Fabrication and lithium storage performance of three-dimensional porous NiO as anode for lithium-ion battery

Three-dimensional porous NiO is prepared on Ni foam by a thermal treatment method at various temperatures. The morphology and structure of porous NiO are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties of three-dimensional porous NiO anode are evaluated by galvanostatic discharge-charge cycling, cyclic voltammery, and impedance spectral measurements on cells with lithium as the counter and reference electrodes. Results show that porous NiO delivers a stable capacity of 520 ± 20 mAh g⁻¹ with no noticeable capacity fading up to 30 cycles when cycled in the voltage range 0.05-3.0 V at rate of 0.2 C. The porous NiO exhibits higher reversible capacity, better cycleability, as well as higher rate capability in comparison to NiO foil. The observed cyclic voltammograms and impedance spectra are analyzed and interpret a redox reaction of NiO-Ni⁰ with formation and decomposition of Li₂O. The excellent electrochemical performance of porous NiO can be attributed to its large surface area, which lowers the current density of NiO reaction interface, and then an alternative anode is provided for lithium-ion batteries.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Co-doped NiO nanoflake arrays toward superior anode materials for lithium ion batteries

Co-doped NiO nanoflake arrays with a cellular-like morphology are fabricated by low temperature chemical bath deposition. As anode material for lithium ion batteries (LIBs), the array film shows a capacity of 600 mAh g⁻¹ after 50 discharge/charge cycles at low current density of 100 mA g⁻¹, and it retains 471 mAh g⁻¹ when the current density is increased to 2 A g⁻¹. Appropriate electrode configuration possesses some unique features, including high electrode-electrolyte contact area, direct contact between each naonflake and current collector, fast Li⁺ diffusion. The Co²⁺ partially substitutes Ni³⁺, resulting in an increase of holes concentration, and therefore improved p-type conductivity, which is useful to reduce charge transfer resistance during the charge/discharge process. The synergetic effect of these two parts can account for the improved electrochemical performance.     

Nanosized Li4Ti5O12/graphene hybrid materials with low polarization for high rate lithium ion batteries

We report a simple strategy to prepare a hybrid of lithium titanate (Li₄Ti₅O₁₂, LTO) nanoparticles well-dispersed on electrical conductive graphene nanosheets as an anode material for high rate lithium ion batteries. Lithium ion transport is facilitated by making pure phase Li₄Ti₅O₁₂ particles in a nanosize to shorten the ion transport path. Electron transport is improved by forming a conductive graphene network throughout the insulating Li₄Ti₅O₁₂ nanoparticles. The charge transfer resistance at the particle/electrolyte interface is reduced from 53.9 Ω to 36.2 Ω and the peak currents measured by a cyclic voltammogram are increased at each scan rate. The difference between charge and discharge plateau potentials becomes much smaller at all discharge rates because of lowered polarization. With 5 wt.% graphene, the hybrid materials deliver a specific capacity of 122 mAh g⁻¹ even at a very high charge/discharge rate of 30 C and exhibit an excellent cycling performance, with the first discharge capacity of 132.2 mAh g⁻¹ and less than 6% discharge capacity loss over 300 cycles at 20 C. The outstanding electrochemical performance and acceptable initial columbic efficiency of the nano-Li₄Ti₅O₁₂/graphene hybrid with 5 wt.% graphene make it a promising anode material for high rate lithium ion batteries.     

Carbon-coated SiO2 nanoparticles as anode material for lithium ion batteries

A simple approach is proposed to prepare C-SiO₂ composites as anode materials for lithium ion batteries. In this novel approach, nano-sized silica is soaked in sucrose solution and then heat treated at 900 °C under nitrogen atmosphere. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis shows that SiO₂ is embedded in amorphous carbon matrix. The electrochemical test results indicate that the electrochemical performance of the C-SiO₂ composites relates to the SiO₂ content of the composite. The C-SiO₂ composite with 50.1% SiO₂ shows the best reversible lithium storage performance. It delivers an initial discharge capacity of 536 mAh g⁻¹ and good cyclability with the capacity of above 500 mAh g⁻¹ at 50th cycle. Electrochemical impedance spectra (EIS) indicates that the carbon layer coated on SiO₂ particles can diminish interfacial impedance, which leads to its good electrochemical performance.     

