Charge–discharge characteristics of all-solid-state thin-filmed lithium-ion batteries using amorphous Nb2O5 negative electrodes

All-solid-state thin-filmed lithium-ion rechargeable batteries composed of amorphous Nb₂O₅ negative electrode with the thickness of 50–300 nm and amorphous Li₂Mn₂O₄ positive electrode with a constant thickness of 200 nm, and amorphous Li₃PO_4−xN_x electrolyte (100 nm thickness), have been fabricated on glass substrates with a 50 mm × 50 mm size by a sputtering method, and their electrochemical characteristics were investigated. The charge–discharge capacity based on the volume of positive electrode increased with increasing thickness of negative electrode, reaching about 600 mAh cm⁻³ for the battery with the negative electrode thickness of 200 nm. But the capacity based on the volume of both the positive and negative electrodes was the maximum value of about 310 mAh cm⁻³ for the battery with the negative electrode thickness of 100 nm. The shape of charge–discharge curve consisted of a two-step for the batteries with the negative electrode thickness more than 200 nm, but that with the thickness of 100 nm was a smooth S-shape curve during 500 cycles.     

Li4Ti5O12/CNTs composite anode material for large capacity and high-rate lithium ion batteries

Li₄Ti₅O₁₂ sub-micro crystallites are synthesized by ball-milling and one-step sintering under different heat treatment temperature from 700 °C to 900 °C. The composite electrode of Li₄Ti₅O₁₂/carbon nanotubes (CNTs) is prepared by mixing powders of Li₄Ti₅O₁₂ and CNTs in different weight ratios. Before mixing, in order to disperse CNTs in Li₄Ti₅O₁₂ particles preferably, the CNTs are cut and dispersed by hyperacoustic shear method and the composite electrodes of low resistance of about 20–30 Ω are obtained. The composite electrodes have steady discharge platform of 1.54 V and large specific capacity, initial discharge capacities are 168, 200, 196, 176 mAh g⁻¹ in different Li₄Ti₅O₁₂:CNTs weight ratios of 94:1, 92:3, 90:5, 88:7 respectively at 0.1 C discharge rate for the Li₄Ti₅O₁₂ synthesized in an optimized heat treatment temperature of 800 °C. In our experimental range, the composite electrode in a CNTs weight ratio of 3:92 shows the best performance under different discharge rate such as the initial capacity is 200 mAh g⁻¹ with discharge capacities retention rate of nearly 100%. Its capacity is about 151 mAh g⁻¹ under 20 C rate discharge condition with excellent high-rate performance. There is almost no decline after 20th cycles under 10 C rate discharging condition.     

Effect of NaI/I2 mediators on properties of PEO/LiAlO2 based all-solid-state supercapacitors

NaI/I₂ mediators and activated carbon were added into poly(ethylene oxide) (PEO)/lithium aluminate (LiAlO₂) electrolyte to fabricate composite electrodes. All solid-state supercapacitors were fabricated using the as prepared composite electrodes and a Nafion 117 membrane as a separator. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements were conducted to evaluate the electrochemical properties of the supercapacitors. With the addition of NaI/I₂ mediators, the specific capacitance increased by 27 folds up to 150 F g⁻¹. The specific capacitance increased with increases in the concentration of mediators in the electrodes. The addition of mediators also reduced the electrode resistance and rendered a higher electron transfer rate between mediator and mediator. The stability of the all-solid-state supercapacitor was tested over 2000 charge/discharge cycles.     

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.     

Effect of electrolyte on electrochemical characteristics of MmNi3.55Co0.72Al0.3Mn0.43 alloy electrode for hydrogen storage

