Characterization of LiCoO2 coated Li1.05Ni0.35Co0.25Mn0.4O2 cathode material for lithium secondary cells

In this study, nano-crystalline LiCoO₂ was coated onto the surface of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ powders via sol–gel method. The influence of the coating on the electrochemical behavior of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ is discussed. The surface morphology was characterized by transmission electron microscopy (TEM). Nano-crystallized LiCoO₂ was clearly observed on the surfaces of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂. The phase and structural changes of the cathode materials before and after coating were revealed by X-ray diffraction spectroscopy (XRD). It was found that LiCoO₂ coated Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ cathode material exhibited distinct surface morphology and lattice constants. Cyclic voltammetry (2.8–4.6 V versus Li/Li⁺) shows that the characteristic voltage transitions on cycling exhibited by the uncoated material are suppressed by the 7 wt.% LiCoO₂ coating. This behavior implies that LiCoO₂ inhibits structural change of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ or reaction with the electrolyte on cycling. In addition, the LiCoO₂ coating on Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ significantly improves the rate capability over the range 0.1–4.0C. Comparative data for the coated and uncoated materials are presented and discussed.     

Electrochemical performance of SrF2-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

SrF₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials with improved cycling performance over 2.5–4.6 V were investigated. The structural and electrochemical properties of the materials were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), charge–discharge tests and electrochemical impedance spectra (EIS). The results showed that the crystalline SrF₂ with about 10–50 nm particle size is uniformly coated on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particles. As the coating amount increased from 0.0 to 2.0 mol%, the initial capacity and rate capability of the coated LiNi_1/3Co_1/3Mn_1/3O₂ decreased slightly owing to the increase of the charge-transfer resistance; however, the cycling stability was improved by suppressing the increase of the resistance during cycling. 4.0 mol% SrF₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ showed remarkable decrease of the initial capacity. 2.0 mol% coated sample exhibited the best electrochemical performance. It presented an initial discharge capacity of 165.7 mAh g⁻¹, and a capacity retention of 86.9% after 50 cycles at 4.6 V cut-off cycling.     

Electrochemical studies on LiCoO2 surface coated with Y3Al5O12 for lithium-ion cells

Synthesized yttrium aluminum garnet (YAG) sol was coated on the surface of the LiCoO₂ cathode particles by an in situ sol–gel process, followed by calcination at 923 K for 10 h in air. Based on XRD, TEM, and ESCA data, a compact YAG kernel with an average thickness of ∼20 nm was formed on the surface of the core LiCoO₂ particles, which ranged from ∼90 to 120 nm in size. The charge–discharge cycling studies for the coated materials suggest that 0.3 wt.% YAG-coated LiCoO₂ heated at 923 K for 10 h in air, delivered a discharge capacity of 167 mAh g⁻¹ and a cycle stability of about 164 cycles with a fading rate of 0.2 mAh cycle⁻¹ at a 0.2C-rate between 2.75 and 4.40 V vs. Li/Li⁺. The differential capacity plots revealed that impedance growth was slower for YAG surface treated LiCoO₂, when cells were charged at 4.40 V. DSC results exemplified that the exothermic peak at ∼468 K corresponded to the release of much less oxygen and greater thermal-stability.     

Fabrication of all solid-state lithium-ion batteries with three-dimensionally ordered composite electrode consisting of Li0.35La0.55TiO3 and LiMn2O4

A composite electrode between three-dimensionally ordered macroporous (3DOM) Li_0.35La_0.55TiO₃ (LLT) and LiMn₂O₄ was fabricated by colloidal crystal templating method and sol–gel process. A close-packed PS beads with the opal structure was prepared by filtration of a suspension containing PS beads. Li–La–Ti–O sol was injected by vacuum impregnation process into the voids between PS beads, and then was heated to form 3DOM-LLT. Three-dimensionally ordered composite material consisting of LiMn₂O₄ and LLT was prepared by sol–gel process. The prepared composite was characterized with SEM and XRD. All solid-state Li-ion battery was fabricated with the LLT–LiMn₂O₄ composite electrode as a cathode, dry polymer electrolyte and Li metal anode. The prepared all solid-state cathode exhibited a volumetric discharge capacity of 220 mAh cm⁻³.     

