Synthesis and electrochemical properties of Li[Ni0.8Co0.1Mn0.1]O2 and Li[Ni0.8Co0.2]O2 via co-precipitation

Spherical Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) with phase-pure and well-ordered layered structure have been synthesized by heat-treatment of spherical [Ni_0.8Co_0.2−xMn_x](OH)₂ and LiOH·H₂O precursors. The structure, morphology, electrochemical properties, and thermal stability of Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) were studied. The average particle size of the powders was about 10–15 μm and the size distribution was narrow due to the homogeneity of the metal hydroxide [Ni_0.8Co_0.2−xMn_x](OH)₂ (x = 0, 0.1). The Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) delivered a discharge capacity of 197–202 mAh g⁻¹ and showed excellent cycling performance. Compared to Li[Ni_0.8Co_0.2]O₂, Li[Ni_0.8Co_0.1Mn_0.1]O₂ exhibited greater thermal stability resulting from improved structural stability due to Mn substitution.     

Morphological,structural, and electrochemical characteristics of LiNi0.5Mn0.4M0.1O2 (M = Li,Mg, Co,Al)

LiNi_0.5Mn_0.4M_0.1O₂ (M = Li, Mg, Al, Co) compound was prepared by a solid-state reaction, and its structural, morphological and electrochemical properties were characterized by XRD, SEM, charge–discharge tests and EIS. The impacts of alien ion introduction on the structural, morphological and electrochemical properties of LiNi_0.5Mn_0.5O₂ depend on the dopants. The substitution of Li, Mg, and Co for Mn can enlarge the particle size and improve the crystallinity. LiNi_0.5Mn_0.4Li_0.1O₂ and LiNi_0.5Mn_0.4Co_0.1O₂ show increased reversible capacities as well as upgraded rate capabilities. LiNi_0.5Mn_0.4Li_0.1O₂ exhibits a retentive capacity of about 200 mAh g⁻¹ at 50 °C.     

Synthesis and characterization of LiNi0.8Co0.2O2 as cathode material for lithium-ion batteries by a spray-drying method

Layered structure LiNi_0.8Co_0.2O₂ cathode material for lithium-ion batteries was synthesized by sintering the precursor, which was obtained from the corresponding metal acetate solution via a spray-drying method. The structure, morphology and reaction mechanism of the powders were characterized by means of XRD, SEM and TG-DTA. The electrochemical properties of the LiNi_0.8Co_0.2O₂ cathode were also investigated by using a coin-type cell containing Li metal as the anode in a potential range of 3.0–4.3 V. Upon sintering the spray-dried powders at 750 °C for 24 h, the LiNi_0.8Co_0.2O₂ particles obtained are fine, narrowly distributed and well crystallized. As a result, the synthesized LiNi_0.8Co_0.2O₂ has excellent electrochemical properties. The simple synthesis procedure is time and energy saving, and thus is promising for commercial application.     

Thermal simulation of large-scale lithium secondary batteries using a graphite–coke hybrid carbon negative electrode and LiNi0.7Co0.3O2 positive electrode

Thermal simulation was applied to 2 Wh-class cells (diameter 14.2 mm, height 50 mm) using LiNi_0.7Co_0.3O₂ or LiCoO₂ as the positive electrode material, in order to clarify the thermal behavior of the cells during charge and discharge. The thermal simulation results for the 2 Wh-class cells showed a good agreement with measured temperature values. The heat generation of a cell using LiNi_0.7Co_0.3O₂ was found to be much less than that using LiCoO₂ during discharge. This difference was considered to be caused by the difference in the change of entropy. A 250 Wh-class cell (diameter 64 mm, height 296 mm) was also constructed using LiNi_0.7Co_0.3O₂ and thermal simulation was applied. We confirmed that the results of the thermal simulation agreed with measured values and that this simulation model is effective for analyzing the thermal behavior of large-scale lithium secondary batteries.     

