Microwave-induced combustion synthesis and electrical properties of Ce1−xSmxO2−1/2x ceramics

Ce_1−xSm_xO_2−1/2x nanopowders were successfully synthesized by microwave-induced combustion process. For the preparation, cerium(III) nitrate hexahydrate, samarium(III) nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only a few minutes to obtain Ce_1−xSm_xO_2−1/2x powders. Ce_1−xSm_xO_2−1/2x ceramics prepared by microwave-induced process sintered at 1400 °C for 3 h, the bulk density of Ce_1−xSm_xO_2−1/2x ceramics were over 95% of the theoretical density. The results revealed that Ce_0.84Sm_0.16O_1.92 possessed the maximum electrical conductivity was 0.0287 S cm⁻¹ at 850 °C and the minimum activity energy, E_a was 0.9565 eV determined from 500 to 850 °C.     

Hydrothermal preparation and electrochemical properties of Gd3+ and Bi3+, Sm3+, La3+, and Nd3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell

The structure, the thermal expansion coefficient, electrical conductivities of Ce_0.8Gd_0.2?xM_xO_2?δ (for M: Bi, x = 0–0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28–59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C. The maximum conductivity, σ_700 °C around 4.46 × 10^?2 S cm^?1 with E_a = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ_700 °C around 2.88 × 10^?2 S cm^?1 with E_a = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce_0.8Gd_0.1Bi_0.1O_2?δ is found to be 1.2 × 10^?19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10^?6 K^?1 for the CeO₂, 12.1 × 10^?6 K^?1 for Ce_0.8Gd_0.2O_2?δ, and increase with co-doping to 14.2 × 10^?6 K^?1 for Ce_0.8Gd_0.18Bi_0.02O_2?δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.     

Electrochemical properties of iodine-containing lithium manganese oxide spinel

Iodine-containing, cation-deficient, lithium manganese oxides (ICCD-LMO) are prepared by reaction of MnO₂ with LiI. The MnO₂ is completely transformed into spinel-structured compounds with a nominal composition of Li_1−δMn_2−2δO₄I_x. A sample prepared at 800 °C, viz. Li_0.99Mn_1.98O₄I_0.02, exhibits an initial discharge capacity of 113 mA h g⁻¹ with good cycleability and rate capability in the 4-V region. Iodine-containing, lithium-rich lithium manganese oxides (ICLR-LMO) are also prepared by reaction of LiMn₂O₄ with LiI, which results in a nominal composition of Li_1+xMn_2−xO₄I_x. Li_1.01Mn_1.99O₄I_0.02 shows a discharge capacity of 124 mA h g⁻¹ on the first cycle and 119 mA h g⁻¹ a on the 20th cycle. Both results indicate that a small amount of iodine species helps to maintain cycle performance.     

Crystal structures,electrical conductivities and electrochemical properties of LiCo1−xMgxO2 (0 ≤ x ≤ 0.11)

LiCoO₂ is commercially available cathode electrode materials of lithium-ion batteries. In an attempt to improve the performance of lithium batteries with enhanced safety, LiCo_1−xMg_xO₂ was synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray diffraction and Rietveld refinement. LiCo_1−xMg_xO₂ give a single phase of a layered structure with the space group R-3m of hexagonal systems for x ≤ 0.11. A second phase of MgO was observed in LiCo_1−xMg_xO₂ for x ≥ 0.13. The calculated cation–anion distances and angles from the Rietveld refinement were changed with Mg content in samples. With the increase in Mg content in LiCo_1−xMg_xO₂, distances between CoO₂ slabs were increased. The electrical conductivities of sintered samples were measured at room temperature by the Van der Pauw method. The electrical conductivities of LiCo_1−xMg_xO₂ increased with Mg content. On the basis of the Hall effect analysis, the increase in electrical conductivities with Mg content is believed due to the increased carrier concentrations, while the carrier mobility was almost invariant with the Mg content. The electrochemical performance of LiCo_1−xMg_xO₂ was evaluated by coin cell test.     

