Synthesis of Mn3O4/N-doped graphene hybrid and its improved electrochemical performance for lithium-ion batteries

Mn₃O₄/N-doped graphene (Mn₃O₄/NG) hybrids were synthesized by a simple one-pot hydrothermal process. The scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TG), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the microstructure, crystallinity and compositions. It is demonstrated that Mn₃O₄ nanoparticles are high-dispersely anchored onto the individual graphene nanosheets, and also found that, in contrast with pure Mn₃O₄ obtained without graphene added, the introduction of graphene effectively restricts the growth of Mn₃O₄ nanoparticles. Simultaneously, the anchored well-dispersed Mn₃O₄ nanoparticles also play a role as spacers in preventing the restacking of graphene sheets and producing abundant nanoscale porous channels. Hence, it is well anticipated that the accessibility and reactivity of electrolyte molecules with Mn₃O₄/NG electrode are highly improved during the electrochemical process. As the anode material for lithium ion batteries, the Mn₃O₄/NG hybrid electrode displays an outstanding reversible capacity of 1208.4 mAh g⁻¹ after 150 cycles at a current density of 88 mA g⁻¹, even still retained 284 mAh g⁻¹ at a high current density of 4400 mA g⁻¹ after 10 cycles, indicating the superior capacity retention, which is better than those of bare Mn₃O₄, and most other Mn₃O₄/C hybrids in reported literatures. Finally, the superior performance can be ascribed to the uniformly distribution of ultrafine Mn₃O₄ nanoparticles, successful nitrogen doping of graphene and favorable structures of the composites.     

Magnetic properties of Er(Co,Mn)O3 perovskites

The erbium-based manganite ErMnO₃ has been partially substituted at the manganese site by Co in the general formula ErCo_xMn_1−xO₃. The perovskite orthorhombic structure is found from x(Co) = 0.3 up to x(Co) = 0.7, provided that the synthesis is performed under oxygenation conditions to favour the presence of Co³⁺. Magnetic properties show unusual phenomena, correlated with the presence of different magnetic entities (i.e., Er³⁺, Co²⁺, Co³⁺, Mn³⁺, Mn⁴⁺): the overall magnetic moment reverses its sign when the sample is cooled under an external magnetic field, while the magnetization loops performed at T < 4 K show intersecting branches at low fields and a sudden jump at high fields. A phenomenological model of two interacting sublattices, coupled by an antiferromagnetic exchange interaction, explains the inversion of the overall spin, while the high-field discontinuity is explained in terms of dynamical models.     

The characteristics of Li(Ni1/3Co1/3Mn1/3)O2 particles prepared from precursor particles with spherical shape obtained by spray pyrolysis

Spherical and fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles were prepared using spray pyrolysis. Precursor particles with mixed Mn₂O₃, Co₃O₄ and NiO compositions were prepared using spray pyrolysis from aqueous and polymeric precursor solutions. The precursor particles prepared from the aqueous solution had hollow and porous morphologies. The precursor particles prepared from the polymeric precursor solution with citric acid and ethylene glycol were spherical in shape and had filled morphologies. The spherical precursor particles with filled morphologies formed spherical, fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles with filled morphologies after post-treatment with LiOH. The mean crystallite sizes of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared from spray solutions with and without lithium at the post-treatment temperature of 800 °C were 56 and 31 nm, respectively. The initial discharge capacities of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared using spray pyrolysis from spray solutions with and without lithium were 178 and 181 mAh g⁻¹, respectively, after a post-treatment temperature of 800 °C.     

