Study on Preparation of Cathode Material of Lithium Iron Phosphate Battery by Self-Craning Thermal Method

The cathode material of carbon-coated lithium iron phosphate(LiFePO4/C)lithium-ion battery was synthesized by a self-winding thermal method.The material was characterized by X-ray diffraction(XRD)and scanning electron microscope(SEM).The electrochemical properties of LiFePO4/C materials were measured by the constant current charge-discharge method and cyclic voltammetry.The results showed that the LiFePO4/C material prepared by the self-propagating heat method has a typical olivine crystal structure,and the product had fine grains and good electrochemical properties.The optimal sintering temperature is 700℃,the sintering time is 24 h,the particle size of the lithium iron phosphate material is about 300 nm,and the maximum discharge capacity is 121 mAh/g at 0.1 C rate.

Synthesis of nanostructured Li_2FeSiO_4/C cathode for lithium-ion battery by solution method

Nanosphere-like Li2FeSiO4/C was synthesized via a solution method using sucrose as carbon sources under a mild condition of time-saving and energy-saving, followed by sintering at high temperatures for crystallization. The amount of carbon in the composite is less than 10% （mass fraction）, and the X-ray diffraction result confirms that the sample is of pure single phase indexed with the orthorhombic Pmn21 space group. The particle size of the Li2FeSiO4/C synthesized at 700 °C for 9 h is very fine and spherical-like with a size of 200 nm. The electrochemical performance of this material, including reversible capacity, cycle number, and charge-discharge characteristics, were tested. The cell of this sample can deliver a discharge capacity of 166 mA-h/g at C/20 rate in the first three cycles. After 30 cycles, the capacity decreases to 158 mA-h/g, and the capacity retention is up to 95%. The results show that this method can prepare nanosphere-like Li2FeSiO4/C composite with good electrochemical performance.

Effects of synthesis conditions on the structural and electrochemical properties of layered LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2 cathode material via oxalate co-precipitation method

The uniform layered LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries was prepared by using （Ni1/3Co1/3Mn1/3）C2O4 as precursor synthesized via oxalate co-precipitation method in air. The effects of calcination temperature and time on the structure and electrochemical properties of the LiNi1/3Co1/3Mn1/3O2 were systemically studied. XRD results revealed that the optimal calcination conditions to prepare the layered LiNi1/3Co1/3Mn1/302 were 950℃ for 15 h. Electrochemical measurement showed that the sample prepared under the such conditions has the highest initial discharge capacity of 160.8 mAh/g and the smallest irreversible capacity loss of 13.5% as well as stable cycling performance at a constant current density of 30 mA/g between 2.5 and 4.3 V versus Li at room temperature.

Synthesis and electrochemical properties of dual doped spinels LiNi_xAl_yMn_(2-x-y)O_4 via facile novel chelated sol–gel method as possible cathode material for lithium rechargeable batteries

LiMnOand LiNiAlyMnO（x= 0.50;y = 0.05-0.50） powders have been synthesized via facile solgel method using Behenic acid as active cheiating agent.The synthesized samples are subjected to physical characterizations such as thermo gravimetric analysis（TG/DTA）,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,field-emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM） and electrochemical studies viz.,galvanostatic cycling properties,electrochemical impedance spectroscopy（EIS） and differential capacity curves（dQ/dE）.Finger print XRD patterns of LiMnOand LiNiAlMnOfortify the high degree of crystallinity with better phase purity.FESEM images of the undoped pristine spinel illustrate uniform spherical grains surface morphology with an average particle size of 0.5 μm while Ni doped particles depict the spherical grains growth（50nm） with ice-cube surface morphology.TEM images of the spinel LiMnOshows the uniform spherical morphology with particle size of（100 nm） while low level of Al-doping spinel（LiNio.5Alo.05Mn1.45O4） displaying cloudy particles with agglomerated particles of（50nm）.The LiMnOsamples calcined at 850℃ deliver the discharge capacity of 130 mAh/g in the first cycle corresponds to 94%coiumbic efficiency with capacity fade of 1.5 mAh/g/cycle over the investigated 10 cycles.Among all four dopant compositions investigated,LiNiAlMnOdelivers the maximum discharge capacity of 126 mAh/g during the first cycle and shows the stable cycling performance with low capacity fade of 1 mAh/g/cycle（capacity retention of 92%） over the investigated 10 cycles.Electrochemical impedance studies of spinel LiMnOand LiNiAlMnOdepict the high and low real polarization of 1562 and 1100 Ω.

