A simple,cheap soft synthesis routine for LiFePO4 using iron(III) raw material

An order olivine structure LiFePO₄ was synthesized with a simple rheological phase reaction (RPR) of LiOH·H₂O and FePO₄·4H₂O in the presence of PEG as a reductive agent and carbon source. A required amount of water was added to the starting materials to form the rheological precursor and decomposed at 700 °C to form the crystalline phase LiFePO₄ directly, without ball-milling, preparation of intermediates, pre-sintering and post-deposition treatment. Fine particles with an average particle size about 216 nm are examined by scanning electron microscopy (SEM) and optical particle size analyzer. An initial discharge capacity of 157 mAh g⁻¹ was achieved for the as-prepared LiFePO₄ material with a rate of 0.1C (17 mA g⁻¹), what's more, this material shows excellent specific capacity, charge–discharge efficiency and cycle efficiency at high current rates, almost no capacity loss can be observed up to 40 cycles with the rate of 1, 2 and 3C at room temperature. The simple, cheap process as well as the excellent high-rate performance makes this RPR method feasible commercially.     

Synthesis of LiFePO4/C composite with high-rate performance by starch sol assisted rheological phase method

LiFePO₄/C composite was synthesized at 600 °C in an Ar atmosphere by a soluble starch sol assisted rheological phase method using home-made amorphous nano-FePO₄ as the iron source. XRD, SEM and TEM observations show that the LiFePO₄/C composite has good crystallinity, ultrafine sphere-like particles of 100-200 nm size and in situ carbon. The synthesized LiFePO₄ could inherit the morphology of FePO₄ precursor. The electrochemical performance of the LiFePO₄ by galvanostatic cycling studies demonstrates excellent high-rate cycle stability. The Li/LiFePO₄ cell displays a high initial discharge capacity of more than 157 mAh g⁻¹ at 0.2C and a little discharge capacity decreases from the first to the 80th cycle (>98.3%). Remarkably, even at a high current density of 30C, the cell still presents good cycle retention.     

Hydrogen production with CO2 capture by coupling steam reforming of methane and chemical-looping combustion: Use of an iron-based waste product as oxygen carrier burning a PSA tail gas

In this work it is analyzed the performance of an iron waste material as oxygen carrier for a chemical-looping combustion (CLC) system. CLC is a novel combustion technology with the benefit of inherent CO₂ separation that can be used as a source of energy for the methane steam reforming process (SR). The tail gas from the PSA unit is used as fuel in the CLC system.The oxygen carrier behaviour with respect to gas combustion was evaluated in a continuous 500 W_th CLC prototype using a simulated PSA off-gas stream as fuel. Methane or syngas as fuel were also studied for comparison purposes. The oxygen carrier showed enough high oxygen transport capacity and reactivity to fully convert syngas at 880 °C. However, lower conversion of the fuel was observed with methane containing fuels. An estimated solids inventory of 1600 kg MW_th⁻¹ would be necessary to fully convert the PSA off-gas to CO₂ and H₂O. An important positive effect of the oxygen carrier-to-fuel ratio up to 1.5 and the reactor temperature on the combustion efficiency was found.A characterization of the calcined and after-used particles was carried out showing that this iron-based material can be used as oxygen carrier in a CLC plant since particles maintain their properties (reactivity, no agglomeration, high durability, etc.) after more than 111 h of continuous operation.     

Morphological characterization of LiFePO4/C composite cathode materials synthesized via a carboxylic acid route

A new type of LiFePO₄/C composite surrounded by a web containing both amorphous and crystalline carbon phases was synthesized by incorporating malonic acid as a carbon source using a high temperature solid-state method. SEM, TEM/SAED/EDS and HRTEM were used to analyze surface morphology and confirmed for the first time that crystalline carbon was present in LiFePO₄/C composites. The composite was effective in enhancing the electrochemical properties such as capacity and rate capability, because its active component consists of nanometer-sized particles containing pores with a wide range of sizes. An EDS elemental map showed that carbon was uniformly distributed on the surface of the composite crystalline particles. TEM/EDS results clearly show a dark region that is LiFePO₄ with a trace of carbon and a gray region that is carbon only. To evaluate the materials’ electrochemical properties, galvanostatic cycling and conductivity measurements were performed. The best cell performance was delivered by the material coated with 60 wt.% malonic acid, which delivered first cycle discharge capacity of 149 mAh g⁻¹ at a C/5 rate and sustained 222 cycles at 80% of capacity retention. When carboxylic acid was used as a carbon source to produce LiFePO₄, overall conductivity increased from 10⁻⁵ to 10⁻⁴ S cm⁻¹, since particle growth was prevented during the final sintering process.     

