A carbothermal reduction method for enhancing the electrochemical performance of LiFePO4/C composite cathode materials

LiFePO₄/C composite cathode material has been synthesized by a carbothermal reduction method using β-FeOOH nanorods as raw materials and glucose as both reducing agent and carbon source. The results indicate that the content of carbon and the morphology of raw material have effect on the electrochemical performance of the final LiFePO₄/C material. Sample LFP14 with a carbon content of 2.79 wt.% can deliver discharge capacities of 158.8, 144.3, 111.0, and 92.9 mAh g^?1 at 0.1, 1, 10, and 15 C, respectively. When decreasing the current from 15 C back to 0.1 C, a discharge capacity of 157.5 mAh g^?1 is recovered, which is 99.2 % of its initial capacity. Therefore, as a kind of cathode material for lithium ion batteries, this LiFePO₄/C material synthesized via a carbothermal reduction method is promising in large-scale production, and has potential application in upcoming hybrid electric vehicles or electric vehicles.     

Silver-coated LiVPO4F composite with improved electrochemical performance as cathode material for lithium-ion batteries

Nano-structured LiVPO₄F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO₄F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO₄F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO₄F material exhibits high discharge capacity, good cycle performance (108.5 mAh g⁻¹ after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g⁻¹ for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (R_ct) of LiVPO₄F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO₄F for lithium-ion batteries cathode material.     

Excellent long-term electrochemical performance of graphite oxide as cathode materials for lithium-ion batteries

A facile, scalable route has been adopted to synthesize graphite oxides with different degrees of oxidation. Subsequently, graphite oxides with rationally designed functional groups have been utilized as cathode materials for lithium-ion batteries (LIBs). The electrodes deliver the initial and second discharge capacities of 332 and 172 mAh g^?1 at a current density of 0.1 A g^?1, respectively. More importantly, a remarkable long-term cycling performance of 130 mAh g^?1 after 800 cycles has been gathered, with an ultralow capacity fading of 0.03% per cycle from the second cycle. The root cause of excellent cycling stability should be ascribed to the admirable reversibility of epoxy and carbonyl groups in graphite oxides during the Li-cycling. Meanwhile, the deep study has provided a novel way to avoid complex and expensive post-treatment process of graphite oxides, whose synthesis conditions are also optimized. Those striking features make graphite oxides as promising cathode materials for lithium-ion batteries.     

Electrochemical performance of surfactant-processed LiFePO4 as a cathode material for lithium-ion rechargeable batteries

This study focuses on the effect of addition of surfactant as a dispersing agent during vibratory ball milling of LiFePO₄ (LFP) precursor materials on the electrochemical performance of solid-state reaction synthesized LFP for lithium-ion battery cathode material. LFP particles formed after calcinations of ball milled LFP precursors (Li₂CO₃, FeC₂O₄, and NH₄H₂PO₄) showed better size uniformity, morphology control, and reduced particle size when anionic surfactant (Avanel S-150) was used. The specific surface area of LFP particles increased by approximately twofold on addition of surfactant during milling. These particles showed significantly enhanced cyclic performance during charge/discharge due to a reduced polarization of electrode material. Electrodes fabricated from LFP particles by conventional milling process showed a 22 % decrease in capacity after 50 cycles, whereas the performance of electrode prepared by surfactant processed LFP showed only 3 % loss in capacity. The LFP particles were characterized using XRD, FE-SEM, particle size distribution, density measurement, and BET-specific surface area measurement. Electrochemical impedance spectra and galvanostatic charge/discharge test were performed for the electrochemical performance using coin-type cell.     

Structure and electrochemical characteristics of LiFePO4 cathode materials for rechargeable Li-Ion batteries

Complex investigations of cathode materials for rechargeable lithium-ion batteries have been carried out using the following techniques: scanning electron microscopy, microanalysis, extended X-ray absorption fine structure (EXAFS) spectroscopy, Mössbauer spectroscopy, and porosimetry. Investigations have been performed on samples prepared according to the original technology at the St. Petersburg State Institute of Technology (Technical University) (SPbSTI (TU)) and on four commercial cathode materials. It has been established that there is a correlation between the nanostructured morphology of the cathode materials, their chemical composition, and electrochemical capacity. It has been found that the internal resistance of the LiFePO₄ cathode material is linearly dependent on the diffusion coefficient of lithium ions. The valence state and local coordination of Fe ions have been studied using the ⁵⁷Fe Mössbauer effect. It has been shown that more than 90% of the iron ions are in the valence state Fe²⁺. Based on the data available in the literature on the methods of synthesizing LiFePO₄ and data on the diagnosis of the studied samples, conclusions have been drawn about a modification of the synthesis for producing high-quality cathode materials for Li-ion batteries.     

