Hydrothermal synthesis of layered Li[Ni1/3Co1/3Mn1/3]O2 as positive electrode material for lithium secondary battery

In attempts to prepare layered Li[Ni_1/3Co_1/3Mn_1/3]O₂, hydrothermal method was employed. The hydrothermal precursor, [Ni_1/3Co_1/3Mn_1/3](OH)₂, was synthesized via a coprecipitation route. The sphere-shaped powder precursor was hydrothermally reacted with LiOH aqueous solution at 170 °C for 4 days in autoclave. From X-ray diffraction and scanning electron microscopic studies, it was found that the as-hydrothermally prepared powders were crystallized to layered α-NaFeO₂ structure and the particles had spherical shape. The as-prepared Li[Ni_1/3Co_1/3Mn_1/3]O₂ delivered an initial discharge of about 110 mA h g⁻¹ due to lower crystallinity. Heat treatment of the hydrothermal product at 800 °C was significantly effective to improve the structural integrity, which consequently affected the increase in the discharge capacity to 157 (4.3 V cut-off) and 182 mA h g⁻¹ (4.6 V cut-off) at 25 °C with good reversibility.     

Characterization of high tap density Li[Ni1/3Co1/3Mn1/3]O2 cathode material synthesized via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by mixing metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂, with 6% excess LiOH followed by calcinations. The (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with secondary particle of about 12 μm was prepared by hydroxide co-precipitation. The tap density of the obtained Li[Ni_1/3Co_1/3Mn_1/3]O₂ powder was 2.56 ± 0.21 g cm⁻³. The powder was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), particle size distribution (PSD) and galvanostatic charge-discharge cycling. The XRD pattern of Li[Ni_1/3Co_1/3Mn_1/3]O₂ revealed a well ordered hexagonal layered structure with low cation mixing. Secondary particles with size of 13-14 μm and primary particles with size of about 1 μm can be identified from the SEM observations. In the voltage range of 2.8-4.3 V, the initial discharge capacity of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ electrode was 166.6 mAh g⁻¹, and 96.5% of the initial capacity was retained after 50 charge-discharge cycling.     

Synthetic optimization of Li[Ni1/3Co1/3Mn1/3]O2 via co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ powders were synthesized from co-precipitated spherical metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂. The preparation of metal hydroxide was significantly dependent on synthetic conditions, such as pH, amount of chelating agent, stirring speed, etc. The optimized condition resulted in (Ni_1/3Co_1/3Mn_1/3)(OH)₂, of which the particle size distribution was uniform and the particle shape was spherical, as observed by scanning electron microscopy. Calcination of the uniform metal hydroxide with LiOH at higher temperature led to a well-ordered layer-structured Li[Ni_1/3Co_1/3Mn_1/3]O₂, as confirmed by Rietveld refinement of X-ray diffraction pattern. Due to the homogeneity of the metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂, the final product, Li[Ni_1/3Co_1/3Mn_1/3]O₂, was also significantly uniform, i.e., the average particle size was of about 10 μm in diameter and the distribution was relatively narrow. As a result, the corresponding tap-density was also high approximately 2.39 g cm−3, of which the value is comparable to that of commercialized LiCoO₂. In the voltage range of 2.8-4.3, 2.8-4.4, and 2.8-4.5 V, the discharge capacities of Li[Ni_1/3Co_1/3Mn_1/3]O₂ electrode were 159, 168, and 177 mAh g⁻¹, respectively. For elevated temperature operation (55 °C), the resulted capacity was of about 168 mAh g⁻¹ with an excellent cyclability.     

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.     

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.     