Morphology and electrochemical performance of Li[Ni1/3Co1/3Mn1/3]O2 cathode material by a slurry spray drying method

The spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders with appropriate porosity, small particle size and good particle size distribution were successfully prepared by a slurry spray drying method. The Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were characterized by XRD, SEM, ICP, BET, EIS and galvanostatic charge/discharge testing. The material calcined at 950 °C had the best electrochemical performance. Its initial discharge capacity was 188.9 mAh g⁻¹ at the discharge rate of 0.2 C (32 mA g⁻¹), and retained 91.4% of the capacity on going from 0.2 to 4 C rate. From the EIS result, it was found that the favorable electrochemical performance of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material was primarily attributed to the particular morphology formed by the spray drying process which was favorable for the charge transfer during the deintercalation and intercalation cycling.     

Synthesis and electrochemical properties of olivine LiFePO4 prepared by a carbothermal reduction method

LiFePO₄/C composite cathode material was prepared by carbothermal reduction method, which uses NH₄H₂PO₄, Li₂CO₃ and cheap Fe₂O₃ as starting materials, acetylene black and glucose as carbon sources. The precursor of LiFePO₄/C was characterized by differential thermal analysis and thermogravimetry. X-ray diffraction (XRD), scanning electron microscopy (SEM) micrographs showed that the LiFePO₄/C is olivine-type phase, and the addition of the carbon reduced the LiFePO₄ grain size. The carbon is dispersed between the grains, ensuring a good electronic contact. The products sintered at 700 °C for 8 h with glucose as carbon source possessed excellent electrochemical performance. The synthesized LiFePO₄ composites showed a high electrochemical capacity of 159.3 mAh g⁻¹ at 0.1 C rate, and the capacity fading is only 2.2% after 30 cycles.     

Study of LiFePO4 cathode materials coated with high surface area carbon

LiFePO₄ is a potential cathode material for 4 V lithium-ion batteries. Carbon-coated lithium iron phosphates were prepared using a high surface area carbon to react precursors through a solid-state process, during which LiFePO₄ particles were embedded in amorphous carbon. The carbonaceous materials were synthesized by the pyrolysis of peanut shells under argon, where they were carbonized in a two-step process that occurred between 573 and 873 K. The shells were also treated with a proprietary porogenic agent with the goal of altering the pore structure and surface area of the pyrolysis products. The electrochemical properties of the as-prepared LiFePO₄/C composite cathode materials were systematically characterized by X-ray diffraction, scanning electron microscope, element mapping, energy dispersive spectroscopy, Raman spectroscopy, and total organic carbon (TOC) analysis. In LiFePO₄/C composites, the carbon not only increases rate capability, but also stabilizes capacity. In fact, the capacity of the composites increased with the specific surface area of carbon. The best result was observed with a composite made of 8.0 wt.% with a specific surface area of 2099 m² g⁻¹. When high surface area carbon was used as a carbon source to produce LiFePO₄, overall conductivity increased from 10⁻⁸ to 10⁻⁴ S cm⁻¹, because the inhibition of particle growth during the final sintering process led to greater specific capacity, improved cycling properties and better rate capability compared to a pure olivine LiFePO₄ material.     

The effect of carbon coating thickness on the capacity of LiFePO4/C composite cathodes

Two types of carbon source and precursor mixing pellets were employed simultaneously to prepare the LiFePO₄/C composite materials: Type I using the LiFePO₄ precursor with 20 wt.% polystyrene (PS) as a primary carbon source, and Type II using the LiFePO₄ precursor with 50 wt.% malonic acid as a secondary carbon vapor source. During final sintering, a Type I pellet was placed down-stream and Type II precursor pellet(s) was(were) placed upstream next to a Type I precursor pellet in a quartz-tube furnace. The carbon-coated product of the sintered Type I precursor pellet was obtained by using both PS and malonic acid as carbon sources. When two Type II pellets were used as a carbon vapor source (defined as Product-2), a more uniform film between 4 and 8 nm was formed, as shown in the TEM images. In the absence of a secondary carbon source (defined as Product-0), the discharge capacity of Product-0 was 137 mAh g⁻¹ with 100 cycles at a 0.2C-rate, but Product-2 demonstrated a high capacity of 151 mAh g⁻¹ with 400 cycles. Our results indicate that electrochemical properties of LiFePO₄ are correlated to the amount of carbon and its coating thickness and uniformity.     

