Electrochemical performance of LiFePO_4/(C+Fe_2P) composite cathode material synthesized by sol-gel method

A LiFePO4/（C＋Fe2P） composite cathode material was prepared by a sol-gel method using Fe（NO3）3.9H20, LiAc·H2O）, NHaH2PO4 and citric acid as raw materials, and the physical properties and electrochemical performance of the composite cathode material were investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical tests. The Fe2P content, morphology and electrochemical performance of LiFePOa/（C＋Fe2P） composite depend on the calcination temperature. The optimized LiFePO4/（C＋FeeP） composite is prepared at 650 ~C and the optimized composite exhibits sphere-like morphology with porous structure and Fe2P content of about 3.2% （mass fraction）. The discharge capacity of the optimized LiFePO4/（C＋FeRP） at 0.1C is 156 and 161 mA.h/g at 25 and 55 ℃, respectively, and the corresponding capacity retentions are 96% after 30 cycles; while the capacity at 1C is 142 and 149 mA.h/g at 25 and 55 ℃, respectively, and the capacity still remains 135 and 142 mA-h/g after 30 cycles at 25 and 55℃, respectively.

Hydrothermal synthesis of spindle-like Li_2FeSiO_4-C composite as cathode materials for lithium-ion batteries

In this paper,we report on the preparation of Li2FeSiO4,sintered Li2FeSiO4,and Li2FeSiO4-C composite with spindle-like morphologies and their application as cathode materials of lithium-ion batteries.Spindle-like Li2FeSi04 was synthesized by a facile hydrothermal method with（NH4）2Fe（SO4）2 as the iron source.The spindle-like Li2FeSiO4 was sintered at 600 ℃ for 6 h in Ar atmosphere.Li2FeSiO4-C composite was obtained by the hydrothermal treatment of spindle-like Li2FeSiO4 in glucose solution at 190 ℃ for 3 h.Electrochemical measurements show that after carbon coating,the electrode performances such as discharge capacity and high-rate capability are greatly enhanced.In particular.Li2FeSiO4-C with carbon content of 7.21 wt%delivers the discharge capacities of 160.9 mAh·g-1 at room temperature and 213 mAh·g-1 at45℃（0.1 C）,revealing the potential application in lithium-ion batteries.

Electrochemical performance of LiFePO_(4)-Li_(3)V_(2)(PO_4)_3 composite material prepared by solid-hydrothermal method

LiFePO4-Li3V2（PO4）3 composites were synthesized by solid-hydrothermal method and by ball milling,respectively.The electrochemical performance of the solid-hydrothermally obtained materials（C-LFVP） was significantly improved compared with LiFePO4（LFP） and Li3V2（PO4）3（LVP）,and it was also much better than that of the ball-milled LiFePO4-Li3V2（PO4）3（P-LFVP）.C-LFVP and P-LFVP both had four REDOX peaks（voltage plateaus）,which coincided with that of LFP and LVP.Some new trace substances were found in C-LFVP which had more perfect morphology,this was responsible for the better electrochemical performance of C-LFVP than P-LFVP.

Synthesis of porous nano/micro structured LiFePO_4/C cathode materials for lithium-ion batteries by spray-drying method

In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.

Synthesis and electrochemical performances of spherical LiFePO_4 cathode materials for Li-ion batteries

Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g-1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g-1. The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.

A novel synthetic route for LiFePO_4/C cathode materials by addition of starch for lithium-ion batteries

LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.

One Step Ball-Milling Synthesis of LiFePO_ 4 Nanoparticles as the Cathode Material of Li-Ion Batteries

A one-step synthetic method was used to synthesize Olivline LiFePO4 powders by direct ball milling the stoichiometric mixture of Fe, Li3PO4 , and FePO4 powders. XRD and TEM measurements revealed that the as-prepared LiFePO4 powder have a homogeneous Olivine structure and a uniform size distribution of ca. 50 nm. Based on this material, a LiFePO4/C composite was prepared and used for the cathode material of Li-ion batteries. The charge-discharge experiments demonstrated that the LiFePO4/C composite material has a high capacity of 132 mAh/g at 0.1 C and a quite highrate capability of 95 mAh/g at 1 C. This new ball-milling method may provide a completely green synthetic route for preparing the materials of this type cost-effectively and in large volume.

