Elevated electrochemical property of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> originated from nano-sized Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>

By employment of nano-sized pre-prepared Mn₃O₄ as precursor, LiMn₂O₄ particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn₃O₄ is studied. The structure, morphology, and element distribution of the as-synthesized LiMn₂O₄ samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn₂O₄ synthesized by facile solid state method (SS-LMO), LiMn₂O₄ synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10^?11 cm² s^?1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g^?1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li⁺ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.     

One-step synthesis of colloidal Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> and γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles at room temperature

A facile room-temperature synthesis has been developed to prepare colloidal Mn₃O₄ and γ-Fe₂O₃ nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process has been proposed.     

Large-scale synthesis of Ag<Subscript>1.8</Subscript>Mn<Subscript>8</Subscript>O<Subscript>16</Subscript> nanorods and their electrochemical lithium-storage properties

Ag_1.8Mn₈O₁₆ nanorods have been synthesized on a large scale by a facile hydrothermal route. The effects of experimental conditions including reaction time and reactant concentration on the phase and morphology of the final products were investigated systematically. The products were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) spectroscopy. Electrochemical lithium-storage capabilities of the as-formed nanostructured Ag_1.8Mn₈O₁₆ were also evaluated. Interestingly, the as-formed Ag_1.8Mn₈O₁₆ nanorods possess the unique one-dimensional structure and in situ silver loading, which are beneficial features for electrochemical lithium-storage applications. The results suggest their potential use as cathode materials for lithium-ion batteries.     

Ultrathin nanosheets of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>: A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy

Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn₃O₄ nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn₃O₄ nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.     

Magnetoresistive effect in RCu<Subscript>3</Subscript>Mn<Subscript>4</Subscript>O<Subscript>12</Subscript> perovskite-like oxides

The electrical properties of and the magnetoresistive effect in RCu₃Mn₄O₁₂ (R=rare-earth ion or Th) are studied. In all compounds of this series, the magnetoresistive effect amounts to 20% at liquid nitrogen temperature in the presence of a field of 0.9 T. An increase in the magnetoresistance with decreasing temperature and a high sensitivity to weak magnetic fields at low temperatures point to the intergranular nature of the effect. The magnetoresistance shows a peak in the vicinity of the Curie temperature T_C. Based on the dependences of the magnetoresistance on an external magnetic field, it is assumed that the magnetoresistance peak near T_C is related to the charge carrier scattering by magnetic inhomogeneities as in substituted orthomanganites. We believe that the magnetoresistance value near the magnetic ordering temperature depends on the synthesis conditions and the effect of the intergranular spacer on the transport properties of these compounds.     

Investigation on the electrochemical performances of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> for battery applications

In this study, well-crystallized Li₄Mn₅O₁₂ powder was synthesized by a self-propagating combustion method using citric acid as a reducing agent. Various conditions were studied in order to find the optimal conditions for the synthesis of pure Li₄Mn₅O₁₂. The precursor obtained was then annealed at different temperatures for 24 h in a furnace. X-ray diffraction results showed that Li₄Mn₅O₁₂ crystallite is stable at relatively low temperature of 400 °C but decompose to spinel LiMn₂O₄ and monoclinic Li₂MnO₃ at temperatures higher than 500 °C. The prepared samples were also characterized by FESEM and charge-discharge tests. The result showed that the specific capacity of 70.7 mAh/g was obtained within potential range of 4.2 to 2.5 V at constant current of 1.0 mA. The electrochemical performances of Li₄Mn₅O₁₂ material was further discussed in this paper.     

Simulation of the magnetic properties of manganese oxide Pb<Subscript>3</Subscript>Mn<Subscript>7</Subscript>O<Subscript>15</Subscript>

The magnetic susceptibility, heat capacity, and spin-spin correlation functions of manganese oxide Pb₃Mn₇O₁₅ are calculated by the Monte Carlo method. Two critical temperatures are determined: T ₁ ≈ 20 K, above which a modulated structure along the hexagonal axis is formed, and T ₂ ≈ 70 K, at which the long-range magnetic order disappears. The antiferromagnetic exchange interaction constant in a hexagonal plane is estimated to be J ₁ ～ 7 K, and the antiferromagnetic and ferromagnetic exchange interaction constants between hexagonal planes are calculated to be J ₂ ～ 3 K and K ～ 50 K, respectively.     

Enhanced electrochemical properties and thermal stability of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by surface modification with Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>

Layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode material is synthesized via a sol-gel method and subsequently surface-modified with Eu₂O₃ layer by a wet chemical process. The effect of Eu₂O₃ coating on the electrochemical performances and thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂@Eu₂O₃ cells is investigated systematically by the charge/discharge testing, cyclic voltammograms, AC impedance spectroscopy, and DSC measurements, respectively. In comparison, the Eu₂O₃-coated sample demonstrates better electrochemical performances and thermal stability than that of the pristine one. After 100 cycles at 1C, the Eu₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode demonstrates stable cyclability with capacity retention of 92.9 %, which is higher than that (75.5 %) of the pristine one in voltage range 3.0–4.6 V. Analysis from the electrochemical measurements reveals that the remarkably improved performances of the surface-modified composites are mainly ascribed to the presence of Eu₂O₃-coating layer, which could efficiently suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of active material.     