Synthesis and characterization of three-dimensional carbon foams-LiFePO4 composites

The characterization of three-dimensional (3D) carbon foams coated with olivine structured lithium iron phosphate is reported for the first time. The LiFePO₄ as cathode material for lithium ion batteries was prepared by a Pechini-assisted reversed polyol process. The coating has been successfully performed on commercially available 3D-carbon foams by soaking in aqueous solution containing lithium, iron salts and phosphates at 70 °C for 2-4 h. After drying-out, the composites were annealed at different temperatures in the range 600-700 °C for 15-20 min under nitrogen. The formation of the olivine-like structured LiFePO₄ was confirmed by X-ray diffraction analysis performed on the powder prepared under similar conditions. The surface investigation of the prepared composites showed the formation of a homogeneous coating by LiFePO₄ on the foams. The cyclic voltammetry curves of the composites show an enhancement of electrode reaction reversibility by decreasing the annealing temperature. The electrochemical measurements on the composites showed good performances delivering a discharge specific capacity of 85 mAh g⁻¹ at a discharging rate of C/25 at room temperature.     

Enhanced electrochemical performance of porous NiO-Ni nanocomposite anode for lithium ion batteries

The nickel foam-supported porous NiO-Ni nanocomposite synthesized by electrostatic spray deposition (ESD) technique was investigated as anodes for lithium ion batteries. This anode was demonstrated to exhibit improved cycle performance as well as good rate capability. Ni particles in the composites provide a highly conductive medium for electron transfer during the conversion reaction of NiO with Li⁺ and facilitate a more complete decomposition of Li₂O during charge with increased reversibility of conversion reaction. Moreover, the obtained porous structure is benefical to buffering the volume expansion/constriction during the cycling.     

Improvement of flexible lithium battery shelf life by pre-discharging

Poly (methyl methacrylate) (PMMA)-based gel electrolyte has been used in flexible lithium batteries. These batteries are flexible and less than 0.5 mm thick, which make them suitable as power sources for smart cards and radio frequency identification (RFID) tags. We investigated the electrochemical properties of flexible lithium batteries using an impedance analyzer and potentiostat/galvanostat to evaluate the electrical capacities. To prevent the formation of gas by decomposition of electrolyte solvent, the batteries had to be pre-discharged about 5% of theoretical MnO₂ capacity. Of the three kinds of pre-discharging methods, especially, battery two-step pre-discharging method was performed showed the best electrical properties after storage at 60 °C for 60 days.     

A novel sol-gel synthesis route to NaVPO4F as cathode material for hybrid lithium ion batteries

Sodium vanadium fluorophosphate, NaVPO₄F, a cathode material for hybrid lithium ion batteries has been synthesized via a modified sol-gel method followed by heat treatment. The vanadium (Ш) gel precursor as the reaction intermediate phase can be facilely prepared in ethanol under ambient conditions, and this synthesis considerably simplifies the conventional high-temperature fabrication of VPO₄. X-ray diffraction (XRD) results indicate a phase transition of NaVPO₄F from the monoclinic crystal to the tetragonal symmetry structure. Meanwhile, the scanning electron microscope (SEM) images show the obvious spatial rearrangements on the morphology of samples. The hybrid lithium ion batteries based on the tetragonal NaVPO₄F exhibit an even discharge plateau at 3.6 V vs. Li in the limited voltage range of 3.0-4.2 V, and the discharge capacity retention is up to 98.7% after 100 cycles at C/4 rate. With voltage excursion to 3.0-4.5 V, the initial charge and discharge deliver the reversible storage capacity of 117.3 and 106.8 mAh g⁻¹, respectively. Furthermore, the prepared NaVPO₄F has a capacity retention of 83% after 100th cycle at 2 C rate. The electrochemical properties reveal the reversible mixed alkali ion (Li⁺, Na⁺) insertion reactions for this fluorophosphate material.     

A high performance silicon/carbon composite anode with carbon nanofiber for lithium-ion batteries

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for lithium-ion batteries. CNF was incorporated into the composite by two methods; direct mixing of CNF with the nano-Si powder coated with carbon produced by pyrolysis of PVC (referred to as Si/C/CNF-1) and mixing of CNF, nano-Si powder, and PVC with subsequent firing (referred to as Si/C/CNF-2). The external Brunauer-Emmett-Teller (BET) surface area of Si/C/CNF-1 was comparable to that of Si/C/CNF-2. The micropore BET surface area of Si/C/CNF-2 (73.86 m² g⁻¹) was extremely higher than that of Si/C/CNF-1 (0.74 m² g⁻¹). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 900 mA h g⁻¹ was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C/CNF-1 was as low as 53%, compared with 73% for Si/C/CNF-2. Impedance analysis of cells containing these anode materials suggested that the charge transfer resistance for Si/C/CNF-1 was not changed by cycling, but that Si/C/CNF-2 had high charge transfer resistance after cycling. A composite electrode prepared by mixing Si/C/CNF-2 and CNF exhibited a high reversible capacity at high rate, excellent cycling performance, and a high coulombic efficiency during the first lithium insertion and extraction cycles.     

