A thin film silicon anode for Li-ion batteries having a very large specific capacity and long cycle life

A thin film of Si was vacuum-deposited onto a 30 μm thick Ni foil from a source of n-type of Si, the film thickness examined being 200–1500 Å. Li insertion/extraction evaluation was performed mainly with cyclic voltammetry (CV) and constant current charge/discharge cycling in propylene carbonate (PC) containing 1 M LiClO₄ at ambient temperature. The cycleability and the Li accommodation capacity were found to depend on the film thickness. Thinner films gave larger accommodation capacity. A 500 Å thick Si film gave a charge capacity over 3500 mAh g⁻¹ being maintained during 200 cycles under 2 C charge/discharge rate, while a 1500 Å film revealed around 2200 mAh g⁻¹ during 200 cycles under 1 C rate. The initial charge loss could not be ignored but it could be reduced by controlling the deposition conditions.     

Nanoparticled Li(Ni1/3Co1/3Mn1/3)O2 as cathode material for high-rate lithium-ion batteries

Nanoparticle of Li(Ni_1/3Co_1/3Mn_1/3)O₂ with size smaller than 40 nm was obtained by non-aqueous system co-precipitation method. The particle morphology and crystal plane orientation were observed by TEM and HRTEM. Electrochemical properties of this nanostructued material were studied with experiment cells. The results show that the material has high capacity of 160 mAh g⁻¹ and excellent rate capability for charge and discharge. For the 50C and 100C rate, its capacity remains above 100 mAh g⁻¹ after tens of cycles.     

Electrochemical properties of amorphous and icosahedral quasicrystalline Ti45Zr35Ni17Cu3 powders

Ti₄₅Zr₃₅Ni₁₇Cu₃ amorphous and single icosahedral quasicrystalline powders were synthesized by mechanical alloying and subsequent annealing at 855 K. Microstructure and electrochemical properties of two alloy electrodes were characterized. When the temperature was enhanced from 303 to 343 K, the maximum discharge capacities increased from 86 to 329 mAh g⁻¹ and 76 to 312 mAh g⁻¹ for the amorphous and quasicrystalline alloy electrodes, respectively. Discharge capacities of two electrodes decrease distinctly with increasing cycle number. The I-phase is stable during charge/discharge cycles, and the main factors for its discharge capacity loss are the increase of the charge-transfer resistance and the pulverization of alloy particles. Besides the factors mentioned above, the formation of TiH₂ and ZrH₂ hydrides is another primary reason for the discharge capacity loss of the amorphous alloy electrode.     

Preparation,characterization and electrolytic behavior of β-nickel hydroxide

Nickel hydroxide is prepared by neutralizing NiSO₄ solution with 4.8 M NaOH, followed by washing the precipitate and treating the slurry hydrothermally at different temperatures. The parameters varied are: initial nickel concentration; effect of presence of sodium ions during hydrothermal treatment; aging time after hydrothermal treatment. The samples so prepared are chemically analyzed and the physical and electrolytic properties such as tap density, percentage weight loss and discharge capacity are determined. On increasing the temperature from 60 to 160 °C, the discharge capacity increases from 52 to 112 mAh g⁻¹. At 200 °C, the discharge capacity decreases to 94 mAh g⁻¹. Allowing the hydroxide precipitate to age after hydrothermal treatment also causes a decrease in discharge capacity. The presence of excess sodium ions during hydrothermal treatment yields nickel hydroxide with a very low discharge capacity. The maximum discharge capacity of 160 mAh g⁻¹ is obtained for nickel hydroxide prepared under the following conditions: nickel concentration 43 g l⁻¹, neutralizing agent sodium hydroxide, time of hydrothermal treatment 2 h, temperature during hydrothermal treatment 160 °C. XRD patterns and FTIR spectra confirm the precipitate to be β-nickel hydroxide. The sample contains 62.89 wt.% Ni with a tap density of 0.96 g cm⁻³. TG–DTA measurements show a weight loss of 19% with an endothermic peak at 325 °C which corresponds to the decomposition of nickel hydroxide to nickel oxide. The present method of preparing nickel hydroxide through hydrothermal treatment reduces the aging time to 2 h and gives a product with good filtration characteristics.     

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%.     

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.     

