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.     

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.     

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.     

Synthesis of LiNi1/3Co1/3Mn1/3O2 cathode materials by using a supercritical water method in a batch reactor

LiNi_1/3Co_1/3Mn_1/3O₂ and LiCoO₂ cathode materials were synthesized by using a supercritical water (SCW) method with a metal salt solution in a batch reactor. Stoichiometric LiNi_1/3Co_1/3Mn_1/3O₂ was successfully synthesized in a 10-min reaction without calcination, while overlithiated LiCoO₂ (Li_1.15CoO₂) was synthesized using the batch SCW method. The physical properties and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ were compared to those of Li_1.15CoO₂ by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge cycling tests. The XRD pattern of LiNi_1/3Co_1/3Mn_1/3O₂ was found to be similar to that of Li_1.15CoO₂, showing clear splitting of the (0 0 6)/(1 0 2) and (1 0 8)/(1 1 0) peak pairs as particular characteristics of the layered structure. In addition, both cathode powders showed good crystallinity and phase purity, even though a short reaction time without calcination was applied to the SCW method. The initial specific discharge capacities of the Li_1.15CoO₂ and LiNi_1/3Co_1/3Mn_1/3O₂ powders at a current density of 0.24 mA/cm² in 2.5-4.5 V were 149 and 180 mAh/g, and their irreversible capacity loss was 20 and 17 mAh/g, respectively. The discharge capacities of the Li_1.15CoO₂ and LiNi_1/3Co_1/3Mn_1/3O₂ powders decreased with cycling and remained at 108 and 154 mAh/g after 30 cycles, which are 79% and 89% of the initial capacities. Compared to the overlithiated LiCoO₂ cathode powders, the LiNi_1/3Co_1/3Mn_1/3O₂ cathode powders synthesized by SCW method had better electrochemical performances.     

Electrochemical performance of all-solid-state lithium secondary batteries with Li-Ni-Co-Mn oxide positive electrodes

LiNi_1/3Co_1/3Mn_1/3O₂ was applied as a promising material to the all-solid-state lithium cells using the 80Li₂S·19P₂S₅·1P₂O₅ (mol%) solid electrolyte. The cell showed the first discharge capacity of 115 mAh g⁻¹ at the current density of 0.064 mA cm⁻² and retained the reversible capacity of 110 mAh g⁻¹ after 10 cycles. The interfacial resistance was observed in the impedance spectrum of the all-solid-state cell charged to 4.4 V (vs. Li) and the transition metal elements were detected on the solid electrolyte in the vicinity of LiNi_1/3Co_1/3Mn_1/3O₂ by the TEM observations with EDX analyses. The electrochemical performance was improved by the coating of LiNi_1/3Co_1/3Mn_1/3O₂ particles with Li₄Ti₅O₁₂ film. The interfacial resistance was decreased and the discharge capacity was increased from 63 to 83 mAh g⁻¹ at 1.3 mA cm⁻² by the coating. The electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ was compared with that of LiCoO₂, LiMn₂O₄ and LiNiO₂ in the all-solid-state cells. The rate capability of LiNi_1/3Co_1/3Mn_1/3O₂ was lower than that of LiCoO₂. However, the reversible capacity of LiNi_1/3Co_1/3Mn_1/3O₂ at 0.064 mA cm⁻² was larger than that of LiCoO₂, LiMn₂O₄ and LiNiO₂.     

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.     

Molten salt synthesis of spherical LiNi0.5Mn1.5O4 cathode materials

This paper describes a novel simple redox process for synthesizing monodispersed MnO₂ powders and preparation of spherical LiNi_0.5Mn_1.5O₄ cathode materials by molten salt synthesis (MSS) method. Monodispersed MnO₂ powders have been synthesized by using potassium permanganate and manganese sulfate as the starting materials. By using this redox method, it was found that monodispersed MnO₂ powders with average particle size ∼5 μm can be easily obtained. Resultant MnO₂ and LiOH, Ni(OH)₂ was then used to synthesis LiNi_0.5Mn_1.5O₄ cathode materials with retention of spherical particle shape by MSS method. The discharge capacity was 129 mAh g⁻¹ in the first cycle and 127 mAh g⁻¹ after 50 cycles under an optimal synthesis condition for 12 h at 800 °C.     

