NiCo2O4 nanosheets supported on Ni foam for rechargeable nonaqueous sodium–air batteries

NiCo₂O₄ nanosheets supported on Ni foam were synthesized by a solvothermal method. A composite of NiCo₂O₄ nanosheets/Ni as a carbon-free and binder-free air cathode exhibited an initial discharge capacity of 1762 mAh g^− 1 with a low polarization of 0.96 V at 20 mA g^− 1 for sodium–air batteries. Na₂O₂ nanosheets were firstly observed as the discharged product in sodium–air battery. High electrocatalytic activity of NiCo₂O₄ nanosheets/Ni made it a promising air electrode for rechargeable sodium–air batteries.     

Structure and electrochemical hydrogen storage behaviors of alloy Co2B

The alloys Co₂B were prepared by two ways of high temperature solid phase process and arc melting, the structure of the alloys was characterized by XRD and SEM. It showed that it was structure of tetragonal Co₂B.The electrochemical experimental results demonstrated that the Co₂B prepared by two means both showed excellent cycling stability. The initial discharge capacity of Co₂B prepared by the high temperature solid phase process was 480.3 mA h g⁻¹, there was no distinct declination after 70 charge–discharge cycles and the capacity kept about 195 mA h g⁻¹. Co₂B prepared by the high temperature solid phase process showed very good electrochemical reversibility in CV curves. The hydrogen storage mechanism was also discussed, it confirmed that the high initial capacity of Co₂B prepared by the high temperature solid phase process was due to the oxidation of Co and B₂O₃, and it was irreversible.     

In situ X-ray absorption and diffraction studies of carbon coated LiFe1/4Mn1/4Co1/4Ni1/4PO4 cathode during first charge

Synchrotron based in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques are used to study electronic and crystal structure changes of the carbon coated LiFe_1/4Mn_1/4Co_1/4Ni_1/4PO₄ (LiFe_1/4Mn_1/4Co_1/4Ni_1/4PO₄/C) cathode material for Li-ion batteries during the first charge. In situ Fe, Mn, Co and Ni K-edge XAS results revealed that the three voltage plateaus at ～3.6, 4.2 and 4.7 V vs. Li/Li⁺ are attributed to the redox reactions of Fe²⁺/Fe³⁺, Mn²⁺/Mn³⁺ and Co²⁺/Co³⁺, respectively, while the apparent capacities above 4.9 V is not originated from the Ni²⁺/Ni³⁺ redox, but very likely from the electrolyte decomposition. Interesting phase transition behaviors of LiFe_1/4Mn_1/4Co_1/4Ni_1/4PO₄/C were observed with the formation of an intermediate phase and the solid solution regions. Combined in situ XAS and XRD techniques indicate fast electronic structural changes and slow bulk crystal structural changes.     

Significant improved electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 cathode on volumetric energy density and cycling stability at high rate

Li(Ni_1/3Co_1/3Mn_1/3)O₂ microspheres with a tap density of 2.41 g cm⁻³ have been synthesized for applications in high power and high energy systems, using a simple rheological phase reaction route. Cyclic voltammograms (CV) showed no shift of anodic and cathodic peaks centred at 3.81, 3.69 V for the Ni²⁺/Ni⁴⁺ couple after first cycle. The results of power pulse area specific impedance (ASI) and differential scanning calorimetry (DSC) tests showed lower power impedance and increased thermal stability of the electrode at high rate. These merits mentioned above provided significant improved capacity and rate performance for Li(Ni_1/3Co_1/3Mn_1/3)O₂ microspheres, which 159, 147 mAh g⁻¹ discharge capacity was delivered after 100 cycles between 2.5–4.6 V vs. Li at a different discharge rate of 2.5 C (500 mA g⁻¹), 5 C and a constant 0.5 C charge rate, respectively.     

Novel electrocatalysts for generating oxygen from alkaline water electrolysis

We have obtained spinel-type Co₃O₄ and La-doped Co₃O₄ in the form of thin film on Ni, using microwave-assisted synthesis, which dramatically exhibit very low overpotentials for the oxygen evolution reaction (OER). Investigations have shown that at the apparent current density of 100 mA cm⁻² in 1 mol dm⁻³ KOH at 25 °C, the new electrodes, Co₃O₄ (oxide loading = 3.4 ± 0.3 mg cm⁻²) and La-doped Co₃O₄ (oxide loading = 2.8 ± 0.4 mg cm⁻²), produce overpotentials, 235 ± 7 and 224 ± 8 mV, respectively. Such low overpotentials for the OER, to our knowledge, have not been found on any mixed oxide electrode material reported in literature till today. Small La addition improved the BET surface area and porosity of the oxide catalyst powder and reduced the charge transfer resistance for the OER on the electrode made of oxide powder.     

