Synthesis of cathode material LiNi<Subscript>1-<Emphasis Type="Italic">y</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>2</Subscript> by a simplified combustion method

The optimum conditions for synthesizing LiNi_1-y Co _y O₂ (y=0.1, 0.3 and 0.5) by a simplified combustion method, in which the preheating step is omitted, and the electrochemical properties of these materials were investigated. The optimum condition for synthesizing LiNi_0.9Co_0.1O₂ by the simplified combustion method is calcination at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate. The LiNi_0.9Co_0.1O₂ synthesized under these conditions shows the smallest R-factor{(I ₀₀₆+I ₁₀₂)/I ₁₀₁} and the largest I ₀₀₃/I ₁₀₄, indicating better hexagonal ordering and less cation mixing, respectively. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate has the largest first discharge capacity 156.2 mA h g⁻¹ at 0.5C and shows relatively good cycling performance. This sample shows better hexagonal ordering and less cation mixing than the other samples. The particle size of the LiNi_0.7Co_0.3O₂ is relatively small and its particles are spherical with uniform particle size.     

Electrochemical properties of LiNiO2 cathode after TiO2 or ZnO addition

LiNiO₂ was prepared by solid state reaction, and LiNiO₂ was mixed with 1-, 2-, or 5 wt% TiO₂ or ZnO for the preparation of cathodes for a lithium ion battery. The electrochemical properties of the cathodes were investigated and the effects of the addition of TiO₂ or ZnO were discussed. The voltage vs. capacity curves for charge and discharge at different numbers of cycles for LiNiO₂, 2 wt% TiO₂-added LiNiO₂, and 2 wt% ZnO₂-added LiNiO₂ showed that in all the samples the first discharge capacity is much smaller than the first charge capacity. The addition of TiO₂ or ZnO decreased the discharge capacities, but improved the cycling performance. The discharge capacities of LiNiO₂ and 2 wt% TiO₂-added LiNiO₂ decreased as the number of cycles increased. However, the discharge capacity of 2 wt% ZnO-added LiNiO₂ increased overall as the number of cycles increased. The −dx/|dV| vs. voltage curves for the 1st and 2nd cycles of 0, 1-, 2-, or 5 wt% TiO₂ or ZnO-added LiNiO₂ showed that all the samples underwent four phase transitions during charging and discharging.     

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.     

Variation of discharge capacities with C-rate for LiNi1−yMyO2 (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 specimens were synthesized by preheating at 400 °C for 30 min in air and calcination at 750 °C for 36 h in an O₂ stream. The variation of the discharge capacities with C-rate for the synthesized samples was investigated. LiNi_0.990Al_0.005Ti_0.005O₂ has the largest first discharge capacities at the 0.1 and 0.2 C rates. LiNi_0.990Ti_0.010O₂ has the largest first discharge capacity at the 0.5 C rate. In case of LiNiO₂ and LiNi_0.990Ti_0.010O₂, the first discharge capacity decreases slowly as the C-rate increases. LiNiO₂ has the largest discharge capacities at n = 10 (after stabilization of the cycling performance) at the 0.1, 0.2 and 0.5 C rates. This is considered to be related with the largest value of I_0 0 3/I_1 0 4 and the smallest value of R-factor (the least degree of cation mixing) among all the samples. LiNi_0.975Ga_0.025O₂ exhibits the lowest discharge capacity degradation rates at 0.1, 0.2 and 0.5 C rates.     

Electrochemical properties of lithium nickel oxide synthesized by the combustion method in an O2 stream

An appropriate mole ratio of urea/nitrate for preheating to synthesize LiNiO₂ was examined by varying the ratio from 1.2 to 9.6. The chemical equation of the combustion reaction was deduced from the XRD analysis result of the mixture after preheating. The XRD pattern of the LiNiO₂ sample calcined at 800 °C for 24 h, after preheating at the mole ratio of urea/nitrate of 3.6 at 400 °C, shows clear split of the 1 0 8 and 1 1 0 peaks, and the largest value of I₀₀₃/I₁₀₄. The sample calcined at 800 °C for 24 h has a relatively high first discharge capacity (164.2 mAh g^?1) and a good cycling performance. Derivative ?dx/|dV| vs. V curve of the LiNiO₂ sample at the voltage range of 2.7–4.4 V for the first cycle exhibits four peaks for charging and discharging, showing that this sample goes through four phase transitions.     

