Wet-chemistry synthesis of Li4Ti5O12 as anode materials rendering high-rate Li-ion storage

Compared with traditional anode materials, spinel-structured Li₄Ti₅O₁₂ (LTO) with “zero-strain” characteristic offers better cycling stability. In this work, by a wet-chemistry synthesis method, LTO anode materials have been successfully synthesized by using CH₃COOLi·2H₂O and C₁₆H₃₆O₄Ti as raw materials. The results show that sintering conditions significantly affect purity, uniformity of particle sizes, and electrochemical properties of as-prepared LTO materials. The optimized LTO product calcined at 650°C for 20 hours demonstrates small particle sizes and excellent electrochemical performances. It delivers an initial discharge capacity of 242.3 mAh g⁻¹ and remains at 117.4 mAh g⁻¹ over 500 cycles at the current density of 60 mA g⁻¹ in the voltage range of 1.0 to 3.0 V. When current density is increased to 1200 mA g⁻¹, its discharge capacity reaches 115.6 mAh g⁻¹ at the first cycle and remains at 64.6 mAh g⁻¹ after 2500 cycles. The excellent electrochemical performances of LTO can be attributed to the introduction of rutile TiO₂ phase and small particle sizes, which increases electrical conductivity and electrode kinetics of LTO. Therefore, as-synthesized LTO in this study can be regarded as a promising anode candidate material for lithium-ion batteries.     

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.     

The synthesis and characterizations of Li4Ti5O12–CNTs anode material

An anode material with Li₄Ti₅O₁₂ nanocrystals entangled by carbon nanotubes is prepared by polymerization of titanium tetra-isopropoxide with ethylene glycol in the presentence of carbon nanotubes. The resulted polymer is hydrolyzed in LiOH/H₂O solution, and then thermally decomposed to obtain the topic anode material. The characterizations show that the synthesis method yields a type of material that has both of high electronic conductivity and high lithium ion diffusion rate. The material has stable deep discharge capability (down to 0.01 V), high specific capacity (237 mAhg⁻¹ at 0.30 Ag^-1), and long cycling life time (254 mAhg⁻¹ at 0.10 Ag^-1, more than 500 discharge/charge cycles). High specific capacities of 258 and 158 mAhg⁻¹ are obtained at current densities of 0.10 and 3.00 Ag^-1, respectively. The deep discharge capability of the material offers an average voltage below 1.0 V (vs metal Li), which is lower than that of pristine Li₄Ti₅O₁₂ (1.55 V).     

Development of long life lithium ion battery for power storage

With the aim of developing lithium ion batteries with a long life and high efficiency for power storage, we experimentally evaluated combinations of cathode and anode active materials, in which batteries are able to obtain over 4000 cycles or 10 years of life. An acceleration method was evaluated using coin cells. We found that changing the current density was effective for evaluating battery life, since the logarithm of the cycle life showed a linear relationship to current density. Based on the current density increasing method, various combinations of cathode and anode active materials were tested. The cell system of LiCoO₂/Li_4/3Ti_5/3O₄ clearly showed a long life of about 4000 cycles. The energy density of the cell using the Li_4/3Ti_5/3O₄ anode is obviously smaller than that using a graphite anode, the cell with Li_4/3Ti_5/3O₄ anode was thought to have some merit especially in the large-scale-layer-built type battery by the applicability of the Al anode collector and a light weight battery case.     

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.     

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.     

Synthesis of lithium insertion material Li4Ti5O12 from rutile TiO2 via surface activation

The synthesis of spinel-type lithium titanate, Li₄Ti₅O₁₂, a promising anode material of secondary lithium-ion battery, from “inert” rutile TiO₂, is investigated. On the purpose of increasing the reactivity of rutile TiO₂, it is treated by concentrated HNO₃. By applying such activated rutile TiO₂ as the titanium source in combination with the cellulose-assisted combustion synthesis, phase-pure Li₄Ti₅O₁₂ is successfully synthesized at 800 °C, at least 150 °C lower than that based on solid-state reaction. The resulted oxide shows a reversible discharge capacity of ～175 mAh g^?1 at 1 C rate, near the theoretical value. The resulted oxide also shows promising high rate performance with a discharge capacity of ～100 mAh g^?1 at 10 C rate and high cycling stability.     

