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 105.2 mA h g⁻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 83.6 mA h g⁻¹ with a capacity retention of 90.3%. Even at 20 C, the discharge capacity of TiN coated LTO sample is 101.3 mA h g⁻¹, compared with 77.3 mA h g⁻¹ for pristine LTO in the potential range 1.0–2.5 V (vs. Li/Li⁺).     

Investigation of Li5Cr7Ti6O25 as novel anode material for high-power lithium-ion batteries

In this work, Li₅Cr₇Ti₆O₂₅ as a new anode material for rechargeable batteries is fabricated through a simple sol-gel method at different calcination temperatures. The X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, charge/discharge curve and cyclic voltammograms are utilized to study the crystal structures, morphologies and electrochemical properties of as-obtained Li₅Cr₇Ti₆O₂₅ samples. The impact of calcination temperatures on morphologies and electrochemical properties of Li₅Cr₇Ti₆O₂₅ is discussed in detail. The test result shows that the 800 °C is a proper calcination temperature for Li₅Cr₇Ti₆O₂₅ with excellent electrochemical properties. Cycled at 200 mA g⁻¹, it displays a high initial reversible capacity of 146.6 mA h g⁻¹ and retains a considerable capacity of 130.8 mA h g⁻¹ after 300 cycles. Even cycled at large current density of 500 mA g⁻¹, the initial reversible capacity of 129.6 mA h g⁻¹ with the capacity retention of 88% after 300 cycles is achieved, which is obviously higher than that of Li₅Cr₇Ti₆O₂₅ prepared at 700 °C (80.5 mA h g⁻¹ and 68%) and 900 °C (98.4 mA h g⁻¹ and 80%). In addition, in-situ XRD analysis reveals that Li₅Cr₇Ti₆O₂₅ exhibits a reversible structural change during lithiation and delithiation processes. The above prominent electrochemical performance indicates the great potential of the Li₅Cr₇Ti₆O₂₅ obtained at 800 °C as anode material for rechargeable batteries.     

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 173 mA h g⁻¹ at 0.1 C and a well maintained capacity of 65 mA h g⁻¹ even at 20 C. The energy density of 14 Wh kg⁻¹ at a power density of 2700 W kg⁻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 0.4 A g⁻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.     

Preparation of Li4Ti5O12 spherical particles for rechargeable lithium batteries

Spherical Li₄Ti₅O₁₂ particles were prepared via an emulsion-gel process. The preparation of spherical Li₄Ti₅O₁₂ such as the concentrations of the starting materials and heat treatment were optimized. The particle size distribution of the Li₄Ti₅O₁₂ prepared under optimized condition was very narrow, and the particle size was 0.45 μm. It was found that a short heat treatment in an infrared furnace was useful to crystallize amorphous LiTiO powders without aggregation of particles or morphology change. The obtained Li₄Ti₅O₁₂ had the spinel structure, and was phase pure. The prepared Li₄Ti₅O₁₂ exhibited a high discharge capacity of 160 mA h g⁻¹ at the potential of 1.5 V versus Li/Li⁺, and the charge–discharge cycle stability was excellent.     

Enhanced electrochemical performance of core-shell Li4Ti5O12/PTh as advanced anode for rechargeable lithium-ion batteries

A nanocomposite of Li₄Ti₅O₁₂ particles coated with polythiophene (PTh) was fabricated as advanced anode for rechargeable lithium-ion batteries. The conducting PTh layer was successfully coated on the surface of Li₄Ti₅O₁₂ through the in-situ oxidative polymerization method. Benefiting from the core-shell structure, specific capacities as high as 171.5, 168.2 and 151.1 mA h g⁻¹ at 0.2, 1 and 10 C are obtained in the Li₄Ti₅O₁₂/PTh composite. The electrochemical results also show that the Li₄Ti₅O₁₂/PTh exhibits remarkably improved cycling performance as compared with the Li₄Ti₅O₁₂ anode. Moreover, the charge-transfer resistance of Li₄Ti₅O₁₂/PTh electrode is much lower than that of the bare Li₄Ti₅O₁₂, revealing that the PTh coating can significantly increase the electron conductivity between the Li₄Ti₅O₁₂ particles. The excellent electrochemical performance of the as-fabricated Li₄Ti₅O₁₂/PTh composite can be ascribed to the PTh layer which can suppress the dissolution of active material into the LiPF₆ electrolyte and enhance the electron conductivity of Li₄Ti₅O₁₂ nanocrystals. Thus, the Li₄Ti₅O₁₂/PTh composite is an advanced anode for use in high performance lithium-ion batteries application.     

