Improvement of electrochemical properties of MgO-coated LiNi0.4Co0.2Mn0.4O2 cathode materials for lithium ion batteries

The surface of LiNi_0.4Co_0.2Mn_0.4O₂ cathode is coated using MgO coating materials. The electrochemical properties of the coated materials are investigated as a function of the pH value of the coating solution and the composition of coating materials. Their microscopic structural features have been investigated using scanning electron microscopy and X-ray diffraction. The electrochemical properties of the samples were monitored using coin-cell by galvanostatic charge–discharge cycling test, EDS test, EIS test, and cyclic voltammetry. The coating solution with pH?=?10.5 is found to be favorable for the formation of stable coating layers, which enhances the electrochemical properties. In contrast, 2 % MgO-coated LiNi_0.4Co_0.2Mn_0.4O₂ shows better cycle performance and rate capability than the bare sample. Such enhancements are attributed to the presence of a stable MgO layer which acts as the interfacial stabilizer on the surface of LiNi_0.4Co_0.2Mn_0.4O₂.     

Sonochemical synthesis of LiNi0.5Mn1.5O4 and its electrochemical performance as a cathode material for 5 V Li-ion batteries

LiNi_0.5Mn_1.5O₄ was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g⁻¹ is obtained for LiNi_0.5Mn_1.5O₄ at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.     

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels： A first-principles study

<正>Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4₃32） space groups,respectively.It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄（P4₃32 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.     

Characterization of Cu1.4Mn1.6O4/PPy composite electrodes

In this work, we have studied the multilayered polypyrrole(PPy)/oxide composite electrode on glassy carbon (GC) having the structure GC/PPy/PPy(Cu_1.4Mn_1.6O₄)/PPy using X-ray Photoelectron Spectroscopy and Mn K-edge and Cu K-edge XANES and EXAFS. The mixed oxide particles have been incorporated into the PPy matrix simultaneously to the electropolymerization of Py from a solution containing 0.1 M Py + 0.15 M KCl + Cu_1.4Mn_1.6O₄. The XPS data have shown that, prior to the incorporation of the oxide into the PPy matrix, it contains Cu⁺, Cu²⁺, Mn³⁺ and Mn⁴⁺. The XPS, XANES and EXAFS results have shown that when the oxide is incorporated into the PPy matrix, the Cu⁺ present in the original oxide suffers dismutation to give Cu²⁺ and metallic Cu. The metallic Cu is segregated out of the spinel structure. The Mn K-edge XANES and EXAFS data show that, after the incorporation into the PPy matrix, Mn is present as Mn³⁺ and Mn⁴⁺ occupying octahedral sites in a spinel-related structure while the Cu K-edge XANES and EXAFS data indicate that copper occupies tetrahedral sites predominantly in that structure but having a large degree of disorder in the second and higher coordination shells.     

Capacity fading reason of LiNi0.5Mn1.5O4 with commercial electrolyte

The cycling performances of LiNi_0.5Mn_1.5O₄ (LNMO) were investigated and the reasons of capacity fading were discussed. The results show that LNMO can deliver about 115 mAh?g^?1 at 1C at different temperatures; however, it retains only 61.57 % of its initial capacity after 130th cycles at 60 °C, which is much lower than 94.46 % of LNMO at 25 °C, and the cycling performance at 1C is better than that at 0.5C. The reason of capacity fading of LNMO at 60 °C is mainly due to the lower decomposition voltage of 4.3 V with commercial electrolyte and the larger decomposition current, of which the electrolyte decomposes and interacts with active materials to lead to the larger irreversible capacity loss. While the worse cycling performance at low rate is attributed to the longer interaction time between the electrolyte with the decomposition voltage of 4.5 V and the active materials.     

Lithium ion batteries cathode material: V2O5

Among all the known electrode materials, vanadium pentoxide (V₂O₅) has high reversible capacity. It is a very valuable material for research of the complexity, rich structure and morphology. However, it also has some disadvantages, such as poor cycle stability, low discharge voltage, low conductivity and Li⁺ diffusion coefficient. In this regard, researchers have carried out a lot of research, such as using various methods to improve the nanostructures, introducing heterostructures, introducing point defects or cation doping in the crystal structure, etc. The electrochemical performance of V₂O₅ has been significantly improved in reversible capacity, high-rate capacity and long-term cycle stability. In this paper, V₂O₅ based nanostructure with different chemical composition are briefly introduced, and it covers V₂O₅ nanomaterials with different morphology, including 1D nanorods, nanobelts, nanotubes, 2D leaf like nanosheets and other nanosheets, and 3D hollow structures, porous nanostructures, porous eggshell microsphere structures. The composite nanomaterials of V₂O₅ and different carbonaceous supports are also introduced. Finally, the V₂O₅ composite materials doped with cations are discussed. The electrochemical performance of V₂O₅ based electrode can be improved effectively by obtaining appropriate nanostructure and optimized chemical composition.     