Anomalous capacity and cycling stability of xLi2MnO3 · (1 − x)LiMO2 electrodes (M = Mn,Ni, Co) in lithium batteries at 50 °C

Transition metal oxides with composite xLi₂MnO₃ ·  (1 − x)LiMO₂ rocksalt structures (M = Mn, Ni, Co) are of interest as a new generation of cathode materials for high energy density lithium-ion batteries. After electrochemical activation to 4.6 or 4.8 V (vs. Li⁰) at 50 °C, xLi₂MnO₃ · (1 − x)LiMn_0.33Ni_0.33Co_0.33O₂ (x = 0.5, 0.7) electrodes deliver initial discharge capacities (>300 mAh/g) at a low current rate (0.05 mA/cm²) that exceed the theoretical values for lithiation back to the rocksalt stoichiometry (240–260 mAh/g), at least during the early charge/discharge cycles of the cells. Attention is drawn to previous reports of similar, but unaccounted and unexplained anomalous behavior of these types of electrode materials. Possible reasons for this anomalous capacity are suggested. Indications are that electrodes in which M = Mn, Ni and Co do not cycle with the same stability at 50 °C as those without cobalt.     

Enhanced supercapacitive behaviors of birnessite

The birnessite type manganese dioxide electrode was prepared by the electrochemical stimulation as we recently described. It showed 190 F g⁻¹ in a Na₂SO₄ aqueous solution between −0.1 and 0.9 V versus Ag/AgCl at 1 A g⁻¹. The specific capacitance of birnessite was decreased by the manganese dissolution when the reduction and oxidation were repeated. By adding small amounts of Na₂HPO₄ or NaHCO₃ into the electrolyte, the capacitance increased to 200–230 F g⁻¹ and the manganese dissolution was successfully suppressed. Thanks to the additives, the birnessite demonstrated the much improved cycleability over >1800 cycles.     

A disordered rock-salt Li-excess cathode material with high capacity and substantial oxygen redox activity: Li1.25Nb0.25Mn0.5O2

A disordered rocksalt Li-excess cathode material, Li_1.25Nb_0.25Mn_0.5O₂, was synthesized and investigated. It shows a large initial discharge capacity of 287 mAh g^− 1 in the first cycle, which is much higher than the theoretical capacity of 146 mAh g^− 1 based on the Mn³⁺/Mn⁴⁺ redox reaction. In situ X-ray diffraction (XRD) demonstrates that the compound remains cation-disordered during the first cycle. Electron energy loss spectroscopy (EELS) suggests that Mn and O are likely to both be redox active, resulting in the large reversible capacity. Our results show that Li_1.25Nb_0.25Mn_0.5O₂ is a promising cathode material for high capacity Li-ion batteries and that reversible oxygen redox in the bulk may be a viable way forward to increase the energy density of lithium-ion batteries.     

Sol–gel preparation and electrochemical performances of LiFe1/3Mn1/3Co1/3PO4/C composites with core–shell nanostructure

LiFe_1/3Mn_1/3Co_1/3PO₄/C solid solution was prepared via a poly(ethylene glycol) assisted sol–gel method and exploited as cathode materials for lithium ion batteries. X-ray diffraction patterns indicate that LiFe_1/3Mn_1/3Co_1/3PO₄/C is crystallized in an orthorhombic structure. The scanning electron microscopy and transmission electron microscopy show that the particles are about 200 nm with a uniform carbon coating of about 8 nm in thickness to form a core–shell nanostructure. During charge–discharge cycles, LiFe_1/3Mn_1/3Co_1/3PO₄/C presented three plateaus corresponding to Fe³⁺/Fe²⁺, Mn³⁺/Mn²⁺ and Co³⁺/Co²⁺ redox couples, and a discharge capacity of 150.8 mAh g^?1 in the first cycle, remaining 121.2 mAh g^?1 after 30 cycles. Core–shell structure can optimize the performances of polyoxoanionic materials for lithium ion batteries.     

Electrothermal vaporization coupled with inductively coupled plasma array–detector mass spectrometry for the multielement analysis of Al2O3 ceramic powders

An electrothermal vaporization (ETV) system useful for the analysis of solutions and slurries has been coupled with a sector-field inductively coupled plasma mass spectrometer (ICP–MS) equipped with an array detector. The ability of this instrument to record the transient signals produced for a number of analytes in ETV–ICP–MS is demonstrated. Detection limits for Mn, Fe, Co, Ni, Cu, Zn and Ga are in the range of 4–60 pg μL^− 1 for aqueous solutions and in the low μg g^− 1 range for the analysis of 10 mg mL^− 1 slurries of Al₂O₃ powders. The dynamic ranges measured for Fe, Cu and Ga spanned 3–5 orders of magnitude when the detector was operated in the low-gain mode and appear to be limited by the ETV system. Trace amounts of Fe, Cu and Ga could be directly determined in Al₂O₃ powders at the 2–270 μg g^− 1 level without the use of thermochemical reagents. The results well agree with literature values for Fe and Cu, whereas deviations of 50% at the 90 μg g^− 1 level for Ga were found.     

