Solution combustion synthesis of LiMn2O4 fine powders for lithium ion batteries

In this work, fine powders of spinel-type LiMn₂O₄ as cathode materials for lithium ion batteries (LIBs) were produced by a facile solution combustion synthesis using glycine as fuel and metal nitrates as oxidizers. Single phase of LiMn₂O₄ products were successfully prepared by SCS with a subsequent calcination treatment at 600–1000 °C. The structure and morphology of the powders were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were characterized by galvanostatic charge–discharge cycling and cyclic voltammetry. The crystallinity, morphology, and size of the products were greatly influenced by the calcination temperature. The sample calcined at 900 °C had good crystallinity and particle sizes between 500 and 1000 nm. It showed the best performance with an initial discharge capacity of 115.6 mAh g⁻¹ and a capacity retention of 93% after 50 cycles at a 1 C rate. In comparison, the LiMn₂O₄ sample prepared by the solid-state reaction showed a lower capacity of around 80 mAh g⁻¹.     

Preparation and electrochemical characterization of lithium cobalt oxide nanoparticles by modified sol–gel method

Uniformly distributed nanoparticles of LiCoO₂ have been synthesized through the simple sol–gel method in presence of neutral surfactant (Tween-80). The powders were characterized by X-ray diffractometry, transmission electron microscopy and electrochemical method including charge–discharge cycling performance. The powder calcined at a temperature of 900 °C for 5 h shows pure phase layered LiCoO₂. The results show that the particle size is reduced in presence of surfactant as compared to normal sol–gel method. Also, the sample prepared in presence of surfactant and calcined at 900 °C for 5 h shows the highest initial discharge capacity (106 mAh g^?1) with good cycling stability as compared to the sample prepared without surfactant which shows the specific discharge capacity of 50 mAh g^?1.     

Electrochemical properties of 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 composite cathode powders prepared by large-scale spray pyrolysis

0.3Li₂MnO₃·0.7LiNi_0.5Mn_0.5O₂ composite cathode powders with a mixed-layer crystal structure comprising Li₂MnO₃ and LiNi_0.5Mn_0.5O₂ phases are prepared by spray pyrolysis. The composition of the cathode powders is found to be Li_1.19Ni_0.39Mn_0.61O₂ by ICP analysis. At a constant current density of 30 mA g^?1, the initial discharge capacities of the composite cathode powders post-treated at 700, 750, 800, and 850 °C are 177, 202, 215, and 212 mAh g^?1, respectively. The discharge capacity of the composite cathode powders post-treated at 800 °C decreases from 215 mAh g^?1 to 205 mAh g^?1 by the 40th cycle, in which the capacity retention is 95%. The first cycle has a low Coulombic efficiency of 75%. However, in the subsequent cycles, the Coulombic efficiency is retained at nearly 100%. The dQ/dV curves show that Mn exists as Mn⁴⁺ in the sample. The Mn⁴⁺ ions in the cathode powders become increasingly active as the cycle number increases and participate in the electrochemical reaction.     

An activated microporous carbon prepared from phenol-melamine-formaldehyde resin for lithium ion battery anode

Microporous carbon anode materials were prepared from phenol-melamine-formaldehyde resin by ZnCl₂ and KOH activation. The physicochemical properties of the obtained carbon materials were characterized by scanning electron microscope, X-ray diffraction, Brunauer–Emmett–Teller, and elemental analysis. The electrochemical properties of the microporous carbon as anode materials in lithium ion secondary batteries were evaluated. At a current density of 100 mA g^?1, the carbon without activation shows a first discharge capacity of 515 mAh g^?1. After activation, the capacity improved obviously. The first discharge capacity of the carbon prepared by ZnCl₂ and KOH activation was 1010 and 2085 mAh g^?1, respectively. The reversible capacity of the carbon prepared by KOH activation was still as high as 717 mAh g^?1 after 20 cycles, which was much better than that activated by ZnCl₂. These results demonstrated that it may be a promising candidate as an anode material for lithium ion secondary batteries.     