Electrochemical performance of Al-substituted Li_3V_2(PO_4)_3 cathode materials synthesized by sol-gel method

The effect of Al-substitution on the electrochemical performances of Li3V2(PO4)3 cathode materials was studied.Samples with stoichiometric proportion of Li3AlxV2-x(PO4)3(x=0,0.05,0.10)were prepared by adding Al(NO3)3 in the raw materials of Li3V2(PO4)3.The XRD analysis shows that the Al-substituted Li3V2(PO4)3 has the same monoclinic structure as the un-substituted Li3V2(PO4)3.The SEM images show that Al-substituted Li3V2(PO4)3 has regular and uniform particles.The electrochemical measurements show that Al-substitution can improve the rate capability of cathode materials.The Li3Al0.05V1.95(PO4)3 sample shows the best high-rate performance.The discharge capacity at 1C rate is 119 mA·h/g with 30th capacity retention rate about 92.97%.The electrode reaction reversibility and electronic conductivity are enhanced,and the charge transfer resistance decreases through Al-substitution.The improved electrochemical performances of Al-substituted Li3V2(PO4)3 cathode materials offer some favorable properties for their commercial application.

Preparation of Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_2 powders for cathode material in secondary battery by solid-state method

Employing Li2CO3, NiO, Co3O4, and MnCO3 powders as starting materials, Li[Ni1/3Co1/3Mn1/3]O2 was synthesized by solid-state reaction method. Various grinding aids were applied during milling in order to optimize the synthesis process. After successive heat treatments at 650 and 950 ℃, the prepared powders were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy, and transmission electron microscopy. The powders prepared by adding salt (NaCl) as grinding aid exhibit a clear R3m layer structure. The powders by other grinding aids like heptane show some impurity peaks in the XRD pattern. The former powders show a uniform particle size distribution of less than 1 μm average size while the latter shows a wide distribution ranging from 1 to 10 μm. Energy dispersive X-ray (EDX) analysiss show that the ratio of Ni, Co, and Mn content in the powder is approximately 1/3, 1/3, and 1/3, respecively. The EDX data indicate no incorporation of sodium or chlorine into the powders. Charge-discharge tests gave an initial discharge capacity of 160 mAh·g-1 for the powders with NaCl addition while 70 mAh·g-1 for the powders with heptane.

NEW METHOD FOR MEASURING SECONDARY ELECTRON EMISSION OF THERMIONIC CATHODE AND ITS APPLICATION

By using correlation-detection technique and improving structure of the test tube,the background noise of thermionic-electrons and space charge effect are restrained.The sec-ondary emission coefficient δ of thermionic cathode at high temperature has been studied.Theδ of impregnated scandate cathodes increases exponentially with increasing temperature at lowenergy and current of the bombardment electrons;at high energy or current of the bombardmentelectrons the temperature has little effect on δ.The research shows that an enhanced thermionicemission occurred when the cathode works at high temperature and under electron bombardment.These phenomena are discussed in terms of “internal field model”.

Preparation and electrochemical performance of Li_2Mn_(0.5)Fe_(0.5)SiO_4 cathode material with sol-gel method for lithium ion batteries

Li2Fe0.5Mn0.5SiO4 material was synthesized by a citric acid-assisted sol-gel method. The influence of the stoichiometric ratio value of n(citric acid) to n(Fe2+-Mn2+) on the electrochemical properties of Li2Fe0.5Mn0.5SiO4 was studied. The final sample was identified as Li2Fe0.5Mn0.5SiO4 with a Pmn21 monoclinic structure by X-ray diffraction analysis. The crystal phases components and crystal phase structure of the Li2Fe0.5Mn0.4SiO4 material were improved as the increase of the stoichiometric ratio value of n(citric acid) to n(Fe2+-Mn2+). Field-emission scanning electron microscopy verified that the Li2Fe0.5Mn0.5SiO4 particles are agglomerates of Li2Fe0.5Mn0.5SiO4 primary particles with a geometric mean diameter of 220 nm. The Li2Fe0.5Mn0.5SiO4 sample was used as an electrode material for rechargeable lithium ion batteries, and the electrochemical measurements were carried out at room temperature. The Li2Fe0.5Mn0.5SiO4 electrode delivered a first discharge capacity of 230.1 mAh/g at the current density of 10 mA/g in first cycle and about 162 mAh/g after 20 cycles at the current density of 20 mA/g.