Li(Ni1/3Co1/3Mn1/3)O2 as a suitable cathode for high power applications

The electrochemical performance of the layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ material have been investigated as a promising cathode for a hybrid electric vehicle (HEV) application. A C/Li(Ni_1/3Co_1/3Mn_1/3)O₂ cell, cycled between 2.9 and 4.1 V at 1.5 C rate, does not show any sign of capacity fade up to 100 cycles, whereas at the 5 C rate, a loss of only 18% of capacity is observed after 200 cycles. The Li(Ni_1/3Co_1/3Mn_1/3)O₂ host cathode converts from the hexagonal to a monoclinic symmetry at a high state of charge. The cell pulse power capability on charge and discharge were found to exceed the requirement for powering a hybrid HEV. The accelerated calendar life tests performed on C/Li(Ni_1/3Co_1/3Mn_1/3)O₂ cells charged at 4.1 V and stored at 50 °C have shown a limited area specific impedance (ASI) increase unlike C/Li(Ni_0.8Co_0.2)O₂ based-cells. A differential scanning calorimetry (DSC) comparative study clearly showed that the thermal stability of Li(Ni_1/3Co_1/3Mn_1/3)O₂ is much better than that of Li(Ni_0.8Co_0.2)O₂ and Li(Ni_0.8Co_0.15Al_0.05)O₂ cathodes. Also, DSC data of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode charged at 4.1, 4.3, and 4.6 V are presented and their corresponding exothermic heat flow peaks are discussed.     

Electrochemical performance behavior of combustion-synthesized LiNi0.5Mn0.5O2 lithium-intercalation cathodes

LiNiO₂, partially substituted with manganese in the form of a LiNi_0.5Mn_0.5O₂ compound, has been synthesized by a gelatin assisted combustion method [GAC] method. Highly crystalline LiNi_0.5Mn_0.5O₂ powders with R3m symmetry have been obtained at an optimum temperature of 850 °C, as confirmed by PXRD studies. The presence of cathodic and anodic CV peaks exhibited by the LiNi_0.5Mn_0.5O₂ cathode at 4.4 and 4.3 V revealed the existence of Ni and Mn in their 2+ and 4+ oxidation states, respectively. The synthesized LiNi_0.5Mn_0.5O₂ cathode has been subjected to systematic electrochemical performance evaluation, via capacity tapping at different cut-off voltage limits (3.0–4.2, 3.0–4.4 and 3.0–4.6 V) and the possible extraction of deliverable capacity under different current drains (0.1C, 0.5C, 0.75C and 1C rates). The LiNi_0.5Mn_0.5O₂ cathode exhibited a maximum discharge capacity of 174 mAh g⁻¹ at the 0.1C rate between 3.0 and 4.6 V. However, a slightly decreased capacity of 138 mAh g⁻¹ has been obtained in the 3.0–4.4 V range, when discharged at the 1C rate. On the other hand, extended cycling at the 0.1C rate encountered an acceptable capacity fade in the 3.0–4.4 V range (<10%) for up to 50 cycles.     

LiNi0.8Co0.2O2 cathode materials synthesized by the maleic acid assisted sol–gel method for lithium batteries

A maleic acid assisted sol–gel method was employed to synthesize LiNi_0.8Co_0.2O₂ cathode materials, which are of interest for potential use in lithium batteries. Various synthesis conditions such as solvent, calcination time, calcination temperature, acid-to-metal ion ratio (R), and lithium stoichiometry were studied to determine the ideal conditions for preparing LiNi_0.8Co_0.2O₂ with the best electrochemical characteristics. The optimal synthesis conditions were found to be an ethanol solvent with a calcination time of 12 h at 800°C under flowing oxygen. The first discharge capacity of the material synthesized using the above conditions was 190 mAh/g, and the discharge capacity after 10 cycles was 183 mAh/g, at a 0.1 C rate between 3.0 and 4.2 V. Details of how varying initial synthesis conditions affected capacity and cycling performance of LiNi_0.8Co_0.2O₂ are discussed.     

Preparation and electrochemical/thermal properties of LiNi0.74Co0.26O2 cathode material

Electrochemical and thermal properties of LiNi_0.74Co_0.26O₂ cathode material with 5, 13 and 25 μm-sized particles have been studied by using a coin-type half-cell Li/LiNi_0.74Co_0.26O₂. The specific capacity of the material ranges from 205 to 210 mA h g⁻¹, depending on the particle size or the Brunauer, Emmett and Teller (BET) surface area. Among the particle sizes, the cathode with a particle size of 13 μm shows the highest specific capacity. Even though the material with a particle size of 5 μm exhibits the smallest capacity value of 205 mA h g⁻¹, no capacity fading was observed after 70 cycles between 4.3 and 2.75 V at the 1 C rate. Differential scanning calorimetry (DSC) studies of the charged electrode at 4.3 V show a close relationship between particle size (BET surface area) and thermal stability of the electrode, namely, a larger particle size (smaller BET surface area) leads to a better thermal stability of the LiNi_0.74Co_0.26O₂ cathode.     

