Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

The influence of Li sources on physical and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials for lithium-ion batteries

LiNi_0.5Mn_1.5O₄ cathode materials were successfully prepared by sol–gel method with two different Li sources. The effect of both lithium acetate and lithium hydroxide on physical and electrochemical performances of LiNi_0.5Mn_1.5O₄ was investigated by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, and electrochemical method. The structure of both samples is confirmed as typical cubic spinel with Fd3m space group, whichever lithium salt is adopted. The grain size of LiNi_0.5Mn_1.5O₄ powder and its electrochemical behaviors are strongly affected by Li sources. For the samples prepared with lithium acetate, more spinel nucleation should form during the precalcination process, which was stimulated by the heat released from the combustion of extra organic acetate group. Therefore, the particle size of the obtained powder presents smaller average and wider distribution, which facilitates the initial discharge capacity and deteriorates the cycling performance. More seriously, there exists cation replacement of Li sites by transition metal elements, which causes channel block for Li ion transference and deteriorates the rate capability. The compound obtained with lithium hydroxide exhibits better electrochemical responses in terms of both cycling and rate properties due to higher crystallinity, moderate particle size, narrow size distribution and lower transition cation substitute content.     

Synthesis,characterization and lithium-intercalation properties of rod-like CaMoO<Subscript>4</Subscript> nanocrystals

Rod-like CaMoO₄ nanocrystals were synthesized via a template-based rheological phase reaction route as a novel method. The physical characterization was carried out by thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elected-area electron diffraction (SAED). A structure-directed role of hexamethylene tetramine (HMTA) was observed during the formation of CaMoO₄ nanocrystals. The electrochemical performance of CaMoO₄ as anode for lithium ion batteries has also been investigated by galvanostatic cycling and AC impedance spectroscopy. CaMoO₄/Li cell can deliver superior capacity than theoretical value in the initial cycle, and the much improved capacity was attributed to the contribution of oxygen besides the reduction of molybdenum during lithium insertion. Furthermore, a charge capacity of 276 and 438 mAh/g was retained after 50 cycles in the range of 0.01–2.50 V vs Li at a current density of 100 and 200 mA/g, respectively. The particle size and morphological properties were found to play an important role in fast lithium insertion/extraction performance and cycling stability at high rate.     

Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> nanoparticles by modified Pechini method and their enhanced rate capability

Layered LiNi_1/3Co_1/3Mn_1/3O₂ nanoparticles were prepared by modified Pechini method and used as cathode materials for Li-ion batteries. The pyrolytic behaviors of the foamed precursors were analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Structure, morphology and electrochemical performance characterization of the samples were investigated by X-ray diffraction (XRD), field emission scanning electron macroscopy(SEM), Brunauer-Emmett-Teller (BET) specific surface area and charge–discharge tests. The results showed that the samples prepared by modified Pechini method caclined at 900 °C for 10 h were indexed to pure LiNi_1/3Co_1/3Mn_1/3O₂ with well hexagonal structure. The particle size was in a range of 100–300 nm. The specific surface area was larger than that of the as-obtained sample by Pechini method. Initial discharge capacity of 163.8 mAh/g in the range 2.8–4.4 V (vs. Li/Li⁺) and at 0.1C for LiNi_1/3Co_1/3Mn_1/3O₂ prepared by modified Pechini method was obtained, higher than that of the sample prepared by Pechini method (143.5 mAh/g). Moreover, the comparison of electrochemical results at different current rates indicated that the sample prepared by modified Pechini method exhibited improved rate capability.     

Influence of Li source on tap density and high rate cycling performance of spherical Li[Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> for advanced lithium-ion batteries

Spherical Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode materials with different microstructure have been prepared by a continuous carbonate co-precipitation method using LiOH⋅H₂O, Li₂CO₃, CH₃COOLi⋅2H₂O and LiNO₃ as lithium source. The effects of Li source on the physical and electrochemical properties of Li[Ni_1/3Co_1/3Mn_1/3]O₂ are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The results show that the morphology, tap density and high rate cycling performance of Li[Ni_1/3Co_1/3Mn_1/3]O₂ spherical particles are strongly affected by Li source. Among the four Li sources used in this study, LiOH⋅H₂O is beneficial to enhance the tap density of Li[Ni_1/3Co_1/3Mn_1/3]O₂, and the tap density of as-prepared sample reaches 2.32 g cm⁻³. Meanwhile, Li₂CO₃ is preferable when preparing the Li[Ni_1/3Co_1/3Mn_1/3]O₂ with high rate cycling performance, upon extended cycling at 1 and 5C rates, 97.5% and 92% of the initial discharge capacity can be maintained after 100 cycles.     