Effect of MoO3 surface coating on electrochemical performances of LiNi0.8Co0.1Mn0.1O2 cathode

In this paper, we synthesize the MoO 3 modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode (denoted as M-NCM81) and compare with pristine LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode (denoted as P-NCM81). The M-NCM81 cathode delivers good cation ordering and typical spherical form. The M-NCM81 cathode shows initial discharge capacity of 203.8 mAh g −1 at 0.1 C, capacity retention of 79.8% under the 5.0 C. In addition, the M-NCM81 cathode still retain a discharge capacity of 172.2 mAh g ⁻¹after 100 cycles. Such electrochemical performances are significantly improved compared to those of P-NCM81. It can be elucidated that MoO ₃ coating layer acts as a HF inhibitor/scavenger. The MoO ₃ modification plays an important role in inhibiting severe structural degradation, derived from a harmful side reaction with electrolyte. It effectively suppresses the increase in charge-transfer resistance, leading to superior electrochemical performances.     

Correlation between the negative magnetoresistance effect and magnon excitations in single-crystalline CuCr1.6V0.4Se4

Structural, electrical and magnetic measurements, as well as electron spin resonance (ESR) spectra, were used to characterise the single-crystalline CuCr_1.6V_0.4Se₄ spinel and study the correlation between the negative magnetoresistance effect and magnon excitations. We established the ferromagnetic order below the Curie temperature T _C ≈ 193 K, a p-type semiconducting behaviour, the ESR change from paramagnetic to ferromagnetic resonance at T _C, a large ESR linewidth value and its temperature dependence in the paramagnetic region. Electrical studies revealed negative magnetoresistance, which can be enhanced with increasing magnetic field and decreasing temperature, while a detailed thermopower analysis showed magnon excitations at low temperatures. Spin–phonon coupling is explained within the framework of a complex model of paramagnetic relaxation processes as a several-stage relaxation process in which the V³⁺ ions, the exchange subsystem and conduction electron subsystem act as the intermediate reservoirs.     

Preparation and characteristics of Pr1.6Sr0.4NiO4+YSZ as composite cathode of solid oxide fuel cells

Composite cathodes of (1?x wt%)Pr_1.6Sr_0.4NiO₄+(x wt%)Y₂O₃-stabilized ZrO₂ (YSZ; x=0, 10, 20, 30, 40) abbreviated as Pr_1.6Sr_0.4NiO₄+xYSZ, were prepared. The composite cathodes with x>0 matched with electrolyte YSZ in thermal expansion coefficient (TEC) better than the cathode Pr_1.6Sr_0.4NiO₄ did. Pr_1.6Sr_0.4NiO₄+20YSZ exhibited the best performance on cathode overpotential and impedance. When the cathode overpotential was 0.1 V, the polarization current density of Pr_1.6Sr_0.4NiO₄+20YSZ was 0.28 A cm^?2, which is about 5.6 times higher than that of Pr_1.6Sr_0.4NiO₄, 0.05 A cm^?2. The area-specific resistance (ASR) for Pr_1.6Sr_0.4NiO₄+20YSZ was about 17.7% of that for Pr_1.6Sr_0.4NiO₄ at 750 °C.     

Structural and electrochemical properties of LiNi0.4Co0.4−xAl0.2+xO2 cathode materials for lithium-ion batteries

Three Al doped lithium nickel cobalt oxide (LiNi_0.4Co_0.4−xAl_0.2+xO₂) cathode materials for lithium ion batteries were synthesized by solid state reaction method at a temperature of 800 °C for 18 hours. The samples were crystalline as revealed by powder X-Ray diffraction (XRD). The ratios of the elements were determined by Energy Dispersive Analysis of X-rays (EDAX). The electrochemical properties obtained by charge/discharge cycling showed that the average discharge capacity for LiNi_0.4Co_0.4Al_0.2O₂ was 117 mAh/g. A good capacity retention was also shown by the material upon cycling. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Study on the electrochemical performance of LiNi0.5Mn1.5O4 with different precursor

