Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

Graphitized carbon and graphene modified Fe2O3/Li4Ti5O12 as anode material for lithium ion batteries

Graphitized carbon (GC) and graphene (GE) modified Fe₂O₃/Li₄Ti₅O₁₂ (LTO) composites have been synthesized via a solid‐state reaction, respectively. The structure, morphology and electrochemical performance of the materials have also been characterized with X‐ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) system, X‐ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and electrochemical measurements. The discharge capacities of Fe₂O₃/LTO, GC/Fe₂O₃/LTO and GE/Fe₂O₃/LTO are 100.2 mAh g^?1, 207.5 mAh g^?1 and 238.9 mAh g^?1 after 100 cycles at the current density of 176 mA g^?1. The cyclic stability and rate capability are in the order of GE/Fe₂O₃/LTO > GC/Fe₂O₃/LTO > Fe₂O₃/LTO because of the synergistic effect between GC (GE) and Fe₂O₃/LTO. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of Li2SnO3 and its application in lithium‐ion batteries

Tin‐based oxide Li₂SnO₃ has been synthesized by a hydrothermal route as negative material for lithium‐ion batteries. The microstructure and electrochemical properties of the as‐synthesized materials were investigated by some characterizations means and electrochemical measurements. The as‐synthesized Li₂SnO₃ is a porous rod, which is composed of many uniform and regular nano‐flakes with a size of 50–60 nm. Li₂SnO₃ also displays an electrochemical performance with high capacity and good cycling stability (510.2 mAh g^?1 after 50 cycles at a current density of 60 mA g^?1 between 0.0 V and 2.0 V verusus Li/Li⁺). Copyright © 2013 John Wiley & Sons, Ltd.     

Solution-Based,Anion-Doping of Li4Ti5O12 Nanoflowers for Lithium-Ion Battery Applications

Solution-based, anionic doping represents a convenient strategy with which to improve upon the conductivity of candidate anode materials such as Li₄Ti₅O₁₂ (LTO). As such, novel synthetic hydrothermally-inspired protocols have primarily been devised herein, aimed at the large-scale production of unique halogen-doped, micron-scale, three-dimensional, hierarchical LTO flower-like motifs. Although fluorine (F) doping has been explored, the use of chlorine (Cl) dopants is the primary focus here. Several experimental variables, such as dopant amount, lithium hydroxide concentration, and titanium butoxide purity, were probed and perfected. Furthermore, the Cl doping process did not damage the intrinsic LTO morphology. The analysis, based on interpreting a compilation of SEM, XRD, XPS, and TEM-EDS results, was used to determine an optimized dopant concentration of Cl. Electrochemical tests demonstrated an increased capacity via cycling of 12 % for a Cl-doped sample as compared with pristine LTO. Moreover, the Cl-doped LTO sample described in this study exhibited the highest discharge capacity yet reported at an observed rate of 2C for this material at 143mAh g⁻¹. Overall, these data suggest that the Cl dopant likely enhances not only the ion transport capabilities, but also the overall electrical conductivity of our as-prepared structures. To help explain these favorable findings, theoretical DFT calculations were used to postulate that the electronic conductivity and Li diffusion were likely improved by the presence of increased Ti³⁺ ion concentration coupled with widening of the Li migration channel.     

Synthesis of Li4Ti5O12 fibers as a high-rate electrode material for lithium-ion batteries

Porous lithium titanate (Li₄Ti₅O₁₂) fibers, composed of interconnected nanoparticles, are synthesized by thermally treating electrospun precursor fibers and utilized as an energy storage material for rechargeable lithium-ion batteries. The material is characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermal analysis. Scanning electron microscopy results show that the Li₄Ti₅O₁₂ fibers calcined at 700?°C have an average diameter of 230?nm. Especially, the individual fiber is composed of nanoparticles with an average diameter of 47.5?nm. Electrochemical properties of the material are evaluated using cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The results show that as-prepared Li₄Ti₅O₁₂ exhibits good cycling capacity and rate capability. At the charge–discharge rate of 0.2, 0.5, 1, 2, 10, 20, 40, and 60?C, its discharge capacities are 172.4, 168.2, 163.3, 155.9, 138.7, 123.4, 108.8, and 90.4?mAh?g^?1, respectively. After 300 cycles at 20?C, it remained at 120.1?mAh?g^?1. The obtained results thus strongly support that the electrospun Li₄Ti₅O₁₂ fibers could be one of the most promising candidate anode materials for lithium-ion batteries in electric vehicles.     

Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion Batteries

Li₄Ti₅O₁₂ (LTO) nanoparticles were prepared by gel‐hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid‐state reaction or by sol‐gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X‐ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge‐discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li₄Ti₅O₁₂ anode material prepared through gel‐hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g^?1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g^?1. The gel‐hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells.     

Synthesis and electrochemical properties of spinel Li4Ti5O12−x Cl x anode materials for lithium-ion batteries

Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were synthesized successfully via high temperature solid-state reaction. X-ray diffraction and scanning electron microscopy were used to characterize their structure and morphology. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge cycling performance tests were used to characterize their electrochemical properties. The results showed that the Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were well-crystallized pure spinel phase and that the grain sizes of the samples were about 3–8 μm. The Li₄Ti₅O_11.8Cl_0.2 sample presented the best discharge capacity among all the samples and showed better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂. When the discharge rate was 0.5 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the superior discharge capacity of 148.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was 129.8 mAh g⁻¹; when the discharge rate was 2 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the discharge capacity of 120.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was only 89.8 mAh g⁻¹.     

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu_xS compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cu_xS structure and repress capacity fading during the electrochemical cycling, but the corresponding Li⁺ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu₂S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu₂S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu₂S (Cu₂S/C) exhibits an initial discharge capacity of 425 mAh g⁻¹ at 0.1 A g⁻¹, with a higher, long-term capacity of 523 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g⁻¹ after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li⁺ storage can mainly be ascribed to the contribution of the capacitive storage.     

Catalytically Active CoSe2 Supported on Nitrogen-Doped Three Dimensional Porous Carbon as a Cathode for Highly Stable Lithium-Sulfur Battery

Lithium-sulfur batteries are promising secondary energy storage devices that are mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe₂ nanoparticles (CoSe₂-PNC) is developed as a cathode for lithium-sulfur battery. A combination of CoSe₂ and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g⁻¹ at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g⁻¹ thus corresponding to a capacity retention of 75.97 %. In a long-term cycling test, discharge specific capacity of 546.7 mAh g⁻¹ was observed after 300 cycles performed at a current density of 1 C.     

Porous Si-Cu3Si-Cu Microsphere@C Core–Shell Composites with Enhanced Electrochemical Lithium Storage

Low-cost Si-based anode materials with excellent electrochemical lithium storage present attractive prospects for lithium-ion batteries (LIBs). Herein, porous Si-Cu₃Si-Cu microsphere@C composites are designed and prepared by means of an etching/electroless deposition and subsequent carbon coating. The composites show a core–shell structure, with a porous Si/Cu microsphere core surrounded by the N-doped carbon shell. The Cu and Cu₃Si nanoparticles are embedded inside porous silicon microspheres, forming the porous Si/Cu microsphere core. The microstructure and lithium storage performance of porous Si-Cu₃Si-Cu microsphere@C composites can be effectively tuned by changing electroless deposition time. The Si-Cu₃Si-Cu microsphere@C composite prepared with 12 min electroless deposition delivers a reversible capacity of 627 mAh g⁻¹ after 200 cycles at 2 A g⁻¹, showing an enhanced lithium storage ability. The superior lithium storage performance of the Si-Cu₃Si-Cu microsphere@C composite can be ascribed to the improved electronic conductivity, enhanced mechanical stability, and better buffering against the large volume change in the repeated lithiation/delithiation processes.     

Effect of Lithia and Substrate on the Electrochemical Performance of a Lithia/Cobalt Oxide Composite Thin‐Film Anode

Highly porous reticular Li₂O/CoO composite thin films fabricated by electrostatic spray deposition were investigated by using X-ray diffraction, scanning electron microscopy, galvanostatic cell-cycling measurements, and AC impedance spectroscopy measurements. The results of the electrochemical tests indicate that the initial coulombic efficiency and capacity retention are dependent on Li₂O content and the specific surface area of the deposited layer. Irrespective of the type of substrate, the electrode gave the best electrochemical performance when the molar ratio of Li to Co was controlled at 1:1. At the optimal composition, at 0.2 C the initial coulombic efficiency was as high as 81.9 % and 83.6 % for the film on Cu foil and on porous Ni, respectively. The Li₂O/CoO (Li/Co=1:1) films on Ni foam and Cu foil had sustained capacities of up to 790 and 715 mAh g⁻¹, respectively, at a rate of 1 C over 100 cycles at 25 °C. Similar cycling experiments carried out at 70 °C showed that the capacity is temperature-sensitive, and it exhibited reversible capacities as high as 1018 (Cu foil) and 1269 mAh g⁻¹ (Ni foam) for up to 100 cycles. The thin-film electrodes on Ni foam always performed better than those on Cu foil. Cycling at elevated temperature (70 °C) also resulted in a significant increase in capacity.     