Improvement the electrochemical performance of Cr doped layered-spinel composite cathode material Li1.1Ni0.235Mn0.735Cr0.03O2.3 with Li4Ti5O12 coating

The Cr doped layered-spinel composite cathode material Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 was synthesized and coated with different content of Li₄Ti₅O₁₂ by a sol–gel method. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of Li₄Ti₅O₁₂ coatings on the electrochemical performance of the pristine material was evaluated from charge/discharge cycles, rate performance, and electrochemical impedance spectroscopy (EIS). The XRD results show that the lattice crystal and the content of spinel phase have been increased in the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials after Li₄Ti₅O₁₂ coating. The results from TEM and selected area electron diffraction (SAED) indicate that the Li₄Ti₅O₁₂ coating assumes a spinel structure on the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3. The discharge capacities, cycling and rate performances of the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials in the first cycle are improved with the addition of Li₄Ti₅O₁₂. Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 coated with 3 wt% Li₄Ti₅O₁₂ shows the highest discharge capacity (271.7 mA h g⁻¹), highest capacity retention (99.4% for 100 cycles), and best rate capability (132 mA h g⁻¹ at 10 C). EIS result indicates that the resistance of Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 electrode decreases with the addition of Li₄Ti₅O₁₂. The enhanced electrochemical performance can be ascribed to the increased spinel content, lower resistance and the enhanced lithium-ion diffusion kinetics.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Nitrogen-doped carbon-coated hierarchical Li4Ti5O12-TiO2 hybrid microspheres as excellent high rate anode of Li-ion battery

Nitrogen-doped carbon-coated Li₄Ti₅O₁₂-TiO₂ (LTO-TO) hybrid microspheres were prepared by heat treating the dry mixture of urea and chemically lithiated dandelion-like TiO₂ microspheres in a stainless steel autoclave at 550 °C for 5 h. The hybrid materials were tested as anode of Li-ion batteries. As compared to the pristine sample, the N-doped carbon-coated LTO-TO microspheres exhibited higher specific capacity at both low and high current rates. Discharge capacities of 184 and 123 mAh g⁻¹ were obtained at 0.2 C and 20 C, respectively. Moreover, the LTO-TO/C electrode showed excellent cycle performance, with a discharge capacity of 121.3 mAh g⁻¹ remained after 300 cycles at 5 C, corresponding to an average capacity degradation rate of 0.073% per cycle. These high specific capacity, excellent rate capability and cycle performance demonstrated the high potentiality of the N-doped carbon-coated LTO-TO microspheres as anode material of both energy storage-type and power-type Li-ion batteries.     

From hydrated layered-spinel lithium manganate composite to high-performance spinel LiMn2O4: A novel synthesis tuned by the concentration of LiOH

To obtain high-performance spinel LiMn₂O₄, various types of hydrated layered-spinel lithium manganate composites have been controllably synthesized through the hydrothermal process. It is found that the composition and morphology of these intermediate products can be tuned by the concentration of LiOH: Li⁺ act as the template and OH^- provide the required alkaline environment. In particular, the nanostructure varies from nanowires to nanosheets at different levels, depending on the phase ratio of the spinel phase ranging from 0% to 100%. Phase purity and the corresponding electrochemical properties of the as-prepared LiMn₂O₄ products are further tailored through the subsequent heat treatment. With the optimized LiOH concentration of 0.08 M, the resulting LiMn₂O₄ cathode material exhibits the best electrochemical performance with the initial discharge capacity of 121.7 mA h g⁻¹ at 1 C and 117.8 mA h g⁻¹ at 30 C, while a retention over 90% can be achieved after 1500 cycles. This study will help deepen understanding of the function mechanisms and further direct the novel synthesis from hydrated layered-spinel lithium manganate composites to high-performance spinel LiMn₂O₄ cathode materials.     