A series of experiments have been performed to investigate the effects of three electrolytes of different compositions (EO, EA and EM) on the electrochemical characteristics of MmNi_3.55Co_0.72Al_0.3Mn_0.43 hydrogen storage alloy electrode. Electrolytes EA and EM were obtained by adding appropriate amounts of Al₂(SO₄)₃ and MnSO₄ to the original electrolyte EO (6 M KOH + 1 wt% LiOH), respectively. Electrode activation, maximum capacity, cycle life, self-discharge and high-rate discharge characteristics have been studied. It was found that a maximum capacity of about 260 mA h/g has been obtained for the alloy electrodes in all these electrolytes after 5–7 cycles of charging/discharging. The alloy electrodes have a good durability in electrolytes EA and EM, especially after 175 cycles. Using the capacity retention as an indication of self-discharge resistance, almost identical degree of capacity retention (82% after 4 days and 45% after 16 days) has been observed at 298 K, regardless of the electrolytes used. When tested at higher temperature, however, a higher capacity retention (46% after 3 days) at 333 K has been observed for electrodes in electrolyte EA, and about 32% for electrodes in both electrolytes EO and EM. As to high-rate discharge behavior of the results of high-rate discharge tests indicated that about 50% of discharge efficiencies were obtained in the three electrolytes at 333 K by continuous-model high-rate discharge method, at a discharge rate of 7C, and 22% in 298 K. The alloy electrode in electrolyte EM has the best durability, in which about 50% of discharge efficiency at DC = 9C was obtained by step-model high-rate discharge method at 333 K, which was even higher than that at 298 K.     

Nano-grain SnO2 electrodes for high conversion efficiency SnO2-DSSC

The nano-grain ZnO/SnO₂ composite electrode was prepared by adding 5 w% of the 200-250 nm ZnO particles to the 5 nm SnO₂ colloid in the presence of hydroxypropylcellulose (M.W.=80,000). The nano-grain SnO₂ electrode was obtained by removing the ZnO particles from the composite electrode using acetic acid. The FE-SEM micrographs revealed that both electrodes consisted of interconnected nano-grains that were ca. 800 nm in size, and the large pores between the grains furnished the wide electrolyte diffusion channels within the electrodes. The photovoltaic properties of the nano-grain electrodes were investigated by measuring the I-V behaviors, the IPCE spectra and the ac-impedance spectra. The nano-grain electrodes exhibited remarkably improved conversion efficiencies of 3.96% for the composite and 2.98% for the SnO₂ electrode compared to the value of 1.66% for the usual nano-particle SnO₂ electrode. The improvement conversion efficiencies were mainly attributed to the formation of nano-grains, which facilitated the electron diffusion within the grains. The improved electrolyte diffusion as well as the light-scattering effects enhanced the photovoltaic performance of the SnO₂ electrode.     

Effects of carbon coating and iron phosphides on the electrochemical properties of LiFePO4/C

Carbon coated LiFePO₄ (LiFePO₄/C) with different contents of high electron conductive iron phosphide phase was synthesized by an aqueous sol–gel method in a reductive sintering atmosphere. Different synthesis parameters were used for adjusting the microstructure and phase compositions of the products. The effects of the carbon coating and iron phosphides on the electrochemical properties of the LiFePO₄/C electrodes were studied by means of testing the discharge capacities at rates of 0.1–5C (1C = 170 mAh g⁻¹) and analyzing the CV curves. The results show that carbon coating in a content of 1.5 wt.% derived from the carbon source of ethylene glycol greatly decreases the particle size of LiFePO₄ in one order in the specific surface area, and significantly improves the rate capability of LiFePO₄. The effect of the content of FeP on the capacity of the carbon coated LiFePO₄ was different at different discharge rates. Increasing the content of FeP from 1.2 to 3.7 wt.% slightly decreases the capacity of LiFePO₄/C at low discharge rate (0.1C and 1C), but obviously increases the capacity of LiFePO₄/C when the discharge rate is increased to 5C. For the carbon free sample, even it also has 1.8 wt.% FeP, it still possesses poor capacity due to the large particle size of LiFePO₄ and the lack of conductivity. And too much iron phosphides lowers the discharge capacity of the electrode since they are inert for the deinsertion/insertion of lithium ion.     

