Formation Of LiFePO4 Research Articles

Novel LiFePO4/very-few-layer-graphene (LFP/VFLG) composites to improve structural and electrochemical properties of lithium-ion battery cathode

LiFePO4/Very-few-layer-graphene (LFP/VFLG) composites have been prepared using the sol-gel method for lithium-ion battery cathode. VFLG dominated by 1∼3 layers was obtained from an economical and environmentally benign process. Structural properties of LFP/VFLG composites were studied using Fourier-transform infrared spectra (FTIR) spectroscopy, X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy, while the electrochemical performance was measured using galvanostatic discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests. The FTIR analysis confirmed that incorporating VFLG neither affected the chemical structure of LiFePO4 nor initiated any side reactions during the LiFePO4 formation reaction. The XRD results showed that LFP/VFLG composites had better lattice parameters, crystallinity, and phase purity than LiFePO4 without VFLG addition. The Raman spectroscopy analysis indicated that LFP/VFLG composites had a lower disorder in the carbon arrangement. HRTEM results indicated that a VFLG was successfully wrapped around the LFP particle offers a versatile way to enhanced electrochemical performance of LFP/VFLG composites. The galvanostatic discharge profiles showed an enhancing specific discharge capacity of up to 58.3% after incorporating VFLG. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests revealed that LFP/VFLG delivered small polarization, low inner resistance, high electrochemical reaction reversibility, and high lithium-ion diffusion coefficient. VFLG is a promising additive to improve the structural and electrochemical properties of the LiFePO4 cathode of lithium-ion batteries.

Synthesis and conductivity of LiFePO4 and solid solutions LiFe1–xМxPO4 (M – Zn, Mg, Cu, x<0.2)

We studied the influence of reagents mixture composition on the formation of LiFePO4 under the conditions of low-temperature solid state synthesis by interaction of NH4FePO4 with molten LiCH3COO and by crystallization from nitrate melt. The interaction of the reagents mixture components was investigated for the systems NH4FePO42H2O–А (where А – LiNO3, Li2CO3, LiCH3COO) and FeC2O42H2O–(NH4)2HPO4)/NH4H2PO4–А (where А – Li2CO3, LiF). A stability of Fe(II) to oxidation under the synthetic conditions was established depending on the reaction mixtures composition. It was found that Fe(II) is the most stable to oxidation under the conditions of solid state synthesis from the system Li2CO3–FeC2O42H2O–(NH4)2HPO4)/NH4H2PO4. For the synthesized solid solutions with partial isovalent substitution of iron LiFe0.8M0.2PO4 (M – Mg, Cu), a unit cell volume, lattice parameters а and с and conductivity increase as compared with undoped LiFePO4, while the unit cell volume, the lattice parameters а and с and conductivity of LiFe0.8Zn0.2PO4 decrease. The obtained results indicate possibility to influence the electrical conductivity of materials based on LiFePO4 by isovalent substitution of iron.

Formation, doping, and lithium incorporation in LiFePO4

For over 25 years, lithium iron phosphate (LiFePO4) has been a material of interest for Li-ion batteries as it is environmentally benign, low cost, and structurally stable. Here, we employed density functional theory calculations to examine the formation of LiFePO4 via different reaction routes, intrinsic defect processes, solution of dopants, and impact of doping on its electronic structure. The most thermodynamically favorable process to synthesize LiFePO4 is predicted to be from its constitute elements in their standard states. The Li–Fe anti-site defect is the lowest defect energy process inferring the presence of a small amount of cation intermixing. The most promising isovalent dopants on the Li, Fe, P, and O are the Na, Ca, As, and S, respectively. The substitution of Ru for Fe is energetically favorable. The doping of Ge on the P site is a possible strategy to generate both Li interstitials and holes in this material. The stability of this material upon Li incorporation (up to four atoms per 112-atom supercell) was investigated. Although incorporation is slightly unfavorable, there is a clear enhancement in the incorporation with volume expansion. The insulating nature of this material is affected by the doping and incorporation of Li, which leads to the reduction of the bandgap.