New freeze-drying method for LiFePO4 synthesis

The freeze-drying method is proposed as an effective synthesis process for the obtaining of LiFePO₄/C composites. The citric acid is used as a complexing agent and carbon source. After the low temperature annealing, the freeze-dried solution leads to a homogeneous carbon covered LiFePO₄ sample. The chemical characterization of the material included ICP and elemental analysis, infrared spectroscopy, X-ray diffraction, magnetic measurements and thermal analysis. SEM and TEM microscopies indicate an aggregate morphology with tiny particles of lithium iron phosphate inside a carbon matrix. Impedance spectroscopy showed a 8.0 × 10⁻⁷ S cm⁻¹ conductivity value. Cyclic voltammetry graphics displayed the two peaks corresponding to the Fe(II)/Fe(III) reaction and demonstrated the good reversibility of the material. The specific capacity value obtained at C/40 rate was 164 mAh g⁻¹, with a slight decrease on greater C-rates reaching 146 mAh g⁻¹ at C/1. The capacity retention study has evidenced good properties, with retention over 97% of the maximum values in the first 50 cycles, which allows an effective performance of the freeze-dried sample as cathodic material in lithium-ion batteries.     

Electrochemical properties of LiFePO4 prepared via hydrothermal route

LiFePO₄ as a cathode material for rechargeable lithium batteries was prepared by hydrothermal process at 170 °C under inert atmosphere. The starting materials were LiOH, FeSO₄, and (NH₄)₂HPO₄. The particle size of the obtained LiFePO₄ was 0.5 μm. The electrochemical properties of LiFePO₄ were characterized in a mixed solvent of ethylene carbonate and diethyl carbonate (1:1 in volume) containing 1.0 mol dm⁻³ LiClO₄. The hydrothermally synthesized LiFePO₄ exhibited a discharge capacity of 130 mA h g⁻¹, which was smaller than theoretical capacity (170 mA h g⁻¹). The annealing of LiFePO₄ at 400 °C in argon atmosphere was effective in increasing the discharge capacity. The discharge capacity of the annealed LiFePO₄ was 150 mA h g⁻¹.     

Synthesis and characterization of submicron-sized LiNi1/3Co1/3Mn1/3O2 by a simple self-propagating solid-state metathesis method

Submicron-sized LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials were synthesized using a simple self-propagating solid-state metathesis method with the help of ball milling and the following calcination. A mixture of Li(ac)·2H₂O, Ni(ac)₂·4H₂O, Co(ac)₂·4H₂O, Mn(ac)₂·4H₂O (ac = acetate) and excess H₂C₂O₄·2H₂O was used as starting material without any solvent. XRD analyses indicate that the LiNi_1/3Co_1/3Mn_1/3O₂ materials were formed with typical hexagonal structure. The FESEM images show that the primary particle size of the LiNi_1/3Co_1/3Mn_1/3O₂ materials gradually increases from about 100 nm at 700 °C to 200–500 nm at 950 °C with increasing calcination temperature. Among the synthesized materials, the LiNi_1/3Co_1/3Mn_1/3O₂ material calcined at 900 °C exhibits excellent electrochemical performance. The steady discharge capacities of the material cycled at 1 C (160 mA g⁻¹) rate are at about 140 mAh g⁻¹ after 100 cycles in the voltage range 3–4.5 V (versus Li⁺/Li) and the capacity retention is about 87% at the 350th cycle.     

Effects of TiO2 coating on high-temperature cycle performance of LiFePO4-based lithium-ion batteries

LiFePO₄ particles were coated with TiO₂ (molar ratio = 3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO₄ cathode at 55 °C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO₄/Li cell, it imposes a deteriorating effect on the LiFePO₄/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO₄ cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO₄/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO₄/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.     

