Li4Ti5O12/poly(methyl)thiophene asymmetric hybrid electrochemical device

Electrochemically prepared poly(methyl)thiophene is characterized by cyclic voltammetry and galvanometry with an activated carbon counter-electrode. It is then used as a cathode in a laminated plastic asymmetric hybrid electrochemical device with a nano-structured Li₄Ti₅O₁₂ anode. This device displays the specific power of a supercapacitor, with a higher specific energy of 10 Wh/kg, and better cycle-life than a Li-ion battery. The matching ratio of the active materials was found to strongly influence cycle-life.     

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).     

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.     

A novel high-performance cylindrical hybrid supercapacitor with Li4−xNaxTi5O12/activated carbon electrodes

A cylindrical hybrid supercapacitor was fabricated using Li_4−xNa_xTi₅O₁₂ as an anode and activated carbon as a cathode. Li_4−xNa_xTi₅O₁₂ (0 ≤ x ≤ 0.6) powder was successfully crystallized, and the grain size of Li_4−xNa_xTi₅O₁₂ decreased with increasing Na content. This indicated that Na can enhance the electrochemical performance due to smaller grain size and ionic conductivity. However, excessive Na content causes a distortion of the original Li₄Ti₅O₁₂ structure during cycling. The hybrid supercapacitor with the Li_3.7Na_0.3Ti₅O₁₂ anode shows similar electrochemical performance to Li_3.4Na_0.6Ti₅O₁₂, and approximately 92% of the maximum cycle performance is retained, even after 5000 cycles at 2.5 Ag⁻¹.     

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.     

High performance hybrid supercapacitors with LiNi1/3Mn1/3Co1/3O2/activated carbon cathode and activated carbon anode

Hybrid supercapacitors have been studied as a next generation energy storage device that combines the advantages of supercapacitors and batteries. One important challenge of hybrid supercapacitors is to improve energy density (8.9–42 Wh/kg) with maintaining excellent power density (800–7989 W/kg) and cyclability (98.9% after 9000 cycles). Herein, we demonstrate an approach to design hybrid supercapacitors based on LiNi_1/3Mn_1/3Co_1/3O₂ (NMC)/activated carbon (AC) cathode and AC anode (NMC/AC//AC). The NMC/AC//AC hybrid supercapacitors shows outstanding electrochemical performances due to the enhanced energy and power densities. These findings suggest that the NMC/AC cathode is an effective method for high performance hybrid supercapacitors.     

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.     

One-dimensional nanostructures as electrode materials for lithium-ion batteries with improved electrochemical performance

One-dimensional (1D) nanosize electrode materials of lithium iron phosphate (LiFePO₄) nanowires and Co₃O₄–carbon nanotube composites were synthesized by the hydrothermal method. The as-prepared 1D nanostructures were structurally characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. We tested the electrochemical properties of LiFePO₄ nanowires as cathode and Co₃O₄–carbon nanotubes as anode in lithium-ion cells, via cyclic voltammetry and galvanostatic charge/discharge cycling. LiFePO₄ nanorod cathode demonstrated a stable performance over 70 cycles, with a remained specific capacity of 140 mAh g⁻¹. Nanocrystalline Co₃O₄–carbon nanotube composite anode exhibited a reversible lithium storage capacity of 510 mAh g⁻¹ over 50 cycles. 1D nanostructured electrode materials showed strong potential for lithium-ion batteries due to their good electrochemical performance.     

Insight into effects of graphene and zinc oxide in Li4Ti5O12 as anode materials for Li-ion full-cell battery

Programmable design of nanocomposites of Li₄Ti₅O₁₂ (LTO) conducted through hydrothermal route in the presence of ethylenediamine as basic and capping agent. In this work, effect of ZnO and Graphene on the Li₄Ti₅O₁₂ based nanocomposites as anode materials investigated for Li-Ion battery performances. The full cells battery assembled with LTO based nanocomposites on Cu foil as the anode electrode and commercial LMO (LiMn₂O₄) on aluminum foil as cathode electrode. X-Ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), along with Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission electron microscopy (TEM) images was applied for study the composition and structure of as-prepared samples. The electrochemical lithium storage capacity of prepared nanocomposites was compared with pristine LTO via chronopotentiometry charge-discharge techniques at 1.5–4.0 V and current rate of 100 mA/g. As a result, the electrode which is provided by LTO/TiO₂/ZnO and LTO/TiO₂/graphene nanocomposites provided 765 and 670 mAh/g discharge capacity compared with pristine LTO/TiO₂ (550 mAh/g) after 15 cycles. Based on the obtained results, fabricated nanocomposites can be promising compounds to improve the electrochemical performance of lithium storage.     

