbon source, respectively. Meanwhile, the as-synthesized sample is characterized by XRD, SEM, EDS mapping, TEM, Raman spectra, XPS and electrochemical techniques. The results reveal that the sulfur-doped carbon is uniformly coated on the surface of LiFePO₄ without destroying the crystal structure of the bulk material. Moreover, both the electronic conductivity and defect level of the carbon clearly increase, as a consequence, the electron and Li-ion diffusion of the electrode is further improved. As a cathode material for lithium-ion batteries, it exhibits a more outstanding electrochemical performance, especially the rate capability and long cyclic performance. Thus, it can be drawn a conclusion that the sulfur-doped carbon coating approach is an effective method to improve the electrochemical performance of LiFePO₄ and could be extended to modify other electrode materials for lithium-ion batteries.     

Synthesis, characterization and electrochemical performance of LiNiVO4 anode material for lithium-ion batteries

A rheological phase reaction method was introduced to synthesize LiNiVO₄ powder material. The product was tested using XRD, SEM and electrochemical measurement methods. It was found that single crystal grain LiNiVO₄ is easily prepared with the rheological phase reaction; the intermediate product NiV(IV)O₃ is the electrochemical active center; the product prepared at 700 °C for 18 h possess the best morphology of single crystal body and exhibits excellent performance as anode material with a small capacity fade. This indicates that LiNiVO₄ is a good anode material for lithium-ion batteries and the rheological phase reaction is a simple, economical and effective method to synthesize a series of functional materials.     

Wet-Chemical Synthesis and Electrochemical Properties of Ce-Doped FeVO4 for Use as New Anode Material in Li-ion Batteries

Ce-doped FeVO₄ nanocomposites were successfully synthesized using reverse micro-emulsion route. Thermal and microstructural characteristics were comprehensively investigated by simultaneous thermal analysis, X-ray diffraction (XRD), scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and laser particle size analyzer. Moreover, as the anode material of lithium-ion batteries, the electrochemical properties were studied by galvanostatic charge and discharge tests and electrochemical impedance spectroscopy. The thermal analysis illustrated that the triclinic crystal structure of FeVO₄ nanoparticles is formed at about 520 °C, which is confirmed by XRD and FT-IR results. Furthermore, the microstructural analyses revealed more regular particles and high specific surface area for wet-chemical derived FeVO₄:Ce, which decreases the diffusion pathway of the lithium ions during the insertion/extraction process. The electrochemical measurements indicated that the electrode cycling performance and rate retention ability of Ce-doped FeVO₄ are better than those of pure FeVO₄ due to the expansion of the crystal lattice, which provided more lattice space for lithium intercalation and de-intercalation. Consequently, the as-prepared Ce-doped FeVO₄ with relatively high specific and reversible capacity, thermal stability and satisfactory cycling performance is a promising candidate for use as a lithium batteries anode material.     

Preparation and characterization of nano-sized LiFePO4 by low heating solid-state coordination method and microwave heating

The precursors of LiFePO₄ were prepared by low heating solid-state coordination method using lithium acetate, ammonium dihydric phosphate, ferrous oxalate and citric acid as raw materials. Olivine phase LiFePO₄ as a cathode material for lithium-ion batteries was successfully synthesized by microwave heating in a few minutes. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize its structure and morphology. Cyclic voltammetry (CV) and charge-discharge cycling performance were used to characterize its electrochemical properties. The results showed that the grain size of the optimal sample was about 40-50 nm, and the as-prepared particles were homogeneous. The nano-sized LiFePO₄ obtained has a high electrochemical capacity (125 mAh g⁻¹) and stable cycle ability.     

Synthesis of spindle-shaped nanoporous C–LiFePO4 composite and its application as a cathodes material in lithium ion batteries

In this work, LiFePO₄/C composites were prepared in hydrothermal system by using iron gluconate as iron source, and two feeding sequences during the preparation were comparatively studied. The morphology, crystal structure and charge–discharge performance of the prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic charge–discharge testing. The results showed that the feeding sequences and iron gluconate seriously affected the microstructures and electrochemical properties of the resulting LiFePO₄ cathodes in lithium ion batteries. The spindle-shaped LiFePO₄ with hierarchical microporous structure self-assembled by nanoparticles has been successfully synthesized by synthesis route B. In addition, the cell performance of the synthesized LiFePO₄ by synthesis route B was better than that of LiFePO₄ by synthesis route A. Specially at high rates, the superior rate performance of the spindle-shaped LiFePO₄/C microstructure (LFP/C-B) was revealed. And special reversible capacities of ∼118 and ∼95 mAh g⁻¹ were obtained at rates of 2 C and 5 C, comparing to ∼96 and ∼68 mAh g⁻¹ for LFP/C-A.     

