Effect of the impurity LixNi1−xO on the electrochemical properties of 5 V cathode material LiNi0.5Mn1.5O4

The formation of impurity Li_xNi_1−xO when synthesizing spinel LiNi_0.5Mn_1.5O₄ using solid state reaction method, and its influence on the electrochemical properties of product LiNi_0.5Mn_1.5O₄ were studied. The secondary phase Li_xNi_1−xO emerges at high temperature due to oxygen deficiency for LiNi_0.5Mn_1.5O₄ and partial reduction of Mn⁴⁺ to Mn³⁺ in LiNi_0.5Mn_1.5O₄. Annealing process can diminish oxygen deficiency and inhibit impurity Li_xNi_1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi_0.5Mn_1.5O₄ that contains Li_xNi_1−xO can deliver about 120 mAh g⁻¹.     

In situ synthesis of Co3O4/graphene nanocomposite material for lithium-ion batteries and supercapacitors with high capacity and supercapacitance

Co₃O₄/graphene nanocomposite material was prepared by an in situ solution-based method under reflux conditions. In this reaction progress, Co²⁺ salts were converted to Co₃O₄ nanoparticles which were simultaneously inserted into the graphene layers, upon the reduction of graphite oxide to graphene. The prepared material consists of uniform Co₃O₄ nanoparticles (15-25 nm), which are well dispersed on the surfaces of graphene nanosheets. This has been confirmed through observations by field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The prepared composite material exhibits an initial reversible lithium storage capacity of 722 mAh g⁻¹ in lithium-ion cells and a specific supercapacitance of 478 F g⁻¹ in 2 M KOH electrolyte for supercapacitors, which were higher than that of the previously reported pure graphene nanosheets and Co₃O₄ nanoparticles. Co₃O₄/graphene nanocomposite material demonstrated an excellent electrochemical performance as an anode material for reversible lithium storage in lithium ion cells and as an electrode material in supercapacitors.     

Porous Li4Ti5O12 anode material synthesized by one-step solid state method for electrochemical properties enhancement

A porous Li₄Ti₅O₁₂ anode material was successfully synthesized from mixture of LiCl and TiCl₄ with 70 wt% oxalic acid by a modified one-step solid state method. The anode material Li₄Ti₅O₁₂ exhibited a cubic spinel structure and only one voltage plateau occurred around 1.5 V. The initial capacity of porous Li₄Ti₅O₁₂ was 167 and 133 mAh g⁻¹ at 0.5 and 1C charge/discharge rate, respectively, and the capacity retention maintained above 98% after 200 cycles. The porous Li₄Ti₅O₁₂ structure showed promising rate performance with a capacity of 70 mAh g⁻¹ at charge/discharge 10C rate after 200 cycles. It was demonstrated that the porous structure could withstand 50C charge/discharge rate and exhibited excellent cycling stability.     

Structural characterization of layered LiNi0.85−xMnxCo0.15O2 with x = 0, 0.1, 0.2 and 0.4 oxide electrodes for Li batteries

We report the synthesis of LiNi_0.85−xCo_0.15Mn_xO₂ positive electrode materials from Ni_0.85−xCo_0.15Mn_x(OH)₂ and Li₂CO₃. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi_0.85−xCo_0.15Mn_xO₂ materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi_0.85−xCo_0.15Mn_xO₂ compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and L_M-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn⁴⁺ with Ni²⁺ and Mn⁴⁺ with Li⁺.     

Cr3+掺杂LiNi0.5Mn1.5O4材料的制备及性能研究

采用高温固相法合成了Cr₃₊掺杂的LiNi_0.5Mn_1.5O₄正极材料,研究了掺杂量对材料物理性能和电化学性能的影响。利用XRD、SEM对材料的结构和形貌进行了表征,结果显示样品具有棱边清晰的尖晶石形貌。讨论了不同Cr₃₊掺杂量对LiCr_xNi_0.5-0.5xMn_1.5-0.5xO₄(x=0,0.05,0.1,0.15,0.2)正极材料性能的影响。充放电测试、循环伏安和交流阻抗测试结果表明：当Cr₃₊的掺杂量为x=0.1时(LiCr_0.1Ni_0.45Mn_1.45O₄)正极材料的性能最好,0.1C、0.5C、1C、2C及5C的首次放电比容量依次为131.54mAh g_-1、126.84mAh g_-1、121.28mAh g_-1、116.49mAh g_-1和96.82mAh g_-1,1C倍率下循环50次,容量保持率仍为96.5%。     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting Mg with Ni

The microwave dielectric properties of La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm³, dielectric constant (?_r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τ_f) of −85 ppm/°C were obtained for La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Synthesis and electrochemical properties of porous LiV3O8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV₃O₈ by using a tartaric acid-assisted sol-gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N₂ adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV₃O₈ calcined at 300 °C (LiV₃O₈-300) exhibits hierarchical porous structure with high surface area of 152.4 m² g⁻¹. The electrochemical performance of the as-prepared porous LiV₃O₈ as cathode materials for lithium ion batteries is investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The porous LiV₃O₈-300 displays a maximum discharge capacity of 320 mAh g⁻¹ and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g⁻¹ due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol⁻¹, suggesting its promising application as the cathode material of Li-ion batteries.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

