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.     

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.     

Electrochemical performance of Yb-doped LiFePO4/C composites as cathode materials for lithium-ion batteries

LiFePO₄/C and LiYb_0.02Fe_0.98PO₄/C composite cathode materials were synthesized by simple solution technique. The samples were characterized by X-ray diffraction, scanning electron microscope, and thermogravimetric–differential thermal analysis. Their electrochemical properties were investigated by cyclic voltammetry, four-point probe conductivity measurements, and galvanostatic charge and discharge tests. The carbon-coated and Yb³⁺-doped LiFePO4 sample exhibited an enhanced electronic conductivity of 1.9 × 10^?3 Scm^?1, and a specific discharge capacity of 146 mAhg^?1 at 0.1 C. The results suggest that the improvement of the electrochemical performance can be attributed to the ytterbium doping, which facilitates the phase transformation between triphylite and heterosite during cycling, and the conductivity improvement by carbon coating.     

Effects of vanadium oxide coating on the performance of LiFePO4/C cathode for lithium-ion batteries

Journal of Solid State Electrochemistry - LiFePO4 cathode material is considered as prospective materials for lithium-ion batteries and attracted great interest because of excellent cyclic...     

Synthesis,characterization and electrochemical performances of LiFePO4/graphene cathode material for high power lithium-ion batteries

LiFePO₄/graphene (LiFePO₄/G) cathode with exciting electrochemical performance was successfully synthesized by liquid phase method. LiFePO₄ nanoparticles wrapped with multi-layered grapheme can be fabricated in a short time. This method did not need external heating source. Heat generated by chemical reaction conduct the process and removed the solvent simultaneously. The LiFePO₄/G were analyzed by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), transmission electron microscopy (TEM), magnetic properties analysis and electrochemical performance tests. The LiFePO₄/G delivered a capacity of 160 mAh g⁻¹ at 0.1C and could tolerate various dis-charge currents with a capacity retention rate of 99.8%, 99.2%, 99.0%, 98.6%, 97.3% and 95.0% after stepwise under 5C, 10C, 15C, 20C, 25C and 30C, respectively.     

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.     

A novel synthetic route for LiFePO_4/C cathode materials by addition of starch for lithium-ion batteries

LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.     

Thermal runaway features of 18650 lithium-ion batteries for LiFePO4 cathode material by DSC and VSP2

In view of availability, accountability, and applicability, LiFePO₄ cathode material has been confirmed to be better than LiCoO₂ cathode material. Nevertheless, few related researches were conducted for thermal runaway reaction of the LiFePO₄ batteries. In this study, vent sizing package 2 (VSP2) and differential scanning calorimetry were employed to observe the thermal hazard of 18650 lithium-ion batteries and their content??LiFePO₄ cathode material, which were manufactured by Commercial Battery, Inc. Two states of the batteries were investigated, which was charged to 3.6?V (fully charged) and 4.2?V (overcharged), respectively, and important parameters were obtained, such as self-heating rate (dT?dt ^?1), pressure-rise rate (dP?dt ^?1), and exothermic onset temperature (T ₀). The results showed that T ₀ for fully charged is about 199.94?°C and T _max is about 243.23?°C. The entire battery for LiFePO₄ cathode material is more stable than other lithium-ion batteries, and an entire battery is more dangerous than a single cathode material. For process loss prevention, the data of battery of VSP2 test were applied as reference for design of safer devices.     

Preparation and characterization of high-rate and long-cycle LiFePO4/C nanocomposite as cathode material for lithium-ion battery

Olivine LiFePO₄/C nanocomposite cathode materials with small-sized particles and a unique electrochemical performance were successfully prepared by a simple solid-state reaction using oxalic acid and citric acid as the chelating reagent and carbon source. The structure and electrochemical properties of the samples were investigated. The results show that LiFePO₄/C nanocomposite with oxalic acid (oxalic acid: Fe²⁺= 0.75:1) and a small quantity of citric acid are single phase and deliver initial discharge capacity of 122.1 mAh/g at 1 C with little capacity loss up to 500 cycles at room temperature. The rate capability and cyclability are also outstanding at elevated temperature. When charged/discharged at 60 °C, this materials present excellent initial discharge capacity of 148.8 mAh/g at 1 C, 128.6 mAh/g at 5 C, and 115.0 mAh/g at 10 C, respectively. The extraordinarily high performance of LiFePO₄/C cathode materials can be exploited suitably for practical lithium-ion batteries.     

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.     

Thermal explosion synthesis of LiFePO4 as a cathode material for lithium ion batteries

Research on Chemical Intermediates - Olivine-type LiFePO4 cathode material was successfully synthesized by a simple method of thermal explosion (TE) using hexamethylenetetramine (C6H12N4) as fuel....     

Low-temperature synthesis of a green material for lithium-ion batteries cathode

Abstract

Battery technology is an important anthropogenic source of the heavy metals which are highly threatening to human health. A category of rechargeable lithium batteries that is of great interest is the set of batteries where the cathode material is a lithium iron phosphate (LiFePO₄). LiFePO₄ is an environmentally friendly and safe lithium-ion battery cathode material, but it has a key limitation, and that is its extremely low-electronic conductivity, a problem that can be greatly overcome by zinc-doping LiFePO₄. For the first time to our knowledge, a low-temperature method, that is advantageous both economically and technologically, for the synthesis of a zinc-doped LiFePO₄ is presented. Since the method appears to be applicable for synthesizing various zinc-doped LiFePO₄ compounds with the general formula LiFe_1?x Zn _x PO₄ (0<x<1), it is very promising for the production of a green cathode material for lithium-ion batteries.     

Li0.995Nb0.005Mn0.85Fe0.15PO4/C as a high-performance cathode material for lithium-ion batteries

Journal of Solid State Electrochemistry - Li0.995Nb0.005Mn0.85Fe0.15PO4/C was prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron...     

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.

     

Electrochemical studies of novel olivine-layered (LiFePO4-Li2MnO3) dual composite as an alternative cathode material for lithium-ion batteries

Journal of Solid State Electrochemistry - In the present work, olivine-layered composites, i.e., LiFePO4-Li2MnO3, are successfully synthesized in the form of a single monolithic electrode and layer...     

Direct reuse of LiFePO4 cathode materials from spent lithium-ion batteries: Extracting Li from brine

Due to the serious imbalance between demand and supply of lithium, lithium extraction from brine has become a research hotspot. With the demand for power lithium-ion batteries (LIBs) increased rapidly, a large number of spent LiFePO₄ power batteries have been scrapped and entered the recycling stage. Herein, a novel and efficient strategy is proposed to extract lithium from brine by directly reusing spent LiFePO₄ powder without any treatment. Various electrochemical test results show that spent LiFePO₄ electrode has appropriate lithium capacity (14.62 mg_Li/g_LiFePO4), excellent separation performance (α_Li-Na = 210.5) and low energy consumption (0.768 Wh/g_Li) in electrochemical lithium extraction from simulated brine. This work not only provides a novel idea for lithium extraction from brine, but also develops an effective strategy for recycling spent LIBs. The concept of from waste to wealth is of great significance to the development of recycling the spent batteries.     

Optimization of hydrothermally synthesized LiFePO4 nanoscaled particles for lithium-ion batteries

Phase-pure nano-LiFePO₄ was successfully fabricated under hydrothermal condition at different temperatures. We found that the obtained particle morphologies and sizes were temperature-dependent. Compared with other samples, the as-received LiFePO₄ synthesized at 200°C for 3 h presented monodisperse state. Moreover, this product possessed excellent electrochemical performance and cycling stability after annealing at 700°C for 1 h with glucose as carbon source.