Regeneration of spent LiFePO4 as a high-performance cathode material by a simultaneous coating and doping strategy

With the number of decommissioned electric vehicles increasing annually,a large amount of discarded power battery cathode material is in urgent need of treatment.However,common leaching methods for recovering metal salts are economically inefficient and polluting.Meanwhile,the recycled material obtained by lithium remediation alone has limited performance in cycling stability.Herein,a short method of solid-phase reduction is developed to recover spent LiFePO4 by simultaneously introducing Mg2+ions for hetero-atom doping.Issues of particle agglomeration,carbon layer breakage,lithium loss,and Fe3+defects in spent LiFePO4 are also addressed.Results show that Mg2+addition during regeneration can remarkably enhance the crystal structure stability and improve the Li+diffusion coefficient.The regenerated LiFePO4 exhibits significantly improved electrochemical performance with a specific discharge capacity of 143.2 mAh·g^(−1)at 0.2 C,and its capacity retention is extremely increased from 37.9%to 98.5%over 200 cycles at 1 C.Especially,its discharge capacity can reach 95.5 mAh·g^(−1)at 10 C,which is higher than that of spent LiFePO4(55.9 mAh·g^(−1)).All these results show that the proposed regeneration strategy of simultaneous carbon coating and Mg2+doping is suitable for the efficient treatment of spent LiFePO4.

Physical and Electrochemical Properties of Doped LiFePO4 as Cathode Material for Lithium-Ion Batteries

LiFePO4 cathode material was synthesized by a solid-state reaction using doping several elements (Nb5 + ,Zr4 + ). The starting materials were mixed with a high-efficient sander and treated thermally under flowing N2. The samples were characterized by X-ray diffraction (XRD), field-emission gun electron microscopy (FEG), and their electrochemical performance was investigated in the term of cycling behavior. Room temperature discharge capacity about 140.6 mA·h·g-1 was obtained at C/5 rate.

Effect of baking processes on properties of TiB_2/C composite cathode material

Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.

Synthesis of LiMnPO_4/C composite material for lithium ion batteries by sol-gel method

The LiMnPO4/C composite material was synthesized via a sol-gel method based on the citric acid. The X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical performance tests were adopted to characterize the properties of LiMnPO4/C. The XRD studies show that the pure olivine phase LiMnPO4 can be obtained at a low temperature of 500 °C. The SEM analyses illustrate that the citric acid used as the chelating reagent and carbon source can restrain the particle size of LiMnPO4/C well. The LiMnPO4/C sample synthesized at 500 °C for 10 h performs the highest initial discharge capacity of 122.6 mA-h/g, retaining 112.4 mA-h/g over 30 cycles at 0.05C rate. The citric acid based sol-gel method is favor to obtain the high electrochemical performance of LiMnPO4/C.

Characterization and Electrochemical Performance of ZnO Modified LiFePO_4/C Cathode Materials for Lithium-ion Batteries

To improve the electrical conductivity of LiFePO4 cathode materials, the ZnO modified LiFePO4/C cathode materials are synthesized by a two-step process including solid state synthesis method and precipitation method. The structures and compositions of ZnO modified LiFePO4/C cathode materials are characterized and analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy, which indicates that the existence of ZnOhas little or no effect on the crystal structure, particles size and morphology of LiFePO4. The electrochemical performances are also characterized and analyzed with charge-discharge test, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the existence of ZnO improves the specific capability and lithium ion diffusion rate of LiFePO4 cathode materials and reduces the charge transfer resistance of cell, and the one with 3 wt% ZnO exhibits the best electrochemical performance.

Synthesis and electrochemical properties of Li_(1-x)V_xCr_yFe_(1-x)PO_4/C as a cathode material

Composites Li1-xVxCryFe1-yPO4/C（x=0.01, 0.02; y = 0.01, 0.02） were synthesized by solid-state reaction method. The influence of the content of doping vanadium and chromium on the structure of Li1-xVxCryFe1-yPO4/C was investigated by XRD, while the morphology of powders was observed by SEM. The investigation of the electrochemical performances showed that the Li0.99V0.01Cr0.02Fe0.98PO4/C material has a higher capacity. At 0.1 C discharging rate, it is capable of delivering reversible specific capacity of 163.8 mAh/g with fairly stable cycleability.

Modified carbothermal reduction method for synthesis of LiFePO_4/C composite

With LiAc-2H2O as Li precursor,pure olivine phase LiFePO4/C was synthesized at a relatively low temperature（650 ℃） and short sintering period（4 h） by molten salt carbothermal reduction method.Scanning electron micrograph shows that particle size of the product is about 1μm,smaller than that of the sample synthesized with Li2CO3 as Li precursor.Electrochemical measurements prove that LiFePO4/C obtained from LiAc-2H2O shows high capacity.The initial discharge capacities are 148 mA-h/g at 0.5C rate and 115 mA-h/g at 5C rate,respectively.After 50 cycles,the capacity retention ratios are 93% and 89% at 0.5C rate and 5C rate,respectively.