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.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Tin–graphite materials prepared by reduction of SnCl4 in organic medium: Synthesis,characterization and electrochemical lithiation

Tin–graphite materials were prepared by chemical reduction of SnCl₄ by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g⁻¹ decayed to a stable value of 415 mAh g⁻¹ after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g⁻¹ corresponding to a Sn/12C molar composition and assuming the formation of LiC₆ and Li₂₂Sn₅. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm⁻³) than that corresponding to graphite (837 mAh cm⁻³). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.     

Preparation of LiMn2O4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn₂O₄ as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g⁻¹ and the discharge capacity retention of 91.5% after 50 cycles.     

Synthesis of olivine-type LiFePO4 by emulsion-drying method

Olivine-type, orthorhombic, LiFePO₄ powders with small particle size have been successfully synthesized by the emulsion-drying method. The electronic and crystal structure is analyzed by X-ray absorption spectroscopy (XAS) and X-ray diffraction Rietveld refinement. The powder calcined at 750 °C shows the highest discharge capacity of 125 mAh g⁻¹ with excellent cycle stability. The discharge capacity of this powder increases to 154 mAh g⁻¹ on increasing the addition of carbon black as a conductive agent up to 40 wt.%. In a rate capability test, the discharge capacity is completely recovered and retained up to the 700th cycle.     

A study of calcium zincate as negative electrode materials for secondary batteries

The properties of calcium zincate as negative electrode materials for secondary batteries were examined by powder microelectrode, cyclic voltammetry, charge–discharge cycle measurements and X-ray diffraction (XRD) analysis. The results show that the cycleability of calcium zincate is obviously superior to that of ZnO and that of the mixture of ZnO and Ca(OH)₂ (the molar ratio of Zn:Ca=2:1). Calcium zincate forms zinc metal during the charging and exhibits an initial discharge capacity 230 mAh g⁻¹. With the discharge cut-off voltage of 1.0 V, the discharge capacity of the experimental Zn/NiOOH cell does not decay much during 500 cycles, exhibiting good prospect for practical use.     

Electrochemical characteristics of needle coke refined by molten caustic leaching as an anode material for a lithium-ion battery

Needle coke, the remaining material after refining petroleum, is used as an anode of a lithium-ion secondary battery. Sulfur is separated from the needle coke to below 0.1 wt.% using the molten caustic leaching (MCL) method developed at the Korea Institute of Energy Research. The needle coke with high-purity is carbonized at various temperatures, namely 0, 500, 700 and 900 °C. The coke treated at 700 °C gives a first and second discharge capacity of more than 560 and 460 mAh g⁻¹, respectively, between 0 and 2.0 V. By contrast, the first and second discharge capacity of untreated coke is over 420 and 340 mAh g⁻¹, respectively, between 0.05 and 2.0 V.The first discharge capacity of 560 mAh g⁻¹ is beyond the theoretical maximum capacity of 372 mAh g⁻¹ for LiC₆. Though the cycle efficiency is not consistent, the needle coke heat-treated at 700 °C persistently maintains an efficiency of over 90% until the 50th cycle, except on the first cycle. This study demonstrates that the needle coke with high-purity could be a good candidate for an anode material in fabricating high-capacity lithium-ion secondary batteries.     

Electrochemical performance of amorphous-silicon thin films for lithium rechargeable batteries

The effect of deposition temperature and film thickness on the electrochemical performance of amorphous-Si thin films deposited on a copper foil is studied. The electrochemical properties show optimum conditions at 200 °C deposition, and thinner films exhibit superior electrochemical performance than thicker ones. A film of 200 nm Si deposited at 200 °C exhibits excellent cycleability with a specific capacity of ∼3000 mAh g⁻¹. This is probably due to optimization between the strong adhesion by Si/Cu interdiffusion and the film stress.     

Sonochemical synthesis of amorphous manganese oxide coated on carbon and application to high power battery

The nanocomposite material of amorphous manganese oxide and acetylene black (HSMO/AB), was synthesized by sonochemical method. The acetylene black particles were homogeneously coated with amorphous manganese oxide. In order to demonstrate that these characteristic structures were suitable for rapid discharge–charge, the composite material was tested under large current density. The result exhibited 185 mAh g⁻¹ in specific discharge capacity under 10 A g⁻¹ in current density. Assuming that an operating voltage of 2.5 V, this capacity corresponded 20 kW kg⁻¹ in power density and 90 Wh kg⁻¹ in energy density.     

