Cycling performance of lithium metal polymer cells assembled with ionic liquid and poly(3-methyl thiophene)/carbon nanotube composite cathode

A poly(3-methylthiophene) (PMT)/multi-walled carbon nanotube (CNT) composite is synthesized by in situ chemical polymerization. The PMT/CNT composite is used as an active cathode material in lithium metal polymer cells assembled with ionic liquid (IL) electrolytes. The IL electrolyte consists of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) and LiBF4. A small amount of vinylene carbonate is added to the IL electrolyte to prevent the reductive decomposition of the imidazolium cation in EMIBF4. A porous poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)) film is used as a polymer membrane for assembling the cells. Electrochemical properties of the PMT/CNT composite electrode in the IL electrolyte are evaluated and the effect of vinylene carbonate on the cycling performance of the lithium metal polymer cells is investigated. The cells assembled with a non-flammable IL electrolyte and a PMT/CNT composite cathode are promising candidates for high-voltage–power sources with enhanced safety.

High performance cobalt-free perovskite cathode for intermediate temperature solid oxide fuel cells

Bi doping of SrFeO3d results in the formation of a structure with high symmetry and extraordinary electrochemical performance for Bi0.5Sr0.5FeO3-d, which is capable of competing effectively with the current Co-based cathode benchmark with additional advantages of lower thermal expansion and cost.

Polyterthiophene/CNT composite as a cathode material for lithium batteries employing an ionic liquid electrolyte

A polyterthiophene (PTTh)/multi-walled carbon nanotube (CNT) composite was synthesised by in situ chemical polymerisation and used as an active cathode material in lithium cells assembled with an ionic liquid (IL) or conventional liquid electrolyte, LiBF₄/EC–DMC–DEC. The IL electrolyte consisted of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄) containing LiBF₄ and a small amount of vinylene carbonate (VC). The lithium cells were characterised by cyclic voltammetry (CV) and galvanostatic charge/discharge cycling. The specific capacity of the cells with IL and conventional liquid electrolytes after the 1st cycle was 50 and 47 mAh g⁻¹ (based on PTTh weight), respectively at the C/5 rate. The capacity retention after the 100th cycle was 78% and 53%, respectively. The lithium cell assembled with a PTTh/CNT composite cathode and a non-flammable IL electrolyte exhibited a mean discharge voltage of 3.8 V vs Li⁺/Li and is a promising candidate for high-voltage power sources with enhanced safety.

Substrate-induced coagulation (SIC) of nano-disperse carbon black in non-aqueous media : a method of manufacturing highly conductive cathode materials for Li-ion batteries by self-assembly

Substrate-induced coagulation (SIC) is a coating process based on self-assembly for coating different surfaces with fine particulate materials. The particles are dispersed in a suitable solvent and the stability of the dispersion is adjusted by additives. When a surface, pre-treated with a flocculant e.g. a polyelectrolyte, is dipped into the dispersion, it induces coagulation resulting in the deposition of the particles on the surface. A non-aqueous SIC process for carbon coating is presented, which can be performed in polar, aprotic solvents such as N-Methyl-2- pyrrolidinone (NMP). Polyvinylalcohol (PVA) is used to condition the surface of substrates such as mica, copperfoil, silicon-wafers and lithiumcobalt oxide powder, a cathode material used for Li-ion batteries. The subsequent SIC carbon coating produces uniform layers on the substrates and causes the conductivity of lithiumcobalt oxide to increase drastically, while retaining a high percentage of active battery material.

Characterization and evaluation of BaCo0.7Fe0.2Nb0.1O3−δ as a cathode for proton-conducting solid oxide fuel cells

