Optimizing preparation conditions for 5 V electrode performance, and structural changes in Li1−xNi0.5Mn1.5O4 spinel

A new lithium-excess method is used for the synthesis of LiNi_0.5Mn_1.5O₄ electrode materials at temperatures in the 600-800 °C range. Higher average manganese oxidation state and lower impurity contents are detected from X-ray diffraction in the spinel samples, as compared with stoichiometric synthesis. These properties cause the virtual elimination of the 4 V capacity, thus allowing a higher performance of these 5 V materials. A two-phase model of lithium extraction-insertion is detected by X-ray diffraction of electrodes prepared at different extensions of charge.     

Synthesis and characterization of abundant Ni-doped LiNixMn2−xO4 (x = 0.1-0.5) powders by spray-drying method

The structure and electrochemical properties of LiNi_xMn_2−xO₄ cathode materials for lithium ion batteries were studied by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), cyclic voltammetry, and galvanostatic charge-discharge tests. The cathodes with different Ni contents (LiNi_xMn_2−xO₄, x = 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by a spray-drying method and showed a single-phase spinel structure without any impurity. The amount of Ni has a large effect on the electrochemical characteristics. Capacity values of different voltage ranges (4- and 5-V ranges) change obviously with amount of Ni-doped. Also, the total discharge capacities increase with the Ni content, and all of them have good cycle stability.     

Improved cycling performance of oxygen-stoichiometric spinel Li1+xAlyMn2−x−yO4+δ at elevated temperature

Li_1+xAl_yMn_2−x−yO_4±δ spinel cathode materials for lithium-ion batteries have been prepared by two methods, a specific two-step and the conventional one-step solid-state calcination methods. Compared with the conventional method, the new two-step method can guarantee the oxygen stoichiometry in spinel samples as well as reduced surface area. These characters lead to the improvement in cycling performance of spinel cathode even at elevated temperature. Moreover, the increase in doping amount of Al into Mn-spinel contributes to smearing the oxygen deficiency at high calcination temperature (1000 °C). The oxygen stoichiometric spinel samples exhibited greatly improved cycling performance. Further, Mn dissolution from spinel cathodes into the electrolyte was sufficiently suppressed even at elevated temperature of 60 °C. This beneficial influence would be reflected more remarkably in the cycles of lithium-ion full cells (spinel/C).     

Preparation and characterization of partially substituted LiMyMn2−yO4 (M=Ni, Co, Fe) spinel cathodes for Li-ion batteries

The electrochemical and thermal behaviors of the spinels-LiMn₂O₄, LiCo_1/6Mn_11/6O₄, LiFe_1/6Mn_11/6O₄, and LiNi_1/6Mn_11/6O₄ were studied using electrochemical and thermochemical techniques. The electrochemical techniques included cyclic voltammetry, charge-discharge cycling of 2016 coin cells and diffusion coefficient measurements using Galvanostatic Intermittent Titration Technique. Better capacity retention was observed for the substituted spinels (0.11% loss per cycle for LiCo_1/6Mn_11/6O₄; 0.3% loss per cycle for LiFe_1/6Mn_11/6O₄; and 0.2% loss per cycle for LiNi_1/6Mn_11/6O₄) than for the lithium manganese dioxide spinel (1.6% loss per cycle for first ten cycles, 0.9% loss per cycle for 33 cycles) during 33 cycles. The Differential Scanning Calorimetry results showed that the cobalt substituted spinel has better thermal stability than the lithium manganese oxide and other substituted spinels.     

Comparisons of graphite and spinel Li1.33Ti1.67O4 as anode materials for rechargeable lithium-ion batteries

The aim of this work was to compare the electrochemical behaviors and safety performance of graphite and the lithium titanate spinel Li_1.33Ti_1.67O₄ with half-cells versus Li metal. Their electrochemical properties in 1 M LiPF₆/EC + DEC (1:1 w/w) or 1 M LiPF₆/PC + DEC (1:1 w/w) at room and elevated temperatures (30 and 60 °C) have been studied using galvanostatic cycling. At 30 °C graphite has higher reversible capacity than Li_1.33Ti_1.67O₄ when using the LiPF₆/EC + DEC as electrolyte. At 60 °C graphite declines in cell capacity yet Li_1.33Ti_1.67O₄ remains almost unchanged. In a propylene carbonate (PC) containing electrolyte, graphite electrode exfoliates and loses its mechanical integrity while Li_1.33Ti_1.67O₄ electrode is very stable. An accelerating rate calorimeter (ARC) and microcalorimeter have been used to compare the thermal stability of lithiated lithium titanate spinel and graphite. Results show that Li_1.33Ti_1.67O₄ may be used as an alternative anode material offering good battery performance and higher safety.     