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.     

A delithiated LiNi0.65Co0.25Mn0.10O2 electrode material: A structural, magnetic and electrochemical study

A crystalline LiNi_0.65Co_0.25Mn_0.10O₂ electrode material was synthesized by the combustion method at 900 °C for 1 h. Rietveld refinement shows less than 3% of Li/Ni disorder in the structure. Lithium extraction involves only the Ni²⁺/Ni⁴⁺ redox couple while Co³⁺ and Mn⁴⁺ remain electrochemically inactive. No structural transition was detected during cycling in the whole composition range 0 < x < 1.0. Furthermore, the hexagonal cell volume changes by only 3% when all lithium was removed indicating a good mechanical stability of the studied compound. LiNi_0.65Co_0.25Mn_0.10O₂ has a discharge capacity of 150 mAh/g in the voltage range 2.5-4.5 V, but the best electrochemical performance was obtained with an upper cut-off potential of 4.3 V. Magnetic measurements reveal competing antiferromagnetic and ferromagnetic interactions - varying in strength as a function of lithium content - yielding a low temperature magnetically frustrated state. The evolution of the magnetic properties with lithium content confirms the preferential oxidation of Ni ions compared to Co³⁺ and Mn⁴⁺ during the delithiation process.     

Optimization of microwave synthesis of Li[Ni0.4Co0.2Mn0.4]O2 as a positive electrode material for lithium batteries

A positive electrode material for lithium ion battery applications was successfully synthesized using microwave irradiation. This microwave synthesis has several merits such as homogeneity of final product and much shorter reaction time compared to conventional synthetic methods. We synthesized spherical [Ni_0.4Co_0.2Mn_0.4](OH)₂ as a precursor by a co-precipitation method. The pelletized mixture of the precursor and lithium hydroxide was calcined under different reaction times and temperatures by applying 1200 W of microwave irradiation at 2.45 GHz. We determined the optimum conditions of microwave synthesis for positive electrode materials. The powders were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical testing. The capacity, its retention, and thermal stability of Li[Ni_0.4Co_0.2Mn_0.4]O₂ synthesized by the microwave synthesis were comparable to the Li[Ni_0.4Co_0.2Mn_0.4]O₂ prepared by the high temperature calcination method.     

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.     

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.     

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%.     

Preparation and electrochemical capacitance of cobalt oxide (Co3O4) nanotubes as supercapacitor material

Cobalt oxide (Co₃O₄) nanotubes have been successfully synthesized by chemically depositing cobalt hydroxide in anodic aluminum oxide (AAO) templates and thermally annealing at 500 °C. The synthesized nanotubes have been characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrochemical capacitance behavior of the Co₃O₄ nanotubes electrode was investigated by cyclic voltammetry, galvanostatic charge-discharge studies and electrochemical impedance spectroscopy in 6 mol L⁻¹ KOH solution. The electrochemical data demonstrate that the Co₃O₄ nanotubes display good capacitive behavior with a specific capacitance of 574 F g⁻¹ at a current density of 0.1 A g⁻¹ and a good specific capacitance retention of ca. 95% after 1000 continuous charge-discharge cycles, indicating that the Co₃O₄ nanotubes can be promising electroactive materials for supercapacitor.     

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%.     

Synthesis and electrochemical properties of submicron LiNi0.8Co0.2O2 by a polymer-pyrolysis method

A polymer-pyrolysis method was used to synthesize LiNi_0.8Co_0.2O₂, which has potential application in lithium ion batteries. The effect of calcination temperature and time on the structure and electrochemical performance of the material was investigated. XRD analysis showed that the powders obtained by calcination at 750 °C for 3 h had the best-ordered hexagonal layer structure. SEM image showed these powders were fine, narrowly distributed with platelet morphology. The charge-discharge tests demonstrated these powders had the best electrochemical properties, with an initial discharge capacity of 189 mAh/g and capacity retention of 95.2% after 50 cycles when cycled at 50 mA/g between 3.0 and 4.3 V. Besides, these powders also had exhibited excellent rate capability.     

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.     

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.     

A comparison of preparation method on the electrochemical performance of cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion battery

Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m² g⁻¹). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g⁻¹ at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.