锂离子电池正极材料LiNi0.5Co0.4Al0.1O2的合成与性能

采用高温固相法制备了锂离子电池正极材料LiNi_0.5Co_0.4Al_0.1O₂,采用X射线衍射(XRD)、傅里叶红外光谱(FTIR)、扫描电子显微镜(SEM)对材料的结构及表观形貌进行分析。通过恒电流充放电以及循环伏安法进行了电化学性能测试。测试结果表明,充放电电压在3~4.5V之间,在0.2C倍率下首次放电比容量达到159.9mAh·g^-1,经50次循环充放电后放电容量为142.6mAh·g^-1,表现出良好的电化学性能。     

锂离子电池正极材料LiNi0.5Co0.4Al0.1O2的合成与性能

采用高温固相法制备了锂离子电池正极材料LiNi_0.5Co_0.4Al_0.1O₂。采用X射线衍射(XRD)、傅里叶红外光谱(FTIR)、扫描电子显微镜(SEM)对材料的结构及表观形貌进行分析。通过恒电流充放电以及循环伏安法进行了电化学性能测试。测试结果表明,充放电电压在3~4.5 V之间,在0.2C倍率下首次放电比容量达到159.9 mAh·g^-1,经50次循环充放电后放电容量为142.6 mAh·g^-1,表现出良好的电化学性能。     

Preparation,characterization, and evaluation of LiNi0.4Co0.6O2 nanofibers for supercapacitor applications

We prepared LiNi_0.4Co_0.6O₂ nanofibers by electrospinning at the calcination temperature of 450 °C for 6 h. The prepared LiNi_0.4Co_0.6O₂ nanofibers was characterized by thermal, X-ray diffraction, and Fourier transform infrared (FTIR) studies. The morphology of LiNi_0.4Co_0.6O₂ nanofibers was characterized by scanning electron microscopy studies. The asymmetric supercapacitor was fabricated using LiNi_0.4Co_0.6O₂ nanofibers as positive electrode and activated carbon (AC) as negative electrode and a porous polypropylene separator in 1 M LiPF₆–ethylene carbonate/dimethyl carbonate (LiPF₆–EC:DMC) (1:1?v/v) as electrolyte. Cyclic voltammetry studies were then carried out in the potential range of 0 to 3.0 V at different scan rates which exhibited the highest specific capacitance of 72.9 F g^?1. The electrochemical impedance measurements were carried out to find the charge transfer resistance and specific capacitance of the cell, and they were found to be 5.05 Ω and 67.4 F g^?1, respectively. Finally, the charge–discharge studies were carried out at a current density of 1 mA cm^?2 to find out the discharge-specific capacitance, energy density, and power density of the capacitor cell, and they were found to be 70.9 F g^?1, 180.2 Wh kg^?1, and 248.0 W kg^?1, respectively.     

Improvement of electrochemical properties of LiNi1/3Mn1/3Co1/3O2 by coating with La0.4Ca0.6CoO3

In this paper, La_0.4Ca_0.6CoO₃-coated LiNi_1/3Mn_1/3Co_1/3O₂ is successfully prepared by the sol–gel method associated with microwave pyrolysis method. The structure and electrochemical properties of the La_0.4Ca_0.6CoO₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ are investigated by using X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. XRD analyses show that the La_0.4Ca_0.6CoO₃ coating does not change the structure of LiNi_1/3Co_1/3Mn_1/3O₂. The electrochemical performance studies demonstrate that 2 wt.% La_0.4Ca_0.6CoO₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ powders exhibit the best electrochemical properties, with an initial discharge capacity of 156.9 mAh g^–1 and capacity retention of 98.9 % after 50 cycles when cycled at a current density of 0.2 C between 2.75 and 4.3 V. La_0.4Ca_0.6CoO₃ coating can improve the rate performance because of the enhancement of the surface electronic/ionic transportation by the coating layer. EIS results suggest that the coating La_0.4Ca_0.6CoO₃ plays an important role in suppressing the increase of cell impedance with cycling especially for the increase of charge-transfer resistance.     