Synthesis and electrochemical properties of layered Li[Li(1/3−x/3)CrxMn(2/3−2x/3)]O2 prepared by sol-gel method

The Li[Li_(1/3−x/3)Cr_xMn_(2/3−2x/3)]O₂ (0.15 ≤ x ≤ 0.3) cathode materials were synthesized by sol-gel process using aqueous solutions of metal acetates and citric acid as the chelating agent. The precipitate of metal citrate was dried in a vacuum oven for 10 h at 100 °C. After drying, the gel precursor was calcined at 300 °C for about 10 h. The resulted powder was ground and heated at 900 °C. The structural characterization was carried out by fitting the XRD data with Rietveld program. The samples exhibited a well defined layered structure and the unit cell parameters linearly increased with increasing chromium contents in Li[Li_(1/3−x/3)Cr_xMn_(2/3−2x/3)]O₂ Surface morphology was determined by SEM and HRTEM and it is found that the cathode material consisted of highly ordered single crystalline particles with layered-hexagonal structure. Test cells were assembled and cycled in the voltage range of 2.0-4.9 V with a current density of 7.947 mA/g. Electrode with (x = 0.2) delivered a high reversible capacity of around 280 mA h/g in cycling.     

Improvement of electrochemical properties of Li[Ni0.4Co0.2Mn(0.4−x)Mgx]O2−yFy cathode materials at high voltage region

Spherical Li[Ni_0.4Co_0.2Mn_(0.4−x)Mg_x]O_2−yF_y (x = 0, 0.04, y = 0, 0.08) with phase-pure and well-ordered layered structure have been synthesized by heat-treatment of spherical [Ni_0.4Co_0.2Mn_0.4−xMg_x]₃O₄ precursors with LiOH·H₂O and LiF salts. The average particle size of the powders was about 10-15 μm and the size distribution was quite narrow due to the homogeneity of the metal carbonate, [Ni_0.4Co_0.2Mn_(0.4−x)Mg_x]CO₃ (x = 0, 0.04) precursors. Although the Li[Ni_0.4Co_0.2Mn_0.36Mg_0.04]O_1.92F_0.08 delivered somewhat slightly lower initial discharge capacity, however, the capacity retention, interfacial resistance, and thermal stability were greatly enhanced comparing to the Li[Ni_0.4Co_0.2Mn_0.4]O₂ and Li[Ni_0.4Co_0.2Mn_0.36Mg_0.04]O₂.     

Relationship between electrochemical behavior and Li/vacancy arrangement in ramsdellite type Li2+xTi3O7

The changes of Li⁺/vacancy arrangement in Li_2+xTi₃O₇ with a ramsdellite-type structure upon topo-electrochemical Li⁺ insertion were investigated by the entropy measurement of reaction combined with the Monte Carlo simulation. The experimental entropy measurement was conducted by potentiometric and calorimetrical methods. The obtained experimental data were in good accordance with simulated results.The results indicated that the ordered Li⁺/vacancy arrangement appeared at the compositions of x ∼ 0.45 and ∼1.20, where the observed entropy of reaction humped. The ordering of Li/vacancy were also indicated at the composition x ∼ 0.24 and 1.16 in Li_2+xTi₃O₇ by the Monte Carlo simulation which considers the most stable Li/vacancy arrangement in terms of Coulombic interaction. This substantial agreement between electrochemical behaviors and computational results confirmed that the formation of superstructure arising from Li/vacancy arrangement during the electrochemical reaction deeply related to the atomic level Coulombic interactions.     

Optimum synthesis of Li2Fe1−xMnxSiO4/C cathode for lithium ion batteries

Li₂Fe_1−xMn_xSi0₄/C cathode materials were synthesized by mechanical activation-solid-state reaction. The effects of Mn-doping content, roasting temperature, soaking time and Li/Si molar ratio on the physical properties and electrochemical performance of the Li₂Fe_1−xMn_xSi0₄/C composites were investigated. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), charge-discharge tests and AC impedance measurements. SEM images suggest that the morphology of the Li₂Fe_1−xMn_xSi0₄/C composite is sensitive to the reaction temperature. Samples synthesized at different temperatures have different extent of agglomeration. Being charged-discharged at C/32 between 1.5 and 4.8 V, the Li₂Fe_0.9Mn_0.1Si0₄/C synthesized at the optimum conditions shows good electrochemical performances with an initial discharge capacity of 158.1 mAh g⁻¹ and a capacity retention ratio of 94.3% after 30 cycles. AC impendence investigation shows Li₂Fe_0.9Mn_0.1SiO₄/C have much lower resistance of electrode/electrolyte interface than Li₂FeSiO₄/C.     

