Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel material by fluorine substitution

LiNi_0.5Mn_1.5O_4−xF_x (0 ≤ x ≤0.1) cathodes, synthesized by ultrasonic spray pyrolysis at 900 °C, exhibit superior structural and electrochemical properties. The samples are characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and electrochemical measurements. During Li⁺ extraction, LiNi_0.5Mn_1.5O_4−xF_x has a smaller lattice variation and area-specific impedance than LiNi_0.5Mn_1.5O₄. This enhances the rate capability, especially at high C-rates. LiNi_0.5Mn_1.5O_4−xF_x also exhibits better resistance than LiNi_0.5Mn_1.5O₄ to attack by HF.     

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.     

Layered Li(Ni0.5−xMn0.5−xM2x′)O2 (M′=Co,Al, Ti; x=0, 0.025) cathode materials for Li-ion rechargeable batteries

Layered Li(Ni_0.5−xMn_0.5−xM_2x′)O₂ materials (M′=Co, Al, Ti; x=0, 0.025) were synthesized using a manganese-nickel hydroxide precursor, and the effect of dopants on the electrochemical properties was investigated. Li(Ni_0.5Mn_0.5)O₂ exhibited a discharge capacity of 120 mAh/g in the voltage range of 2.8–4.3 V with a slight capacity fade up to 40 cycles (0.09% per cycle); by doping of 5 mol% Co, Al, and Ti, the discharge capacities increased to 140, 142, and 132 mAh/g, respectively, and almost no capacity fading was observed. The cathode material containing 5 mol% Co had the lowest impedance, 47 Ω cm², while undoped, Ti-doped, and Al-doped materials had impedance of 64, 62, and 99 Ω cm², respectively. Unlike the other dopants, cobalt was found to improve the electronic conductivity of the material. Further improvement in the impedance of these materials is needed to meet the requirement for powering hybrid electric vehicle (HEV, <35 Ω cm²). In all materials, structural transformation from a layered to a spinel structure was not observed during electrochemical cycling. Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) data suggested that Ni and Mn exist as Ni²⁺ and Mn⁴⁺ in the layered structure. Differential scanning calorimetry (DSC) data showed that exothermic peaks of fully charged Li_1−y(Ni_0.5−xMn_0.5−xM_2x′)O₂ appeared at higher temperature (270–290 °C) than LiNiO₂-based cathode materials, which indicates that the thermal stability of Li(Ni_0.5−xMn_0.5−xM_2x′)O₂ is better than those of LiNiO₂-based cathode materials.     

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 characterization of spherical morphology [Ni0.4Co0.2Mn0.4]3O4 materials for lithium secondary batteries

Spherical morphology [Ni_0.4Co_0.2Mn_0.4]₃O₄ materials have been synthesized by ultrasonic spray pyrolysis. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ powders were prepared at various pyrolysis temperatures between 500 and 900 °C. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ material prepared at a pyrolysis temperature of 600 °C samples are exhibited excellent electrochemical cycling performance and delivered the highest discharge capacity at over 180 mAh g⁻¹ between 2.8 and 4.4 V. The structural, electrochemical, morphological property and thermal stability of the powders were characterized by X-ray diffraction (XRD), galvanostatic charge/discharge testing, scanning electron microscopy (SEM), and differential scanning calorimeter (DSC), respectively.     

Synthesis,structural and electrochemical properties of pulsed laser deposited Li(Ni,Co)O2 films

We report the epitaxial growth of the LiNi_1−yM_yO₂ films (M = Co, Co–Al) on heated nickel foil using pulsed laser deposition in oxygen environment from lithium-rich targets. The structure and morphology was characterized by X-ray diffractometry, electron scanning microscopy and Raman spectroscopy. Data reveal that the formation of oriented films is dependent on two important parameters: the substrate temperature and the gas pressure during ablation. The charge–discharge process conducted in Li-microcells demonstrates that effective high specific capacities can be obtained with films 1.35 μm thick. Stable capacities of 83 and 92 μAh cm⁻² μm are available in the potential range 4.2–2.5 V for LiNi_0.8Co_0.2O₂ and LiNi_0.8Co_0.15Al_0.05O₂ films, respectively. The self-diffusion coefficient of Li ions determined from galvanostatic intermittent titration experiments is found to be 4 × 10⁻¹² cm² s⁻¹.     