LiNi_0.5Mn_1.5O₄ cathodes were synthesized by three different raw materials at high temperature. The samples were characterized by X-ray diffraction and scanning electron microscopy tests, respectively. The results indicate that the synthesized samples show pure spinel structure, and the samples synthesized by nickel?Cmanganese hydrate and nickel?Cmanganese oxide show regular geometrical shape. The electrochemical performance of sample synthesized by nickel?Cmanganese oxide is best. The first discharge capacity is 141 mAh/g, and the capacity retention is 98.6% after 50 cycles at 0.5?C rate. The discharge capacity at 5?C rate is still 120 mAh/g. Better crystallization, smaller specific surface area, and lower polarization may be responsible for the excellent electrochemical performance of the LiNi_0.5Mn_1.5O₄.     

LiNi_(0.5)Mn_(0.5)O_2制备及表征

采用共沉淀法制备了LiNi0.5Mn0.5O2.XRD,Raman测试都表明材料是六方结构.XPS检测得出镍主要以正二价存在,锰元素主要以正四价存在.合成的LiNi0.5Mn0.5O2得到了50次的循环,但比容量较低.充放电循环性能比较研究表明,经过40次循环后,0.3,0.6,1.5 C的放电比容量分别是65.88,61.56,52.23 mA.h.g-1.     

Enhanced electrochemical performances of layered LiNi0.5Mn0.5O2 as cathode materials by Ru doping for lithium-ion batteries

Ionics - The pristine and Ru-doped LiNi0.5Mn0.5O2 cathode materials are synthesized by a wet chemical method, followed by a high-temperature calcination process. The influence of Ru substitution on...     

Enhanced electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode material co-coated by graphene/TiO2

The electrochemical performances of LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) layered cathode material, such as poor rate capacity and cycling stability caused by undesirable intrinsic conductivity and low rate of lithium ion transportation, are not fairly good especially at elevated rate and cut-off voltage. To improve these properties, in this study, the co-coating layer of graphene and TiO₂ was constructed on NCM523 surface. The graphene/TiO₂ coating layer could effectively prevent hydrofluoric acid (HF) attacks, suppress the side reaction, accelerate the lithium ion diffusion and facilitate the electron migration. The enhancement of cycle performance and rate capacity was contributed to the uniform co-modified surface, interacting each other and thus exhibiting synergistic effects.     

Synthesis of LiNi0.6Co0.2Mn0.2O2 cathode material by a carbonate co-precipitation method and its electrochemical characterization

Using Na₂CO₃ and Me(NO₃)₂ (Me = Ni, Co and Mn) as starting materials, the precursor of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium rechargeable batteries has been synthesized by carbonate co-precipitation. The precursor was mixed with Li₂CO₃ and heated in air. Thermogravimetric analysis (TG–DTA), laser particle size analysis, X-ray diffraction (XRD) and electron scanning microscopy (SEM) were employed to study the reaction process and the structures of the powders. The D₅₀ of precursor was 2.509 μm and the distribution was relatively narrow. The optimum calcination temperature was 850–900 °C. Galvanostatic cell cycling and cyclic voltammetry were also used to evaluate the electrochemical properties. The initial discharge capacity for the powders calcined at 900 °C was about 180 mA h/g at room temperature when cycled between 2.8 and 4.3 V at 0.2 C rate.     

La_(1．6-x)Nd_(0．4)Sr_xCuO_4超导电性的反常特性

分析并讨论了La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列单相性样品(x=0．08～0．25)的晶体结构和超导电性。结果表明,晶体结构随着Sr掺杂量的变化规律与La_(2-x)Sr_x CuO_4系列相似。超导电性方面,La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列超导转变温度均远小于相应的La_(2-x)Sr_xCuO_4系列组分。同La_(1．875)Ba_(0．125)CuO_4相似,La_(1．48)Nd_(0．4)Sr_(0．12)CuO_4处出现显著的极小值8K但高于La_(1．875)Ba_(0．125)CuO_4。La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列的超导电性明显与La_(2-x)Sr_x CuO_4系列有着不同的特性,虽然同La_(2-x) Ba_xCuO_4系列相似但仍有区别。我们从其晶体结构的反常变化的角度对La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列反常的超导电性做了初步的解释。     

Effects of ultrasound irradiation on Au nanoparticles deposition on carbon-coated LiNi0.5Mn1.5O4 and its performance as a cathode material for Li ion batteries