Electrochemical properties of lithium polymer batteries with doped polyaniline as cathode material

Polyaniline (PANI) was doped with different lithium salts such as LiPF₆ and LiClO₄ and evaluated as cathode-active material for application in room-temperature lithium batteries. The doped PANI was characterized by FTIR and XPS measurements. In the FTIR spectra, the characteristic peaks of PANI are shifted to lower bands as a consequence of doping, and it is more shifted in the case of PANI doped with LiPF₆. The cathodes prepared using PANI doped with LiPF₆ and LiClO₄ delivered initial discharge capacities of 125 mAh g^?1 and 112 mAh g^?1 and stable reversible capacities of 114 mAh g^?1 and 81 mAh g^?1, respectively, after 10 charge–discharge cycles. The cells were also tested using polymer electrolyte, which delivered highest discharge capacities of 142.6 mAh g^?1 and 140 mAh g^?1 and stable reversible capacities of 117 mAh g^?1 and 122 mAh g^?1 for PANI-LiPF₆ and PANI-LiClO₄, respectively, after 10 cycles. The cathode prepared with LiPF₆ doped PANI shows better cycling performance and stability as compared to the cathode prepared with LiClO₄ doped PANI using both liquid and polymer electrolytes.     

Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO₂ particles (O3-LiFeO₂) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO₂ precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO₂. 40-nm LiFeO₂ exhibited a higher discharge capacity (115 mAh g^?1) than 400-nm LiFeO₂ (80 mAh g^?1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO₂ particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO₂ to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe²⁺/Fe³⁺ and Fe²⁺/Fe⁰ redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO₂ were ca. 115, 210, and 390 mAh g^?1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.     

A low temperature synthesis of nanocrystalline spinel NiFe2O4 and its electrochemical performance as anode of lithium-ion batteries

Nanocrystalline spinel NiFe₂O₄ was synthesized by a novel low temperature route. The crystal structure, composition and morphology of the as-prepared powder were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The average diameter of the particles prepared at 700 °C is about 30 nm. The electrochemical reaction mechanism and charge–discharge mechanism of the nanocrystalline NiFe₂O₄ were proposed based on thermogravimetric analysis (TGA) and cyclic voltammogram study. The charge–discharge tests indicated that the sample calcined at 700 °C shows the highest initial discharge capacity (1400 mAh g⁻¹) attributed to the nanometer size and the better crystallinity of the powder. A discharge capacity stabilizes at about 600 mAh g⁻¹ after 10 cycles. The columbic efficiency is improved. The synthesis method is relatively low cost and convenient for large-scale production.     

One-step preparation of six-armed Fe3O4 dendrites with carbon coating applicable for anode material of lithium-ion battery

Six-armed Fe₃O₄ dendrites with carbon coating were synthesized by a simple one-step reaction between ferrocene and urea at 550 °C. Electron microscopy examinations indicate the formation of large numbers of Fe₃O₄ dendrites with mutually vertical arms and uniform carbon shells. Electrochemical measurement demonstrates that the dendrites using as anode materials for lithium-ion battery exhibit an initial capacity of 658 mAh g^? 1 and a reversible capacity of 473 mAh g^? 1 after 100 cycles at a rate of C/10, as well as a high cycling efficiency of 97% after the forth cycle. The formation mechanism of the six-armed dendrites was also discussed.     

Synthesis and electrochemical properties of LiNi0.9Co0.1O2 cathode material for lithium secondary battery

Layered LiNi_0.9Co_0.1O₂ cathode material has been successfully synthesized with a calcination time of 0.5 h by a rheological phase reaction method. The obtained powder was characterized by X-ray diffraction (XRD), particle size and particle size distribution, scanning electronic microscope (SEM) and electrochemical measurements. The powder is confirmed to be α-NaFeO₂ structure. Cyclic voltammetry (CV) studies imply that the phase transitions from hexagonal to monoclinic exist during charge–discharge cycling. The LiNi_0.9Co_0.1O₂ cathode demonstrated a good electrochemical property with an initial discharge capacity of 193 mAh g^?1 and capacity retention of 88.6% after 15 cycles.     

Flocculant-assisted synthesis of Fe2O3/carbon composites for superior lithium rechargeable batteries

High-performance iron oxide/carbon (Fe₂O₃/C) composites for lithium-ion batteries are synthesized by the combination of flocculant-assisted process and thermo-chemical treatment. Carboxymethylcellulose is used simultaneously as the flocculant and carbon source. This facile and scalable method lends itself to the fabrication of other metal oxide/carbon composites based on the flocculation mechanism. The lithium storage mechanism and cycling performance of Fe₂O₃/C composites are investigated by cyclic voltammetry and charge–discharge tests. As the rates increase from 50 to 1000 mA g^?1, the composites display high charge capacities of 834 mAh g^?1 for the first cycle at 50 mA g^?1 and 497 mAh g^?1 at 1000 mA g^?1 over 100 cycles. Excellent rate capability and cyclability are ascribed presumablely to the isolation and buffer functions of the conductive carbon matrix against particle aggregation and large volume variety upon cycling.     