This study characterizes BaCo0.7Fe0.2Nb0.1O3−δ (BCFN) perovskite oxide and evaluates it as a potential cathode material for proton-conducting SOFCs with a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. A four-probe DC conductivity measurement demonstrated that BCFN has a modest electrical conductivity of 2–15 S cm−1 in air with p-type semiconducting behavior. An electrical conductivity relaxation test showed that BCFN has higher Dchem and Kchem than the well-known Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxide. In addition, it has relatively low thermal expansion coefficients (TECs) with values of 18.2 × 10−6 K−1 and 14.4 × 10−6 K−1 at temperature ranges of 30–900 °C and 30–500 °C, respectively. The phase reaction between BCFN and BZCY was investigated using powder and pellet reactions. EDX and XRD characterizations demonstrated that BCFN had lower reactivity with the BZCY electrolyte than strontium-containing perovskite oxides such as SrCo0.9Nb0.1O3-δ and Ba0.6Sr0.4Co0.9Nb0.1O3−δ. The impedance of BCFN was oxygen partial pressure dependent. Introducing water into the cathode atmosphere reduced the size of both the high-frequency and low-frequency arcs of the impedance spectra due to facilitated proton hopping. The cathode polarization resistance and overpotential at a current density of 100 mA cm−2 were 0.85 Ω cm−2 and 110 mV in dry air, which decreased to 0.43 Ω cm−2 and 52 mV, respectively, in wet air (∼3% H2O) at 650 °C. A decrease in impedance was also observed with polarization time; this was possibly caused by polarization-induced microstructure optimization. A promising peak power density of ∼585 mW cm−2 was demonstrated by an anode-supported cell with a BCFN cathode at 700 °C.

Deactivation and regeneration of oxygen reduction reactivity on double perovskite Ba2Bi0.1Sc0.2Co1.7O6−x cathode for intermediate-temperature solid oxide fuel cells

in situ high-temperature X-ray diffraction and thermal gravimetric- differential thermal analysis on room-temperature powder, as well as X-ray diffraction, Raman spectroscopy, and transmission electron microscopy on quenched powder, were applied to study crystal structure and phase transformations in Ba₂Bi_0.1Sc_0.2Co _1.7O_6-x (BBSC). Heating BBSC in air to over 800 °C produces a pure cubic phase with space group Fm3m (no. 225), and cooling down below 800 °C leads to a mixture of three noncubic phases including an unknown phase between 200 and 650 °C, a 2H hexagonal BaCoO3 with space group P63/mmc (no. 194) between 600 and 800 °C, and an intermediate phase at 800 °C. These three phases exist concurrently with the major cubic phase. The weight gain and loss between 300 and 900 °C suggest the occurrence of cobalt reduction, oxidation, and disproportion reactions with dominant reduction reaction at above 600 °C. The thermal expansion of BBSC was also examined by dilatometry. BBSC has a highly temperature-dependent thermal expansion coefficient which relates well with its structure evolution. Furthermore, the oxygen reduction reaction (ORR) of BBSC was probed by symmetrical cell and three-electrode configurations. The presence of hexagonal phase at 700 °C rarely affects the ORR performance of BBSC as evidenced by a slight increase of its area-specific resistance (ASR) value following 48 h of testing in this three-electrode configuration. This observation is in contrast to the commonly held point of view that noncubic phase deteriorates performance of perovskite compounds (especially in oxygen transport applications). Moreover, cathodic polarization treatment, for example, current discharge from BBSC (tested in three-electrode configuration), can be utilized to recover the original ORR performance. The cubic structure seems to be retained on the cathodic polarization - the normal cathode operating mode in fuel cells. Stable 72-h performance of BBSC in cathodic polarization mode further confirms that despite the presence of phase impurities, BBSC still demonstrates good performance between 500 and 700 °C, the desired intermediate operating temperature in solid oxide fuel cells.

A single-step synthesized cobalt-free barium ferrites-based composite cathode for intermediate temperature solid oxide fuel cells

Cobalt-free perovskite cathode with excellent oxygen reduction reaction (ORR) properties below 800 °C is a key material toward wide implementation of intermediate-temperature solid oxide fuel cells. This work reports the phase structure, microstructure and performance of such cathode based on the composite phases of triclinic Ba0.9Bi0.1FeO3-δ, cubic BaFeO3 and orthorhombic BaFe2O4 prepared by sol–gel route. The resultant barium ferrites composite cathode exhibits uniform particles, pores and elements distribution. In particular, favorable ORR properties of this cathode is demonstrated by very low interfacial resistance of only 0.036 and 0.072 Ω cm2 at 750 and 700 °C and maximum power density of 1295 and 840 mW cm−2 at 750 and 700 °C.

