Enhanced electrochemical properties of LiMnPO4/C via doping with Cu

Li_0.98Cu_0.01MnPO₄/C composite cathode materials for lithium ion battery are synthesized by sol-gel method followed by heat treatment in the air. Field-emission scanning electron microscopy measurements show that both firing temperature and carbon content affect the morphology of the end products. X-ray powder diffraction analysis indicates that the samples are olivine-structured. The galvanostatic charge?Cdischarge results show that the optimal firing temperature registers 500°C and that the electrochemical performances of Li_0.98Cu_0.01MnPO₄/C are improved by elevating its carbon amount. The cyclic ability and rate performances of LiMnPO₄ are greatly improved by doping Cu.     

Enhanced high-temperature performances of LiMn2O4 cathode by LiMnPO4 coating

Ionics - LiMnPO4/LiMn2O4 (LMP/LMO) composite cathodes with LMP coating on the surface of LMO were synthesized by hydrothermal method at 180 °C for 10 h. The crystal...     

Enhanced rate performance of polypyrrole-coated sulfur/MWCNT cathode material: a kinetic study by electrochemical impedance spectroscopy

Lithium-sulfur batteries have a poor cyclability and inferior rate capability due to the shuttle effect of lithium polysulfides. To solve these problems, a sulfur-coated MWCNT composite (S/MWCNT) was coated with conductive polypyrrole (PPy) to trap the polysulfides and facilitate charge and lithium ion transport. From the contact angle measurement, it is found that the PPy coating improves the wettability of the S/MWCNT composite. Compared with the bare S/MWCNT composite, the PPy-coated S/MWCNT composite cathode exhibited improved cycle stability and high-rate performance. A reversible discharge capacity of 671 mAh g^?1 was maintained after 50 cycles at 3 C for the PPy-coated composite. The effect of PPy coating on kinetic property was investigated by electrochemical impedance spectroscopy (EIS). The electrolyte resistance, surface film resistance, charge transfer resistance, lithium ion diffusion coefficient, and exchange current density were evaluated from the EIS measurements. The EIS results reveal that the PPy coating increases both Li ion diffusion into the cathode and exchange current density. The as-prepared PPy-coated S/MWCNT composite can be considered to be a promising candidate for high capacity and high-rate performance cathode material.     

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.     

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.     

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.     

Enhanced electrochemical performance of lithium vanadium phosphate as cathode by LiBOB/LiTFSI with additive in EC/EMC

A series of Li₃V₂(PO₄)₃/C (LVP/C) samples with monoclinic structure indexed to P2₁/n space group were synthesized using V₂O₃ as vanadium source by solid state reaction method by different sintering temperatures. It was found that the LVP/C sintered at 750 °C with a carbon content 3 wt.% was the optimum condition for this synthesis. The structural, morphological, superficial, and textural properties of LVP/C were characterized by XRD, SEM, TEM, and XPS. The electrochemical performance was evaluated by galvanostatic charge–discharge cycling using new high voltage electrolyte. The optimized cell delivered an initial discharge capacity of 187 mAh g^?1 in the higher cut-off voltage of 3.0–4.8 V vs. Li⁺/Li⁰ at 0.2 C rate, with a capacity retention of 88 %, 89 %, and 61 % after 50 cycles discharging at 1 C, 2 C, and 4 C, respectively. The capacity can be almost recovered at 0.5 C after long cycles. The excellent stability is contributed to the new high-voltage electrolyte.     

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.     

Synthesis and electrochemical properties of nanostructured Li2FeSiO4/C cathode material for Li-ion batteries

Nanostructured Li₂FeSiO₄/C was synthesized by high-energy ball-milling and the amorphous citrate-assisted techniques. Similar redox behaviour is observed for samples prepared by the amorphous citrate-assisted route followed by a 4 h heat treatment: 0.3 V polarization and more sloping behaviour was observed when cycling between 2.0 V and 3.7 V at 60 °C; lower capacity fade is also observed compared to Li₂FeSiO₄/C prepared by the solid-state reaction technique. A discharge capacity of 102 mA h g^− 1 is obtained for samples prepared by the high-energy ball-milling method, while capacities decrease from 95 to 77 mA h g^− 1 using the amorphous citrate method for heat-treatment times increasing successively from 4 h to 18 h.     

