Preparation and characterization of spherical La-doped Li4Ti5O12 anode material for lithium ion batteries

The lithium secondary batteries with high power density need the electrode materials with both high specific capacity and high tap density. An “outer gel” method by TiCl₄ as the raw material has been developed to prepare spherical precursor. High tap density spherical Li₄Ti₅O₁₂ is synthesized by sintering the mixture of precursor and Li₂CO₃. La-doped Li₄Ti₅O₁₂ is also prepared by this method. X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, tap density testing, and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂ powders prepared by this method are spherical and exhibits high tap density. La³⁺ dopant improved the electrochemical performance over the pristine Li₄Ti₅O₁₂. It is tested that the tap density of the pristine and La³⁺-doped products is as high as 1.80 and 1.78 g•cm⁻³, respectively. Between 1.0 and 3.0 V versus Li, the initial discharge capacity of the La³⁺ dopant is as high as 161.5 mAh•g⁻¹ at 0.1C rate. After 50 cycles, the reversible capacity is still 135.4 mAh•g⁻¹.     

Preparation and characterization of spinel Li4Ti5O12 nanoparticles anode materials for lithium ion battery

Spinel Li₄Ti₅O₁₂ nanoparticles were prepared via a high-temperature solid-state reaction by adding the prepared cellulose to an aqueous dispersion of lithium salts and titanium dioxide. The precursors of Li₄Ti₅O₁₂ were characterized by thermogravimetry and differential scanning calorimetry. The obtained Li₄Ti₅O₁₂ nanoparticles were characterized using X-ray diffraction, transmission electron microscopy (TEM) and electrochemical measurements. The TEM revealed that the Li₄Ti₅O₁₂ prepared with cellulose is composed of nanoparticles with an average particle diameter of 20–30 nm. Galvanostatic battery testing showed that nano-sized Li₄Ti₅O₁₂ exhibit better electrochemical properties than submicro-sized Li₄Ti₅O₁₂ do especially at high current rates, which can deliver a reversible discharge capacity of 131 mAh g⁻¹ at the rate of 10 C, whereas that of the submicro-sized sample decreases to 25 mAh g⁻¹ at the same rate (10 C). Its reversible capacity is maintained at ~172.2 mAh g⁻¹ with the voltage range 1.0–3.0 V (vs. Li) at the current rate of 0.5 C for over 80 cycles.     

Effects of dopant on the electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode materials

The effects of dopant on the electrochemical properties of spinel-type Li_3.97M_0.1Ti_4.94O₁₂ (M = Mn, Ni, Co) and Li_(4-x/3)Cr_xTi_(5-2x/3)O₁₂(x = 0.1, 0.3, 0.6, 0.9, 1.5) were systematically investigated. Charge-discharge cycling were performed at a constant current density of 0.5 mA/cm² between the cut-off voltages of 3.0 and 1.0 V, the experimental results showed that Cr³⁺ dopant improved the reversible capacity and cycling stability over the pristine Li₄Ti₅O₁₂. The substitution of the Mn³⁺ and Ni³⁺ slightly decreased the capacity of the Li₄Ti₅O₁₂. Dopants such as Co³⁺ to some extent worsened the electrochemical performance of the Li₄Ti₅O₁₂.     

LiFePO<Subscript>4</Subscript>/C with high capacity synthesized by carbothermal reduction method

The olivine-type LiFePO₄/C cathode materials were prepared via carbothermal reduction method using cheap Fe₂O₃ as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO₄ particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g⁻¹ at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g⁻¹ at 0.5C rate.     

Preparation and electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>4</Subscript>O<Subscript>7</Subscript> composite for lithium-ion batteries

In order to improve the rate capability of Li₄Ti₅O₁₂, Ti₄O₇ powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li₄Ti₅O₁₂/Ti₄O₇ has been synthesized as anode material for lithium-ion batteries. It is found that the Li₄Ti₅O₁₂/Ti₄O₇ composite shows higher reversible capacity and better rate capability compared to Li₄Ti₅O₁₂. According to the charge-discharge tests, the Li₄Ti₅O₁₂/Ti₄O₇ composite exhibits excellent rate capability of 172.3 mAh g^?1 at 0.2 C, which is close to the theoretical value of the spinel Li₄Ti₅O₁₂. More impressively, the reversible capacity of Li₄Ti₅O₁₂/Ti₄O₇ composite is 103.1 mAh g^?1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li₄Ti₅O₁₂ is only 22.3 mAh g^?1 with a capacity retention of 31.1%. The results indicate that Li₄Ti₅O₁₂/Ti₄O₇ composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries.     

Effect of sintering conditions on the properties of sol-gel-derived Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets. The Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li_1.3Al_0.3Ti_1.7(PO₄)₃. Among the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10⁻⁴ S cm⁻¹ and the lowest activation energy of 0.2821 eV.     

