Synthesis and characterizations of Li[CrxLi(1−x)/3Mn2(1−x)/3]O2 (0.15 ≤ x ≤ 0.3) cathode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ (0.15 ≤ x ≤ 0.3) cathode materials was prepared by citric acid-assisted, sol–gel process. Sub-micron sized particles were obtained and the X-ray diffraction (XRD) results showed that the crystal structure was similar to layered lithium transition metal oxides (R-3m space group). The electrochemical performance of the cathodes was evaluated over the voltage range 2.0–4.9 V at a current density of 7.947 mA g⁻¹. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of up to 280 mAh g⁻¹ during cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ yielded a promising cathode material.     

Phosphides with zinc blende structure as anodes for lithium-ion batteries

The phosphides InP and GaP with a zinc blende structure are examined as anode materials for lithium-ion batteries. During discharge, X-ray diffraction phase analysis reveals the formation of Li–In/Li–Ga alloy and amorphous Li₃P. On charge, lithium is extracted from both Li_xM (M = In, Ga) alloy and Li₃P. InP shows a reversible capacity of ∼475 mAh g⁻¹ in the voltage range between 0.2 and 1.5 V, whereas GaP exhibits poor capacity retention compared with that of InP.     

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.     

Preparation and electrochemical studies of Fe-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

The Fe-doped Li₃V₂(PO₄)₃ cathode materials for Li-ion batteries were synthesized by a conventional solid-state reaction, and the Fe-doping effects on the Li electrochemical extraction/insertion performance of Li₃V₂(PO₄)₃ were investigated by galvanostatic charge/discharge and cyclic voltammetry measurements. The optimal Fe-doping content x is 0.02–0.04 in Li₃Fe_xV_2−x(PO₄)₃ system. The Fe-doped Li₃V₂(PO₄)₃ samples showed a better cyclic ability between 3.0 and 4.9 V, for example, the discharge capacity of Li₃Fe_0.02V_1.98(PO₄)₃ was 177 mAh g⁻¹ in the 1st cycle and 126 mAh g⁻¹ in the 80th cycle. The retention rate of discharge capacity is about 71%, much higher than 58% of the undoped system. The improved electrochemical performances of the Li₃V₂(PO₄)₃ could be attributed to the increased electrical conductivity and structural stability deriving from the incorporation of the Fe³⁺ ions.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

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.     

Novel architecture of composite electrode for optimization of lithium battery performance

We show that the polymeric binder of the composite electrode may have an important role on the lithium trivanadate Li_1.2V₃O₈ electrode performance. We describe a new tailored polymeric binder combination with controlled polymer–filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li_1.2V₃O₈ display a room temperature cycling capacity of 280 mAh g⁻¹ (C/5 rate, 3.3–2 V) instead of 150 mAh g⁻¹ using a standard-type (poly(vinylidene fluoride)–hexafluoropropylene (PVdF–HFP) binder) composite electrode. We have coupled scanning electron microscopy (SEM) observations, galvanostatic cycling and electrochemical impedance spectroscopy in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors that provide efficient charge carrier collection within the composite electrode complex medium are discussed.     

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.     

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.     

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.     

Synthesis and characterization of spinel Li4Ti5O12 anode material by oxalic acid-assisted sol–gel method

Anode material Li₄Ti₅O₁₂ for lithium-ion batteries has been prepared by a novel sol–gel method with oxalic acid as a chelating agent and Li₂CO₃ and tetrabutyl titanate [Ti(OC₄H₉)₄] as starting materials. Various initial conditions were studied in order to find the optimal conditions for the synthesis of Li₄Ti₅O₁₂. Oxalic acid used in this method functioned as a fuel, decomposed the metal complexes at low temperature and yielded the free impurity Li₄Ti₅O₁₂ compounds. Thermal analyses (TG–DTA) and XRD data show that powders grown with a spinel structure (Fd3m space group) have been obtained at 800 °C for 16 h. SEM analyses indicated that the prepared Li₄Ti₅O₁₂ powders had a uniform cubic morphology with average particle size of 200 nm. The influence of synthesis conditions on the electrochemical properties was investigated and discussed. The discharge capacity of Li₄Ti₅O₁₂ synthesized with an oxalic acid to titanium ratio R = 1.0 was 171 mAh g⁻¹ in the first cycle and 150 mAh g⁻¹ after 35 cycles under an optimal synthesis condition at 800 °C for 20 h. The very flat discharge and charge curves indicated that the electrochemical reaction based on Ti⁴⁺/Ti³⁺redox couple was a typical two-phase reaction.     