All-solid-state lithium secondary batteries with oxide-coated LiCoO2 electrode and Li2S–P2S5 electrolyte

All-solid-state lithium secondary batteries using LiCoO₂ active materials coated with Li₂SiO₃ and SiO₂ oxide films and Li₂S–P₂S₅ solid electrolytes were fabricated and their electrochemical performance was investigated. The electrochemical performace of the all-solid-state cells at a high voltage region was highly improved by using oxide-coated LiCoO₂. The oxide coatings are effective in suppressing the formation of an interfacial resistance between LiCoO₂ and the solid electrolyte at a high cutoff voltage of 4.6 V (vs. Li). As a result, charge–discharge capacities and cycle performance at the cutoff voltage were improved. The cell with Li₂SiO₃-coated LiCoO₂ showed a large initial discharge capacity of 130 mAh g⁻¹ and a good capacity retention of 110 mAh g⁻¹ after 50th cycles at the cutoff voltage of 4.6 V (vs. Li).     

Effect of TiO2-coating on the electrochemical performances of LiCo1/3Ni1/3Mn1/3O2

A novel method to improve the cycling performance of LiCo_1/3Ni_1/3Mn_1/3O₂ in lithium-ion batteries by TiO₂-coating with an in situ dipping and hydrolyzing method was presented in this work. The microstructure of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was characterized by XRD, SEM and TEM, and their electrochemical performances were evaluated by EIS and galvonostatic charge-discharge test. SEM and TEM images show that the TiO₂ are pasted on the surface of the LiCo_1/3Ni_1/3Mn_1/3O₂ with nano-size. The XRD patterns indicate that the crystal structure of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ shows no obvious change compares with the bare material. The TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ possesses improved cycle performance and rate capability. The capacity retention of 1.0 wt.% TiO₂-coated material is more than 99.0% after 12 cycles at 3.0 C while that of the bare sample is only 86.6%. The capacity of coated material at 5.0 C remains 66.0% of the capacity at 0.2 C, while that of the bare LiCo_1/3Ni_1/3Mn_1/3O₂ is only 31.5%.     

AlF3-coated LiCoO2 and Li[Ni1/3Co1/3Mn1/3]O2 blend composite cathode for lithium ion batteries

Surface modifications of electrode materials can improve the electrochemical and thermal properties of cathodes for use in lithium batteries. In this study, AlF₃-coated LiCoO₂ and AlF₃-coated Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode materials are blended, as both have the same crystal structure and exhibit similar electrochemical properties. The composite electrodes exhibit high discharge capacities of 180-188 mAh g⁻¹ in a voltage range of 3.0-4.5 V at room temperature. The capacity retention of the composite electrode is greater than 95% of the initial capacity after 50 cycles. The thermal stability of these composite electrodes is greatly improved because of the superior thermal stability of AlF₃-coated Li[Ni_1/3Co_1/3Mn_1/3]O₂. The blended AlF₃-coated LiCoO₂ and AlF₃-coated Li[Ni_1/3Co_1/3Mn_1/3]O₂ electrode shows two exothermic peaks, one at 227 °C from AlF₃-coated LiCoO₂ and another at 277 °C from AlF₃-coated Li[Ni_1/3Co_1/3Mn_1/3]O₂, accompanied by significantly reduced exothermic heat generation.     

Effect of FePO4 coating on electrochemical and safety performance of LiCoO2 as cathode material for Li-ion batteries

LiCoO₂ was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO₄-coated LiCoO₂ was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO₄-coated LiCoO₂ exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g⁻¹ and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO₂ is greatly enhanced. These improvements are attributed to the FePO₄ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. The FePO₄-coated LiCoO₂ could be a high performance cathode material for lithium-ion battery.     