Self-discharge behavior of polyacenic semiconductor and graphite negative electrodes for lithium-ion batteries

Variations in open-circuit potential (OCP) of artificial graphite and polyacenic semiconductor (PAS) negative electrodes have been investigated as a function of the storage time in alkylcarbonate-based electrolyte solutions after their cathodic charging (electrochemical lithiation) to discuss self-discharge phenomena of these negative electrodes for lithium ion batteries. The OCP of the graphite showed a plateau at ca. 90 mV vs. Li/Li⁺ for a long period (>8 × 10⁵ s), which suggested the retention of a stage structure of lithiated graphite during the storage. The lithiated PAS electrode gave gradual changes in OCP during the storage in the carbonate-based electrolyte solutions, suggesting continuous loss of Li species in the electrode. Variations in the interfacial resistance determined by an ac method, corresponding to the changes in the structure and properties at the electrode/electrolyte interface, also showed different features for the lithiated graphite and PAS electrodes. The mechanisms of self-discharging for these carbonaceous electrodes are discussed from the results of the influences of temperature and additives on the OCP variations.     

Lithium polymer batteries and proton exchange membrane fuel cells as energy sources in hydrogen electric vehicles

This paper deals with the application of lithium ion polymer batteries as electric energy storage systems for hydrogen fuel cell power trains. The experimental study was firstly effected in steady state conditions, to evidence the basic features of these systems in view of their application in the automotive field, in particular charge-discharge experiments were carried at different rates (varying the current between 8 and 100 A). A comparison with conventional lead acid batteries evidenced the superior features of lithium systems in terms of both higher discharge rate capability and minor resistance in charge mode. Dynamic experiments were carried out on the overall power train equipped with PEM fuel cell stack (2 kW) and lithium batteries (47.5 V, 40 Ah) on the European R47 driving cycle. The usage of lithium ion polymer batteries permitted to follow the high dynamic requirement of this cycle in hard hybrid configuration, with a hydrogen consumption reduction of about 6% with respect to the same power train equipped with lead acid 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.     

Functional interface of polymer modified graphite anode

Graphite electrodes were modified by polyacrylic acid (PAA), polymethacrylic acid (PMA), and polyvinyl alcohol (PVA). Their electrochemical properties were examined in 1 mol dm⁻³ LiClO₄ ethylene carbonate:dimethyl carbonate (EC:DMC) and propylene carbonate (PC) solutions as an anode of lithium ion batteries. Generally, lithium ions hardly intercalate into graphite in the PC electrolyte due to a decomposition of the PC electrolyte at ca. 0.8 V vs. Li/Li⁺, and it results in the exfoliation of the graphene layers. However, the modified graphite electrodes with PAA, PMA, and PVA demonstrated the stable charge–discharge performance due to the reversible lithium intercalation not only in the EC:DMC but also in the PC electrolytes since the electrolyte decomposition and co-intercalation of solvent were successfully suppressed by the polymer modification. It is thought that these improvements were attributed to the interfacial function of the polymer layer on the graphite which interacted with the solvated lithium ions at the electrode interface.     

Highly conductive composites made of phase change materials and graphite for thermal storage

Conventional phase change materials (PCMs) are already well known for their high thermal capacity and constant working temperature for thermal storage applications. Nevertheless, their low thermal conductivity (around 1 W m⁻¹ K⁻¹) leads to low and decreasing heat storage and discharge powers. Up to now, this major drawback has drastically inhibited their possible applications in industrial or domestic fields. The use of graphite to enhance the thermal conductivity of those materials has been already proposed in the case of paraffin but the corresponding applications are restricted to low-melting temperatures (below 150 °C). For many applications, especially for solar concentrated technologies, this temperature range is too low. In the present paper, new composites made of salts or eutectics and graphite flakes, in a melting temperature range of 200-300 °C are presented in terms of stability, storage capacity and thermal conductivity. The application of those materials to thermal storage is illustrated through simulated results according to different possible designs. The synergy between the storage composite properties and the interfacial area available for heat transfer with the working fluid is presented and discussed.     

A novel carbon-silicon composite nanofiber prepared via electrospinning as anode material for high energy-density lithium ion batteries

Electrospun carbon-silicon composite nanofiber is employed as anode material for lithium ion batteries. The morphology of composite nanofiber is optimized on the C/Si ratio to make sure well distribution of silicon particles in carbon matrix. The C/Si (77/23, w/w) nanofiber exhibits large reversible capacity up to 1240 mAh g⁻¹ and excellent capacity retention. Ex situ scanning electron microscopy is also conducted to study the morphology change during discharge/charge cycle, and the result reveals that fibrous morphology can effectively prevent the electrode from mechanical failure due to the large volume expansion during lithium insertion in silicon. AC impedance spectroscopy reveals the possible reason of unsatisfactory rate capability of the nanofiber. These results indicate that this novel C/Si composite nanofiber may has some limitations on high power lithium ion batteries, but it can be a very attractive potential anode material for high energy-density lithium-ion batteries.     