A green strategy for the synthesis of graphene supported Mn3O4 nanocomposites from graphitized coal and their supercapacitor application

A by-product free strategy based on modified Hummers method was proposed to synthesize graphene/Mn₃O₄ composites without any additional manganese source. Coal-derived graphite (CDG) was used as carbon source instead of conventional natural graphite flakes and MnSO₄ produced from the modified Hummers was in situ transformed into Mn₃O₄ by precipitation in air. After reduction with hydrazine, the reduced coal-derived graphene oxide/Mn₃O₄ (RCDGO/Mn₃O₄) was obtained and employed as the electrode material for the supercapacitors. In addition, K₂SO₄ produced from the modified Hummers was used as electrolyte, as a result, residual-free was achieved during the whole process, and the atom utilization was calculated as high as about 97%. A maximum specific capacitance of 260 F g⁻¹ was achieved for RCDGO/Mn₃O₄ composite with 86% Mn₃O₄ in saturated K₂SO₄ electrolyte solution based on the synergetic effects between coal-derived graphene and attached Mn₃O₄ nanoparticles. Its specific energy density reached 8.7 Wh kg⁻¹ at a current density of 50 mA g⁻¹ when used as a symmetrical supercapacitor. The good capacitance retention (92–94%) was also observed after 1000 continuous cycles of galvanostatic charge–discharge.     

CeF3-modified LiNi1/3Co1/3Mn1/3O2 cathode material for high-voltage Li-ion batteries

A facile chemical deposition method has been adopted to prepare cerium fluoride (CeF₃) surface modified LiNi_1/3Co_1/3Mn_1/3O₂ as cathode material for lithium-ion batteries. Structure analyses reveal that the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particles is uniformly coated by CeF₃. Electrochemical tests indicate that the optimal CeF₃ content is 1 wt%. The 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ can deliver a discharge capacity of 107.1 mA h g⁻¹ even at 5 C rate, while the pristine does only 57.3 mA h g⁻¹. Compared to the pristine, the 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ exhibits the greatly enhanced capacity and cycling stability in the voltage range of 3.0–4.5 V, which suggests that the CeF₃ coating has the positive effect on the high-voltage application of LiNi_1/3Co_1/3Mn_1/3O₂. According to the analyses from electrochemical impedance spectra, enhanced electrochemical performance is mainly because the stable CeF₃ coating layer can prevent the HF-containing electrolyte from continuously attacking the LiNi_1/3Co_1/3Mn_1/3O₂ cathode and retard the passivating layer growth on the cathode.     

Dielectric and magnetoelectric properties of BaTiO3–Co0.6Zn0.4Fe1.7Mn0.3O4 composite

In this paper we studied the structural, dielectric, magnetic and magnetoelectric properties of (x)BaTiO₃–(1 ? x)Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ particulate composite series where x = 0.50, 0.60 and 0.70. BaTiO₃–Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ composite has the advantage of being non-toxic and environmental friendly from the point of view of device fabrication. High ME voltage coefficients were obtained in the whole series with the highest value of α_E ～ 73 mV/cm Oe achieved in sample x = 0.50 containing equal mole fractions of both the component phases. This value of α_E is an order of magnitude higher than that of particulate sintered BaTiO₃–CoFe₂O₄ composites (～2–4 mV/cm Oe). Dielectric characteristics for these samples indicated two anomalies: (i) one at low temperature close to ferroelectric to paraelectric transition temperature of pure BaTiO₃ and (ii) another at higher temperature related to the magnetic transition in ferrite, a characteristic dielectric feature of composite sample.     

Co0.35Mn0.65Fe2O4 magnetic particles: Preparation and kinetics research of thermal process of the precursor

Precursor of nanocrystalline Co_0.35Mn_0.65Fe₂O₄ was synthesized by solid-state reaction at low heat using CoSO₄·7H₂O, MnSO₄·H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. Nanocrystalline Co_0.35Mn_0.65Fe₂O₄ with spinel structure was obtained via calcining the precursor. The precursor and its calcined products were characterized using TG/DSC, FT-IR, XRD, SEM, EDS, and vibrating sample magnetometer. The results showed that the precursor dried at 353 K was a mixture consisted of CoC₂O₄·2H₂O, MnC₂O₄·2H₂O, and FeC₂O₄·2H₂O. However, when the precursor was calcined at 623 K for 2 h, highly crystallization Co_0.35Mn_0.65Fe₂O₄ [space group R-3 m (166)] was obtained with a crystallite size of 22 nm. Magnetic characterization indicated that the specific saturation magnetization of Co_0.35Mn_0.65Fe₂O₄ obtained at 773 K was 66.14 Am²/kg. The thermal process of precursor experienced two steps, which involves the dehydration of the waters of crystallization at first, and then decomposition of Co_0.35Mn_0.65Fe₂(C₂O₄)₃ and formation of crystalline Co_0.35Mn_0.65Fe₂O₄ together. Based on the Kissinger equation, the values of the activation energy associated with the thermal processes of the precursor were determined to be 78 and 146 kJ/mol for the first and second thermal process steps, respectively.     