Nano Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> as sulfur host for high-performance Li-S battery

S/Li₄Ti₅O₁₂ cathode with high lithium ionic conductivity was prepared for Li-S battery. Herein, nano Li₄Ti₅O₁₂ is used as sulfur host and fast Li⁺ conductor, which can adsorb effectively polysulfides and improve remarkably Li⁺ diffusion coefficient in sulfur cathode. At 0.5 C, S/Li₄Ti₅O₁₂ cathode has a stable discharge capacity of 616 mAh g^?1 at the 700th cycle and a capacity loss per cycle of 0.0196% from the second to the 700th cycle, but the corresponding values of S/C cathode are 437 mAh g^?1 and 0.0598%. Even at 2 C, the capacity loss per cycle of S/Li₄Ti₅O₁₂ cathode is only 0.0273% from the second to the 700th cycle. The results indicate that Li₄Ti₅O₁₂ as the sulfur host plays a key role on the high performance of Li-S battery due to reducing the shuttle effect and enhancing lithium ionic conductivity.     

A novel approach to employ Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> as anode active material for lithium batteries

In the present paper, we describe utilization of cathode active material as anode active material, for example, Li₂MnSiO₄. The lithium manganese silicate has been successfully synthesized by solid-state reaction method. The X-ray diffraction pattern confirms the orthorhombic structure with Pmn2 ₁ space group. The Li/Li₂MnSiO₄ cell delivered the initial discharge capacity of 420 mA h g⁻¹, which is 110 mA h g⁻¹ higher than graphitic anodes. The electrochemical reversibility and solid electrolyte interface formation of the Li₂MnSiO₄ electrode was emphasized by cyclic voltammetry.     

Preparation of carbon encapsulated Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode material for lithium ion battery through pre-coating method

Carbon encapsulated Li₄Ti₅O₁₂ (C/Li₄Ti₅O₁₂) anode material for lithium ion battery was prepared by using the pre-coat method of two steps, and the TiO₂ was pre coated before the reaction with Li₂CO₃. The structure and morphology of the resultant C/Li₄Ti₅O₁₂ materials were characterized by X-ray diffraction (XRD) and scanning microscopy (SEM). Electrochemical tests showed that at 0.1 C, the initial discharge capacity was 169.9 mAh g^?1, and the discharge capacity was 80 mAh g^?1 at 5 C. After 100 cycles at 2 C, the discharge specific capacity was 108.5 mAh g^?1. Compare with one step coating method, results showed the C/Li₄Ti₅O₁₂ prepared by pre-coat method can reduce the particle’s size and effectively improve the electrochemical performance.     

Electrospinning preparation of one-dimensional Co<Superscript>2+</Superscript>-doped Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanofibers for high-performance lithium ion battery

One-dimensional Co²⁺-doped Li₄Ti₅O₁₂ nanofibers with a diameter of approximately 500 nm have been synthesized via a one-step controllable electrospinning method. The Co²⁺-doped Li₄Ti₅O₁₂ nanofibers were systematically characterized by XRD, ICP, TEM, SEM, BET, EDS mapping, and XPS. Based on the cubic spinel structure and one-dimensional effect of Li₄Ti₅O₁₂, Co²⁺-doped Li₄Ti₅O₁₂ nanofibers exhibit the enlarged lattice volume, reduced particle size and enhanced electrical conductivity. More importantly, Co²⁺-doped Li₄Ti₅O₁₂ nanofibers as a lithium ion battery anode electrode performs superior electrochemical performance than undoped Li₄Ti₅O₁₂ electrode in terms of electrochemical measurements. Particularly, the reversible capacity of Co²⁺-doped Li₄Ti₅O₁₂ electrode reaches up to 140.1 mAh g^?1 and still maintains 136.5 mAh g^?1 after 200 cycles at a current rate of 5 C. Therefore, one-dimensional Co²⁺-doped Li₄Ti₅O₁₂ nanofiber electrodes, showing high reversible capacity and remarkable recycling property, could be a potential candidate as an anode material.     

Enhanced electrochemical performance of Cu<Subscript>2</Subscript>O-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode material for lithium-ion batteries

Li₄Ti₅O₁₂/Cu₂O composite was prepared by ball milling Li₄Ti₅O₁₂ and Cu₂O with further heat treatment. The structure and electrochemical performance of the composite were investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Li₄Ti₅O₁₂/Cu₂O composite exhibited much better rate capability and capacity performance than pristine Li₄Ti₅O₁₂. The discharge capacity of the composite at 2 C rate reached up to 122.4 mAh g^?1 after 300 cycles with capacity retention of 91.3 %, which was significantly higher than that of the pristine Li₄Ti₅O₁₂ (89.6 mAh g^?1). The improvement can be ascribed to the Cu₂O modification. In addition, Cu₂O modification plays an important role in reducing the total resistance of the cell, which has been demonstrated by the electrochemical impedance spectroscopy analysis.     