Effect of synthesis conditions on the properties of LiFePO4 for secondary lithium batteries

LiFePO₄ is one of the promising materials for cathode of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. However, LiFePO₄ has very poor electronic conductivity (∼10⁻⁹ S cm⁻¹) and Li-ion diffusion coefficient (∼1.8 × 10⁻¹⁴ cm² s⁻¹) at room temperature. In an attempt to improve electrochemical properties, Li_XFePO₄ with various amounts of Li contents were investigated in this study. Li_XFePO₄ (X = 0.7–1.1) samples were synthesized by solid-state reaction. High resolution X-ray diffraction, Rietveld analysis, BET, scanning electron microscopy, and hall effect measurement system were used to characterize these samples. Electronic conductivities of the samples with Li-deficient and Li-excess in Li_xFePO₄ were 10⁻³ to 10⁻¹ S cm⁻¹. Discharge capacities and rate capabilities of the samples with Li-deficient and Li-excess in Li_XFePO₄ were higher than those of stoichiometric LiFePO₄ sample. Li_0.9FePO₄ samples fired at 700 °C had discharge capacity of 156 and 140 mAh g⁻¹ at 0.1 C- and 2 C-rate, respectively.     

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.     

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.     

Electrochemical performance behavior of combustion-synthesized LiNi0.5Mn0.5O2 lithium-intercalation cathodes

LiNiO₂, partially substituted with manganese in the form of a LiNi_0.5Mn_0.5O₂ compound, has been synthesized by a gelatin assisted combustion method [GAC] method. Highly crystalline LiNi_0.5Mn_0.5O₂ powders with R3m symmetry have been obtained at an optimum temperature of 850 °C, as confirmed by PXRD studies. The presence of cathodic and anodic CV peaks exhibited by the LiNi_0.5Mn_0.5O₂ cathode at 4.4 and 4.3 V revealed the existence of Ni and Mn in their 2+ and 4+ oxidation states, respectively. The synthesized LiNi_0.5Mn_0.5O₂ cathode has been subjected to systematic electrochemical performance evaluation, via capacity tapping at different cut-off voltage limits (3.0–4.2, 3.0–4.4 and 3.0–4.6 V) and the possible extraction of deliverable capacity under different current drains (0.1C, 0.5C, 0.75C and 1C rates). The LiNi_0.5Mn_0.5O₂ cathode exhibited a maximum discharge capacity of 174 mAh g⁻¹ at the 0.1C rate between 3.0 and 4.6 V. However, a slightly decreased capacity of 138 mAh g⁻¹ has been obtained in the 3.0–4.4 V range, when discharged at the 1C rate. On the other hand, extended cycling at the 0.1C rate encountered an acceptable capacity fade in the 3.0–4.4 V range (<10%) for up to 50 cycles.     

Advanced manganese oxide material for rechargeable lithium cells

A family of potassium-doped manganese oxide materials were synthesized with the stoichiometric formula Li_0.9−XK_XMn₂O₄, where X = 0.0–0.25 and evaluated for their viability as a cathode material for a rechargeable lithium battery. A performance maximum was found at X = 0.1 where the initial specific capacity for the lithium–potassium-doped manganese dioxide electrochemical couple was 130 mAh g⁻¹ of active cathode material. The discharge capacity of the system was maintained through 90 cycles (95% initial capacity). Additionally, the capacity was maintained at greater than 90% initial discharge through 200 cycles. Other variants demonstrated greater than 75% initial discharge through 200 cycles at comparable capacity.     

Electrochemical behavior of Sn/SnO2 mixtures for use as anode in lithium rechargeable batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li₂O generated in situ by the electrochemical reduction of SnO₂ can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li_4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO₂, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO₂ = 1:2 exhibited a specific capacity of 549 mAh g⁻¹ (13% higher than that for SnO₂) with an irreversible capacity, which was 7% lower than that for SnO₂ and a capacity fade of 1.4 mAh g⁻¹ cycle⁻¹. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.     

Synthesis and electrochemical properties of Li[Li(1−2x)/3NixMn(2−x)/3]O2 as cathode materials for lithium secondary batteries

Layered Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ materials with x=0.41, 0.35, 0.275 and 0.2 are synthesized by means of a sol–gel method. The layered structure is stabilized by a solid solution between LiNiO₂ and Li₂MnO₃. The discharge capacity increases with increasing lithium content at the 3a sites in the Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂. A Li[Li_0.2Ni_0.2Mn_0.6]O₂ electrode delivers discharge capacities of 200 and 240 mAh g⁻¹ with excellent cycleability at 30 and 55 °C, respectively.     

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5 − x(Al0.5Mo0.5)x (x = 0–0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La_0.7Mg_0.3Ni_3.5 − x(Al_0.5Mo_0.5)_x (x = 0–0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase, and the lattice parameter and the cell volume of both the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase increases with increasing Al and Mo content in the alloys. The P–C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (x = 0) to 397.6 mAh g⁻¹ (x = 0.6) and then decreases to 370.4 mAh g⁻¹ (x = 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x = 0) to 73.8% (x = 0.8) at the discharge current density of 1200 mA g⁻¹. Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x. The hydrogen diffusion coefficient in the alloy bulk increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability of the alloy electrode.     

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%.