Pristine Li4Ti5O12 Research Articles

Effective enhancement in rate capability and cyclability of Li4Ti5O12 enabled by coating lithium magnesium silicate

In terms of the unique features of good suspensibility in water, superior absorbability, adhensivity, cation exchangeability and rapid ion diffusion channels, lithium magnesium silicate (LMSO) might be an appropriate modifier for Li4Ti5O12 (LTO) by simply forming coating on LTO particles. According to a series of comparative experiments performed under various conditions, when the mixture of LTO and LMSO was roasted at 700 °C to form LMSO-coated LTO, the rate properties were significantly boosted (attaining cycling capacities of 160.2, 157.8, 155.8, 151.3 and 145.5 mAh g−1 with multiplying current density from 0.1 to 1.6 A g−1). Upon cycling at 0.5 A g−1 for 900 cycles, a capacity of 140.6 mAh g−1 was maintained. Compared to the pristine LTO, the markedly boosted rate properties and cyclability are ascribed to the LMSO coating for suppressing grain aggregation and growth, the optimized Li+ and electron transfer in electrolyte by interacting with LMSO, the enhanced electronic conductivity of LTO resulted from superficial co-doping of Mg2+ and Si4+, the meliorated ionic conductivity associating with the Li+ diffusion channels and cation exchangeability of LMSO, as well as the diminished polarization after the modification by LMSO.

Doping and surface modification enhance the applicability of Li4Ti5O12 microspheres as high-rate anode materials for lithium ion batteries

In this study we prepared Mg2+ and Cr3+ co-doped and phosphidated Li4Ti5O12 (LTO) microspheres using a spray-drying method. Doping with both Mg2+ and Cr3+ improved the electronic conduction of LTO, due to partial reduction of Ti4+ (from Ti4+ to Ti3+) and narrowing of the band gap, respectively. Moreover, the phosphidation process formed a uniform conductive glass layer on the LTO surface, leading to higher ionic conductivity. As a result, the modified LTO exhibited improved rate capability and cyclic stability, compared with those of the pristine LTO. In particular, the Mg2+ and Cr3+ co-doped and phosphidated LTO exhibited superior performance as a result of the combined effects of ion-doping and interfacial modification. Finally, the capacity improved significantly, especially at high C rates [e.g., 127.72 mA h g–1 at 20 C—77.6% of the value recorded at 0.1 C (164.62 mA h g–1)], due to the dual effects of the enhanced electric and ionic conductivities.

Conductive PEDOT-decorated Li4Ti5O12 as next-generation anode material for electrochemical lithium storage

Spinel Li4Ti5O12 material has been regarded as the next-generation anode for lithium-ion batteries owing to its excellent safety and good structural stability. Nevertheless, the low electrical conductivity and bad Li+-ion diffusion efficiency of pristine Li4Ti5O12 greatly limit its wide applications in electrochemical energy storage. Herein, the nanosized Li4Ti5O12 crystals are prepared via a simple sol-gel method to shorten the diffusion pathway of Li+-ion. Meanwhile, the conductive PEDOT layer is adopted to modify the electrical conductivity of Li4Ti5O12. The PEDOT-coated Li4Ti5O12 composite is successfully prepared by using the in-situ polymerization method. Benefit from the advantages of nanosized Li4Ti5O12 particles and conductive PEDOT coating, the obtained electrode exhibits enhanced electrochemical performances. It can deliver the initial discharge capacities of 169.6 and 125.2 mAh g−1 at 0.1 and 20 C. These results demonstrate that the designed composite is a potential electrode for high-rate electrochemical lithium storage.

P- and n-type Doping Effects on the Electrical and Ionic Conductivities of Li4Ti5O12 Anode Materials

We systematically investigated p- and n-type doping effects on the electrical conductivity of spinel Li4Ti5O12 (LTO) by designing theoretically stoichiometric Li11Ti13O32 (p-type) and Li10Ti14O32 (n-type) because LTO has a nonstoichiometric (Li)8[Li8/3Ti40/3]O32 formula with the Fd3m space group. In this work, we present evidence that the electronic modification plays a fundamental role in the electrical conductivity of LTO, especially, n-type Li10Ti14O32, which has superior electrical conductivity compared to p-type Li11Ti13O32. We proposed a way to improve the electrical conductivity of pristine LTO by halogen ion doping, Li4Ti5O12–xHalx (Hal: F, Cl, and Br), for an n-type doping effect. However, the substitution of halogen ions can enhance the electrical conductivity by mixing Ti4+/Ti3+ and impede the Li ion diffusion in the lattice. The larger size of Cl and Br increases the Li ion diffusion energy barrier with van der Waals repulsion. Therefore, our theoretical investigations of the effects of halog...