Origin of Capacity Fading in Nano-Sized Co3O4 Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co₃O₄, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co₃O₄ with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co₃O₄ anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.     

Co2SnO4–multiwalled carbon nanotubes composite as a highly reversible anode material for lithium-ion batteries

We report a facile strategy to synthesize the composite of Co₂SnO₄ nanoparticles and multiwalled carbon nanotubes (MWCNTs) as a highly reversible anode material for high-performance lithium-ion batteries. Galvanostatic charge/discharge, cyclic voltammograms(CVs) and electrochemical impedance spectra (EIS) testing results indicate that the Co₂SnO₄–MWCNTs composite display large reversible capacity, excellent cyclic performance and good rate performance, highlighting the importance of the added MWCNTs for maximum utilization of electrochemically active Co₂SnO₄ nanoparticles for energy storage applications in high-performance lithium-ion batteries.     

The study on the Li-storage performances of bamboo charcoal (BC) and BC/Li2SnO3 composites

Bamboo charcoal/Li₂SnO₃ composites for lithium-ion batteries were synthesized by a sol–gel route. The structure, morphology, and electrochemical properties of the composites were detected by means of X-ray diffraction, scanning electron microscope, Raman spectroscopy, thermal gravimetric analysis, and electrochemical measurements. The results showed that Li₂SnO₃ particles were loaded on the surface of bamboo charcoal and some of them entered into the hole. The bamboo charcoal/Li₂SnO₃ composites exhibited good electrochemical performance with high capacity and good cycling stability (616.5 mAh g^?1 after 50 cycles). The composites showed a better electrochemical property than Li₂SnO₃ and bamboo charcoal.     

Preparation and electrochemical properties of composites of carbon nanotubes loaded with Ag and TiO2 nanoparticle for use as anode material in lithium-ion batteries

Carbon nanotubes (CNTs) loaded with Ag and TiO₂ nanoparticles (Ag-TiO₂/CNTs) are a composite showing promise as an anode material in lithium-ion batteries. Here we prepare Ag-TiO₂/CNTs via hydrolysis and reduction processes. The morphology, structure, and electrochemical performance of the composite were investigated by transmission electron microscopy, X-ray diffraction, and a variety of electrochemical techniques. The results show that the TiO₂ and Ag nanoparticles were uniformly deposited on the surface of CNTs with crystallite sizes of ∼12 and 30 nm, respectively. The Ag-TiO₂/CNTs anode materials showed superior cycling stability and a high reversible capacity of 172 mAh/g after 30 cycles. Ag addition not only increases the electronic conductivity of the composites, but also allows convenient transfer of Li-ion in the composite structure.     

Carbon-Coated ZnS-FeS2 Heterostructure as an Anode Material for Lithium-Ion Battery Applications

The construction of carbon-coated heterostructures of bimetallic sulfide is an effective technique to improve the electrochemical activity of anode materials in lithium-ion batteries. In this work, the carbon-coated heterostructured ZnS-FeS₂ is prepared by a two-step hydrothermal method. The crystallinity and nature of carbon-coating are confirmed by the investigation of XRD and Raman spectroscopy techniques. The nanoparticle morphology of ZnS and plate-like morphology of FeS₂ is established by TEM images. The chemical composition of heterostructure ZnS-FeS₂@C is discovered by an XPS study. The CV results have disclosed the charge storage mechanism, which depends on the capacitive and diffusion process. The BET surface area (37.95 m²g⁻¹) and lower R_ct value (137 Ω) of ZnS-FeS₂@C are beneficial to attain higher lithium-ion storage performance. It delivered a discharge capacity of 821 mAh g⁻¹ in the 500th continuous cycle @ A g⁻¹, with a coulombic efficiency of around 100%, which is higher than the ZnS-FeS₂ heterostructure (512 mAh g⁻¹). The proposed strategy can improve the electrochemical performance and stability of lithium-ion batteries, and can be helpful in finding highly effective anode materials for energy storage devices.     