Improved electrochemical performance of LiNi0.5Mn1.5O4 as cathode of lithium ion battery by Co and Cr co-doping

Three samples, LiNi_0.5Mn_1.5O₄, LiNi_0.4Mn_1.4Co_0.2O₄, and LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, were prepared by sol–gel method and characterized by powder X-ray diffraction, Fourier transformed infrared spectroscope, scanning electron microscopy, Brunauer–Emmett–Teller surface area, four-probe resistance, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge test. It is found that the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ exhibits an improved performance compared with the Co-doped sample LiNi_0.4Mn_1.4Co_0.2O₄ and the undoped sample LiNi_0.5Mn_1.5O₄, especially at elevated temperature. At 25 °C, the discharge capacity of LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄ is 130 mAh g^?1 at 0.1 C and 103 mAh g^?1 at 10 C. At an elevated temperature (55 °C), its 1 C discharge capacity is 136 mAh g^?1 and maintains 95.6 % of its initial capacity after 100 cycles. Compared with the reported results of LiNi_0.4Mn_1.4Co_0.2O₄ and LiNi_0.475Mn_1.475Co_0.05O₄, the co-doped sample LiNi_0.4Mn_1.4Cr_0.15Co_0.05O₄, with least content of Co, 0.05, possesses not only the high C-rate capacity but also the structural stability. The mechanism on the electrochemical performance improvement of LiNi_0.5Mn_1.5O₄ by the co-doping was discussed.     

A soft chemistry synthetic method for preparing LiNi0.8Co0.2O2 with enhanced electrochemical performances

Polycrystalline LiNi_0.8Co_0.2O₂ powders were synthesized via the citric acid-assisted liquid phase evaporation method. The precursors are homogenously mixed in the solutions at an atomic scale which is also reflected by the particle distribution of the final products. The optimal synthesis temperature is located at 750?°C where the particle size, crystalline structure, and the cation disorder between Li⁺ and Ni²⁺ ions have been balanced. A high discharge capacity of 191?mAh?g^?? (3.0??.3?V at 30?mA/g) is achieved in the first cycle for the 750?°C-prepared sample with a capacity retention of 89.37% after 96 cycles. Cyclic voltammetry and the differential capacity curves also reveal a moderate stable crystal structure of 750?°C-prepared LiNi_0.8Co_0.2O₂ during the prolonged cycles.     

High-Resolution Transmission Electron Microscopy Study of LiNi<Subscript>x</Subscript>Co<Subscript>1−x</Subscript>O<Subscript>2</Subscript> Synthesized by Unconventional Methods

Single phase LiNi_xCo_1–xO₂ (x=0.3) with fine particles were prepared by two low-temperature methods: the modified Pechini sol-gel method and the Self-Propagating Combustion Synthesis (SPCS). It was found that bulk quantities of nano-sized particles of layered LiNi_xCo_1–xO₂ could be obtained at temperatures below 400°C by these solutions technique. The synthesized products were characterized by structural (XRD) and thermal (DTA-TG) analyses. HRTEM was used to evaluate the purity and the phase composition of LiNi_xCo_1–xO₂. Lattice plane images give information about crystal structure and SAED patterns help us to identify the phase. Nano-crystals were obtained with minimum mean diameter about 5nm for both methods.     

掺F影响LiNi0.8Co0.1Mn0.1O2结构和性能的微观机制

以氟化锂为氟源,通过高温固相法合成了F掺杂的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2。采用X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)和电化学测试等手段研究F影响LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2结构和性能的微观机制。结果表明:适量F掺杂可以提高正极材料的放电比容量,改善其倍率性、循环性和热稳定性。当F掺杂量(物质的量分数)为1.5%时,材料的综合电化学性能最优,初始放电比容量(0.2C)和50周循环容量保持率(1C)分别由原始的174.0 mAh·g~(-1)(78.7%)提高到178.6 mAh·g~(-1)(85.7%)。LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2材料性能的改善可归因于F能够增强过渡金属层、锂层与氧层之间的结合力,提高材料的结构稳定性。此外,F掺杂还有利于降低电化学反应中的界面电阻和电荷转移阻抗。     

Thermal processes in the systems with Li-battery cathode materials and LiPF6 -based organic solutions

Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li₂MnO₃, xLi₂MnO₃ ^.(1???x)Li(MnNiCo)O₂,LiNi_0.33Mn_0.33Co_0.33O₂, LiNi_0.4Mn_0.4Co_0.2O₂, LiNi_0.8Co_0.15Al_0.05O₂ LiMn_1.5Ni_0.5O₄, LiMn(or Fe)PO₄, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF₆ salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF₆-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li₂CO₃ is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures.     

Electrochemical performance of nano-sized ZnO-coated LiNi0.5Mn1.5O4 spinel as 5 V materials at elevated temperatures

ZnO-coated LiNi_0.5Mn_1.5O₄ powders with excellent electrochemical cyclability and structural stability have been synthesized. The electrochemical performance and structural stability of ZnO-coated LiNi_0.5Mn_1.5O₄ electrodes in the 5 V region at elevated temperature has been studied as function of the level of ZnO coating. The 1.5 wt% ZnO-coated LiNi_0.5Mn_1.5O₄ electrode delivers an initial discharge capacity of 137 mAh g⁻¹ with excellent cyclability at elevated temperature even at 55 °C. The reason for the excellent cycling performance of ZnO-coated LiNi_0.5Mn_1.5O₄ electrode is largely attributed to ZnO playing an important role of HF getting in the electrolyte.     