Synthesis and electrochemical characterization of InSn4 and InSn4/C as new anode materials for lithium-ion batteries

The InSn₄ intermetallic powders are synthesized via carbothermal reduction route from In₂O₃ and SnO₂. The reaction possibility is estimated by thermodynamic calculation. Pure InSn₄ intermetallic powders with spherical morphology can be obtained at 900 °C in flowing nitrogen. The micro-sized InSn₄ particle is actually composed of a large number of nano-sized grains with polycrystalline and loose structure. The synthesized InSn₄ shows high reversible specific capacity (ca. 500 mAhg^?1) and a good cycling performance as an anode material for lithium-ion batteries. Coating InSn₄ with carbon can increase the reversible specific capacity and improve significantly the rate capability. The InSn₄/C composite displays a stable specific capacity of ca. 600 mAhg^?1. In consideration of the simple and moderate synthesis route and the mass productive feature, the InSn₄/C composite is a promising anode material for lithium-ion batteries.     

Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

We present a review of the structural properties of LiFePO₄. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries.     

Rapid preparation of high electrochemical performance LiFePO4/C composite cathode material with an ultrasonic-intensified micro-impinging jetting reactor

A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO₄ particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO₄ nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO₄ nano precursor particles and the electrochemical properties of amalgamated LiFePO₄/C have been investigated. Additionally, the effects of the reactant concentration (C = 0.5, 1.0 and 1.5 mol L⁻¹), and volumetric flow rate (V = 17.15, 51.44, and 85.74 mL min⁻¹) on synthesis of FePO₄·2H₂O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO₄ nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6 nm, an average pore size of 15.2 nm, and a specific surface area of 134.54 m² g⁻¹ when the reactant concentration and volumetric flow rate are 1.0 mol L⁻¹ and 85.74 mL min⁻¹ respectively. The amalgamated LiFePO₄/C composites can deliver good electrochemical performance with discharge capacities of 156.7 mA h g⁻¹ at 0.1 C, and exhibit 138.0 mA h g⁻¹ after 100 cycles at 0.5 C, which is 95.3% of the initial discharge capacity.     

Preparation and electrochemical performance of bramble-like ZnO array as anode materials for lithium-ion batteries

A bramble-like ZnO array with a special three-dimensional (3D) nanostructure was successfully fabricated on Zn foil through a facile two-step hydrothermal process. A possible growth mechanism of the bramble-like ZnO array was proposed. In the first step of hydrothermal process, the crystal nucleus of Zn(OH) ₄ ^2? generated by the zinc atoms and OH^? ions fold together preferentially along the positive polar (0001) to form the needle-like ZnO array. In the second step of hydrothermal process, the crystal nuclei of Zn(OH) ₄ ^2? adjust their posture to keep their c-axes vertical to the perching sites due to the sufficient environmental force and further grow preferentially along the (0001) direction so as to form bramble-like ZnO array. The electrochemical properties of the needle- and bramble-like ZnO arrays as anode materials for lithium-ion batteries were investigated and compared. The results show that the bramble-like ZnO material exhibits much better lithium storage properties than the needle-like ZnO sample. Reasons for the enhanced electrochemical performance of the bramble-like ZnO material were investigated.     

Enhanced electrochemical performance of La- and Zn-co-doped LiMn2O4 spinel as the cathode material for lithium-ion batteries

We report on the nanoparticle uptake into MCF10A neoT and PC-3 cells using flow cytometry, confocal microscopy, SQUID magnetometry, and transmission electron microscopy. The aim was to evaluate the influence of the nanoparticles?? surface charge on the uptake efficiency. The surface of the superparamagnetic, silica-coated, maghemite nanoparticles was modified using amino functionalization for the positive surface charge (CNPs), and carboxyl functionalization for the negative surface charge (ANPs). The CNPs and ANPs exhibited no significant cytotoxicity in concentrations up to 500???g/cm³ in 24?h. The CNPs, bound to a plasma membrane, were intensely phagocytosed, while the ANPs entered cells through fluid-phase endocytosis in a lower internalization degree. The ANPs and CNPs were shown to be co-localized with a specific lysosomal marker, thus confirming their presence in lysosomes. We showed that tailoring the surface charge of the nanoparticles has a great impact on their internalization.     