The effect of Al(OH)3 coating on the Li[Li0.2Ni0.2Mn0.6]O2 cathode material for lithium secondary battery

Layered Li[Li_0.2Ni_0.2Mn_0.6]O₂ powder was modified by coating its surface with amorphous Al(OH)₃. Energy dispersive spectroscopy (EDS) showed that nano-sized Al(OH)₃ powders were homogeneously dispersed in the parent Li[Li_0.2Ni_0.2Mn_0.6]O₂ powders. Al(OH)₃ coated Li[Li_0.2Ni_0.2Mn_0.6]O₂ exhibited an greater retention capacity at higher rates compared to uncoated Li[Li_0.2Ni_0.2Mn_0.6]O₂. The low area specific impedance (ASI) value of the Al(OH)₃ is the major factor for its higher rate performance. The 1.4 wt.% Al(OH)₃ coated sample had an impedance of 41 Ω cm² while uncoated Li[Li_0.2Ni_0.2Mn_0.6]O₂ had a 57 Ω cm² at 30-80% state of charge. Electrochemical impedance spectroscopy (EIS) also showed that the Al(OH)₃ coated sample had a lower charge transfer resistance (R_ct) than the uncoated sample. Differential scanning calorimetry (DSC) analysis showed that Al(OH)₃ coating improved the thermal stability. Al(OH)₃ coating increased the onset temperature of thermal decomposition and reduced the amount of heat for the exothermic peak.     

The first cycle characteristics of Li[Ni1/3Co1/3Mn1/3]O2 charged up to 4.7 V

In this research, we studied the first cycle characteristics of Li[Ni_1/3Co_1/3Mn_1/3]O₂ charged up to 4.7 V. Properties, such as valence state of the transition metals and crystallographic features, were analyzed by X-ray absorption spectroscopy and X-ray and neutron diffractions. Especially, two plateaus observed around 3.75 and 4.54 V were investigated by ex situ X-ray absorption spectroscopy. XANES studies showed that the oxidation states of transition metals in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are mostly Ni²⁺, Co³⁺ and Mn⁴⁺. Based on neutron diffraction Rietveld analysis, there is about 6% of all nickel divalent (Ni²⁺) ions mixed with lithium ions (cation mixing). Meanwhile, it was found that the oxidation reaction of Ni²⁺/Ni⁴⁺ is related to the lower plateau around 3.75 V, but that of Co³⁺/Co⁴⁺ seems to occur entire range of x in Li_1−x[Ni_1/3Co_1/3Mn_1/3]O₂. Small volume change during cycling was attributed to the opposite variation of lattice parameter “c” and “a” with charging-discharging.     

Effect of synthesis condition on the structure and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by hydroxide co-precipitation method

The layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ powder with good crystalline and spherical shape was prepared by hydroxide co-precipitation method. The effects of pH value, NH₄OH amount, calcination temperature and extra Li amount on the morphology, structure and electrochemical properties of the cathode material were investigated in detail. SEM results indicate that pH value affected both the morphology and the property of the cathode material, and the highest discharge capacity in the first cycle of 163 mAh g⁻¹ (2.8-4.3 V) was obtained at pH value was 12. On the contrary, the NH₄OH amount, which was used as a chelating agent, only affected the particle size distribution of the material. The calcination temperatures caused great difference in the structure and property of layered Li[Ni_1/3Co_1/3Mn_1/3]O₂, and the best electrochemical properties were obtained at the calcination temperature of 800 °C. Extra Li amount not only caused difference in the material structure, but also affected their electrochemical properties. With increasing Li amount, the lattice parameters (a and c) increased monotonously, and the highest first cycle coulombic efficiency (the ratio of discharge capacity to charge capacity in the first cycle) was obtained with the Li/M of 1.10. Therefore, the optimum synthetic conditions for the hydroxide co-precipitation reaction were: pH value was 12, NH₄OH amount was 0.36 mol L⁻¹, calcination temperature was 800 °C and the Li/M molar ratio was 1.10.     

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.     

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%.     