Outstanding lithium-storage performance of carbon-free Li4Ti5O12 anode material for rechargeable lithium-ion batteries

In this work, carbon-free Li4Ti5O12 material has been successfully prepared by using a conventional sol-gel method. X-ray diffraction (XRD) result reveals that the as-prepared pristine Li4Ti5O12 sample has the spinel-type structure with a cubic lattice. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicate that the morphology of Li4Ti5O12 material is well-crystallized with a uniform size distribution in the range of 300–700 nm. Moreover, high-resolution TEM image demonstrates that the surface of Li4Ti5O12 particle is very smooth without any carbon coating. When used as anode material for lithium-ion batteries, the pristine Li4Ti5O12 exhibits outstanding lithium-storage performances such as high reversible capacity, excellent rate capability and stable cycling property. Therefore, we can speculate that the as-prepared Li4Ti5O12 sample without any carbon materials is a promising candidate for the application of high-performance anode for lithium-ion batteries.

Surface modified Li4Ti5O12 by paper templated approach for enhanced interfacial Li+ charge transfer in Li-ion batteries.

The Li4Ti5O12 (LTO) and lithium silicate (LS) surface modified LTO have been demonstrated by a unique paper templated method. Comparative study of structural characterization with electrochemical analysis was demonstrated for pristine and modified Li4Ti5O12. Structural and morphological study shows the existence of the cubic spinel structure with highly crystalline 250–300 nm size particles. The LS modified LTO shows the deposition of 10–20 nm sized LS nanoparticles on cuboidal LTO. Further, X-ray photoelectron spectroscopy (XPS) confirms the existence of Li2SiO3 (LS) in the modified LTO. The electrochemical performance was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge. The modified LTO with 2% LS (LTS2) exhibited excellent rate capability compare to pristine LTO i.e. 182 mA h g−1 specific capacity at a current rate, 50 mA g−1 with remarkable cycling stability up to 1100 cycles at a current rate of 800 mA g−1. The lithium ion full cell of modified LTO with LS as an anode and LiCoO2 as a cathode exhibited a remarkably reversible specific capacity i.e. 110 mA h g−1. Both electronic and ionic conductivities of pristine LTO are observed to be enhanced by incorporation of appropriate amount of LS in LTO due to a larger surface contact at the interface of electrode and electrolyte. More significantly, the versatile paper templated synthesis approach of modified LTO with LS provides densely packed highly crystalline particles. Additionally, it exhibits lower Warburg coefficient and higher Li ion diffusion coefficient which in turn accelerate the interfacial charge transfer process, which is responsible for enhanced stable electrochemical performance. The detailed mechanism is expressed and elaborated for better understanding of enhanced electrochemical performance due to the surface modification.

Graphene-wrapped Li4Ti5O12 hollow spheres consisting of nanosheets as novel anode material for lithium-ion batteries

Flower-like Li4Ti5O12 hollow microspheres consisting of nanosheets are prepared via a hydrothermal process, and subsequently wrapped by graphene through electrostatic interactions. In comparison with pristine Li4Ti5O12, Li4Ti5O12@graphene exhibited higher capacities and improved rate capability in the 0.01–3.0V or 1.0–3.0V potential range. Li4Ti5O12@graphene composite shows specific capacity of 272.7mAhg−1 at 750mAg−1 after 200 cycles in the potential range from 0.01 to 3.0V, while the pristine Li4Ti5O12 only delivered a discharge capacity of 235.6mAhg−1. The improved electrochemical performances of Li4Ti5O12@graphene should be attributed to lower charge-transfer resistances, larger lithium-ion diffusion coefficient and lower activation energy. The electrons transfer at Li4Ti5O12/graphene heterojunction interface, originating from difference in the work function of two composites, reduces the localized work function of the composites, decreases energy required for electrons to escape and consequently results in the improved electrochemical performances.

MoO2 nanoparticle-modified Li4Ti5O12 as high rate anode material for lithium ion batteries

Abstract MoO2 nanoparticle-modified Li4Ti5O12 materials were prepared via a facile solution-based method. X-ray diffraction patterns (XRD) and high resolution transmission electron microscopy (HRTEM) analyses revealed that the MoO2 nanoparticles were anchored on the surface of spinel Li4Ti5O12, and energy dispersive X-ray spectroscopy (EDX) mapping indicated the MoO2 nanoparticles distributed uniformly. Compared with the pristine Li4Ti5O12, the appropriate amount of MoO2 on the surface of the Li4Ti5O12 could not only effectively reduce the electrochemical polarization of Li4Ti5O12, but also contribute to specific capacity for lithium storage. The 3% MoO2 modified Li4Ti5O12 exhibited excellent rate capability of 116 mA h g−1 at 10 C, and superior cycling performance of 124 mA h g−1 after 450 cycles at 5 C. Since the MoO2 modification process was easy to handle and the source of Mo has affordable costs, MoO2-modified Li4Ti5O12 would be promising for industrial application.