Impact of titanium precursors on formation and electrochemical properties of Li4Ti5O12 anode materials for lithium-ion batteries

This work describes comparative study on the application of Li₄Ti₅O₁₂ (LTO) as anode materials for lithium-ion batteries which were successfully prepared by sol-gel synthesis with the use of two titanium sources. One of them was anatase-type titanium dioxide (TiO₂), whereas the second was tetrabutyl titanate (TBT). Both obtained LTO materials were very similar in terms of their crystallinity and purity. In turn, the sample synthetized with TBT source revealed better particle dispersibility, and its particles were slightly lower in size. These particular features resulted in higher Li⁺ diffusion coefficient and better kinetic of Li⁺ ions during charge transfer reactions for the LTO synthetized with TBT source. This reflected in specific capacitance values for both electrodes which equalled 150 mAh g⁻¹, 120 mAh g⁻¹, and 63 mAh g⁻¹ for TBT-LTO and 120 mAh g⁻¹, 80 mAh g⁻¹, and 58 mAh g⁻¹ for TiO₂-LTO at C-rates of 1, 5, and 10 C, respectively.

     

Toward Understanding the Enhanced Pseudocapacitive Storage in 3D SnS/MXene Architectures Enabled by Engineered Surface Reactions

The optimization of three-dimensional (3D) MXene-based electrodes with desired electrochemical performances is highly demanded. Here, a precursor-guided strategy is reported for fabricating the 3D SnS/MXene architecture with tiny SnS nanocrystals (≈5 nm in size) covalently decorated on the wrinkled Ti₃C₂T_x nanosheets through Ti−S bonds (denoted as SnS/Ti₃C₂T_x-O). The formation of Ti−S bonds between SnS and Ti₃C₂T_x was confirmed by extended X-ray absorption fine structure (EXAFS). Rather than bulky SnS plates decorated on Ti₃C₂T_x (SnS/Ti₃C₂T_x-H) by one-step hydrothermal sulfidation followed by post annealing, this SnS/Ti₃C₂T_x-O presents size-dependent structural and dynamic properties. The as-formed 3D hierarchical structure can provide short ion-diffusion pathways and electron transport distances because of the more accessible surface sites. In addition, benefiting from the tiny SnS nanocrystals that can effectively improve Na⁺ diffusion and suppress structural variation upon charge/discharge processes, the as-obtained SnS/Ti₃C₂T_x-O can generate pseudocapacitance-dominated storage behavior enabled by engineered surface reactions. As predicted, this electrode exhibits an enhanced Na storage capacity of 565 mAh g⁻¹ at 0.1 A g⁻¹ after 75 cycles, outperforming SnS/Ti₃C₂T_x-H (336 mAh g⁻¹), SnS (212 mAh g⁻¹), and Ti₃C₂T_x (104 mAh g⁻¹) electrodes.     

Nitridated mesoporous Li4Ti5O12 spheres for high-rate lithium-ion batteries anode material

Nitridated mesoporous Li₄Ti₅O₁₂ spheres were synthesized by a simple ammonia treatment of Li₄Ti₅O₁₂ derived from mesoporous TiO₂ particles and lithium acetate dihydrate via a solid state reaction in the presence of polyethylene glycol 20000. The carbonization of polyethylene glycol could effectively restrict the growth of primary particles, which was favorable for lithium ions diffusing into the nanosized TiO₂ lattice during the solid state reaction to form a pure phase Li₄Ti₅O₁₂. After a subsequent thermal nitridation treatment, a high conductive thin TiO _x N _y layer was in situ constructed on the surface of the primary nanoparticles. As a result, the nitridated mesoporous Li₄Ti₅O₁₂ structure, possessing shorter lithium-ion diffusion path and better electrical conductivity, displays significantly improved rate capability. The discharge capacity reaches 138 mAh?g^?1 at 10 C rate and 120 mAh?g^?1 at 20 C rate in the voltage range of 1–3 V.     