Pr-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanofibers as an anode material for lithium-ion batteries with outstanding cycling performance and rate performance

Pr-doped Li₄Ti₅O₁₂ in the form of Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0, 0.01, 0.03, 0.05, and 0.07) was synthesized successfully by an electrospinning technique. ICP shows that the doped samples are closed to the targeted samples. XRD analysis demonstrates that traces of Pr³⁺ can enlarge the lattice parameter of Li₄Ti₅O₁₂ from 8.3403 to 8.3765 Å without changing the spinel structure. The increase of lattice parameter is beneficial to the intercalation and de-intercalation of lithium-ion. XPS results identify the existence form of Ti is mainly Ti⁴⁺ and Ti³⁺ in minor quantity in Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) samples due to the small amount of Pr³⁺. The transition from Ti⁴⁺ to Ti³⁺ is conducive to the electronic conductivity of Li₄Ti₅O₁₂. FESEM images show that all the nanofibers are well crystallized with a diameter of about 200 nm and distributed uniformly. The results of electrochemical measurement reveal that the 1D Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) nanofibers display enhanced high-rate capability and cycling stability compared with that of undoped nanofibers. The high-rate discharge capacity of the Li_4?x/3Ti_5?2x/3Pr_xO₁₂ (x = 0.05) samples is excellent (101.6 mAh g^?1 at 50 °C), which is about 58.48 % of the discharge capacity at 0.2 °C and 4.3 times than that of the bare Li₄Ti₅O₁₂ (23.5 mA g^?1). Even at 10 °C (1750 mA g^?1), the specific discharge capacity is still 112.8 mAh g^?1 after 1000 cycles (87.9 % of the initial discharge capacity). The results of cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) illustrate that the Pr-doped Li₄Ti₅O₁₂ electrodes possess better dynamic performance than the pure Li₄Ti₅O₁₂, further confirming the excellent electrochemical properties above.     

Fast ionic conduction in cubic hafnium garnet Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Hf<Subscript>2</Subscript>O<Subscript>12</Subscript>

A new member of the family of garnets with fast lithium ion conduction has been found with the composition Li₇La₃Hf₂O₁₂. The anion arrangement corresponds to the oxygen framework in garnets, e.g., in Ca₃Fe₂Si₃O₁₂. Hafnium is coordinated octahedrally while the lanthanum environment can be described as a distorted cube. Lithium occupies a large number of positions with tetrahedral, trigonal planar, and metaprismatic coordination. Li₇La₃Hf₂O₁₂ shows a lithium bulk ion conductivity of 2.4 × 10⁻⁴ Ω⁻¹ cm⁻¹ at room temperature with an activation energy of 0.29 eV.     

Improved of cathode performance of LiFePO<Subscript>4</Subscript>/C composite using different carboxylic acids as carbon sources for lithium-ion batteries

Among the several materials under development for use as a cathodes in lithium-ion batteries olivine-type LiFePO₄ is one of the most promising cathode material. However, its poor conductivity and low lithium-ion diffusion limits its practical application. In this study, we report seven different carboxylic acids used to synthesize LiFePO₄/C composite, and influences of carbon sources on electrochemical performance were intensively studied. The structure and electrochemical properties of the LiFePO₄/C were characterized by X-ray diffraction, scanning electron microscopy, electrical conductivity, and galvanostatic charge–discharge measurements. Among the materials studied, the sample E with tartaric acid as carbon source exhibited the best cell performance with a maximum discharge capacity of 160 mAh g⁻¹ at a 0.1 C-rate. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.     

Li4Ti2.5Cr2.5O12 as anode material for lithium battery

Chromium-substituted Li₄Ti₅O₁₂ has been investigated as a negative electrode for future lithium batteries. It has been synthesized by a solid-state method followed by quenching leading to a micron-sized material. The minimum formation temperature of Li₄Ti_2.5Cr_2.5O₁₂ was found to be around 600 °C using thermogravimetric and differential thermal analysis. X-ray diffraction, scanning electron microscopy, cyclic voltammetry (CV), impedance spectroscopy, and charge–discharge cycling were used to evaluate the synthesized Li₄Ti_2.5Cr_2.5O₁₂. The particle size of the powder was around 2–4 μm. CV studies reveal a shift in the deintercalation potential by about 40 mV, i.e., from 1.54 V for Li₄Ti₅O₁₂ to 1.5 V for Li₄Ti_2.5Cr_2.5O₁₂. High-rate cyclability was exhibited by Li₄Ti_2.5Cr_2.5O₁₂ (up to 5  C) compared to the parent compound. The conduction mechanism of the compound was examined in terms of the dielectric constant and dissipation factor. The relaxation time has been evaluated and was found to be 0.07 ms. The mobility was found to be 5.133 × 10⁻⁶ cm² V⁻¹ s⁻¹.     