Surface modification of LiNi1/2Mn3/2O4 thin-films by zirconium alkoxide/PMMA composites and their effects on electrochemical properties

Three kinds of surface modifications were carried out on LiNi_1/2Mn_3/2O₄ thin-films to improve the charge and discharge characteristics of LiNi_1/2Mn_3/2O₄ positive electrodes. Among them, Zr(OBu)₄/poly(methyl methacrylate) (PMMA)-treated LiNi_1/2Mn_3/2O₄ thin-film electrodes showed charge and discharge efficiency of 80–84% in the first cycle, which was much higher than that for an untreated LiNi_1/2Mn_3/2O₄ thin-film electrode (73%). The values of the charge and discharge efficiency were still higher than that for an untreated electrode after the 30th cycle. The charge and discharge curves gave two plateaus at around 4.72 and 4.76 V, which were very similar to those for the untreated electrode. Ac impedance spectroscopy revealed that the surface film resistance should not increase by Zr(OBu)₄/PMMA treatment. XPS measurements suggest that a composite layer should be formed on a LiNi_1/2Mn_3/2O₄ thin-film electrode from PMMA and Zr(OBu)₄-derived compounds introducing an electrolyte. This composite layer was lithium-ion conductive, and was sustainable enough to suppress subsequent decomposition of an electrolyte at potentials as high as 4.7 V.     

Electrochemical properties of LiFe0.9Mn0.1PO4/Fe2P cathode material by mechanical alloying

LiFePO₄, olivine-type LiFe_0.9Mn_0.1PO₄/Fe₂P composite was synthesized by mechanical alloying of carbon (acetylene back), M₂O₃ (M = Fe, Mn) and LiOH·H₂O for 2 h followed by a short-time firing at 900 °C for only 30 min. By varying the carbon excess different amounts of Fe₂P second phase was achieved. The short firing time prevented grain growth, improving the high-rate charge/discharge capacity. The electrochemical performance was tested at various C/x-rate. The discharge capacity at 1C rate was increased up to 120 mAh g⁻¹ for the LiFe_0.9Mn_0.1PO₄/Fe₂P composite, while that of the unsubstituted LiFePO₄/Fe₂P and LiFePO₄ showed only 110 and 60 mAh g⁻¹, respectively. Electronic conductivity and ionic diffusion constant were measured. The LiFe_0.9Mn_0.1PO₄/Fe₂P composite showed higher conductivity and the highest diffusion coefficient (3.90 × 10⁻¹⁴ cm² s⁻¹). Thus the improvement of the electrochemical performance can be attributed to (1) higher electronic conductivity by the formation of conductive Fe₂P together with (2) an increase of Li⁺ ion mobility obtained by the substitution of Mn²⁺ for Fe²⁺.     

The electrochemical behaviour of the carbon-coated Ni0.5TiOPO4 electrode material

Ni_0.5TiOPO₄ oxyphosphate exhibits good electrochemical properties as an anode material in lithium ion batteries but suffers from its low conductivity. We present here the electrochemical performances of the synthesized Ni_0.5TiOPO₄/carbon composite by using sucrose as the carbon source. X-ray diffraction study confirms that this phosphate crystallizes in the monoclinic system (S.G. P2₁/c). The use of the Ni_0.5TiOPO₄/C composite in lithium batteries shows enhanced electrochemical performances compared with the uncoated material. Capacities up to 200 mAh g⁻¹ could be reached during cycling of this electrode. Furthermore, an acceptable rate capability was obtained with very low capacity fading even at 0.5C rate. Nevertheless, a considerable irreversible capacity was evidenced during the first discharge. In situ synchrotron X-ray radiation was utilized to study the structural change during the first discharge in order to evidence the origin of this irreversible capacity. Lithium insertion during the first discharge induces an amorphization of the crystal structure of the parent material accompanied by an irreversible formation of a new phase.     

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.     

Ti/PbO2 + nano-Co3O4 composite electrode material for electrocatalysis of O2 evolution in alkaline solution

Ti/PbO₂ + nano-Co₃O₄ composite electrode materials with different compositions were prepared by anodic composite electrodeposition on Ti substrate, with a SnO₂-Sb₂O₅ intermediate layer in Pb²⁺ plating solution containing suspended nano-Co₃O₄ particles. The composition, structure, and morphology of the composite materials were investigated by XRD, XPS, and SEM analyses. The composite electrodes were studied as anodes for oxygen evolution reaction (OER) in 1 mol/L NaOH solution. The activities for the OER of the composites were explained by recording linear scanning voltammograms and Tafel plots. Results indicate that the onset potential of oxygen evolution at the composite electrode was lowered by approximately 160 mV compared to the PbO₂ electrode without nano-Co₃O₄. The catalytic activity of the composite electrode towards OER was improved significantly.     

