Electrochemical properties of LiNi<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>M<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>2</Subscript> (M=Ni,Ga, Al and/or Ti) cathodes synthesized by the combustion method

LiNiO₂, LiNi_0.995Al_0.005O₂, LiNi_0.975Ga_0.025O₂, LiNi_0.990Ti_0.010O₂ and LiNi_0.990Al_0.005Ti_0.005O₂ were synthesized by preheating at 400 °C for 30 min in air and calcination at 750 °C for 36 h in an O₂ stream with excess lithium amount z = 0.10 in Li_1+z Ni_1−y M _y O₂. For these samples, the discharge capacities and discharge capacity degradation rate are compared. LiNiO₂ has the largest discharge capacity at the 20th cycle (n = 20) and the 50th cycle (n = 50). LiNiO₂ and LiNi_0.995Al_0.005O₂ have relatively good cycling performances and their discharge capacities at n = 50 are 134 and 123 mAh/g, respectively, at 0.1 C rate. The crystallite sizes and strains were calculated by the Williamson–Hall method with XRD patterns and compared for the samples as prepared and after 50 charge–discharge cycles.     

Effects of Zn or Ti substitution for Ni on the electrochemical properties of LiNiO2

LiNiO₂ and LiNi_1−yM_yO₂ (M = Zn and Ti, y = 0.005, 0.01, 0.025, 0.05, and 0.1) were synthesized with a solid-state reaction method by calcination at 750 °C for 30 h under oxygen stream after preheating at 450 °C for 5 h in air. LiNi_0.995Zn_0.005O₂ among the Zn-substituted samples and LiNi_0.995Ti_0.005O₂ among the Ti-substituted samples showed the best electrochemical properties. For similar values of y, LiNi_1−yTi_yO₂ had in general better electrochemical properties than LiNi_1−yZn_yO₂. Electrochemical properties seem to be closely related to R-factor but less related to I_0 0 3/I_1 0 4 value. In the FT-IR absorption spectra of LiNiO₂ and LiNi_1−yM_yO₂ (M = Zn and Ti, y = 0.005, 0.01, 0.025, 0.05 and 0.1), Li₂CO₃ was detected even if it is not observed from XRD pattern, with the samples LiNi_1−yZn_yO₂ (y = 0.05 and 0.1) showing Li₂ZnO₂ additionally. The smaller cation mixing of the Ti-substituted samples is considered to lead to their better electrochemical properties than the Zn-substituted samples.     

Electrochemical characterizations of Fe-substituted LiNiO2 synthesized in air by the combustion method

The phases that appear in the intermediate reaction steps for the formation of lithium nickel oxide were deduced from XRD and DTA analyses. XRD analysis and electrochemical measurements were performed for LiNi_1−yFe_yO₂ (0.000 ≤ y ≤ 0.300) samples calcined in air after preheating in air at 400 °C for 30 min. Rietveld refinement of the LiNi_1−yFe_yO₂ XRD patterns (0.000 < y ≤ 0.100) was carried out from a [Li,Ni]_3b[Li,Ni,Fe]_3a[O₂]_6c starting structure model. The samples of LiNi_1−yFe_yO₂ with y = 0.025 and 0.050 had higher first discharge capacities when compared with LiNiO₂ and exhibited better or similar cycling performance at a 0.1 C rate in the voltage range of 2.7–4.2 V. The LiNi_0.975Fe_0.025O₂ sample had the highest first discharge capacity of 176.5 mAh/g and a discharge capacity of 121.0 mAh/g at n = 100. With the exception of Co-substituted LiNiO₂, such a high first discharge capacity has not been previously reported.     

Effects of cathode fabrication conditions and cycling on the electrochemical performance of LiNiO2 synthesized by combustion and calcination

LiNiO₂ was synthesized by the combustion method with various excess lithium amount z in Li_1 + zNiO₂ (z = 0.04, 0.08, 0.10, 0.12, and 0.15). The sample with z = 0.10 has the largest first discharge capacity of 195 mAh/g at 0.1 C rate and voltage range 2.7-4.4 V with the weight ratio of active material:acetylene black:binder = 85:10:5. The LiNiO₂ cathodes, in which the excess lithium amount z for the synthesis of LiNiO₂ was 0.10, were fabricated with various weight ratios of active material:acetylene black:binder (85:10:5, 85:12:3, and 90:7:3). The cathode with the ratio of active material:acetylene black:binder 85:10:5 has the best electrochemical properties. The variation, with C-rate, of discharge capacity vs. number of cycles curve for the LiNiO₂ cathode with the weight ratio of active material:acetylene black:binder = 85:10:5 was investigated. At 0.1 C rate, the LiNiO₂ cathode has the largest first discharge capacity, the discharge capacity degradation rate of 0.70 mAh/g/cycle and a discharge capacity at n = 50 of 134 mAh/g.     