锂离子电池正极材料LiV3O8-xClx的低温固相法合成及电化学性能研究

采用低温固相法成功地合成了锂离子电池正极材料LiV3O8-xClx (x=0.00,0.05,0.10,0.15)。分别用XRD、SEM、充放电实验、循环伏安、交流阻抗等测试方法研究了Cl- 的掺入对LiV3O8结构、形貌及电化学性能的影响。结果表明, Cl-的掺入显著地提高了材料的充放电循环性能。当掺杂量 x=0.10时,材料的循环性能最好, 循环100周后放电容量仍为198.6 mAh/g。     

Electrochemical properties of spinel Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles prepared via a low-temperature solid route

Spinel phase Li₄Ti₅O₁₂ (s-LTO) with an average primary particle size of 150 nm was synthesised via a solid state route by calcining a precursor mixture at 600 °C. The precursor was prepared from a stoichiometric mixture of TiO₂ nanoparticles and an ethanolic solution of Li acetate and activated by ball-milling. Effects of the calcination temperature and atmosphere are examined in relation to the coexistence of impurity phases by X-ray diffraction and ⁶Li MAS NMR. The charge capacity of s-LTO, determined from cyclic voltammogram at a scan rate of 0.1 mV/s, was 142 mAh/g. The capacity of our optimised material is superior to that of commercially available spinel (a-LTO), despite the considerably smaller BET-specific surface area of the former. The superior properties of our material were also demonstrated by galvanostatic charging/discharging. From these observations, we conclude that the presented low-temperature solid state synthesis route provides LTO with improved electrochemical performance.     

Synthesis and characterization of submicron size particles of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by microemulsion route

Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn₂O₄ is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles of LiMn₂O₄ in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm, as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g⁻¹ at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer resistance, a value of 0.62 eV is obtained for the activation energy of Mn³⁺/Mn⁴⁺ redox process, which accompanies the intercalation/deintercalation of the Li⁺ ion in LiMn₂O₄.     

Enhanced electrochemical performance of submicron LiCoO<Subscript>2</Subscript> synthesized by polymer pyrolysis method

Submicron LiCoO₂ was synthesized by a polymer pyrolysis method using LiOH and Co(NO₃)₂ as the precursor compounds. Experimental results demonstrated that the powders calcined at 800 °C for 12 h appear as well-crystallized, uniform submicron particles with diameter of about 200 nm. As a result, the as-prepared LiCoO₂ electrode displayed excellent electrochemical properties, with an initial discharge capacity of 145.5 mAh/g and capacity retention of 86.1% after 50 cycles when cycled at 50 mA/g between 3.5 and 4.25 V. When cycled between 3.5 and 4.5 V, the discharge capacity increased to 177.9 mAh/g with capacity retention of 85.6% after 50 cycles.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and LiCoO<Subscript>2</Subscript> composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn₂O₄/(1 ? x) LiCoO₂(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn₂O₄ and LiCoO₂ partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ～100 mAh/g.     

Effect of PEG molecular weight on the crystal structure and electrochemical performance of LiV3O8

This paper describes systematic studies on the effect of polyethylene glycol (PEG) molecular weight on the crystal structure and particularly the electrochemical performance of LiV₃O₈. Scanning electron microscopy results indicate that after the decomposition of PEG, the structure of resultant products exhibits differences in morphology (shape, particle size, and specific surface area). The electrochemical results show that LiV₃O₈ cathode material treated by PEG (mean molecular weight of 10,000) has greater initial discharge capacity and better cyclic stability than other materials treated with PEG of different molecular weight. Its initial discharge capacity is 282.1 mAh g⁻¹ and maintains 222.2 mAh/g after 50 cycles in 0.5 C rates (150 mA g⁻¹).     

Lithium AlPO<Subscript>4</Subscript> composite polymer battery with nanostructured LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode

The borate ester plasticized AlPO₄ composite solid polymer electrolytes (SPE) have been synthesized and studied as candidates for lithium polymer battery (LPB) application. The electrochemical and thermal properties of SPE were shown to be suitable for practical LPB. Nanostructured LiMn₂O₄ with spherical particles was synthesized via ultrasonic spray pyrolysis technique and has shown a superior performance to the one prepared via conventional methods as cathode for LPB. Furthermore, the AlPO₄ addition to the polymer electrolyte has improved the polymer battery performance. Based on the AC impedance spectroscopy data, the performance improvement was suggested as being due to the cathode/polymer electrolyte interface stabilization in the presence of AlPO₄. The Li/composite polymer electrolyte/nanostructured LiMn₂O₄ electrochemical cell showed stable cyclability during the various current density tests, and its performance was found to be quite acceptable for practical utilities at ambient temperature and showed remarkable improvements at 60 °C compared with the solid state reaction counterpart.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Electrochemical performance of LiVPO<Subscript>4</Subscript>F/C composite cathode prepared through amorphous vanadium phosphorus oxide intermediate

LiVPO₄F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus oxide (VPO) intermediate synthesized by a sol–gel method using H₃PO₄, V₂O₅ and citric acid as raw materials. The properties of LiVPO₄F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel method is amorphous and VPO₄ may exist in VPO intermediate. The compositions of LiVPO₄F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO₄F. The electrochemical tests show that LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This LiVPO₄F/C composite displays discharge capacity of 133 mAh g⁻¹ at 0.5 C (78 mA g⁻¹) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge capacity of 115 mAh g⁻¹ and capacity retention of 97% after 100 cycles.     