丝网印刷氧化石墨烯对锂离子电池LiNi1/3Co1/3Mn1/3O2 三元正极的改性及性能影响

通过丝网印刷方法,在由LiNi_1/3Co_1/3Mn_1/3O₂、导电添加剂和聚偏氟乙烯制成的电极表面涂覆了一层薄薄的氧化石墨烯。在充电截止电压为4.3 V的条件下进行了循环性能和倍率性能测试。结果表明：未改性电极在恒电流充放电测试中容量下降且极化增加,而包覆改性后电极的容量衰减程度和极化增加速度降低。这是由于氧化石墨烯涂层抑制了LiNi_1/3Co_1/3Mn_1/3O₂电极和电解质之间的部分副反应,使得改性电极的循环稳定性和倍率性能显著提高,为提升LiNi_1/3Co_1/3Mn_1/3O₂电极性能提供了一种环境友好且非常有效的方法。     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

Power factor enhancement in Zn-doped Na0.8CoO2

The thermoelectric properties of Na_0.8Zn_xCo_1−xO₂/(ZnO)_y (x ≤ 0.01, 0 ≤ y ≤ 0.14) have been systematically investigated. The results suggest that doping divalent Zn ions within solubility limit x^* ∼ 0.01 leads to simultaneous reduction in resistivity and enhancement of thermopower. Analysis of the results show that the reduction of resistivity may be attributed to improved mobility of carriers, while the enhancement of thermopower may originate from the geometric relaxation of distorted CoO₆ octahedra caused by partial Zn substitution, leading to a narrower band width in the strongly correlated environment, consequently resulting in a remarkable 20% improvement in power factor.     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

Preparation and electrical properties of perovskite ceramics in the system BaBi1−xSbxO3 (0 ≤ x ≤ 0.5)

The effect of the composition on the electrical properties of BaBi_1−xSb_xO₃ (0 ≤ x ≤ 0.5) negative temperature coefficient (NTC) thermistors was studied. Major phases present in the sintered bodies of BaBi_1−xSb_xO₃ (0 < x < 0.5) ceramics were BaBi_0.5Sb_0.5O₃ compounds with a rhombohedral structure and BaBiO₃ compounds with a monoclinal structure. Most pores were located in the grains of BaBiO₃ and BaBi_0.5Sb_0.5O₃ ceramics. It was apparent that the ρ₂₅ and B_25/85 constant of the thermistors increased with increasing Sb content.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Dielectric and piezoelectric properties of Sb doped (NaBi)0.38(LiCe)0.05[]0.14Bi2Nb2O9 ceramics

Sb⁵⁺-doped (NaBi)_0.38(LiCe)_0.05[]_0.14Bi₂Nb₂O₉ (represented as NBNLCS-x, where [] represents A-site vacancies) ceramics were prepared by the conventional solid-state route. The ceramics well sintered to approach ∼98.5% theoretical density and the tetragonality of crystal structure increased with Sb⁵⁺ additions. However, the Curie temperature (T_C) and the piezoelectric coefficient (d₃₃) of Sb⁵⁺-modified ceramics gradually decreased. The 3 mol% Sb⁵⁺-doped samples exhibited optimum properties with a d₃₃ value of ∼22 pC/N planar electromechanical coupling factor (k_p) of ∼11.2% and relatively high T_C of ∼765 °C. These results indicate that NBNLCS-x material is a promising candidate for high-temperature piezoelectric applications.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Low temperature sintering and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics with BaCu(B2O5) additions

The effects of BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were investigated. The (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were not able to be sintered below 1000 °C. However, when BaCu(B₂O₅) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?_r = 18.5.0 and τ_f = −51 ppm/°C were obtained for the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics containing 7 wt.% mol% BaCu(B₂O₅) sintered at 950 °C for 4 h.     

Effect of Ag-doping on crystal structure and high temperature thermoelectric properties of c-axis oriented Ca3Co4O9 thin films by pulsed laser deposition

Ag-doped Ca₃Co₄O₉ thin films with nominal composition of Ca_3−xAg_xCo₄O₉ (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca₃Co₄O₉ thin films could reach 0.73 mW m⁻¹ K⁻² at around 700 K, which was about 16% higher than that of the pure Ca₃Co₄O₉ thin film.     

Characterization and electrochemical properties of carbon-coated Li4Ti5O12 prepared by a citric acid sol-gel method

Since carbon coating can effectively improve electrical wiring of Li₄Ti₅O₁₂ and thus enhance its high rate performance, a novel and simple citric acid sol-gel method for in situ carbon coating is employed in this study. The effects of the amount of the carbon source in the starting xerogel on the particle size, the resistance and the electrochemical performance of the synthesized Li₄Ti₅O₁₂ samples are systematically studied. The physical and electrochemical properties of the obtained samples have been characterized by XRD, TG-DSC, SEM, TEM, BET, A.C. impedance, galvanostatically charge-discharge and cyclic voltammetry tests. The results show that the initial amount of the carbon source in the starting xerogel is a critical factor which determines the content of the coated carbon and the pore volume, therefore governs the high rate performance of the Li₄Ti₅O₁₂/C composites. The Li₄Ti₅O₁₂/C composite with in situ carbon coating of 3.5 wt% exhibits the best electrochemical performance which delivers delithiation capacities of 143.6 and 133.5 mAh g⁻¹ with fairly stable cycling performance even after 50 cycles at 0.5C and 1C rate, respectively.