Modified carbothermal synthesis and electrochemical performance of LiFePO4/C composite as cathode materials for lithium-ion batteries

LiFePO₄/C active materials were synthesized via a modified carbothermal method, with a low raw material cost and comparatively simple synthesis process. Rheological phase technology was introduced to synthesize the precursor, which effectively decreased the calcination temperature and time. The LiFePO₄/C composite synthesized at 700 °C for 12 h exhibited an optimal performance, with a specific capacity about 130 mAh g^?1 at 0.2C, and 70 mAh g^?1 at 20C, respectively. It also showed an excellent capacity retention ratio of 96 % after 30 times charge–discharge cycles at 20C. EIS was applied to further analyze the effect of the synthesis process parameters. The as-synthesized LiFePO₄/C composite exhibited better high-rate performance as compared to the commercial LiFePO₄ product, which implied that the as-synthesized LiFePO₄/C composite was a promising candidate used in the batteries for applications in EVs and HEVs.     

Advanced electrochemical performance of LiMn1.4Cr0.2Ni0.4O4 as 5 V cathode material by citric-acid-assisted method

Spinel LiMn₂O₄ and LiMn_1.4Cr_0.2Ni_0.4O₄ cathode materials were successfully synthesized by the citric-acid-assisted sol-gel method with ultrasonic irradiation stirring. The structure and electrochemical performance of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometer, cyclic voltamogram (CV) and the galvanostatic charge-discharge test in detail. XRD shows that all the samples have high phase purity, and the powders are well crystallized. SEM exhibits that LiMn_1.4Cr_0.2Ni_0.4O₄ has more uniform cubic-structure morphology than that of LiMn₂O₄. EDX reveals that a small amount of Mn³⁺ still exists in LiMn_1.4Cr_0.2Ni_0.4O₄. The galvanostatic charge-discharge test indicates that the initial discharge capacities for the LiMn_1.4Cr_0.2Ni_0.4O₄ and LiMn₂O₄ at 0.15 C discharge rates are 130.8 and 130.2 mAh g⁻¹, respectively. After 50 cycles, their capacity are 94.1% and 85.1%, respectively. The CV curve implies that Ni and Cr dual substitutions are beneficial to the reversible intercalation and deintercalation of Li⁺, and suppress Mn³⁺ generation at high temperatures and provide improved structural stability.     

Enhanced electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode material co-coated by graphene/TiO2

The electrochemical performances of LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) layered cathode material, such as poor rate capacity and cycling stability caused by undesirable intrinsic conductivity and low rate of lithium ion transportation, are not fairly good especially at elevated rate and cut-off voltage. To improve these properties, in this study, the co-coating layer of graphene and TiO₂ was constructed on NCM523 surface. The graphene/TiO₂ coating layer could effectively prevent hydrofluoric acid (HF) attacks, suppress the side reaction, accelerate the lithium ion diffusion and facilitate the electron migration. The enhancement of cycle performance and rate capacity was contributed to the uniform co-modified surface, interacting each other and thus exhibiting synergistic effects.     

Structure and electrochemical performance of LiCoO2 cathode material in different voltage ranges

LiCoO₂ sample prepared by high-temperature solid state calcination shows a typical hexagonal structure with a single phase and fine particle size distribution. The high-voltage electrolyte with additive fluoroethylene carbonate (FEC) has been used. Electrochemical results show that the initial discharge capacities of the prepared LiCoO₂ cathode are 157.7, 169.5, 191.0, and 217.5 mAh g^?1 in the voltage ranges of 3.0–4.3, 3.0–4.4, 3.0–4.5, and 3.0–4.6 V, respectively. The capacity increases, while the initial coulombic efficiency and capacity retention decrease with increasing the charge cutoff voltage. The capacity retention is only 10.4 % after 200 cycles at 1C rate in the voltage range of 3.0–4.6 V. X-ray diffraction measurements confirm structural changes of the layered material in the different voltage ranges. A phase transition from the O3 to the H1-3 phase can be observed when LiCoO₂ is charged above 4.5 V. The AC impedance analysis indicates that the resistances (R _(sf+b), R _ct) of the prepared LiCoO₂ rapidly increase when the cell is charged to higher voltage. The amount of dissolved Co into the electrolyte also greatly increases with increasing the charge cutoff voltage.     

Synthesis and electrochemical studies of LiMn1−xCuXO4 cathode material

LiMn_1.8Cu_0.2O₄ was investigated in order to improve the electrochemical properties of LiMn₂O₄. We report the synthesis and characterization of materials prepared by solid-state reaction. The structural properties evaluated by the X-ray diffraction and vibrational spectroscopy show that a single phase was formed. Conductivity of LiMn_1.8Cu_0.2O₄ cathode is found to be 8×10⁻⁶ S/cm at 25 °C. The cyclic voltammetry data shows the reversibility of the electrode material. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Electrochemical performance of Mo-doped LiFePO4/C composites prepared by two-step solid-state reaction

To improve the performance of LiFePO₄, LiFe_1?x Mo _x PO₄/C (x?=?0, 0.005, 0.010, 0.015, 0.020, 0.025) cathode materials were synthesized via two-step ball milling solid-state reaction. The prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectra, and galvanostatic charge–discharge test. It is apparent from XRD analysis that Mo doping enlarges the interplanar distance of crystal plane parallel to [010] direction in LiFePO₄. In other words, it widens one-dimensional diffusion channels of Li⁺ along the [010] direction. The results of electrochemical test indicate that the LiFe_0.99Mo_0.01PO₄/C composite exhibits a discharge capacity of 144.8 mAh g^?1 at 1 C rate, a decreased charge transfer resistance of 162.4 Ω and better reversibility of electrode reactions. The present synthesis route is promising and practical for the preparation of LiFePO₄ materials.     