Al,B, and F doped LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as cathode material of lithium-ion batteries

A series of the mixed transition metal compounds, Li[(Ni_1/3Co_1/3Mn_1/3)_1–x-y Al _x B _y ]O_2-z F _z (x = 0, 0.02, y = 0, 0.02, z = 0, 0.02), were synthesized via coprecipitation followed by a high-temperature heat-treatment. XRD patterns revealed that this material has a typical α-NaFeO₂ type layered structure with R3^- m space group. Rietveld refinement explained that cation mixing within the Li(Ni_1/3Co_1/3Mn_1/3)O₂ could be absolutely diminished by Al-doping. Al, B and F doped compounds showed both improved physical and electrochemical properties, high tap-density, and delivered a reversible capacity of 190 mAh/g with excellent capacity retention even when the electrodes were cycled between 3.0 and 4.7 V.     

Physicochemical Properties of Li<Subscript>6</Subscript>V<Subscript>5</Subscript>O<Subscript>15</Subscript> as the Cathode Material for Lithium-Ion Batteries

Lithium-vanadium oxide with the formal composition Li₆V₅O₁₅, uniform microsctructure, and the particle size of 100 nm is synthesized by a solution method. The synthesized compound is characterized by the methods of X-ray diffraction analysis, Raman spectroscopy, and synchronous thermal analysis. The total electric conductivity is measured by the method of impedance spectroscopy and its electronic component is estimated by dc method. In the temperature range of 200–400°C, Li₆V₅O₁₅ represents a mixed electronic- ionic conductor with predomination of the ionic component and is thermally stable up to 550°С. Preliminary tests of a laboratory model of electrochemical cell Li|LiPF₆|Li₆V₅O₁₅ are carried out.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

Effect of lithium boron oxide glass coating on the electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript>

The effect of the lithium boron oxide glass coating on the electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ has been investigated via solution method. The morphology, structure, and electrochemical properties of the bare and coated LiNi_1/3Co_1/3Mn_1/3O₂ are characterized by scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and charge–discharge tests. The results showed that the lattice structure of LiNi_1/3Co_1/3Mn_1/3O₂ is not changed after coating. The coating sample shows good high-rate discharge performance (148 mAh g⁻¹ at 5.0 C rate) and cycling stability even at high temperature (with the capacities retention about 99% and 87% at room and elevated temperature after 50 cycles). The Li⁺ diffusion coefficient is also largely improved, while the charge transfer resistance, side reactions within cell, and the erosion of Hydrofluoric Acid all reduced. Consequently, the good electrochemical performances are obtained.     

Oleic acid-assisted preparation of LiMnPO<Subscript>4</Subscript> and its improved electrochemical performance by Co doping

LiMnPO₄, with a particle size of 50–150 nm, was prepared by oleic acid-assisted solid-state reaction. The materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the materials were investigated by galvanostatic cycling. It was found that the introduction of oleic acid in the precursor led to smaller particle size and more homogeneous size distribution in the final products, resulting in improved electrochemical performance. The electrochemical performance of the sample could be further enhanced by Co doping. The mechanism for the improvement of the electrochemical performance was investigated by Li-ion chemical diffusion coefficient ( [(D)\tilde]_\textLi ) \left( {{{\tilde{D}}_{\text{Li}}}} \right) and electrochemical impedance spectroscopy measurements. The results revealed that the [(D)\tilde]_\textLi {\tilde{D}_{\text{Li}}} values of LiMnPO₄ measured by cyclic voltammetry method increase from 9.2 × 10⁻¹⁸ to 3.0 × 10⁻¹⁷ cm² s⁻¹ after Co doping, while the charge transfer resistance (R _ct) can be decreased by Co doping.     

Comparison of different soft chemical routes synthesis of submicro-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and their influence on its electrochemical properties

A comparative study of submicro-crystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as hydrothermal and sol–gel methods is made. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammogram, charge–discharge test, and electrochemical impedance spectroscopy (EIS). The results show that the electrochemical performances of spinel LiMn₂O₄ depend strongly upon the synthesis method. The LiMn₂O₄ powder prepared by hydrothermal route has higher specific capacity and better cycling performance than the one synthesized from sol–gel method. The former has the max discharge capacity of 114.36 and 99.78 mAh g⁻¹ at the 100th cycle, while the latter has the max discharge capacity of 98.67 and 60.25 mAh g⁻¹ at the 100th cycle. The selected equivalent circuit can fit well the EIS results of synthesized LiMn₂O₄. For spinel LiMn₂O₄ from sol–gel method and hydrothermal route in the first charge process R _SEI remain almost invariable, R _e and R _ct first decreasing and then increasing with the increase of polarization potential.