Grinding sol gel synthesis and electrochemical performance of mesoporous Li_3V_2(PO_4)_3 cathode materials

Li3V2（PO4）3 precursor was obtained with V2Os.nH2O , LiOH＇H2O, NH4H2PO4 and sucrose as starting materials by grinding-sol-gel method, and then the monoclinic-typed Li3Vz（PO4）3 cathode material was prepared by sintering the amorphous Li3V2（PO4）3. The as-sintered samples were investigated by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, N2 adsorption-desorption and electrochemical measurement. It is found that Li3Vz（PO4）3 sintered at 700 ℃ possesses good wormhole-like mesoporous structure with the largest specific surface area of 188 cmZ/g, and the smallest pore size of 9.3 nm. Electrochemical test reveals that the initial discharge capacity of the 700 ℃ sintered sample is 155.9 mA.h/g at the rate of 0.2C, and the capacity retains 154 mA.h/g after 50 cycles, exhibiting a stable discharge capacity at room temperature.

Influence of pH value and chelating reagent on performance of Li_3V_2(PO_4)3/C cathode material

The Li3V2（PO4）3/C composite cathode material was synthesized via sol-gel method using three different chelating agents （citric acid, salicylic acid and polyacrylic acid） at pH value of 3 or 7. The crystal structure, morphology, specific surface area and electrochemical performance of the prepared samples were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and galvanostatic charge/discharge test. The results show that the effects of pH value on the performance of the prepared materials are greatly related to the chelating agents. With salicylic acid or polyacrylic acid as the chelating reagent, the structure, morphology and electrochemical performance of the samples are greatly influenced by the pH values. However, the structure of the materials with citric acid as the chelating agent does not change as pH value changes, and the materials own uniform particle size distribution and good electrochemical performance. It delivers an initial discharge capacity of 113.58 mA·h/g at 10C, remaining as high as 108.48 mA·h/g after 900 cycles, with a capacity retention of 95.51%.

Synthesis and electrochemical properties of LiNi_(0.87)Co_(0.10)Mg_(0.03)O_2 cathode materials

A Co-Mg co-substituted LiNi0.87Co0.10Mg0.03O2 cathode material was prepared by a co-precipitation method. The prepared LiNi0.87Co0.10Mg0.03O2 exhibits excellent electrochemical properties, such as initial discharge capacities of 202.6 mA.h/g and 190.5 mA.h/g at 0.2C and 1C rate, respectively, in operating voltage range of 3.0-4.3 V （versus Li^＋/Li）. The capacity retentions are 96.1% and 93.4% at 0.2C and 1C, respectively, after 50 cycles. Moreover, the cycle performance of the sample was investigated in a 053048-type square Li ion battery. This type of battery can keep 81.7% of initial capacity after 500 charge-discharge cycles at 1C rate, which is close to that of commercial LiCoO2 battery. Therefore, the as-prepared material is capable of such high energy applications as portable product power.

Graphene oxide assisted facile hydrothermal synthesis of LiMn_(0.6)Fe_(0.4)PO_4 nanoparticles as cathode material for lithium ion battery

Assisted by graphene oxide（GO）,nano-sized LiMn0.6Fe0.4PO4 with excellent electrochemical performance was prepared by a facile hydrothermal method as cathode material for lithium ion battery.SEM and TEM images indicate that the particle size of LiMn0.6Fe0.4PO4（S2）was about 80 nm in diameter.The discharge capacity of LiMn0.6Fe0.4PO4 nanoparticles was 140.3 mAh-g^1 in the first cycle.It showed that graphene oxide was able to restrict the growth of LiMn0.6Fe0.4PO4 and it in situ reduction of GO could improve the electrical conductivity of LiMn0.6Fe0.4PO4 material.