Optimization of electrochemical properties of LiFePO4/C prepared by an aqueous solution method using sucrose

LiFePO₄ can be used as a positive electrode material for lithium-ion batteries by making composite with electrical conductive carbonaceous materials. In this study, LiFePO₄/C (carbon) composite was prepared by a soft chemistry route, in which sucrose was used as a carbon source of a low price. We tried to optimize a Li/(LiFePO₄/C) cell performance through changing synthetic conditions and discussed the factors affecting the electrochemical performances of the cell, such as the amount of the carbon source, synthetic temperature, gas flow rate of pyrolysis and the formation of secondary phases. It was found that the connection of the residual carbon and Fe₂P to LiFePO₄ particles and the amount of these two phases were important factors. In our experimental conditions, LiFePO₄/C including 9.72 wt.% of residual carbon, prepared at 800 °C for 12 h showed the highest reversible capacity and the best C rate performance among the synthesized materials; 130 mAh g⁻¹ at 10C rate and 50 °C.     

Preparation and electrochemical properties of LiMn2O4 by the microwave-assisted rheological phase method

Pure-phase and well-crystallized spinel LiMn₂O₄ powders as cathode materials for lithium-ion batteries were successfully synthesized by a new simple microwave-assisted rheological phase method, which was a timesaving and efficient method. The physical properties of the as-synthesized samples compared with the pristine LiMn₂O₄ obtained from the rheological phase method were investigated by thermogravimetry analysis (TGA), X-ray diffraction (XRD) and scanning electronic microscope (SEM). The as-prepared powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance were examined in detail. The powders resulting from the microwave-assisted rheological phase method were pure, spinel structure LiMn₂O₄ particles of regular shapes with distribution uniformly, and exhibited promising electrochemical properties for battery. Furthermore, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reactions of Li-ion insertion into and extraction from LiMn₂O₄ electrode.     

Study on synthesis routes and their influences on chemical and electrochemical performances of Li3V2(PO4)3/carbon

In this study, Li₃V₂(PO₄)₃/carbon samples were synthesized by two different synthesis routes. Their influence on chemical and electrochemical performances of Li₃V₂(PO₄)₃/carbon as cathode materials for lithium-ion batteries was investigated. The structure and morphology of Li₃V₂(PO₄)₃/carbon were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM) measurements. TEM revealed that the Li₃V₂(PO₄)₃ grains synthesized through the sol-gel route had a depressed grain size. Electrochemical behaviors were characterized by galvanostatic charge/discharge, cyclic voltammetry and AC impedance measurements. Li₃V₂(PO₄)₃/carbon with smaller grain size showed better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of the Li₃V₂(PO₄)₃/carbon were attributed to the depressed grain size and enhanced electrical contacts produced via the sol-gel route. AC impedance measurements also showed that the sol-gel route significantly decreased the charge-transfer resistance and shortened the migration distance of lithium ion.     

Efficient microwave hydrothermal synthesis of nanocrystalline orthorhombic LiMnO2 cathodes for lithium batteries

Rod-like orthorhombic LiMnO₂ nanocrystals were successfully synthesized using temperature-controlled microwave hydrothermal route (TCMH) in a short time (30 min) at a temperature as low as 160 °C. o-LiMnO₂ obtained by two different methods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemistry test. SEM revealed that the product obtained in case of TCMH was rod-like with a diameter of 40 nm, while the nanoparticles with 200 nm diameter were obtained by traditional hydrothermal route (TH). The dramatic formation of o-LiMnO₂ in the microwave hydrothermal field influenced the morphology and crystal structure of the final products. The formation and preferred growth orientation mechanism of o-LiMnO₂ in the microwave irradiation process was discussed. Electrochemistry performance exhibited that the as-synthesized o-LiMnO₂ nanorods reached the maximum discharge capacity of 194.2 mAh g⁻¹ at 0.1 C rate after several cycles between 2.2 and 4.4 V vs. Li⁺/Li at room temperature, which was higher than the electrochemical performance of o-LiMnO₂ obtained by TH. The experimental results showed that the TCMH method provided an effective way for preparing o-LiMnO₂ cathode material in lithium-ion batteries.     

Synthesis and electrochemical performance of carbon nanofiber-cobalt oxide composites

Carbon nanofiber (CNF) supported cobalt oxide composites as high-capacity anode materials were prepared through a facile, effective method for potential use in rechargeable lithium-ion batteries. The effects of the calcining temperature on the crystallinity, grain size, specific surface area of Co₃O₄ and phase transformation from Co₃O₄ to CoO were studied in detail. Both the specific surface area and CNF content in CNF-cobalt oxide composites strongly affect the electrochemical performance of these series composites. The CNF-Co₃O₄ composite with 24.3% CNF pyrolyzed at 500 °C in Ar shows an excellent cycling performance, retaining a specific capacity of 881 mAh g⁻¹ beyond 100 cycles. Homogeneous deposition and distribution of nanosized Co₃O₄ particles on the surface of CNF can stabilize the electronic and ionic conductivity as well as the morphology of Co₃O₄ phase, which may be the main reason for the markedly improved electrochemical performance.     