Formation kinetics of sol-gel derived LiFePO4 olivine analyzed by reliable non-isothermal approach

The formation kinetics of LiFePO4 Olivine synthesized through sol-gel route has been studied by non-isothermal approach. LiFePO4 precursors were prepared by mixing lithium dihydrogen phosphate (LiH2PO4) and iron (III) citrate (C6H5FeO7) and subsequently calcined in an Argon atmosphere at temperatures ranged from of 300–900 °C to form LiFePO4 products. Thermal behaviors of calcination process were analyzed by thermogravimetry (TGA) and differential scanning calorimetry (DSC) simultaneously, while the mineralogical properties of LiFePO4 were characterized using X-ray diffractometer (XRD). The kinetic parameters were determined by Ozawa–Flynn–Wall (OFW), Kissinger, and Kissinger-Akahira-Sunose (KAS) methods, and the reaction mechanism model was evaluated by Coats–Redfern approach. The results indicated that the reaction model of LiFePO4 formation agreed with the three-dimensional diffusion mechanism. The temperature had an essential role in the synthesis of LiFePO4. The optimum calcination temperature was 700 °C where this condition produced LiFePO4 Olivine with high degree of crystallinity, better lattice parameters and phase purity.

Performance of Vanadium Doped and Carbon Bamboo/Carbon Black Coated Lithium Iron Phosphate for Battery Cathode

Synthesis of lithium iron phosphate (LiFePO4) via wet chemical followed by a hydrothermal method has been carried out. The preparation of LiFePO4 was begun with the precursor of LiOH, NH4H2PO4, and FeSO4.7H2O mixed stoichiometrically. After the synthesis, LiFePO4 was doped using vanadium and then coated using two types of carbon sources, i.e. carbon black blended with activated carbon pyrolyzed from bamboo, through a solid-state reaction. The materials were mixed using a ball-mill and subsequently characterized using a thermal analyzer (STA) to determine the sintering temperature. The result shows that LiFePO4 formation temperature is at 639°C. The sintering process was performed for 4 hours and the characterization was done using X-ray diffraction (XRD) and electron microscope (SEM) equipped with energy dispersive x-ray spectroscopy (EDX). The electrochemical impedance spectroscopy (EIS) testing was performed to show the conductivity of the formed materials. XRD result showed that LiFePO4/V/C phase has formed with an olivine structure, while the SEM result showed fair distribution and small particle size with some agglomerated microstructures. The EIS results showed that carbon coating on the active material increases the conductivity, whereas the addition of vanadium increases the conductivity of up to 5 wt.% vanadium but decreases at 7 wt.% vanadium.

Ultrathin LiFePO4/C cathode for high performance lithium-ion batteries: Synthesis via solvothermal transformation of iron hydroxyl phosphate Fe3(PO4)2(OH)2 nanosheet

A novel two-step solvothermal approach was firstly applied to acquire ultrathin lithium iron (II) phosphate (LiFePO4) nanosheet (with thickness about 28 nm) with exposed (010) surface facets. The iron hydroxyl phosphate Fe3(PO4)2(OH)2 nanosheet fabricated in the first solvothermal step was proved to be effective template for ultrathin LiFePO4 formation after solvothermal lithiation in the second solvothermal step. Importantly, the two-step solvothermal lithiation could produce ultrathin nanosheets while one-step solvothermal based on Fe(II) fabrication could only produce nanoplate-like particles. The as-synthesized nanosheets has shortened Li-ion diffusion path and high robustness in the structure during high C-rate electrochemical tests. Based on comparison with bulk LiFePO4 and nano-plate LiFePO4, the LiFePO4 nanosheet exhibits quite high specific discharge capacity of 169, 165, 159, 142, and 121 mAh g−1, at C-rate of 0.1, 0.2, 0.5, 1, and 5C, respectively, and excellent cycling performance with capacity kept at 121 mAh g−1 with no obvious fading under 500 times cycles. The newly developed method can provide useful references to other olivine type LiMPO4 cathodes and even have potential to find more applications in the synthesis of functional materials.

