Synthesis and electrochemical properties of nanostructured LiCoO2 fibers as cathode materials for lithium-ion batteries

Nanostructured LiCoO2 fibers were prepared by the sol-gel related electrospinning technique using metal acetate and citric acid as starting materials. The transformation from the xerogel fibers to the LiCoO2 fibers and the nanostructure of LiCoO2 fibers have been investigated in detail. The LiCoO2 fibers with 500 nm to 2 mum in diameter were composed of polycrystalline nanoparticles in sizes of 20-35 nm. Cyclic voltammetry and charge-discharge experiments were applied to characterize the electrochemical properties of the fibers as cathode materials for lithium-ion batteries. The cyclic voltammogram curves indicated faster diffusion and migration of Li+ cations in the nanostructured LiCoO2 fiber electrode. In the first charge-discharge process, the LiCoO2 fibers showed the initial charge and discharge capacities of 216 and 182 (mA.h)/g, respectively. After the 20th cycle, the discharge capacity decreased to 123 (mA.h)/g. The X-ray diffraction and high-resolution transmission electron microscopy analyses indicated that the large loss of capacity of fiber electrode during the charge-discharge process might mainly result from the dissolution of cobalt and lithium cations escaping from LiCoO2 to form the crystalline Li2CO3 and CoF2 impurities.     

Physical and electrochemical properties of La-doped LiFePO4/C composites as cathode materials for lithium-ion batteries

Olivine-type LiFePO₄ is one of the most promising cathode materials for lithium-ion batteries, but its poor conductivity and low lithium-ion diffusion limit its practical application. The electronic conductivity of LiFePO₄ can be improved by carbon coating and metal doping. A small amount of La-ion was added via ball milling by a solid-state reaction method. The samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM)/mapping, differential scanning calorimetry (DSC), transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS), and total organic carbon (TOC). Their electrochemical properties were investigated by cyclic voltammetry, four-point probe conductivity measurements, and galvanostatic charge and discharge tests. The results indicate that these La-ion dopants do not affect the structure of the material but considerably improve its rate capacity performance and cyclic stability. Among the materials, the LiFe_0.99La_0.01PO₄/C composite presents the best electrochemical behavior, with a discharge capacity of 156 mAh g^?1 between 2.8 and 4.0 V at a 0.2 C-rate compared to 104 mAh g^?1 for undoped LiFePO₄. Its capacity retention is 80% after 497 cycles for LiFe_0.99La_0.01PO₄/C samples. Such a significant improvement in electrochemical performance should be partly related to the enhanced electronic conductivities (from 5.88?×?10^?6 to 2.82?×?10^?3 S cm^?1) and probably the mobility of Li⁺ ion in the doped samples. The LiFe_0.99La_0.01PO₄/C composite developed here could be used as a cathode material for lithium-ion batteries.     

Microwave solid-state synthesis of LiV(3)O(8) as cathode material for lithium batteries

A novel and economical microwave route has been developed for the synthesis of electrochemically active LiV(3)O(8) material by using a domestic microwave oven. The heating behavior of the designed reaction system guided the preparation of LiV(3)O(8) at a suitable irradiation power (i.e. heating rate), reaction time, and temperature. At the lowest irradiation power, the conversion fraction of reactants was mainly controlled by reaction temperature. Characterization results of X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy, scanning (SEM) and transmission (TEM) electron microscopy, and BET surface areas indicated that the phases of samples prepared by microwave and traditional methods were in good agreement. Nevertheless, the crystallinity, crystallite configuration, and morphology of the samples were different, and were affected by the irradiation time and power. A floppy superposition structure of nanosheets (the size of one nanosheet was about 4.5 microm x 1.2 microm x 3 nm) was preferentially grown at the lowest irradiation power, and this effect on structure was more in evidence as the nanorods formed at the highest irradiation power. Electrochemical studies on ionic conductivity, electrochemical impedance spectroscopy (EIS), and charge-discharge capacity were carried out. It was found that the conductivity, first discharge capacity, and cycle performances of the samples were affected by the crystal size, crystallinity, and crystal configuration and defection concentration. The sample L30 prepared at the lowest irradiation power and the shortest time (30 min) showed the highest discharge capacity (335 mAh/g), but its discharge capacity decreased rapidly. By comparison, the sample L100 had a floppy superposition structure of nanosheets and a high surface area, provided a good two-dimensional channel for the transition of Li(+) ions, and was stable during the intercalation/deintercalation process of Li(+) ions, therefore the high ionic conductivity, high discharge capacity, and good cycle performance were presented. The relationship between the electrochemical properties and the irradiation power was discussed.     

