Preparation of LiCoO2 from spent lithium-ion batteries

A recycling process involving mechanical, thermal, hydrometallurgical and sol–gel steps has been applied to recover cobalt and lithium from spent lithium-ion batteries and to synthesize LiCoO₂ from leach liquor as cathodic active materials. Electrode materials containing lithium and cobalt can be concentrated with a two-step thermal and mechanical treatment. The leaching behavior of lithium and cobalt in nitric acid media is investigated in terms of reaction variables. Hydrogen peroxide in 1 M HNO₃ solution is found to be an effective reducing agent by enhancing the leaching efficiency. Of the many possible processes to produce LiCoO₂, the amorphous citrate precursor process (ACP) has been applied to synthesize powders with a large specific surface area and an exact stoichiometry. After leaching used LiCoO₂ with nitric acid, the molar ratio of Li to Co in the leach liquor is adjusted to 1.1 by adding a fresh LiNO₃ solution. Then, 1 M citric acid solution at a 100% stoichiometry is added to prepare a gelatinous precursor. When the precursor is calcined at 950 °C for 24 h, purely crystalline LiCoO₂ is successfully obtained. The particle size and specific surface-area of the resulting crystalline powders are 20 μm and 30 cm² g⁻¹, respectively. The LiCoO₂ powder is found to have good characteristics as a cathode active material in terms of charge–discharge capacity and cycling performance.     

Electrochemical properties of the Li-ion polymer batteries with P(VdF-co-HFP)-based gel polymer electrolyte

Gel polymer electrolytes consisting of 25 wt.% P(VdF-co-HFP), 65 wt.% ethylene carbonate + propylene carbonate and 10 wt.% LiN(CF₃SO₂)₂ are prepared using by a solvent-casting technique. The electrodes are for use in lithium-ion polymer batteries. The electrochemical characteristics of the gel polymer electrolytes are evaluated by means of ac impedance and cyclic voltammetry. The charge–discharge performance of lithium polymer and lithium-ion polymer batteries is examined. A LiCoO₂ | gel polymer electrolyte (GPE) | mesocarbon microbeads (MCMB) cell delivers a discharge capacity of 146.8 and 144.5 mAh g⁻¹ on the first and the 20th cycle, respectively. The specific discharge capacity is greater than 140 mAh g⁻¹ for up to 20 cycle at all the current densities examined.     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

Nanocrystalline TiO2 (anatase) for Li-ion batteries

Nanocrystalline TiO₂ (anatase) was synthesized successfully by the direct conversion of TiO₂-sol at 85 °C. The as-prepared TiO₂ at 85 °C were calcined at different temperatures and time in order to optimize the system with best electrochemical performance. The particle sizes of the synthesized materials were found to be in the range of 15–20 nm as revealed by the HR-TEM studies. Commercial TiO₂ anatase (micron size) was also studied for its Li-insertion and deinsertion properties in order to compare with the nanocrystalline TiO₂. The full cell studies were performed with LiCoO₂ cathode with the best performing nano-TiO₂ as anode. The specific capacity of the nanocrystalline TiO₂ synthesized at 500 °C/2 h in a half-cell configuration was 169 mAh g⁻¹ while for the cell with LiCoO₂ cathode, it was 95 mAh g⁻¹ in the 2 V region. The specific reversible capacity and the cycling performance of the synthesized nano-TiO₂ anode in full cell configuration across LiCoO₂ cathode are superior to that reported in the literature. Cyclic voltammetry measurements showed a larger peak separation for the micro-TiO₂ than the nano-TiO₂, clearly indicating the influence of nano-particle size on the electrochemical performance.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Polymeric gel electrolytes reinforced with glass-fibre cloth for lithium secondary batteries

Polymeric gel electrolytes (PGE), based on polyacrylonitrile blended with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)), which are reinforced with glass-fibre cloth (GFC) to increase the mechanical strength, are prepared for the practical use in lithium secondary batteries. The resulting electrolytes exhibit electrochemical stability at 4.5 V against lithium metal and a conductivity value of (2.0–2.1)×10⁻³ S cm⁻¹ at room temperature. The GFC–PGE electrolytes show excellent strength and flexibility when used in batteries even if they contain a plasticiser. A test cell with LiCoO₂ as a positive electrode and mesophase pich-based carbon fibre (MCF) as a negative electrode display a capacity of 110 mAh g⁻¹ based on the positive electrode weight at the 0.2 C rate at room temperature. Over 80% of the initial capacity is retained after 400 cycles. This indicates that GFC is suitable as a reinforcing material to increase the mechanical strength of gel-based electrolytes for lithium secondary batteries.     