Bluish Li4Ti5O12 with enhanced rate performance

Bluish Li4Ti5O12 anode powder containing oxygen vacancies (O-LTO) was synthesized by solid state reaction under reductive atmosphere with 5 vol% H2/Ar, while white Li4Ti5O12 powder (reference Li4Ti5O12, R-LTO) was obtained in air in the experiment. XRD results revealed spinel structure for both anode materials and further Rietveld refinements of the patterns implied the formation of a non-stoichiometric compound, rather than the pristine Li4Ti5O12 phase, after calcinating in reductive atmosphere. SEM observation revealed spherical secondary particles for both powders composed of fine primary grains with size of submicron. The observed color difference between the O-LTO (bluish) and R-LTO (white), as revealed by DR UV–Vis investigation, could be ascribed to the formation of Ti3+ ions in the reductive atmosphere. XPS and EPR results confirmed the coexistence of Ti3+ ions and oxygen vacancies. The existence of oxygen vacancies resulted in significant increase in both Li ion diffusion coefficient and electric conductivity of the anode material, as proved by the CV tests and impedance measurements. The O-LTO sample showed advantages over the R-LTO sample, with a high specific capacity of 182.6 mAh/g at 0.2 C and a stable capacity retention of 98.7% after 100 cycles. Excellent rate performance was also observed for the O-LTO anode material. The specific capacities at 1C, 5C and 20C after 100 runs were recorded as 169 mAh/g, 153 mAh/g and 139 mAh/g for the O-LTO samples. All the results obtained in the experiment suggested high potential of the bluish O-LTO for the application as anode material for secondary Li ion batteries at high rates.

Hierarchical Li4Ti5O12/C composite for lithium-ion batteries with enhanced rate performance

Considering the charming merits and natural defects of Li4Ti5O12 (LTO), we build a hierarchical LTO/C composite through a rational hydrothermal route by utilizing the low-cost glucose as carbon source. The obtained composite consists of some grain-like secondary particles (10–15nm) pasted on the relatively bulk LTO sheets (50–100nm). Due to the introduction of carbon, the composite has the smaller particle size, lower polarization and superior electrical conductivity. Besides, the as-prepared sample exhibits good cycling stability and outstanding rate performance. It delivers the discharge capacity of 174.1mAhg−1 at 1C and left 131.7mAhg−1 even at 50C, which is apparently superior than pristine LTO. Furthermore, the discharge capacity maintains 93.4% after 500 cycles at 1C and 80.5% after 1000 cycles at 50C. Even after 3000 ultralong cycles at 5C, the value still retains 74.2% which is much higher than that of pure LTO (38.4%). The ideal proportion of carbon modified in LTO is also explored. The LTO/C-3.74wt% composite is demonstrated to possess optimal electrochemical performance.

Effect of graphene nanosheets on electrochemical performance of Li4Ti5O12 in lithium-ion capacitors

In order to improve the electrochemical performance of lithium titanium oxide, Li4Ti5O12 (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173mAhg−1 at 0.1C and a well maintained capacity of 65mAhg−1 even at 20C. The energy density of 14Whkg−1 at a power density of 2700Wkg−1 was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4Ag−1. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels.

New chemical approach to obtain dense layer phosphate-based ionic conductor coating on negative electrode material surface: Synthesis way, outgassing and improvement of C-rate capability

Li4Ti5O12 (LTO) based batteries have severe gassing behavior during charge/discharge and storage process, due to interfacial reactions between active material and electrolyte solution. In the same time, the electronic and ionic conductivity of pristine LTO is very poor and induces the use of nanoparticles which increase the outgassing phenomena. The coating of LTO particles could be a solution. For this the LTO spinel particles are modified with ionic conductor Li3PO4 coating using a spray-drying method. For the first time a homogeneous thin dense layer phosphate based conductor is obtained without nanoparticles, as a thin film material. It is so possible to study the influence of ionic conductor deposited on the negative electrode material on performances by the controlled layer thickness. This coating was characterized by XRD, SEM, XPS and TEM. The electrochemical performance of Li3PO4 coated Li4Ti5O12 is improved at high C-rate by the surface modification (improvement of 30mAhg−1 at 5 C-rate compared to pristine LTO for 5nm of coating), inducing by a modification of surface energy. An optimum coating thickness was studied. This type of coating allows a significant decrease of outgassing phenomena due the conformal coating and opens the way to a great number of studies and new technologies.

