Improved capacity and rate capability of Ru-doped and carbon-coated Li4Ti5O12 anode material

Pure Li₄Ti₅O₁₂, modified Li₄Ti₅O₁₂/C, Li₄Ru_0.01Ti_4.99O₁₂ and Li₄Ru_0.01Ti_4.99O₁₂/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li₄Ru_0.01Ti_4.99O₁₂/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li₄Ru_0.01Ti_4.99O₁₂/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li₄Ti₅O₁₂.It is expected that the Li₄Ru_0.01Ti_4.99O₁₂/C will be a promising anode material to be used in high-rate lithium ion battery.     

Porous Li4Ti5O12 anode material synthesized by one-step solid state method for electrochemical properties enhancement

A porous Li₄Ti₅O₁₂ anode material was successfully synthesized from mixture of LiCl and TiCl₄ with 70 wt% oxalic acid by a modified one-step solid state method. The anode material Li₄Ti₅O₁₂ exhibited a cubic spinel structure and only one voltage plateau occurred around 1.5 V. The initial capacity of porous Li₄Ti₅O₁₂ was 167 and 133 mAh g⁻¹ at 0.5 and 1C charge/discharge rate, respectively, and the capacity retention maintained above 98% after 200 cycles. The porous Li₄Ti₅O₁₂ structure showed promising rate performance with a capacity of 70 mAh g⁻¹ at charge/discharge 10C rate after 200 cycles. It was demonstrated that the porous structure could withstand 50C charge/discharge rate and exhibited excellent cycling stability.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Characterization and electrochemical properties of carbon-coated Li4Ti5O12 prepared by a citric acid sol-gel method

Since carbon coating can effectively improve electrical wiring of Li₄Ti₅O₁₂ and thus enhance its high rate performance, a novel and simple citric acid sol-gel method for in situ carbon coating is employed in this study. The effects of the amount of the carbon source in the starting xerogel on the particle size, the resistance and the electrochemical performance of the synthesized Li₄Ti₅O₁₂ samples are systematically studied. The physical and electrochemical properties of the obtained samples have been characterized by XRD, TG-DSC, SEM, TEM, BET, A.C. impedance, galvanostatically charge-discharge and cyclic voltammetry tests. The results show that the initial amount of the carbon source in the starting xerogel is a critical factor which determines the content of the coated carbon and the pore volume, therefore governs the high rate performance of the Li₄Ti₅O₁₂/C composites. The Li₄Ti₅O₁₂/C composite with in situ carbon coating of 3.5 wt% exhibits the best electrochemical performance which delivers delithiation capacities of 143.6 and 133.5 mAh g⁻¹ with fairly stable cycling performance even after 50 cycles at 0.5C and 1C rate, respectively.     

二步煅烧法制备高振实密度钛酸锂负极材料

以Li2CO3和纳米TiO2为原料,通过二步煅烧固相反应法制备Li4Ti5O12负极材料。研究前驱体球磨以及球磨时间对合成Li4Ti5O12样品振实密度和电化学性能的影响。借助XRD、SEM、振实密度仪和充放电测试仪、电化学综合测试仪表征Li4Ti5O12材料的物理性能和电化学性能。结果表明:球磨工艺能够提高Li4Ti5O12的纯度,并有效提高其振实密度和电化学性能;球磨时间为2 h时,所得材料的振实密度达1.70 g/cm3,0.1C首次放电比容量为174 mA.h/g,5C放电比容量达124.2 mA.h/g。     

Nanostructured MgFe2O4 as anode materials for lithium-ion batteries

Transition metal oxides in the nano size region are enormous attention as a new generation of anode materials for high energy density Li-ion batteries. MgFe₂O₄ is used for the first time as active electrode vs. lithium metal in test cells. The research has been focused on the effect of grain size of MgFe₂O₄ and their electrochemical performance studied. In this studies, nanostructured milled MgFe₂O₄ (grain size 19 nm) sample have been compared with relatively large-sized as-prepared sample (grain size 72 nm). From the result, the 19 nm grain size sample delivered an improved discharge capacity of around 850 mAh/g, whereas it is only 630 mAh/g for as-prepared sample (72 nm). These values are two times higher than that of a carbon anode (372 mAh/g). The anomalous capacity may be associated with the formation of oxygen rich MgFe₂O₄ samples.     

