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1.
Nanocrystalline LiFePO 4 and LiFe 0.97Sn 0.03PO 4 cathode materials were synthesized by an inorganic-based sol–gel route. The physicochemical properties of samples were characterized
by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and
elemental mapping. The doping effect of Sn on the electrochemical performance of LiFePO 4 cathode material was extensively investigated. The results showed that the doping of tin was beneficial to refine the particle
size, increase the electrical conductivity, and facilitate the lithium-ion diffusion, which contributed to the improvement
of the electrochemical properties of LiFePO 4, especially the high-rate charge/discharge performance. At the low discharge rate of 0.5 C, the LiFe 0.97Sn 0.03PO 4 sample delivered a specific capacity of 158 mAh g −1, as compared with 147 mAh g −1 of the pristine LiFePO 4. At higher C-rate, the doping sample exhibited more excellent discharge performance. LiFe 0.97Sn 0.03PO 4 delivered specific capacity of 146 and 128 mAh g −1 at 5 C and 10 C, respectively, in comparison with 119 and 107 mAh g −1 for LiFePO 4. Moreover, the doping of Sn did not influence the cycle capability, even at 10 C. 相似文献
2.
The olivine-type samarium-doped LiFe 1 ? x Sm x PO 4/C ( x?=?0, 0.01, 0.02, 0.03, 0.04, and 0.05) composites were synthesized via liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive spectroscopy, galvanostatic charge–discharge, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. The results showed that the small amount of Sm 3+ ion-doped can keep the olivine microstructure of LiFePO 4, modify the particle morphology, decrease polarization overpotential and charge transfer resistance, and enhance exchange current density, thus improve the electrochemical performance of the LiFePO 4/C. However, the large doped content of Sm 3+ ion can form more SmPO 4, which can weaken the electrochemical performance of LiFePO 4/C. Among all the doped samples, LiFe 0.99Sm 0.01PO 4/C showed the best rate capacity, cycling stability, and low temperature performance. The LiFe 0.99Sm 0.01PO 4/C sample exhibited the initial discharge capacity of 148.1, 133.4, 117.5, and 106.6 mAh g ?1 at 1C, 2C, 5C, and 10C, respectively. In addition, the discharge capacity of the material was 94.8 mAh g ?1 after 800 cycles at 10C. Moreover, the initial discharge capacity of 0.1C, 0.2C, 0.5C, and 1C were 104.4, 96.2, 53.9, and 50.8 mAh g ?1 at ?20 °C. 相似文献
3.
The effect of fluorine doping on the electrochemical performance of LiFePO 4/C cathode material is investigated. The stoichiometric proportion of LiFe(PO 4) 1−x
F 3x
/C ( x = 0.01, 0.05, 0.1, 0.2) materials was synthesized by a solid-state carbothermal reduction route at 650 °C using NH 4F as dopant. X-ray diffraction, scanning electron microscope, energy-dispersive X-ray, and X-ray photoelectron spectroscopy
analyses demonstrate that fluorine can be incorporated into LiFePO 4/C without altering the olivine structure, but slightly changing the lattice parameters and having little effect on the particle
sizes. However, heavy fluorine doping can bring in impurities. Fluorine doping in LiFePO 4/C results in good reversible capacity and rate capability. LiFe(PO 4) 0.95 F 0.15/C exhibits highest initial capacity and best rate performance. Its discharge capacities at 0.1 and 5 C rates are 156.1 and
119.1 mAh g −1, respectively. LiFe(PO 4) 0.95 F 0.15/C also presents an obviously better cycle life than the other samples. We attribute the improvement of the electrochemical
performance to the smaller charge transfer resistance ( R
ct) and influence of fluorine on the PO 43− polyanion in LiFePO 4/C. 相似文献
4.