Synthesis of LiFePO_4 using FeSO_4·7H_2O byproduct from TiO_2 production as raw material

As the byproduct of TiO2 industrial production, impure FeSO4.7H2O was used for the synthesis of LiFePO4. With the purified solution of FeSO4-7H2O, FePO4.xH2O was prepared by a normal titration method and a controlled crystallization method, respectively. Then LiFePO4 materials were synthesized by calcining the mixture of FePO4,xH2O, LizCO3, and glucose at 700℃ for 10 h in flowing Ar. The results indicate that the elimination of FeSO4.TH2O impurities reached over 95%, and using FePO4-xH2O prepared by the controlled crystallization method, the obtained LiFePO4 material has fine and sphere-like particles. The material delivers a higher initial discharge specific capacity of 149 mAh.g^-1 at a current density of 0.1C rate （1C = 170 mA.g^-0）; the discharge specific capacity also maintains above 120 rnAh.g^-1 after 100 cycles even at 2C rate. Thus, the employed processing is promising for easy control, low cost of raw material, and high electrochemical performance of the prepared material.

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.

An olivine LiFe_(0.5)Mn_(0.5)PO_(4)/rGO composite cathode material prepared from manganese ore tailings with excellent lithium storage performance

The high-value utilization of manganese ore tailings is of great significance for saving mineral resources and achieving environmental protection.Herein,an olivine LiFe_(0.5)Mn_(0.5)PO_(4)/rGO composite is synthesized by a simple precipitation method and subsequent high-temperature calcination process using the manganese ore tailings as raw material.The prepared LiFe_(0.5)Mn_(0.5)PO_(4)/rGO composite exhibits superior cycling stability(with 113.5 mAh·g^(-1)after 300 cycles at1.0C(1.0C=170 mA·g^(-1)))and superior rate performance(with 65.6 mAh·g^(-1)at 10.0C).Ex-situ XRD and electrochemical impedance spectroscopy(EIS)analyses evidence that the LiFe_(0.5)Mn_(0.5)PO_(4)/rGO material has excellent structural stability and electrochemical reversibility during charge and discharge processes.Furthermore,the LiFe_(0.5)Mn_(0.5)PO_(4)/rGO//graphite full Li-ion battery also exhibits excellent cycling stability indicating its potential commercialization value.

高密度锂离子电池正极复合材料LiFePO_4/C

以FeC2O4·2H2O、NH4H2PO4、Li2CO3和乙炔黑为原料,采用两步固相反应法制备了高密度LiFePO4/C正极复合材料。利用差热(DSC),热重(TGA)和X射线衍射(XRD)等分析手段具体探讨了第一步固相反应中可能存在的反应过程和中间产物。利用扫描电镜表征了复合材料LiFePO4/C中LiFePO4微粒形貌和接触状态。结果表明,乙炔黑的含量是影响LiFePO4微粒尺寸和微粒间接触界面的重要因素。在一次热处理的基础上,二次球磨和烧结有利于第二次固相反应过程中反应物质的接触和传质,较一步固相法提高了生成的LiFePO4的振实密度。当乙炔黑的含量(质量分数)为0.1%-1.5%时,两步固相法所制正极材料LiFePO4/C的振实密度可达到1.7 g/cm3,初次放电容量达到105 mA·h/g。

不同碳源对LiFePO_4/C复合材料性能的影响

采用机械液相活化法与高温固相法相结合制备了锂离子电池正极材料LiFePO4和LiFePO4/C。考察了蔗糖、柠檬酸、葡萄糖、酒石酸等不同碳源对材料性能的影响,并采用XRD、SEM和恒电流充放电测试等方法对材料的结构、表面形貌及电化学性能进行了研究,利用Raman光谱和TEM分析材料中碳的存在状态。结果表明,得到的样品结构均为橄榄石型,碳源的加入能有效地减小材料的颗粒尺寸,并且材料的电导率比纯LiFePO4的电导率提高了5个数量级。LiFePO4/C样品的表面包覆层均为非晶碳,以柠檬酸为碳源合成的LiFePO4/C材料,具有较小的颗粒尺寸,均匀多孔的表面碳包覆层和最佳的电化学性能。在0.1C下第3次的放电比容量达141.0mAh/g,循环10次后容量无衰减。

固相法合成LiFePO_4/C正极材料的电化学性能

以廉价原材料FeSO4·7H2O为铁源,以蔗糖为碳源,采用固相法合成了锂离子电池正极材料——LiFePO4/C复合材料。用X射线衍射(XRD)、扫描电镜(SEM)和电化学测试技术对不同铁源合成的LiFePO4/C复合材料的结构、形貌和电化学性能进行研究。结果表明:合成的样品具有均一的橄榄石型结构,以FeSO4·7H2O为铁源合成的LiFePO4/C复合材料的循环性能和高倍率放电性能均优于以FeC2O4·2H2O为铁源合成的LiFePO4/C复合材料的;由FeSO4·7H2O合成的LiFePO4/C复合材料的5C倍率放电比容量为105.9mA·h/g,经循环30次后,容量仍高达105.2mA·h/g。