Charge compensation, electrical and dielectric behavior of lanthanum doped CaCu3Ti4O12

Mechanism of charge compensation on lanthanum, (La³⁺) substitution on Ca site in calcium copper titanate (CaCu₃Ti₄O₁₂), and its effect on resulting electrical and dielectric properties has been studied in the present investigation. For this purpose samples were prepared according to two stoichiometries viz. La_xCa_(1−3x/2)Cu₃Ti₄O₁₂ (x ≤ 0.09) and La_xCa_(1−x)Cu₃Ti₄O₁₂ (x = 0.03) by solid state ceramic route. The former represents ionic compensation while the later is in accordance with electronic compensation. Nature of charge carriers is identified by measuring Seebeck coefficient which is found to be negative in the entire range of measurement. In order to understand the mechanism of conduction, ac conductivity is measured as a function of temperature and frequency. Space charge polarization is the dominant polarization mechanism phenomenon at low frequency and high temperature while orientation polarization dominates at low temperature and high frequency. Impedance analysis confirms the formation of internal barrier layers which is responsible for high dielectric constant in these samples.     

Dielectric relaxation behaviors of pure and Pr6O11-doped CaCu3Ti4O12 ceramics in high temperature range

Pure and Pr₆O₁₁-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz-3 MHz and 290-490 K. The third phase of Ca₂CuO₃ was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr³⁺ and Pr⁴⁺) substituting Ca²⁺. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 10²-10⁵ Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr₆O₁₁ doping.     

In situ synthesis and characterization of polyaniline–CaCu3Ti4O12 nanocrystal composites

High dielectric constant (ca. 2.4 × 10⁶ at 1 kHz) nanocomposite of polyaniline (PANI)/CaCu₃Ti₄O₁₂ (CCTO) was synthesized using a simple procedure involving in situ polymerization of aniline in dil. HCl. The PANI and the composite were subjected to X-ray diffraction, Fourier transform infrared, thermo gravimetric, scanning electron microscopy and transmission electron microscopy analyses. The presence of the nanocrystallites of CCTO embedded in the nanofibers of PANI matrix was established by TEM. Frequency dependent characteristics of the dielectric constant, dielectric loss and AC conductivity were studied for the PANI and the composites. The dielectric constant increased as the CCTO content increased in PANI but decreased with increasing frequency (100 Hz–1 MHz) of measurement. The dielectric loss was two times less than the value obtained for pure PANI around 100 Hz. The AC conductivity increased slightly up to 2 kHz as the CCTO content increased in the PANI which was attributed to the polarization of the charge carriers.     

Preparation of Fe2O3/graphene composite and its electrochemical performance as an anode material for lithium ion batteries

The micro-sized sphere Fe₂O₃ particles doped with graphene nanosheets were prepared by a facile hydrothermal method. The obtained Fe₂O₃/graphene composite as the anode material for lithium ion batteries showed a high discharge capacity of 660 mAh g⁻¹ during up to 100 cycles at the current density of 160 mA g⁻¹ and good rate capability. The excellent electrochemical performance of the composite can be attributed to that graphene served as dispersing medium to prevent Fe₂O₃ microparticles from agglomeration and provide an excellent electronic conduction pathway.     

Improved dielectric and non-ohmic properties of Ca2Cu2Ti4O12 ceramics prepared by a polymer pyrolysis method

Non-ohmic and dielectric properties of Ca₂Cu₂Ti₄O₁₂ (CaCu₃Ti₄O₁₂/CaTiO₃ composite) ceramics prepared by a polymer pyrolysis method (PP-ceramic samples) are investigated. The PP-ceramics show a highly dense structure and improved non-ohmic and dielectric properties compared to the ceramics obtained by a solid state reaction method (SSR-ceramic samples). ?′ (tan δ) of the PP-ceramic samples is found to be higher (lower) than that of the SSR-ceramic samples. Interestingly, the PP-ceramic sintered at 1050 °C for 10 h exhibits the high ?′ of 2530 with weak frequency dependence below 1 MHz, the low tan δ less than 0.05 in the frequency range of 160 Hz-177 kHz, and the little temperature coefficient, i.e., |Δ?′| ≤ 15 % in the temperature range from −55 to 85 °C. These results indicate that the CaCu₃Ti₄O₁₂/CaTiO₃ composite system prepared by PP method is a promising high-?′ material for practical capacitor application.     

