Electrochemical performance of LiFePO4/C synthesized by solid state reaction using different lithium and iron sources

LiFePO₄/C cathode materials were prepared from different lithium and iron sources, using glucose as the carbon source and the reducing agent, via a solid state reaction. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammetry (CV). The results showed that the LiFePO₄/C is olivine-type phase, and composed of relatively large particles of about 400 nm and some nano-sized particles, which favor the electronic conductivity. The LiFePO₄/C cathode material synthesized from Li₂CO₃ and Fe₂O₃ had the smallest particles and the highest uniformity. It delivered the capacity of 145.8 mA h/g at 0.2 C, and had good reversibility and high capacity retention. The precursor of LiFePO₄/C was characterized by thermogravimetry (TG) to discuss the crystallization formation mechanism of LiFePO₄.     

Stable cycle-life properties of Ti-doped LiFePO4 compounds synthesized by co-precipitation and normal temperature reduction method

Submicron-sized LiFePO₄ and Ti-doped LiFePO₄ cathode materials were synthesized by a reformative co-precipitation and normal temperature reduction method, for which Ti ions were added in the process of preparing precursors to pursue a kind of sufficient and homogenous doping way. ICP and XRD analyses indicate that Ti ions were sufficiently doped in LiFePO₄ and did not alter its crystal structure. It is noted that higher Ti ions doping levels are conducive to electrochemical performance of LiFePO₄, especially on the aspect of stable cycle-life at higher C rates. The sample doped with 3 at% Ti shows the most impressive cycling performance, even after 100 cycles, discharge capacity of 133 mAh g⁻¹ was obtained (102.3% of its initial value) at 1C rate, and the discharge decreased little from 124 to 120 mAh g⁻¹ (96.8% of its initial value) at 2C rate.     

Structural and electrochemical properties of Nd-doped LiFePO4/C prepared without using inert gas

To further improve the electrochemical performance of LiFePO₄/C, Nd doping has been adopted for cathode material of the lithium ion batteries. The Nd-doped LiFePO₄/C cathode was synthesized by a novel solid-state reaction method at 750 °C without using inert gas. The Li_0.99Nd_0.01FePO₄/C composite has been systematically characterized by X-ray diffraction, EDS, SEM, TEM, charge/discharge test, electrochemical impedance spectroscopy and cyclic stability. The results indicate that the prepared sample has olivine structure and the Nd³⁺ and carbon modification do not affect the structure of the sample but improve its kinetics in terms of discharge capacity and rate capability. The Li_0.99Nd_0.01FePO₄/C powder exhibited a specific initial discharge capacity of about 161 mAh g^− 1 at 0.1 C rate, as compared to 143 mAh g^− 1 of LiFePO₄/C. At a high rate of 2 C, the discharge capacity of Li_0.99Nd_0.01FePO₄/C still attained to 115 mAh g^− 1 at the end of 20 cycles. EIS results indicate that the charge transfer resistance of LiFePO₄/C decreases greatly after Nd doping.     

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.     

Effects of nano-carbon webs on the electrochemical properties in LiFePO4/C composite

LiFePO₄/C composite is one of ways to surmount the lower electrical conductivity of LiFePO₄. In this paper, we suggest a new type of LiFePO₄/C composite in which amorphous nano-carbon webs are wrapping and connecting LiFePO₄ particles. This type of composite was obtained by adapting a new liquid-based powder preparation method, that is, all raw materials (LiFePO₄ and carbon precursor materials) were dissolved in liquid and solidified. This composite was very effective in enhancing the electrochemical properties such as capacity and rate capability. Even as high as at 400 m Ag⁻¹ current density, a capacity of about 105 m Ahg⁻¹ was obtained at 25 °C.     

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.     

Synthesis of spherical LiFePO4/C via Ni doping

Spherical LiFePO₄/C powders were synthesized by the conventional solid-state reaction method via Ni doping. Low-cost asphalt was used as both the reduction agent and the carbon source. An Ni-doped spherical LiFePO₄/C composite exhibited better electrochemical performances compared to an un-doped one. It presented an initial discharge capacity of 161 mAhg⁻¹ at 0.1 C rate (the theoretical capacity of LiFePO₄ with 5 wt% carbon is about 161 mAhg⁻¹). After 50 cycles at 0.5 C rate, its capacity remained 137 mAhg⁻¹ (100% of the initial capacity) compared to 115 mAhg⁻¹ (92% of the initial capacity) for an un-doped one. The electrochemical impedance spectroscopy analysis and cyclic voltammograms results revealed that Ni doping could decrease the resistance of LiFePO₄/C composite electrode drastically and improve its reversibility.     