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO₂ powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO₂(R3¯m). In the crystallization process of LiNiO₂, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO₂ powders. For LiNiO₂ prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO₂ prepared at lower oxygen flow rates.     

Electrochemical properties of LiCoyMn2−yO4 synthesized using a combustion method in a voltage range of 3.5–5.0 V

LiCo_yMn_2−yO₄ (y = 0.00, 0.04 and 0.08) were synthesized using a combustion method, and the electrochemical properties were examined in the voltage range of 3.5–5.0 V. The XRD patterns of the synthesized samples were similar, and the samples had a spinel phase structure. The first charge capacity curves exhibited an inflection in the voltage range of 4.2–5.0 V, where it is believed that additional, previously unreported phase transition occurs. The voltage vs. x curves for the first to fifth cycle exhibited two distinct voltage plateaus, corresponding well to a two-phase reaction and a one-phase reaction, respectively, as reported previously. For the voltage range of 3.5–5.0 V, the first discharge capacity increased and the cycling performance improved as y increased. Among these samples, LiCo_0.08Mn_1.92O₄ had the largest first discharge capacity of 132.5 mA h/g at 600 μA/cm², and its cycling efficiency was 91.1% at the 15th cycle in the voltage range of 3.5–5.0 V.     

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.     

Electrochemical properties of cathode materials LiNi1−y Co y O2 synthesized using various starting materials

LiNi_1−y Co _y O₂ samples were synthesized at 800 °C and 850 °C, by the solid-state reaction method, using the starting materials LiOH·H₂O, Li₂CO₃, NiO, NiCO₃, Co₃O₄ and CoCO₃. The LiNi_1−y Co _y O₂ synthesized using Li₂CO₃, NiO and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group ). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of the Co ion is smaller than that of the Ni ion. The increase in c/a shows that a two-dimensional structure develops better as the Co content increases. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C using LiOH · H₂O, NiO and Co₃O₄ exhibited a larger first discharge capacity of 162 mAh g⁻¹ than the other samples. The cycling performances of the samples with the first discharge capacity larger than 150 mAh g⁻¹ were investigated. LiNi_0.9Co_0.1O₂ synthesized at 850 °C using Li₂CO₃, NiO and Co₃O₄ showed excellent cycling performance. Samples with larger first discharge capacity will have a greater tendency for lattice destruction due to expansion and contraction during intercalation and deintercalation, than samples with smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.     

Facile high yield synthesis of MgCo2O4 and investigation of its role as anode material for lithium ion batteries

In this article, we have reported a one-step scalable synthesis of MgCo₂O₄ nanostructures as efficient anode material for Li-ion batteries and investigated the role of post-synthesis calcination temperature (400, 600 and 800 °C) on its physiochemical properties and electrochemical performances. The XRD pattern of the calcinated sample at 400 °C (MC 400) indicates a pure phase of MgCo₂O₄. However, on increasing the calcination temperature to 600 °C (MC 600), an additional phase corresponding to MgO was detected and the corresponding XRD peak intensity further increased on increasing the calcination temperature to 800 °C (MC 800 °C). This was accompanied by a morphological transformation from flake and rod-like nanostructures, to an agglomerated dense flake-like morphology. Electrochemical studies revealed that the calcination temperature plays an important role in determining the electrochemical performance of the MgCo₂O₄ as anode material. In a half cell, the MC 600 showed the best electrochemical performance with high discharge capacity of 980 mA h g⁻¹ (2nd discharge at 60 mA g⁻¹) and a reversible discharge capacity of 886 mA h g⁻¹ at the end of 50 cycles with high coulombic efficiency of 98%. Long term stability was carried out at 0.5C which showed a capacity retention of 358 mA h g⁻¹ at the end of 500 cycles. The superior electrochemical performance of the MC600 can be attributed to the presence of the small amount of MgO, which is believed to provide the anode materials better structural stability during cycling. The claim was further supported by ex-situ TEM analysis of the anode material of a cycled cell (50 cycles).     