Enhanced photoelectrochemical performance of Ti-doped hematite thin films prepared by the sol-gel method

Ti-doped α-Fe₂O₃ thin films were successfully prepared on FTO substrates by the sol-gel route. Hematite film was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The XRD data showed α-Fe₂O₃ had a preferred (1 1 0) orientation which belonged to the rhombohedral system. Interestingly, the grains turned into worm-like shape after annealed at high temperature. The IPCE could reach 32.6% at 400 nm without any additional potential vs. SCE. Titanium in the lattice can affect the photo electro chemical performance positively by increasing the conductivity of the thin film. So the excited electrons and holes could live longer, rather than recombining with each other rapidly as undoped hematite. And the efficient carrier density on the Ti-doped anode surface was higher than the undoped anode, which contribute to the well PEC performance.     

Synthesis and structural investigation of Pd/Ag bimetallic nanoparticles prepared by the solvothermal method

Pd/Ag bimetallic nanoparticles have been synthesized successfully by reducing PdCl₂ and AgNO₃ mixture in ethylene glycol solution using the solvothermal method. The prepared samples have been characterized by UV–vis, XRD, TEM, HRTEM, EDS, and XPS, respectively. Moreover, the bimetallic particles possess alloy and core-shell structure from the HRTEM images. Here, the lattice fringe spacing of Pd/Ag bimetallic nanoparticles corresponds to its (111) plane, which is between that of the Pd and Ag nanoparticles prepared under the same conditions. Furthermore, the possible formation mechanism and factors influencing the formation of Pd/Ag bimetallic nanoparticles, such as reaction temperature and time, have also been investigated.     

Enhanced conductivity and electrical relaxation studies of carbon-coated LiMnPO4 nanorods

Lithium manganese phosphate (LiMnPO₄) nanorods were synthesized using the modified polyol method. Polyvinylpyrrolidone was used as a stabilizer to control the shape and size of LiMnPO₄ nanorods. Resin coating process was used to coat the carbon over the LiMnPO₄ nanorods. X-ray diffraction and Fourier transform infrared spectroscopy results showed the formation of LiMnPO₄ crystalline phase. The TEM image shows a uniform coating of the nano size (2.3 nm) carbon over the surface of LiMnPO₄ nanorods and the EDS spectrum of the carbon-coated LiMnPO₄ nanorods confirming the presence of carbon element along with the other Mn, P, and O elements. Impedance measurements were made on pure and carbon-coated LiMnPO₄ nanorods, and their conductivities were evaluated by analyzing the measured impedance data using the WinFIT software. More than two orders of magnitude of conductivity enhancement was observed in the carbon-coated LiMnPO₄ nanorods compared to pure ones, and the conductivity enhancement may be attributed to the presence of carbon over LiMnPO₄ nanorods. Temperature dependence of conductivity and ac conductivity were calculated using impedance data of pure and carbon-coated LiMnPO₄ nanorods. CR2032 type lithium ion coin cells were fabricated using pure and carbon-coated LiMnPO₄ nanorods and characterized by measuring charge–discharge cycles between 2.9 and 4.5 V at room temperature. More than 25 % of improved capacity was achieved in the carbon-coated LiMnPO₄ nanorods when compared to pure ones synthesized using modified polyol and resin coating processes.     

Particle size distribution and electrochemical properties of LiFePO4 prepared by a freeze-drying method

The electrochemical performance of carbon-coated nanocrystalline LiFePO₄ prepared by a freeze-drying method is examined. This method is based on the thermal decomposition of homogeneous phosphate-formate precursors. Structural and morphological characterization of LiFePO₄ is carried out by powder XRD, BET measurements, SEM and XPS analyses. The electrochemical behaviour is tested in model lithium cells using galvanostatic mode. By changing the solution concentration, the freeze-drying method allows preparing LiFePO₄ with mean particle sizes between 60 and 100 nm and different particle size distributions. The content of carbon appearing mainly on the particle surface depends on both the solution concentration and the annealing temperature. The effect of particle size distribution on the voltage profile of LiFePO₄ is also demonstrated. The specific capacity is mainly determined by the amount of carbon deposited on the particle surfaces.