Al2O3-coated nanoporous TiO2 electrode for solid-state dye-sensitized solar cell

This paper reports the preparation of a core-shell nanoporous electrode consisting of an inner TiO₂ porous matrix and a thin overlayer of Al₂O₃, and its application for solid-state dye-sensitized solar cell using p-CuI as hole conductor. Al₂O₃ overlayer was coated onto TiO₂ porous film by the surface sol–gel process. The role of Al₂O₃ layer thickness on the cell performance was investigated. The solar cells fabricated from Al₂O₃-coated electrodes showed superior performance to the bare TiO₂ electrode. Under illumination of AM 1.5 simulated sunlight (89 mW/cm²), a ca. 0.19 nm Al₂O₃ overlayer increased the photo-to-electric conversion efficiency from 1.94% to 2.59%.     

In-situ XRD investigations on structure changes of ZrO2-coated LiMn0.5Ni0.5O2 cathode materials during charge

The structural changes of pristine and ZrO₂-coated LiMn_0.5Ni_0.5O₂ cathode materials were investigated by using in situ X-ray diffraction (XRD) during charging process. An obviously solid solution phase transition from a hexagonal structure (H1) to another hexagonal structure (H2) was observed during the charging process at a constant current of 0.3 mA in the potential range of 2.5–5.7 V. The second hexagonal structure has a shorter a-axis and a longer c-axis before the crystal collapse. Before the structure collapses the c-axis length increases to maximum and then significantly decreases to 14.1 Å. The c-axis length of the pristine and ZrO₂-coated LiMn_0.5Ni_0.5O₂ increases to the maximum at the charge capacity of 119.2 and 180.9 mAh g⁻¹, respectively. It can be concluded that the ZrO₂ coating can strongly stabilize the crystal structure of the LiMn_0.5Ni_0.5O₂ compound from the comparison of the lattice parameter variations between the pristine and the ZrO₂-coated LiMn_0.5Ni_0.5O₂ compounds upon charge. The potential fluctuation resulting from the decomposition of electrolytes starts at the charge capacity of around 200 and 260 mAh g⁻¹ for the pristine and ZrO₂-coated LiMn_0.5Ni_0.5O₂, respectively. It suggests that the ZrO₂ coating layer can impede the reaction between the cathode material and electrolyte.     

Improvement in dye-sensitized solar cells employing TiO2 electrodes coated with Al2O3 by reactive direct current magnetron sputtering

A novel surface modification method was carried out by reactive dc magnetron sputtering to fabricate TiO₂ electrodes coated with Al₂O₃ for improving the performance of dye-sensitized solar cells (DSSCs). The Al₂O₃-coated TiO₂ electrodes had been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis spectrophotometer, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The study results revealed that the modification to TiO₂ increases dye absorption amount, reduces trap sites on TiO₂, and suppresses interfacial recombination. The impact of sputtering time on photoelectric performance of DSSCs was investigated. Sputtering Al₂O₃ for 4 min on 5-μm thick TiO₂ greatly improves all cell parameters, resulting in enhancing the conversion efficiency from 3.93% to 5.91%. Further increasing sputtering time decreases conversion efficiency.     

Electrochemical effects of ALD surface modification on combustion synthesized LiNi1/3Mn1/3Co1/3O2 as a layered-cathode material

Combustion synthesized Li(Ni_1/3Mn_1/3Co_1/3)O₂ particles are coated with thin, conformal layers of Al₂O₃ by atomic layer deposition (ALD). XRD, Raman, and FTIR are used to confirm that no change to the bulk, local structure occurs after coating. Electrochemical impedance spectroscopy (EIS) results indicate that the surface of the Li(Ni_1/3Mn_1/3Co_1/3)O₂ are protected from dissolution and HF attack after only 4-layers, or ∼8.8 Å of alumina. Electrochemical performance at an upper cutoff of 4.5 V is greatly enhanced after the growth of Al₂O₃ surface film. Capacity retention is increased from 65% to 91% after 100 cycles at a rate of C/2 with the addition of only two atomic layers. Due to the conformal coating, the effects on Li(Ni_1/3Mn_1/3Co_1/3)O₂ overpotential and capacity are negligible below six ALD-layers. We propose that the use of ALD for coating on Li(Ni_1/3Mn_1/3Co_1/3)O₂ particles makes the material a stronger replacement candidate for LiCoO₂ as a positive electrode in lithium ion batteries.     