High-voltage performance of concentration-gradient Li[Ni0.67Co0.15Mn0.18]O2 cathode material for lithium-ion batteries

A novel Li[Ni_0.67Co_0.15Mn_0.18]O₂ cathode material encapsulated completely within a concentration-gradient shell was successfully synthesized via co-precipitation. The Li[Ni_0.67Co_0.15Mn_0.18]O₂ has a core of Li[Ni_0.8Co_0.15Mn_0.05]O₂ that is rich in Ni, a concentration-gradient shell having decreasing Ni concentration and increasing Mn concentration toward the particle surface, and a stable outer-layer of Li[Ni_0.57Co_0.15Mn_0.28]O₂. The electrochemical and thermal properties of the material were investigated and compared to those of the core Li[Ni_0.8Co_0.15Mn_0.05]O₂ material alone. The discharge capacity of the concentration-gradient Li[Ni_0.67Co_0.15Mn_0.18]O₂ electrode increased with increasing upper cutoff voltage to 4.5 V, and cells with this cathode material delivered a very high capacity, 213 mAh/g, with excellent cycling stability even at 55 °C. The enhanced thermal and lithium intercalation stability of the Li[Ni_0.67Co_0.15Mn_0.18]O₂ was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.     

Structural and electrochemical behaviors of metastable Li2/3[Ni1/3Mn2/3]O2 modified by metal element substitution

Layered metastable lithium manganese oxides, Li_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ precursors. The Al and Co doping produced the T^#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni_1/3−xMn_2/3−yM_x+yO₂ slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T^#2-Li_2/3[Ni_1/3Mn_2/3]O₂ were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g⁻¹ in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g⁻¹ along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T^#2 into the O2 structure was observed during the initial lithium deintercalation.     

Hydrothermal synthesis of Li(Ni1/3Co1/3Mn1/3)O2 for lithium rechargeable batteries

Ultrafine powders of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials for lithium-ion secondary batteries were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/(Ni + Co + Mn) was studied. The products were investigated by XRD, TEM and EDS. The final products were found to be well crystallized Li(Ni_1/3Co_1/3Mn_1/3)O₂ with an average particle size of about 10 nm.     

Comparative study of Li[Co1−zAlz]O2 prepared by solid-state and co-precipitation methods

Li[Co_1−zAl_z]O₂ (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Li_x[Co_0.9Al_0.1]O₂ samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li_x[Co_0.9Al_0.1]O₂ samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co_1−zAl_z]O₂ samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/(z = 1). Literature work on Li[Ni_1/3Mn_1/3Co_1/3−zAl_z]O₂, Li[Ni_1−zAl_z]O₂ and Li[Mn_2−yAl_y]O₄ demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co_1−zAl_z]O₂ in electrolyte.     

Synthesis of spherical Li[Ni(1/3−z)Co(1/3−z)Mn(1/3−z)Mgz]O2 as positive electrode material for lithium-ion battery

Li[Ni_(1/3−z)Co_(1/3−z)Mn_(1/3−z)Mg_z]O₂ (z = 0, 0.04) positive electrode materials were synthesized via a co-precipitation method. These materials have α-NaFeO₂ () structure, as confirmed by X-ray diffraction (XRD) studies. Cation mixing in Li layer seemed to be decreased by Mg substitution as examined by Rietveld refinements of XRD data. Spherical morphologies were observed for the as-synthesized final products by scanning electron microscopy. Their electrochemical properties during charge and discharge were discussed. When magnesium ions are substituted, the initial reversible capacity reduced. However, the substitution for Mn sites in Li[Ni_1/3Co_1/3Mn_1/3]O₂ did not decrease the capacity because Mn sites substitution did not result in loss of electroactive elements in the compound. Differential scanning calorimetric studies showed the exothermic peaks of the charged electrode Li[Ni_(1/3−z)Co_(1/3−z)Mn_(1/3−z)Mg_z]O₂ (z = 0.04) were significantly smaller than that of Li[Ni_1/3Co_1/3Mn_1/3]O₂, which means that thermal stability was greatly improved by Mg substitution even at highly delithiated state.     