Morphology dependent electrochemical performance of sputter deposited Sn thin films

This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge–discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g^?1 but reduced to 94 mAh g^?1 at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g^?1 during 1st cycle with improved capacity retention of 521 mAh g^?1 on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition.     

The effect of ZnO coating on LiMn2O4 cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn₂O₄ was modified with zinc oxide by a chemical process to improve its electrochemical performance at high temperatures. The physical properties of the prepared products have been investigated by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-rays analysis (EDAX). The charge/discharge of the materials was carried at 1 mA/cm² in the range of 3.0 and 4.4 V at 55 °C. The discharge capacity of ZnO-coated LiMn₂O₄ (117 mAh/g) showed only 3% loss of the initial capacity (121 mAh/g) over 60 cycles. The cycle ability improvement of the spinel LiMn₂O₄ coated with ZnO is demonstrated at high temperatures. From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycle ability may be attributed to the suppression on the formation of the passivation film and the reduction of Mn dissolution, which result from the modifying the surface of the spinel LiMn₂O₄ with zinc oxide.     

Improvement of cycle stability at elevated temperature and high rate for LiNi0.5−xCuxMn1.5O4 cathode material after Cu substitution

A series of Cu-substituted LiNi_0.5−xCu_xMn_1.5O₄ (x = 0, 0.03, 0.05 and 0.08) spinels have been synthesized using a sol–gel method. The results demonstrate that when x = 0.05, the sample (LiNi_0.45Cu_0.05Mn_1.5O₄) exhibits the best electrochemical performance, achieving 124.5 mAh g⁻¹ and 115.0 mAh g⁻¹ at the discharge rates of 5 C and 20 C with the capacity retention of 97.7% and 95.7% after 150 cycles, respectively. Besides, the excellent cycle stability at 55 °C has been demonstrated to retain 96.8% of the maximum attainable discharge capacity (127.3 mAh g⁻¹) at the discharge rate of 5 C after 100 cycles. These data indicate that the LiNi_0.45Cu_0.05Mn_1.5O₄ cathode material has the real potential to be used for high power and high energy lithium ion battery in electric vehicle applications.     

Electrochemical properties of all solid state Li/S battery

All-solid-state lithium/sulfur (Li/S) battery is prepared using siloxane cross-linked network solid electrolyte at room temperature. The solid electrolytes show high ionic conductivity and good electrochemical stability with lithium and sulfur. In the first discharge curve, all-solid-state Li/S battery shows three plateau potential regions of 2.4 V, 2.12 V and 2.00 V, respectively. The battery shows the first discharge capacity of 1044 mAh g^?1-sulfur at room temperature. This first discharge capacity rapidly decreases in 4th cycle and remains at 512 mAh g^?1-sulfur after 10 cycles.     

Nb2O5 hollow nanospheres as anode material for enhanced performance in lithium ion batteries

Nb₂O₅ hollow nanospheres of average diameter ca. ～29 nm and hollow cavity size ca. 17 nm were synthesized using polymeric micelles with core–shell–corona architecture under mild conditions. The hollow particles were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal (TG/DTA) and nitrogen adsorption analyses. Thus obtained Nb₂O₅ hollow nanospheres were investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers high capacity of 172 mAh g^?1 after 250 cycles of charge/discharge at a rate of 0.5 C. More importantly, the hollow particles based electrodes maintains the structural integrity and excellent cycling stability even after exposing to high current density 6.25 A g^?1. The enhanced electrochemical behavior is ascribed to hollow cavity coupled with nanosized Nb₂O₅ shell domain that facilitates fast lithium intercalation/deintercalation kinetics.     

Comparison of electrochemical performances of LiFePO4/C composite materials by two preparation routes

This study reports on the preparation of LiFePO₄/C composite materials prepared by the hydrothermal and sol–gel processes for comparison. The synthesis condition on the hydrothermal process was performed at 170 °C for 19 h. The polystyrene (PS) polymer was used as a carbon source; the PS was added at a range of 0–5 wt.%. The temperature of the post-thermal process was set at 750–850 °C. The citric acid (denoted as CA) was used as the reducing agent and the carbon source in the sol–gel process. The temperatures of the sintering process were set at a range of 650–850 °C. The optimal sintering temperature was at 850 °C for 12 h in the hydrothermal process; the optimal carbon residue content was approximately 3.20 wt.%. It was revealed that the highest discharge capacity of LiFePO₄/C composites by the hydrothermal process at 0.1 C is 163 mAh g^?1. The optimal sintering temperature was found to be at 750 °C for the sol–gel process. The highest carbon content was approximately 11.94 wt.% as the molar ratio of CA is 1.0. The highest discharge capacity of LiFePO₄/C composites by the sol–gel process at 0.1 C was approximately 130.35 mAh g^?1.     