Electrochemical performance of TiVNi-Quasicrystal and AB3-Type hydrogen storage alloy composite materials

The Ti_1.4V_0.6Ni ribbon alloy and AB₃-type (La_0.65Nd_0.12Mg_0.23Ni_2.9Al_0.1) alloy ingot are prepared by melt-spinning technique and induction levitation melting technique, respectively. The Ti_1.4V_0.6Ni + 20 wt.% AB₃ mixture powders are synthesized by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, Ti₂Ni, BCC structural solid solution and AB₃-type phases are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 294.7 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti_1.4V_0.6Ni and AB₃ composite holds better high-rate discharge ability than that of Ti_1.4V_0.6Ni.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Optimisation of the Solid Oxide Fuel Cell (SOFC) cathode material Ca3Co4O9−δ

This paper focuses on the electrochemical potentialities of the 2D misfit compound Ca₃Co₄O_9−δ, so far mainly investigated for its thermoelectric properties. Its expansion coefficient (TEC = (9-10) × 10⁻⁶ °C⁻¹) and its chemical stability are compatible with standard CGO IT-electrolyte and the first optimisation steps of the deposited cathode have been performed with the aim to minimise the ASR and increase the cell durability. Particular attention has been paid on the effect of thickness and microstructure for pure and composite cathodes. The electrode reaction was performed on symmetrical cells. The preliminary results presented here show that the composite (70 wt.% Ca₃Co₄O_9−δ-30 wt.% CGO) gives the lowest ASR values compare to single-phased electrodes. Strikingly, the ASR values increase for thinner deposited layers. The effect of various current collectors (gold grid vs. platinum paste) has been also checked.     

IrO2-SiO2 binary oxide films: Geometric or kinetic interpretation of the improved electrocatalytic activity for the oxygen evolution reaction

Our previous paper (Electrochim Acta 2010; 55: 4587-4593) reported that doping silica, the largest reserved oxide in the world, significantly improved the apparent electrochemical activity of Ti/IrO₂ electrodes for oxygen evolution reaction (OER). In the present work, the electrochemical surface structure of Ti/IrO₂-SiO₂ composite electrodes and the reaction kinetics of the OER thereon are investigated in details, to deeper understand the positive role of silica incorporation. Both the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements indicate either “inner” or “outer” active surface area of the mixed oxide electrodes, which is quantified by the voltammetric charge (q∗) or by the double-layer capacitance (C_dl), constantly increases when increasing the silica content therein under the investigated range of Ir/Si molar ratio. The “porosity”, defined as the ratio of the “inner” to “total” surface area, of the binary oxide films exhibits much higher values than pure IrO₂ film. Although the apparent electrocatalytic activity for the OER at composite electrodes is obviously higher than that at IrO₂ electrode, the real surface area-normalized activity declines after silica incorporation. The kinetic rate constants of the OER, approximated from the normalized polarization curves, also show dramatically decreased values at silica-doped electrodes. The above-mentioned results suggest that the enhanced apparent electrocatalytical activity of silica-doped IrO₂ electrodes might be merely a result of geometric effect.     

Fabricating CdS/BiVO4 and BiVO4/CdS heterostructured film photoelectrodes for photoelectrochemical applications

The photoelectrochemical (PEC) properties of heterostructured CdS/BiVO₄ and BiVO₄/CdS film electrodes on conducting glass for hydrogen production under visible light were investigated. These two types heterostructured film electrodes were prepared using spin coating method and ultrasonic spray pyrolysis method. The structural analyses of the prepared films were determined by using XRD, SEM, EDX and UV–vis. Photoelectrochemical measurements were carried out in a convenient three electrodes cell with 0.5 M Na₂SO₃ aqueous solution. In order to investigate band gap influence of electrode PEC property, a series ITO/Cd_1−xZn_xS/BiVO₄ and ITO/BiVO₄/Cd_1−xZn_xS (x = 0 ∼ 1) film electrodes were also synthesized. After PEC test, a maximum photocurrent density from ITO/CdS/BiVO₄ film electrode was confirmed. The maximum photocurrent density, 3 times and 113 times as that of single CdS film electrode and single BiVO₄ film electrode, respectively. Incident photon to current conversion (IPCE) of as prepared film electrodes were measured and the value were 65% (ITO/CdS/BiVO₄), 22% (single CdS film) and 10% (ITO/BiVO₄/CdS) at 480 nm with 0.3 V external bias. Comparison with ITO/BiVO₄/CdS electrode and single Cd_1−xZn_xS electrodes, the heterostructured ITO/CdS/BiVO₄ electrode can effectively suppress photogenerated electron-hole recombination and enhance light harvesting. Therefore, the ITO/CdS/BiVO₄ electrode gave the maximum photocurrent density and IPCE value.     

