Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.     

A simple and effective method to synthesize layered LiNi0.8Co0.1Mn0.1O2 cathode materials for lithium ion battery

Nanocrystalline materials of Ni_0.8Co_0.1Mn_0.1(OH)₂ are successfully synthesized by fast co-precipitation method. The crystalline structure and morphology of the precursors and LiNi_0.8Co_0.1Mn_0.1O₂ materials are characterized by XRD, SEM and Rietveld refinement analyses. It is found that the nanocrystalline phase and low crystallinity of Ni_0.8Co_0.1Mn_0.1(OH)₂ could help achieve its uniform mixing with lithium source, and further attribute to highly ordered layered LiNi_0.8Co_0.1Mn_0.1O₂ with low cation mixing degree. Electrochemical studies confirm that the LiNi_0.8Co_0.1Mn_0.1O₂ exhibits a good electrochemical property with initial discharge specific capacity of 192.4 mAh g^− 1 at a current density of 18 mA g^− 1, and the capacity retention after 40 cycles is 91.56%. This method is a simple and effective method to synthesize cathode material.     

Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml_1−xMg_xNi_2.80Co_0.50Mn_0.10Al_0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi₅ and (La,Mg)Ni₃ phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g⁻¹ (x = 0.08) to 375 mAh g⁻¹ (x = 0.12), and then decreases to 351 mAh g⁻¹ (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g⁻¹ and discharge capacity at 233 K reaches 41.7% and 256 mAh g⁻¹, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml_0.72Mg_0.28Ni_2.80Co_0.50Mn_0.10Al_0.10 at the 200th cycle is 71%.     

Modeling the impedance versus voltage characteristics of LiNi0.8Co0.15Al0.05O2

The power-delivery capability of lithium-ion cells based on LiNi_0.8Co_0.15Al_0.05O₂-based positive electrodes shows a significant dependence on the cell's state-of-charge. One reason for this behavior is the variation of the positive electrode's impedance with the oxide's lithium content. In this article, an electrochemical model based on concentrated solution porous electrode theory is used to model impedance data obtained on LiNi_0.8Co_0.15Al_0.05O₂-based positive electrodes charged to potentials ranging from 3.55 to 4.55 V versus Li. The parameters obtained from model fits include the exchange-current density and Li-ion diffusion coefficients in the oxide. The variations in these parameters with oxide potential are correlated with structural changes in the material observed during Li-ion intercalation-deintercalation reactions.     

Spray-drying synthesized LiNi0.6Co0.2Mn0.2O2 and its electrochemical performance as cathode materials for lithium ion batteries

Layered LiNi_0.6Co_0.2Mn_0.2O₂ materials were synthesized at different sintering temperatures using spray-drying precursor with molar ratio of Li/Me = 1.04 (Me = transition metals). The influences of sintering temperature on crystal structure, morphology and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge-discharge test. As a result, material synthesized at 850 °C has excellent electrochemical performance, delivering an initial discharge capacity of 173.1 mAh g^− 1 between 2.8 and 4.3 V at a current density of 16 mA g^− 1 and exhibiting good cycling performance.     

Effect of fluorine in the preparation of Li(Ni1/3Co1/3Mn1/3)O2 via hydroxide co-precipitation

Uniform and spherical Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ powders were synthesized via NH₃ and F⁻ coordination hydroxide co-precipitation. The effect of F⁻ coordination agent on the morphology, structure and electrochemical properties of the Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ were studied. The morphology, size, and distribution of (Ni_1/3Co_1/3Mn_1/3)(OH)_(2−δ)F_δ particle diameter were improved in a shorter reaction time through the addition of F⁻. The study suggested that the added F improves the layered characteristics of the lattice and the cyclic performance of Li(Ni_1/3Co_1/3Mn_1/3)O₂ in the voltage range of 2.8-4.6 V. The initial capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O_1.96F_0.04 was 178 mAh g⁻¹, the maximum capacity was 186 mAh g⁻¹ and the capacity after 50 cycles was 179 mAh g⁻¹ in the voltage range of 2.8-4.6 V.     

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.     