Boron doped lithium trivanadate as a cathode material for an enhanced rechargeable lithium ion batteries

Boron was doped into lithium trivanadate through an aqueous reaction process followed by heating at 100 °C. The B-LiV₃O₈ materials as a cathode in lithium batteries exhibits a specific discharge capacity of 269.4 mAh g⁻¹ at first cycle and remains 232.5 mAh g⁻¹ at cycle 100, at a current density of 150 mAh g⁻¹ in the voltage range of 1.8–4.0 V. The B-LiV₃O₈ materials show excellent stability, with the retention of 86.30% after 100 cycles. These result values are higher than those previous reports indicating B-LiV₃O₈ prepared by our synthesis method is a promising candidate as cathode material for rechargeable lithium batteries. The enhanced discharge capacities and their stabilities indicate that boron atoms promote lithium transferring and intercalating/deintercalating during the electrochemical processes and improve the electrochemical performance of LiV₃O₈ cathode.     

Preparation of the composite LaNi3.7Al1.3/Ni–S–Co alloy film and its HER activity in alkaline medium

The composite LaNi_3.7Al_1.3/Ni–S–Co alloy film was prepared by molten salt electrolysis and aquatic electrodeposition orderly. With Na₃AlF₆–La₂O₃–Al₂O₃ (91:8:1) system as molten salt electrolyte, the LaNi_3.7Al_1.3 alloy film was obtained by galvanostatic electrolysis at 100 mA cm⁻². The results showed that the La³⁺ and Al³⁺ ions could be co-reduced on the nickel cathode to form LaNi_3.7Al_1.3 film, i.e. La³⁺ + 1.3Al³⁺ + 6.9e + 3.7Ni = LaNi_3.7Al_1.3 at c.a. −0.5 V, which is much lower than that of the theoretical decomposition potential of lanthanum and aluminum. With high HER activity, the composite LaNi_3.7Al_1.3/Ni–S–Co film (η₁₅₀ = 65 mV, 353 K) could absorb large amount of H atoms, which would be oxidized and therefore effectively avoid the dissolution of the Ni–S–Co film under the state of open-circuit and consequently prolong the lifetime of the cathode.     

Glass-containing composite cathode contact materials for solid oxide fuel cells

The feasibility of adding glass to conventional SOFC cathode contact materials in order to improve bonding to adjacent materials in the cell stack is assessed. A variety of candidate glass compositions are added to LSM and SSC. The important properties of the resulting composites, including conductivity, sintering behavior, coefficient of thermal expansion, and adhesion to LSCF and Mn_1.5Co_1.5O₄-coated 441 stainless steel are used as screening parameters. Adhesion of LSM to LSCF improved from 3.9 to 5.3 MPa upon addition of SCZ-8 glass. Adhesion of LSM to coated stainless steel improved from 1.8 to 3.9 MPa upon addition of Schott GM31107 glass. The most promising cathode contact material/glass composites are coated onto Mn_1.5Co_1.5O₄-coated 441 stainless steel substrates and subjected to area-specific resistance testing at 800 °C. In all cases, area-specific resistance is found to be in the range 2.5-7.5 mOhm cm² and therefore acceptable. Indeed, addition of glass is found to improve bonding of the cathode contact material layer without sacrificing acceptable conductivity.     

Hydrogen permeation on Al2O3-based nickel/cobalt composite membranes

Al₂O₃ was synthesized using the sol-gel process with aluminum isopropoxide as the precursor and primary distilled water as the solvent. Nickel and cobalt metal powders were used to increase the strength of the membranes. The Al₂O₃-based membranes were prepared using HPS following a mechanical alloying process. The phase transformation, thermal evolution, surface and cross-section morphology of Al₂O₃ and Al₂O₃-based membranes were characterized by XRD, TG-DTA and FE-SEM. The hydrogen permeation of Al₂O₃-based membranes was examined at 300–473 K under increasing pressure. Hydrogen permeation flux through an Al₂O₃-20wt%Co membrane was obtained to 2.36 mol m⁻² s⁻¹. Reaction enthalpy was calculated to 4.5 kJ/mol using a Van’t Hoff’s plot.     

