Li4Ti5O12/CNTs composite anode material for large capacity and high-rate lithium ion batteries

Li₄Ti₅O₁₂ sub-micro crystallites are synthesized by ball-milling and one-step sintering under different heat treatment temperature from 700 °C to 900 °C. The composite electrode of Li₄Ti₅O₁₂/carbon nanotubes (CNTs) is prepared by mixing powders of Li₄Ti₅O₁₂ and CNTs in different weight ratios. Before mixing, in order to disperse CNTs in Li₄Ti₅O₁₂ particles preferably, the CNTs are cut and dispersed by hyperacoustic shear method and the composite electrodes of low resistance of about 20–30 Ω are obtained. The composite electrodes have steady discharge platform of 1.54 V and large specific capacity, initial discharge capacities are 168, 200, 196, 176 mAh g⁻¹ in different Li₄Ti₅O₁₂:CNTs weight ratios of 94:1, 92:3, 90:5, 88:7 respectively at 0.1 C discharge rate for the Li₄Ti₅O₁₂ synthesized in an optimized heat treatment temperature of 800 °C. In our experimental range, the composite electrode in a CNTs weight ratio of 3:92 shows the best performance under different discharge rate such as the initial capacity is 200 mAh g⁻¹ with discharge capacities retention rate of nearly 100%. Its capacity is about 151 mAh g⁻¹ under 20 C rate discharge condition with excellent high-rate performance. There is almost no decline after 20th cycles under 10 C rate discharging condition.     

Experimental and modeling kinetic study of the CO2 absorption by Li4SiO4

Nowadays, research aims to produce H₂ efficiently through modifying conventional processes by removing CO₂ at high temperature (T ≥ 500 °C). The sorption enhanced reforming (SER) is an example of such a process where CO₂ capture offers significant energy savings (≈23%). Besides, feedstock to this process may include different sources of biofuels. An essential part of this new reaction system is the use of a solid CO₂ absorbent. Among absorbents stands lithium orthosilicate (Li₄SiO₄) for its high absorption capacity and thermal stability. Therefore, the present research aims to study and model the kinetics of CO₂ absorption by Li₄SiO₄ in a temperature range of 550–650 °C. Results were consistent with a first order reaction dependence with respect to CO₂ concentration. Apparent activation energy of the gas–solid reaction (22.5 kcal/mol) is approximately equal the intrinsic activation energy (28.6 kcal/mol), suggesting that the surface reaction resistance determines the overall reaction rate.     

Electrochemical properties of Li2ZrO3-coated silicon/graphite/carbon composite as anode material for lithium ion batteries

Silicon/graphite/disordered carbon (Si/G/DC) is coated by Li₂ZrO₃ using Zr(NO₃)₄·5H₂O and CH₃COOLi·2H₂O as coating reagents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize Li₂ZrO₃-coated Si/G/DC composite. The Li₂ZrO₃-coated Si/G/DC composite exhibits a high reversible capacity with no capacity fading from 2nd to 70th cycle, indicating its excellent cycleability when used as anode materials for lithium ion batteries. A compact and stable solid-electrolyte interphase (SEI) layer is formed on the surface of Li₂ZrO₃-coated Si/G/DC electrode. Analysis of electrochemical impedance spectra (EIS) shows that the resistance of the coated material exhibits less variation during cycling, which indicates the integrity of electrode structure is kept during cycling. XPS shows that F and P elements do not appear in the SEI layers of Li₂ZrO₃-coated Si/G/DC electrode, while they have a relatively high content in SEI layers of Si/G/DC electrode. The improvement of Li₂ZrO₃-coated Si/G/DC is attributed to the decrease of lithium insertion depth and the formation of stable SEI film.     

High-density spherical Li4Ti5O12/C anode material with good rate capability for lithium ion batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. To improve the material's rate capability and pile density is considered as the important researching direction. One effective way is to prepare powders composed of spherical particles containing carbon black. A novel technique has been developed to prepare spherical Li₄Ti₅O₁₂/C composite. The spherical precursor containing carbon black is prepared via an “outer gel” method, using TiOCl₂, C and NH₃ as the raw material. Spherical Li₄Ti₅O₁₂/C powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃ in N₂. The investigation of TG/DSC, SEM, XRD, Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂/C composite prepared by this method are spherical, has high tap-density and excellent rate capability. It is observed that the tap-density of spherical Li₄Ti₅O₁₂/C powders (the mass content of C is 4.8%) is as high as 1.71 g cm⁻³, which is remarkably higher than the non-spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, the initial discharge specific capacity of the sample is as high as 144.2 mAh g⁻¹, which is still 128.8 mAh g⁻¹ after 50 cycles at a current density of 1.6 mA cm⁻².     