Surface modification by silver coating for improving electrochemical properties of LiFePO4

LiFePO₄ is a potential candidate for the cathode material of the lithium secondary battery. Fine particle LiFePO₄ was synthesized by the simple co-precipitation method, and aqueous coating on the LiFePO₄ was tried using silver nitrate solution in order to increase electronic conductivity. Highly dispersed silver on the particles enhances the electronic conductivity and increases the capacity. The electrochemical properties of the silver coated LiFePO₄ with the various current densities are analogous to those of highly conductive LiFePO₄. The silver coating can be a promising tool to preserve the capacity even at the high current densities.     

Recent developments in the doping and surface modification of LiFePO4 as cathode material for power lithium ion battery

Lithium ion batteries have become attractive for portable devices due to their higher energy density compared to other systems. With a growing interest to develop rechargeable batteries for electric vehicles, lithium iron phosphate (LiFePO₄) is considered to replace the currently used LiCoO₂ cathodes in lithium ion cells. LiFePO₄ is a technically important cathode material for new-generation power lithium ion battery applications because of its abundance in raw materials, environmental friendliness, perfect cycling performance, and safety characteristics. However, the commercial use of LiFePO₄ cathode material has been hindered to date by their low electronic conductivity. This review highlights the recent progress in improving and understanding the electrochemical performance like the rate ability and cycling performance of LiFePO₄ cathode. This review sums up some important researches related to LiFePO₄ cathode material, including doping and coating on surface. Doping elements with coating conductive film is an effective way to improve its rate ability.     

Improved performance of porous LiFePO4/C as lithium battery cathode processed by high energy milling comparison with conventional ball milling

Porous LiFePO₄ is synthesized and coated with amorphous carbon by using high energy nano-mill (HENM) processed solid-state reaction method. FeCl₃ (38%) containing water solution which is originated from pickling of steel scrap (waste liquid) is used as a source material in this study. The result indicates that LiFePO₄ powders are well coated with the amorphous carbon. HENM process successfully produces the porous LiFePO₄ with homogeneously distributed pores and a well networked carbon web, which delivers an enhanced electrochemical rate capability. HENM process is incorporated as an effective route for reducing particle size, distributing particle homogeneously and averting agglomeration of particles of precursor in this study. X-ray diffraction, scanning electron microscopy with elemental mapping, transmission electron microscopy with selected area (electron) diffraction, Raman spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge are employed to characterize the final product. Electrochemical measurement shows that the synthesized LiFePO₄/C composite cathode delivers an initial discharge capacity of 161 mAhg⁻¹ at 0.1C-rate between 4.2 and 2.5 V. Remarkably, the cathode delivers 101.9 mAhg⁻¹ at high charge/discharge rate (10 C).     

A lithium ion battery using nanostructured Sn-C anode, LiFePO4 cathode and polyethylene oxide-based electrolyte

In this work we report a lithium ion battery based on a nanostructured Sn-C anode, an improved lithium iron phosphate, LiFePO₄, cathode and a polyethylene oxide-based electrolyte. The battery has a solid-like configuration, high safety and can operate at room temperature with a stable capacity of the order of 120 mAh g^− 1 at a voltage of 2.8 V. These properties candidate the battery as very appealing energy accumulation system suitable for environmentally friendly, safe, applications.     

Porous LiNi0.75Co0.25O2 microspheres prepared via a hydrothermal process as cathode material for lithium ion batteries

Porous LiNi_0.75Co_0.25O₂ microspheres are successfully prepared by a simple hydrothermal process by using H[Ni_0.75Co_0.25OOH]₃ and LiOH as starting materials in the presence of urea for the first time. The synthesized samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (S_BET), and electrochemical performance. The synthesized LiNi_0.75Co_0.25O₂ has a good electrochemical performance with an initial discharge capacity of 169.3 mA g⁻¹ and good capacity retention of 96.7% after 50 cycles at 0.2 C (25 mA g⁻¹). The electrochemical lithium ion insertion/extraction process is quite reversible even at 5 C. Furthermore, the structure in the charge-discharge process is stable and the impedance increased slowly during cycling.     

An efficient process to fabricate spherical hierarchical LiFePO<Subscript>4</Subscript>/C cathode composites with controllable coating thickness

Hierarchical lithium iron phosphate/carbon (LiFePO₄/C) microspheres were fabricated successfully using a facile spray drying-assisted coprecipitation method. A relatively short calcination time and a relatively low calcination temperature were adopted to prepare the hierarchical LiFePO₄/C microspheres. The hierarchical microspheres consisted of nanoparticles with a uniform coating of amorphous carbon. The thickness of the carbon layer was controlled by the addition of glucose. The hierarchical LiFePO₄/C microspheres exhibited a high tap density and a large specific surface area. The electrochemical properties of the sample were investigated. The sample exhibited a better rate capability and a better cyclability than the coral-like LiFePO₄/C cathode material, and these were ascribed to the highly uniform carbon coating and the self-assembled nanoparticles.     