Layered Li(Ni0.5−xMn0.5−xM2x′)O2 (M′=Co,Al, Ti; x=0, 0.025) cathode materials for Li-ion rechargeable batteries

Layered Li(Ni_0.5−xMn_0.5−xM_2x′)O₂ materials (M′=Co, Al, Ti; x=0, 0.025) were synthesized using a manganese-nickel hydroxide precursor, and the effect of dopants on the electrochemical properties was investigated. Li(Ni_0.5Mn_0.5)O₂ exhibited a discharge capacity of 120 mAh/g in the voltage range of 2.8–4.3 V with a slight capacity fade up to 40 cycles (0.09% per cycle); by doping of 5 mol% Co, Al, and Ti, the discharge capacities increased to 140, 142, and 132 mAh/g, respectively, and almost no capacity fading was observed. The cathode material containing 5 mol% Co had the lowest impedance, 47 Ω cm², while undoped, Ti-doped, and Al-doped materials had impedance of 64, 62, and 99 Ω cm², respectively. Unlike the other dopants, cobalt was found to improve the electronic conductivity of the material. Further improvement in the impedance of these materials is needed to meet the requirement for powering hybrid electric vehicle (HEV, <35 Ω cm²). In all materials, structural transformation from a layered to a spinel structure was not observed during electrochemical cycling. Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) data suggested that Ni and Mn exist as Ni²⁺ and Mn⁴⁺ in the layered structure. Differential scanning calorimetry (DSC) data showed that exothermic peaks of fully charged Li_1−y(Ni_0.5−xMn_0.5−xM_2x′)O₂ appeared at higher temperature (270–290 °C) than LiNiO₂-based cathode materials, which indicates that the thermal stability of Li(Ni_0.5−xMn_0.5−xM_2x′)O₂ is better than those of LiNiO₂-based cathode materials.     

Characterization of Zn- and Fe-substituted LiMnO2 as cathode materials in Li-ion cells

Layered LiMn_1−xM_xO₂ (M = Zn or Fe) (0 ≤ x ≤ 0.3) samples are synthesized from the corresponding sodium analogues by an ion-exchange method using LiBr in n-hexanol at 160 °C. The samples are subjected to physicochemical and electrochemical characterization. X-ray diffraction data indicate the formation of layered structures for the LiMn_1−xZn_xO₂ samples up to x = 0.3 and for LiMn_1−xFe_xO₂ samples up to x = 0.2. Among these, LiMn_0.95Zn_0.05O₂ and LiMn_0.95Fe_0.05O₂ provide the highest capacity values of 180 and 193 mAh g⁻¹, respectively. Both Zn- and Fe-substituted samples display good capacity retention up to 30 charge–discharge cycles. Electrochemical impedance spectroscopy and galvanostatic intermittent titration data corroborate the results obtained from cyclic volatmmetry and charge–discharge cycling.     

Synthesis and characterizations of Li[CrxLi(1−x)/3Mn2(1−x)/3]O2 (0.15 ≤ x ≤ 0.3) cathode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ (0.15 ≤ x ≤ 0.3) cathode materials was prepared by citric acid-assisted, sol–gel process. Sub-micron sized particles were obtained and the X-ray diffraction (XRD) results showed that the crystal structure was similar to layered lithium transition metal oxides (R-3m space group). The electrochemical performance of the cathodes was evaluated over the voltage range 2.0–4.9 V at a current density of 7.947 mA g⁻¹. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of up to 280 mAh g⁻¹ during cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ yielded a promising cathode material.     

Chemical and structural instabilities of lithium ion battery cathodes

The chemical and structural stabilities of various layered Li_1−xNi_1−y−zMn_yCo_zO₂ cathodes are compared by characterizing the samples obtained by chemically extracting lithium from the parent Li_1−xNi_1−y−zMn_yCo_zO₂ with NO₂BF₄ in an acetonitrile medium. The nickel- and manganese-rich compositions such as Li_1−xNi_1/3Mn_1/3Co_1/3O₂ and Li_1−xNi_0.5Mn_0.5O₂ exhibit better chemical stability than the LiCoO₂ cathode. While the chemically delithiated Li_1−xCoO₂ tends to form a P3 type phase for (1 − x) < 0.5, Li_1−xNi_0.5Mn_0.5O₂ maintains the original O3 type phase for the entire 0 ≤ (1 − x) ≤ 1 and Li_1−xNi_1/3Mn_1/3Co_1/3O₂ forms an O1 type phase for (1 − x) < 0.23. The variations in the type of phases formed are explained on the basis of the differences in the chemical lithium extraction rate caused by the differences in the degree of cation disorder and electrostatic repulsions. Additionally, the observed rate capability of the Li_1−xNi_1−y−zMn_yCo_zO₂ cathodes bears a clear relationship to cation disorder and lithium extraction rate.     