An aqueous rechargeable lithium-ion battery based on LiCoO2 nanoparticles cathode and LiV3O8 nanosheets anode

Nanoparticles of lithium cobalt oxide (LiCoO₂) and nanosheets of lithium vanadium oxide (LiV₃O₈) were synthesized by a citrate sol–gel combustion route. The physical characterizations of the electrodic materials were carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and also X-ray diffraction (XRD) measurements. Near spherical nanoparticles of ≈100 nm and compact nanosheets with a few nanometers thick were observed by SEM and TEM for LiCoO₂ and LiV₃O₈, respectively. XRD data indicated that the as-prepared active materials presented pure phase of rhombohedral LiCoO₂ with R-3m symmetry and monoclinic LiV₃O₈ with p2₁/m symmetry. The kinetics of electrochemical intercalation of lithium ion into the nanoparticles of LiCoO₂ and nanosheets of LiV₃O₈ from 1.0 mol l⁻¹ LiNO₃ aqueous solution were investigated by cyclic voltammetry and chronoamperometry. An aqueous rechargeable lithium-ion battery consisting of LiCoO₂ nanoparticles as positive and LiV₃O₈ nanosheets as negative electrode was assembled. This battery represented a discharge voltage of about 1 V with good cycling performance.     

锂电池正极材料LiV3O8制备及电化学性能影响因素

采用溶胶-凝胶法制备锂离子电池正极材料LiV3O8,研究了LiOH溶液的浓度对LiV3O8的结构、粒径、电导率和电化学性能的影响。实验发现,LiV3O8衍射峰的强度、粒径与电导率可以通过改变LiOH溶液浓度来控制。测试了LiV3O8材料的结构、粒径分布和电化学性能。结果表明,随着LiOH溶液浓度的增加,样品的结晶度降低,晶粒的择优取向(100)晶面的衍射峰强度明显减弱;当LiOH溶液浓度为0.030 mol/L时,可以得到较为理想的粒径分布和较高的电导率为9.06×10-2s/cm;LiV3O8材料的容量及循环性能均与LiOH溶液浓度有关,选择0.030 mol/L的LiOH溶液时,样品的比容量最大为310 mA.h/g;循环15次后,容量衰减最少为4%。     

Effects of microwave irradiation on the electrochemical performance of manganese-based cathode materials for lithium-ion batteries

Microwave-assisted synthesis has continued to be adopted for the preparation of high-performance manganese-based cathode materials for lithium-ion batteries. The technique is fast, energy-efficient and has significant positive impacts on the general physico-chemical properties of the cathode materials: LiMn₂O₄, LiMn_1.5Ni_0.5O₄, and lithium nickel manganese cobalt oxides. Despite the advantages of microwave-assisted synthesis, this review reveals that the application is still limited. In our opinion, increased basic knowledge of the microwave process and availability of safe and reliable instrumentation could be a great opportunity for the commercial realization of low-cost and energy-dense Mn-based cathode materials for the next-generation lithium-ion batteries.     

Preparation and electrochemical properties of Si0.8Sb/C nanofiber composite anode materials for lithium-ion batteries

Journal of Solid State Electrochemistry - The Si0.8Sb/C nanofiber composite anode materials were synthesized with the method of high-energy ball milling combined with electrospinning. The...     

Intrinsic characteristics of cathode and anode materials for lithium-ion batteries

Fundamental aspects of solving the problem of how the working capacity of lithium-ion batteries in prolonged cycling can be raised and the basic tendencies in the relationship between the intrinsic parameters of active materials of various brands and the electrochemical behavior of anodes and cathodes fabricated from these materials are considered.     

