Studies on the LiMnO spinel system (obtained from melt-impregnation method) as positive electrodes for 4 V lithium batteries. Part III. Characterization of capacity and rechargeability

A series of ‘lithium-rich’ or ‘oxygen-rich’ spinel compounds are prepared from the reaction of LiNO₃ with electrochemically prepared manganese dioxide (EMD) via the melt-impregnation method. The capacity and rechargeability of these compounds are semi-quantitatively discussed in terms of an LiMn₂O₄Li₄Mn₅O₁₂Li₂Mn₄O₉ phase diagram. The capacity decreases as the lithium or oxygen content increases in the spinel matrix. By contrast, the rechargeability is improved.     

Studies on Li–Mn–O spinel system (obtained from melt-impregnation method) as a cathode for 4 V lithium batteries: Part V. Enhancement of the elevated temperature performance of Li/LiMn2O4 cells

Stoichiometric LiMn₂O₄, metal-ion doped (Li⁺ and Co³⁺) spinels, Li_1+xMn_2−x−yM_yO₄, and fluorine substituted spinel, Li_1+xMn₂O_4−zF_z, are examined as cathodes in Li/organic electrolyte/Li_xMn₂O₄ cells containing various electrolytes at both room temperature and 50°C. The elevated temperature performance is improved with the metal-ion doped and fluorine substituted spinels in LiBF₄ base electrolyte solution.     

Synthesis and performance of lithium vanadium phosphate as cathode materials for lithium ion batteries by a sol–gel method

Monoclinic lithium vanadium phosphate, Li₃V₂(PO₄)₃, was synthesized by a sol–gel method under Ar/H₂ (8% H₂) atmosphere. The influence of sintering temperatures on the synthesis of Li₃V₂(PO₄)₃ has been investigated using X-ray diffraction (XRD), SEM and electrochemical methods. XRD patterns show that the Li₃V₂(PO₄)₃ crystallinity with monoclinic structure increases with the sintering temperature from 700 to 800 °C and then decreases from 800 to 900 °C. SEM results indicate that the particle size of as-prepared samples increases with the sintering temperature increase and there is minor carbon particles on the surface of the sample particles, which are very useful to enhance the conductivity of Li₃V₂(PO₄)₃. Charge–discharge tests show the 800 °C-sample exhibits the highest initial discharge capacity of 131.2 mAh g⁻¹ at 10 mA g⁻¹ in the voltage range of 3.0–4.2 V with good capacity retention. CV experiment exhibits that there are three anodic peaks at 3.61, 3.70 and 4.11 V on lithium extraction as well as three cathodic peaks at 3.53, 3.61 and 4.00 V on lithium reinsertion at 0.02 mV s⁻¹ between 3.0 and 4.3 V. It is suggested that the optimal sintering temperature is 800 °C in order to obtain pure monoclinic Li₃V₂(PO₄)₃ with good electrochemical performance by the sol–gel method, and the monoclinic Li₃V₂(PO₄)₃ can be used as candidate cathode materials for lithium ion batteries.     

Electrochemical properties of Co3O4, Ni–Co3O4 mixture and Ni–Co3O4 composite as anode materials for Li ion secondary batteries

By varying the synthetic temperature and time, Co₃O₄ with highly optimized electrochemical properties was obtained from the solid state reaction of CoCO₃. As a result, Co₃O₄ showed a high capacity around 700 mAh/g and stable capacity retention during cycling (93.4% of initial capacity was retained after 100 cycles). However, its initial irreversible capacity reached about 30% of capacity. Several phenomenological examinations in our previous results told us that the main causes of low initial coulombic efficiency, that is, large initial irreversible capacity, were solid electrolyte interphase (SEI) film formation on surface and incomplete decomposition of Li₂O during the first discharge process. SEI film formation cannot be restrained without the development of a special electrolyte, and there has been little research on the proper electrolyte composition, whereas in our research, Ni had the catalytic activity to facilitate Li₂O decomposition. Thus, in order to improve the low initial coulombic efficiency of Co₃O₄ (69%), Ni was added to Co₃O₄ using two methods like physical mixing and mechanical milling. When adding the same amount of Ni, the mechanical milling showed the improvement in initial coulombic efficiency, 79%, but physical mixing had no effect. Finally, when the charge–discharge mechanism of Co₃O₄ was considered and the morphologies of Ni–Co₃O₄ mixture obtained by physical mixing and Ni–Co₃O₄ composite prepared by mechanical milling were compared, it was revealed that the initial coulombic efficiency of Ni–Co₃O₄ composite depends on the contact area between the Ni and the Co₃O₄.     