Analysis of the current distribution in an aluminum electrolysis cell with copper collector-bar cathode assembly

Understanding the magneto-hydrodynamic forces generated due to the external magnetic field and current density distribution within the cell (current in cell linings) is important in the optimization of cell dynamics. It is well documented that these factors play a crucial role in establishing the metal-pad stability of the cell. Conventional cells use the cathode-collector-bar assembly to carry the current through molten aluminium, the cathode and the steel collector-bar to nearest external bus. The electrical conductivity of the steel is so poor relative to the molten aluminium that the outer third of the collector bar carries the maximum load, which in turn increases the horizontal components of the current within the cell. Previous studies have modelled improvement in the cell instability through external magnetic compensation by redistributing current in the cathode busbar. Very little to date has been published on work to improve the current distribution within the cell. In this work, the current distribution in an aluminium electrolysis cell with copper collector-bar was predicted using finite element modelling. A 2D cross-section of a commercial cell was used under steady conditions of electrical fields in anode, electrolyte, molten aluminium and copper cathode-assembly. Different shapes and sizes of the cathode assembly are also considered to optimise the distribution of current throughout the cathode lining. The findings indicated that the copper-bar of similar size to steel could save voltage up to 150 mV. There is a reduction of more than 70% in peak current density value due to the copper inserts. The predicted trends of current distribution show a good agreement with previously published data.

Current distribution and Lorentz field modelling using cathode designs : a parametric approach

A mathematical model of magnetohydrodynamic (MHD) effects in an aluminium cell using numerical approximation of a finite element method is presented. The model predicts the current distribution in the cell and calculates the Lorentz force from the external magnetic field in molten metal for cathode blocks with different surface inclinations.

The findings indicated that the cathode surface inclinations have significant influence on cathode current density and Lorentz field distribution in the molten metal. The results establish a trend for the current density and associated MHD force distributions with increase in cathode inclination angle, φ. It has been found that cathode with φ = 5^o inclination could decrease 16 to 20 % of Lorentz force in the molten metal.

Electrospun spinel LiNi0.5Mn1.5O4 hierarchical nanofibers as 5 v cathode materials for lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 hierarchical nanofibers with diameters of 200–500 nm and lengths of up to several tens of micrometers were synthesized using low-cost starting materials by electrospinning combined with annealing. Well-separated nanofiber precursors impede the growth and agglomeration of Li-Ni0.5Mn1.5O4 particles. The hierarchical nanofibers were constructed from attached LiNi0.5Mn1.5O4 nanooctahedrons with sizes ranging from 200 to 400 nm. It is proven that these Li-Ni0.5Mn1.5O4 hierarchical nanofibers exhibit a favorable electrochemical performance. At a 0.5C (coulombic) rate, it shows an initial discharge capacity of 133 mAhg_1 with a capacity retention over 94% after 30 cycles. Even at 2, 5, 10, and 15C rates, it can still deliver a discharge capacity of 115, 100, 90, and 80 mAhg_1, respectively. Compared with self-aggregated nanooctahedrons synthesized using common sol–gel methods, the LiNi0.5Mn1.5O4 hierarchical nanofibers exhibit a much higher capacity. This is owing to the fact that the self-aggregation of the unique nanooctahedron-in-nanofiber structure has been greatly reduced because of the attachment of nanopolyhedrons in the long nanofibers. This unique microstructured cathode results in the large effective contact areas of the active materials, conductive additives and fully realize the advantage of nanomaterial-based cathodes.

The significant effect of the phase composition on the oxygen reduction reaction activity of a layered oxide cathode

Layered oxides of Sr4Fe4Co2O13 (SFC2) which contains alternating perovskite oxide octahedral and polyhedral oxide double layers are attractive for their mixed ionic and electronic conducting and oxygen reduction reaction properties. In this work, we used the EDTA–citrate synthesis technique to prepare SFC2 and vary the calcination temperature between 900 and 1100 _C to obtain SFC2, containing different phase content of perovskite (denoted as SFC-P) and (Fe,Co) layered oxide phases (SFC-L). Rietveld refinements show that the SFC-P phase content increased from _39 wt% to _50 wt% and _61 wt% as the calcination temperature increased from 900 _C (SFC2-900) to 1000 _C (SFC2-1000) and 1050 _C (SFC2-1050). At 1100 _C (SFC2-1100), SFC-P became the dominant phase. The oxygen transport properties (e.g. oxygen chemical diffusion coefficient and oxygen permeability), electrical conductivity and oxygen reduction reaction activity is enhanced in the order of SFC2-1000, SFC2-1100 and SFC2-1050. The trend established here therefore negates the hypothesis that the perovskite phase content correlates with the oxygen transport property enhancement. The results suggest instead that there is an optimum composition value (e.g. 61 wt% of SFC-L for SFC2-1050 in this work) on which synergistic effects take place between the SFC-P and SFC-L phase.