Preparation and cycling performance of Aland F co-substituted compounds Li4AlxTi5−xFyO12−y

Li₄Al_xTi_5−xF_yO_12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al³⁺ and F⁻ ions entered the structure of spinel-type Li₄Ti₅O₁₂. Charge-discharge cycling results at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.5 and 0.5 V showed that the Al³⁺ and F⁻ substitutions improved the first total discharge capacity of Li₄Ti₅O₁₂. However, Al³⁺ substitution greatly increased the reversible capacity and cycling stability of Li₄Ti₅O₁₂ while F⁻ substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al³⁺-F⁻-co-substituted specimen was better than the F⁻-substituted one but worse than the Al³⁺-substituted one.     

Electrochemical characteristics of cobalt-substituted lithium nickel oxides synthesized from lithium hydro-oxide and nickel and cobalt oxides

LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from LiOH·H₂O, NiO and Co₃O₄ as starting materials. The electrochemical properties of the synthesized LiNi_1−yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size distribution gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest intercalated and deintercalated Li quantity Δx among LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5). LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (178 mAh/g), followed by LiNi_0.7Co_0.3O₂ (162 mAh/g) synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 800 °C has discharge capacities of 162 and 125 mAh/g at n=1 and n=5, respectively.     

Hydrothermal synthesis of LiNixCo1−xO2 cathode materials

Ultrafine powders of LiCoO₂, nonstoichiometric LiNiO₂ and LiNi_0.9Co_0.1O₂ were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/Co, Li/Ni and Li/(Ni + Co) was studied. The final products were investigated by XRD, TEM and EDS. To synthesize a stoichiometric LiNiO₂ under mild hydrothermal conditions was found to be a big challenge. Transmission electron microscopies (TEM) revealed the formation of well-crystallized LiCoO₂ and LiNi_0.9Co_0.1O₂ with average size of 100 nm and 10 nm, respectively.     

Evolution of the local structure and electrochemical properties of spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5)

A series of Ni substituted spinel LiNi_xMn_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNi_xMn_2−xO₄ (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni²⁺ cations were partially oxidized to Ni³⁺. The local structures of LiNi_xMn_2−xO₄ were studied by analyzing the and A_1g Raman bands. The most compact [Mn(Ni)O₆] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi_0.2Mn_1.8O₄, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm⁻¹. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni³⁺ in the materials.     

Transesterification of palm oil on KyMg1 − xZn1 + xO3 catalyst: Effect of Mg-Zn interaction

The Mg-Zn interaction effect of K_yMg_1 − xZn_1 + xO₃ heterogeneous type catalyst and its performance on transesterification of palm oil have been studied using the response surface methodology and the factorial design of experiments. The catalyst was synthesized using the co-precipitation method and the activity was assessed by transesterification of palm oil into fatty acid methyl esters. The ratio of the Mg/Zn metal interaction, temperature and time of calcination were found to have positive influence on the conversion of palm oil to fatty acid methyl ester (FAME) with the effect of metal to metal ratio and temperature of calcination being more significant. The catalytic activity was found to decrease at higher calcination temperature and the catalyst type K₂Mg_0.34Zn_1.66O₃ with Mg/Zn ratio of 4.81 gave FAME content of 73% at a catalyst loading of 1.404 wt.% of oil with molar ratio of methanol to oil being 6:1 at temperature of 150 °C in 6 h. A regression model was obtained to predict conversions to methyl esters as a function of metal interaction ratio, temperature of calcination and time. The observed activity of the synthesized catalyst was due to its synergetic structure and composition.     