Synthesis and electrochemical performance of carbon-coated LiMnBO<Subscript>3</Subscript> as cathode materials for lithium-ion batteries

Carbon-coated LiMnBO₃/C is synthesized by a sol-gel method using polyethylene glycol 6000 (PEG-6000) as carbon source. The influences of different sintering temperatures on the crystal structure, morphology, and electrochemical performance of LiMnBO₃/C composites are investigated. XRD results indicate that the samples consist of the monoclinic phase LiMnBO₃ (m-LiMnBO₃) and the hexagonal phase LiMnBO₃ (h-LiMnBO₃), and the amount of m-LiMnBO₃ is reduced and the h-LiMnBO₃ is increased with the increasing sintering temperature. The particle size of the samples is about 500 nm, and the surface of the particles is coated with a thick amorphous carbon layer. The LiMnBO₃/C synthesized at 750 °C exhibits the initial discharge capacities of 213.4, 170.8, and 109.7 mAh g^?1 at 0.025, 0.05, and 0.5 C rates, respectively, and shows better cycling performance than that of bare LiMnBO₃. The enhanced electrochemical performance might be largely attributed to the uniformly coated carbon layers from decomposition of the PEG-6000.     

Synthesis and electrochemical performance of carbon-coated LiCoBO<Subscript>3</Subscript> as cathode materials for lithium-ion batteries

Carbon-coated LiCoBO₃ (LiCoBO₃/C) is prepared by sol-gel method and polyethylene glycol 6000 (PEG-6000) is chosen as carbon source. The LiCoBO₃/C sample exhibits an initial discharge capacity of 76.7 mAh g^?1 at 0.1 C, and it can deliver a discharge capacity of 65.9 mAh g^?1 after 50 cycles, while the LiCoBO₃ sample only presents a first discharge capacity of 34.3 and 16.8 mAh g^?1 at the 50th cycle, LiCoBO₃/C sample shows better cycling performance than that of LiCoBO₃. The improved electrochemical properties could be mainly ascribed to the conductive carbon network and the reduced particle size of the LiCoBO₃ powders. Electrochemical impedance spectroscopy (EIS) results confirm that carbon coating decreases the charge transfer resistance and improve the electrochemical reaction kinetics.     

Synthesis and characterization of LiFePO4/3-dimensional carbon nanostructure composites as possible cathode materials for Li-ion batteries

Composites of three-dimensional (3D) carbon nanostructures coated with olivine-structured lithium iron phosphates (LiFePO₄) as cathode materials for lithium ion batteries have been prepared through a Pechini-assisted reversed polyol process for the first time. The coating has been successfully performed on nonfunctionalized commercially available 3D carbon used as catalysts. Thermal analysis revealed no phase transitions till crystallization occurred at 579 °C. Morphological investigation of the prepared composites showed a very good quality of the coating on the 3D carbon structures. A great enhancement of the crystallinity of the olivine structure and of the composites was revealed by the structural investigation performed on pure LiFePO₄ and composites after annealing at 600 °C for 10 h under nitrogen atmosphere. The cyclic voltammetry curves of the composites show well-defined peaks and smaller value of the polarization overpotential indicating an enhancement of electrode reaction reversibility compared to the LiFePO₄ phase.     

Synthesis and electrochemical performance of LiNi0.6Co0.2Mn0.2O2/reduced graphene oxide cathode materials for lithium-ion batteries

A LiNi_0.6Co_0.2Mn_0.2O₂/reduced graphene oxide (RGO) composite with RGO content of 1.2 % was prepared by a simple spray-drying method instead of high-energy ball milling method. The composite has been characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive spectroscopy, and charge/discharge test. The X-ray diffractometry result showed that composite possessed a typical hexagonal structure. The RGO sheets served as efficient electronically conductive frameworks benefitting from its 2D structure and outstanding electronic conductivity. The scanning electron microscope and transmission electron microscopy verified that LiNi_0.6Co_0.2Mn_0.2O₂ particles were wrapped with RGO sheets, which facilitated electronic conductivity between particles. The electrochemical results indicated that composite delivered a higher discharge capacity at various discharge rates. The cycling performance was also evaluated. The composite exhibited better cycling performance than pristine sample. Electrochemical impedance spectroscopy showed that the RGO can greatly reduce the charge transfer resistance. The results here gave clear evidence of RGO to improve electrochemical performance.     