Al-doping induced superior lithium ion storage capability of LiNiO2 spheres

To optimize the performance of LiNiO₂ with minimal modification of the pristine structure, a facile solid-state approach, based on the interdiffusion of elements at the solid/solid interface, is developed to achieve uniformly Al-doped LiNiO₂ using alumina coated Ni(OH)₂ spheres as the precursor. The resulting LiNi_0.95Al_0.05O₂ material exhibits excellent discharge capacity (209.9 mAh g⁻¹ at 0.1 C) and cycling stability with a capacity retention of 85.10% after 200 cycles at 0.5 C. This is ascribed to the improved reversibility of the phase transitions by Al-doping as revealed by in-situ XRD characterization. The Al-doping also endows the material with superior rate capability due to the enlarged interlayer spacing in the structure and alleviation of the side reactions at the electrode/electrolyte interface, favorable for lithium ion diffusion. An optimal amount of doped Al is necessary for ensuring the structure stability and interface ionic conductivity of the LiNiO₂ spheres. Thus, the present strategy may provide an opportunity to optimize the performance of LiNiO₂, with uniform doping of a small amount of Al, producing a promising cathode material for advanced lithium ion batteries.     

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.     

Variation of LiNiO<Subscript>2</Subscript> cathode properties with substitution of Ga,In and Tl by the combustion method

LiNi_1-y M_yO₂ (M = Ga, In and Tl, y = 0.010, 0.025 and 0.050) with small y were synthesized by the combustion method by calcining in an O₂ stream at 750 °C for 36 h. XRD analyses, SEM observation and measurement of the variation of discharge capacity with the number of cycles were carried out. All the samples had the Rm structure and LiNi_1-y In _y O₂ contained LiInO₂ phase as an impurity. Among LiNi_1-y Ga _y O₂ the sample with y = 0.025 had a relatively large first discharge capacity (172.2 mAh g⁻¹) and relatively good cycling performance (discharge capacity 140.3 mAh g⁻¹ at n = 20). For LiNi_0.975M_0.025O₂ (M = Ga, In and Tl), the first discharge capacity decreased in the order of the substituted element Ga, In and Tl. The variations of cation mixing and hexagonal ordering with the substituted element (decrease in I₀₀₃/I₁₀₄ and increase in R-factor from M = Ga through M = Tl) are considered to lead to the behavior of the first discharge capacity with the substituted element. LiNi_0.975Tl_0.025O₂ had the smallest degradation rate of the discharge capacity.     

Lithium insertion into V4O9

Coulometric titration and galvanostatic cycling results are reported for Li/V₄O₉ cells with solid polymeric electrolyte operating at 80°C. It was shown that x = 4 is the upper limit of the electrochemical insertion leading to a single-phase in the range 0 < x < 4. The results are in good agreement with the model proposed by Armand. In cycling, 80% of capacity is obtained at the first discharge at low current (0.023 mA cm⁻²), but a low efficiency is yield in the following cycles and at higher current (0.063 mA cm⁻²).     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

Synthesis and electrochemical properties of lithium nickel oxysulfide (LiNiSyO2−y) material for lithium secondary batteries

The layered oxysulfide LiNiS_yO_2−y compounds were synthesized and characterized to investigate the effect of sulfur on the electrode performance of LiNiO₂. LiNiO₂ precursors were first synthesized by a sol-gel method using adipic acid as a chelating agent and then doped with sulfur powders by a solid-state reaction under the flow of oxygen to prepare LiNiS_yO_2−y compounds. Pure LiNiO₂ electrode showed a gradual decrease of discharge capacity with cycle number, whereas the capacity retention rate of LiNiS_yO_2−y electrodes significantly improved. The initial discharge capacity of the LiNiS_yO_2−y cells was lower than that of LiNiO₂ cell and decreased with the increasing content of sulfur substituted in LiNiS_yO_2−y.     