Zr-doped Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) as cathode material for lithium ion batteries

Layered Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi_0.475Mn_0.475Zr_0.05O₂ has a rougher surface than that of LiNi_0.5Mn_0.5O₂. The Li/Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi_0.475Mn_0.475Zr_0.05O₂ cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi_0.5Mn_0.5O₂ cell. We found that the oxidation of oxygen and the Mn³⁺ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) cathode was improved by Zr doping.     

Study on the rapid synthesis of LiNi1−xCoxO2 cathode material for lithium secondary battery

LiNi_1−xCo_xO₂ (x = 0, 0.1, 0.2) cathode materials were successfully synthesized by a rheological phase reaction method with calcination time of 0.5 h at 800 °C. All obtained powders are pure phase with α-NaFeO₂ structure (R-3m space group). The samples deliver an initial discharge capacity of 182, 199 and 189 mAh g⁻¹ (25 mA g⁻¹, 4.35-3.0 V), respectively. The reaction mechanism was also discussed, which consists of a series of defect reactions. As a result of these defect reactions, the reaction of forming LiNi_1−xCo_xO₂ takes place in high speed.     

Lithium-deficient LiYMn2O4 spinels (0.9 ≤ Y < 1): Lithium content, synthesis temperature, thermal behaviour and electrochemical properties

Lithium-deficient Li_YMn₂O₄ spinels (LD-Li_YMn₂O₄) with nominal composition (0.9 ≤ Y < 1) have been synthesized by melt impregnation from Mn₂O₃ and LiNO₃ at temperatures ranging from 700 °C to 850 °C. X-ray diffraction data show that LD-Li_YMn₂O₄ spinels are obtained as single phases in the range Y = 0.975-1 at 700 °C and 750 °C. Morphological characterization by transmission electron microscopy shows that the particle size of LD-Li_YMn₂O₄ spinels increases on decreasing the Li-content. The influence of the Li-content and the synthesis temperature on the thermal and electrochemical behaviours has been systematically studied. Thermal analysis studies indicate that the temperature of the first thermal effect in the differential thermal analysis (DTA)/thermogravimetric (TG) curves, T_C1, linearly increases on decreasing the Li-content. The electrochemical properties of LD-Li_YMn₂O₄ spinels, determined by galvanostatic cycling, notably change with the synthesis conditions. So, the first discharge capacity, Q_disch., at C rate increases on rising the Li-content and the synthesis temperature. The sample Li_0.975Mn₂O₄ synthesized at 700 °C has a Q_disch. = 123 mAh g⁻¹ and a capacity retention of 99.77% per cycle. This LD-Li_YMn₂O₄ sample had the best electrochemical characteristics of the series.     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).     

Amorphous LiCoO2 thin films on Li1+x+yAlxTi2−xSiyP3−yO12 prepared by radio frequency magnetron sputtering for all-solid-state Li-ion batteries

Amorphous LiCoO₂ thin films were deposited on the NASICON-type glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 180 °C. The as-deposited LiCoO₂ thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscope. All-solid-state Li/PEO₁₈-Li (CF₃SO₂)₂N/LATSP/LiCoO₂/Au cells were fabricated using the amorphous film. The electrochemical performance of the cells was investigated by galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. It was found that the amorphous LiCoO₂ thin film shows a promising electrochemical performance, making it a potential application in microbatteries for microelectronic devices.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

Preparation, characterization and electrical conductivity studies of NdYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics

Several compositions of NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 1.0) ceramics were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, microstructure and electrical conductivity of NdYb_1−xGd_xZr₂O₇ ceramics were analyzed by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance plots measurements. NdYb_1−xGd_xZr₂O₇ (0 ≤ x ≤ 0.3) ceramics have a single phase of defect fluorite-type structure, and NdYb_1−xGd_xZr₂O₇ (0.7 ≤ x ≤ 1.0) ceramics exhibit a single phase of pyrochlore-type structure; however, the NdYb_0.5Gd_0.5Zr₂O₇ composition shows mixed phases of both defect fluorite-type and pyrochlore-type structures. The measured values of the grain conductivity obey the Arrhenius relation. The grain conductivity of each composition in NdYb_1−xGd_xZr₂O₇ ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb_1−xGd_xZr₂O₇ ceramics are oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 1.79 × 10⁻² S cm⁻¹ at 1173 K for NdYb_0.3Gd_0.7Zr₂O₇ composition.