Hierarchical Li4Ti5O12 nanosheet arrays anchoring on carbon fiber cloth as ultra-stable free-standing anode of Li-ion battery

A flexible, free-standing composite anode with Li₄Ti₅O₁₂ nanosheet arrays anchoring on plain-weaved carbon fiber cloth (LTO@CC) is prepared by a hydrothermal and post-annealing process assisted by a TiO₂ seed layer. The LTO@CC anode free from polymeric binder and conducting agent exhibited much higher lithium storage capacity and cycling stability than the conventional slurry-processed electrode using the dandelion-like Li₄Ti₅O₁₂ microspheres prepared by the same hydrothermal process. A high specific capacity of 128.8 mA h g^?1 was obtained at a current rate of 30 C (1 C = 175 mA g^?1), and almost negligible capacity loses was observed when the cell was cycled at 10, 20 and 30 C each for 100 cycles. The carbon fiber matrix contributed to Li storage at low current rate, but the LTO nanosheet arrays have played the dominant role on the excellent rate capability. The improved electrochemical performance can be attributed to the synergetic effect between the hierarchical Li₄Ti₅O₁₂ nanosheet arrays and the carbon fiber matrix, which integrated short Li⁺ diffusion length, three-dimensional conductive architecture and well preserved structural integrity during the high rate and repeated charge-discharge measurements.     

Graphene nanosheet and carbon layer co-decorated Li4Ti5O12 as high-performance anode material for rechargeable lithium-ion batteries

In this study, we report a facile strategy for anchoring Li₄Ti₅O₁₂ (LTO) particles wrapped within carbon shells onto graphene nanosheet (GNS) using the freeze-drying assisted microwave irradiation method. In this designed structure, a conductive three-dimensional network can be formed by connecting the GNS and carbon layer which is benefit for the transport of electron and Li⁺-ion. When used as anode material for lithium-ion batteries, this hybrid composite exhibits an excellent high-rate performance with specific capacities of 171.5, 168.2, 160.1, 151.7 and 136.4 mAh g⁻¹ at various current rates of 1, 2, 5, 10 and 20 C, respectively. Furthermore, the specific capacity of the obtained anode still retains 99.6% of the initial value after 20 cycles at 20 C. The enhanced battery performance can be attributed to the improved electronic conductivity of each LTO grain via uniform carbon coating and GNS wrapping. As a consequence, this novel strategy developed in this study may open a new way to fabricate other electrodes for advanced renewable energy conversion and storage applications.     

Nb2O5 nanospheres/surface-modified graphene composites as superior anode materials in lithium ion batteries

Uniform Nb₂O₅ nanospheres/surface-modified graphene (SMG) composites for anode materials in lithium ion batteries were synthesized by hydrothermal method. The microstructure and morphology of composites were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscope techniques. The experimental results showed that Nb₂O₅ nanospheres were tightly and uniformly grown on the surface of SMG nanosheets. Nb₂O₅ nanospheres/SMG composites exhibited an impressive reversible capacity of 404.6 mA h g⁻¹ at the current density of 40 mA g⁻¹ after 100 cycles, and an excellent rate capacity of 345.5 mA h g⁻¹ at the current density of 400 mA g⁻¹.     

Investigation on performances of Li1.2Co0.4Mn0.4O2 prepared by self-combustion reaction as stable cathode for lithium-ion batteries

Poor rate capability and cycling performance are the major barriers for Li-rich layered cathode materials to be applied as the next generation cathode materials for lithium-ion batteries. In our work, Li_1.2Co_0.4Mn_0.4O₂ has been successfully synthesized via a self-combustion reaction (SCR) and a calcination procedure. Compared with the material produced by the solid state method (SSM), the one by SCR exhibits both better rate capability and cycling performance. Its initial discharge capacity is 166.01 mA h g⁻¹ with the capacity retention of 85.98% after 50 cycles at a current density of 200 mA h g⁻¹. Its remarkable performance is attributed to a thin carbon coating layer, which not only slows down the transformation rate of layered to spinel structure, but provides a good electronic pathway to increase the Li⁺ diffusion coefficient.     

