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%.     

Synthesis and electrochemical properties of Mo-doped Li[Ni1/3Mn1/3Co1/3]O2 cathode materials for Li-ion battery

The layered Li[Ni_(1−x)/3Mn_(1−x)/3Co_(1−x)/3Mo_x]O₂ cathode materials (x = 0, 0.005, 0.01, and 0.02) were prepared by a solid-state pyrolysis method (700, 800, 850, and 900 °C). Its structure and electrochemical properties were characterized by XRD, SEM, XPS, cyclic voltammetry, and charge/discharge tests. It can be learned that the doped sample of x = 0.01 calcined at 800 °C shows the highest first discharge capacity of 221.6 mAh g⁻¹ at a current density of 20 mA g⁻¹ in the voltage range of 2.3–4.6 V, and the Mo-doped samples exhibit higher discharge capacity and better cycle-ability than the undoped one at room temperature.     

Effects of synthesis conditions on the structural and electrochemical properties of layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via the hydroxide co-precipitation method LIB SCITECH

The uniform layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by using (Ni_1/3Co_1/3Mn_1/3)(OH)₂ synthesized by a liquid phase co-precipitation method as precursor. The effects of calcination temperature and time on the structural and electrochemical properties of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ were systemically studied. XRD results revealed that the optimal prepared conditions of the layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ were 850 °C for 18 h. Electrochemical measurement showed that the sample prepared under the above conditions has the highest initial discharge capacity of 162.1 mAh g⁻¹ and the smallest irreversible capacity loss of 9.2% as well as stable cycling performance at a constant current density of 16 mA g⁻¹ between 3 and 4.3 V versus Li at room temperature.     

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 and characterization of layered LiMn1/3Ni1/3Co1/3O2 as a cathode material by an oxalate co-precipitation method

The layered LiMn_1/3Ni_1/3Co_1/3O₂ cathode materials were synthesized by an oxalate co-precipitation method using different starting materials of LiOH, LiNO₃, [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O and [Mn_1/3Ni_1/3Co_1/3]₃O₄. The morphology, structural and electrochemical behavior were characterized by means of SEM, X-ray diffraction analysis and electrochemical charge–discharge test. The cathode material synthesized by using LiNO₃ and [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O showed higher structural integrity and higher reversible capacity of 178.6 mAh g⁻¹ in the voltage range 3.0–4.5 V versus Li with constant current density of 40 mA g⁻¹ as well as lower irreversible capacity loss of 12.9% at initial cycle. The rate capability of the cathode was strongly influenced by particle size and specific surface area.     

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.     

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.     

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.     

Exfoliation-induced nanoribbon formation of poly(3,4-ethylene dioxythiophene) PEDOT between MoS2 layers as cathode material for lithium batteries

A new type of layered nanocomposite synthesized by delaminated MoS₂ nanosheets and poly(3,4-ethylenedioxythiophene) (PEDOT) are restacked to produce alternate polymer nanoribbons between layers of MoS₂ with an interlayer distance of ∼1.38 nm. The unique properties of resulting nanocomposite are investigated by powder XRD, XPS, SEM, TEM, and four-probe conductivity measurements. The obtained nanocomposite can be used as a cathode material for a small power rechargeable lithium battery as demonstrated by the electrochemical insertion of lithium into the PEDOT/MoS₂ nanocomposite. A significant enhancement in the discharge capacity (100 mAh g⁻¹) is observed compared with that (40 mAh g⁻¹) for MoS₂.     

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.     

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.     

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.     

Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel

LiNi_0.5Mn_1.5O₄ material with a spinel structure is prepared by a sol–gel method. The material is initially fired at 850 °C and then subjected to a post-reaction annealing at 600 °C in order to minimize the nickel deficiency. The elevated firing temperature produces materials with a small surface-area which is beneficial for good capacity retention. Indeed, the spinel LiNi_0.5Mn_1.5O₄ not only shows a good cycle performance, but exhibits an excellent discharge capacity, i.e. 114 mAh g⁻¹ at 4.66 V plateau and 127 mAh g⁻¹ in total. Cyclic voltammetry and ac impedance spectroscopy are employed to characterize the reactions of lithium insertion and extraction in the LiNi_0.5Mn_1.5O₄ electrode. Excellent electrochemical performance and low material cost make this compound an attractive cathode for advanced lithium batteries.     

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.     

Porous olivine composites synthesized by sol–gel technique

Porous LiMPO₄/C composites (where M stands for Fe and/or Mn) with micro-sized particles were synthesised by sol–gel technique. Particles porosity is discussed in terms of qualitative results obtained from SEM micrographs and in terms of quantitative results obtained from N₂ adsorption isotherms. Porous particles could be described as an inverse picture of nanoparticulate arrangement, where the pores serve as channels for lithium supply and the distance between the pores determines the materials kinetics. Tests show that the electrochemical behaviour of porous LiMPO₄/C composite is comparable with the results from the literature. The best electrochemical results were obtained with a LiFePO₄/C composite (over 140 mAh g⁻¹ at C/2 rate during continuous cycling). The capacity obtained with LiMnPO₄/C composite is much lower (40 mAh g⁻¹ at C/20 rate), although the textural properties are similar to those observed in the LiFePO₄/C composite.     

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.     

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.     

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.     

One-step synthesis LiMn2O4 cathode by a hydrothermal method

Spinel LiMn₂O₄ powders have been successfully synthesized by a hydrothermal method directly, which is no any pretreatment and following treatment in the process. The structure and morphology of the powders were studied in detail by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). The data reveal that the products have well-defined stable spinel structure, and the particles show distinctive crystal faces with 50–300 nm in particle sizes. The electrochemical characteristics of the spinel materials are measured in the coin-type cells in a potential range of 3.2–4.35 V versus Li/Li⁺. The as-synthesized LiMn₂O₄ delivers reversible capacity of about 121 mAh g⁻¹ at a current density of 1/10 C. Cycled the cell to 40 cycles, the capacity remains at about 111 mAh g⁻¹ at 1/2 C.     

Synthesis of lithium insertion material Li4Ti5O12 from rutile TiO2 via surface activation

The synthesis of spinel-type lithium titanate, Li₄Ti₅O₁₂, a promising anode material of secondary lithium-ion battery, from “inert” rutile TiO₂, is investigated. On the purpose of increasing the reactivity of rutile TiO₂, it is treated by concentrated HNO₃. By applying such activated rutile TiO₂ as the titanium source in combination with the cellulose-assisted combustion synthesis, phase-pure Li₄Ti₅O₁₂ is successfully synthesized at 800 °C, at least 150 °C lower than that based on solid-state reaction. The resulted oxide shows a reversible discharge capacity of ～175 mAh g^?1 at 1 C rate, near the theoretical value. The resulted oxide also shows promising high rate performance with a discharge capacity of ～100 mAh g^?1 at 10 C rate and high cycling stability.