Synthesis and electrochemical properties of P2-Na<Subscript>2/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>2/3</Subscript>O<Subscript>2</Subscript>

The pure phase P2-Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a solid reaction process. The optimum calcination temperature was 850 °C. The as-prepared product delivered a capacity of 158 mAh g^?1 in the voltage range of 2–4.5 V, and there was a phase transition from P2 to O2 at about 4.2 V in the charge process. The P2 phase exhibited excellent intercalation behavior of Na ions. The reversible capacity is about 88.5 mAh g^?1 at 0.1 C in the voltage range of 2–4 V at room temperature. At an elevated temperature of 55 °C, it could remain as an excellent capacity retention at low current rates. The P2-Na_2/3Ni_1/3Mn_2/3O₂ is a potential cathode material for sodium-ion batteries.     

Effects of lithium excess amount on the microstructure and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material

Spinel LiNi_0.5Mn_1.5O₄ cathode materials with different lithium excess amount (0, 2%, 6%, 10%) were synthesized by a facile solid-state method. The effect of lithium excess amount on the microstructure, morphology, and electrochemical properties of LiNi_0.5Mn_1.5O₄ materials was systematically investigated. The results show that the lithium excess amount does not change the particle morphology and size obviously; thus, the electrochemical properties of LiNi_0.5Mn_1.5O₄ are mainly determined by structural characteristics. With the increase of lithium excess amount, the cation disordering degree (Mn³⁺ content) and phase purity first increase and then decrease, while the cation mixing extent has the opposite trend. Among them, the LiNi_0.5Mn_1.5O₄ material with 6% lithium excess amount exhibits higher disordering degree and lower impurity content and cation mixing extent, thus leading to the optimum electrochemical properties, with discharge capacities of 125.0, 126.1, 124.2, and 118.9 mAh/g at 0.2-, 1-, 5-, and 10-C rates and capacity retention rate of 96.49% after 100 cycles at 1-C rate.     

AlF<Subscript>3</Subscript> coating of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for high-performance Li-ion batteries

AlF₃-coating is attempted to improve the performance of LiNi_0.5Mn_1.5O₄ cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray diffraction, charge/discharge, and impedance. The coated LiNi_0.5Mn_1.5O₄ samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples. Among the coated samples, 1.0 mol% AlF₃-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF₃-coated LiNi_0.5Mn_1.5O₄, while only 84.3 mAh/g for the uncoated sample.     

Polyaspartic-acid-pyrolysis route for the synthesis of nanocrystalline LiCo<Subscript>0.15</Subscript>Mn<Subscript>1.85</Subscript>O<Subscript>4</Subscript> powder for Li-ion batteries

Nanocrystalline cubic spinel LiCo_0.15Mn_1.85O₄ powder was prepared by a novel method based on in situ polymerization of aspartic acid along with metal salts. Thermal study shows that the complete crystallization and/or formation of the compound is at 358 °C. The structural property of the synthesized material was characterized by X-ray diffraction studies. The X-ray diffractogram reveals the single-phase formation of the product. Scanning electron microscope study shows that the average grain size of the powder is less than 1 μm. To assess the electrochemical performance of the synthesized cathode material, the C/LiCo_0.15Mn_1.85O₄ cell with 1 M LiPF₆ in 1:1 (v/v) mixture of ethylene carbonate and dimethyl carbonate as the electrolyte was assembled, and the charge and discharge studies were made in between 3.0 and 4.8 V at a constant current density of 0.1 mAcm⁻². It shows that capacity loss is only 2% even after the 50th cycle. As this preparation method is simple and particularly suitable for preparation of highly homogeneous mixed metal oxides for Li-ion batteries.     

A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi_0.5Mn_1.5O₄ as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C₆H₅)₂SnCl₂ and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi_0.5Mn_1.5O₄ is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.     

Analysis of the exchange magnetic structure in Pb<Subscript>3</Subscript>Mn<Subscript>7</Subscript>O<Subscript>15</Subscript>

The indirect-coupling model is used to analyze the exchange magnetic structure of Pb₃Mn₇O₁₅ in the hexagonal setting. The ratios of manganese ions Mn⁴⁺/Mn³⁺ in each nonequivalent position are determined. Pb₃(Mn_0.95Ge_0.05)₇O₁₅ and Pb₃(Mn_0.95Ga_0.05)₇O₁₅ single crystals are grown by the solution–melt method in order to test the validity of the proposed model. The structural and magnetic properties of the single crystals are studied. The magnetic properties of the grown single crystals are compared with those of nominally pure Pb₃Mn₇O₁₅.     