Synthesis and electrochemical properties of Li[Ni0.8Co0.1Mn0.1]O2 and Li[Ni0.8Co0.2]O2 via co-precipitation

Spherical Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) with phase-pure and well-ordered layered structure have been synthesized by heat-treatment of spherical [Ni_0.8Co_0.2−xMn_x](OH)₂ and LiOH·H₂O precursors. The structure, morphology, electrochemical properties, and thermal stability of Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) were studied. The average particle size of the powders was about 10–15 μm and the size distribution was narrow due to the homogeneity of the metal hydroxide [Ni_0.8Co_0.2−xMn_x](OH)₂ (x = 0, 0.1). The Li[Ni_0.8Co_0.2−xMn_x]O₂ (x = 0, 0.1) delivered a discharge capacity of 197–202 mAh g⁻¹ and showed excellent cycling performance. Compared to Li[Ni_0.8Co_0.2]O₂, Li[Ni_0.8Co_0.1Mn_0.1]O₂ exhibited greater thermal stability resulting from improved structural stability due to Mn substitution.     

Effect of titanium substitution in layered LiNiO2 cathode material prepared by molten-salt synthesis

LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) compounds have been synthesized by a direct molten-salt method that uses a eutectic mixture of LiNO₃ and LiOH salts. According to X-ray diffraction analysis, these materials have a well-developed layered structure (R3-m) and are an isostructure of LiNiO₂. The LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) compounds have average particle sizes of 1–5 μm depending on the amount of Ti salt. Charge–discharge tests show that a LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) cathode prepared at 700 °C has an initial discharge capacity as high as 171 mA h g⁻¹ and excellent capacity retention in the range 4.3–2.8 V at a current density of 0.2 mA cm⁻².     

Synthesis and characterization of lithium aluminum-doped spinel (LiAlxMn2−xO4) for lithium secondary battery

LiAl_xMn_2−xO₄ has been synthesized using various aluminum starting materials, such as Al(NO₃)₃, Al(OH)₃, AlF₃ and Al₂O₃ at 600–800°C for 20 h in air or oxygen atmosphere. A melt-impregnation method was used to synthesize Al-doped spinel with good battery performance in this research. The Al-doped content and the intensity ratio of (3 1 1)/(4 0 0) peaks can be important parameters in synthesizing Al-doped spinel which satisfies the requirements of high discharge capacity and good cycleability at the same time. The decrease in Mn³⁺ ion by Al substitution induces a high average oxidation state of Mn ion in the LiAl_xMn_2−xO₄ material. The electrochemical behavior of all samples was studied in Li/LiPF₆-EC/DMC (1:2 by volume)/LiAl_xMn_2−xO₄ cells. Especially, the initial and last discharge capacity of LiAl_0.09Mn_1.97O₄ using LiOH, Mn₃O₄ and Al(OH)₃ complex were 128.7 and 115.5 mAh/g after 100 cycles. The Al substitution in LiMn₂O₄ was an excellent method of enhancing the cycleability of stoichiometric spinel during electrochemical cycling.     

Rapid thermal annealing effect on surface of LiNi1−xCoxO2 cathode film for thin-film microbattery

The effect of rapid thermal annealing (RTA) on the surface of a LiNi_1−xCo_xO₂ cathode film is examined by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and auger electron spectroscopy (AES). It is found that the as-deposited LiNi_1−xCo_xO₂ film undergoes a surface reaction with oxygen in the air, due to the high activity of lithium in the film. AES spectra indicate that the surface layer consists of lithium and oxygen atoms. The RTA process at 500 °C eliminates the surface layer to some extent. An increase in annealing temperature to 700 °C results in complete elimination of the surface layer. The surface evolution of the LiNi_1−xCo_xO₂ film with increasing annealing time at 700 °C is examined by means of AFM examination. It is found that the surface layer, which is initially present in the form of an amorphous like-film, becomes agglomerated and then vaporizes after 5 min of annealing. A thin-film microbattery (TFB), fabricated by using the LiNi_1−xCo_xO₂ film without a surface layer, exhibits more stable cycliability and a higher specific discharge capacity of 60.2 μAh cm⁻² μm than a TFB with an unannealed LiNi_1−xCo_xO₂ film. Therefore, it is important to completely eliminate the surface layer in order to achieve high performance from all solid-state thin-film microbatteries.     