Zn4Sb3(C7) powders as a potential anode material for lithium-ion batteries

The electrochemical properties of β-Zn₄Sb₃ and Zn₄Sb₃C₇ as new lithium-ion anode materials were investigated. The reversible capacities of the pure Zn₄Sb₃ alloy electrode and 100 h milled Zn₄Sb₃ in the first cycle reached 503 and 566 mA h/g, respectively, but the cycle stability of Zn₄Sb₃ whether milled or not were obviously bad. It was demonstrated that cycle stability of Zn₄Sb₃ could be largely improved by milling after mixing with graphite. It was shown that Zn₄Sb₃C₇ composite has a lithium-ion extraction capacity of 581 mA h/g at the first cycle and 402 mA h/g at 10th cycle.     

Synthesis and physicochemical properties of LiAl0.05Mn1.95O4 cathode material by the ultrasonic-assisted sol–gel method

Spinel LiAl_0.05Mn_1.95O₄ has been successfully synthesized by a new ultrasonic-assisted sol–gel (UASG) method. The structure and physicochemical properties of this as-prepared powder compared with the pristine LiMn₂O₄ and LiAl_0.05Mn_1.95O₄ synthesized by the traditional sol–gel method were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), and galvanostatic charge–discharge testing in detail. The results show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; LiAl_0.05Mn_1.95O₄ has higher Mn oxidation state, and the absorption peak of Mn(III)O and Mn(IV)O bonds has blue shift because of the doped Al. CV confirms that the LiAl_0.05Mn_1.95O₄ sample (UASG) has a good reversibility and its structure is very advantageous for the transportation of lithium ions. The charge–discharge tests indicate that LiAl_0.05Mn_1.95O₄ (UASG) has nearly equal initial capacity with LiMn₂O₄ (sol–gel) at 1C discharge rate, but LiAl_0.05Mn_1.95O₄ (UASG) has higher discharge potential than that of LiMn₂O₄ (sol–gel). In addition, LiAl_0.05Mn_1.95O₄ (UASG) has higher discharge potential and capacity than that of LiAl_0.05Mn_1.95O₄ (sol–gel) at 1C discharge rate, and LiAl_0.05Mn_1.95O₄ (UASG) has high capacity retention at C/3 and 1C discharge rate among three samples after 50 cycles, which reveals that the sample obtained via UASG method, has the best electrochemical performance among three samples.     

Synthesis and characterisation of high-performance 3Li4Ti5O12·NiO composite anode material for lithium-ion batteries

A 3Li₄Ti₅O₁₂·NiO composite anode material was prepared by a spray-drying method. The physical and electrochemical properties of samples were characterised by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical test. X-ray diffraction results revealed that incorporation of NiO did not alter the structure of Li₄Ti₅O₁₂. Scanning electron microscopy images of both Li₄Ti₅O₁₂ and 3Li₄Ti₅O₁₂·NiO exhibited spherical particles with the sizes of 0.5–3?μm. Electrochemical tests showed that the 3Li₄Ti₅O₁₂·NiO composite material exhibited much better rate and cycling performances than those of Li₄Ti₅O₁₂ per se. It delivered the specific capacities of 372.8, 252.6 and 204.8?mAh?g^??1 at 0.1, 1 and 2°C rates, respectively. After 300 cycles, the discharge specific capacity remained as high as 202.1?mAh?g^??1 at 2°C rate.     

Study of the interface nickel/composite cathode of industrially made Li/V2O5 polymer (POE) batteries working at 90 °C

ωLi/V₂O₅ spirally wound polymer (POE) batteries functioning at 90 °C presented an important capacity fading ca. 20th cycle. This behavior could arise from the cathode material itself, including its in situ formation during the first reduction step from αLi/V₂O₅, or from a technical problem linked either to the composite cathode or one of the other cell components. In this paper, after rejection of the two first hypothesis, we clearly demonstrate the negative role of the nickel foil used as cathodic collector.     

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.     