Nanostructured electrodes for next generation rechargeable electrochemical devices

Nanostructured intercalating electrodes offer immense potential for significantly enhancing the performance of rechargeable rocking chair (e.g. Li⁺ and Mg²⁺) and asymmetric hybrid batteries. The objective of this work has been to develop a variety of cathode (e.g. V₂O₅, LiMnO₂ and LiFePO₄) and anode (e.g. Li₄Ti₅O₁₂) materials with unique particle characteristics and controlled composition to reap the maximum benefits of nanophase electrodes for rechargeable Li-based batteries. Different processing routes, which were chosen on the basis of the final composition and the desired particle characteristics of electrode materials, were developed to synthesize a variety of electrode materials. Vapor phase processes were used to synthesize nanopowders of V₂O₅ and TiO₂. TiO₂ was the precursor used for producing ultrafine particles of Li₄Ti₅O₁₂. Liquid phase processes were used to synthesize nanostructured LiMn_xM_1−xO₂ and LiFePO₄ powders. It was found that (i) nanostructured V₂O₅ powders with a metastable structure have 30% higher retention capacity than their coarse-grained counterparts, for the same number of cycles; (ii) the specific capacity of nanostructured LiFePO₄ cathodes can be significantly improved by intimately mixing nanoparticles with carbon particles and that cathodes made of LiFePO₄/C composite powder exhibited a specific capacity of ∼145 mAh/g (85% of the theoretical capacity); (iii) nanostructured, layered LiMn_xM_1−xO₂ cathodes demonstrated a discharge capacity of ∼245 mAh/g (86% of the theoretical capacity) at a slow discharge rate; however, the composition and structure of nanoparticles need to be optimized to improve their rate capabilities and (iv) unlike micron-sized (1–10 μm) powders, ultrafine Li₄Ti₅O₁₂ showed exceptional retention capacity at a discharge rate as high as 10 C in Li-test cells.     

A novel battery-supercapacitor system with extraordinarily high performance

In this paper, a battery-supercapacitor system is developed and its electrochemical performance is investigated. The battery-supercapacitor system is composed of a separated LiFePO₄/activated carbon cathode and a separated Li₄Ti₅O₁₂/activated carbon anode onto both sides of a piece of aluminum foil. We demonstrated the superior electrochemical performance of this battery-supercapacitor system, such as its energy density of 4.9–48.5 Wh/kg, power density of 167.7–5243.2 W/kg, rate capability of 73.9% at a current density of 20 A and cycle life (91.5% after 1800 cycles) which outperforms that of a hybrid supercapacitor. This can be explained by the synergistic effect of a Faradaic and non-Faradaic system in a single cell. The results clearly show that the battery-supercapacitor system, including a LiFePO₄ cathode/Li₄Ti₅O₁₂ anode and an activated carbon anode/activated carbon cathode, has great potential for use in advanced energy storage devices.     

Structural evolution of ramsdellite-type LixTi2O4 upon electrochemical lithium insertion–deinsertion (0 ≤ x ≤ 2)

Structural evolution during topotactical electrochemical lithium insertion and deinsertion reactions in ramsdellite-like Li_xTi₂O₄ has been followed by means of in situ X-ray diffraction techniques. The starting Li_xTi₂O₄ (x = 1) exists as a single phase with variable composition which extends in the range 0.50 ≤ x ≤ 1.33. However, beyond the lower and upper compositional limits, two other single phases, with ramsdellite-like structure, are detected. The composition of these single phases are: TiO₂ upon lithium deinsertion and Li₂Ti₂O₄ upon lithium insertion. Both TiO₂ and Li₂Ti₂O₄ are characterized by narrow compositional ranges. The close structural relationship between pristine LiTi₂O₄ and the inserted and deinserted compounds together with the relative small volume change over the whole insertion–deinsertion range (not more than 1.1% upon reduction) is a guaranty for the high capacity retention after long cycling in lithium batteries. The small changes in cell parameters well reflect the remarkable flexibility of the ramsdellite framework against lithiation and delithiation reactions.     

Safe and fast-charging Li-ion battery with long shelf life for power applications

We report a Li-ion battery that can be charged within few minutes, passes the safety tests, and has a very long shelf life. The active materials are nanoparticles of LiFePO₄ (LFP) and Li₄Ti₅O₁₂ (LTO) for the positive and negative electrodes, respectively. The LiFePO₄ particles are covered with 2 wt.% carbon to optimize the electrical conductivity, but not the Li₄Ti₅O₁₂ particles. The electrolyte is the usual carbonate solvent. The binder is a water-soluble elastomer. The “18650” battery prepared under such conditions delivers a capacity of 800 mAh. It retains full capacity after 20,000 cycles performed at charge rate 10C (6 min), discharge rate 5C (12 min), and retains 95% capacity after 30,000 cycles at charge rate 15C (4 mn) and discharge rate 5C both at 100% DOD and 100% SOC.     