Sol–gel template synthesis of highly ordered MnO2 nanowire arrays

In this paper, anodic aluminum oxide (AAO) templates with uniform pore diameter and periodicity were fabricated using a two-step oxidizating method at a constant current of 1.5 A dm⁻² in a mixed solution of 0.5 M sulfate acid and 5 g L⁻¹ oxalic acid at room temperature, pore-widening was done in 5 wt.% phosphoric acid. Then, arrays of manganese dioxide nanowires were prepared by combining the AAO template and a sol–gel solution containing Mn(CH₃COO)₂ and citric acid. SEM was used to characterize the structure of AAO and MnO₂ nanowires. The results show that uniform length and diameter of MnO₂ nanowires were obtained, and the length and diameter of MnO₂ nanowires are dependent on the pore diameter and the thickness of the applied AAO template. The pore diameter of the AAO was about 70 nm, the diameter of the MnO₂ nanowires was 70 nm and the length of the MnO₂ nanowires was about 500–700 nm. XRD analysis indicate the MnO₂ nanowires was α-MnO₂ polymorph. The results of cyclic voltammetry indicated that the α-MnO₂ nanowires are promising electrode materials for application in supercapacitors, the specific capacity of the electrode was 165 F g⁻¹.     

Tin and tin-based intermetallics as new anode materials for lithium-ion cells

The galvanostatic cycling behaviour of Sn/SnSb composite electrodes has been studied in 1 mol l⁻¹ LiClO₄/propylene carbonate (PC), 1 mol l⁻¹ LiPF₆/ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1), and 1 mol l⁻¹ LiClO₄/PC saturated with trans-decalin (t-Dec). Capacities between 500 and 600 mA h g⁻¹ (with respect to the mass of active material) were obtained. Reasons for the irreversible capacities are given and film formation on lithium storage metals and alloys is discussed. The observed coulombic efficiencies were slightly higher for the EC-containing electrolyte than for the PC-based one. Alternatively, improved efficiencies and stand-time behaviour were obtained when the PC electrolyte was saturated with t-Dec, which acts as a surfactant.     

Characterization of a LiCoO2 thick film by screen-printing for a lithium ion micro-battery

A thick film cathode has been fabricated by a screen-printing technique using LiCoO₂ paste to improve the discharge capacity in lithium ion micro-batteries. The LiCoO₂ thick film (about 6 μm) was obtained by screen-printing, but high discharge capacity and a suitable surface roughness of printed LiCoO₂ film cathodes could not be obtained by adding carbon black only to the LiCoO₂ paste. On the other hand, the printed cathode which was prepared using the mixture of carbon-coated LiCoO₂ powders and carbon black showed a typical discharge curve of a LiCoO₂ cathode with a high discharge capacity (179 μAh cm⁻²).     

Cracking causing cyclic instability of LiFePO4 cathode material

The capacity of pure LiFePO₄ faded gradually from initial 149 mAh g⁻¹–117 mAh g⁻¹ under current density of 30 mA g⁻¹ at room temperature after 60 cycles. Some obvious cracks are observed in LiFePO₄ particles after cycling. The formation of cracks would lead to poor electric contact and capacity fading. A possible mechanism is proposed for the appearance of the cracks.     

A study on the irreversible capacity of initial doping/undoping of lithium into carbon

The initial irreversible capacity, Q_i, is one of the parameters to express the material balancing of the cathode to anode in lithium-ion cells. In this work, a new terms are introduced, namely, the initial intercalation Ah efficiency (IIE) and the initial irreversible specific capacity at the surface (Q_is), to express precisely the irreversibility of an electrode/electrolyte system. The terms depend on the active-materials and composition of the electrode, but do not change with charging state. Mesophase carbon microbeads (MPCF) have the highest value of IIE and the lowest value of Q_is in 1 M LipF₆/ethylene carbonate (EC)+diethyl carbonate (DEC) (1:1 volume ratio) electrolyte. The IIE value of a LiCoO₂ electrode is 97–98%, although the preparation conditions of the material and the electrolyte are different. The Q_is value of LiCoO₂ is 0–1 mAh g⁻¹. The MPCF-LiCoO₂ cell system has the lowest latent capacity. The Q_is value increases slightly on adding conductive material. The IIE and Q_is values vary with the electrolyte. By introducing propylene carbonate to the EC+DEC mixed solvent, the IIE values are retained, but Q_is is increased. With the addition of methyl propionate, the IIE value is increased, and the Q_is value is also increased slightly.     