Radiotracer and analytical evidences proving the reduction of ClO4− ions at the cobalt/electrolyte solution interface

The occurrence of the reduction of ClO₄⁻ ions in the course of the dissolution (corrosion) of Co was indicated through the study of the adsorption of radio labelled (³⁶Cl) Cl⁻ ions. A detailed analytical study determining the Co²⁺ and Cl⁻ content of the solution phase furnished firm evidences that under suitable chosen experimental conditions the 4Co + ClO₄⁻ + 8H⁺=4Co²⁺ + Cl⁻ + 4H₂O reaction could be as important as the Co + 2H⁺=Co²⁺ + H₂ reaction considered in the literature as the only reaction path.     

Syntheses and crystal structures of new vanadium(IV) oxyphosphates M(VO)2(PO4)2 with M = Co,Ni

We have extended our research interest on titanium oxyphosphates (M^II(TiO)₂(PO₄)₂, with M^II = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates M^II(V^IVO)₂(PO₄)₂ (M^II = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)₂(PO₄)₂ (α and β for M = Co, Ni) have been determined in monoclinic P2₁/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO₄) (orthorhombic Pnma) and LiNi_0.50(TiO)₂(PO₄)₂ (monoclinic P2₁/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)₂(PO₄)₂-type (monoclinic P2₁/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO₆] octahedra, cross-linked by corner-sharing [PO₄] tetrahedra. The M²⁺ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO₆] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M²⁺ (M = Co, Ni) are inserted. A thermal study of the α ? β transition is also presented.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.     

Macroporous Co3O4 platelets with excellent rate capability as anodes for lithium ion batteries

This paper reports the microwave-assisted synthesis of Co₃O₄ nanomaterials with different morphologies including nanoparticles, rod-like nanoclusters and macroporous platelets. The new macroporous platelet-like Co₃O₄ morphology was found to be the best suitable for reversible lithium storage properties. It displayed superior cycling performances than nanoparticles and rod-like nanoclusters. More interestingly, excellent high rate capabilities (811 mAh g^?1 at 1780 mA g^?1 and 746 mAh g^?1 at 4450 mA g^?1) were observed for macroporous Co₃O₄ platelet. The good electrochemical performance could be attributed to the unique macroporous platelet structure of Co₃O₄ materials.     

A hierarchical micro/nanostructured 0.5Li2MnO3·0.5LiMn0.4Ni0.3Co0.3O2 material synthesized by solvothermal route as high rate cathode of lithium ion battery

A hierarchical micro/nanostructured Li-rich layered 0.5Li₂MnO₃·0.5LiMn_0.4Ni_0.3Co_0.3O₂ (H-LMNCO) material is prepared for the first time through the development of a solvothermal method, and served as cathode of lithium ion batteries. Electrochemical tests indicate that the H-LMNCO exhibits both a high reversible capacity and an excellent rate capability. The reversible discharge capacity of the H-LMNCO has been measured as high as 300.1 mAh·g^− 1 at 0.2 C rate. When the rate is increased to 10 C, the discharge capacity could still maintain a high value of 163.3 mAh·g^− 1. The results demonstrate that the developed solvothermal route is a novel synthesis strategy of preparing high rate performance Li-rich layered cathode material for lithium ion batteries.     

Self-assembled Li4Ti5O12/TiO2/Li3PO4 for integrated Li–ion microbatteries

This work aims to maximize the number of active sites for energy storage per geometric area, by approaching the investigation to 3D design for microelectrode arrays. Self-organized Li₄Ti₅O₁₂/TiO₂/Li₃PO₄ composite nanoforest layer (LTL) is obtained from a layer of self organized TiO₂/Li₃PO₄ nanotubes. The electrochemical response of this thin film electrode prepared at 700 °C exhibited lithium insertion and de-insertion at 1.55 and 1.57 V respectively, which is the typical potential found for lithium titanates. The effects of lithium phosphate on lithium titanate are explored for the first time. By cycling between 2.7 and 0.75 V the LTL/LiFePO₄ full cell delivered 145 mA h g^− 1 at an average potential of 1.85 V leading to an energy density of 260 W h kg^− 1 at C/2. Raman spectroscopy revealed that the γ-Li₃PO₄/lithium titanate structure is preserved after prolonged cycling. This means that Li₃PO₄ plays an important role for enhancing the electronic conductivity and lithium ion diffusion.     