Reaction Mechanisms on Solvothermal Synthesis of Nano LiFePO4 Crystals and Defect Analysis

A solvothermal process was used to synthesize LiFePO4 nanomaterials for lithium ion batteries. Reaction parameters such as reaction temperature and residence time were explored to obtain the optimal LiFePO4 sample. A three-stage reaction mechanism is proposed to better understand the solvothermal synthesis process. X-ray diffraction, scanning electron microscopy, and Fourier transform IR spectroscopy were used to investigate the prepared samples under different conditions. The LiFePO4 formation reaction occurred at a temperature as low as 89 °C. Defect analysis results showed that after 4 h of solvothermal treatment the concentration of lithium vacancy and Li–Fe antisite defects was too low to be detected. The charge–discharge data of the obtained LiFePO4 showed that the carbon-coated LiFePO4 samples prepared at 180 °C after 4 h of solvothermal treatment had a discharge capacity of 160.6 mA h g–1 at a discharge rate of 0.1C and 129.6 mA h g–1 at 10C.

Composited reduced graphene oxide into LiFePO4/Li2SiO3 and its electrochemical impedance spectroscopy properties

LiFePO4 is commonly used as cathode material for Li-ion batteries due to its stable operational voltage and high specific capacity. However, it suffers from certain disadvantages such as low intrinsic electronic conductivity and low ionic diffusion. This study was conducted to analyse the effect of reduced graphene oxide (rGO) on the electrochemical properties of LiFePO4/Li2SiO3 composite. This composite was synthesized by a hydrothermal method. Fourier transform infrared spectroscopy measurement identified the O–P–O, Fe–O, P–O, and O–Si–O− bands in the LiFePO4/Li2SiO3 composite. X-ray diffraction measurement confirmed the formation of LiFePO4. Meanwhile, Raman spectroscopy confirmed the number of rGO layers. Further, scanning electron microscopy images showed that rGO was distributed around the LiFePO4/Li2SiO3 particles. Finally, the electrochemical impedance spectroscopy results showed that the addition of 1 wt% of rGO to the LiFePO4/Li2SiO3 composite reduced charge transfer resistance. It may be concluded that the addition of 1 wt% rGO to LiFePO4/Li2SiO3 composite can enhance its electrochemical performance as a cathode material.

Effect of manganese doping on conduction in olivine LiFePO4

Lithium ion batteries play a crucial role in terms of good rechargeability, long cycles and higher shelf life. For the fabrication of such a Li ion battery, properties of cathode material can be engineered keeping anode and electrolyte fixed. In the present work, lithium iron phosphate (LiFePO4) has been utilized as cathode material and the properties of LiFePO4 have been tuned by doping manganese (Mn). LiFePO4 and different concentrations of Mn doped LiFePO4 were prepared by solid state route. X-Ray diffraction and Raman studies were performed to confirm the formation of LiFePO4 and Mn doped LiFePO4 in olivine structure. Cyclic voltammetry studies revealed maximum peak oxidation current (2.96 mA) and largest surface coverage (0.066 nanoMoles/cm2) for the LiFePO4 doped with 15% Mn (LiMn0.15Fe0.85PO4). AC-conductivity study was carried out for different frequencies at room temperature. The conductivity parameters estimated using Almond and West formalism support the cyclic voltammetry results. Ion-hopping rate (ω p ) and charge carrier concentration (K) maximize for 15% Mn doping (ω p : 582974.48719 Hz; K: 2.62447 × 10−6) and drop on either increasing (ω p : 167134.73521 Hz; K: 1.25647 × 10−7) or decreasing (ω p : 130726.49084 Hz; K: 2.52435 × 10−6) the Mn doping. The increase till 15% Mn doping has been attributed to the increase in unit cell volume with Mn doping while the sudden decrease at 20% Mn doping is due to dominance of back-hopping mechanism. The results clearly indicate that 15% Mn doped LiFePO4 is the most appropriate for the realization of a cathode for Li-ion battery.