Enhanced electrochemical performances of LiNi0.5Mn1.5O4 spinel via ethylene glycol-assisted synthesis

A simple and effective method, ethylene glycol-assisted co-precipitation method, has been employed to synthesize LiNi_0.5Mn_1.5O₄ spinel. As a chelating agent, ethylene glycol can realize the homogenous distributions of metal ions at the atomic scale and prevent the growth of LiNi_0.5Mn_1.5O₄ particles. XRD reveals that the prepared material is a pure-phase cubic spinel structure (Fd3m) without any impurities. SEM images show that it has an agglomerate structure with the primary particle size of less than 100 nm. Electrochemical tests demonstrate that the as-prepared LiNi_0.5Mn_1.5O₄ possesses high capacity and excellent rate capability. At 0.1 C rate, it shows a discharge capacity of 137 mAh g⁻¹ which is about 93.4% of the theoretical capacity (146.7 mAh g⁻¹). At the high rate of 5 C, it can still deliver a discharge capacity of 117 mAh g⁻¹ with excellent capacity retention rate of more than 95% after 50 cycles. These results show that the as-prepared LiNi_0.5Mn_1.5O₄ is a promising cathode material for high power Li-ion batteries.     

Effects of surface modification on the cycling stability of LiNi0.8Co0.2O2 electrodes by CeO2 coating

A high-performance LiNi_0.8Co_0.2O₂ cathode was successfully fabricated by a sol-gel coating of CeO₂ to the surface of the LiNi_0.8Co_0.2O₂ powder and subsequent heat treatment at 700 °C for 5 h. The surface-modified and pristine LiNi_0.8Co_0.2O₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), slow rate cyclic voltammogram (CV), and differential scanning calorimetry (DSC). Unlike pristine LiNi_0.8Co_0.2O₂, the CeO₂-coated LiNi_0.8Co_0.2O₂ cathode exhibits no decrease in its original specific capacity of 182 mAh/g (versus lithium metal) and excellent capacity retention (95% of its initial capacity) between 4.5 and 2.8 V after 55 cycles. The results indicate that the surface treatment should be an effective way to improve the comprehensive properties of the cathode materials for lithium ion batteries.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

Synthesis and characterization of LiNi1/3Mn1/3Co1/3O2 by wet-chemical method

A series of LiNi_1/3Mn_1/3Co_1/3O₂ samples with α-NaFeO₂ structure belonging to the D_3d⁵ space group were synthesized using tartaric acid as a chelating agent by wet-chemical method. Different acid to metal-ion ratios R have been used to investigate the effect of this parameter on the physical and electrochemical properties. We have characterized the reaction mechanism, the structure, and morphology of the powders by TGA, XRD, SEM and TEM imaging, completed by magnetic measurements, Raman scattering spectroscopy, and complex impedance experiments. We find that the LiNi_1/3Mn_1/3Co_1/3O₂ sintered at 900 °C for 15 h with an acid to metal-ion ratio R = 2 was the optimum condition for this synthesis. For this optimized sample, only 1.3% of nickel-ions occupied the 3b Wyckoff site of the lithium-ions sublattice. The electrochemical performance has been investigated using a coin-type cell containing Li metal as the anode. The electronic performance is correlated to the concentration of the Ni(3b) defects that increase the charge transfer resistance and reduce the lithium diffusion coefficient. The optimized cell delivered an initial discharge capacity of 172 mAh g⁻¹ in the cut-off voltage of 2.8-4.4 V, with a coulombic efficiency of 93.4%.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

Synthesis of compounds, Li(MMn11/6)O4 (M = Mn1/6, Co1/6, (Co1/12Cr1/12), (Co1/12Al1/12), (Cr1/12Al1/12)) by polymer precursor method and its electrochemical performance for lithium-ion batteries