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~?200 °C), ionic conductivity (6.42?×?10^?4 S cm^?1), lithium ion conductivity (1.40?×?10^?4 S cm^?1 at 30 °C), and wide electrochemical stability window (~?4.10 V versus Li/Li⁺ at 30 °C). Furthermore, the surface of LiFePO₄ cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO₄ cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO₄. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g^?1 for graphene oxide-coated LiFePO₄ and without coated LiFePO₄ at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO₄ cathode after coating with graphene oxide.     

Sc2O3-W matrix impregnated cathode with spherical grains

Sc₂O₃-W matrix cathodes have been prepared by using a liquid-liquid doping method combined with high-temperature sintering. The microstructure and physical behavior of active substances of scandia-doped tungsten matrix and impregnated cathode has been studied by SEM and AES methods. The results show that the matrix has a homogeneous structure composed of W grains with spherical shape and superfine Sc₂O₃ particles dispersed uniformly over and among W grains. After impregnation, this Sc-type impregnated cathode has high emission capability. Space-charge-limited current density could reach 52 A/cm² at 850 °C_b. The high emission results from a Ba-Sc-O active layer with a thickness of about 80 nm, which is formed at the cathode surface during the activation period. Both the decrease of the thickness of active surface layer and the decrease of the content of Sc at the surface could lead to the degradation of current density during operation.     

A carbon–LiFePO<Subscript>4</Subscript> nanocomposite as high-performance cathode material for lithium-ion batteries

A cathode material of an electrically conducting carbon–LiFePO₄ nanocomposite is synthesized by wet ball milling and spray drying of precursor powders prior to a solid-state reaction. The structural characterization shows that the composite is composed of LiFePO₄ crystals and 4.8 wt.% amorphous carbon. Galvanostatic charge/discharge measurements indicate that the composite exhibits a superior high energy and high cycling stability. This composite delivers a discharge capacity of 159.1 mAh g⁻¹ at 0.1 C, 150.8 mAh g⁻¹ at 1 C, and 140.1 mAh g⁻¹ at 2 C rate. The capacity retention of 99% is achieved after 200 cycles at 2 C. The 18,650 cylindrical batteries are assembled using the composite as cathode materials and demonstrate the capacity of 1,400 mAh and the capacity retention of 97% after 100 cycles at 1 C. These results reveal that the as-prepared LiFePO₄–carbon composite is one of the promising cathode materials for high-performance, advanced lithium-ion batteries directed to the hybrid electric vehicle and pure electric vehicle markets.     

LiFePO<Subscript>4</Subscript>/C with high capacity synthesized by carbothermal reduction method

The olivine-type LiFePO₄/C cathode materials were prepared via carbothermal reduction method using cheap Fe₂O₃ as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO₄ particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g⁻¹ at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g⁻¹ at 0.5C rate.     

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.     

碳热还原法制备V2O3-C双层包覆磷酸铁锂及其电化学性能

通过V₂O₅的碳热还原反应制备了具有优异倍率性能和循环稳定性的V₂O₃-C双层包覆的磷酸铁锂正极材料. 粉末X射线衍射、元素分析、高分辨投射电镜和拉曼光谱研究表明V2O3相与碳层共包覆于磷酸铁锂颗粒表面. 在V₂O₅的碳热还原反应后,碳含量明显降低,但石墨化程度未发生明显改变. 电化学测试结果表明少量V₂O₃显著改善了磷酸铁锂正极材料的倍率性能和高温循环性能,包含1%氧化钒的复合正极材料在0.2 C放电容量为167 mAh/g,5 C时放电容量为129 mAh/g,并且循环稳定性优异;在55 oC和1 C时放电容量为151 mAh/g,循环100次后无明显容量衰减.     

Investigations on Pr1.6Sr0.4NiO4-YSZ-Ag composite cathode for solid oxide fuel cells

Ag-network was successfully deposited by VA-EP (vacuum assisted electroless plating) method on Pr_1.6Sr_0.4NiO₄-YSZ cathode to form (1−x) wt% Pr_1.6Sr_0.4NiO₄−x wt% YSZ-Ag (x=0, 10, 20, 30, 40) (abbr. PYx-Ag) composite cathode. XRD results suggested that there was a good chemical stability between Pr_1.6Sr_0.4NiO₄ and YSZ at temperatures below 1050 °C. PY20-Ag cathode exhibited higher exchange current density, lower overpotential and ASR (Area Specific Resistance) than PY20 cathode. At 650 °C, the ASR of PY20-Ag cathode was 2.5 Ω cm², which was only about 42% of that of PY20, 5.9 Ω cm². PY20-Ag can be a promising candidate for SOFC cathode.