Complex hydrides as solid storage materials: First safety tests

Hydrogen technology requires efficient and safe hydrogen storage systems. For this purpose, storage in solid materials, such as high capacity complex hydrides, is studied intensely. Independent from the actual material to be used eventually, any tank design will combine nanoscale powders of highly reactive material with pressurized hydrogen gas and so far, little is known about the behavior of these mixtures in case of incidents. For a first evaluation of a complex hydride in case of a tank failure, NaAlH₄ (doped with Ti) was investigated in a small-scale tank failure test. 80–100 ml of the material was filled into a heat exchanger tube, and sealed under argon atmosphere with a burst disk. Subsequently, the NaAlH₄ was partially desorbed by heating. When the powder temperature reached 130 °C and the burst disk ruptured at 9 bar hydrogen overpressure the behavior of the expelled powder was monitored using a high speed camera, an IR camera as well as sound level meters. Expulsion of the hydrogen storage material into (dry) ambient atmosphere yields a dust cloud of finely dispersed powder which does not ignite spontaneously. Similar experiments including an external source of ignition (spark/water reacting with NaAlH₄) yield a flame of reacting powder. The intensity will be compared to the reaction of an equivalent amount of pure hydrogen.     

Electrochemical properties of LiFePO4 prepared via ball-milling

LiFePO₄ cathode materials with distinct particle sizes were prepared by a planetary ball-milling method. The effects of particle size on the morphology, thermal stability and electrochemical performance of LiFePO₄ cathode materials were investigated. The ball-milling method decreased particle size, thereby reducing the length of diffusion and improving the reversibility of the lithium ion intercalation/deintercalation. It is worth noting that the small particle sample prepared using malonic acid as a carbon source achieved a high capacity of 161 mAh g⁻¹ at a 0.1 C rate and had a very flat capacity curve during the early 50 cycles. However, the big particle samples (∼400 nm) decayed more dramatically in capacity than the small particle size samples (∼200 nm) at high current densities. The improvement in electrode performance was mainly due to the fine particles, the small size distribution, and the increase in electronic conductivity as a result of carbon coating. The structure and morphology of the ground LiFePO₄ samples were characterized with XRD, FE-SEM, TEM, EDS, and DSC techniques.     

Electrochemical performances in temperature for a C-containing LiFePO4 composite synthesized at high temperature

C-LiFePO₄ composite was synthesized by mechano-chemical activation using iron and lithium phosphates and also cellulose as carbon precursor; this mixture was heated at 800 °C under argon during a short time. Long-range cyclings at different temperatures (RT, 40 and 60 °C) and at C/20 rate between 2 and 4.5 V vs. Li⁺/Li were carried out with this C-LiFePO₄ material as positive electrode material in lithium cells. Whatever the cycling conditions used, rather good electrochemical performances were obtained, with a capacity close to the theoretical one and a good cycle life, especially at RT – up to 100 cycles – and at 40 °C with ∼80% of the initial capacity maintained after 100 cycles. The electrodes recovered after long-range cyclings were characterized by X-ray diffraction; whatever the cycling temperature no significant structural changes (cell parameters, bond lengths, etc.) were shown to occur. Nevertheless, iron was found to be present at the negative electrode – as already observed by Amine et al. – after long-range cycling at 60 °C: other analyses have to be done to identify the origin of this iron (from an impurity or from LiFePO₄ itself) and to quantify this amount vs. that of active C-LiFePO₄ material using larger cells.     

LiFePO4 water-soluble binder electrode for Li-ion batteries

A new water-soluble elastomer from ZEON Corp. was evaluated as binder with LiFePO₄ cathode material in Li-ion batteries. The mechanical characteristic of this cathode was compared to that with PVdF-based cathode binder. The elastomer-based cathode shows high flexibility with good adhesion. The electrochemical performance was also evaluated and compared to PVdF-based cathodes at 25 and at 60 °C. A lower irreversible capacity loss was obtained with the elastomer-based cathode, however, aging at 60 °C shows a comparable cycle life to that observed with PVdF-based cathodes. The LiFePO₄–WSB at high rate shows a good performance with 120 mAh g⁻¹ at 10C rate at 60 °C.     