Effect of poly(acrylic acid) on adhesion strength and electrochemical performance of natural graphite negative electrode for lithium-ion batteries

High-capacity natural graphite negative electrodes for use in prismatic lithium-ion batteries are fabricated from an aqueous suspension precursor. The effects of poly(acrylic acid) (PAA) on suspension stability and the resulting mechanical properties of the electrodes are investigated. Precursor suspensions consisting of graphite particles, sodium carboxymethyl cellulose (CMC), emulsified styrene-butadiene (SB) copolymer latex and PAA are prepared in an aqueous medium and tape-cast on to a copper foil. The addition of PAA enhances the stability of the suspension at low shear rates without compromising the solvent-thickening effect of CMC. Peel test results showed that the adhesion strength of the graphite electrode on the copper substrate is significantly improved by PAA. Graphite negative electrodes fabricated using PAA are characterized by gravimetric and volumetric energy densities of more than 340 mAh g⁻¹ and 560 mAh cm⁻³, respectively. The PAA formulation also leads to improved cycle life, with a discharge capacity exceeding 90% of initial capacity after 500 cycles.     

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.     

A novel sol–gel method to synthesize nanocrystalline LiVPO4F and its electrochemical Li intercalation performances

Lithium vanadium fluorophosphate, LiVPO₄F, a cathode material for lithium ion batteries, was synthesized by a sol–gel method followed by low temperature calcinations. V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, LiF and carbon were used as starting materials to prepare a precursor, and LiVPO₄F was finally obtained by sintering the precursor at 550 °C for 2 h. X-ray diffraction results show that the LiVPO₄F sample is triclinic structure. TEM image indicates that the LiVPO₄F particles are about 70 nm in diameter embedded in carbon network. The LiVPO₄F system showed the discharge capacity of about 130 mAh g⁻¹ in the range of 3.0–4.6 V at the first cycle, and the discharge capacity remained about 124 mAh g⁻¹ after 30 cycles. The sol–gel method is suitable for the preparation of LiVPO₄F cathode materials with good electrochemical Li intercalation performances.     

Properties of containing Sn nanoparticles activated carbon fiber for a negative electrode in lithium batteries

Activated carbon fiber (ACF) containing Sn nanoparticles were prepared by impregnation and were investigated as a negative electrode material in lithium batteries. The tin particle size was controlled by selecting an ACF with an adequate surface structure. This Sn/ACF composite cycled versus Li metal showed a first discharge capacity as high as 200 mAh g⁻¹ compared to the pristine ACF which showed only 87 mAh g⁻¹. Excellent cyclability with these composites was obtained with ACF BET SSA as large as 2000 m² g⁻¹ and 30 wt.% Sn.     

Effects of ball-milling on lithium insertion into multi-walled carbon nanotubes synthesized by thermal chemical vapour deposition

The effects of ball-milling on Li insertion into multi-walled carbon nanotubes (MWNTs) are presented. The MWNTs are synthesized on supported catalysts by thermal chemical vapour deposition, purified, and mechanically ball-milled by the high energy ball-milling. The purified MWNTs and the ball-milled MWNTs were electrochemically inserted with Li. Structural and chemical modifications in the ball-milled MWNTs change the insertion–extraction properties of Li ions into/from the ball-milled MWNTs. The reversible capacity (C_rev) increases with increasing ball-milling time, namely, from 351 mAh g⁻¹ (Li_0.9C₆) for the purified MWNTs to 641 mAh g⁻¹ (Li_1.7C₆) for the ball-milled MWNTs. The undesirable irreversible capacity (C_irr) decreases continuously with increase in the ball-milling time, namely, from 1012 mAh g⁻¹ (Li_2.7C₆) for the purified MWNTs to 518 mAh g⁻¹ (Li_1.4C₆) for the ball-milled MWNTs. The decrease in C_irr of the ball-milled samples results in an increase in the coulombic efficiency from 25% for the purified samples to 50% for the ball-milled samples. In addition, the ball-milled samples maintain a more stable capacity than the purified samples during charge–discharge cycling.