Power-ion battery: bridging the gap between Li-ion and supercapacitor chemistries

A 40 Wh/kg Li-ion battery using a Li₄Ti₅O₁₂ nanostructured anode and a composite activated carbon LiCoO₂ cathode was built using plastic Li-ion processing based on PVDF-HFP binder and soft laminate packaging. The specific power of the device is similar to that of an electrochemical double-layer supercapacitor (4000 W/kg). The high power is enabled by a combination of a nanostructured negative electrode, an acetonitrile based electrolyte and an activated carbon/LiCoO₂ composite positive electrode. This enables very fast charging (full recharge in 3 min). The effect of electrode formulation and matching ratio on energy, power and cycle-life are described. Optimization of these parameters led to a cycle-life of 20% capacity loss after 9000 cycles at full depth of discharge (DOD).     

Electrochemical performance of Li4Ti5O12/carbon nanotubes/graphene composite as an anode material in lithium-ion batteries

A three-dimensional Li₄Ti₅O₁₂/carbon nanotubes/graphene composite (LTO-CNT-G) was prepared by ball-milling method, followed by microwave heating. The as-prepared LTO-CNT-G composite as anode material in lithium-ion battery exhibited superior rate capability and cycle performance under relative high current density compared with that of Li₄Ti₅O₁₂/CNTs (LTO-CNT) and Li₄Ti₅O₁₂/graphene (LTO-G) composites. Graphene nanosheets and CNTs were used to construct 3D conducting networks, leading to faster electron transfer and lower resistance during the lithium ion reversible reaction, which significantly enhanced the electrochemical activity of LTO-CNT-G composite. The synergistic effect of graphene and CNTs can greatly improve the rate capability and cycling stability of Li₄Ti₅O₁₂-based anodes. The LTO-CNT-G composite exhibited a high initial discharge capacity of 172 mAh g^?1 at 0.2 C and 132 mAh g^?1 at 20 C, as well as an excellent cycling stability. The electrochemical impedance spectroscopy demonstrated that the LTO-CNT-G composite has the smallest charge-transfer resistance compared with the LTO-CNT and LTO-G composites, indicating that the fast electron transfer from the electrolyte to the LTO-CNT-G active materials during the lithium ion intercalation/deintercalation owing to the three-dimensional networks of graphene and CNTs.     

Preparation and characterization of high-density spherical Li4Ti5O12 anode material for lithium secondary batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. A novel technique has been developed to prepare Li₄Ti₅O₁₂. The spherical precursor is prepared via an “inner gel” method by TiCl₄ as the raw material. Spherical Li₄Ti₅O₁₂ powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃. The investigation of XRD, SEM and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂ powders prepared by this method are spherical, and have high tap-density and excellent electrochemical performance. It is tested that the tap-density of the product is as high as 1.64 g cm⁻³, which is remarkably higher than the non spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, a reversible capacity is as high as 161 mAh g⁻¹ at a current density of 0.08 mA cm⁻².     

Electrochemical performance of all-solid-state lithium secondary batteries improved by the coating of Li2O-TiO2 films on LiCoO2 electrode

All-solid-state lithium secondary batteries using LiCoO₂ particles coated with amorphous Li₂O-TiO₂ films as an active material and Li₂S-P₂S₅ glass-ceramics as a solid electrolyte were fabricated; the electrochemical performance of the batteries was investigated. The interfacial resistance between LiCoO₂ and solid electrolyte was decreased by the coating of Li₂O-TiO₂ films on LiCoO₂ particles. The rate capability of the batteries using the LiCoO₂ coated with Li₂Ti₂O₅ (Li₂O·2TiO₂) film was improved because of the decrease of the interfacial resistance of the batteries. The cycle performance of the all-solid-state batteries under a high cutoff voltage of 4.6 V vs. Li was highly improved by using LiCoO₂ coated with Li₂Ti₂O₅ film. The oxide coatings are effective in suppressing the resistance increase between LiCoO₂ and the solid electrolyte during cycling. The battery with the LiCoO₂ coated with Li₂Ti₂O₅ film showed a large initial discharge capacity of 130 mAh/g and good capacity retention without resistance increase after 50 cycles at the current density of 0.13 mA/cm².     