基于第一性原理密度泛函理论计算了LiFePO 4和LiFe 1-xMo xPO 4( x=0.005,0.01,0.015,0.02,和0.025)的电子结构和锂离子扩散能垒。结果显示掺杂后的LiFe 0.99Mo 0.01PO 4样品具有最大的(101)晶面间距,由此可知LiFe 0.99Mo 0.01PO 4沿[101]晶向具有最宽的锂离子扩散通道。未掺杂的LiFePO 4的锂离子扩散能垒为4.289eV,而掺杂后LiFe 0.99Mo 0.01PO 4降为4.274eV,经过计算得出掺杂样品LiFe 0.99Mo 0.01PO 4的锂离子扩散系数增为未掺杂LiFePO 4的1.79倍,表明Mo掺杂有利于改善LiFePO 4的锂离子扩散能力。态密度图显示,掺杂Mo后导带底附近的峰强度增强,对LiFePO 4电子导电性能的提高是有利的。因此,掺杂Mo有益于提高LiFePO 4的锂离子扩散能力和电子导电能力。结合我们的实验结果比较得知,在磷酸铁锂性能的改善上,相比电子导电能力,锂离子扩散能力的提高起到了更重要的作用。 相似文献
5.
Based on the method of in situ polymerization synthesis combined with two-step sinter-ing process, LiFe 1-xV x(PO 4) (3-y)/ 3F y/C was prepared. The e ects of V and F co-doping on the structure, morphology, and electrochemical performances of LiFePO 4/C were in-vestigated by X-ray di raction, Fourier transform infrared spectra, scanning electron mi-croscope, charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results indicated that the V and F co-doping did not destroy the olivine structure of LiFePO 4/C, but it can stabilize the crystal structure, decrease charge transfer resistance, enhance Li ion di usion velocity, further improve its cycling and high-rate capabilities of LiFePO 4/C. 相似文献
6.
Olivine-type LiFePO 4 is one of the most promising cathode materials for lithium-ion batteries, but its poor conductivity and low lithium-ion diffusion limit its practical application. The electronic conductivity of LiFePO 4 can be improved by carbon coating and metal doping. A small amount of La-ion was added via ball milling by a solid-state reaction method. The samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM)/mapping, differential scanning calorimetry (DSC), transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS), and total organic carbon (TOC). Their electrochemical properties were investigated by cyclic voltammetry, four-point probe conductivity measurements, and galvanostatic charge and discharge tests. The results indicate that these La-ion dopants do not affect the structure of the material but considerably improve its rate capacity performance and cyclic stability. Among the materials, the LiFe 0.99La 0.01PO 4/C composite presents the best electrochemical behavior, with a discharge capacity of 156 mAh g ?1 between 2.8 and 4.0 V at a 0.2 C-rate compared to 104 mAh g ?1 for undoped LiFePO 4. Its capacity retention is 80% after 497 cycles for LiFe 0.99La 0.01PO 4/C samples. Such a significant improvement in electrochemical performance should be partly related to the enhanced electronic conductivities (from 5.88?×?10 ?6 to 2.82?×?10 ?3 S cm ?1) and probably the mobility of Li + ion in the doped samples. The LiFe 0.99La 0.01PO 4/C composite developed here could be used as a cathode material for lithium-ion batteries. 相似文献
7.
Dy doping and carbon coating are adopted to synthesize a LiFePO 4 cathode material in a simple solution environment. The samples were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Their electrochemical properties were investigated by cyclic voltammetry (CV) and galvanostatic charge‐discharge tests. An initial discharge capacity of 153 mAh/g was achieved for the LiDy 0.02Fe 0.98PO 4/C composite cathode with a rate of 0.1 C. In addition the electronic conductivity of Dy doped LiFePO 4/C was enhanced to 1.9 × 10 ?2 Scm ?1. The results suggest that the improvement of the electrochemical properties are attributed to the dysprosium doping and carbon coating which facilitates the phase transformation between triphylite and heterosite during cycling. XRD data indicate that doping did not destroy the lattice structure of LiFePO 4. To evaluate the effect of Dy substitution, cyclic voltammetry was used at room temperature. prepared. From Cv measurement a more symmetric curve with smaller interval between the cathodic and anodic peak current was obtained by Dy substitution. This denoted a decreasing of polarization with Dy substitution, which illustrated an enhancement of electrochemical performances. 相似文献
8.