Study of the electrochemical properties of Ga-doped LiNi0.8Co0.2O2 synthesized by a sol–gel method

The effects of gallium doping on the structure and electrochemical properties of LiNi_0.8Co_0.2O₂ were investigated by X-ray diffraction, cyclic voltammetry and charge-discharge tests. LiNi_0.8Co_0.2−xGa_xO₂ (x = 0.01, 0.03, 0.05) was synthesized using a sol–gel method and it showed the average particle size less than 1 μm in diameter. Results showed that gallium-doping had no effect on the crystal structure (α-NaFeO₂) of the cathode material in the range x ≤ 0.05. On the other hand, two transitions at 3.7–3.9 and 4.2–4.7 V observed during the cycle test were merged into one when the amount of gallium doping increases to 0.05, implying that the enhanced capacity retention with gallium doping is attributed to the suppression of the phase transition of the cathode. However, the increase of gallium content in LiNi_0.8Co_0.2O₂ slightly decreases the initial discharge capacity.     

The improved physical and electrochemical performance of LiNi0.35Co0.3−xCrxMn0.35O2 cathode materials by the Cr doping for lithium ion batteries

We have successfully prepared the layered structure LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ with various Cr contents by a co-precipitation method. Many measurement methods have been applied to characterize the physical and electrochemical properties of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂, such as XRD, SEM, BET and electrochemical test. SEM showed that the addition of Cr has obviously changed the morphologies of their particles and increased the size of grains. The specific surface area of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ decreases lineally from 4.9 m² g⁻¹ (x = 0) to 1.8 m² g⁻¹ (x = 0.1) with the increasing of Cr contents. Moreover, we have found that the Cr doping can greatly improve the density of the powder, which is beneficial to solve the problem of lower electrode density for these layered LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ cathode materials. Electrochemical test indicated that the cycling performance of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ can be significantly improved with the increasing of Cr contents, although the initial discharge capacity of the sample has a little decrease.     

Enhanced electrochemical properties of LiNi1/3Co1/3Mn1/3O2 cathode material by coating with LiAlO2 nanoparticles

Surface coating of LiNi_1/3Co_1/3Mn_1/3O₂ with LiAlO₂ nanoparticles has been attempted to improve the electrochemical properties of these materials as cathodes in lithuim-ion batteries. The coating is undertaken by a sol–gel method that uses C₉H₂₁O₃Al, LiOH·H₂O and LiNi_1/3Co_1/3Mn_1/3O₂. X-ray diffraction analysis shows that the LiAlO₂ is composed of both α- and β-LiAlO₂ phases. The average size of the particles is about 15 nm. The structure of LiNi_1/3Co_1/3Mn_1/3O₂ is not affected by the LiAlO₂ nanoparticle coating. A 3 wt.% LiAlO₂-coating increases the specific discharge capacity, provides excellent cycling performance (i.e. 96.7% capacity retention after 50 cycles at the 1 C rate) and improves the rate capability. By contrast, heavier coatings (5 wt.%) on LiNi_1/3Co_1/3Mn_1/3O₂ dramatically decrease both the discharge capacity and the rate capability, but enhance the cycle life.     

Stannum doping of layered LiNi3/8Co2/8Mn3/8O2 cathode materials with high rate capability for Li-ion batteries

Sn doped lithium nickel cobalt manganese composite oxide of LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ (0 ≤ x ≤ 0.10) was synthesized by stannum substitute of manganese to enhance its rate capability at first time. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), SEM, cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and charge/discharge tests. LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ had stable layered structure with α-NaFeO₂ type as x up to 0.05, meanwhile, its chemical diffusion coefficient D_Li of Li-ion was enhanced by almost one order of magnitude, leading to notable improvement of the rate capability of LiNi_3/8Co_2/8Mn_3/8O₂. The compound of x = 0.10 showed the best rate capability among Sn doped samples, but its discharge capacity reduced markedly due to secondary phase Li₂SnO₃ and increase of cation-disorder. The compound with x = 0.05 showed high rate capability with initial discharge capacity in excess of 156 mAh g⁻¹. It is a promising alternative cathode material for EV application of Li-ion batteries.     