Preparation and characterization of high-density spherical Li4Ti5O12 anode material for lithium secondary batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. A novel technique has been developed to prepare Li₄Ti₅O₁₂. The spherical precursor is prepared via an “inner gel” method by TiCl₄ as the raw material. Spherical Li₄Ti₅O₁₂ powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃. The investigation of XRD, SEM and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂ powders prepared by this method are spherical, and have high tap-density and excellent electrochemical performance. It is tested that the tap-density of the product is as high as 1.64 g cm⁻³, which is remarkably higher than the non spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, a reversible capacity is as high as 161 mAh g⁻¹ at a current density of 0.08 mA cm⁻².     

Electrochemical behavior of plasma-fluorinated graphite for lithium ion batteries

Electrochemical properties of plasma-fluorinated graphite samples have been investigated in 1 mol dm⁻³ LiClO₄ ethylene carbonate (EC)/diethyl carbonate (DEC) solution at 25 °C. Fluorine contents in plasma-fluorinated graphite samples were in the range of 0–0.3 at.% by elemental analysis and surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) were in the range of 3–12 at.%. Raman spectroscopy revealed that surface disordering of graphite was induced by plasma fluorination. Plasma treatment increased the surface areas of graphite samples by 26–55% and the pore volumes for the mesopores with diameters of 1.5–2 and 2–3 nm. Plasma-fluorinated graphites showed capacities higher than those of original graphites and even higher than the theoretical capacity of graphite, 372 mAh g⁻¹, without any change of the profile of charge–discharge potential curves. The increments in the capacities were approximately 5, 10 and 15% for graphites with average particle diameters, 7, 25 and 40 μm, respectively. Furthermore, the coulombic efficiencies in first cycle were nearly the same as those for original graphites or higher by several percents.     

Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor

Cobalt silicate hydroxide (Co₃[Si₂O₅]₂[OH]₂) was prepared by chemical method for use in electrochemical capacitors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests indicate that the material was pure hexagonal phase with uniform nanometer size distribution. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the cobalt silicate hydroxide-based electrode has stable electrochemical capacitor properties between potential range of 0.1–0.55 V with a maximum specific capacitance of 237 F g⁻¹ in alkaline solution and 95% of capacity efficiency was reached after 150 cycles. Electrochemical impedance spectra (EIS) investigation illustrates that the capacitance of the test electrode was mainly consisted of pseudo-capacitance, which was caused by underpotential deposition of H₃O⁺ at the electrode surface.     

Polymer electrolytes based on modified natural rubber for use in rechargeable lithium batteries

Modified natural rubber (NR) polymer hosts having low transition glass temperatures have been investigated. Three types of modified NR, namely 25% epoxidised NR (ENR-25), 50% ENR (ENR-50) and polymethyl methacrylate grafted NR (MG-49) were employed. Results are reported for ionic conductivity and thermal properties for both unplasticised and plasticised polymer electrolyte systems. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticisers. Unplasticised modified NR based systems exhibit ionic conductivities in 10⁻⁶–10⁻⁵ S cm⁻¹ range at ambient temperatures. Incorporating 50–100% of EC/PC by weight to the systems yielded mechanically stable films and ionic conductivities in 10⁻⁴–10⁻³ S cm⁻¹ range at ambient temperature. The thermal event of the systems has displayed an increasing trend of transition glass temperature at elevated salt concentration whereas incorporation of EC and PC into the systems leads to marked reduction in their T_g values.     