Fabrication of carbon encapsulated Co3O4 nanoparticles embedded in porous graphitic carbon nanosheets for microwave absorber

Carbon-encapsulated Co₃O₄ nanoparticles homogeneously embedded 2D (two-dimensional) porous graphitic carbon (PGC) nanosheets were prepared by a facile and scalable synthesis method. With assistance of sodium chloride, the Co₃O₄ nanoparticles (10–20 nm) with magnetic loss were well encapsulated by onion-like carbon shells homogeneously embedded porous graphitic carbon nanosheets (thickness of less than 50 nm) with dielectric loss. In the architecture, the well impedance matching for microwave absorption can be obtained by the synergetic effect between Co₃O₄ nanoparticles and encapsulated porous carbon nanosheets. The minimum reflection loss value of −32.3 dB was observed at 11.4 GHz with a matching thickness of 2.3 mm for 2D Co₃O₄@C@PGC nanosheets. The 2D Co₃O₄@C@PGC nanosheets can be used as a kind of candidate for microwave absorbing materials.     

One-pot dual product synthesis of hierarchical Co3O4@N-rGO for supercapacitors,N-GDs for label-free detection of metal ion and bio-imaging applications

Cobalt oxide nanoparticles@nitrogen-doped reduced graphene oxide (Co₃O₄@N-rGO) composite and nitrogen-doped graphene dots (N-GDs) were synthesized by a one-pot simple hydrothermal method. The average sizes of the synthesized bare cobalt oxide nanoparticles (Co₃O₄ NPs) and Co₃O₄ NPs in the Co₃O₄@N-rGO composite were around 22 and 24 nm, respectively with an interlayer distance of 0.21 nm, as calculated using the XRD patterns. The Co₃O₄@N-rGO electrode exhibits superior capacitive performance with a high capability of about 450 F g^?1 at a current density of 1 A g^?1 and has excellent cyclic stability, even after 1000 cycles of GCD at a current density of 4 A g^?1. The obtained N-GDs exhibited high sensitivity and selectivity towards Fe²⁺ and Fe³⁺, the limit of detection was as low as 1.1 and 1.0 μM, respectively, representing high sensitivity to Fe²⁺ and Fe³⁺. Besides, the N-GDs was applied for bio-imaging. We found that N-GDs were suitable candidates for differential staining applications in yeast cells with good cell permeability and localization with negligible cytotoxicity. Hence, N-GDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe³⁺/Fe²⁺) and also for early detection of opportunistic yeast infections in biological samples.     

(La,Sr)(Mn,Me)O3 manganites doped with d metals: Study of charge compensation mechanisms by crystallographic and magnetic characterizations

A comparison between theoretically calculated unit cell volume and interatomic distances in the system La_0.7Sr_0.3Mn_1−xMe_xO_3+δ (where Me = Cu, Fe, Cr, Ti) and the experimental data obtained by the full-profile Rietveld X-ray analysis as well as an analysis of magnetic properties allowed us to suggest possible mechanisms of charge compensation occurring when d metals substitute for manganese. It has been shown that in the case when copper, iron, chromium and titanium ions substitute for manganese ions in the system La_0.7Sr_0.3Mn_1−xMe_xO₃ charge compensation is described by the model 2Mn³⁺ → Mn⁴⁺ + Cu²⁺, Mn³⁺ → Fe³⁺, Mn³⁺ → Cr³⁺ and Mn⁴⁺ → Ti⁴⁺, respectively. In the latter case, a decrease in oxygen nonstoichiometry occurs with increasing x.     