Greatly improved elevated-temperature cycling behavior of Li1+xMgyMn2−x−yO4+δ spinels with controlled oxygen stoichiometry

A new type of oxygen stoichiometric and Mg-doped LiMn₂O₄ spinel with improved crystallinity and decreased surface area was synthesized by a special “two-step” method: first, calcinate the mixture of metal oxides at “ultra-high” temperatures (950-1100 °C) to obtain an intermediate product with improved crystallinity, larger particle size and oxygen defects; then, anneal the intermediate at relatively low temperatures (600-800 °C) with the addition of extra LiOH to achieve oxygen stoichiometry. These spinels with general formula Li_1+xMg_yMn_2−x−yO_4+δ or (Li, Mg, Mn)₃O_4+δ are oxygen-rich based on chemical analysis (O/(Li+Mg+Mn) ratio larger than 4:3), and they can be called oxygen stoichiometric spinels with metal cation vacancies and rewritten as [Li]_8a[Li_nMg_mMn_{2−n−m−p}□_p]_16d[O₄]_32e. This new kind of materials with controlled oxygen stoichiometry exhibited greatly improved cycling performance and reduced Mn dissolution at elevated temperatures over that of other Mg-doped materials prepared by conventional “one-step” method.     

Amorphous LiCoO2 thin films on Li1+x+yAlxTi2−xSiyP3−yO12 prepared by radio frequency magnetron sputtering for all-solid-state Li-ion batteries

Amorphous LiCoO₂ thin films were deposited on the NASICON-type glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 180 °C. The as-deposited LiCoO₂ thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscope. All-solid-state Li/PEO₁₈-Li (CF₃SO₂)₂N/LATSP/LiCoO₂/Au cells were fabricated using the amorphous film. The electrochemical performance of the cells was investigated by galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. It was found that the amorphous LiCoO₂ thin film shows a promising electrochemical performance, making it a potential application in microbatteries for microelectronic devices.     

Preparation and cycling performance of Aland F co-substituted compounds Li4AlxTi5−xFyO12−y

Li₄Al_xTi_5−xF_yO_12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al³⁺ and F⁻ ions entered the structure of spinel-type Li₄Ti₅O₁₂. Charge-discharge cycling results at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.5 and 0.5 V showed that the Al³⁺ and F⁻ substitutions improved the first total discharge capacity of Li₄Ti₅O₁₂. However, Al³⁺ substitution greatly increased the reversible capacity and cycling stability of Li₄Ti₅O₁₂ while F⁻ substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al³⁺-F⁻-co-substituted specimen was better than the F⁻-substituted one but worse than the Al³⁺-substituted one.     

Fabrication and characterization of Li1+x−yNb1−x−3yTix+4yO3 substrates using aqueous tape casting process

An aqueous system for tape casting Li_1+x−yNb_1−x−3yTi_x+4yO₃ (LNT) ceramics was developed using poly(vinyl alcohol) (PVA) binder, ethylene alcohol (EG) plasticizer and ammonium salt of polycarboxylate (PCA-NH₄) dispersant. The zeta potential measurement showed that the isoelectric point of the LNT particles moved slightly toward more acid region after the dispersant absorbed on the particles, while the zeta potential increased significantly. The rheological test indicated that the ceramic slurry exhibited a typical pseudoplastic behavior without thixotropy. The effect of solid loading on the properties of the green tapes was investigated. The increase in the solid loading increased the tensile strength and the green density of the tapes. TGA analysis indicated that the organic additives in the green tapes can be completely removed by heat treatment at 600 °C. SEM micrographs showed that the microstructure of the green and sintered tapes was homogeneous.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

Electrochemical performance of LiV3−xNixO8 cathode materials synthesized by a novel low-temperature solid-state method

A series of cathode materials for lithium ion batteries with the formula LiV_3−xNi_xO₈ (x = 0.000, 0.025, 0.050 and 0.100) have been synthesized by a novel low-temperature solid-state method. The synthesized cathode materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), discharge-charge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These results indicate that LiV_2.95Ni_0.050O₈ shows much better electrochemical performances than LiV₃O₈. This is due to better electrochemical reversibility and lower particle-to-particle resistance after Ni²⁺ doping.     

