Electrochemical and structural analysis of Mg substitution in lithium-rich layered oxide for lithium-ion battery

Mg-doped lithium-rich layered oxide Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ with smooth morphology is synthesized by co-precipitation followed by calcination. The morphologies of bare particles and electrodes have been studied through scanning electron microscopy (SEM), which illustrates that, compared with the Mg-doped particles, the pristine particles are characteristic of angular and corrosion is much more likely to happen. Additionally, the Mg substitution can make the crystal structure stable during the electrode process and then enhance the cycle performance. Electrochemical impedance spectroscopy and transmission electron microscopy have been utilized to gain insight to the properties of pristine and Mg-doped particles before and after the electrode process. Mg-doped particles show lower charge transfer resistance and higher diffusion coefficients (D) of the diffusing lithium ions. After 100 cycles at 250 mA g^?1, the morphology and crystal structure of Mg-doped materials show smaller changes than those of pristine particles.     

Enhancement of electrochemical performance in lithium-ion battery via tantalum oxide coated nickel-rich cathode materials

Nickel-rich cathode materials are increasingly being applied in commercial lithium-ion batteries to realize higher specific capacity as well as improved energy density. However, low structural stability and rapid capacity decay at high voltage and temperature hinder their rapid large-scale application. Herein, a wet chemical method followed by a post-annealing process is utilized to realize the surface coating of tantalum oxide on LiNi_0.88Mn_0.03Co_0.09O₂, and the electrochemical performance is improved. The modified LiNi_0.88Mn_0.03Co_0.09O₂ displays an initial discharge capacity of ～ 233 mAh/g at 0.1 C and 174 mAh/g at 1 C after 150 cycles in the voltage range of 3.0 V-4.4 V at 45℃, and it also exhibits an enhanced rate capability with 118 mAh/g at 5 C. The excellent performance is due to the introduction of tantalum oxide as a stable and functional layer to protect the surface of LiNi_0.88Mn_0.03Co_0.09O₂, and the surface side reactions and cation mixing are suppressed at the same time without hampering the charge transfer kinetics.     

Solvothermal synthesis and electrochemical performance of Ag-doped V6O13 as cathode material for lithium-ion battery

For the first time, belt-like V₆O₁₃ precursor was synthesized via a simple solvothermal method. Rod-like Ag-doped V₆O₁₃ was successfully synthesized by this method followed by heating at 350 °C. Both crystal domain size, electronic conductivity, and the lithium diffusion coefficient of the Ag-doped V₆O₁₃ samples are influenced by the added amount of AgNO₃. When the amount of AgNO₃ is 0.008 g, the product is rod-like particles, which are 0.1–0.3 μm wide and 1–2 μm long, and exhibits the best electrochemical performance. The enhanced electrochemical performance originates from its higher total conductivity, higher lithium diffusion coefficient, and better structural reversibility.     

Excellent long-term electrochemical performance of graphite oxide as cathode materials for lithium-ion batteries

A facile, scalable route has been adopted to synthesize graphite oxides with different degrees of oxidation. Subsequently, graphite oxides with rationally designed functional groups have been utilized as cathode materials for lithium-ion batteries (LIBs). The electrodes deliver the initial and second discharge capacities of 332 and 172 mAh g^?1 at a current density of 0.1 A g^?1, respectively. More importantly, a remarkable long-term cycling performance of 130 mAh g^?1 after 800 cycles has been gathered, with an ultralow capacity fading of 0.03% per cycle from the second cycle. The root cause of excellent cycling stability should be ascribed to the admirable reversibility of epoxy and carbonyl groups in graphite oxides during the Li-cycling. Meanwhile, the deep study has provided a novel way to avoid complex and expensive post-treatment process of graphite oxides, whose synthesis conditions are also optimized. Those striking features make graphite oxides as promising cathode materials for lithium-ion batteries.     

Synthesis and characterization of mixed vanadium oxide cathode materials for lithium-ion batteries

A family of mixed vanadium oxides LiCo_yNi_(1−y)VO₄ (x=0.2, 0.5 and 0.8) of potential use as high voltage cathode materials in lithium batteries, has been synthesized and characterized. In general the x-ray diffraction analysis showed that these compounds have an inverse spinel structure where about 85 % of the Ni²⁺ and Co²⁺ ions occupies octahedral sites and the rest tetrahedral sites along with the V⁵⁺ ions. Moreover, the annealing temperature plays a key role in determining the particle size, as demonstrated by scanning electron microscope analysis. Cycling voltammetry tests showed that the lithium insertion-extraction process in the LiCo_yNi_(1−y)VO₄ electrode materials occurs reversibly at around 4.3–4.4 V vs. Li and these results are confirmed by cycling tests. The cycling capacity is modest; however the trend of the cycling curves leads to foresee that an increase in capacity may be obtained by extending the charging process beyond 4.6 V vs. Li, once a stable electrolyte will be available. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