The improved physical and electrochemical performance of LiNi0.35Co0.3−xCrxMn0.35O2 cathode materials by the Cr doping for lithium ion batteries

We have successfully prepared the layered structure LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ with various Cr contents by a co-precipitation method. Many measurement methods have been applied to characterize the physical and electrochemical properties of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂, such as XRD, SEM, BET and electrochemical test. SEM showed that the addition of Cr has obviously changed the morphologies of their particles and increased the size of grains. The specific surface area of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ decreases lineally from 4.9 m² g⁻¹ (x = 0) to 1.8 m² g⁻¹ (x = 0.1) with the increasing of Cr contents. Moreover, we have found that the Cr doping can greatly improve the density of the powder, which is beneficial to solve the problem of lower electrode density for these layered LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ cathode materials. Electrochemical test indicated that the cycling performance of LiNi_0.35Co_0.3−xCr_xMn_0.35O₂ can be significantly improved with the increasing of Cr contents, although the initial discharge capacity of the sample has a little decrease.     

Synthesis and electrochemical properties of Mo-doped Li[Ni1/3Mn1/3Co1/3]O2 cathode materials for Li-ion battery

The layered Li[Ni_(1−x)/3Mn_(1−x)/3Co_(1−x)/3Mo_x]O₂ cathode materials (x = 0, 0.005, 0.01, and 0.02) were prepared by a solid-state pyrolysis method (700, 800, 850, and 900 °C). Its structure and electrochemical properties were characterized by XRD, SEM, XPS, cyclic voltammetry, and charge/discharge tests. It can be learned that the doped sample of x = 0.01 calcined at 800 °C shows the highest first discharge capacity of 221.6 mAh g⁻¹ at a current density of 20 mA g⁻¹ in the voltage range of 2.3–4.6 V, and the Mo-doped samples exhibit higher discharge capacity and better cycle-ability than the undoped one at room temperature.     

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.     

Effect of (Al,Mg) substitution in LiNiO2 electrode for lithium batteries

Stabilized lithium nickelate is receiving increased attention as a low-cost alternative to the LiCoO₂ cathode now used in rechargeable lithium batteries. Layered LiNi_1−x−yM_xM_yO₂ samples (M_x = Al³⁺ and M_y = Mg²⁺, where x = 0.05, 0.10 and y = 0.02, 0.05) are prepared by the refluxing method using acetic acid at 750 °C under an oxygen stream, and are subsequently subjected to powder X-ray diffraction analysis and coin-cell tests. The co-doped LiNi_1−x−yAl_xMg_yO₂ samples show good structural stability and electrochemical performance. The LiNiAl_0.05Mg_0.05O₂, cathode material exhibits a reversible capacity of 180 mA h g⁻¹ after extended cycling. These results suggest that the threshold concentration for aluminum and magnesium substitution is of the order of 5%. The co-substitution of magnesium and aluminium into lithium nickelate is considered to yield a promising cathode material.     

Preparation and properties of ceramic interconnecting materials,La0.7Ca0.3CrO3−δ doped with GDC for IT-SOFCs

One of the challenges for improving the performance and cost-effectiveness of solid oxide fuel cells (SOFCs) is the development of effective interconnect materials. A widely used interconnect ceramic for SOFCs is doped lanthanum chromite. In this paper, we report a doped lanthanum chromite, La_0.7Ca_0.3CrO_3−δ (LCC) + x wt.% Gd_0.2Ce_0.8O_1.9 (GDC) (x = 0–10), with improved electrical conductivity and sintering capability. In this composite material system, LCC + GDC were prepared by an auto-ignition process and the electrical conductivity was characterized in air and in H₂. The LCC powders exhibited a better sintering ability and could reach a 94.7% relative density at 1400 °C for 4 h in air and with the increase of GDC content the relative density increased, reached 98.5% when the GDC content was up to 10 wt.%. The electrical conductivity of the samples dramatically increased with GDC addition until a maximum of 134.48 S cm⁻¹ in air at 900 °C when the materials contained 3 wt.% GDC. This is 5.5 times higher than pure LCC (24.63 S cm⁻¹). For the sample with a 1 wt.% GDC content, the conductivity in pure H₂ at 900 °C was a maximum 5.45 S cm⁻¹, which is also higher than that of pure LCC ceramics (4.72 S cm⁻¹). The average thermal expansion coefficient (TEC) increased with the increase of GDC content, ranging from 11.12 to 14.32 × 10⁻⁶ K⁻¹, the majority of which unfortunately did not match that of 8YSZ. The oxygen permeation measurement presented a negligible oxygen ionic conduction, indicating that it is still an electronically conducting ceramic. Therefore, it is a very promising interconnect material for higher performance and cost-effectiveness for SOFCs.     