The compounds, Li(MMn_11/6)O₄ (M = Mn_1/6, Co_1/6, (Co_1/12Cr_1/12), (Co_1/12Al_1/12), (Cr_1/12Al_1/12)) are synthesised by the polymer precursor method. The structure and the morphology of the compounds are studied by the Rietveld refined X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, respectively. Density and the Brunauer, Emmet and Teller surface area (BET) of the compounds are also studied. The cobalt doped compound, Li(Co_1/6Mn_11/6)O₄ is found to be nanosized particles in the range of 60-100 nm, when compared to the other compounds in our present study. The oxidation state and the local structure of the compounds are analysed by the X-ray absorption spectroscopy (XAS) technique. Cyclic voltammetry (CV) and the galvanostatic charge-discharge cycling (30 mA g⁻¹) studies are made in the voltage range of 3.5-4.3 V at room temperature for all the compounds under study. The bare and (Co_1/6), and (Co_1/12Cr_1/12) substituted spinels are cycled at high current rates of 1, 2 and 5C (assuming 1C∼120 mA g⁻¹). Cycling results of Co-substituted spinels show better and long-term capacity retention at all the current rates. At the end of the second cycle, Li(Co_1/6Mn_11/6)O₄ compound delivers a discharge capacity value of 100 (±3) and 87 (±3) mAh g⁻¹ for the current rate of 2 and 5C, respectively. An excellent capacity retention value of 94% is observed at the end of the 1000 cycles for both 2 and 5C rates.     

Synthesis and electrochemical characteristics of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials have been coated with Al₂O₃ nano-particles using sol-gel processing to improve its electrochemical properties. The X-ray diffraction (XRD) pattern of the as-prepared Al₂O₃ nano-particles was indexed to the cubic structure of the γ-Al₂O₃ phase and had an average size of ∼4 nm. The XRD showed that the structure of LiNi_1/3Co_1/3Mn_1/3O₂ was not affected by the Al₂O₃ coating. However, the Al₂O₃ coatings on LiNi_1/3Co_1/3Mn_1/3O₂ improved the cyclic life performance and rate capability without decreasing its initial discharge capacity. These electrochemical properties were also compared with those of LiAlO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material. The electrochemical impedance spectroscopy (EIS) was studied to understand the enhanced electrochemical properties of the Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ compared to uncoated LiNi_1/3Co_1/3Mn_1/3O₂.     

Synthesis and characterization of high-density non-spherical Li(Ni1/3Co1/3Mn1/3)O2 cathode material for lithium ion batteries by two-step drying method

Non-spherical Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm⁻³. This value is remarkably higher than that of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders obtained by other methods, which range from 1.50 g cm⁻³ to 2.40 g cm⁻³. The precursor and Li(Ni_1/3Co_1/3Mn_1/3)O₂ are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2⁺, 3⁺ and 4⁺, respectively. XRD results show that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g⁻¹ is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g⁻¹ is retained at the end of 30 charge-discharge cycle with a capacity retention of 95%.     

Fine-sized LiNi0.8Co0.15Mn0.05O2 cathode particles prepared by spray pyrolysis from the polymeric precursor solutions

Fine-sized LiNi_0.8Co_0.15Mn_0.05O₂ cathode particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from the polymeric precursor solutions. The cathode particles obtained from the spray solution without polymeric precursors had irregular morphology and hardly aggregated morphology. On the other hand, the cathode particles obtained from the spray solution with citric acid and ethylene glycol had fine size and regular morphologies. The cathode particles obtained from the spray solution containing adequate amounts of citric acid and ethylene glycol had several hundreds nanometer and narrow size distribution. The maximum discharge capacity of the cathode particles was 218 mAh/g when the excess of lithium component added to the spray solution was 6 mol% of the stoichiometric amount to obtain the LiNi_0.8Co_0.15Mn_0.05O₂ particles. The discharge capacities of the fine-sized LiNi_0.8Co_0.15Mn_0.05O₂ particles dropped from 218 to 213 mAh/g by the 50th cycle at a current density of 0.1 C.     

Structure and morphology evolution in solid-phase synthesis lithium ion battery LiNi0.80Co0.15Al0.05O2 cathode materials with different micro-nano sizes of raw materials