Electrochemical activity of Li2FeTiO4 and Li2MnTiO4 as potential active materials for Li ion batteries: A comparison with Li2NiTiO4

We demonstrate, for the first time, a considerable electrochemical activity of two members of lithium transition element titanates: Li₂FeTiO₄ and Li₂MnTiO₄. Both materials consist of 10–20 nm particles embedded in a conductive carbon coating. We show that not the coating but the small particle size is decisive for materials’ activity. Li₂FeTiO₄ shows a stable reversible capacity of up to 123 mA hg⁻¹ at C/20 and 60 °C which is 83% of the theoretical value for exchange of 1 electron (148 mA hg⁻¹). Li₂MnTiO₄ could only be prepared in a nanosized form that contained about 30% of impurities. The capacity of the whole material (including impurities) is comparable to that of Li₂FeTiO₄ but the cycling stability is much poorer. In contrast to the Fe and Mn analogues, the third member of the titanate family, Li₂NiTiO₄, shows a good electrochemistry even when the particle size is much larger (about 100 nm). During initial cycles at C/10 and 60 °C, exchange of more than 1 electron per compound formula has been observed. The cycling stability at high temperatures, however, is poor.     

Effects of dopant on the electrochemical performance of Li4Ti5O12 as electrode material for lithium ion batteries

The effects of dopant on the electrochemical properties of spinel-type Li_3.95M_0.15Ti_4.9O₁₂ (M = Al, Ga, Co) and Li_3.9Mg_0.1Al_0.15Ti_4.85O₁₂ were systematically investigated. Charge–discharge cycling were performed at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.3 and 0.5 V, the experimental results showed that Al³⁺ dopant greatly improved the reversible capacity and cycling stability over the pristine Li₄Ti₅O₁₂. The substitution of the Ga³⁺ slightly increased the capacity of the Li₄Ti₅O₁₂, but did not essentially alleviate the degradation of cycling stability. Dopants such as Co³⁺ and Mg²⁺ to some extent worsened the electrochemical performance of the Li₄Ti₅O₁₂.     

A novel CuO-nanotube/SnO2 composite as the anode material for lithium ion batteries

A novel CuO-nanotubes/SnO₂ composite was prepared by a facile solution method and its electrochemical properties were investigated as the anode material for Li-ion battery. The as-prepared composite consisted of monoclinic-phase CuO-nanotubes and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were dramatically decorated on the CuO-nanotubes. The composite showed higher reversible capacity, better durability and high rate performance than the pure SnO₂. The better electrochemical performance could be attributed to the introducing of the CuO-nanotubes. It was found that the CuO-nanotubes were reduced to metallic Cu in the first discharge cycle, which can retain tube structure of the CuO-nanotubes as a tube buffer to alleviate the volume expansion of SnO₂ during cycling and act as a good conductor to improve the electrical conductivity of the electrodes.     

Nano-sized SiOx/C composite anode for lithium ion batteries

Nano-sized SiO_x/C composite with core-shell structure is prepared by a modified Stöber method. After heat-treatment, the O/Si ratio in SiO_x/C composite is near 1 and the core of SiO_x presents a structure composing of amorphous Si clusters and ordered SiO₂ domains. SiO_x/C composite anode shows high specific capacity (ca. 800 mAh g⁻¹), excellent cycling stability, good rate-capability but low initial coulombic efficiency. Li₂O and Li₄SiO₄ may generate in the initial lithiation process, which, combining with the carbon shell, can buffer the volume change caused by the alloying of Si with Li, and thereby improving the cycling stability of electrode. The nano feature of SiO_x/C particle and the electronic conductive nature of carbon coating layer ensure the good rate-capability of SiO_x/C electrode.     

Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries

Nano-CuCo₂O₄ is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10–20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo₂O₄ at 60 mA g⁻¹ in the voltage range 0.005–3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g⁻¹ per cycle. Good rate capability is also found in the range 0.04–0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g⁻¹ (∼6.9 mol of Li per mole of CuCo₂O₄) and 745(±10) mAh g⁻¹ (∼6.8 mol of Li), respectively at a current of 60 mA g⁻¹. The average discharge and charge potentials are ∼1.2 and ∼2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co₃O₄ and Cu ↔ CuO aided by Li₂O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo₂O₄ compares well with that of iso-structural nano-Co₃O₄ as reported in the literature.     

