Effects of drying control chemical additive on properties of Li4Ti5O12 negative powders prepared by spray pyrolysis

High-density Li₄Ti₅O₁₂ powders comprising spherical particles are prepared by spray pyrolysis from a solution containing dimethylacetamide (drying control chemical additive) and citric acid and ethylene glycol (organic additives). The prepared powders have high discharge capacities and good cycle properties. The optimum concentration of dimethylacetamide is 0.5 M. The addition of dimethylacetamide to the polymeric spray solutions containing citric acid and ethylene glycol helps in the effective control of the morphology of the Li₄Ti₅O₁₂ powders. At a constant current density of 0.17 mA g⁻¹, the initial discharge capacities of the powders obtained from the spray solution with and without the organic additives are 171 and 167 mAh g⁻¹, respectively.     

Electrochemical properties of Cu6Sn5 alloy powders directly prepared by spray pyrolysis

Spherical shape Cu–Sn alloy powders with fine size for lithium secondary battery were directly prepared by spray pyrolysis. The mean size and geometric standard deviation of the Cu–Sn alloy powders prepared at a temperature of 1100 °C were 0.8 μm and 1.2, respectively. The powders prepared at a temperature of 1100 °C with low flow rate of carrier gas as 5 l min⁻¹ had main XRD peaks of Cu₆Sn₅ alloy and copper-rich Cu₃Sn alloy phases. Cu and Sn components were well dispersed inside the submicron-sized alloy powders. The discharge capacities of the Cu₆Sn₅ alloy powders prepared at a flow rate of 5 l min⁻¹ dropped from 485 to 313 mAh g⁻¹ by the 20th cycle at a current density of 0.1 C. On the other hand, the discharge capacities of the Cu–Sn alloy powder prepared at a flow rate of 20 l min⁻¹ dropped from 498 to 169 mAh g⁻¹ by the 20th cycle at a current density of 0.1 C.     

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.     

Preparation and electrochemical properties of Li4Ti5O12 thin film electrodes by pulsed laser deposition

Spinel Li₄Ti₅O₁₂ thin film anode material for lithium-ion batteries is prepared by pulsed laser deposition. Thin film anodes are deposited at ambient temperature, then annealed at three different temperatures under an argon gas flow and the influence of annealing temperatures on their electrochemical performances is studied. The microstructure and morphology of the films are characterized by XRD, SEM and AFM. Electrochemical properties of the films are evaluated by using galvanostatic discharge/charge tests, cyclic voltammetry and a.c. impedance spectroscopy. The results reveal that all annealed films crystallize and exhibit good cycle performance. The optimum annealing temperature is about 700 °C. The steady-state discharge capacity of the films is about 157 mAh g⁻¹ at a medium discharge/charge current density of 10 μA cm⁻². At a considerably higher discharge/charge current density of 60 μA cm⁻² (about 3.45 C) the discharge capacity of the films remains steady at a relative high value (146 mAh g⁻¹). The cycleability of the films is excellent. This implies that such films are suitable for electrodes to be used at high discharge/charge current density.     

Lithium diffusion in Li4Ti5O12 at high temperatures

Synthesis of the spinel lithium titanate Li₄Ti₅O₁₂ by an alkoxide-free sol-gel method is described. This method yields highly pure and crystalline Li₄Ti₅O₁₂ samples at relatively low temperature (850 °C) and via short thermal treatment (2 h). ⁶Li magic angle spinning nuclear magnetic resonance (MAS NMR) measurements on these samples were carried out at high magnetic field (21.1 T) and over a wide temperature range (295-680 K). The temperature dependence of the chemical shifts and integral intensities of the three ⁶Li resonances demonstrates the migration of lithium ions from the tetrahedral 8a to the octahedral 16c sites and the progressive phase transition from a spinel to a defective NaCl-type structure. This defective structure has an increased number of vacancies at the 8a site, which facilitate lithium diffusion through 16c → 8a → 16c pathways, hence providing an explanation for the reported increase in conductivity at high temperatures. Molecular dynamics simulations of the spinel oxides Li_4+xTi₅O₁₂, with 0 ≤ x ≤ 3, were also performed with a potential shell model in the temperature range 300-700 K. The simulations support the conclusions drawn from the NMR measurements and show a significant timescale separation between lithium diffusion through 8a and 16c sites and that out of the 16d sites.     