Stabilizing the structure and suppressing the voltage decay of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode materials for Li-ion batteries via multifunctional Pr oxide surface modification

The development of Li-rich layer cathode materials has been limited by poor cycle, rate performance, phase transformation and voltage decay. To improve these properties, a facile and low-cost wet method is employed to fabricate Pr₆O₁₁ coating layer on Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles. The 3–6 nm Pr₆O₁₁ coating layer is observed on the surface of Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ by HRTEM. Interestingly, HAADF-STEM and EDS analyses show that the transition metal ions and the praseodymium ions mutually infiltrate in the Pr₆O₁₁ coating layer and Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles during calcination. A combination of HAADF-STEM with EDS and XPS studies reveals that Pr₆O₁₁ coating layer is bridged to Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles by the chemical bonds of transition phase Li_1.2M_XPr_1−xO₂. XRD patterns show that all samples are indexed to the layered structure α-NaFeO₂, but the lattice parameters are influenced lightly after Pr₆O₁₁ coating. HRTEM and SAED analyses elucidate that the super large Pr ions surface-doping and the Pr₆O₁₁ coating are verified to suppress the transformation of layer to spinel structure in the bulk nanoparticles after cycles. The sample coated with 3 wt% Pr₆O₁₁ exhibits wonderful electrochemical performance with the first coulomb efficiency of 85.6%, the capacity retention ratio of 97.9% after 50 cycles and the discharge capacity of 162.2 mAh g⁻¹ at 5 C. The resistant of charge transfer and the electrodes polarization are reduced by Pr₆O₁₁ coating according to EIS. Therefore, Pr₆O₁₁, which contains the super large Pr ions, plays two roles: the first one, it is coated on the Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles to optimize the environment of the interface reaction between electrodes and electrolyte; the other one, its Pr ions surface-doping stabilizes the structure in the superficial region of Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles and suppresses the voltage decay. The multifunctional Pr₆O₁₁ can play a significant role in accelerating development of new materials with excellent stabilization and high capacity.     

Structural and electrical properties of MgO-doped Mn1.4Ni1.2Co0.4−xMgxO4 (0 ≤ x ≤ 0.25) NTC thermistors

We have prepared polycrystalline Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ (0 ≤ x ≤ 0.25) samples using a solid-state reaction process and investigated the MgO doping effect on the microstructure and the electrical properties. It was found that, as the amount of Mg content in the Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ samples increased, both the grain size and density decreased. The as-sintered Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ samples contained Mn- and Ni-rich phases with cubic spinel structure. The MgO-doped Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ negative temperature coefficient (NTC) thermistors provided various electrical properties, depending on Mg content. The electrical resistivity, B_25/85 constant, and activation energy of the Mn_1.4Ni_1.2Co_0.4−xMg_xO₄ NTC thermistors increased with increasing Mg content. The values of ρ₂₅, B_25/85 constant, and activation energy of the NTC thermistors were 11,185–20,016 Ω cm, 3635–4032 K, and 0.313–0.348 eV, respectively.     

La2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials with enhanced specific capacity and cycling stability for lithium-ion batteries

Li-rich layered oxides are the most promising cathode candidate for new generation rechargeable lithium-ion batteries. In this work, La₂O₃-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were fabricated via a combined method of sol-gel and wet chemical processes. The structural and morphological characterizations of the materials demonstrate that a thin layer of La₂O₃ is uniformly covered on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particles, and the coating of La₂O₃ has no obvious effect on the crystal structure of Li-rich oxide. The electrochemical performance of La₂O₃-coated Li-rich cathodes including specific capacity, cycling stability and rate capability has been significantly improved with the coating of La₂O₃. The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with 2.5 wt% La₂O₃ exhibits the highest discharge capacity, improved cycling stability and reduced charge transfer resistance, delivering a large discharge capacity of 276.9 mAh g⁻¹ in the 1st cycle and a high capacity retention of 71% (201.4 mAh g⁻¹) after 100 cycles. The optimal rate capability of the materials is observed at the coating level of 1.5 wt% La₂O₃ such that the material exhibits the highest discharge capacity of 90.2 mAh g⁻¹ at 5 C. The surface coating of La₂O₃ can effectively facilitate Li⁺ interfacial diffusion, reduce the structural change and secondary reactions between cathode materials and electrolyte during the charge-discharge process, and thus induce the great enhancement in the electrochemical properties of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials.     