NMR spectrum in a Mn<Subscript>3</Subscript>Al<Subscript>2</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> noncollinear antiferromagnet

The dependence of the NMR frequencies on the external magnetic field in a Mn₃Al₂Ge₃O₁₂ non-collinear 12-sublattice antiferromgnet is calculated using the exchange approximation for the spin dynamics.     

Preparation of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials by electrospinning

LiNi_0.5Mn_1.5O₄ cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi_0.5Mn_1.5O₄ composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg^?1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.     

Tunneling conductivity in lithiated transition metal oxide cathode Li<Subscript>0.9</Subscript>[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>1.95</Subscript>

Electrical complex ac conductivity of the compound Li_0.9[Ni_1/3Mn_1/3Co_1/3]O_1.95 has been studied in the frequency range 10 Hz–2 MHz and in the temperature range 93–373 K. It has been observed that the frequency dependence of the ac conductivity obeys a power law and the temperature dependence of the ac conductivity is quite weak. The experimental data have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping over barriers. It has been observed that the electron tunneling is dominant in the temperature range from 93 K to 193 K. A crossover of relaxation mechanism from electron tunneling to polaron tunneling is observed at 193 K. Out of the several models discussed, the electron tunneling and the polaron tunneling models are quite consistent with the experimental data for the complex ac conductivity. The various parameters obtained from the fits of the experimental results for the real and imaginary parts of the conductivity to the predictions of these models are quite reasonable.     

Improved electrochemical performance of Li<Subscript>1.2</Subscript>Ni<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>O<Subscript>2</Subscript> cathode material with fast ionic conductor Li<Subscript>3</Subscript>VO<Subscript>4</Subscript> coating

Layered lithium-enriched nickel manganese oxides Li_1.2Ni_0.2Mn_0.6O₂ have been synthesized and coated by fast ionic conductor Li₃VO₄ with varying amounts (1, 3, and 5 wt%) in this paper. The effect of Li₃VO₄ on the physical and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), discharge, cyclic performance, rate capability, and electrochemical impedance spectroscopy (EIS). The discharge capacity and coulomb efficiency of Li_1.2Ni_0.2Mn_0.6O₂ in the first cycle have been improved after Li₃VO₄ coating. And, the 3 wt% Li₃VO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ shows the best discharge capacity (246.8 mAh g^?1), capacity retention (97.3 % for 50 cycles), and rate capability (90.4 mAh g^?1 at 10 C). Electrochemical impedance spectroscopy (EIS) results show that the R _ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode decreases after Li₃VO₄ coating, which is due to high lithium ion diffusion coefficient of Li₃VO₄, is responsible for superior rate capability.     

A lithium salt additive Li<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> for enhancing the electrochemical performance of high-voltage LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

In this work, Li₂ZrF₆, a lithium salt additive, is reported to improve the interface stability of LiNi_0.5Mn_1.5O₄ (LNMO)/electrolyte interface under high voltage (4.9 V vs Li/Li⁺). Li₂ZrF₆ is an effective additive to serve as an in situ surface coating material for high-voltage LNMO half cells. A protective SEI layer is formed on the electrode surface due to the involvement of Li₂ZrF₆ during the formation of SEI layer. Charge/discharge tests show that 0.15 mol L^?1 Li₂ZrF₆ is the optimal concentration for the LiNi_0.5Mn_1.5O₄ electrode and it can improve the cycling performance and rate property of LNMO/Li half cells. The results obtained by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that Li₂ZrF₆ can facilitate the formation of a thin, uniform, and stable solid electrolyte interface (SEI) layer. This layer inhibits the oxidation decomposition of the electrolyte and suppresses the dissolution of the cathode materials, resulting in improved electrochemical performances.     

CaCuMn<Subscript>6</Subscript>O<Subscript>12</Subscript> vs. CaCu<Subscript>2</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>: A comparative study

The ferrimagnetic compounds Ca(Cu_xMn_3?x)Mn₄O₁₂ of the double distorted perovskites AC₃B₄O₁₂ family exhibit a rapid increase of the ferromagnetic component in magnetization at partial substitution of square coordinated (Mn³⁺)_C for (Cu²⁺)_C. In the transport properties, this is seen as a change of the semiconducting type of resistivity for the metallic one. The evolution of magnetic properties of Ca(Cu_xMn_3?x)Mn₄O₁₂ is driven by strong antiferromagnetic exchange interaction of (Cu²⁺)_C with (Mn³⁺/Mn⁴⁺)_B coordinated octahedra. The competing interactions of (Mn³⁺)_C with (Mn³⁺/Mn⁴⁺)_B lead to the formation of noncollinear magnetic structures that can be aligned by magnetic fields.