尖晶石型LiMn2O4正极材料的最新研究进展

尖晶石型锰酸锂以成本低廉、资源丰富和良好的安全性能,成为动力锂离子电池的理想正极材料。但尖晶石LiMn2O4高温循环性能差限制了其应用。阐述了尖晶石LiMn2O4容量衰减的机理;详细介绍了国内外在LiMn2O4正极材料体相掺杂和表面包覆改性的研究进展,并对体相掺杂和表面包覆改性LiMn2O4正极材料电化学性能提高的机理进行了讨论。最后对尖晶石LiMn2O4正极材料今后的发展方向进行了展望。     

Spray pyrolysis synthesis of nanostructured LiFexMn2−xO4 cathode materials for lithium-ion batteries

A series of partially Fe-substituted lithium manganese oxides LiFe_xMn_2−xO₄ (0 ≦ x ≦ 0.3) was successfully synthesized by an ultrasonic spray pyrolysis technique. The resulting powders were spherical nanostructured particles which comprised the primary particles with a few tens of nanometer in size, while the morphology changed from spherical and porous to spherical and dense with increasing Fe substitution. The densification of particles progressed with the amount of Fe substitution. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns.The as-prepared powders were then sintered at 750 °C for 4 h in air. However, the particles morphology and pure spinel phase of LiFe_xMn_2−xO₄ powders did not change after sintering. The as-sintered powders were used as cathode active materials for lithium-ion batteries, and cycle performance of the materials was investigated using half-cells Li/LiFe_xMn_2−xO₄. The first discharge capacity of Li/LiFe_xMn_2−xO₄ cell in a voltage 3.5-4.4 V decreased as the value x increased, however these cells exhibited stable cycling performance at wide ranges of charge-discharge rates.     

Synthesis of spinel Li4Mn5O12 with an aid of mechanochemical treatment

A mechanochemically assisted method for synthesizing spinel Li₄Mn₅O₁₂ has been proposed in this paper. The method involves grinding a mixture of LiOH·H₂O and γ-MnO₂ in ambient air, followed by heating the ground product. The grinding of the mixture was conducted by using a planetary ball mill, causing their structural changes into amorphous state, which is lithium manganese oxides hydrated (Li-Mn-O·nH₂O). The ground product can be crystallized into lithium manganese oxide by heating at about 400 °C or more. Heating the ground product at around 600 °C for 12 h results in the formation of pure phase of the spinel. Temperature in the heating stage is an important factor in crystallization of the spinel from the amorphous mixture, and heating up to about 600 °C is suitable for the formation of pure phase spinel. The product synthesized is very fine powder with mean grain size of 100 nm.     

Zr-doped Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) as cathode material for lithium ion batteries

Layered Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi_0.475Mn_0.475Zr_0.05O₂ has a rougher surface than that of LiNi_0.5Mn_0.5O₂. The Li/Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi_0.475Mn_0.475Zr_0.05O₂ cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi_0.5Mn_0.5O₂ cell. We found that the oxidation of oxygen and the Mn³⁺ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni_0.5−xMn_0.5−xZr_2x]O₂ (x = 0, 0.025) cathode was improved by Zr doping.     

Synthesis and properties of mullite-type (Bi1−xSrx)2(M1−yMy)4O9−x (M = Al, Ga, Fe)

Mullite-type A₂M₄O₉ phases (M = Al, Ga, Fe), representing promising oxygen conducting materials for solid oxide fuel cells (SOFCs), were synthesized using the glycerine- and the EDTA/citric acid synthesis method. For strontium-doped material pure phases could be obtained only by washing the samples after the heating in both synthesis methods. Temperature dependent investigations were carried out to show the influence of the metal atoms on the structural stability and thermal expansion coefficients. Whereas the Sr-free phases show a quasi linear thermal expansion behavior in all three directions up to their incongruent melting points, a discontinuity in the measured range is observed for the investigated strontium doped dibismuth-nonaoxotetrametallate(III) caused by the decomposition into Bi₂M₄O₉, strontium metallates and bismuthoxide. Big single crystals were only observed for the Sr-free compound, of which the structure of Bi₂(Ga_0.45Fe_0.55)₄O₉ will be presented here in the Bärnighausen tree corresponding mullite-type setting.