Co3O4 and Mn3O4 Nanoparticles Dispersed on SBA-15: Efficient Catalysts for Methane Combustion

Co₃O₄ and Mn₃O₄ nanoparticles were successfully impregnated on SBA-15 mesoporous silica. A high dispersion of these metal oxide particles was achieved while using a “two-solvents” procedure, allowing a proper control of the metal oxides loading (7 wt%) and size (10–12 nm). These Co₃O₄ and Mn₃O₄ supported oxides on SBA-15 were characterised by means of XRD, BET and TEM techniques. The influence of the nature of the silica support was investigated in terms of porosity and specific surface area. Since, an improved catalytic activity was achieved over SBA-15 mesoporous silica; it appears that its organised porous meso-structure creates a confinement medium which permits a high dispersion of metal oxide nanoparticles. Supported Co₃O₄/SBA-15 (7 wt%) showed the highest catalytic performance in the combustion of methane under lower explosive limit conditions, comparable to perovskites. These materials become therefore novel efficient combustion catalysts at low metal loading.     

Well-dispersed ultrafine Mn3O4 nanoparticles on graphene as a promising catalyst for the thermal decomposition of ammonium perchlorate

Mn₃O₄–graphene (Mn₃O₄–GR) hybrids were synthesized using a one-step strategy under solvothermal conditions. During this process graphene oxide (GO) was reduced to GR and at the same time ultrafine Mn₃O₄ nanoparticles (NPs) with a size of ∼10 nm were uniformly anchored on the GR sheets. The Mn₃O₄–GR hybrids showed promising catalytic effects for the thermal decomposition of ammonium perchlorate (AP). The decomposition temperature was decreased by 141.9 °C and only one decomposing step was observed instead of common two in reported literature. This improved performance in the catalytic reaction is closely related to the synergistic effect of Mn₃O₄ and GR.     

Bi-Co3O4 catalyzing N2O decomposition with strong resistance to CO2

Bi added to Co₃O₄ by coprecipitation method significantly decreased the average crystalline size of Co₃O₄ and increased the surface area and the active sites of the catalyst in population for catalyzing the N₂O decomposition. Over Bi_0.02Co that was the optimized from the Bi_xCo catalysts, 2000 ppm of N₂O in pure Ar was completely decomposed at 400 °C in GHSV of 20,000 h^− 1. Outstandingly, the catalyst exhibited a strong resistance to CO₂, stable N₂O conversion larger than 95% was obtained over the catalyst in the presence of 10% CO₂ at the reaction temperature.     

In situ monitoring of the adsorption of Co2+ on the surface of Fe3O4 nanoparticles in high-temperature aqueous fluids

Developing an understanding of the reaction processes occurring at the surface⿿fluid interface at the atomic level of nanostructured materials in high-temperature aqueous environments is necessary for establishing general principles of behavior of nanomaterials operating in such extremes. In situ Co K-edge X-ray absorption spectroscopy (XAS) measurements were made on Fe₃O₄ nanoparticles in the presence of Co²⁺ ions in aqueous fluids to 500 °C and approximately 220 MPa. The results from analysis of the in situ EXAFS data, along with SEM-EDX spectra measured from reacted nanoparticles, indicate that adsorption of Co²⁺ ions on the surface of Fe₃O₄ nanoparticles is negligible at temperatures below 200 °C but becomes significant in the 250⿿500 °C temperature range. The low reaction temperature threshold of the Co²⁺ aqua ion with Fe₃O₄ nanoparticles is consistent with a relatively low value of the crystal field stabilization energy (CFSE) of Co²⁺ in octahedral site symmetry in spinels. Modeling of the pre-edge feature of the XANES and analysis of the extended X-ray absorption fine structure (EXAFS) shows that Co²⁺ adsorbs predominantly on octahedral sites of the surface of nanoparticles in aqueous fluids. Structural analyses using EXAFS and high resolution TEM show that the inverse spinel structure is preserved in the Co-incorporated surface atomic layers of the Fe₃O₄ nanoparticles. Our results suggest that the dissolved radioactive isotope ⁶⁰Co in the primary cooling loop of supercritical water-cooled nuclear reactors have a high likelihood of precipitating on the surfaces of spalled ferrite nanomaterial.     