Cathode material LiFe 0.7?V 0.2PO 4/C is successfully synthesized by multistep sintering through carbon thermal reaction including 650 °C for 10 h and 750 °C for 6 h. The crystal structure and surface morphology of the synthesized materials are characterized by X-ray diffractometer and scanning electron microscope, respectively. Cycle voltammetry, electrochemical impedance spectroscopy, and charge–discharge test are used to investigate the electrochemical performances of these samples. The results revealed that the synthesized LiFe 0.7?V 0.2PO 4/C material simultaneously contains olivine structure LiFePO 4 and monoclinic structure Li 3V 2(PO 4) 3. It shows improved conductivity, Li-ion diffusion coefficient, excellent charge/discharge performance, and reversibility due to both the incorporation of Li 3V 2(PO 4) 3 fast ion conductor and the employed multistep sintering. The initial discharge specific capacities of LiFe 0.7?V 0.2PO 4/C by multistep sintering are 167.8, 154.7, and 140.8 mAh g ?1 at 0.5, 1, and 2 C, respectively. After a total of 230 cycles at different rates, the sample still shows good performances. After 100 cycles at 2 C, the capacity retention is 99.1 %, and the capacity is 139.6 mAh g ?1. The LiFe 0.7?V 0.2PO 4/C material synthesized by this method can be used as a cathode material for advanced lithium-ion batteries. 相似文献
9.
以LiH 2PO 4和FeC 2O 4·2H 2O为原料, 采用分步添加聚乙烯醇和葡萄糖两种碳源的方式, 通过两步固相法合成了碳包覆的LiFePO 4材料. 700℃下处理的产物结晶良好, 颗粒分布均匀, 具有良好的电化学性能, 0.1C和1C倍率下放电比容量分别为157.3 和138.3 mAh·g -1. 在碳包覆的基础上, 选择高价Nb 5+进行铁位取代获得了复合改性的LiFe 1-xNb xPO 4/C (x=0.005, 0.01, 0.015, 0.02)材料. 优化的LiFe 0.99Nb 0.01PO 4/C 材料显示了良好的倍率充放电能力和循环稳定性, 0.1C和5C倍率下放电比容量分别为160.5 和136.0 mAh·g -1, 5C倍率下循环50 次后比容量保持在134.8 mAh·g -1, 容量保持率为99.1%. 循环伏安测试结果表明, Nb 5+离子掺杂减少了锂离子扩散阻力, 降低了充放电过程中的动力学限制, 提高了电极的可逆性. 相似文献
10.
The olivine-typed cathode materials of LiFePO 4were prepared via solid-state reaction under argon atmosphere and co-doped by manganese and fluorine to improve their electrochemical
performances. The crystal structure, morphology, and electrochemical properties of the prepared samples were investigated
using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy,
cyclic voltammetry, and charge–discharge cycle measurements. The result showed that the electrochemical performance of LiFePO 4 had been improved dramatically by Mn–F co-doping. The initial discharge capacity of LiFe 0.99Mn 0.01 (PO 4) 2.99/3F 0.01/C samples reached 140.2 mAh/g at 1C rate and only had a small amount of fading in 50 cycles. 相似文献
11.
基于第一性原理密度泛函理论计算了LiFePO4和LiFe1-xMoxPO4(x=0.005,0.01,0.015,0.02,和0.025)的电子结构和锂离子扩散能垒。结果显示掺杂后的LiFe0.99Mo0.01PO4样品具有最大的(101)晶面间距,由此可知LiFe0.99Mo0.01PO4沿[101]晶向具有最宽的锂离子扩散通道。未掺杂的LiFePO4的锂离子扩散能垒为4.289 eV,而掺杂后LiFe0.99Mo0.01PO4降为4.274 eV,经过计算得出掺杂样品LiFe0.99Mo0.01PO4的锂离子扩散系数增为未掺杂LiFePO4的1.79倍,表明Mo掺杂有利于改善LiFePO4的锂离子扩散能力。态密度图显示,掺杂Mo后导带底附近的峰强度增强,对LiFePO4电子导电性能的提高是有利的。因此,掺杂Mo有益于提高LiFePO4的锂离子扩散能力和电子导电能力。结合我们的实验结果比较得知,在磷酸铁锂性能的改善上,相比电子导电能力,锂离子扩散能力的提高起到了更重要的作用。 相似文献
12.