熔融盐法合成锂离子电池正极材料纳米LiNiO2

采用熔融盐法,在较低的温度和较短的时间制备了符合理论化学计量比的纳米LiNiO₂.研究表明,经过空气中的低温预烧,可以使制备的纯相纳米LiNiO₂具有更加优良的结晶性能和更佳的电化学特性.添加预烧步骤前后所得最终产物的初始容量分别为151和148 mAh ·g^-1,经过100周的循环,容量衰减到55和118 mAh ·g^-1,容量保持率分别为36.4%和79.7%.原因在于预烧后再进行煅烧降低了阳离子无序度,减少了混杂 关键词： 2')" href="#">LiNiO₂ 熔融盐法 锂离子电池 电化学性能     

Modified carbothermal synthesis and electrochemical performance of LiFePO4/C composite as cathode materials for lithium-ion batteries

LiFePO₄/C active materials were synthesized via a modified carbothermal method, with a low raw material cost and comparatively simple synthesis process. Rheological phase technology was introduced to synthesize the precursor, which effectively decreased the calcination temperature and time. The LiFePO₄/C composite synthesized at 700 °C for 12 h exhibited an optimal performance, with a specific capacity about 130 mAh g^?1 at 0.2C, and 70 mAh g^?1 at 20C, respectively. It also showed an excellent capacity retention ratio of 96 % after 30 times charge–discharge cycles at 20C. EIS was applied to further analyze the effect of the synthesis process parameters. The as-synthesized LiFePO₄/C composite exhibited better high-rate performance as compared to the commercial LiFePO₄ product, which implied that the as-synthesized LiFePO₄/C composite was a promising candidate used in the batteries for applications in EVs and HEVs.     

Synthesis of LiCoPO4 as a cathode material for lithium-ion battery by a polymer method

A polymer method has been used to synthesize high operation voltage LiCoPO₄ cathode material. Thermogravimetric analysis and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM),galvanostatic charge–discharge test and cyclic voltammetry (CV) are used to study the LiCoPO ₄ . The results show LiCoPO₄ has a well-crystallized olivine structure with submicron size. In the range of 3.0–5.1 V, the initial discharge capacities of polymer material are 97.3, 91.5, and 86.5 mAh g^?1 at 0.1, 0.2. and 1 C, respectively. Thus, the polymer method has a great potential in preparing electrode materials for lithium-ion batteries.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

Synthesis,characterization, and electrochemical properties of lithium-based fluorosulfate nanoparticles as cathode for lithium-ion batteries

Lithium-based fluorosulfate nanoparticles were synthesized by a simple and fast solid state reaction from the precursors FeSO₄?7H₂O and LiF ground by high energy ball milling. Through the introduction of excess of LiF, relatively pure LiFeSO₄F phase with polycrystalline structure was obtained. The structure, morphology, and element valence state were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS). The results demonstrate uniformly distributed particles and larger particles consisted of single crystalline structure, besides the valence states for different elements were analyzed and Fe²⁺ was confirmed. The cyclic voltammograms (CV) and charge-discharge cycling performances were employed to characterize electrochemical properties of prepared cathode material. It is very interesting that double redox peaks appeared reversibly. Meanwhile, it exhibited a relatively higher first-discharge capacity of 115 mAh/g at 0.05C and it still maintained above 60 mAh/g capacity after experiencing 30 times cycles at final 2C rate.     

Electrochemical performance of surfactant-processed LiFePO4 as a cathode material for lithium-ion rechargeable batteries

This study focuses on the effect of addition of surfactant as a dispersing agent during vibratory ball milling of LiFePO₄ (LFP) precursor materials on the electrochemical performance of solid-state reaction synthesized LFP for lithium-ion battery cathode material. LFP particles formed after calcinations of ball milled LFP precursors (Li₂CO₃, FeC₂O₄, and NH₄H₂PO₄) showed better size uniformity, morphology control, and reduced particle size when anionic surfactant (Avanel S-150) was used. The specific surface area of LFP particles increased by approximately twofold on addition of surfactant during milling. These particles showed significantly enhanced cyclic performance during charge/discharge due to a reduced polarization of electrode material. Electrodes fabricated from LFP particles by conventional milling process showed a 22 % decrease in capacity after 50 cycles, whereas the performance of electrode prepared by surfactant processed LFP showed only 3 % loss in capacity. The LFP particles were characterized using XRD, FE-SEM, particle size distribution, density measurement, and BET-specific surface area measurement. Electrochemical impedance spectra and galvanostatic charge/discharge test were performed for the electrochemical performance using coin-type cell.     