LiNi_0.5Mn_1.5O₄ (LMNO) has attracted considerable attention as a Li-ion battery cathode material, owing to its high discharge voltage of 4.7 V (vs. Li/Li⁺) and high energy density. However, the electronic conductivity of LMNO is low, resulting in a low discharge capacity at high current density. To overcome this limitation, we deposited Au nanoparticles (NPs), which have a high conductivity and chemical stability at high battery voltages, on carbon-coated LMNO (LMNO/C) using ultrasound irradiation. Consequently, Au NPs that are ∼16 nm in size were deposited on LMNO/C, and ultrasound irradiation was reported to disperse the NPs on LMNO/C more effectively than stirring. Furthermore, the deposition of Au NPs on LMNO/C using ultrasound irradiation improved its electronic conductivity, which is related to an increase in the discharge capacity due to the reduction of Ni⁴⁺ to Ni²⁺ in LMNO/C at a high current density.     

Multi-faceted highly crystalline LiMn2O4 and LiNi0.5Mn1.5O4 cathodes synthesized by a novel carbon exo-templating method

LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ powders have been synthesized by a novel cost-effective carbon exo-templating process. It has been observed that controlled nucleation in the pores of highly surface active carbon produces a distinct effect on the powder morphology and crystallinity. Quantitative X-ray phase analyses show single phase spinel structure having Fd3m symmetry for both samples. Field emission electron microscopy reveals particles of size 0.5–1.0 µm with well defined multi-faceted crystals. Cyclic voltammetry results show well separated distinct redox peaks at 4.05/3.92 and 4.17/4.08 V for LiMn₂O₄/Li and 4.91/4.61 V for LiNi_0.5Mn_1.5O₄/Li coin cells indicating good crystallinity and reversibility of the cathodes compared to that of pristine LiMn₂O₄ synthesized by conventional combustion process. The LiMn₂O₄/Li and LiNi_0.5Mn_1.5O₄/Li cells deliver an initial discharge capacity of 110 mA h/g and 122 mA h/g respectively at a current density of 0.05 mA/cm² and when cycled at 0.2 mA/cm², the cells maintain 81% and 96% of their initial discharge capacity respectively even after 20 cycles. On the other hand, at the same current density, LiMn₂O₄ synthesized by conventional combustion process suffers from severe capacity fading (only 37.5% capacity retention after the 25th cycle). The capacity fading rate is found to be very less even at further higher current densities (0.4–0.8 mA/cm²) for both LiMn₂O₄/Li and LiNi_0.5Mn_1.5O₄/Li cells synthesized by the templating process. The present study reveals that high crystallinity along with multi-faceted morphology shows a remarkable enhancement in capacity as well as rate performance of pristine LiMn₂O₄ and its Ni derivative.     

Investigations on Pr1.6Sr0.4NiO4-YSZ-Ag composite cathode for solid oxide fuel cells

Ag-network was successfully deposited by VA-EP (vacuum assisted electroless plating) method on Pr_1.6Sr_0.4NiO₄-YSZ cathode to form (1−x) wt% Pr_1.6Sr_0.4NiO₄−x wt% YSZ-Ag (x=0, 10, 20, 30, 40) (abbr. PYx-Ag) composite cathode. XRD results suggested that there was a good chemical stability between Pr_1.6Sr_0.4NiO₄ and YSZ at temperatures below 1050 °C. PY20-Ag cathode exhibited higher exchange current density, lower overpotential and ASR (Area Specific Resistance) than PY20 cathode. At 650 °C, the ASR of PY20-Ag cathode was 2.5 Ω cm², which was only about 42% of that of PY20, 5.9 Ω cm². PY20-Ag can be a promising candidate for SOFC cathode.     

Synthesis of spherical LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was successfully prepared by controlled crystallization. The preparation started with the spherical coprecipitate of Ni_1/3Co_1/3Mn_1/3CO₃ from NiSO₄, CoSO₄, MnSO₄, NH₄HCO₃, and NH₃·H₂O, followed by pyrolysis of Ni_1/3Co_1/3Mn_1/3CO₃ at 600°C for 3 h. The X-ray diffraction analysis showed that the homogeneous cubic (Ni_1/3Co_1/3Mn_1/3)₃O₄ was obtained after the pyrolysis. Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was obtained by sintering of the mixture of as-obtained (Ni_1/3Co_1/3Mn_1/3)₃O₄ and LiOH·H₂O at 900°C for 6 h in air. As-prepared spherical LiNi_1/3Co_1/3Mn_1/3O₂ presented initial discharge capacity of 162.9 mA h g⁻¹ and capacity retention of 98% at 50th cycle.