A novel La2NiO4+δ-La3Ni2O7-δ-Ce0.55La0.45O2-δ ternary composite cathode prepared by the co-synthesis method for IT-SOFCs

A novel La₂NiO_4+δ-La₃Ni₂O_7?δ-Ce_0.55La_0.45O_2?δ (L2N1-L3N2-LDC) ternary composite with a weight ratio of 0.3:2.5:2.2 was prepared by a one-step co-synthesis method and employed as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction (XRD) profiles confirmed the successful synthesis of the composite consisted of L2N1, L3N2 and LDC phases, without any other impurity. Compared with the cathode prepared by the physical mixing method, the co-synthesized composite cathode possessed a porous microstructure with the smaller particle size and more uniform distribution of various elements. The ternary composite cathode on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte revealed improved electrochemical performance, achieving the polarization resistance value of 0.06 Ω cm² at 800° C in stationary air. Electrochemical impedance spectra under various oxygen partial pressures indicated the charge transfer process was the rate limiting step for oxygen reduction reaction. Furthermore, a SDC electrolyte (about 350 μm) supported single cell with L2N1-L3N2-LDC as cathode and Ni-SDC as anode demonstrated a maximum power density of 253 mW cm^?2 at 800° C. These results confirmed that L2N1-L3N2-LDC ternary composite prepared by co-synthesized method is a very promising cathode material for IT-SOFCs.     

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.     

Preparation of Pr2NiO4+δ-La0.6Sr0.4CoO3-δ as a high-performance cathode material for SOFC by an impregnation method

As a Ruddlesden-Popper (RP) phase solid oxide fuel cell (SOFC) cathode material, Pr₂NiO_4+δ (PNO) is a critical challenge for SOFC commercialization due to the lack of oxygen vacancies and insufficient redox reaction (ORR) activity. In this paper, various concentrations of La_0.6Sr_0.4CoO_3-δ (LSC) nanoparticles are coated on the surface of PNO by an impregnation method, and the ORR kinetics of PNO is found to be improved by constructing a composite cathode with heterointerfaces. The formation of the heterointerface effectively enhances the transfer of interstitial oxygen in the PNO and the oxygen vacancies in LSC, which can promote the conduction of O^2? in the cathode and thus improves the ORR activity of the material. When the impregnation concentration of LSC reached C_LSC = 0.2 mol L^?1, the ORR activity can reach the highest level. At 700 °C, the area-specific resistance of PNO-LSC reaches 0.024 Ω cm², which is 83.4% lower than that of PNO (0.145 Ω cm²). And the peak power density of PNO-LSC reaches 0.618 W cm^?2, which is 1.89 times larger than that of PNO (0.327 W cm^?2). Therefore, the construction of composite cathodes with heterointerfaces via impregnation provides an alternative strategy for enhancing the ORR activity of the cathode materials in SOFC.     

Metal-organic frameworks derived spinel NiCo2O4/graphene nanosheets composite as a bi-functional cathode for high energy density Li–O2 battery applications

Electrode materials having a combined heterostructure morphology can boost the electrochemical performance of energy conversion and storage applications. In this paper, we prepared three-dimensional (3D) porous NiCo₂O₄ dodecahedron nanosheets (NCO) from a metal–organic framework template (ZIF-67) and incorporated them with two-dimensional (2D) multilayer graphene nanosheets (GNS) through a simple and rapid ultrasonication process. The combination of these 3D/2D nanostructures created effective interfaces between the NCO and GNS components that enhanced the intrinsic electronic properties and increased the number of active catalytic sites on the NCO@GNS surfaces. Accordingly, the NCO@GNS electrocatalyst displayed superior kinetics for both the oxygen reduction and evolution reactions in both aqueous and non-aqueous electrolytes and could be fabricated into an air-cathode for Li–O₂ battery applications. The NCO@GNS air-cathode delivered a specific storage capacity (7201 mA h g^?1) higher than those of the NCO and commercial carbon black electrodes. We tested the durability of the Li–O₂ battery featuring the NCO@GNS cathode in a new PAT-cell configuration; it exhibited long-term cyclability for 200 cycles with a limited capacity of 500 mA h g^?1 at a current density of 100 mA g^?1. This cathode design featuring meso- and micropores shortened the pathways for Li⁺ ion diffusion and ensured rapid electron and oxygen transfer, thereby increasing the lifetime of its corresponding Li–O₂ battery.     