The modification techniques of applying carbon coating on particle surface and doping vanadium at Fe site were applied to make the LiFePO 4 cathode materials achieve high rate performance in lithium ion batteries. To design and synthesize these LiFe (1?x)V x PO 4/C ( x?=?0, 0.02, 0.05, or 0.08) composites, an aqueous solution–evaporation method was taken, in which every kind of raw material was distributed at a high degree of uniformity. The LiFe 0.95V 0.05PO 4/2.57 wt% C composite displayed the best electrochemical performances. At rates of 0.1, 0.5, 2, 5, and 10 C (1 C?=?170 mAg ?1), it delivered a discharge capacity of 157.8, 156.9, 149, 139.6, and 130.1 mAh g ?1, respectively. The composite exhibited perfect cycle stabilities as well, maintaining 100 % (0.5 C), 99.7 % (2 C), 98.9 % (5 C), and 96.6 % (10 C) of the first discharge capacity after 100 cycles at different rates, respectively. 相似文献
13.
采用两步固相反应合成了锂、铁双位掺杂的锂离子电池正极材料Li0.99Nb0.01Fe1-xMgxPO4/C(x=0,0.01,0.02,0.03,0.04)。通过X射线衍射(XRD)、扫描电镜(SEM)以及恒电流充放电测试,研究了复合材料的晶体结构、形貌以及电化学性能。实验结果表明,制备的Li0.99Nb0.01Fe1-xMgxPO4/C(x=0,0.01,0.02,0.03,0.04)为纯相,掺杂适量的Nb5+、Mg2+离子可减小材料的晶粒尺寸,当Nb离子掺杂量为1mol%、Mg离子掺杂量为3mol%时,Li0.99Nb0.01Fe0.97Mg0.03PO4/C的电化学性能最佳。室温下,0.2C、1C、2C、4C(1C=170mA·g-1)倍率充放电其首次放电比容量分别为153.7、149.7、144.6、126.4mAh·g-1,即使在8C倍率下放电其放电比容量也有92.2mAh·g-1,并表现出良好的循环性能。 相似文献
14.
Well-shaped and uniformly dispersed LiFePO_4 nanorods with a length of 400–500 nm and a diameter of about 100 nm, are obtained with participation of a proper amount of anion surfactant sodium dodecyl sulfonate(SDS) without any further heating as a post-treatment. The surfactant acts as a self-assembling supermolecular template, which stimulated the crystallization of LiFePO_4 and directed the nanoparticles growing into nanorods between bilayers of surfactant(BOS). LiFePO_4 nanorods with the reducing crystal size along the b axis shorten the diffusion distance of Li~+ extraction/insertion, and thus improve the electrochemical properties of LiFePO_4 nanorods. Such prepared LiFePO_4 nanorods exhibited excellent specific capacity and high rate capability with discharge capacity of 151 mAh/g, 122 mAh/g and 95 mAh/g at 0.1C, 1 C and 5 C, respectively. Such excellent performance of LiFePO_4 nanorods is supposed to be ascribed to the fast Li~+ diffusion velocity from reduced crystal size along the b axis and the well electrochemical conductivity. The structure, morphology and electrochemical performance of the samples were characterized by XRD, FE-SEM, HRTEM, charge/discharge tests, and EIS(electrochemical impedance spectra). 相似文献
15.