Electrochemical study on LiCo1/6Mn11/6O4 as cathode material for lithium ion batteries at elevated temperature

A novel process via sintering of a precursor from the solution of metal acetates by spray-drying technology was used to synthesize Co-substituted LiCo_1/6Mn_11/6O₄ material for lithium ion batteries. The as-prepared particles were identified as single-phase spinel structure without any impurities in the XRD pattern. The SEM image showed that the particles had good cubic shapes and uniform size distribution with sizes of about 100–200 nm. An ex situ XRD technique was used to characterize the first charge process of the LiCo_1/6Mn_11/6O₄ electrode. The result suggested that the material configuration maintained invariability. The electrochemical properties of the synthesized cathode material were investigated using Li-ion model cells at room and elevated temperature, respectively. In the charge/discharge potential of 3.5–4.4 V at 1/10 C rate, the LiCo_1/6Mn_11/6O₄ electrode delivered high initial capacities of 123 and 127 mAh g⁻¹ at 25 and 55 °C, respectively. Electrochemical cycling tests revealed that the capacity fading occurred mainly in the high-voltage region of 4.08–4.40 V, and the fading rate was 0.107% and 0.302% per cycle at 25 and 55 °C, respectively. The excellent cycling stability and low material cost make it an attractive cathode for high-temperature lithium ion batteries.     

Optimized solid-state synthesis of LiFePO4 cathode materials using ball-milling

Olivine-type LiFePO₄ cathode materials were synthesized by a solid-state reaction method and ball-milling. The ball-milling time, heating time and heating temperature are optimized. A heating temperature higher than 700 °C resulted in the appearance of impurity phase Fe₂P and growth of large particle, which was shown by high resolution X-ray diffraction and field emission scanning electron microscopy. The impurity phase Fe₂P exhibited a considerable capacity loss at the 1st cycle and a gradual increase in discharge capacity upon cycling. Moreover, it exhibited an excellent high-rate capacity of 104 mAh g⁻¹ at 3 C in spite of the large particle size. The optimum synthesis conditions for LiFePO₄ were ball-milling for 24 h and heat-treatment at 600 °C for 3 h. LiFePO₄/Li cells showed an enhanced cycling performance and a high discharge capacity of 160 mAh g⁻¹ at 0.1 C.     

Cycling degradation of an automotive LiFePO4 lithium-ion battery

Degradation of a high capacity prismatic LiFePO₄ cell with deep cycling at elevated temperature of 50 °C is studied by electrochemical impedance spectroscopy as well as capacity and power fading characterization at different test temperatures (45, 25, 0 and −10 °C). Capacity fade after 600 cycles is 14.3% at 45 °C and 25.8% at −10 °C. There is little power fade at 45 °C after 600 cycles, whereas the power fade after 600 cycles is 61.6% and 77.2%, respectively, at 0 and −10 °C. The capacity and power fade evidently becomes more severe at lower temperature. In particular, the power fade at low temperatures (e.g., 0 and −10 °C) rather than capacity loss is a major limitation of the LiFePO₄ cell. The primary mechanism for capacity fade is loss of cyclable lithium in the cell resulting from lithium-consuming solid electrolyte interphase (SEI) layer growth and side reactions. The increased interfacial resistance (R_w) due to the catalytic growth of SEI layer on the graphite anode and increased electrolyte resistance are the main sources for power fade.     

Fabrication and electrochemical properties of lithium-ion batteries for power tools

204056-Type prismatic lithium-ion battery for power tools was developed by using LiMn₂O₄ as cathode and CMS (carbonaceous mesophase spheres) as anode. The performance of batteries and their electrodes were characterized by SEM, ac impedance and electrochemical tests. The bulk density of cathode after pressing was selected as a main factor and it effects on high current rate capability and discharge plateau distinctly, which were investigated in details. Being charged/discharged in the voltage range of 2.5–4.2 V, the normal LiMn₂O₄ battery with cathode bulk density of 2.7 g cm⁻³ shows excellent electrochemical performances. The discharge capacity at 20C rate is 94.1% of that at 1C rate, and the capacity retention ratio charged at 1C and discharged at 5C is 91.7% after 100 cycles at 25 °C. While modified LiMn₂O₄ is used as the cathode material, the cycling performance of batteries is better than that of batteries made from normal LiMn₂O₄. The capacity retention ratios of modified LiMn₂O₄ batteries after 100 cycles at 25 °C and 55 °C are 95.0% and 85.3%, respectively. The discharge capacity at low temperature was tested both at 1C rate and 5C rate, and the capacities discharged at −20 °C were 96.3% and 94.2% of that at 1C at 25 °C. Furthermore, the batteries also show good safety in the test of short circuit, overcharge, and nail penetration.