Cresol–formaldehyde based carbon aerogel as electrode material for electrochemical capacitor

Carbon aerogels have been prepared through a polycondensation of cresol (Cm) with formaldehyde (F) and an ambient pressure drying followed by carbonization at 900 °C. Modification of the porous structures of the carbon aerogel can be achieved by CO₂ activation at various temperatures (800, 850, 900 °C) for 1–3 h. This process could be considered as an alternative economic route to the classic RF gels synthesis. The obtained carbon aerogels have been attempted as electrode materials in electric double-layer capacitors. The relevant electrochemical behaviors were characterized by constant current charge–discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy in an electrolyte of 30% KOH aqueous solution. The results indicate that a mass specific capacitance of up to 78 F g⁻¹ for the non-activated aerogel can be obtained at current density 1 mA cm⁻². CO₂ activation can effectively improve the specific capacitance of the carbon aerogel. After CO₂ activation performed at 900 °C for 2 h, the specific capacitance increases to 146 F g⁻¹ at the same current. Only a slight decrease in capacitance, from 146 to 131 F g⁻¹, was observed when the current density increases from 1 to 20 mA cm⁻², indicating a stable electrochemical property of carbon aerogel electrodes in 30% KOH aqueous electrolyte with various currents.     

Manganese oxide film electrodes prepared by electrostatic spray deposition for electrochemical capacitors from the KMnO4 solution

Manganese oxide film electrodes for electrochemical capacitors were deposited on the polished Pt foils by electrostatic spray deposition (ESD) from KMnO₄ precursor solution. The electrochemical properties of electrodes were systematically studied using cyclic voltammetry (CV), constant current charge–discharge tests, and electrochemical impedance spectroscopy (EIS). The specific capacitance (SC) of thick deposited film was 149 F g⁻¹ at the very high scan rate of 500 mV s⁻¹, in comparison with 209 F g⁻¹ at the low scan rate of 5 mV s⁻¹. The electrode shows good cyclic performance. The initial SC value was 163 F g⁻¹ and 103% of the initial SC can be retained after 10,000 cycles at the scan rate of 50 mV s⁻¹.     

Opportunity of metallic interconnects for ITSOFC: Reactivity and electrical property

Iron-base alloys (Fe–Cr) are proposed hereafter as materials for interconnect of planar-type intermediate temperature solid oxide fuel cell (ITSOFC); they are an alternative solution instead of the use of ceramic interconnects. These steels form an oxide layer (chromia) which protects the interconnect from the exterior environment, but is an electrical insulator. One solution envisaged in this work is the deposition of a reactive element oxide coating, that slows down the formation of the oxide layer and that increases its electric conductivity. The oxide layer, formed at high temperature on the uncoated alloys, is mainly composed of chromia; it grows in accordance with the parabolic rate law (k_p = 1.4 × 10⁻¹² g² cm⁻⁴ s⁻¹). On the reactive element oxide-coated alloy, the parabolic rate constant, k_p, decreases to 1.3 × 10⁻¹³ g² cm⁻⁴ s⁻¹. At 800 °C, the area-specific resistance of Fe–30Cr alloys is about 0.03 Ω cm² after 24 h in laboratory air under atmospheric pressure. The Y₂O₃ coating reduces the electrical resistance 10-fold. This indicates that the application of Y₂O₃ coatings on Fe–30Cr alloy allows to use it as an interconnect for SOFC.     

Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Performance of a polyaniline(DMcT)/carbon fiber composite as cathode for rechargeable lithium batteries

The redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) is slow at room temperature, but it can be accelerated when the electron transfer reaction is coupled with that of polyaniline (Pani). Films of polyaniline were electrosynthesized onto carbon fiber substrates by cyclic voltammetry from a 0.5 mol L⁻¹ H₂SO₄/0.1 mol L⁻¹ aniline aqueous solution; DMcT was incorporated into the films by two different procedures: A – previous adsorption on the carbon fiber substrate, and B – electropolymerization onto a Pani film from a 20 mmol L⁻¹ DMcT solution in acetonitrile. The Pani(DMcT)/carbon fiber composites were tested as cathodes at 0.1 mA cm⁻² in a cell containing lithium as anode in a 0.5 mol L⁻¹ LiClO₄ solution in propylene carbonate, in a dry box under an argon atmosphere at 25 ± 2 °C. Discharge capacity values of 159 mA h g⁻¹ (after 90 cycles) and 39 mA h g⁻¹ (after 50 cycles) were obtained for the composites prepared by procedures A and B, respectively. The high capacity value and the high electrochemical stability during the cycling indicate that there is a synergetic effect of Pani and DMcT in the composites prepared by procedure A.