The LiNi_0.80Co_0.15Al_0.05O₂ (NCA) cathode is endowed with a high energy density and excellent cycling performance. However, the preparation conditions for this material are quite harsh. Therefore, it is rather significant to obtain well-qualified NCA by simple solid-phase synthesis. In this study, the solid-phase synthesis of NCA cathode material is carried out by mixing two types of raw materials via stirring or sand milling. The effects of different particle sizes on the structure and morphology of NCA materials are analyzed. Owing to the different particle sizes of the raw materials, the diffusion path of Li⁺ between the solid phases differs greatly. The XRD results show that the samples mixed by stirring have a worse cation mixture than those mixed by sand milling due to the larger particle size, smaller sintering surface energy, and insufficient sintering strength. The electrochemical results show that the sample mixed by sand milling has a higher specific capacity at a low rate, the initial discharge capacity is 199.22?mAh?g^?1, and the capacity retention rate is 86.9% after 50 cycles. In contrast, the initial discharge capacity of the sample mixed by stirring is 184.86?mAh?g^?1, and the capacity is 171.93?mAh?g^?1 after 50 cycles with a 93.0% capacity retention rate.     

Synthetic optimization of spherical Li[Ni1/3Mn1/3Co1/3]O2 prepared by a carbonate co-precipitation method

A carbonate co-precipitation method was employed to prepare spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material. The precursor, [Ni_1/3Co_1/3Mn_1/3]CO₃, was prepared using ammonia as chelating agent under CO₂ atmosphere. The spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing the precalcined [Ni_1/3Co_1/3Mn_1/3]CO₃ with LiOH followed by high temperature calcination. The preparation conditions such as ammonia concentration, co-precipitation temperature, calcination temperature and Li/[Ni_1/3Co_1/3Mn_1/3] ratio were varied to optimize the physical and electrochemical properties of the prepared Li[Ni_1/3Co_1/3Mn_1/3]O₂. The structural, morphological, and electrochemical properties of the prepared LiNi_1/3Co_1/3Mn_1/3O₂ were characterized by XRD, SEM, and galvanostatic charge-discharge cycling. The optimized material has a spherical particle shape and a well ordered layered structure, and it also has an initial discharge capacity of 162.7 mAh g^− 1 in a voltage range of 2.8-4.3 V and a capacity retention of 94.8% after a hundred cycles. The optimized ammonia concentration, co-precipitation temperature, calcination temperature, and Li/[Ni_1/3Co_1/3Mn_1/3] ratio are 0.3 mol L^− 1, 60 °C, 850 °C, and 1.10, respectively.     

Characterization of yttrium substituted LiNi0.33Mn0.33Co0.33O2 cathode material for lithium secondary cells

LiNi_0.33−xMn_0.33Co_0.33Y_xO₂ materials are synthesized by Y³⁺ substitute of Ni²⁺ to improve the cycling performance and rate capability. The influence of the Y³⁺ doping on the structure and electrochemical properties are investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and galvanostatic charge/discharge tests. LiNi_0.33Mn_0.33Co_0.33O₂ exhibits the capacity retentions of 89.9 and 87.8% at 2.0 and 4.0 C after 40 cycles, respectively. After doping, the capacity retentions of LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ are increased to 97.2 and 95.9% at 2.0 and 4.0 C, respectively. The discharge capacity of LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ at 5.0 C remains 75.7% of the discharge capacity at 0.2 C, while that of LiNi_0.33Mn_0.33Co_0.33O₂ is only 47.5%. EIS measurement indicates that LiNi_0.305Mn_0.33Co_0.33Y_0.025O₂ electrode has the lower impedance value during cycling. It is considered that the higher capacity retention and superior rate capability of Y-doped samples can be ascribed to the reduced surface film resistance and charge transfer resistance of the electrode during cycling.     

Microwave solid-state synthesis and electrochemical properties of carbon-free Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using microwave solid-state synthesis method. The refined cell parameters and atomic coordination of the sample MW5m show some deviations compared with those of the sample synthesized in conventional solid-state synthesis method, especially the coordinate of Li atoms. Compared with the electrochemical properties of the carbon-coating sample Li₃V₂(PO₄)₃, the carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage of 3.0-4.3 V, MW5m sample presents a specific charge capacity of 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and specific discharge capacity of 126.4 mAh g⁻¹. In the cut-off voltage of 3.0-4.8 V, MW5m shows an initial specific discharge capacity of 183.4 mAh g⁻¹ at 0.1 C, near the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method, more capacity lost at relatively higher charge/discharge voltage. The reasons for the excellent electrochemical properties of Li₃V₂(PO₄)₃ rapidly synthesized in microwave field are discussed in detail.