Synthesis and characterization of in situ carbon-coated Li2FeSiO4 cathode materials for lithium ion battery

Li₂FeSiO₄/C composites with in situ carbon coating were synthesized via sol-gel method based on acid-catalyzed hydrolysis/condensation of tetraethoxysilane (TEOS) with sucrose and l-ascorbic acid as carbon additives, respectively. As-obtained Li₂FeSiO₄/C composites prepared with l-ascorbic acid as a carbon additive are composed of nanoparticulate Li₂FeSiO₄ in an intimate contact with a continuous thin layer of residual carbon and exhibit large specific surface area up to 395.7 m² g⁻¹. The results indicate that structure of the residual carbon is graphene-rich with obviously lower disordered/graphene (D/G) ratio. These as-obtained Li₂FeSiO₄/C composites exhibit first discharge capacity of 135.3 mAh g⁻¹ at C/16 and perform cycling stability, which are superior to those of Li₂FeSiO₄/C composites synthesized with sucrose as a carbon additive.     

Sol-gel synthesis of Bi3.25La0.75Ti3O12 nanotubes

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) nanotubes were synthesized by sol-gel technique using nanochannel porous anodic aluminum oxide (AAO) templates, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). BLT nanotubes with diameter of around 240 nm and the wall thickness of about 25 nm exhibited a single orthorhombic perovskite structure and highly preferential crystal growth along the [1 1 7] orientation, which have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. The formation mechanism of BLT nanotubes was discussed.     

A literature review and test: Structure and physicochemical properties of spinel LiMn2O4 synthesized by different temperatures for lithium ion battery

A series of LiMn₂O₄ spinel was prepared by adipic acid-assisted sol–gel method at different temperatures. The structure and physicochemical properties of spinel LiMn₂O₄ synthesized by different temperatures were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron micrographs (SEM), inductively coupled plasma-mass spectroscopy (ICP-MS), galvanostatic charge–discharge test, and cyclic voltammetry (CV), respectively. TG–DTA shows that the weight loss occurs in four temperature regions during the synthesis of LiMn₂O₄. XRD indicates that the sintering temperature affects the formation of spinel phase, and prominent LiMn₂O₄ spinel powder with smaller atom location confusion forms about 800 °C. XPS reveals that the manganese oxidation state in spinel lithium manganese oxide synthesized at different temperatures is between +3 and +4. SEM shows that LiMn₂O₄ spinel synthesized at 800 °C has the uniform, nearly cubic structure morphology with narrow size distribution. ICP-MS indicates that the average chemical valence of Mn element of LiMn₂O₄ synthesized at 800 °C is the most close to 3.5 among the samples synthesized at different temperatures. CV illustrates that the LiMn₂O₄ synthesized at 800 °C has the best electrochemical activity. Charge–discharge test explains that the capacity retention sintered at 350, 700 and 800 °C over the first 50 cycles is 93.6%, 86.1% and 85.2%, respectively, but the discharge capacity at the 50th cycle is 82.2, 104.8 and 110.8 mAh g⁻¹, respectively.     