Electrochemical characterization of polypyrrole–LiNi<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>O<Subscript>2</Subscript> composite cathode material for aqueous rechargeable lithium batteries

A series of polypyrrole (PPy)–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrodes are formed by physical mixing of polypyrrole with LiNi_1/3Mn_1/3Co_1/3O₂ cathode material. LiNi_1/3Mn_1/3Co_1/3O₂ is synthesized by reaction under autogenic pressure at elevated temperature method. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide an evidence to well-ordered layered structure of the compound. The ratios of the intensities of 003 and 104 peaks are found to be >1, which indicate no pronounced mixing of the cation. Cyclic voltammetry and AC impedance studies revealed that the addition of polypyrrole significantly decreases the charge-transfer resistance of LiNi_1/3Mn_1/3Co_1/3O₂ electrodes. The electrochemical reactivity of PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode is examined during lithium ion insertion and de-insertion by galvanostatic charge–discharge testing; 10 wt.% PPy–LiNi_1/3Mn_1/3Co_1/3O₂ composite electrode exhibits better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiNi_1/3Mn_1/3Co_1/3O₂ electrode. The cell with 10 wt.% PPy added cathode shows significant improvement in the electrochemical performance compared with that having pristine cathode. The capacity remains about 70% of the initial value after 50 cycles while for cell with pristine cathode only about 28% of initial capacity remains after 40 cycles.     

Synthesis and characterization of ultrafine spinel ferrite obtained by precursor combustion technique

Nanoparticles of the spinel ferrite, Co_0.6Ni_0.4Fe₂O₄ have been synthesized by the precursor combustion technique. This synthetic route makes use of a novel precursor viz. metal fumarato hydrazinate which decomposes autocatalytically after ignition to yield nanosized spinel ferrite. The X-ray powder diffraction of the ??as prepared?? oxide confirms the formation of monophasic nanocrystalline cobalt nickel ferrite. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been fixed as Co_0.6Ni_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄. The Curie temperature of the ??as prepared?? oxide was determined by ac susceptibility measurements.     

Towards high-performance cathode materials for lithium-ion batteries: Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-coated LiNi<Subscript>0.8</Subscript>Co<Subscript>0.15</Subscript>Zn<Subscript>0.05</Subscript>O<Subscript>2</Subscript>

Zn-doped LiNi_0.8Co_0.2O₂ exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi_0.8Co_0.15Zn_0.05O₂ as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al₂O₃ layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂ cathode delivers a highly reversible capacity of 182 mA h g^?1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi_0.8Co_0.15Zn_0.05O₂ cathode. The enhanced electrochemistry performance can be attributed to the Al₂O₃-coated protective layer, which prevents the direct contact between the LiNi_0.8Co_0.15Zn_0.05O₂ and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al₂O₃-coated LiNi_0.8Co_0.15Zn_0.05O₂, which rationally illuminates the protection mechanism of the Al₂O₃-coated layer.     

Synthesis and characterization of LiNi1/3Co1/3Mn1/3O2 cathode material for rechargeable lithium batteries by polyacrylic acid-assisted sol–gel method

Nanocrystalline LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials are synthesized by sol–gel method using polyacrylic acid as a chelating agent. The effects of the calcination temperature and calcination time on the structure, morphology, and electrochemical performances of the LiNi_1/3Co_1/3Mn_1/3O₂ electrode materials are investigated by X-ray diffraction, scanning electron microscopy and charge–discharge cycling test, respectively. All experiments show that the microscopic structural features and the morphology properties are deeply related with the electrochemical performance. The results show that the nanocrystalline LiNi_1/3Co_1/3Mn_1/3O₂ with a particle size of 80 nm sintered at 700 °C for 2 h presents good α-NaFeO₂ layer structure and the best electrochemical performance. When it is discharged between 4.4 and 2.8 V at 20 mAg^?1, the initial specific capacity of the LiNi_1/3Co_1/3Mn_1/3O₂ obtained at 700 °C for 2 h is 169.2 mAhg^?1. The investigated electrode materials retain 151 mAhg^?1 after 30 cycles when cycled at 20 mAg^?1.     

Thermal investigations of transitional metal oxide cathodes in Li-ion cells

Accelerating rate and differential scanning calorimeters were used to investigate the thermal behavior of LiCoO₂ and LiNi_0.8Co_0.2O₂ cathodes in fully charged Li-ion cells. The heat flow for LiNi_0.8Co_0.2O₂ was observed to be three times higher than that for LiCoO₂. The net heat transferred out of the cell fabricated with a LiNi₀.₈Co_0.2O₂ cathode was found to be 51% higher than the net heat transferred out of the cell fabricated with LiCoO₂. Although LiNi₀.₈Co_0.2O₂ was found to be thermally less stable than LiCoO₂, the electrochemical performance of the LiNi₀.₈Co_0.2O₂ cathode under high power discharge was found superior to LiCoO₂.     