Carbon coated Li 1 + x
FePO 4 ( x = 0, 0.01, 0.02, 0.03, 0.04) and doped compositions Li 1.03Fe 0.99Ti 0.01PO 4 have been synthesized by thermal reduction method in this paper. The results showed that increasing the content in Li 1 + x
FePO 4 result in better electrochemical properties and cyclic performances until x = 0.03, which had similar change law with the particle size of samples; and the initial discharge capacity and cycle life
of Li 1.03Fe 0.9Ti 0.01PO 4 was better than other samples under 1 C rate. When the Li 1.03Fe 0.99Ti 0.01PO 4/C sample cycled before 60 times, this sample exhibited a trend of increased capacity, and reached the highest discharging
rate capacity of 156 mA h g −1 at 60 cycles. The electrochemical performances of LiFePO 4 compositions synthesized by thermal reduction method, to some extent, can be improved by Li excess content and Ti doping. 相似文献
16.
Three kinds of LiFePO 4 materials, mixed with carbon (as LiFePO 4/C), doped with Ti (as Li 0.99Ti 0.01FePO 4), and treated both ways (as Li 0.99Ti 0.01FePO 4/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical
behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle
measurements. It was found that the electrochemical behavior of LiFePO 4 could be increased by carbon coating and Ti-doping methods. Among the materials, Li 0.99Ti 0.01FePO 4/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge
rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity.
The Li 0.99Ti 0.01FePO 4/C composite developed here can be used as the cathode material for lithium ion batteries. 相似文献
17.
A series of LiMn 1-x V x PO 4 samples have been synthesized successfully via a conventional solid-state reaction method. The active materials are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. The electrochemical performances of the samples are tested using cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge measurement techniques. It is confirmed that the samples are in single phase when the content of vanadium ( x) is lower than 0.05. If that content is higher than 0.1, the samples are shown to contain an additional conductive phase of Li 3V 2(PO 4) 3. The vanadium doping significantly enhances the electrochemical properties of LiMnPO 4. It is underlined that the optimal ratio for a low-vanadium doping with the best electrochemical performance is 0.1 and this material exhibits a corresponding initial charge and discharge capacity of 98.9 and 98.1 mAh g ?1 at 0.1 C under 50 °C. The capacity retention is higher than 99 % after 30 cycles. The dramatic electrochemical improvement of the LiMnPO 4 samples is ascribed to the strengthened ability of lithium-ion diffusion and enhanced electronic conductivity for the V-doped samples. 相似文献
18.
Li 3Ni x V 2?x (PO 4) 3/C ( x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li 3Ni 0.04?V 1.96(PO 4) 3/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g ?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li 3V 2(PO 4) 3 have also been effectively improved through Ni doping. 相似文献
19.
Lithium iron phosphate (LiFePO4) cathode materials were synthesized by the solvothermal method with the assistance of different surfactants. The influences of polyethylene glycol 2000 (PEG 2000), polyvinylpyrrolidone (PVP), and cetyltrimethyl ammonium bromide (CTAB) on the microstructure and electrochemical performance of LiFePO4 were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The particle size of the LiFePO4 synthesized with the assistance of PEG was uniform and showed a flat rhombohedron-like shape. The initial discharge specific capacity is up to 122.80 mAh/g with an initial coulombic efficiency of 95.50% at 0.1C. LiFePO4 synthesized with PVP-assisted presents a porous structure with an initial discharge specific capacity of 91.01 mAh/g. LiFePO4 synthesized with CTAB-assisted shows a flower-like morphology with an initial discharge specific capacity of 100.44 mAh/g. Though the initial discharge capacities of the LiFePO4 materials prepared with the assistance of CTAB and PVP are lower than those of the LiFePO4 prepared without the assistance of surfactant, the two materials exhibited excellent cyclic stability at 0.1C. 相似文献
20.
Exotic metal (EM) doping in LiFePO4 materials could mitigate their poor electronic conductivity and electrochemical performance. This effect is believed to be dependent on the EM dwelling site, which has yet been well clarified due to experimental difficulty. Herein, we report on Mg-doped LiFePO 4 samples with dopant in two distinct sites, namely the Li 1 − 2xMg xFePO 4 and LiFe 1 − xMg xPO 4, using a specially designed two-step reaction. The conductivity and electrochemical test results are a clear indication that the performance of the doped LiFePO 4 samples is highly Mg site dependent, consistent with theoretical analysis. 相似文献
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