Preparation of high-entropy ceramic oxide powder at different calcination temperatures and electrochemical applications

High entropy ceramic oxide (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O (HEO) powders were synthesized by precipitation. X-ray diffraction (XRD), thermogravimetric analysis (TG-DSC), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to characterize the morphologies and structures of powders obtained at different calcination temperatures. The results showed that with increasing calcination temperature, the powder changed from a flocky precursor to a compact block shape. Due to the influence of the diffusion rates of different elements, the powder morphologies and structures differed for different calcination temperatures. Finally, the electrochemical properties of HEO powders prepared by the precipitation method were tested. The results showed that HEOs exhibited good electrochemical performance. The initial cyclic discharge capacity was 624.3 F/g; after cycling with different current densities, the discharge capacity still reached 591.3 F/g when cycled at 0.1 A/g, which was attributed to the good cycling performance and rate performance.     

The effects of oxygen flow rate and anion doping on the performance of the LiNio<Subscript>2</Subscript> electrode for lithium secondary batteries

This work presents the effects of O₂ flow rate and S-doping on structural and electrochemical properties of LiNiO₂. Layered LiNiO₂ were prepared using a sol-gel method. It was found that oxygen plays an important role in the crystallization of layered LiNiO₂. The deficiency of oxygen in the crystallization process induced the inclusions of impurities and cubic rock-salt structure in LiNiO₂ powders. For LiNiO₂ prepared at high O₂ flow rates, the electrode delivered high initial discharge capacity with a relatively good retention rate. S-doped LiNiO₂ not only stabilized the structural integrity of the electrode material, but also increased the electrode performance.     

Improved electrochemical properties of Li(Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript>)O<Subscript>2</Subscript> cathode for lithium ion batteries with controlled sintering conditions

Improved electrochemical properties of Li(Ni_0.7Co_0.3)O₂ cathode material are reported. Samples were synthesized by the co-precipitation method with various sintering conditions, namely temperature, time and atmosphere. Li(Ni_0.7Co_0.3)O₂ sintered at 850 °C for 14 h in air exhibited the lowest unit cell volume accompanied with relatively higher values of c/a and I ₁₀₃/I ₁₀₄ reflection peaks ratios. This also exhibited superior electrochemical properties, such as high charge–discharge capacity, high Coulombic efficiency, and low irreversible capacity loss. This can be attributed to improved hexagonal ordering, crystallinity and morphology. The electrochemical cell parameters were better than the reported ones, probably due to controlled sintering conditions.     

Electrochemical performance of spherical Li-rich LMNCO cathode materials prepared using a two-step spray-drying method

In this study we synthesized Li-rich Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (LMNCO) as a composite cathode material through a two-step spray-drying method, using transition metal (TM) acetates and citric acid (CA, as a chelating agent) at various molar ratios and then calcining at various temperatures for various periods of time. This two-step spray-drying method created hierarchical nano/micro-sphere structures of the LMNCO cathode material. The LMNCO cathode exhibited the best electrochemical performance when synthesized with a TM:CA ratio of 3:2, a calcination temperature of 900 °C, and a calcination time of 5 h. This as-prepared LMNCO composite was then modified with polyimide (PI) at various weight ratios (PI/LMNCO = 0.5, 1.0, and 1.5 wt%) to improve its electrochemical properties. Among the various structures, the LMNCO cathode material coated with 1.0 wt% of PI at a layer thickness of approximately 1.88 nm achieved the best initial discharge capacities. This modified electrode also displayed enhanced cycle stability, with over 93.3 and 87.9% of the capacity retained after 30 cycles at 0.1C and 100 cycles at 1C, respectively. In comparison, the capacity retention of the unmodified LMNCO electrode measured under the same conditions was no more than 91.3% at 0.1C and 70.1% at 1C. Thus, surface modification with PI was an effective method for improving the coulombic efficiency, discharge capacity, and long-term cycling performance of the LMNCO cathode. Such PI-coated LMNCO composite cathode materials appear to be potential candidates for use in next-generation high-performance lithium-ion batteries.