A binder-free thin film anode composed of Co2 +-intercalated buserite grown on carbon cloth for oxygen evolution reaction

We present a binder-free catalytic anode for highly efficient and stable oxygen evolution reaction in alkaline media. The catalyst consists of a thin film of buserite-type layered manganese dioxide (MnO₂) intercalated with Co^2 + ions, resulting from electrodeposition of the layered MnO₂ film with tetrabutylammonium (Bu₄N⁺) ions on a carbon cloth, followed by ion-exchange of the initially incorporated Bu₄N⁺ with Co^2 + in solution. The electrode is capable to produce a current density of 10 mA cm^− 2 at an overpotential (η) of 377 mV with a Tafel slope of 48 mV dec^− 1, much superior to the layered MnO₂ without Co^2 +.     

Highly mesoporous and high surface area carbon: A high capacitance electrode material for EDLCs with various electrolytes

Activated carbon fibers (ACFs) with high surface area and highly mesoporous structure for electrochemical double layer capacitors (EDLCs) have been prepared from polyacrylonitrile fibers by NaOH activation. Their unique microstructural features enable the ACFs to present outstanding high specific capacitance in aqueous, non-aqueous and novel ionic liquid electrolytes, i.e. 371 F g⁻¹ in 6 mol L⁻¹ KOH, 213 F g⁻¹ in 1 mol L⁻¹ LiClO₄/PC and 188 F g⁻¹ in ionic liquid composed of lithium bis(trifluoromethane sulfonyl)imide (LiN(SO₂CF₃)₂, LiTFSI) and 2-oxazolidinone (C₃H₅NO₂, OZO), suggesting that the ACF is a promising electrode material for high performance EDLCs.     

Synthesis and crystal structure of sodium copper tetrametaphosphimate heptahydrate Na2Cu(PO2NH)4·7H2O and sodium potassium copper tetrametaphosphimate heptahydrate KxNa2−xCu(PO2NH)4·7H2O

Na₂Cu(PO₂NH)₄·7H₂O and K_xNa_2−xCu(PO₂NH)₄·7H₂O (x ≈ 0.5) were synthesized by gel crystallization in sodium silicate gels. The crystal structures were solved by single-crystal X-ray methods and found to be isotypic (Pnma, Z = 4; Na₂Cu(PO₂NH)₄·7H₂O: a = 627.5(2) pm, b = 1456.0(3) pm, c = 1900.5(4) pm, R1 = 0.0352; K_0.47Na_1.53Cu(PO₂NH)₄·7H₂O: a = 632.2(2) pm, b = 1460.0(3) pm, c = 1936.4(4) pm, R1 = 0.0345). The P₄N₄ rings of the tetrametaphosphimate anion exhibit a distorted chair-2 conformation with admixtures of saddle and crown conformation. The M⁺ ions are six- and sevenfold coordinated by oxygen atoms, the Cu²⁺ ions are fivefold coordinated, respectively. The MO₇ and the CuO₅ units form pairs of face-sharing polyhedra, which are connected by common corners forming chains and are further interconnected by tetrametaphosphimate anions, forming a three-dimensional network structure with channels along [100] and [010]. The MO₆ units form chains of face-sharing polyhedra, which are situated in the channels along [100]. Extended hydrogen bonding reinforces the three-dimensional framework structure of the compounds. ²³Na-MAS NMR experiments were conducted to verify the K/Na distribution on the M sites derived from the X-ray crystal structure refinement.     

Study on electrochemical performance of activated carbon in aqueous Li2SO4, Na2SO4 and K2SO4 electrolytes

The electrochemical performances of activated carbon (AC) in 0.5 mol/l Li₂SO₄, Na₂SO₄ and K₂SO₄ aqueous electrolytes were investigated. The cyclic voltammetric results at different scan rates show that the rate behaviors of AC in the three electrolytes improve in the order of Li₂SO₄ < Na₂SO₄ < K₂SO₄. This improvement can be mainly ascribed to the following two reasons: (1) the decreasing equivalent series resistance in the order of Li₂SO₄ > Na₂SO₄ > K₂SO₄, which is the main factor influencing the maximum output power, and (2) the increasing migration speed of hydrated ions in the bulk electrolyte and in the inner pores of AC electrode in the order of Li⁺ < Na⁺ < K⁺. Their cycling behaviors do not show any differences in capacitive fading. The above results provide valuable information to explore new hybrid supercapacitors.