Steady-state polarization measurements of lithium insertion electrodes for high-power lithium-ion batteries

Steady-state polarization measurements of lithium titanium oxide (LTO; Li[Li_1/3Ti_5/3]O₄) were carried out using the 0-V lithium-ion cells consisting of two identical LTO-electrodes with a parallel-plate symmetrical electrode configuration. The sinusoidal voltage with the peak amplitude of 1.0 V was imposed at 0.1 Hz upon the 0-V cells and the current response was measured as a function of time. The steady-state polarization, obtained by plotting the current versus applied voltage, was linear in current up to approximately 60 mA cm^?2 or 4 A g^?1 based on the LTO weight and suggested the resistance polarization only for the lithium insertion electrode of the LTO. The method was also applied to lithium aluminum manganese oxide (LAMO; Li[Li_0.1Al_0.1Mn_1.8]O₄) and the resistance polarization of the LAMO-electrode was determined for currents up to approximately 25 mA cm^?2 or 2 A g^?1 based on the LAMO weight. The validity of the results was examined for the polarization measurements of the 2.5-V lithium-ion battery consisting of LTO and LAMO, and the significance of the polarization measurements of lithium insertion electrodes for high-power applications was discussed.     

Effect of starting materials on electrochemical performance of sol-gel-synthesized Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode materials for lithium-ion batteries

In this study, the effect of the sol-gel starting materials with different particle sizes on the sol-gel-synthesized spinel Li₄Ti₅O₁₂ (LTO) was systematically investigated. The physical and electrochemical properties of the synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller-specific surface area analyses, galvanostatic charge/discharge tests, cyclic voltammetry, and electrochemical impedance spectroscopy. It was found that the initial particle size of sol-gel starting material played a crucial role on the properties of as-prepared LTOs. The LTO synthesized with the relatively finer particle size of starting materials possessed relatively smaller particle size and larger specific surface area and therefore resulted in the superior electrochemical properties. The initial discharge capacity of the as-prepared LTO exhibited 168.2, 150.6, and 142.7 mAh g^?1 at current densities of 1, 5, and 10 C, respectively, and up to 95, 95, and 90 % of the corresponding initial discharge capacity was retained after 50 cycles.     

Sulfur–carbon nano-composite as cathode for rechargeable lithium battery based on gel electrolyte

Sulfur–carbon nano-composite with elemental sulfur incorporated in porous carbon was prepared by thermal treatment of a mixture of sulfur and active carbon. The new material was characterized by X-ray diffraction, BET and scanning electron microscopy. The nano-composite, tested at room temperature as cathode in a nonaqueous lithium cell based on PVDF gel electrolyte, exhibited a reversible capacity of 440 mAh g⁻¹ at a current density of 0.3 mA cm⁻². The utilization of electrochemically active sulfur was about 90% assuming a complete reaction to the product of Li₂S during cycling.     

A strategy for scalable synthesis of Li4Ti5O12/reduced graphene oxide toward high rate lithium-ion batteries

Li₄Ti₅O₁₂/reduced graphene oxide (RGO) composites were prepared via a simple strategy. The as-prepared composites present Li₄Ti₅O₁₂ nanoparticles uniformly immobilized on the RGO sheets. The Li₄Ti₅O₁₂/RGO composites possess excellent electrochemical properties with good cycle stability and high specific capacities of 154 mAh g^− 1 (at 10C) and 149 mAh g^− 1 (at 20C), much higher than the results found in other literatures. The superior electrochemical performance of the Li₄Ti₅O₁₂/RGO composites is attributed to its unique hybrid structure of conductive graphene network with the uniformly dispersed Li₄Ti₅O₁₂ nanoparticles.     

Low‐temperature Synthesis of Peony‐like Spinel Li4Ti5O12 as a High‐performance Anode Material for Lithium Ion Batteries

Peony‐like spinel Li₄Ti₅O₁₂ was synthesized via calcination of precursor at the temperature of 400°C, and the precursor was prepared through a hydrothermal process in which the reaction of hydrous titanium oxide with lithium hydroxide was conducted at 180°C. The as‐prepared product was investigated by SEM, TEM and XRD, respectively. As anode material for lithium ion battery, the Li₄Ti₅O₁₂ obtained was also characterized by galvanostatic tests and cyclic voltammetry measurements. It is found that the peony‐like Li₄Ti₅O₁₂ exhibited high rate capability of 119.7 mAh·g⁻¹ at 10 C and good capacity retention of 113.8 mAh·g⁻¹ after 100 cycles at 5 C, and these results indicate the peony‐like Li₄Ti₅O₁₂ has promising applications for lithium ion batteries with high performance.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.