Synthesis of a LiFePO4/C cathode material by using a high-energy nano mill

Olivine lithium iron phosphate (LiFePO4) is a promising cathode material for Li-ion battery. A temperature around 700 – 800 ℃ is generally required to prepare LiFePO4 powder with good crystallinity. The LiFePO4 materials are synthesized via a solid-state method by using a highenergy nano mill (HENM). The conventional ball-milling process is also conducted for the same material for a comparative study. The effect of the precursor’s mixing processes on the synthesis temperature of LiFePO4 is investigated in this study. The required reaction temperature of LiFePO4 is 432 ℃ for the HENM process and 480 ℃ for the ball-mill process as found from the differential scanning calorimetry (DSC) results. The HENM process improves the reaction activity and the homogeneity of the materials used throughout process and lowers the reaction temperature as compared with the conventional ball-mill process. The milled powders are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sample synthesized by using the HENM process exhibits a discharge capacity of 136 mAhg −1 at 0.1 C rate. The results in this study indicate that the HENM process is a substantial and promising process for LiFePO4 cathode preparation owing to its short fabrication time and ability to improve the reaction condition. A HENM can be used to promote formation of LiFePO4 at lower temperatures.

High rate performance of LiF modified LiFePO4/C cathode material

Nonstoichiometric LiF modified F-LiFePO4/C cathode material is successfully synthesized by solid-state-reaction using LiF as the additive and FePO4 and Li2CO3 as precursors. The synthesized F-LiFePO4/C powders are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectrum, X-ray photoelectron emission microscopy (XPS) and potentiostatic intermittent titration technique (PITT). The XRD results show that the LiF additive modification can improve the crystallinity of LiFePO4 without introducing any impurities. LiF modification has little influence on LiFePO4 crystal structure based on lattice parameters, calculated by MDI Jade 6. The DSC curve shows that a LiF additive can lower the LiFePO4 formation temperature by about 100°C. F1s signal and a CF bond have been discovered on the surface of the modified sample via XPS analysis, indicating that LiF has an influence on the chemical reaction. The final particle size varied with LiF additive content based on SEM and HRTEM images. F-LiFePO4/C samples have better and clearer crystal fringes than the untreated LiFePO4/C sample from HRTEM, which suggests that LiF modification can improve the crystallinity of LiFePO4. Charge–discharge curves indicate that the F-LiFePO4/C sample has excellent capacities at high discharge rates: 130.0mAhg−1 at 5C. PITT indicates that the F-LiFePO4/C sample has a higher Li+ ion diffusion coefficient than the LiFePO4/C sample.

A Facile Route for Synthesis of LiFePO4/C Cathode Material with Nano-sized Primary Particles

A facile and practical route was introduced to prepare LiFePO4/C cathode material with nano-sized primary particles and excellent electrochemical performance. LiH2PO4 was synthesized by using H3PO4 and LiOH as raw materials. Then, as-prepared LiH2PO4, reduced iron powder and a-D-glucose were ball-milled, dried and sintered to prepare LiFePO4/C. X-ray diffractometry was used to characterize LiH2PO4, ball-milled product and LiFePO4/C. Differential scanning calorimeter-thermo gravimetric analysis was applied to investigate possible reactions in sintering and find suitable temperature for LiFePO4 formation. Scanning electron microscopy was employed for the morphology of LiFePO4/C. As-prepared LiH2PO4 is characterized to be in P21cn(33) space group, which reacts with reduced iron powder to form Li3PO4, Fe3(PO4)2 and H2 in ball-milling and sintering. The appropriate temperature for LiFePO4/C synthesis is 541.3-976.7 °C. LiFePO4/C prepared at 700 °C presents nano-sized primary particles forming aggregates. Charge-discharge examination indicates that as-prepared LiFePO4/C displays appreciable discharge capacities of 145 and 131 mA·h·g−1 at 0.1 and 1 C respectively and excellent discharge capacity retention.