Synthesis of pristine and carbon-coated Li4Ti5O12 and their low-temperature electrochemical performance

Pristine and carbon-coated Li₄Ti₅O₁₂ oxide electrodes are synthesized by a cellulose-assisted combustion technique with sucrose as organic carbon source and their low-temperature electrochemical performance as anodes for lithium-ion batteries are investigated. X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) are applied to characterize the phase structure, composition, and morphology of the composites. It is found that the sequence of sucrose addition has significant effect on the phase formation of Li₄Ti₅O₁₂. Carbon-coated Li₄Ti₅O₁₂ is successfully prepared by coating the pre-crystallized Li₄Ti₅O₁₂ phase with sucrose followed by thermal treatment. Electrochemical lithium insertion/extraction performance is evaluated by the galvanostatic charge/discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), from room temperature (25 °C) to −20 °C. The carbon-coated composite anode materials show improved lithium insertion/extraction capacity and electrode kinetics, especially at high rates and low temperature. Both of the two samples show fairly stable cycling performance at various temperatures, which is highly promising for practical applications in power sources of electric or electric-hybrid vehicles.     

Characteristics of Li3V2(PO4)3/C powders prepared by ultrasonic spray pyrolysis

Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/C powders are prepared by ultrasonic spray pyrolysis from spray solutions with and without sucrose. The precursor powders have a spherical shape and the crystal structure of V₂O₃ irrespective of the concentration of sucrose in the spray solution. The powders post-treated at 700 °C have the pure crystal structure of the Li₃V₂(PO₄)₃ phase irrespective of the concentration of sucrose in the spray solution. The Li₃V₂(PO₄)₃ powders prepared from the spray solution without sucrose have a non-spherical shape and hard aggregation. However, the Li₃V₂(PO₄)₃/C powders prepared from the spray solution with sucrose have a spherical shape and non-aggregation characteristics. The Li₃V₂(PO₄)₃ powders prepared from the spray solution without sucrose have a low initial discharge capacity of 122 mAh g⁻¹. However, the Li₃V₂(PO₄)₃/C powders prepared from the spray solutions with 0.1, 0.3, and 0.5 M sucrose have initial discharge capacities of 141, 130, and 138 mAh g⁻¹, respectively. After 25 cycles, the discharge capacities of the powders formed from the spray solutions with and without 0.1 M sucrose are 70% and 71% of the initial discharge capacities, respectively.     

Electrochemical behaviors of wax-coated Li powder/Li4Ti5O12 cells

The wax-coated Li powder specimen was effectively synthesized using the drop emulsion technique (DET). The wax layer on the powder was verified by SEM, Focused Ion Beam (FIB), EDX and XPS. The porosity of a sintered wax-coated Li electrode was measured by linear sweep voltammetry (LSV) and compared with that of a bare, i.e., un-coated Li electrode. The electrochemical behavior of the wax-coated Li powder anode cell was examined by the impedance analysis and cyclic testing methods. The cyclic behavior of the wax-coated Li powder anode with the Li₄Ti₅O₁₂ (LTO) cathode cell was examined at a constant current density of 0.35 mA cm⁻² with the cut-off voltages of 1.2–2.0 V at 25 °C. Over 90% of the initial capacity of the cell remained even after the 300th cycle. The wax-coated Li powder was confirmed to be a stable anode material.     

Synthesis, structure and electrochemical Li insertion behaviour of Li2Ti6O13 with the Na2Ti6O13 tunnel-structure

Li₂Ti₆O₁₃ has been prepared from Na₂Ti₆O₁₃ by Li ion exchange in molten LiNO₃ at 325 °C. Chemical analysis and powder X-ray diffraction study of the reaction product respectively indicate that total Na/Li exchange takes place and the Ti-O framework of the Na₂Ti₆O₁₃ parent structure is kept under those experimental conditions. Therefore, Li₂Ti₆O₁₃ has been obtained with the mentioned parent structure. An important change is that particle size is decreased significantly which is favoring lithium insertion. Electrochemical study shows that Li₂Ti₆O₁₃ inserts ca. 5 Li per formula unit in the voltage range 1.5-1.0 V vs. Li⁺/Li, yielding a specific discharge capacity of 250 mAh g⁻¹ under equilibrium conditions. Insertion occurs at an average equilibrium voltage of 1.5 V which is observed for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. However, a capacity loss of ca. 30% is observed due to a phase transformation occurring during the first discharge. After the first redox cycle a high reversible capacity is obtained (ca. 160 mAh g⁻¹ at C/12) and retained upon cycling. Taking into consideration these results, we propose Li₂Ti₆O₁₃ as an interesting material to be further investigated as the anode of lithium ion batteries.     