Improved of cathode performance of LiFePO<Subscript>4</Subscript>/C composite using different carboxylic acids as carbon sources for lithium-ion batteries

Among the several materials under development for use as a cathodes in lithium-ion batteries olivine-type LiFePO₄ is one of the most promising cathode material. However, its poor conductivity and low lithium-ion diffusion limits its practical application. In this study, we report seven different carboxylic acids used to synthesize LiFePO₄/C composite, and influences of carbon sources on electrochemical performance were intensively studied. The structure and electrochemical properties of the LiFePO₄/C were characterized by X-ray diffraction, scanning electron microscopy, electrical conductivity, and galvanostatic charge–discharge measurements. Among the materials studied, the sample E with tartaric acid as carbon source exhibited the best cell performance with a maximum discharge capacity of 160 mAh g⁻¹ at a 0.1 C-rate. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.     

Effect of pyrolytic polyacrylonitrile on electrochemical performance of Si/graphite composite anode for lithium-ion batteries

The silicon/graphite (Si/G) composite was prepared using pyrolytic polyacrylonitrile (PAN) as carbon precursor, which is a nitrogen-doped carbon that provides efficient pathway for electron transfer. The combination of flake graphite and pyrolytic carbon layer accommodates the large volume expansion of Si during discharge-charge process. The Si/G composite was synthesized via cost-effective liquid solidification followed by carbonization process. The effect of PAN content on electrochemical performance of composites was investigated. The composite containing 40 wt% PAN exhibits a relatively better rate capability and cycle performance than others. It exhibits initial reversible specific capacity of 793.6 mAh g^?1 at a current density of 100 mA g^?1. High capacity of 661 mAh g^?1 can be reached after 50 cycles at current density of 500 mA g^?1.     

Solvothermal synthesis and electrochemical performance of Ag-doped V6O13 as cathode material for lithium-ion battery

For the first time, belt-like V₆O₁₃ precursor was synthesized via a simple solvothermal method. Rod-like Ag-doped V₆O₁₃ was successfully synthesized by this method followed by heating at 350 °C. Both crystal domain size, electronic conductivity, and the lithium diffusion coefficient of the Ag-doped V₆O₁₃ samples are influenced by the added amount of AgNO₃. When the amount of AgNO₃ is 0.008 g, the product is rod-like particles, which are 0.1–0.3 μm wide and 1–2 μm long, and exhibits the best electrochemical performance. The enhanced electrochemical performance originates from its higher total conductivity, higher lithium diffusion coefficient, and better structural reversibility.     

Effect of carbon coating on the electrochemical performance of LiFePO<Subscript>4</Subscript>/C as cathode materials for aqueous electrolyte lithium-ion battery

Organic electrolyte is widely used for lithium-ion rechargeable batteries but might cause flammable fumes or fire due to improper use such as overcharge or short circuit. That weakness encourages the development of tools and materials which are cheap and environmental friendly for rechargeable lithium-ion batteries with aqueous electrolyte. Lithium iron phosphate (LiFePO₄) with olivine structure is a potential candidate to be used as the cathode in aqueous electrolyte lithium-ion battery. However, LiFePO₄ has a low electronic conductivity compared to other cathodes. Conductive coating of LiFePO₄ was applied to improve the conductivity using sucrose as carbon source by heating to 600 °C for 3 h on an Argon atmosphere. The carbon-coated LiFePO₄ (LiFePO₄/C) was successfully prepared with three variations of the weight percentage of carbon. From the cyclic voltammetry, the addition of carbon coatings could improve the stability of cell battery in aqueous electrolyte. The result of galvanostatic charge/discharge shows that 9 % carbon exhibits the best result with the first specific discharge capacity of 13.3 mAh g^?1 and capacity fading by 2.2 % after 100 cycles. Although carbon coating enhances the conductivity of LiFePO₄, excessive addition of carbon could degrade the capacity of LiFePO₄.