Macaroon-like FeCo2O4 modified activated carbon anode for enhancing power generation in direct glucose fuel cell

Macaroon-like FeCo₂O₄ nanomaterial was prepared and used as electrocatalyst in direct glucose alkaline fuel cell (DGAFC), which exhibited high catalytic activity towards glucose oxidation reaction. Maximum power density of 35.91 W m⁻² was achieved in the DGAFC equipped with a FeCo₂O₄ modified activated carbon (AC) anode, which was almost 151% higher than the control. Physical and electrochemical characterizations were performed to provide further understanding of the origin of its high activity. Our results show that the introduction of FeCo₂O₄ into the AC anode remarkably increase the exchange current density and reduce the charge transfer resistance. It is supposed that there is a synergistic effect between Fe (III) and Co (III), which accelerates electron transfer from glucose to external circuits. This study will promote the development of cost effective and environmentally benign catalysts for electrochemical energy applications.     

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.     

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.     

Nano Li4Ti5O12–LiMn2O4 batteries with high power capability and improved cycle-life

We report the effects of electrode thickness, cathode particle size and morphology, cathode carbon coating matching ratio and laminate structure on the electrochemical characteristics of nanosized Li₄Ti₅O₁₂–LiMn₂O₄ batteries. We show that a correct adjustment of these parameters resulted in significant improvements in power capability and cycle-life of such devices, making them competitive, low-cost and safe battery chemistry for next generation Li-ion batteries. In addition, Li₄Ti₅O₁₂ reversible specific capacity beyond three Li-ions intercalation is reported.     

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.     

Effect of capacity matchup in the LiNi0.5Mn1.5O4/Li4Ti5O12 cells

The effect of the capacity matchup between cathode and anode in the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ cell system on cycling property, choice of electrolyte, high voltage and overcharge tolerances was investigated by comparing the cells with Li₄Ti₅O₁₂ limiting capacity with the cells with LiNi_0.5Mn_1.5O₄ limiting capacity. The former exhibits better cycling performance and less limitation of electrolyte choice than the latter. Furthermore, the Li₄Ti₅O₁₂-limited cell exhibits better tolerance to high voltage and overcharge than the LiNi_0.5Mn_1.5O₄-limited cell, owing to taking advantage of the extra capacity of Li₄Ti₅O₁₂ below 1 V. It is thus recommended that the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ cell whose capacity is limited by Li₄Ti₅O₁₂ anode should be used to extend the application of the state-of-the-art lithium-ion batteries.     

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.     

Kinetic characteristics of mixed conductive electrodes for lithium ion batteries

The rate performances of four mixed conductive electrodes (Li_4/3Ti_5/3O₄, LiFePO₄, LiCoO₂ and LiCo_1/3Ni_1/3Mn_1/3O₂) were investigated using galvanostatic charge/discharge, electrochemical impedance Spectroscopy (EIS) and galvanostatic intermittent titration (GITT). These four electrode materials can be roughly divided into two groups according to the structure change during Li intercalation/extraction, i.e. the phase transition materials (Li_4/3Ti_5/3O₄ and LiFePO₄) and mixed phase transformation and solid solution materials (LiNi_1/3Mn_1/3Co_1/3O₂ and LiCoO₂). Both the ionic conductivity and phase transition kinetics have a strong impact on the rate capability of the electrode material in addition to the generally accepted factors such as particle size and electronic conductivity. The rate capabilities of Li_4/3Ti_5/3O₄ and LiFePO₄, which have an extended flat region in the charge/discharge curves, mainly depended on their phase transition kinetics. The rate performance of the solid solution materials were controlled by the ionic conductivity, with some influence from the electronic conductivity.     

Synthesis and electrochemical properties of olivine LiFePO4 prepared by a carbothermal reduction method

LiFePO₄/C composite cathode material was prepared by carbothermal reduction method, which uses NH₄H₂PO₄, Li₂CO₃ and cheap Fe₂O₃ as starting materials, acetylene black and glucose as carbon sources. The precursor of LiFePO₄/C was characterized by differential thermal analysis and thermogravimetry. X-ray diffraction (XRD), scanning electron microscopy (SEM) micrographs showed that the LiFePO₄/C is olivine-type phase, and the addition of the carbon reduced the LiFePO₄ grain size. The carbon is dispersed between the grains, ensuring a good electronic contact. The products sintered at 700 °C for 8 h with glucose as carbon source possessed excellent electrochemical performance. The synthesized LiFePO₄ composites showed a high electrochemical capacity of 159.3 mAh g⁻¹ at 0.1 C rate, and the capacity fading is only 2.2% after 30 cycles.     

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.     

Optimization of a direct carbon fuel cell for operation below 700 °C

Direct carbon fuel cells (DCFCs) are the most efficient technology to convert solid carbon energy to electricity and thus could have a major impact on reducing fuel consumption and CO₂ emissions. The development of DCFCs to commercialisation stage is largely prohibited by their poor power densities due to the high resistive loss from anode. Here, we report a high-performance Sm_0.2Ce_0.8O_1.9 electrolyte-supported hybrid DCFC with Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ cathode and optimised anode configuration. The catalytic oxidation of carbon is improved, which results in an area specific resistance of only 0.41 Ω cm² at 650 °C at the anode. The hybrid DCFC achieves a peak power density of 113.1 mW cm⁻² at 650 °C operating on activated carbon. The stability of the fuel cell has also been improved due to the optimised current collection.