Nanosized LiMn2O4 powders prepared by flame spray pyrolysis from aqueous solution

LiMn₂O₄ powders have been directly prepared by flame spray pyrolysis from an aqueous spray solution of the metal salts. The powders prepared at a low fuel gas flow rate (3 L min⁻¹) comprise particles with a bimodal size distribution, i.e., submicron- and nanometer-sized particles, and have crystal structures of LiMn₂O₄ and Mn₃O₄ phases. However, the powders prepared at a high fuel gas flow rate (5 L min⁻¹) comprise nanometer-sized particles and have pure crystal structure of LiMn₂O₄ phase. The powders comprising nanosized particles are well crystallized, and the particles have a polyhedral structure. The mean particle size of these powders is 27 nm. The powders prepared directly by flame spray pyrolysis comprise nanosized particles and have the pure crystal structure of LiMn₂O₄, irrespective of the amount of excess lithium in the precursor solution. The initial discharge capacities of these powders increase from 91 to 112 mAh g⁻¹ when the amount of excess lithium is increased from 0% to 30% of the stoichiometric amount. The optimum amount of excess lithium required to prepare LiMn₂O₄ powders with nanosized particles and the maximum possible initial discharge capacity is 10%.     

Improved rate capability of carbon coated Li3.9Sn0.1Ti5O12 porous electrodes for Li-ion batteries

A new sol-gel process is developed to modify the Li₄Ti₅O₁₂ anode material for improved rate capability. The new process brings about the following effects, namely (i) doping of Sn²⁺ to form Li_3.9Sn_0.1Ti₅O₁₂, (ii) carbon coating and (iii) creation of a porous structure. The doping of Sn²⁺ results in the lattice distortion without changing the phase composition. A thin layer of amorphous carbon is coated on the doped particles that contain numerous nanopores. The rate capability of the anode material made from the modified powder is significantly improved when discharged at high current rates due to the reduced charge transfer resistance.     

Effect of calcination temperature on morphology,crystallinity and electrochemical properties of nano-crystalline metal oxides (Co3O4, CuO,and NiO) prepared via ultrasonic spray pyrolysis

Nano-crystalline metal oxides (Co₃O₄, CuO, and NiO) are synthesized as anode materials for lithium-ion batteries by an ultrasonic spray pyrolysis method. The effects of calcination temperature on the morphology, crystallite size and electrochemical properties of the metal oxides are investigated. X-ray diffraction (XRD) studies show that the crystallite size varies with the final calcination temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the calcination temperature strongly influences the morphology of the prepared metal oxides and this results in different electrochemical performance. The existence of a nano-scale microstructure for the prepared metal oxides has a strong relationship with irreversible capacity and capacity retention.     

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.     

Nanosized Li4Ti5O12/graphene hybrid materials with low polarization for high rate lithium ion batteries

We report a simple strategy to prepare a hybrid of lithium titanate (Li₄Ti₅O₁₂, LTO) nanoparticles well-dispersed on electrical conductive graphene nanosheets as an anode material for high rate lithium ion batteries. Lithium ion transport is facilitated by making pure phase Li₄Ti₅O₁₂ particles in a nanosize to shorten the ion transport path. Electron transport is improved by forming a conductive graphene network throughout the insulating Li₄Ti₅O₁₂ nanoparticles. The charge transfer resistance at the particle/electrolyte interface is reduced from 53.9 Ω to 36.2 Ω and the peak currents measured by a cyclic voltammogram are increased at each scan rate. The difference between charge and discharge plateau potentials becomes much smaller at all discharge rates because of lowered polarization. With 5 wt.% graphene, the hybrid materials deliver a specific capacity of 122 mAh g⁻¹ even at a very high charge/discharge rate of 30 C and exhibit an excellent cycling performance, with the first discharge capacity of 132.2 mAh g⁻¹ and less than 6% discharge capacity loss over 300 cycles at 20 C. The outstanding electrochemical performance and acceptable initial columbic efficiency of the nano-Li₄Ti₅O₁₂/graphene hybrid with 5 wt.% graphene make it a promising anode material for high rate lithium ion batteries.     

High-rate nano-crystalline Li4Ti5O12 attached on carbon nano-fibers for hybrid supercapacitors

A lithium titanate (Li₄Ti₅O₁₂)-based electrode which can operate at unusually high current density (300 C) was developed as negative electrode for hybrid capacitors. The high-rate Li₄Ti₅O₁₂ electrode has a unique nano-structure consisting of unusually small nano-crystalline Li₄Ti₅O₁₂ (ca. 5-20 nm) grafted onto carbon nano-fiber anchors (nc-Li₄Ti₅O₁₂/CNF). This nano-structured nc-Li₄Ti₅O₁₂/CNF composite are prepared by simple sol-gel method under ultra-centrifugal force (65,000 N) followed by instantaneous annealing at 900 °C for 3 min. A model hybrid capacitor cell consisting of a negative nc-Li₄Ti₅O₁₂/CNF composite electrode and a positive activated carbon electrode showed high energy density of 40 Wh L⁻¹ and high power density of 7.5 kW L⁻¹ comparable to conventional EDLCs.     