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.     

Improvement of 12 V overcharge behavior of LiCoO2 cathode material by LiNi0.8Co0.1Mn0.1O2 addition in a Li-ion cell

The 12 V overcharge instability of the LiCoO₂ cathode material was improved by the physical blending it with LiNi_0.8Co_0.1Mn_0.1O₂. Even though a Li-ion cell containing a LiCoO₂ cathode did not exhibit thermal runaway at 12 V at the 1 C overcharging rate, it showed thermal runaway at the 2 C overcharging rate, and the cell surface temperature reached more than 400 °C. However, the LiCoO₂ cell containing 40, 50, and 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ did not exhibit thermal runaway at the 2 C overcharging rate. In conclusion, 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ in the LiCoO₂ cathode showed the lowest cell surface temperature of <90 °C even at a 3 C overcharging rate.     

Electrochemical performances of lithium-ion polymer battery using LiNi1/3Co1/3Mn1/3O2 as cathode materials

In this work, a gel polymer electrolyte (GPE) was prepared using polyoxyalkylene glycol acrylate (POAGA) as a macromonomer. LiNi_1/3Mn_1/3Co_1/3O₂/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures. The ionic conductivity of the GPE was more than 6.2 × 10⁻³ S cm⁻¹ at room temperature. The GPE had good electrochemical stability up to 5.0 V versus Li/Li⁺. POAGA-based cells were showed good electrochemical performances such as rate capability, low-temperature performance, and cycleability. No leakage of the electrolyte or an explosion was observed at the overcharge test.     

Studies of cycling behavior,ageing, and interfacial reactions of LiNi0.5Mn1.5O4 and carbon electrodes for lithium-ion 5-V cells

The cycling and storage behavior of LiNi_0.5Mn_1.5O₄ and MCMB electrodes for 5-V Li-ion batteries was investigated at elevated temperatures using a variety of electrochemical (CV, EIS) and spectroscopic (XPS, micro-Raman) tools. It was established that LiNi_0.5Mn_1.5O₄ electrodes could be cycled highly reversibly, demonstrating sufficient capacity retention at 60 °C by a constant current/constant voltage mode in DMC–EC/1.5 M LiPF₆ solutions. By studying the influence of temperature on the impedance of LiNi_0.5Mn_1.5O₄ electrodes, we conclude that when the initial electrode's surface chemistry is developed at a high temperature (60 °C) it becomes nearly invariant, and hence, their impedance remains steady upon cycling and storage. Prolonged storage of these electrodes at 60 °C may result in local Mn and Ni dissolution and transformation of the active material to λ-MnO₂. We have found that the surface chemistry of aged LiNi_0.5Mn_1.5O₄ electrodes (free of carbon black and PVdF) involves the formation of LiF, C–F and P–F_x species. Storage of MCMB electrodes in LiPF₆ containing solutions at open circuit conditions (before their first lithiation) leads to significant morphological changes and the formation of lithium fluoride on the electrode surface, as determined by the XRD studies. LiF is probably a product of a catalytic thermal decomposition of LiPF₆. These initial changes further influence the impedance and kinetics of the lithiated electrodes.     

Transport and electrochemical properties of the LiyCrxMn2−xO4 (0 < x < 0.5) cathode material

In this paper structural, electrical, electrochemical and thermal (DSC) characterization of series of manganese spinel samples with manganese substituted to different degree (x = 0–0.5) with chromium are presented. The conductivity and thermoelectric power measurements were performed in wide temperature range also versus oxygen partial pressure and for deintercalated samples. Electrochemical studies of these cathode materials were conducted in Li/Li⁺/Li_yCr_xMn_2−xO₄ type cells. Substitution of manganese with chromium causes disappearance of the phase transition characteristic of LiMn₂O₄ spinel. Studies of electrical properties reveal that Cr ions do not participate in charge transport at low temperatures. In the charge curves of Li/Li⁺/Li_yCr_xMn_2−xO₄ cells there are two visible plateaux, separated with distinct potential jump (∼0.5 V), which position on Li content perfectly matches the Mn³⁺ content in the doped cathode material. The lower plateau is related to the Mn³⁺ → Mn⁴⁺ oxidation, while the next of higher voltage, of the dopant Cr³⁺ → Cr⁴⁺ oxidation. The schematic diagrams of relative Mn–Cr electronic levels alignment are proposed.     