Preparation, structure and photoluminescence of nanoscaled-Nd: Lu3Al5O12

Nd:Lu₃Al₅O₁₂ (Nd:LuAG) nano-crystalline was synthesized by co-precipitation method. Its phase transformation, structure, absorption and photoluminescence properties were studied. The Nd:LuAG polycrystalline phase is formed above 900 °C and its particle sizes are in the range of 18-36 nm. The structure of Nd:LuAG was refined by Rietveld method. The lattice parameters and the distortion of Lu³⁺-O²⁻ polyhedron in Nd:LuAG are larger than that of in pure LuAG. Because the distortion of Lu³⁺-O²⁻ polyhedron is larger than that of Y³⁺-O²⁻ polyhedron in YAG and the distance of Lu³⁺-O²⁻ is smaller than that of Y³⁺-O²⁻ in YAG, Nd³⁺ in LuAG experiences a stronger crystal field effect, which is proved by the crystal field strength and the chemical environment parameter. The absorption spectrum shows that Nd:LuAG has a broad absorption band at 808 nm with FWHM above 6 nm, which is favorable for improving laser efficiency. The fluorescence lifetime from ⁴F_3/2 → ⁴I_11/2 transition is 320 μs and longer than that of Nd:YAG. The longer lifetime is propitious to energy storage. The emission cross section at 1064 nm is 2.89 × 10⁻¹⁹ cm², taking into account the Boltzmann distribution of the excited state. The emission cross section in Nd:LuAG is also larger than that of Nd:YAG, which is useful for laser operation. All results indicate that Nd:LuAG is a promising crystal material to apply in high energy lasers.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Heat treatment effect on electrochemical properties of spinel Li4Ti5O12

Anode material Li4Ti5O12 was prepared at 800℃ by a solid-state reaction, followed by heat-treatment at 600℃ for different times （0, 2, 8, and 12 h）. The effects of heat-treatment time on the particle morphology, rate-capability, and electrode kinetic process of the Li4Ti5O12 electrode, and on the lithium ion diffusion coefficient inside the Li4Ti5O12 electrode were investigated. Proper heat treatment could smoothen the particle surface of Li4Ti5O12 particles and increase the rate-capability of the electrode. Overlong heat treatment might cause particle aggregation and hence result in a poor electrode kinetic process. A sample with 8 h of heat treatment showed the best rate-capability and the lowest electrode reaction resistance. Heat treatment for 2-8 h does not significantly change the lithium ion diffusion coefficient inside the Li4Ti5O12 electrode, whereas, 12-h treatment results in a lower lithium ion diffusion coefficient.     

Synthesis and electrochemical properties of porous LiV3O8 as cathode materials for lithium-ion batteries

In this paper, we report on the synthesis of porous LiV₃O₈ by using a tartaric acid-assisted sol-gel process and their enhanced electrochemical properties for reversible lithium storage. The crystal structure, morphology and pore texture of the as-synthesized samples are characterized by means of XRD, SEM, TEM/HRTEM and N₂ adsorption/desorption measurements. The results show that the tartaric acid plays a pore-making function and the calcination temperature is an important influential factor to the pore texture. In particular, the porous LiV₃O₈ calcined at 300 °C (LiV₃O₈-300) exhibits hierarchical porous structure with high surface area of 152.4 m² g⁻¹. The electrochemical performance of the as-prepared porous LiV₃O₈ as cathode materials for lithium ion batteries is investigated by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The porous LiV₃O₈-300 displays a maximum discharge capacity of 320 mAh g⁻¹ and remains 96.3% of its initial discharge capacity after 50 charge/discharge cycles at the current density of 40 mA g⁻¹ due to the enhanced charge transfer kinetics with a low apparent activity energy of 35.2 kJ mol⁻¹, suggesting its promising application as the cathode material of Li-ion batteries.     

Preparation and characterization of flake-like polypyrrole/SrFe12O19 composites with different surface active agents

Flake-like polypyrrole/SrFe₁₂O₁₉ composites were synthesized by in situ polymerization method. The samples were characterized by SEM, XRD and IR technology. Flocs-like SrFe₁₂O₁₉ was synthesized by sol–gel method using the absorbent cotton as template for the first time. A possible mechanism for the formation of flocs-like SrFe₁₂O₁₉ had been proposed. Then the flocs-like SrFe₁₂O₁₉ was used as template for the preparation of polypyrrole/SrFe₁₂O₁₉ composites. Two kinds of surface active agents were used for the surface treatment of the flocs-like SrFe₁₂O₁₉. It was found that the comprehensive magnetic property for the flocs-like SrFe₁₂O₁₉ was superior to the sphericity-like SrFe₁₂O₁₉ for the excellent magnetic aeolotropism of the flocs-like SrFe₁₂O₁₉. The coercivity (Hc) for the flake polypyrrole/SrFe₁₂O₁₉ composites was far greater than the pure flocs-like SrFe₁₂O₁₉. The effect of the surface active agents on the morphology and properties of flake-like polypyrrole/SrFe₁₂O₁₉ composites was studied in the text.