SiOx-graphite as negative for high energy Li-ion batteries

Negative electrodes containing SiO_x were investigated as alternative negative electrodes to carbon for Li-ion batteries. The results obtained on the effect of binders and carbon additives on the electrochemical performance (i.e., reversible capacity, coulombic efficiency, charge-discharge rate capability) of the SiO_x-graphite electrode and SiO_x electrode are presented. SEM analysis that utilizes facilities for in situ and ex situ studies were applied to better understand the performance and cycle life of the SiO_x-based electrodes. The SEM analysis clearly showed that the SiO_x particles expand and contract during charge-discharge cycling, and that some of the particles undergo mechanical degradation during this process. The SiO_x-graphite electrode with polyimide binder exhibited a stable capacity of 600 mAh g⁻¹ during high-rate charge-discharge from C/4 to 1C. These results suggest that the use of a flexible binder like polyimide and reasonably small SiO_x particles (nano-particles) facilitates improved cycle life and higher rate capability.     

Effect of Al content on structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys

The structure and electrochemical properties of LaNi_4.4 − xCo_0.3Mn_0.3Al_x hydrogen storage alloys have been investigated by XRD and simulated battery test, including maximum capacity, cyclic stability, self-discharge, high-rate dischargeability (HRD). Samples A, B, C and D were used to represent alloys LaNi_4.4Co_0.3Mn_0.3Al, LaNi_4.3Co_0.3Mn_0.3Al_0.1, LaNi_4.2Co_0.3Mn_0.3Al_0.2 and LaNi_4.1Co_0.3Mn_0.3Al_0.3 respectively. The results indicated that as-prepared LaNi_4.4 − xCo_0.3Mn_0.3Al_x alloys are all single-phase alloys with hexagonal CaCu₅ type structure. The maximum discharge capacity is 330.4 mAh g⁻¹ (Alloy C). With the increase of Al content from A to D, cycle life of alloy electrode has been improved. Higher capacity retention of 89.29% (after 50 charge/discharge cycles) has been observed for electrode D, while with a smaller capacity loss of 12.5% in its self-discharge test. Better high-rate charge/discharge behaviors have been observed in electrode B, and the maximum data is 54.7% at charge current of 900 mA/g) and 68.54% at discharge current of 1800 mA/g). Furthermore, the electrochemical impedance spectroscopy (EIS) analysis shown that the reaction of alloy electrode is controlled by charge-transfer step. The addition of Al results in the formation of protective layer of aluminum oxides on the surface of the alloy electrode, which is good for the improvement of electrode properties in alkaline solution and is detrimental for the charge-transfer process. Therefore, a suitable addition of Al is needed to improve its electrode properties.     

Electrochemical performance of nanostructured spinel LiMn2O4 in different aqueous electrolytes

A nanostructured spinel LiMn₂O₄ electrode material was prepared via a room-temperature solid-state grinding reaction route starting with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O) and citric acid (C₆H₈O₇·H₂O) raw materials, followed by calcination of the precursor at 500 °C. The material was characterized by X-ray diffraction (XRD) and transmission electron microscope techniques. The electrochemical performance of the LiMn₂O₄ electrodes in 2 M Li₂SO₄, 1 M LiNO₃, 5 M LiNO₃ and 9 M LiNO₃ aqueous electrolytes was studied using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. The LiMn₂O₄ electrode in 5 M LiNO₃ electrolyte exhibited good electrochemical performance in terms of specific capacity, rate dischargeability and charge/discharge cyclability, as evidenced by the charge/discharge results.