Hydrogen storage properties of lithium silicon alloy synthesized by mechanical alloying

A lithium silicon alloy was synthesized by mechanical alloying method. Hydrogen storage properties of this Li-Si-H system were studied. During hydrogenation of the lithium silicon alloy, lithium atom was extracted from the alloy and lithium hydride was generated. Equilibrium hydrogen pressures for desorption and absorption reactions were measured in a temperature range from 400 to 500 °C to investigate the thermodynamic characteristics of the system, which can reversibly store 5.4 mass% hydrogen with smaller reaction enthalpy than simple metal Li. Li absorbing alloys, which have been widely studied as a negative electrode material for Li ion rechargeable batteries, can be used as hydrogen storage materials with high hydrogen capacity.     

Novel electrolytes based on aliphatic oligoether dendrons

A novel electrolyte system having well structurally controlled aliphatic oligoether dendrons with a carbonate core is developed for lithium ion batteries. The synthetic dendrons have high boiling point, much higher dielectric constant up to 7.4–8.7 and better stability against oxidation than the conventional linear carbonates such as DEC. The ionic conductivities of the electrolyte with 80 wt% of dendrons and 20 wt% of LiTFSI are 0.11–0.61 mS cm⁻¹ at 20 °C. A 463443-type prismatic battery having the electrolyte solution with 20 wt% dendrons was prepared and its battery performance such as capacity and cycleability was investigated. The prismatic battery with dendron-based electrolyte has the same level of capacity to that with the conventional carbonate-based electrolyte, and shows good cycleability, suggesting a high possibility to use as a kind of cosolvents for lithium ion batteries.     

MoO2 synthesized by reduction of MoO3 with ethanol vapor as an anode material with good rate capability for the lithium ion battery

MoO₂ synthesized through reduction of MoO₃ with ethanol vapor at 400 °C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its electrochemical performance as an anode material for lithium ion battery was tested by cyclic voltammetry (CV) and capacity measurements. During the reduction process, the starting material (MoO₃) collapsed into nanoparticles (∼100 nm), on the nanoparticles remains a carbon layer from ethanol decomposition. Rate capacity and cycling performance of the as-prepared product is very satisfactory. It displays 318 mAh g⁻¹ in the initial charge process with capacity retention of 100% after 20 cycles in the range of 0.01–3.00 V vs. lithium metal at a current density of 5.0 mA cm⁻², and around 85% of the retrievable capacity is in the range of 1.00–2.00 V. This suggests the application of this type of MoO₂ as anode material in lithium ion batteries.     

PdCo supported on multiwalled carbon nanotubes as an anode catalyst in a microfluidic formic acid fuel cell

This work reports the synthesis of Pd-based alloys of Co and their evaluation as anode materials in a microfluidic formic acid fuel cell (μFAFC). The catalysts were prepared using the impregnation method followed by thermal treatment. The synthesized catalysts contain 22 wt.% Pd on multiwalled carbon nanotubes (Pd/MWCNT) and its alloys with two Co atomic percent in the sample with 4 at.% Co (PdCo1/MWCNT) and 10 at.% Co (PdCo2/MWCNT). The role of the alloying element was determined by XRD and XPS techniques. Both catalysts were evaluated as anode materials in a μFAFC operating with different concentrations of HCOOH (0.1 and 0.5 M), and the results were compared to those obtained with Pd/MWCNT. A better performance was obtained for the cell using PdCo1/MWCNT (1.75 mW cm⁻²) compared to Pd/MWCNT (0.85 mW cm⁻²) in the presence of 0.5 M HCOOH. By means of external electrode measurements, it was also possible to observe shifts in the formic acid oxidation potential due to a fuel concentration increment (ca. 0.05 V for both PdCo1/MWCNT and PdCo2/MWCNT catalysts and 0.23 V for Pd/MWCNT) that was attributed to deactivation of the catalyst material. The maximum current densities obtained were 8 mA cm⁻² and 5.2 mA cm⁻² for PdCo2/MWCNT and Pd/MWCNT, respectively. In this way, the addition of Co to the Pd catalyst was shown to improve the tolerance of intermediates produced during formic acid oxidation that tend to poison Pd, thus improving the catalytic activity and stability of the cell.