Synthesis and electrochemical properties of La-doped Li4Ti5O12 as anode material for Li-ion battery

La-doped Li₄Ti₅O₁₂ was successfully synthesized from Li₂CO₃, La₂O₃ and tetrabutyl titanate by a simple ball milling assisted modified solid-state method. The impact of La-doping on crystalline structure, particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂ was investigated. The samples were characterized by XRD, SEM, galvanostatically charge–discharge and electrochemical impedance spectroscopy. The results demonstrated that the in-situ coated and ball-milling method could decrease the particle size and prevent the aggregation of Li₄Ti₅O₁₂. La-doping obviously improved the rate capability of Li₄Ti₅O₁₂ via the generation of less electrode polarization and higher electronic conductivity. Li_3.95La_0.05Ti₅O₁₂ exhibited a relatively excellent rate capability and cycling stability. At the charge–discharge rate of 0.5 C and 40 C, its discharge capacities were 176.8 mAh/g and 54.7 mAh/g. After 10 cycles, fairly stable cycling performance was achieved without obvious capacity fade at 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C and 40 C. In addition, compared to Li₄Ti₅O₁₂, Li_3.95La_0.05Ti₅O₁₂ almost did not have the initial capacity loss. It indicated that Li_3.95La_0.05Ti₅O₁₂ was a promising candidate material for anodes in Li-ion battery application.     

Synthesis and electrochemical performance of Li4Ti5O12/Ag composite prepared by electroless plating

To improve the electrochemical and anti flatulence performance of Li₄Ti₅O₁₂, Ag modified Li₄Ti₅O₁₂ (LTO) with high electrochemical performance as anode materials for lithium-ion battery was synthesized successfully by two-step solid phase sintering and subsequent electroless plating process in the presence of silver. The effect of Ag modification on the physical and electrochemical properties were investigated by the extensive material characterization of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM). The results showed that the samples possessed single spinel structure, it could be observed that the LTO/Ag composite and the pure LTO shared the same vibration frequencies, which indicated that the crystal structure of LTO didn’t change after electroless plating process, and the particles were uniformly and regularly shaped within 0.5–1.0 µm. Electrochemical performance of the samples were evaluated by the charging and discharging, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. It's obvious that the LTO/Ag composite prepared at the 10 min of electroless plating showed the highest performance with capacitance of 182.3 mA h/g at 0.2 C current rates. What's more, the LTO/Ag composites still maintained 92% of its initial capacity even after 50 charge/discharge cycles. Modification of appropriate Ag not only benefits the reversible intercalation and deintercalation of Li⁺, but also improves the diffusion coefficient of lithium ion. Besides, modification of appropriate Ag lower electrochemical polarization leads to higher conductivity and cycle performance of LTO, which is consistent with the results of the best reversible capacities.     

Combustion synthesis of high-performance Li4Ti5O12 for secondary Li-ion battery

Spinel Li₄Ti₅O₁₂ was synthesized by a simple glycine-nitrate auto-combustion by applying aqueous medium and constricting the reactions in the pores of cellulose fibers. The products from the auto-combustion and further calcination at various temperatures were characterized by XRD, SEM, BET surface area and TEM examinations. Pure phase and well-crystallized nano-Li₄Ti₅O₁₂ oxides were obtained at a calcination temperature of 700 °C or higher. The 700 °C calcined one shows the best and high electrochemical performance, which reached a capacity of ～125 mAh/g at 10 C discharge rate with fairly stable cycling performance even at 40 °C. Electrochemical impedance spectroscopy tests demonstrated that the surface reaction kinetics of Li₄Ti₅O₁₂ was improved significantly with the increase of its electronic conductivity.     