溶胶-凝胶法合成锂离子电池正极材料LiV3O8

锂钒氧化物;扩散系数;溶胶-凝胶法合成锂离子电池正极材料LiV3O8     

Carboxylic acid-assisted solid-state synthesis of LiFePO4/C composites and their electrochemical properties as cathode materials for lithium-ion batteries

To enhance the capability of LiFePO₄ materials, we attempted to coat carbon by incorporating various organic carboxylic acids as carbon sources. The purity of LiFePO₄ was confirmed by XRD analysis. Galvanostatic cycling, cyclic voltammetry, electric impedance spectroscopy, and conductivity measurements were used to evaluate the material’s electrochemical performance. The best cell performance was delivered by the sample coated with 60 wt.% malonic acid. Its first-cycle discharge capacity was 149 mA h g^?1 at a 0.2 C rate or 155 mA h g^?1 at a 0.1 C rate. The presence of carbon in the composite was verified by total organic carbon and Raman spectral analysis. The actual carbon content of LiFePO₄ was 1.90 wt.% with the addition of 60 wt.% malonic acid. The LiFePO₄/C samples sintered with 60 wt.% various carboxylic acids were measured by Raman spectral analysis. The intense broad bands at 1,350 and 1,580 cm^?1 are assigned to the D and G bands of residual carbon in LiFePO₄/C composites, respectively. The peak intensity (I _D/I _G) ratio of the synthesized powders is from 0.907 to 0.935. Carbon coatings of LiFePO₄ with low I _D/I _G ratios can be produced by incorporating carboxylic acid additives before the final calcining process. The use of carboxylic acid as a carbon source increases the overall conductivity (～10^?4 S cm^?1) of the material.     

Structure and electrochemical performances of co-substituted LiSm x La0.2-x Mn1.80O4 cathode materials for rechargeable lithium-ion batteries

Spinel LiMn₂O₄ and Sm, La co-substituted LiSm _x La_0.2-x Mn_1.80O₄ (x?=?0.05, 0.10 and 0.15) cathode materials were synthesized by sol–gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 °C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using thermogravimetric/differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy studies. XRD analysis indicated that all the prepared samples were mainly belong to cubic crystal form with Fd3m space group. LiSm_0.10La_0.10Mn_1.80O₄ exhibits capacity retention of 90 % and 82 % after 100 cycles at room temperature (30 °C) and at elevated temperature (50 °C) at a rate of 0.5-C, respectively, much higher than those of the pristine LiMn₂O₄ (74 % and 60 %). Among all the compositions, LiSm_0.10La_0.10Mn_1.80O₄ cathode has improved the structural stability, high-capacity retention, better elevated temperature performance and excellent electrochemical performances of the rechargeable lithium-ion batteries.     

Preparation and electrochemical properties of Cu3P/rGO nanocomposite protection strategy for lithium-ion batteries

Journal of Solid State Electrochemistry - Copper phosphide (Cu3P) has emerged as a promising new lithium-ion electrode material due to its high theoretical capacity and abundant earth resources....     

3d-Transition metal doped spinels as high-voltage cathode materials for rechargeable lithium-ion batteries

Finding appropriate positive electrode materials for Li-ion batteries is the next big step for their application in emerging fields like stationary energy storage and electromobility. Among the potential materials 3d-transition metal doped spinels exhibit a high operating voltage and, therefore, are highly promising cathode materials which could meet the requirements regarding energy and power density to make Li-ion batteries the system of choice for the above mentioned applications. The compounds considered here include substituted Mn-based spinels such as LiM_0.5Mn_1.5O₄ (M = Ni, Co, Fe), LiCrMnO₄ and LiCrTiO₄. In this review, the recent researches conducted on these spinel materials are summarized. These include different routes of synthesis, structural studies, electrode preparation, electrochemical performance and mechanism of Li-extraction/insertion, thermal stability as well as degradation mechanisms. Note that even though the Ni-, Co-, and Fe-doped materials share the same chemical formula, the oxidation state distributions as well as the operating voltages are different among them. Furthermore, apart from the initial structural similarity, the Li-intercalation takes place through different mechanisms in different materials. In addition, this difference in mechanism is found to have considerable influence on the long-term cycling stability of the material. The routes to improve the electrochemical performance of some of the above candidates are discussed. Further emphasis is given to the parameters that limit their application in current technology, and strategies to overcome them are addressed.     