Preparation and rate capability of Li4Ti5O12 hollow-sphere anode material

Spinel lithium titanate, Li₄Ti₅O₁₂, with novel hollow-sphere structure was fabricated by a sol–gel process using carbon sphere as template. The effect of the hollow-sphere structure as well as the wall thickness on the Li storage capability and high rate performance was electrochemically evaluated. High specific capacity, especially better high rate performance was achieved with this Li₄Ti₅O₁₂ hollow-sphere electrode material with thin wall thickness. It is believed that this macroporous hollow-sphere structure has shortened the Li diffusion distance, increased the contact area between Li₄Ti₅O₁₂ and electrolyte, and also led to better mixing of the active material with AB. All these factors have resulted in the good rate capability of the hollow-sphere structured Li₄Ti₅O₁₂ electrode material.     

Synthesis and characterization of Li3V(2 − 2x/3)Mgx(PO4)3/C cathode material for lithium-ion batteries

Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C (x = 0, 0.15, 0.30, 0.45) composites have been synthesized by the sol-gel assisted solid state method, using adipic acid C₆H₁₀O₄ (hexanedioic acid) as carbon source. The particle size of the composites is ∼1 μm. During the pyrolysis process, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C network structure is formed. The effect of Mg²⁺ doped on the electrochemical properties of Li₃V₂(PO₄)₃/C positive materials has been studied. Li₃V_1.8Mg_0.30(PO₄)₃/C as the cathode materials of Li-ion batteries, the retention rate of discharge capacity is 91.4% (1 C) after 100 cycles. Compared with Li₃V₂(PO₄)₃/C, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C composites have shown enhanced capacity and retention rate capability. The long-term cycles and ex situ XRD tests disclose that Li₃V_1.8Mg_0.30(PO₄)₃ exhibits higher structural stability than the undoped system.     

Preparation and electrochemical investigation of Li2CoPO4F cathode material for lithium-ion batteries

In this paper, we report the electrochemical characteristics of a novel cathode material, Li₂CoPO₄F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li₂CoPO₄F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li₂CoPO₄F samples present one, fully reversible anodic reaction at 4.81 V. When cycled between 2.0 V and 5.5 V, peaks occurring at 4.81 V and 5.12 V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li₂CoPO₄F electrode discharged from 5.5 V to 2.0 V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0 V to 2.0 V. This difference may correspond to a structural relaxation that appears above 5 V. In the constant current cycling measurements, the Li₂CoPO₄F samples exhibited a capacity as high as 109 mAh g⁻¹ and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li⁺. XRD measurements confirmed that the discharged state is Li₂CoPO₄F. Combining these XRD results and electrochemical data proved that up to 1 mol Li⁺ is extractable when charged to 5.5 V.     

Li4Ti5O12/Sn composite anodes for lithium-ion batteries: Synthesis and electrochemical performance

Li₄Ti₅O₁₂/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li₄Ti₅O₁₂ matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li₄Ti₅O₁₂/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge-discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li₄Ti₅O₁₂ at a calcination of 500 °C, due to the steric effect of Li₄Ti₅O₁₂ and chemical interaction between Li₄Ti₅O₁₂ and tin oxide. The experimental results indicate that Li₄Ti₅O₁₂/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g⁻¹ is maintained after 50 cycles at 100 mA g⁻¹ current density, which is still higher than 195 mAh g⁻¹ for the pure Li₄Ti₅O₁₂ after the same charge/discharge cycles. It suggests Li₄Ti₅O₁₂/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.     

Template-free reverse micelle process for the synthesis of a rod-like LiFePO4/C composite cathode material for lithium batteries

The synthesis of rod-like LiFePO₄/C cathodes using template-free reverse micelle process is reported for high performance lithium batteries. We have demonstrated that the size of the primary particles could be controlled based on sintering temperature and sintering time and size of the large aggregates is adjustable based on the carbon content of the sample. Thermogravimetry and differential thermal analysis have been used to propose a possible mechanism for the formation rod-like LiFePO₄/C cathode material. X-ray diffraction, scanning electron microscopy, impedance spectroscopy and charge-discharge measurements have been used to characterize the material. Electrochemical performance of rod-like LiFePO₄/C cathode material offers higher initial capacity and excellent rate capability than that obtained by loose porous LiFePO₄/C material due to unique rod-like composite material formed by primary nanoparticles. Hence, it can be suggested that that the rod-like nanostructured morphology improves structural stability, lithium ion diffusion and electronic conductivity of the LiFePO₄/C composite material. The template-free reverse micelle process for the synthesis of the rod-like LiFePO₄/C cathode material opens up a new route to synthesize lithium transition metal oxides with controlled morphologies for applications in high power lithium batteries.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.     