Electrical and electrochemical behaviour of several LiFe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> solid solutions as cathode materials for lithium ion batteries

Several olivine phosphates were investigated in the last years as cathode materials for secondary lithium ion batteries. Among these compounds, LiFe _x Co_1 − x PO₄ solid solutions might be interesting candidates because they should combine the high potential value of Co³⁺/Co²⁺ (higher than 4.5 V vs Li⁺/Li) with the relatively high charge–discharge rate of LiFePO₄. Solid solutions were prepared by solid-state route and characterised by X-ray powder diffraction, cyclic voltammetry, impedance spectroscopy and the Hebb–Wagner method. The results show that also low amount of iron induces high electronic conductivity in the solid solutions.     

Integrated investigation of the Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> phase stability

The Li₄Ti₅O₁₂ is applied in lithium ion batteries as anode material, which can be synthesized by various synthesis techniques. In this study, the molten salt synthesis technique at low temperatures, i.e. 350 °C, was applied to synthesize Li₄Ti₅O₁₂. Surprisingly, the Li₄Ti₅O₁₂ was not formed according to XRD analysis, which raised question about the stability range of Li₄Ti₅O₁₂. To investigate the stability of Li₄Ti₅O₁₂ at low temperatures, the high-temperature calcined Li₄Ti₅O₁₂ powder was equilibrated in the LiCl-KCl eutectic salt at 350 °C. The result of experiment revealed that the Li₄Ti₅O₁₂ is not decomposed. Results of ab initio calculations also indicated that the Li₄Ti₅O₁₂ phase is a stable phase at 0 K. The products of molten salt synthesis technique were then annealed at 900 °C, which resulted in the Li₄Ti₅O₁₂ formation. It was concluded that the Li₄Ti₅O₁₂ is a stable phase at low temperatures and the reasons for not forming the Li₄Ti₅O₁₂ by molten salt technique at low temperature are possibly related to activation energy and kinetic barriers. The Li₄Ti₅O₁₂ formation energy is also very small, due to the results of ab initio calculations.     

Relationship between local structure and electrochemical performance of LiFePO<Subscript>4</Subscript> in Li-ion batteries

This work is devoted to the study of fundamental properties of LiFePO₄ (LFP) olivine in view of the optimization of this material for its use as a positive electrode material in Li-ion batteries. The investigation of the electronic and magnetic properties appears to be successful for the detection of a small amount of impurities. By the combination of X-ray diffraction, optical spectroscopy, and magnetometry, we characterize the local structure and the morphology of LFP particles. The impact of the ferromagnetic clusters (γ-Fe₂O₃ or Fe₂P) on the electrochemical response is examined. The electrochemical performance of the optimized LFP powders investigated at 60 °C is excellent in terms of capacity retention (153 mAh/g at 2 C) as well as cycling life. No iron dissolution was observed after 200 charge–discharge cycles at 60 °C for cells containing Li foil, Li₄Ti₅O₁₂, or graphite as negative electrodes. Paper presented at the 11th Euro-Conference on Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007.     

Nanocrystalline CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> powders prepared by egg white solution route: synthesis,characterization and its giant dielectric properties

Nanocrystalline CaCu₃Ti₄O₁₂ powders with particle sizes of 50–90 nm were synthesized by a simple method using Ca(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O, titanium(diisoproproxide) bis(2,4-pentanedionate) and freshly extracted egg white (ovalbumin) in aqueous medium. The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 400 °C. The precursor was calcined at 700 and 800 °C in air for 8 h to obtain nanocrystalline powders of CaCu₃Ti₄O₁₂. The calcined CaCu₃Ti₄O₁₂ powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu₃Ti₄O₁₂ structure and a small amount of CuO, although the sintered sample of the 700 °C calcined powders contained some amount of CaTiO₃. SEM micrographs showed the average grain sizes of 12.0±7.8 and 15.5±8.9 μm for the sintered CaCu₃Ti₄O₁₂ ceramics prepared using the CaCu₃Ti₄O₁₂ powders calcined at 700 and 800 °C, respectively. The sintered samples exhibit a giant dielectric constant, ε^′ of ∼ 1.5–5×10⁴. The dielectric behavior of both samples exhibits Debye-like relaxation, and can be explained based on a Maxwell–Wagner model. PACS 77.22.Gm; 81.05.Je; 81.07.Wx; 81.20.Ev     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.