Catalytic performance of LaCo0.5M0.5O3 (M = Mn,Cr, Fe,Ni, Cu) perovskite-type oxides and LaCo0.5Mn0.5O3 supported on cordierite for CO oxidation

Catalytic combustion of CO over perovskite-type oxides LaCo_0.5M_0.5O₃ (M = Mn, Cr, Fe, Ni, Cu) and LaCo_0.5Mn_0.5O₃ supported on cordierite were investigated. The catalysts were synthesized by impregnation method with citrate and characterized by XRD, SEM and TPR. The LaCo_0.5Mn_0.5O₃ catalyst showed much higher activity in CO oxidation compared with LaCo_0.5M_0.5O₃ (M = Cr, Fe, Ni, Cu) due to different kinds of valence state and lattice oxygen content. When LaCo_0.5Mn_0.5O₃ was supported on cordierite, the activity was improved significantly. However, calcining temperature and the presence of water vapor affected the catalytic activity due to sintering and competition of H₂O with CO for adsorption, respectively.     

Control of coring effect in BaTi4O9 microwave dielectric ceramics by doping with Mn4+

In the present work, we have attempted to reduce the effect of coring effect in the titanate ceramic system BaTi₄O₉ (BT4) by doping it with Mn⁴⁺. The microwave dielectric BaTi₄O₉ ceramics doped with 0, 0.5 and 1.0 mol% Mn⁴⁺ were synthesized by conventional ceramic processing route. The XRD studies confirmed a single phase crystalline structure for all the ceramic samples studied. The SEM micrographs of the ceramics reveal a microstructural change leading towards a more uniform grain size distribution as the Mn⁴⁺ content increases to 1.0 mol%. In the low frequency region (100 Hz to 1 MHz), the temperature stability of dielectric properties exhibits a marked improvement with the increasing amount of Mn⁴⁺ in the ceramic system. In the microwave frequency region (9.3 GHz), Q-factor increases from 11,625 GHz to 46,500 GHz for BaTi₄O₉ ceramic doped with 1.0 mol% Mn⁴⁺. The present paper reveals that the commonly observed degradation of dielectric properties due to coring effect in the BaTi₄O₉ ceramic system can be controlled by doping it with an appropriate quantity of Mn⁴⁺.     

Synthesis and electrochemistry of 5 V LiNi0.4Mn1.6O4 cathode materials synthesized by different methods

Spinel LiNi_0.4Mn_1.6O₄ has been successfully synthesized by ultrasonic-assisted co-precipitation (UACP) method. The structure and physicochemical properties of this as-prepared powder compared with the LiNi_0.4Mn_1.6O₄ synthesized by co-precipitation method were investigated by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test in detail. XRD and SEM show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; FT-IR reveals that the Mn(III)–O stretching band at 511 cm^?1 has a red shift to 503 cm^?1, and the Mn(IV)–O stretching band at 612 cm^?1 has a blue shift to 622 cm^?1 because of the doped Ni. CV confirms that the LiNi_0.4Mn_1.6O₄ sample (UACP) has bigger area of the reduction peaks than that of sample synthesized by co-precipitation method, indicating that the former has higher discharge capacity than that of the latter. Galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiNi_0.4Mn_1.6O₄ (UACP) at C/5 and 1C are 129 and 116 mAh g^?1, respectively. After 100 cycles, their capacity retentions are 94.6% and 85.3%, respectively. EIS indicates that LiNi_0.4Mn_1.6O₄ samples synthesized by UACP method have smaller charge transfer resistance than that of samples synthesized by co-precipitation method corresponding to the extraction of Li⁺ ions.