ZnMn2O4/milk-derived Carbon hybrids with enhanced Lithium storage capability

One of the effective ways to improve the conductivity and structural stability of binary metal oxide nanostructures is to tightly composite them with nano-carbon materials with excellent conductivity. However, the introduction of low density carbon materials also reduces the energy density of batteries. Therefore, we provides a new idea to enhance the lithium storage performance of carbon/binary transition metal oxide anode materials by multi-element co-doping carbon. ZnMn₂O₄ provides high lithium storage capacity; non-metallic heteroatoms in milk-derived carbon greatly improve the conductivity of carbon materials; metal heteroatoms in milk-derived carbon increase the density of carbon materials. Multicomponent co-doping carbon can build up the mass specific capacity, ratio performance, cyclic life and mechanical properties of binary metal oxides/porous carbon nanocomposites. As the anode materials of lithium-ion batteries, the ZnMn₂O₄/MC (milk-derived carbon) hybrids deliver a high reversible capacity of 1352 mAh g⁻¹ after 400 cycles at 0.1 A g⁻¹, and a remarkable long-term cyclability with 635 mAh g⁻¹ after 300 cycles at 1.0 A g⁻¹.     

Advanced electrochemical performance of Li4Ti4.95V0.05O12 as a reversible anode material down to 0 V

Li₄Ti_4.95V_0.05O₁₂ and Li₄Ti₅O₁₂ powders were successfully prepared by a solid-state method. XRD reveals that both samples have high phase purity. Raman spectroscopy indicates that the Ti–O vibration have a blue shift. SEM shows that Li₄Ti_4.95V_0.05O₁₂ has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of Li₄Ti₅O₁₂. Galvanostatic charge–discharge testing indicates both samples have nearly equal initial capacities at different discharge voltage ranges (0–2 and 0.5–2 V), but Li₄Ti_4.95V_0.05O₁₂ has a higher cycling performance than that of Li₄Ti₅O₁₂. CV suggests that Li₄Ti_4.95V_0.05O₁₂ has lower electrode polarization and high lithium ion diffusivity in solid-state body of sample, implying that the vanadium doping is beneficial to the reversible intercalation and de-intercalation of Li⁺. The novel Li₄Ti_4.95V_0.05O₁₂ materials may find promising applications in lithium ion batteries and electrochemical cells due to the excellent electrochemical performace and simple synthesis route.     

Anodic behavior of zinc in Zn-MnO2 battery using ERDA technique

The commercial, alkaline zinc-manganese dioxide (Zn-MnO₂) primary battery has been transformed into a secondary battery using lithium hydroxide electrolyte. Galvanostatic discharge–charge experiments showed that the capacity decline of the Zn-MnO₂ battery is not caused by the MnO₂ cathode, but by the zinc anode. The electrochemical data indicated that a rechargeable battery made of porous zinc anode can have a larger discharge capacity of 220 mAh/g than a planar zinc anode of 130 mAh/g. The cycling performance of these two anodes is demonstrated. Structural and depth profile analyses of the discharged anodes are examined by X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) techniques.     

Submicron‐sized Sb2O3 with hierarchical structure as high‐performance anodes for Na‐ion storage

Submicron‐sized Sb₂O₃ with hierarchical structure was successfully prepared via a synthesis of one‐step solvothermal chemical route. Na‐ion storage performance of Sb₂O₃ material was investigated. Sb₂O₃ anode exhibits a high reversible capacity (approximately 350 mAh/g) and stable cycle stability (greater than 95%) over 100 cycles at 100 or 200 mA/g. A full battery with Sb₂O₃ anode and P2‐Na_2/3Ni_1/3Mn_1/2Ti_1/6O₂ (PTO) cathode indicated a high energy density of 216.6 Wh/kg.     

A high rate,high capacity and long life (LiMn2O4 + AC)/Li4Ti5O12 hybrid battery–supercapacitor

A hybrid battery–supercapacitor (LiMn₂O₄ + AC)/Li₄Ti₅O₁₂ using a Li₄Ti₅O₁₂ anode and a LiMn₂O₄/activated carbon (AC) composite cathode was built. The electrochemical performances of the hybrid battery–supercapacitor (LiMn₂O₄ + AC)/Li₄Ti₅O₁₂ were characterized by cyclic voltammograms, electrochemical impedance spectra, rate charge–discharge and cycle performance testing. It is demonstrated that the hybrid battery–supercapacitor has advantages of both the high rate capability from hybrid capacitor AC/Li₄Ti₅O₁₂ and the high capacity from secondary battery LiMn₂O₄/Li₄Ti₅O₁₂. Moreover, the electrochemical measurements also show that the hybrid battery–supercapacitor has good cycle life performance. At 4C rate, the capacity loss in constant current mode is no more than 7.95% after 5000 cycles, and the capacity loss in constant current–constant voltage mode is no more than 4.75% after 2500 cycles.