Synthesis and characterization of phosphate-modified LiMn_2O_4 cathode materials for Li-ion battery

LiMn2O4 spinel cathode materials were modified with 2 wt.%Li-M-PO4（M=Co,Ni,Mn） by polyol synthesis method.The phosphate surface-modified LiMn2O4 cathode materials were physically characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and energy dispersive X-ray spectroscopy（EDS）.The charge-discharge test showed that the cycling and rate capacities of LiMn2O4 cathode materials were significantly enhanced by stabilizing the electrode surface with phosphate.

Preparation and electrochemical properties of Y-doped Li_3V_2(PO_4)_3 cathode materials for lithium batteries

Y-doped Li3V2（PO4）3 cathode materials were prepared by a carbothermal reduction（CTR） process.The properties of the Y-doped Li3V2（PO4）3 were investigated by X-ray diffraction（XRD） and electrochemical measurements.XRD studies showed that the Y-doped Li3V2（PO4）3 had the same monoclinic structure as the undoped Li3V2（PO4）3.The Y-doped Li3V2（PO4）3 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram（CV）, and electrochemical impedance spectra（EIS）.The optimal doping content of Y was x=0.03 in Li3V2-xYx（PO4）3 system.The Y-doped Li3V2（PO4）3 samples showed a better cyclic ability.The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Y-doping.The improved electrochemical perormances of the Y-doped Li3V2（PO4）3 cathode materials were attributed to the addition of Y3＋ ion by stabilizing the monoclinic structure.

Synthesis and electrochemical properties of Al-doped LiVPO_4F cathode materials for lithium-ion batteries

Al-doped LiVPO4F cathode materials LiAlxV1-xPO4F were prepared by two-step reactions based on a car-bothermal reduction （CTR） process. The properties of the Al-doped LiVPO4F were investigated by X-ray diffraction （XRD）,scanning electron microscopy （SEM）,and electrochemical measurements. XRD studies show that the Al-doped LiVPO4F has the same triclinic structure （space group p-↑1 ） as the undoped LiVPO4F. The SEM images exhibit that the particle size of Al-doped LiVPO4F is smaller than that of the undoped LiVPO4F and that the smallest particle size is only about 1 μm. The Al-doped LiVPO4F was evaluated as a cathode material for secondary lithium batteries,and exhibited an improved reversibility and cycleability,which may be attributed to the addition of Al^3＋ ion by stabilizing the triclinic structure.

Amorphous Zr(OH)4 coated LiNi0.915Co0.075Al0.01O2 cathode material with enhanced electrochemical performance for lithium ion batteries

LiNiCoAlO（NCA） with Zr（OH）coating is demonstrated as high performance cathode material for lithium ion batteries（LIBs）. The coated materials are synthesized via a simple dry coating method of NCA with Zr（OH）powders, and then characterized with scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and X-ray photoelectron spectroscopy（XPS）. Experimental results show that amorphous Zr（OH）powders have been successfully coated on the surface of spherical NCA particles, exhibiting improved electrochemical performance. 0.50 wt% Zr（OH）coated NCA delivers a capacity of 197.6 mAh/g at the first cycle and 154.3 mAh/g after 100 cycles with a capacity retention of 78.1% at 1 C rate. In comparison, the pure NCA shows a capacity of 194.6 mAh/g at the first cycle and 142.5 mAh/g after 100 cycles with a capacity retention of 73.2% at 1 C rate. Electrochemical impedance spectroscopy（EIS） results show that the coated material exhibits a lower resistance, indicating that the coating layer can efficiently suppress transition metals dissolution and decrease the side reactions at the surface between the electrode and electrolyte. Therefore, surface coating with amorphous Zr（OH）is a simple and useful method to enhance the electrochemical performance of NCA-based materials for the cathode of LIBs.

Effects of different iron sources on the performance of LiFePO_4/C composite cathode materials

Olivine LiFePO4/C composite cathode materials were synthesized by a solid state method in N2 ＋ 5vol% H2 atmosphere. The effects of different iron sources, including Fe（OH）3 and FeC2O4·2H2O, on the performance of as-synthesized cathode materials were investigated and the causes were also analyzed. The crystal structure, the morphology, and the electrochemical performance of the prepared samples were characterized by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, laser particle-size distribution measurement, and other electrochemical techniques. The results demonstrate that the LiFePO4/C materials obtained from Fe（OH）3 at 800℃ and FeC2O4·2H2O at 700℃ have the similar electrochemical performances. The initial discharge capacities of LiFePO4/C synthesized from Fe（OH）3 and FeC2O4·2H2O are 134.5 mAh.g^-1 and 137.4 mAh.g^-1 at the C/5 rate, respectively. How- ever, the tap density of the LiFePO4/C materials obtained from Fe（OH）3 are higher, which is significant for the improvement of the capacity of the battery.