Evaluation of reduced graphene oxide-supported NiSb2O6 nanocomposites for reversible lithium storage

NiSb₂O₆ and reduced graphene oxide (NiSb₂O₆/rGO) nanocomposites are successfully fabricated by a solid-state method combined with a subsequent solvothermal treatment and further used as anode material of lithium-ion battery. The NiSb₂O₆/rGO nanocomposites exhibit a higher reversible capacity (of ca. 1240.5 mA h g⁻¹ at a current density of 50 mA g⁻¹), along with a good rate capability (395.2 mA h g⁻¹ at a current density of 1200 mA g⁻¹) and excellent capacity retention (684.5 mA h g⁻¹ after 150 cycles). These good performances could be attributed to the incorporated reduced grapheme oxide, which significantly improves the electronic conductivity of the NiSb₂O₆.     

Synthesis and electrochemical performance of Li4Ti5O12/C composite by a starch sol assisted method

Li₄Ti₅O₁₂/C composite anode materials were synthesized by a simple starch sol assisted method using TiO₂-anatase and Li₂CO₃ as raw materials and soluble starch as carbon source. The influences of calcination temperature and starch amounts on the microstructure and electrochemical performance were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and constant-current charge/discharge cycling tests. The results showed that the Li₄Ti₅O₁₂/C composite with 10 wt.% starch synthesized at 800 °C for 6 h had homogeneous particle size distribution with an average particle size of 200–300 nm and exhibited the optimal electrochemical performance with specific discharge capacities of 168.5, 160.8, 155.1 and 141.8 mAh g^? 1 at 0.2 °C, 1 °C, 2 °C and 5 °C rates, respectively, and satisfactory cycling stability. It could be attributed to the homogeneous ultrafine particles and in situ carbon coating, which enhanced the electronic conductivity and diffusion of lithium ions in the electrode.     

Effect of Fe-doping followed by C+SiO2 hybrid layer coating on Li3V2(PO4)3 cathode material for lithium-ion batteries

A novel Li₃V₂(PO₄)₃ composite modified with Fe-doping followed by C+SiO₂ hybrid layer coating (LVFP/C-Si) is successfully synthesized via an ultrasonic-assisted solid-state method, and characterized by XRD, XPS, TEM, galvanostatic charge/discharge measurements, CV and EIS. This LVFP/C-Si electrode shows a significantly improved electrochemical performance. It presents an initial discharge capacity as high as 170.8 mA h g⁻¹ at 1 C, and even delivers an excellent initial capacity of 153.6 mA h g⁻¹ with capacity retention of 82.3% after 100 cycles at 5 C. The results demonstrate that this novel modification with doping followed by hybrid layer coating is an ideal design to obtain both high capacity and long cycle performance for Li₃V₂(PO₄)₃ and other polyanion cathode materials in lithium ion batteries.     

Preparation and characterization of SrLi2Ti6O14@C/Ag as lithium storage anode material for rechargeable batteries

In this work, silver and carbon co-coated SrLi₂Ti₆O₁₄ is synthesized by using a solid-state assisted solution method, with glucose as carbon source and silver nitrate as Ag source. The structural and morphological properties of as-prepared samples are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which confirm that C/Ag composite layer is uniformly coated on the surface of SrLi₂Ti₆O₁₄. Electrochemical measurements like galvanostatic charge/discharge tests, rate performance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis are also undertaken to evaluate and compare the lithium storage capability of SrLi₂Ti₆O₁₄ before and after coating. According to the results, SrLi₂Ti₆O₁₄@C/Ag presents enhanced electrochemical capability compared with bare material. It can be found that bare SrLi₂Ti₆O₁₄ only delivers the reversible capacity of 140.32 mA h g⁻¹ with capacity retention of 90.7% at 100 mA g⁻¹ after 200 cycles. In contrast, SrLi₂Ti₆O₁₄@C/Ag presents the reversible capacity of 151.20 mA h g⁻¹ with only 6.7% capacity loss after 200 cycles. The improvement is owing to the increase of electronic conductivity and the decrease in the redox polarization after coating. In order to further investigate the structural stability of SrLi₂Ti₆O₁₄@C/Ag, in-situ XRD was performed as well. All the results prove that the C/Ag co-coating has positive effect on the electrochemical performance of SrLi₂Ti₆O₁₄.