Improvement of electrochemical and thermal properties of Li[Ni0.8Co0.1Mn0.1]O2 positive electrode materials by multiple metal (Al, Mg) substitution

Al and/or Mg-substituted Li[Ni_0.8Co_0.1Mn_0.1−x−yAl_xMg_y]O₂ were prepared by a co-precipitation method and characterized by X-ray diffraction with Rietveld refinement, thermogravimetric analysis, differential scanning calorimetry (DSC), and electrochemical measurements. The Rietveld refinement results show that cation mixing of Al and/or Mg-substituted Li[Ni_0.8Co_0.1Mn_0.1−x−yAl_xMg_y]O₂ was reduced with increased doping amounts of Al and Mg. The Al and/or Mg substitution in Li[Ni_0.8Co_0.1Mn_0.1]O₂ also resulted in improved electrochemical cycling behavior, structural stability, and thermal stability compared to pristine Li[Ni_0.8Co_0.1Mn_0.1]O₂. The improvements of electrochemical and thermal properties resulted from the stabilized host structure by Al and/or Mg incorporation into Li[Ni_0.8Co_0.1Mn_0.1]O₂.     

Insignificant impact of designed oxygen release from high capacity Li[(Ni1/2Mn1/2)xCoy(Li1/3Mn2/3)1/3]O2 (x + y = 2/3) positive electrodes during the cycling of Li-ion cells

The properties of graphite/Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3, y = 1/12 and 1/6) Li-ion cells are reported. There is an extended plateau near 4.5 V during the first charging of the cells that corresponds to the simultaneous removal of Li and oxygen from the Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3, y = 1/12 and 1/6) electrodes. The release of this oxygen directly within a Li-ion cell has been a cause for concern. However, it was found that subsequent to O₂ release, Li-ion cells delivered a high reversible positive electrode specific capacity near 250 mAh/g at C/30 between 2.5 and 4.8 V, the cells did not display increased irreversible capacity relative to counterparts having Li metal negative electrodes and the cells retained 85% of their initial capacity after 70 cycles at C/6 between 2.5 and 4.6 V. Therefore, the O₂ released during the first charge does not significantly impact the electrochemical properties of graphite/Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3) lithium-ion cells.     

Electrochemical properties of Li[Ni1/3Mn1/3Al1/3−xCox]O2 as a cathode material for lithium ion battery

Layered Li[Ni_1/3Mn_1/3Al_1/3−xCo_x]O₂ (0 ≤ x ≤ 1/3) cathode materials are synthesized by a solvent evaporation method. Although XRD shows that Li[Ni_1/3Mn_1/3Al_1/3]O₂ has no obvious impurity phase, it has poor electrochemical properties. To improve its capability, part of Al in Li[Ni_1/3Mn_1/3Al_1/3]O₂ compound is replaced by Co in this study. The samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and charge–discharge test. The results indicate that the introduction of Co has a large influence on the morphology, structure and electrochemical performances of the samples, which become more excellent with an increase of Co content in compounds. Meanwhile, the high-temperature behavior of the samples is also investigated.     

Particle size effect of Li[Ni0.5Mn0.5]O2 prepared by co-precipitation

Spherical (Ni_0.5Mn_0.5)(OH)₂ with different secondary particle size (3 μm, 10 μm in diameter) was synthesized by co-precipitation method. Mixture of the prepared hydroxide and lithium hydroxide was calcined at 950 °C for 20 h in air. X-ray diffraction patterns revealed that the prepared material had a typical layered structure with space group. Spherical morphologies with mono-dispersed powders were observed by scanning electron microscopy. It was found that the layered Li[Ni_0.5Mn_0.5]O₂ delivered an initial discharge capacity of 148 mAh g⁻¹ (3.0-4.3 V) though the particle sizes were different. Li[Ni_0.5Mn_0.5]O₂ having smaller particle size (3 μm) showed improved area specific impedance due to the reduced Li⁺ diffusion path, compared with that of Li[Ni_0.5Mn_0.5]O₂ possessing larger particle size (10 μm). Although the Li[Ni_0.5Mn_0.5]O₂ (3 μm) was electrochemically delithiated to Li_0.39[Ni_0.5Mn_0.5]O₂, the resulting exothermic onset temperature was around 295 °C, of which the value is significantly higher than that of highly delithiated Li_1−δCoO₂ (∼180 °C).     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.