Fluorine-substituted O3-type NaNi_(0.4)Mn_(0.25)Ti_(0.3)Co_(0.05)O_(2-x)F_(x) cathode with improved rate capability and cyclic stability for sodium-ion storage at high voltage

O3-type Na NiO_(2)-based cathode materials undergo irreversible phase transition and serious capacity decay at high voltage above 4.0 V in sodium-ion batteries. To address these challenges, effects of Fsubstitution on the structure and electrochemical performance of Na Ni_(0.4)Mn_(0.25)Ti_(0.3)Co_(0.05)O_(2) are investigated in this article. The F-substitution leads to expanding of interlayer, which can enhance the mobility of Na+. NaNi_(0.4)Mn_(0.25)Ti_(0.3)Co_(0.05)O_(1.92)F_(0.08)(NMTC-F_(0.08)) with the optimal F-substitution degree exhibits much improved rate capability and cyclic stability. It delivers reversible capacities of 177 and 97 m Ah g^(-1) at 0.05 and 5 C within 2.0–4.4 V, respectively. Galvanostatic intermittent titration technique verifies faster kinetics of Na+diffusion in NMTC-F_(0.08). And in-situ XRD investigation reveals the phase evolution of NMTC-F_(0.08), indicating enhanced structural stability results from F-substitution. This study may shed light on the development of high performance cathode materials for sodium-ion storage at high voltage.

Synthesis and characterization of triclinic structural LiVPO_4F as possible 4.2 V cathode materials for lithium ion batteries

A potential 4.2 V cathode material LiVPO4F for lithium batteries was prepared by two-step reaction method based on a carbon-thermal reduction （CTR） process. Firstly, V2O5, NH4H2PO4 and acetylene black are reacted under an Ar atmosphere to yield VPO4. The transition-metal reduction is facilitated by the CTR based on C→CO transition. These CTR conditions favor stabilization of the vanadium as V^3＋ as well as leaving residual carbon, which is useful in the subsequent electrode processing. Secondly, VPO4 reacts with ElF to yield LiVPO4F product. The property of the LiVPO4F was investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electrochemical measurement. XRD studies show that LiVPO4F synthesized has triclinic structure（space group p I ）, isostructural with the naturally occurring mineral tavorite, EiFePO4-OH. SEM image exhibits that the particle size is about 2μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of LiVPO4F powder is 119 mA·h/g at the rate of 0.2C with an average discharge voltage of 4.2V （vs Ei/Li^＋）, and the capacity retains 89 mA·h/g after 30 cycles.

Synthesis and electrochemical properties of Li[Ni_xCo_yMn_(1-x-y)]O_2 (x, y = 2/8, 3/8) cathode materials for lithium ion batteries

The tmiform layered Li（Ni2/8Co3/8Mn3/8）O2, Li（Ni3/8Co2/8Mn3/8）O2, and Li（Ni3/8Co3/8Mn2/8）O2 cathode materials for lithium ion batteries were prepared using the hydroxide co-precipitation method. The effects of calcination temperature and transition metal contents on the structure and electrochemical properties of the Li-Ni-Co-Mn-O were systemically studied. The results of XRD and electrochemical performance measurement show that the ideal preparation conditions were to prepare the Li（Ni3/8Co3/8Mn2/8）O2 cathode material calcined at 900℃ for 10 h. The well-ordered Li（Ni3/8Co3/8Mn2/8）O2 synthesized under the optimal conditions has the I003/I104 ratio of 1.25 and the R value of 0.48 and delivers the initial discharge capacity of 172.9 mA·h·g^-1, the discharge capacity of 166.2 mA·h·g^-1 after 20 cycles at 0.2C rate, and the impedance of 558 Ω after the first cycle. The decrease of Ni content results in the decrease of discharge capacity and the bad cycling performance of the Li-Ni-Co-Mn-O cathode materials, but the decreases of Mn content and Co content to a certain extent can improve the electrochemical properties of the Li-Ni-Co-Mn-O cathode materials.