One-pot combustion synthesis of Li3VO4-Li4Ti5O12 nanocomposite as anode material of lithium-ion batteries with improved performance

Li3VO4-decorated Li4Ti5O12 (denoted as V-LTO) composites were synthesized via a facile one-pot cellulose-assisted combustion route. Homogeneous distribution of the Li3VO4 phase to introduce additional lithium ion transport paths in the composites and slight doping of vanadium into the lattice of Li4Ti5O12 phase were realized simultaneously through the one-pot synthesis, resulting in enhanced apparent ionic and electronic conductivity of the electrode materials. The product with optimal V content, i.e., V-LTO (1:8), showed much improved rate capacities compared with the pristine Li4Ti5O12. The effect of vanadium incorporation on the over-discharge capability of anode materials at a lower voltage was also studied, and the V-LTO (1:8) electrode demonstrated a capacity of 193.6mAhg−1 at a current density of 2000mAg−1 in the potential window of 0.2-3.0V, much higher than that of pristine Li4Ti5O12 (141.0mAhg−1). A fairly good cycling stability was also achieved with a capacity retention ratio of 90.0% after working at 1000mAg−1 between 0.2 and 3.0V for 200 times for the V-LTO (1:8) electrode, which is much higher compared with the capacity retention ratio of 73% for electrodes prepared with pristine Li4Ti5O12 under the same condition.

Influence of iron doping on structure and electrochemical properties of Li4Ti5O12

Iron doped lithium titanates Li4+z-3yTi5-zFez+yO12 (0≤z+y≤0.3) have been synthesized and characterized by X-ray diffraction, scanning and transmission electron microscopy, 57Fe Mössbauer spectroscopy, and cyclic voltammetry. Their performance as anode materials for lithium-ion batteries was studied in a wide potential range (0.01 − 3V). Rietveld refinements and 57Fe Mössbauer spectroscopy data show that iron cations occupy both tetrahedral 8a and octahedral 16d sites in the spinel structure. At that, iron occupancy of the octahedral sites is approximately twice as much as the occupancy of the tetrahedral ones. Occupancy of octahedral sites by Fe3+ ions increases after cycling. Li4+z-3yTi5-zFez+yO12 (z+y=0.2) exhibits higher electrochemical capacity at high current densities than the pristine Li4Ti5O12. Moreover, capacity of doped material increases after cycling at high current densities.

Using potassium ferricyanide as a dopant to prepare K and Fe co-doped Li4Ti5O12

For the first time, K and Fe co-doped Li4Ti5O12 (LTO) was prepared using potassium ferricyanide as the dopant by a sol-gel assisted solid state method. To simplify, the effect of Fe to Ti atomic ratio on the properties of the prepared materials was mainly investigated. The characteristics of the obtained samples were mainly analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge tests. The XRD patterns strongly demonstrated the formation of Li4Ti5O12 (LTO) though some impurities like TiO2 were formed in the final products, and the SEM images indicated that smaller and regular particles with an average size of about 350nm could be prepared when the Fe to Ti atomic ratio was 0.5% (sample c). The results of electrochemical measurements revealed that sample c delivered a high specific capacity of 168mAhg−1 after 20 cycles at 0.2C rate, which was significantly larger than that of the pristine LTO (83.5mAhg−1) prepared by the same method. This work was believed to have developed a novel way to produce K and Fe co-doped LTO, which was very beneficial to the development of LTO.

Synthesis and electrochemical performance of Li4Ti5O12 submicrospheres coated with TiN as anode materials for lithium-ion battery

The TiN coated Li4Ti5O12 (LTO) submicrospheres with high electrochemical performance as anode materials for lithium-ion battery were synthesized successfully by solvothermal method and subsequent nitridation process in the presence of ammonia. The XRD results revealed that the crystal structure of LTO did not change after thermal nitridation process. The submicrospheres morphology of LTO and TiN film on the surface of LTO submicrospheres were characterized by FESEM and HRTEM, respectively. XPS result confirmed that a small amount of Ti changed from Ti4+ to Ti3+ after nitridation process, which will increase the electronic conductivity of LTO. Electrochemical results showed that electrochemical performance of TiN coated LTO anode materials compared favorably with that of pure LTO. Also its rate capability and cycling performance were apparently superior to those of pure LTO. The reversible capacity of TiN-LTO is 105.2mAhg−1 at a current density of 10 C after 100 cycles and maintain 92.9% of its initial discharge capacity, while that of pure LTO is only 83.6mAhg−1 with a capacity retention of 90.3%. Even at 20 C, the discharge capacity of TiN coated LTO sample is 101.3mAhg−1, compared with 77.3mAhg−1 for pristine LTO in the potential range 1.0–2.5V (vs. Li/Li+).