Stannum doping of layered LiNi3/8Co2/8Mn3/8O2 cathode materials with high rate capability for Li-ion batteries

Sn doped lithium nickel cobalt manganese composite oxide of LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ (0 ≤ x ≤ 0.10) was synthesized by stannum substitute of manganese to enhance its rate capability at first time. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), SEM, cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and charge/discharge tests. LiNi_3/8Co_2/8Mn_3/8−xSn_xO₂ had stable layered structure with α-NaFeO₂ type as x up to 0.05, meanwhile, its chemical diffusion coefficient D_Li of Li-ion was enhanced by almost one order of magnitude, leading to notable improvement of the rate capability of LiNi_3/8Co_2/8Mn_3/8O₂. The compound of x = 0.10 showed the best rate capability among Sn doped samples, but its discharge capacity reduced markedly due to secondary phase Li₂SnO₃ and increase of cation-disorder. The compound with x = 0.05 showed high rate capability with initial discharge capacity in excess of 156 mAh g⁻¹. It is a promising alternative cathode material for EV application of Li-ion batteries.     

Composition and porosity graded La2−xNiO4+δ (x ≥ 0) interlayers for SOFC: Control of the microstructure via a sol–gel process

We have developed composition and porosity graded La_2−xNiO_4+δ (x ≥ 0) cathode interlayers for low-temperature solid oxide fuel cell that exhibit good adhesion with the electrolyte, controlled porosity and grain size and good electrochemical behaviour. La_2−xNiO_4+δ (x ≥ 0) monolayers are elaborated from a derived sol–gel method using nitrate salts, acetylacetone and hexamethylenetetramine in acetic acid. As a function of the organic concentration and the molar ratio of lanthanum to nickel, these layers present platelets or spherical shape grains with a size distribution ranging from 50 to 200 nm, as verified by SEM-FEG. On the basis of this processing protocol, we prepared porosity and composition graded lanthanum nickelates interlayers with effective control of the pore distribution, the nanocrystalline phase, the thickness and the subsequent electrochemical properties.     

Ni1−xCux alloy-based anodes for low-temperature solid oxide fuel cells with biomass-produced gas as fuel

Ni–Cu alloy-based anodes, Ni_1−xCu_x (x = 0, 0.05, 0.2, 0.3)–Ce_0.8Sm_0.2O_1.9 (SDC), were developed for direct utilization of biomass-produced gas in low-temperature solid oxide fuel cells (LT-SOFCs) with thin film Ce_0.9Gd_0.1O_1.95 electrolytes. The alloys were formed by in situ reduction of Ni_1−xCu_xO_y composites synthesized using a glycine-nitrate technique. The electrolyte films were fabricated with a co-pressing and co-firing technique. Electrochemical performance of the Ni_1−xCu_x–SDC anode supported cells was investigated at 600 °C when humidified (3% H₂O) biomass-produced gas (BPG) was used as the fuel and stationary air as the oxidant. With Ni–Cu alloys as anodes, carbon deposition was substantially suppressed and electrochemical performance of the cells was sustained for much longer periods of time. For example, the power export of a Ni–SDC supported cell was only 50% of the initial value (200 mW cm⁻² at 0.5 V) after 20 min, while Ni_0.8Cu_0.2–SDC supported cells could maintain 90% of the initial power density (250 mW cm⁻² at 0.5 V) over a period of 10 h. The improved performance of the Ni–Cu alloy-based anodes is worth considering in developing SOFCs fueled directly with dilute hydrocarbons such as gases derived from biomass.