Influence of conductive additives and surface fluorination on the charge/discharge behavior of lithium titanate (Li4/3Ti5/3O4)

Effect of conductive additives and surface modification with NF₃ and ClF₃ on the charge/discharge behavior of Li_4/3Ti_5/3O₄ (≈4.6 μm) was investigated using vapor grown carbon fiber (VGCF) and acetylene black (AB). VGCF and mixtures of VGCF and AB increased charge capacities of original Li_4/3Ti_5/3O₄ and those fluorinated with NF₃ by improving the electric contact between Li_4/3Ti_5/3O₄ particles and nickel current collector. Surface fluorination increased meso-pore with diameter of 2 nm and surface area of Li_4/3Ti_5/3O₄, which led to the increase in first charge capacities of Li_4/3Ti_5/3O₄ samples fluorinated by NF₃ at high current densities of 300 and 600 mA g⁻¹. The result shows that NF₃ is the better fluorinating agent for Li_4/3Ti_5/3O₄ than ClF₃.     

Thermal properties of Li4/3Ti5/3O4/LiMn2O4 cell

The thermal properties of Li_4/3Ti_5/3O₄ and Li_1+xMn₂O₄ electrodes were investigated by isothermal micro-calorimetry (IMC). The 150-mAh g⁻¹ capacity of a Li/Li_4/3Ti_5/3O₄ half cell was obtained through the voltage plateau that occurs at 1.55 V during the phase transition from spinel to rock salt. Extra capacity below 1.0 V was attributed to the generation of a new phase. The small and constant entropy change of Li_4/3Ti_5/3O₄ during the spinel/rock-salt phase transition indicated its good thermal stability. Accelerated rate calorimetry confirmed that Li_4/3Ti_5/3O₄ has better thermal characteristics than graphite. The IMC results for a Li/Li_1+xMn₂O₄ half cell indicated less heat variation due to the suppression of the order/disorder change by lithium doping. The heat profiles of the Li_4/3Ti_5/3O₄/Li_1+xMn₂O₄ full cell indicated less heat generation compared with a mesocarbon-microbead graphite/Li_1+xMn₂O₄ cell.     

Micron-sized, carbon-coated Li4Ti5O12 as high power anode material for advanced lithium batteries

Spherical, high tap density, carbon-coated Li₄Ti₅O₁₂ powders are synthesized by a spray-drying process followed by a facile pitch coating. XRD, SEM, TEM analyses show that the carbon layer uniformly coats the Li₄Ti₅O₁₂ particles without producing any crystalline changes. We demonstrate that the carbon coating significantly increases the electrical conductivity of Li₄Ti₅O₁₂ making it an efficient, high rate electrode for lithium cells. The electrochemical tests in fact confirm that the 3.25 wt% carbon-coated Li₄Ti₅O₁₂ electrode operates with ultra high rate capacity levels, i.e., 100 C and has excellent capacity retention and charge-discharge efficiency for a life extending over 100 cycles.     

Electrochemistry and safety of Li4Ti5O12 and graphite anodes paired with LiMn2O4 for hybrid electric vehicle Li-ion battery applications

A promising anode material for hybrid electric vehicles (HEVs) is Li₄Ti₅O₁₂ (LTO). LTO intercalates lithium at a voltage of ∼1.5 V relative to lithium metal, and thus this material has a lower energy compared to a graphite anode for a given cathode material. However, LTO has promising safety and cycle life characteristics relative to graphite anodes. Herein, we describe electrochemical and safety characterizations of LTO and graphite anodes paired with LiMn₂O₄ cathodes in pouch cells. The LTO anode outperformed graphite with regards to capacity retention on extended cycling, pulsing impedance, and calendar life and was found to be more stable to thermal abuse from analysis of gases generated at elevated temperatures and calorimetric data. The safety, calendar life, and pulsing performance of LTO make it an attractive alternative to graphite for high power automotive applications, in particular when paired with LiMn₂O₄ cathode materials.     

Compatibility of the Py24TFSI-LiTFSI ionic liquid solution with Li4Ti5O12 and LiFePO4 lithium ion battery electrodes

Ionic liquids are assuming a constantly growing importance as preferred media for the progress of various energy devices such as solar cells, supercapacitors and lithium batteries. However, their electrochemical properties are not yet fully recognized and in this paper we try to contribute to fill the gap by investigating the stability window of a sample IL-based solution, as well as its interfacial properties with two typical lithium ion battery electrodes, namely lithium titanate, Li₄Ti₅O₁₂ and lithium iron phosphate, LiFePO₄. The results of a detailed impedance spectroscopy analysis demonstrate that, although operating well within the stability domain of the selected IL-based electrolyte, both electrodes undergo passivation phenomena with the formation on their surface of a solid electrolyte interface, SEI, layer. The impedance spectra show that the resistance of the SEI is very low and stable, this suggesting that its occurrence is highly beneficial in terms of assuring reversible and safe electrode processes.