Hydrothermal synthesis and electrochemical performance of Mn-doped V<Subscript>6</Subscript>O<Subscript>13</Subscript> as cathode material for lithium-ion battery

Mn_xV_6?xO₁₃ (x?=?0.01, 0.02, 0.03, 0.04) were successfully synthesized via a simple hydrothermal method followed by heat-treatment. Both crystal domain size, electronic conductivity and the lithium diffusion coefficient of the Mn_xV_6?xO₁₃ samples were influenced by the doping amount of Mn²⁺. When x?=?0.02, the product was nano-sized particles and exhibited the best electrochemical performance. The enhanced electrochemical performance originated from its higher total conductivity and higher lithium diffusion coefficient.     

Synthesis of Co-coated lithium manganese oxide and its characterization as cathode for lithium ion battery

Co-coated LiMn₂O₄ was synthesized by electroless plating. The phase identification, surface morphology, and electrochemical properties of the synthesized powders were studied by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge–discharge experiments, respectively. The result shows that Co-coated LiMn₂O₄ particle has a coarse surface with a lot of holes. The specific capacity of Co-coated LiMn₂O₄ is 118 mAh g⁻¹, which is a bit less than 123 mAh g⁻¹ for the uncoated LiMn₂O₄. The capacity retention of Co-coated LiMn₂O₄ is 11% higher than the uncoated LiMn₂O₄ when the electrode is cycled at room temperature for 20 times. When cycled at the temperature of 55 °C, the capacity retention of Co-coated LiMn₂O₄ becomes 15% higher than the uncoated one.     

Synthesis and characterization of Co-doped lithium manganese oxide as a cathode material for rechargeable Li-ion battery

An attempt has been made to prepare cobalt-doped lithium manganese oxide with three different concentrations by simple molten salt method to enhance the electrical property of Li₄Mn₅O₁₂. Prepared samples were examined by XRD and SEM to identify its structure and morphology. Electrical properties were identified by impedance and conductivity analysis, and it was found that the material exhibits negative temperature coefficient (NTCR) property, i.e., semi-conducting nature. Among the various concentrations, 0.5 mol of Co-doped lithium manganese oxide has shown good conductivity of 3.1 × 10^?5 S cm^?1 at 433 K.     

A review of recent developments in the surface modification of LiMn2O4 as cathode material of power lithium-ion battery

LiMn₂O₄ (LMO) is a very attractive choice as cathode material for power lithium-ion batteries due to its economical and environmental advantages. However, LiMn₂O₄ in the 4-V region suffers from a poor cycling behavior. Recent research results confirm that modification by coating is an important method to achieve improved electrochemical performance of LMO, and the latest progress was reviewed in the paper. The surface treatment of LMO by coating oxides and nonoxide systems could decrease the surface area to retard the side reactions between the electrode and electrolyte and to further diminish the Mn dissolution during cycling test. At present, LiMn₂O₄ is the mainstreaming cathode material of power lithium-ion battery, and, especially the modified LMO, is the trend of development of power lithium-ion battery cathode material in the long term.     

Controllable synthesis of spherical silicon and its performance as an anode for lithium-ion batteries

Spherical silicon is controllably synthesized by the hydrolysis of tetraethylorthosilicate (TEOS) with the addition of different contents of ammonia to form SiO₂, then reduced by magnesium powder in argon atmosphere at 900 °C for 3 h. The experimental results show that the electrochemical performance of the as-prepared silicon anode is much affected by the morphology of silicon, and the spherical silicon with a particle size of 250–300 nm shows a reversible capacity of 1,345.8 mAh g^?1 with the capacity retention of 83.2 % after 20 cycles. The relationship between the electrochemical performance of the spherical silicon and the diameters of silicon sphere makes it possible to control the performance of the silicon anode by adjusting the hydrolysis conditions of TEOS.     

Enhanced electrochemical performance of LiMnBO<Subscript>3</Subscript> with conductive glassy phase: a prospective cathode material for lithium-ion battery

LiMnBO₃ has been identified as a promising cathode material for next-generation lithium-ion batteries. In this study, LiMnBO₃ along with glassy lithium borate material (LiMnBO₃ (II)) is synthesized by sol-gel method. X-ray diffraction (XRD) analysis depicts the existence of LiBO₂ glassy phase along with m-LiMnBO₃ phase. Transmission electron microscopy (TEM) analysis confirms the presence of LiBO₂ glassy phase. An enhanced electrical conductivity of 3.64 × 10^?7 S/cm is observed for LiMnBO₃ (II). The LiBO₂ glassy phase is found to promote the Li reaction kinetics in LiMnBO₃ (II). The synthesized LiMnBO₃ (II) delivers a first discharge capacity of 310 mAh g^?1 within a potential window of 1.5–4.5 V at C/10 rate. Further, a discharge capacity of 186 mAh g^?1 at the 27th cycle shows a better cycle performance. The enhanced capacity is due to the presence of LiBO₂ glassy phase and more than one Li-ion transfer in the lithium-rich stoichiometry of LiMnBO₃ (II). Density functional theory calculation reveals the exact electronic structure of m-LiMnBO₃ with a band gap of 3.05 eV. A charge transfer mechanism is predicted for delithiation process of m-LiMnBO₃.