Crystal chemistry and electrochemical characterization of layered LiNi0.5−yCo0.5−yMn2yO2 and LiCo0.5−yMn0.5−yNi2yO2 (0 ≤ 2y ≤ 1) cathodes

The crystal chemistry and electrochemical performance of the layered LiNi_0.5−yCo_0.5−yMn_2yO₂ and LiCo_0.5−yMn_0.5−yNi_2yO₂ oxide cathodes for 0 ≤ 2y ≤ 1 have been investigated. Li₂MnO₃ impurity phase is observed for Mn-rich compositions with 2y > 0.6 in LiNi_0.5−yCo_0.5−yMn_2yO₂ and 2y < 0.2 in LiCo_0.5−yMn_0.5−yNi_2yO₂. Additionally, the Ni-rich compositions encounter a volatilization of lithium at the high synthesis temperature of 900 °C. Compositions around 2y = 0.33 are found to be optimum with respect to maximizing the capacity values and retention. The rate capabilities are found to bear a strong relationship to the cation disorder in the layered lattice. Moreover, the evolution of the X-ray diffraction patterns on chemically extracting lithium has revealed the presence of Li₂MnO₃ phase in addition to the layered phase for the composition LiNi_0.25Co_0.25Mn_0.5O₂ with an oxidation state of manganese close to 4+, which results in a large anodic peak at around 4.5 V due to the extraction of both lithium and oxygen.     

Synthesis and electrochemical properties of LiNi0.80(Co0.20−xAlx)O2 (x = 0.0 and 0.05) cathodes for Li ion rechargeable batteries

The effect of simultaneous cobalt as well as aluminum doping was studied to understand their effect on the phase formation behavior and electrochemical properties of solution derived lithium nickel oxide cathode materials for rechargeable batteries. The discharge capacities of LiNi_0.80Co_0.20O₂ and LiNi_0.80Co_0.15Al_0.05O₂ cathodes, measured at constant current densities of 0.45 mA cm⁻² in the cut-off voltage range of 4.3–3.2 V, were 100 and 136 mAh g⁻¹, respectively. LiNi_0.80Co_0.15Al_0.05O₂ had better cycleability than the LiNi_0.80Co_0.20O₂ cathodes. The retention of undesirable Li₂CO₃ phase both in LiNi_0.80Co_0.20O₂ and LiNi_0.80Co_0.15Al_0.05O₂ cathodes was argued to be responsible for the relatively lower discharge capacity of these materials.     

A stabilized NiO cathode prepared by sol-impregnation of LiCoO2 precursors for molten carbonate fuel cells

Layers of LiCoO₂ were formed on the internal surface of a porous NiO cathode to reduce the rate of NiO dissolution into the molten carbonate. A sol-impregnation technique assisted by acrylic acid (AA) was used to deposit gel precursors of LiCoO₂ on the pore surface of the Ni plate. Thermal treatment of the gel-coated cathode above 400 °C produced LiCoO₂ layers on the porous cathode. A number of bench-scale single cells were fabricated with LiCoO₂-coated cathodes and the cell performance was examined at atmospheric pressure for 1000 h. With the increase in the LiCoO₂ content in the cathode, the initial cell voltage decreased, but the cell performance gradually improved during the cell test. It was found from symmetric cathode cell test that the cathode was initially flooded with electrolyte, but redistribution of the electrolyte took place during the test and cell performance became comparable to that of a conventional NiO cathode. The amount of Ni precipitated in the matrix during the cell operation for 1000 h was significantly reduced by the LiCoO₂ coating. For instance, coating 5 mol% of LiCoO₂ in the cathode led to a 56% reduction of Ni precipitation in the matrix. The results obtained in this study strongly suggest that LiCoO₂ layers formed on the internal surface of the porous NiO cathode effectively suppress the rate of NiO dissolution for 1000 h.     

The elevated temperature performance of LiMn2O4 coated with LiNi1−XCoXO2 (X = 0.2 and 1)

The surface coating of LiMn₂O₄ using a gel precursor of LiNi_1−XCo_XO₂ (X=0.2 and 1) prepared from a solution-based chemical process was attempted in order to enhance the electrochemical performances of LiMn₂O₄ at elevated temperature. After the surface of LiMn₂O₄ was coated with LiNi_1−XCo_XO₂ (X=0.2 and 1) coating solution and heated at 750 °C, the surface of LiMn₂O₄ was covered with fine LiNi_1−XCo_XO₂ (X=0.2 and 1) particles. LiNi_1−XCo_XO₂ (X=0.2 and 1)-coated LiMn₂O₄ showed an excellent capacity retention at 65 °C compared to pure LiMn₂O₄. While pure LiMn₂O₄ retained 81% of the initial capacity after storage in the discharged state at 65 °C for 300 h, LiCoO₂-coated LiMn₂O₄ showed no capacity loss. The improvement of storage performance at 65 °C is attributed to the suppression of electrolyte decomposition and the reduction of Mn dissolution resulting from encapsulating the surface of LiMn₂O₄ with LiCoO₂. The surface coating with LiNi_0.8Co_0.2O₂ also enhanced the high temperature cycle performance of LiMn₂O₄. Consequently, It is proposed that the surface encapsulation of LiMn₂O₄ with fine LiNi_1−XCo_XO₂ (X=0.2 and 1) particles improve its high temperature performance.     

Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel

LiNi_0.5Mn_1.5O₄ material with a spinel structure is prepared by a sol–gel method. The material is initially fired at 850 °C and then subjected to a post-reaction annealing at 600 °C in order to minimize the nickel deficiency. The elevated firing temperature produces materials with a small surface-area which is beneficial for good capacity retention. Indeed, the spinel LiNi_0.5Mn_1.5O₄ not only shows a good cycle performance, but exhibits an excellent discharge capacity, i.e. 114 mAh g⁻¹ at 4.66 V plateau and 127 mAh g⁻¹ in total. Cyclic voltammetry and ac impedance spectroscopy are employed to characterize the reactions of lithium insertion and extraction in the LiNi_0.5Mn_1.5O₄ electrode. Excellent electrochemical performance and low material cost make this compound an attractive cathode for advanced lithium batteries.     

Rapid thermal annealing effect on surface of LiNi1−xCoxO2 cathode film for thin-film microbattery

The effect of rapid thermal annealing (RTA) on the surface of a LiNi_1−xCo_xO₂ cathode film is examined by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and auger electron spectroscopy (AES). It is found that the as-deposited LiNi_1−xCo_xO₂ film undergoes a surface reaction with oxygen in the air, due to the high activity of lithium in the film. AES spectra indicate that the surface layer consists of lithium and oxygen atoms. The RTA process at 500 °C eliminates the surface layer to some extent. An increase in annealing temperature to 700 °C results in complete elimination of the surface layer. The surface evolution of the LiNi_1−xCo_xO₂ film with increasing annealing time at 700 °C is examined by means of AFM examination. It is found that the surface layer, which is initially present in the form of an amorphous like-film, becomes agglomerated and then vaporizes after 5 min of annealing. A thin-film microbattery (TFB), fabricated by using the LiNi_1−xCo_xO₂ film without a surface layer, exhibits more stable cycliability and a higher specific discharge capacity of 60.2 μAh cm⁻² μm than a TFB with an unannealed LiNi_1−xCo_xO₂ film. Therefore, it is important to completely eliminate the surface layer in order to achieve high performance from all solid-state thin-film microbatteries.     

Electrochemical characterization of high-performance LiNi0.8Co0.2O2 cathode materials for rechargeable lithium batteries

The cathode material, LiNi_0.8Co_0.2O₂ was synthesized by acid dissolution method using lithium carbonate, nickel hydroxide (carbonate), cobalt hydroxide (carbonate) as insoluble starting materials, and acrylic acid, which acts as an organic acid as well as a chelating agent. Structural and chemical characterization of the spray-dried xerogel precursor was performed through its compositional and thermogravimetric analysis (TGA), which shows that the xerogel can be expressed as Li[MA]₃, where M is the transition metal atom. The electrochemical performance of the synthesized powder was tested manufacturing the coin-type cells with lithium metal as an anode material. With the voltage range of 3.0–4.2 V, the capacity retentions after 50 cycles were 98.6 and 94.5%, respectively, for the powders calcined at 800 °C for 15 and 20 h. At the rate capability test, discharge capacity ratio between 3.0 and 0.5 C rate is about 91–84% till 60 cycles.     

Study of cobalt-doped lithium–nickel oxides as cathodes for MCFC

Cobalt substituted lithium–nickel oxides were synthesized by a solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor and were characterized as cathodes for molten carbonate fuel cell (MCFC). LiNi_0.8Co_0.2O₂ cathodes were prepared using non-aqueous tape casting technique followed by sintering in air. The X-ray diffraction (XRD) analysis of sintered LiNi_1−xCo_xO₂ indicated that lithium evaporation occurs during heating. The lithium loss decreases with an increase of the cobalt content in the mixed oxides. The stability studies showed that dissolution of nickel into the molten carbonate melt is smaller in the case of LiNi_1−xCo_xO₂ cathodes compared to the dissolution values reported in the literature for state-of-the-art NiO. Pore volume analysis of the sintered electrode indicated a mean pore size of 3 μm and a porosity of 40%. A current density of 160 mA/cm² was observed when LiNi_0.8Co_0.2O₂ cathodes were polarized at 140 mV. The electrochemical impedance spectroscopy (EIS) studies done on LiNi_0.8Co_0.2O₂ cathodes under different gas conditions indicated that the rate of the cathodic discharge reaction depends on the O₂ and CO₂ partial pressures.