Preparation of carbon coated LiMnPO4 powders by a combination of spray pyrolysis with dry ball-milling followed by heat treatment

Nanostructured LiMnPO₄ particles could be successfully synthesized by an ultrasonic spray pyrolysis method from the precursor solution; LiNO₃, Mn(NO₃)₂·6H₂O and H₃PO₄ were stoichiometrically dissolved into distilled water. The X-ray diffraction analysis showed that the as-prepared powders which had the desired olivine structure without any impurity phase could be obtained in the reactor temperatures ranging from 500 to 800 °C. Carbon coated LiMnPO₄ could be prepared from the as-prepared powders by a dry ball-milling followed by heat treatment for 4 h in a N₂ + 3% H₂ atmosphere. Transmission Electron Microscopy observation confirmed that a carbon layer was formed on the surface of LiMnPO₄ particles, which aimed to enhance the electronic conductivity of the material as well as inhibit the agglomeration during annealing. The carbon coated LiMnPO₄ was used as cathode active materials for lithium-ion batteries, and electrochemical performance was investigated using the Li|1 M LiClO₄ in EC:DEC = 1:1|LiMnPO₄ cells at room temperature and 55 °C. At a charge/discharge rate of 0.05 C, the cell exhibited first discharge capacities of 70 mAh g^?1 at room temperature and 140 mAh g^?1 at 55 °C. Moreover, it showed excellent cycleability even at elevated temperature and a high charge/discharge rate of 2 C.     

Synthesis of SnO2 nanoparticles inside mesoporous carbon via a sonochemical method for highly reversible lithium batteries

A sonochemical method was introduced to synthesize SnO₂ nanoparticles in the pores of mesoporous carbon without any other agents. The nitrogen adsorption measurement and transmission electron microscopy results revealed that the SnO₂ nanoparticles with the average particle size of around 10 nm were homogeneous distribution in the matrix. The aggregation of SnO₂ was hindered by the three-dimensioned porous frameworks, resulting in a relatively large surface area of 362 m² g^? 1, which is beneficial for lithium-ion storage in batteries. The resultant composites with 43% SnO₂ exhibited a high reversible capacity of 200 mAh g^? 1 even after 300 cycles, which is 186% higher than that of the initial mesoporous carbon matrix. This strategy is expected to incorporate other functional nanoparticles inside mesoporous carbon for many applications.     

Lithium storage capability of CuGeO3 nanorods

Copper metagermanate (CuGeO₃) nanorods were synthesized through a low temperature hydrothermal method at 180 °C. The as-synthesized CuGeO₃ nanorods show a well crystallined nanostructure with diameters in the range from 40 to 70 nm, and a length from 250 to 350 nm. Electrochemical measurements demonstrate that the CuGeO₃ nanorods exhibit a first charge capacity of 924 mAh g^?1 and 690 mAh g^?1 after 50 cycles, which is remarkably improved than the pure nanosize GeO₂ electrode. This investigation indicates that CuGeO₃ nanorods could be utilized as a high capacity anode material in lithium-ion batteries by reducing particle size and metal oxide addition. The lithium storage mechanisms for the improved capacity retention were also studied.     

Solvothermal synthesis of Mn2P2O7 and its application in lithium-ion battery

Manganese pyrophosphate, Mn₂P₂O₇ was synthesized by a simple solvothermal method using Mn metal powder and P₂S₅ in ethylene glycol medium at 190–220 °C. Morphology and crystalline structure of the products were characterized by X-ray diffraction and scanning electron microscopy. The flower-like microspheres with diameters of about 2–5 μm are composed of a number of nanoplatelets with thickness of 20–40 nm. The effect of reaction temperature and reaction time on the microstructure of Mn₂P₂O₇ was investigated. The samples were used as active anode materials for lithium-ion battery and their electrochemical properties were examined by constant current charge–discharge cycling. The Mn₂P₂O₇ electrodes exhibited initial reversible capacities of 440–330 mAh g^? 1 depending on the synthetic conditions. From these results, a possible reaction mechanism of Mn₂P₂O₇ with lithium was proposed.