Study of the electrochemical properties of Fe3O4/C–Bi composites prepared by spray drying and their use in cylindrical sealed nickel iron batteries

In this paper, Fe₃O₄/C–Bi composites with carbon coating and bismuth added were prepared by step-by-step precipitation, spray carbon coating drying and high temperature treatment. The composite materials are spherical particles, which are composed of primary nanoparticles coated with carbon, and the thickness of the carbon coating layer is 2 nm. Electrochemical test results show that the synergistic effect of Bi and C can effectively inhibit hydrogen evolution and passivation of iron electrodes. The Fe₃O₄/C–Bi composite materials have excellent electrochemical properties, among which the Fe₃O₄/C–Bi(5%) electrode has the best performance. At a current density of 300 mA g^?1, the discharge capacitance is close to 700.0 mAh g^?1, the coulombic efficiency is as high as 95.2%, and the rate performance is also excellent. At a current density of 2400 mA g^?1, the discharge capacity reaches 500.0 mAh g^?1. AA600 cylindrical iron nickel batteries prepared with an Fe₃O₄/C–Bi(5%) composite as the active material for iron negative electrodes realized sealing for the first time.     

Cu supported on ZnAl-LDHs precursor prepared by in-situ synthesis method on γ-Al2O3 as catalytic material with high catalytic activity for methanol steam reforming

A novel catalyst precursor ZnAl-LDHs/γ-Al₂O₃ was prepared by in-situ synthesis method, and the copper was supported on calcined hydrotalcite catalyst precursor by wet impregnation. The correlation between the structure and the catalytic activity for methanol steam reforming was studied by XRD, SEM, TPR, chemisorption N₂O, IR and N₂ adsorption techniques. The results showed that the ZnAl-LDHs was successfully synthesized by in-situ synthesis method on γ-Al₂O₃ and the copper mass fraction had a great effect on the interactions between support and copper species. Furthermore, the catalyst reducibility and copper surface area evidently influenced catalytic activity for methanol steam reforming. The 10% Cu/γ-Al@MMO exhibited the best catalytic activity, that was, the methanol conversion was 99.98% and the CO concentration was only 0.92% at 300 °C in hydrogen production by methanol steam reforming.     

La0.4Sr0.6Co0.7Fe0.2Nb0.1O3-δ perovskite prepared by the sol-gel method with superior performance as a bifunctional oxygen electrocatalyst

The advancement of efficient noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucially important for energy storage devices such as fuel cells and metal-air batteries. This paper reports the development of a novel bifunctional perovskite, La_0.4Sr_0.6Co_0.7Fe_0.2Nb_0.1O_3-δ (LSCFN). The crystal structure, morphology, adsorption, valence, and oxygen catalytic activity of LSCFN were systematically studied. In addition, an investigation of the influence of the synthetic method on the oxygen catalytic activity was performed. Sol-gel and solid-phase methods were applied for the synthesis of LSCFN, and the resulting perovskites were denoted as LSCFN-SG and LSCFN-SP, respectively. The catalyst LSCFN-SG exhibited excellent bifunctional catalytic activity, with a low overpotential (360 mV) and superior stability in the OER. Subsequently, LSCFN-SG was used as the cathode catalyst in an aluminum-air battery and exhibited a high power density. The results of this study indicate that LSCFN-SG is a promising bifunctional oxygen electrocatalyst for metal-air batteries.     

The surfactant-assisted Ni–Al2O3 catalyst prepared by a homogeneous precipitation method for CH4 steam reforming

The surfactant-assisted Ni–Al₂O₃ catalysts are prepared by the homogeneous precipitation method with a surfactant/Al molar ratio ranging from 0.0 to 2.0. It has been investigated the effects of the surfactant on the physicochemical properties and the catalytic activities of the Ni–Al₂O₃ catalysts. The BET surface area of the catalysts decreases with increasing the surfactant content. The pore volume and pore size of the catalysts increase with increasing the surfactant content. XRD results indicate that all of the catalysts exhibit strong diffraction peaks corresponding to NiO and weak peaks corresponding to NiAl₂O₄. In the TPR results, the reduction peaks which indicates that the Ni particles strongly interacted with the support are present at between 668 and 688 °C. The activities of the prepared catalysts for methane steam reforming increase with increasing surfactant content in fresh and poisoned state due to an increase of pore volume and pore size.     

Carbon supported MnOx–Co3O4 as cathode catalyst for oxygen reduction reaction in alkaline media

The electroreduction of oxygen of MnO_x–Co₃O₄/C was firstly studied in alkaline media. The MnO_x–Co₃O₄/C showed better electrocatalytic activity towards ORR than MnO_x/C and Co₃O₄/C. Compared to Pt/C, MnO_x–Co₃O₄/C showed better methanol tolerance and durability in alkaline solution. Thus, the MnO_x–Co₃O₄/C catalyst had potential for applications in metal–air batteries and alkaline fuel cells.