High-strength all-solid lithium ion electrodes based on Li4Ti5O12

A Li₄Ti₅O₁₂-Li_0.29La_0.57TiO₃-Ag electrode composite was fabricated via sintering the corresponding powder mixture. The process achieved a final relative density of 97% the theoretical. Relatively thick, ∼100 μm, electrodes were fabricated to enhance the energy density relatively to the traditional solid-state thin film battery electrodes. The sintered electrode composite delivered full capacity in the first discharge at C/40 discharge rate. Full capacity utilization resulted from the 3D percolated network of both solid electrolyte and metal, which provide paths for ionic and electronic transport, respectively. The electrodes retained 85% of the theoretical capacity after 10 cycles at C/40 discharge rate. The tensile strength and the Young's modulus of the sintered electrode composite are the highest reported values to date, and are at least an order of magnitude higher than the corresponding value of traditional tapecast “composite electrodes”. The results demonstrate the concept of utilizing thick all-solid electrodes for high-strength batteries, which might be used as multifunctional structural and energy storage materials.     

Nano Li4Ti5O12–LiMn2O4 batteries with high power capability and improved cycle-life

We report the effects of electrode thickness, cathode particle size and morphology, cathode carbon coating matching ratio and laminate structure on the electrochemical characteristics of nanosized Li₄Ti₅O₁₂–LiMn₂O₄ batteries. We show that a correct adjustment of these parameters resulted in significant improvements in power capability and cycle-life of such devices, making them competitive, low-cost and safe battery chemistry for next generation Li-ion batteries. In addition, Li₄Ti₅O₁₂ reversible specific capacity beyond three Li-ions intercalation is reported.     

Preparation of LiCoPO4/C nanocomposite cathode of lithium batteries with high rate performance

LiCoPO₄/C nanocomposites could be successfully prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment. X-ray diffraction analysis confirmed that the LiCoPO₄/C nanocomposites were well crystallized in an orthorhombic structure with Pmna space group. Scanning electron microscopy and transmission electron microscopy with equipped energy dispersive spectroscopy verified that the LiCoPO₄/C nanocomposites were the agglomerates of LiCoPO₄ primary particles with a geometric mean diameter of 87 nm, and the carbon was well distributed on the surface of the agglomerates. The LiCoPO₄/C nanocomposites were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF₆ in EC:DMC = 1:1|LiCoPO₄/C at various charge-discharge rates. The cells delivered first discharge capacities of 142 and 109 mAh g⁻¹ at 0.05 and 20 C, respectively. Furthermore, the discharge capacity after 40 cycles corresponded to 87% of initial one at 0.1 C rate. The excellent rate capability of the cells is mainly due to the well distributed carbon on the LiCoPO₄ agglomerates, and a much smaller lithium ion diffusion distance in the electrode.     

Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode

Li₂FeSiO₄/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li₂FeSiO₄/C cathode were investigated. The XRD patterns of the Li₂FeSiO₄/C samples indicate that all the samples are of good crystallinity, and a little Fe₃O₄ impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750 °C. The Li₂FeSiO₄/C sample synthesized at 650 °C has good electrochemical performances with an initial discharge capacity of 144.9 mAh g⁻¹ and the discharge capacity remains 136.5 mAh g⁻¹ after 10 cycles. The performance of Li₂FeSiO₄/C cathode is further improved by modification of Ni substitution. The Li₂Fe_0.9Ni_0.1SiO₄/C composite cathode has an initial discharge capacity of 160.1 mAh g⁻¹, and the discharge capacity remains 153.9 mAh g⁻¹ after 10 cycles. The diffusion coefficient of lithium in Li₂FeSiO₄/C is 1.38 × 10⁻¹² cm² s⁻¹ while that in Li₂Fe_0.9Ni_0.1SiO₄/C reaches 3.34 × 10⁻¹² cm² s⁻¹.