Electrochemical behavior of spherical LiNi1/3Co1/3Mn1/3O2 as cathode material for aqueous rechargeable lithium batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ powders have been synthesized from co-precipitated spherical metal hydroxide. The electrochemical performances of the LiNi_1/3Co_1/3Mn_1/3O₂ electrodes in 1 M LiNO₃, 5 M LiNO₃, and saturated LiNO₃ aqueous electrolytes have been studied using cyclic voltammetry and ac impedance tests in this work. The results show that LiNi_1/3Co_1/3Mn_1/3O₂ electrode in saturated LiNO₃ electrolyte exhibits the best electrochemical performance. An aqueous rechargeable lithium battery containing LiNi_1/3Co_1/3Mn_1/3O₂ cathode, LiV_2.9Ni_0.050Mn_0.050O₈ anode, and saturated LiNO₃ electrolyte is fabricated. The battery delivers an initial capacity of 98.2 mAh g⁻¹ and keeps a capacity of 63.9 mAh g⁻¹ after 50 cycles at a rate of 0.5 C (278 mA g⁻¹ was assumed to be 1 C rate).     

流变相法合成LiNi0.85Co0.15O2的结构与电化学性能

以一种新型的软化学方法——流变相法, 成功地合成了锂离子电池正极材料LiNi_0.85Co_0.15O₂. 将在600～850 ℃氧气氛下处理6 h后得到的LiNi_1－yCo_yO₂ (y＝0.10, 0.15, 0.20, 0.25), 进行X射线粉末衍射(XRD)与电化学测试. 测试结果表明, 流变相前体经过800 ℃烧结后合成的LiNi_0.85Co_0.15O₂晶胞参数a＝0.2866 nm, c＝1.4193 nm及晶胞体积V＝0.1010 nm³, 以0.1 C倍率在3.0～4.3 V (vs. Li^＋/Li)放电时, 首次放电容量可以达到198.2 mAh/g, 20次循环后, 其放电容量仍在174 mAh/g以上.     

Surface modification of LiNi0.8Co0.1Mn0.1O2 with conducting polypyrrole

A facile method for the surface modification of high-voltage and high-temperature LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials is demonstrated. In order to prepare polypyrrole (PPy) coating LiNi_0.8Co_0.1Mn_0.1O₂ material, the facile chemical polymerization method uses Fe(III) tosylate as oxidant and ethanol as solvent to avoid the side reaction with solvent. TEM depicts that LiNi_0.8Co_0.1Mn_0.1O₂ serves as hard template and the nanoscale PPy layer grows along the surface of LiNi_0.8Co_0.1Mn_0.1O₂ during the synthesis process. Because of flocculent and nanofiber coating layer, much improved rate performance, high temperature cycling, as well as high voltage performance are obtained. Cyclic voltammetry (CV) and electrochemical impedance spectroscopic (EIS) results demonstrate that the PPy coating layer effectively alleviates the side reactions between liquid electrolytes and LiNi_0.8Co_0.1Mn_0.1O₂ surface that are highly unstable at high temperature and high charge voltage.     

Thermal Conversion of Gels Prepared by the Complex Sol-Gel Process (CSGP) from Li+-Me2+-CH3COO−-Ascorbic Acid (ASC)-NH4 +-OH−-H2O Systems to LiMn2O4 and LiNi x Co1 − x O2

The spinel LiMn₂O₄ and layered oxides LiNi _x Co_{1 – x} O₂ (x = 1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140°C. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320–500°C dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn₂O₄ and LiCoO₂), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO₃ was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO₃.     

A simple and effective strategy to synthesize Al2O3-coated LiNi0.8Co0.2O2 cathode materials for lithium ion battery

A facile method has been developed to synthesize Al₂O₃-coated LiNi_0.8Co_0.2O₂ cathode materials. The sample was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive analysis of X-rays (EDAX). Electrochemical tests show that the cycling stability of LiNi_0.8Co_0.2O₂ at room temperature is effectively improved by Al₂O₃ coating. The differential scanning calorimetry (DSC) and high temperature (60 °C) cycling tests indicate that Al₂O₃ coating can also improve the thermal stability of LiNi_0.8Co_0.2O₂, which is attributed to that the coating layer can protect the LiNi_0.8Co_0.2O₂ particles from reacting with the electrolyte.