Polyol Synthesis of Lithium Iron Phosphate with Carbon Nanotubes: Effect of Dispersion on Crystallinity and Electrochemical Performance

ABSTRACTCarbon nanotubes (CNTs) have been shown to be a viable conductive additive in Li-Ion batteries [1]. By using CNTs battery life, energy, and power capability can all be improved over carbon black, the traditional conductive additive. A significantly smaller weight percentage (5% CNTs) is needed to get the same conductivity as 20% carbon black. Many of the previous efforts found that a combination of conductive additives was most advantageous [2]. Unfortunately many of these efforts did not attend to the unique challenge that dispersing nanotubes presents and used non-optimal methods to disperse CNTs (e.g. ball milling) [3,4]. With poor dispersion a stable and resilient conductive network in the cathode is hard to form with CNTs alone. Here we investigate the formation of LiFePO₄ with CNTs using a polyol process synthesis.

Rapid Synthesis of LiFePO4 by Coprecipitation

Abstract LiFePO4 nanoplates with an average thickness of less than 50 nm are synthesized through a simple coprecipitation in ethylene glycol solution at 180 °C. The evolution of the product species and intensity distribution of XRD patterns during coprecipitation are investigated to verify the formation and growth of the LiFePO4 nanoplates. The results indicate that the time for the formation of LiFePO4 nanoplates with high crystallinity is only 20 min. It is found that the feeding sequence has an important influence on LiFePO4 crystal growth and is useful for the tuning of crystal orientation and particle size.

Non-isothermal kinetics study on synthesis of LiFePO4 via carbothermal reduction method

Non-isothermal kinetics of lithium ion phosphate synthesis via carbothermal reduction method with raw materials Li2CO3, FePO4·2H2O and C6H12O6·2H2O is studied by thermogravimetry-differential scanning calorimetry (TG–DSC) technology. The results indicate the synthesis process can be divided into two stages: dehydration and LiFePO4 formation. The apparent activation energy and natural logarithm frequency factor (lnA-value) for dehydration reaction is respectively 83.4±4.7kJmol−1 and 22.1±1.5s−1, and that for LiFePO4 formation reaction is in turn 184.2±10.4kJmol−1 and 28.3±1.9s−1. Additionally, the mechanism for dehydration and LiFePO4 formation stages is Avrami's A1.5 and A4, respectively. Furthermore, the dehydration process is diffusion controlled, and the crystallization of LiFePO4 formation is controlled by nuclei being formed randomly and growing in three-dimensions, and the kinetic equations for each stage are shown as follows:Dehydration stage: [−ln(1−a)]2/3=3.96×109 exp−8.34×104RTt;LiFePO4 formation stage: [−ln(1−a)]1/4=1.95×1012 exp−1.84×105RTt;where α is the fractional conversion, T the calcination temperature (K), t the calcination time (s), R the gas constant (8.314Jmol−1K−1).

Mechanism and kinetic studies on the synthesis of LiFePO4via solid-state reactions

Three classical iron sources including FePO4·2H2O, FeC2O4·2H2O and Fe2O3 are explored to study the mechanism and kinetics of LiFePO4 synthesis via solid-state reactions. During the initial formation of LiFePO4, the reactivity of FePO4 appears to be higher than that of FeC2O4 because the latter involves two stages including the decomposition of FeC2O4 and then the formation of LiFePO4. Fe2O3 shows the lowest reactivity among the solid-state reactions. Meanwhile, the optimal sintering temperature for FePO4 to form LiFePO4 is lower than those for FeC2O4·2H2O and Fe2O3. A larger primary particle size should be responsible for the lower specific capacity of LiFePO4 synthesized with micro-Fe2O3. The kinetic mechanism for obtaining single-phase LiFePO4 corresponds to the diffusion model, calculated by using Coats–Redfern and Doyle equations in which FeC2O4·2H2O and FePO4·2H2O obey 3-dimensional diffusion (cylinder, GB equation) and Fe2O3 obeys 1-dimensional diffusion.