Enhanced electrochemical performance of LiFePO4 of cathode materials for lithium-ion batteries synthesized by surfactant-assisted solvothermal method

Lithium iron phosphate (LiFePO₄) cathode materials were synthesized by the solvothermal method with the assistance of different surfactants. The influences of polyethylene glycol 2000 (PEG 2000), polyvinylpyrrolidone (PVP), and cetyltrimethyl ammonium bromide (CTAB) on the microstructure and electrochemical performance of LiFePO₄ were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The particle size of the LiFePO₄ synthesized with the assistance of PEG was uniform and showed a flat rhombohedron-like shape. The initial discharge specific capacity is up to 122.80 mAh/g with an initial coulombic efficiency of 95.50% at 0.1C. LiFePO₄ synthesized with PVP-assisted presents a porous structure with an initial discharge specific capacity of 91.01 mAh/g. LiFePO₄ synthesized with CTAB-assisted shows a flower-like morphology with an initial discharge specific capacity of 100.44 mAh/g. Though the initial discharge capacities of the LiFePO₄ materials prepared with the assistance of CTAB and PVP are lower than those of the LiFePO₄ prepared without the assistance of surfactant, the two materials exhibited excellent cyclic stability at 0.1C.

     

Synthesis and electrochemical characterizations of nano-crystalline LiFePO4 and Mg-doped LiFePO4 cathode materials for rechargeable lithium-ion batteries

Nano-crystalline LiFePO₄ and LiMg_0.05Fe_0.95PO₄ cathode materials were synthesized by sol–gel method in argon atmosphere using succinic acid as a chelating agent. Physico-chemical characterizations were done by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and Raman spectroscopy. Electrochemical behavior of the cathode materials were analyzed using cyclic voltammetry, and galvanostatic charge/discharge cycling studies were employed to characterize the reaction of lithium-ion insertion into and extraction from virginal and magnesium-doped LiFePO₄, in the voltage range 2.5 to 4.5 V (Vs Li/Li⁺) using 1 M LiPF₆ with 1:1 ratio of ethylene carbonate and dimethyl carbonate as electrolytes. LiMg_0.05Fe_0.95PO₄ exhibits initial charge and discharge capacities of 159 and 141 mAh/g at 0.2 C rate respectively, as compared to 121 and 107 mAh/g of pristine LiFePO₄. Furthermore, LiMg_0.05Fe_0.95PO₄ has retained more than 89% of the capacity even after 60 cycles. Hence, LiMg_0.05Fe_0.95PO₄ is a promising cathode material for rechargeable lithium-ion batteries.     

Effects of AgNPs-coating on the electrochemical performance of LiMn2O4 cathode material for lithium-ion batteries

Journal of Solid State Electrochemistry - The Jahn–Teller effect and severe side reactions with liquid electrolyte have been considered as the main obstacles to the further application of...     

Morphology regulation and electrochemical properties of cathode material V6O13 for lithium-ion battery

Journal of Solid State Electrochemistry - A V6O13 micro-flower was synthesized via a facial hydrothermal method using ammonium metavanadate and oxalic acid dihydrate and combined with subsequent...     

Synthesis and electrochemical properties of K-doped LiFePO4/C composite as cathode material for lithium-ion batteries

Li_1 − x K _x FePO₄/C (x = 0, 0.03, 0.05, and 0.07) composites were synthesized at 700 °C in an argon atmosphere by carbon thermal reduction method. Based on X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis, the composite was ultrafine sphere-like particles with 100–300 nm size, and the lattice structure of LiFePO₄ was not destroyed by K doping, while the lattice volume was enlarged. The electrochemical properties were investigated by four-point probe conductivity measurements, galvanostatic charge and discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the capacity performance at high rate and cyclic stability were improved by doping an appropriate amount of K, which might be ascribed to the fact that the doped K ion expands Li ion diffusion pathway. Among the doped materials, the Li_0.97K_0.03FePO₄/C samples exhibited the best electrochemical activity, with the initial discharge capacity of 153.7 mAh g⁻¹ at 0.1 C and the capacity retention rate of about 92% after 50 cycles at above 1 C, 11% higher than undoped sample. Remarkably, it still showed good cycle retention at a high current rate of 10 C.