Preparation and electrochemical characterization of TiO2 nanowires as an electrode material for lithium-ion batteries

Anatase TiO₂ nanowires containing minor TiO₂(B) phase were prepared by a hydrothermal chemical reaction followed by the post-heat treatment at 400 °C. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, transmission electron microscope, and field-emission scanning electron microscopy. The electrochemical properties were investigated by employing constant current discharge-charge test, cyclic voltammetry, and electrochemical impedance techniques. These nanowires exhibited high rate capacity of 280 mAh g⁻¹ even after 40 cycles, and the coulombic efficiency was approximately 98%, indicating excellent cycling stability and reversibility. The electrochemical impedance spectra showed a stable kinetic process of the electrode reaction. These results indicated that the TiO₂ nanowires have promising application for high energy density lithium-ion batteries.     

Fabrication,structure, electrochemical properties and lithium-ion storage performance of Nd:BiVO4 nanocrystals

Nd:BiVO₄ nanocrystals were synthesized by an effective and simple approach. Nd was incorporated into BiVO₄ host to enhance electronic conductivity and lithium-ion diffusion kinetics, thus promoting the electrochemical performance. When employed as anode materials in lithium-ion batteries, a good cycling stability and high capacity of ~611 mAh g⁻¹ at 100 mA g⁻¹ were delivered. The work can be extensively employed for fabricating other electrode materials and promoting the electrochemical performance in energy storage correlative domains.     

Effects of precursor treatment with reductant or oxidant on the structure and electrochemical properties of LiNi0.5Mn1.5O4

LiNi_0.5Mn_1.5O₄, a lithium-ion battery cathode material, is prepared using co-precipitation via a two-step drying method with Ni-Mn mixed hydroxide as the precursor. This study examines the effects of precursor pretreatment with hydrazine (a reductant) or with H₂O₂ (an oxidant) in solutions of NiSO₄ and MnSO₄. The results indicate substantial differences in the structure and electrochemical properties of LiNi_0.5Mn_1.5O₄ depending on whether the precursor is pretreated with reductant or oxidant. For the hydrazine-treated precursor, the synthesized LiNi_0.5Mn_1.5O₄ has a very pure spinel phase and an ordered, octahedral crystal morphology (ca. 100-300 nm). In contrast, the material synthesized using the H₂O₂-treated precursor shows numerous impurity phases (Na_0.7MnO_2.05) with a layer-by-layer crystal structure. The control sample (prepared without precursor pretreatment) maintains an octahedral structure but still retains a few impurity phases of Na_0.7MnO_2.05. The electrochemical results show that LiNi_0.5Mn_1.5O₄ synthesized using a hydrazine-treated precursor has a higher specific capacity (especially under high discharge current) and a higher cyclic life than the control sample, whereas the sample using H₂O₂-treated precursor shows almost no special capacity due to changes in crystal structure.     

The synthesis of Li(Ni1/3Co1/3Mn1/3)O2 using eutectic mixed lithium salt LiNO3–LiOH

A lithium-ion battery cathode material, Li(Ni_1/3Co_1/3Mn_1/3)O₂, with excellent electrochemical properties was prepared via two-step isothermal sintering, using eutectic lithium salts (0.38LiOH·H₂O–0.62LiNO₃) mixed with Co, Ni, or Mn hydroxides. Based on analysis using X-ray diffraction (XRD), scanning electron microscopy (SEM), a thermogravimetric-differential scanning calorimetric (TG–DSC) analyzer, and Fourier-transform Infrared (FT-IR), this synthetic process consists of procedures including lithium salt melting, permeation, reaction, crystalline transformation, and crystallization. Due to the lower melting point of the eutectic molten salts compared with that of the single lithium salt, a relatively mild synthetic condition (low temperature) is needed, and the product can be highly crystallized with low cation mixing, which facilitates maintenance of the precursor morphology. The electrochemical properties of the product were investigated by constant current discharge–charge and cyclic voltammetry. The results show that the initial discharge capacity is 160 mhA g⁻¹, with excellent cycling stability even after 50 cycles. We conclude that this novel eutectic molten salt method is a promising and practical approach for synthesizing cathode materials for lithium-ion batteries.