Phase Transition Analysis between LiFePO4 and FePO4 by In-Situ Time-Resolved X-ray Absorption and X-ray Diffraction

In-situ time-resolved X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are applied to investigate the phase transition mechanism between LiFePO4 and FePO4. Phase formation kinetics is discussed by using the phase fractions of LiFePO4 and FePO4 directly obtained from the XRD measurement and the amount of the passed current synchronized by the XRD measurement with Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. For both of the lithium extraction and insertion process, the KJMA analysis from the XRD and amount of the passed current data indicate that the phase formation of LiFePO4 and FePO4 proceeds via one-dimensional phase boundary movement. For the lithium extraction process, the two phase coexistence of LiFePO4 and FePO4 is observed under the potential step conditions, and the KJMA plot based on the passed current data is relatively in good agreement with the one based on the XRD data. On the other hand, for the lithium insertion process, considerable peak boarding which implies intermediate state formation during the phase transition occurs, and the LiFePO4 phase formation is delayed compared with the amount of the passed current, especially in the case of small particle size. These results indicate that the phase transition behavior during lithium insertion is different from that of the typical two phase reaction.

Formation Mechanism of LiFePO4 Sticks Grown by a Microwave‐Assisted Liquid‐Phase Process

A time-dependent study on the formation of LiFePO₄ with olivine-type structure is presented. The material is synthesized through a non-aqueous route in benzyl alcohol assisted by microwave radiation. The LiFePO₄ forms with an anisotropic morphology of microscale stick-like particles. The detailed structure of these particles and their evolution with reaction time is revealed by transmission electron microscopy; a 3D reconstruction of a particle by electron tomography provides insight into the formation mechanism of these sticks. Without applying a thermal post-annealing treatment or a carbon coating, the electrochemical behavior of the LiFePO₄ microsticks is assessed for the preparation of cathodes in lithium-ion batteries.

In Situ Hydrothermal Synthesis of LiFePO4 Studied by Synchrotron X-ray Diffraction

The development of high capacity, safe lithium battery materials requires new tools to better understand how reaction conditions affect nucleation and crystallization, particle size, morphology, and defects. We present a general approach for studying the synthesis of Li battery electrode materials in real time. The formation of LiFePO4 was investigated by time-resolved in situ synchrotron X-ray diffraction under hydrothermal conditions, and the reaction kinetics were determined by changes of the Bragg reflections. We provide the first evidence in support of a dissolution–reprecipitation process for the formation of LiFePO4, which occurs at temperatures as low as 105 °C and appears to be a three-dimensional diffusion-controlled process. Lattice parameters and their evolution were monitored in situ, as well as the formation of antisite defects and their subsequent elimination under various synthesis conditions. The ability to characterize and tailor synthesis reactions in situ is essential for rapid optimiz...

Real-time synchrotron powder X-ray diffraction study of the antisite defect formation during sub- and supercritical synthesis of LiFePO4and LiFe1−xMnxPO4nanoparticles

In situsynchrotron powder X-ray diffraction (PXRD) is used to study the formation of LiFePO4nanoparticles during hydrothermal synthesis from LiOH, H3PO4, and two different iron precursors, FeSO4and (NH4)2Fe(SO4)2. Furthermore, the synthesis of Li(Fe1−xMnx)PO4(x= 0.25, 0.50 and 0.75) from LiOH, H3PO4and FeSO4/MnSO4is studied. The reactions involve an unknown intermediate phase, which is not the previously observed intermediate NH4FePO4·H2O. The intermediate phase quickly transforms into LiFePO4and Li(Fe1−xMnx)PO4even at rather low temperatures. The presence of ammonium enhances the formation of LiFePO4, and it also leads to a significant reduction in the concentration of Li–Fe antisite defects. Thein situPXRD technique allows one to follow the influence of time, temperature and manganese doping on the antisite defect concentration, and it is shown that even under supercritical conditions a reaction time of several minutes is required to suppress the defects. This makes flow synthesis of defect-free LiFePO4and Li(Fe1−xMnx)PO4nanoparticles challenging.