Synthesis and characterizations of Li[CrxLi(1−x)/3Mn2(1−x)/3]O2 (0.15 ≤ x ≤ 0.3) cathode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ (0.15 ≤ x ≤ 0.3) cathode materials was prepared by citric acid-assisted, sol–gel process. Sub-micron sized particles were obtained and the X-ray diffraction (XRD) results showed that the crystal structure was similar to layered lithium transition metal oxides (R-3m space group). The electrochemical performance of the cathodes was evaluated over the voltage range 2.0–4.9 V at a current density of 7.947 mA g⁻¹. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of up to 280 mAh g⁻¹ during cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ yielded a promising cathode material.     

Exploration of high capacity LiNi0.5Mn1.5O4 synthesized by solid-state reaction

LiNi_0.5Mn_1.5O₄ was prepared by an improved solid-state reaction at high heating and cooling rates, the mixed precursors were initially heated up to 900 °C, then directly cooled down to 600 °C and heated for 24 h in air. X-ray diffraction (XRD) pattern shows that LiNi_0.5Mn_1.5O₄ has cubic spinel structure; scanning electron microscopic (SEM) image shows that the particle size is about 0.2 μm together with homogenous distribution. Electrochemical measurements show that LiNi_0.5Mn_1.5O₄ powders delivered up to 143 mAh g⁻¹ with superior cycling performance at the rate of 5/7C.     

Synthesis and electrochemical characteristics of LiCrxNi0.5−xMn1.5O4 spinel as 5 V cathode materials for lithium secondary batteries

A series of electrochemical spinel compounds, LiCr_xNi_0.5−xMn_1.5O₄ (x=0, 0.1, 0.3), are synthesized by a sol–gel method and their electrochemical properties are characterized in the voltage range of 3.5–5.2 V. Electrochemical data for LiCr_xNi_0.5−xMn_1.5O₄ electrodes show two reversible plateaus at 4.9 and 4.7 V. The 4.9 V plateau is related to the oxidation of chromium while the 4.7 V plateau is ascribed to the oxidation of nickel. The LiCr_0.1Ni_0.4Mn_1.5O₄ electrode delivers a high initial capacity of 152 mAh g⁻¹ with excellent cycleability. The excellent capacity retention of the LiCr_0.1Ni_0.4Mn_1.5O₄ electrode is largely attributed to structural stabilization which results from co-doping (chromium and nickel) and increased theoretical capacity due to substitution of chromium.     

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.     

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.     

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.     

Effect of sulfur and nickel doping on morphology and electrochemical performance of LiNi0.5Mn1.5O4−xSx spinel material in 3-V region

The effect of nickel and sulfur substitution for manganese and oxygen on the structure and electrochemical properties of the LiNi_0.5Mn_1.5O_4−xS_x is examined. The LiNi_0.5Mn_1.5O_4−xS_x (x = 0 and 0.05) compounds are successfully synthesized at 500 and 800 °C by co-precipitation using the metal carbonate (Ni_0.5Mn_1.5)CO₃ as a precursor. The resulting powder with sulfur doping exhibits different morphology from a Ni-only doped spinel in terms of particle size and surface texture. The LiNi_0.5Mn_1.5O_4−xS_x (x = 0 and 0.05) powders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge–discharge cycling. The nickel- and sulfur-doped spinel displays excellent capacity retention and rate capability in the 3-V region, compared with Ni-only doped spinel material.     

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.     

Synthesis and electrochemical properties of Li[Li(1−2x)/3NixMn(2−x)/3]O2 as cathode materials for lithium secondary batteries

Layered Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ materials with x=0.41, 0.35, 0.275 and 0.2 are synthesized by means of a sol–gel method. The layered structure is stabilized by a solid solution between LiNiO₂ and Li₂MnO₃. The discharge capacity increases with increasing lithium content at the 3a sites in the Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂. A Li[Li_0.2Ni_0.2Mn_0.6]O₂ electrode delivers discharge capacities of 200 and 240 mAh g⁻¹ with excellent cycleability at 30 and 55 °C, respectively.