TiN-coated micron-sized tantalum-doped Li4Ti5O12 with enhanced anodic performance for lithium-ion batteries

Micron-sized Li4Ti5O12 with both surface modification (TiN) and inner Ta5+ doping has been synthesized via a combination of solid-state reaction and surface thermal nitridation. The physical and chemical properties of all samples are tested systematically. The results demonstrate that tantalum is successfully doped in the lattice of Li4Ti5O12 and a thin amorphous TiN coated on the surface of the Li4Ti5O12 particles. The TiN coating layer enhances surface electronic conductivity and electrical contact between particles, while Ta5+ bulk doping in the lattice improves the intrinsic ionic conductivity and electronic conductivity inside particles. Being used as anode materials for lithium-ion batteries, the co-doped Li4Ti5O12 electrode shows much better electrochemical performance (144.5 mAh g−1 at 5 C after 500 cycles with a capacity retention of 91.63%) than that of pristine Li4Ti5O12 and mono tantalum doped or TiN coated Li4Ti5O12, only Ta-doped Li4Ti5O12 delivers 112.1 mAh g−1 at 5 C after 500 cycles and the TiN-coated Li4Ti5O12 electrode only retains 122.6 mAh g−1 at 5 C after 500 cycles. This design by exploring both surface modification and bulk doping is highly attractive for high performance Li4Ti5O12 manufacturing and may be applicative to other micron-sized electrode materials with inferior conductivity.

Synthesis of carbon-coated Li4Ti5O12 nanosheets as anode materials for high-performance lithium-ion batteries

Pristine and carbon-coated Li4Ti5O12 nanosheets are synthesized by a hydrothermal process, followed by calcination at 750 °C for 10 h. The structural properties of the as-prepared composites are characterized systematically by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and N2 adsorption–desorption analysis, respectively. Electrochemical lithium insertion/extraction performances are evaluated by the galvanostatic charge/discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. In comparison, Li4Ti5O12@C exhibits higher specific capacity, better rate capability and capacity retention than the pristine Li4Ti5O12. Analysis from the electrochemical measurements indicates that the enhanced electrochemical performances Li4Ti5O12@C might be attributed to the shorter Li-ion diffusion distance, lower charge-transfer resistance, better electrode kinetics and lower activation energy as a result of thinner nanosheet and the presence of carbon layer.

Synthesis and electrochemical performance of hole-rich Li4Ti5O12 anode material for lithium-ion secondary batteries

Hole-rich Li4Ti5O12 composites are synthesized by spray drying using carbon nanotubes as additives in precursor solution, subsequently followed calcinated at high temperature in air. The structure, morphology, and texture of the as-prepared composites are characterized with XRD, Raman, BET and SEM techniques. The electrochemical properties of the as-prepared composites are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine Li4Ti5O12, the hole-rich Li4Ti5O12 induced by carbon nanotubes exhibits superior electrochemical performance, especially at high rates. The obtained excellent electrochemical performances of should be attributed to the hole-rich structure of the materials, which offers more connection-area with the electrolyte, shorter diffusion-path length as well faster migration rate for both Li ions and electrons during the charge/discharge process.

High rate cycling performance of nanosized Li4Ti5O12/graphene composites for lithium ion batteries

Nanosized Li4Ti5O12/graphene(LTO/graphene) materials have been successfully synthesized by a sol-gel method. The LTO/graphene composites exhibit a well-defined cubic spinel structure with an average particle size of approximately 200–500nm. Compared with pure Li4Ti5O12, LTO/graphene composites show higher specific capacity, much improved rate capability and better cycle stability when used as anode materials for lithium ion batteries. The initial capacity of the LTO/graphene composite(0.5wt%) reaches 170.7mAhg−1at 1C, which slightly decreases to 168.5mAhg−1 after 100 cycles with a capacity loss of 1.3%. More importantly, the resulting LTO/graphene (0.5wt%) sample demonstrates remarkable rate capability in that it delivers a reversible capacity of 108.4mAhg−1 in the 1000th cycle at 10C charge-discharge rate, about 2.5 times that of pristine Li4Ti5O12 particles (44.1mAhg−1). The improved high-rate capability, cycling stability, fast charge-discharge performance of LTO/graphene composites can be ascribed to the improvement of lithium ion diffusion and ionic conductivity by graphene-coating.