Influence of metal oxide on LiBH4/2LiNH2/MgH2 system for hydrogen storage properties

In this study, various nanoscale metal oxide catalysts, such as CeO₂, TiO₂, Fe₂O₃, Co₃O₄, and SiO₂, were added to the LiBH₄/2LiNH₂/MgH₂ system by using high-energy ball milling. Temperature programmed desorption and MS results showed that the Li–Mg–B–N–H/oxide mixtures were able to dehydrogenate at much lower temperatures. The order of the catalytic effect of the studied oxides was Fe₂O₃ > Co₃O₄ > CeO₂ > TiO₂ > SiO₂. The onset dehydrogenation temperature was below 70 °C for the samples doped with Fe₂O₃ and Co₃O₄ with 10 wt.%. More than 5.4 wt.% hydrogen was released at 140 °C. X-ray diffraction indicated that the addition of metal oxides inhibited the formation of Mg(NH₂)₂ during ball milling processes. It is thought that the changing of the ball milling products results from the interaction of oxide ions in metal oxide catalysts with hydrogen atoms in MgH₂. The catalytic effect depends on the activation capability of oxygen species in metal oxides on hydrogen atoms in hydrides.     

Effects of TiO2 coating on high-temperature cycle performance of LiFePO4-based lithium-ion batteries

LiFePO₄ particles were coated with TiO₂ (molar ratio = 3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO₄ cathode at 55 °C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO₄/Li cell, it imposes a deteriorating effect on the LiFePO₄/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO₄ cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO₄/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO₄/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.     

Intermediate-to-low temperature protonic ceramic membrane fuel cells with Ba0.5Sr0.5Co0.8Fe0.2O3-δ–BaZr0.1Ce0.7Y0.2O3-δ composite cathode

The perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ–BaZr_0.1Ce_0.7Y_0.2O_3-δ (BSCF–BZCY) composite oxides were synthesized by a modified Pechini method and examined as a novel composite cathode for intermediate-to-low temperature protonic ceramic membrane fuel cells (ILT-PCMFCs). Thin proton-conducting BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) electrolyte and NiO–BaZr_0.1Ce_0.7Y_0.2O_3-δ (NiO–BZCY) anode functional layer were prepared over porous anode substrates composed of NiO–BaZr_0.1Ce_0.7Y_0.2O_3-δ by a one-step dry-pressing/co-firing process. A laboratory-sized quad-layer cell of NiO–BZCY/NiO–BZCY(∼50 μm)/BZCY(∼20 μm)/BSCF–BZCY(∼50 μm) was operated from 550 to 700 °C with humidified hydrogen (∼3% H₂O) as fuel and the static air as oxidant. A high open-circuit potential of 1.009 V, a maximum power density of 418 mW cm⁻², and a low polarization resistance of the electrodes of 0.10 Ω cm² was achieved at 700 °C. These investigations have indicated that proton-conducting BZCY electrolyte with BSCF perovskite cathode is a promising material system for the next generation solid oxide fuel cells (SOFCs).     

Novel Al2O3-based compressive seals for IT-SOFC applications

Novel compressive Al₂O₃-based seals were developed and characterized under simulated intermediate temperature solid oxide fuel cell (IT-SOFC) environment. The seals were prepared by tape casting, mainly composed of fine Al₂O₃ powder with various contents of fine Al powder addition. The leakage rates were determined at 800 °C under 0.14–0.69 MPa compressive stresses, and the stabilities were evaluated at 750 °C under constant 0.35 MPa compressive stress. The leakage rates at 800 °C were in range of 0.2–0.01 sccm cm⁻¹, decreasing with increasing the compressive stress and Al content; Al addition significantly improved the stability, the leakage rate with 20 wt% Al addition was as low as 0.025 sccm cm⁻¹ at 800 °C under 0.35 MPa compressive stress with a gauge pressure of 6.9 kPa, and exhibited good stability at 750 °C. Single cell test also confirmed the effectiveness of the tape cast Al₂O₃-based seal for planar IT-SOFC applications.