Li4Ti5O12 Surface Research Articles

Is Li4Ti5O12a solid-electrolyte-interphase-free electrode material in Li-ion batteries? Reactivity between the Li4Ti5O12electrode and electrolyte

Does the Li4Ti5O12 electrode need a carbon additive in lithium-ion batteries? We answered this question in our previous work by showing that the partially reduced Ti4+ on the surface of Li4Ti5O12 could provide enough electronic conductivity to initiate the electrochemical process. In this work, we discuss the generally accepted fact that a solid electrolyte interphase (SEI) is hardly formed on the surface of the Li4Ti5O12 electrode owing to its high redox potential by using the carbon-free Li4Ti5O12 electrode to exclude the influences of carbon. In contrast to the previous argument, Li4Ti5O12 was found to have certain reactivity towards electrolytes at room and high temperature (60 °C). Moreover, in the presence of carbon in the electrode (i.e. the conventional electrode formulation), the reactivity of the electrode towards an electrolyte was significantly increased at high temperatures. These results were discussed based on surface analyses and electrode morphology observation before and after cycling, and correlated with the electrochemical performance.

Bio-Derivative Galactomannan Gum Binders for Li4Ti5O12 Negative Electrodes in Lithium-Ion Batteries

Two types of galactomannan gum derived from plant seeds, guar gum (GG) and tara gum (TG), were used for the first time as the binders for Li4Ti5O12 (LTO) negative electrodes in lithium-ion batteries; they were thoroughly compared to typical carboxymethyl cellulose (CMC) binder using various characterization techniques. The galactomannan gums, branched polysaccharides, better facilitate the transport of lithium ions in LTO electrodes than CMC binder, a cellulose (linear polysaccharide) derivative, even though their binding capability is not as strong as CMC. This is attributed to a large extent of electrolyte uptake and a large LTO surface exposed to electrolyte when the gum binders are used. In particular, the GG-containing LTO electrode exhibits a high reversible capacity of 160.0 mAh g−1 at the 100th cycle with 1 C current rate, whereas the CMC-containing LTO electrode has a reversible capacity of 150.1 mAh g−1. The difference in capacity between the GG and CMC electrodes increased at higher current rates and was approximately 25 mAh g−1 at 10 C current rate.

Highly dispersed copper nanoparticle modified nano Li4Ti5O12 with high rate performance for lithium ion battery

We report a simple strategy to prepare Li4Ti5O12/Cu nanoparticles as an anode material for high rate lithium ion batteries. The copper nanoparticles are highly dispersed on the surface of Li4Ti5O12 through hydrothermal process and a short post -annealing. X-ray diffraction, Field-emission scanning electron microscopy and transmission electron microscopy are performed to characterize their structures and morphologies. The cyclic voltammetry, galvanostatic charge/discharge and alternate current impedance are used to evaluate their electric performance. Compared to pure Li4Ti5O12, the Li4Ti5O12/Cu composites has high rate capability, capacity retention and excellent cycling performance. The results show that copper nanoparticles enhance the electric conductivity of Li4Ti5O12/Cu, and prevent agglomeration.

Surface structure and high-rate performance of spinel Li4Ti5O12 coated with N-doped carbon as anode material for lithium-ion batteries

We have reported a straightforward strategy to fabricate Li4Ti5O12 composites coated with N-doped carbon layer by using NH3 as N source and sugar as C source, which is a benefit for optimizing carbon layer thickness and tuning atomic ratio of N/C. The composite was synthesized by a conventional solid state reaction with ball milled mixture of TiO2, Li2CO3, and sugar as the precursor, then followed by a high temperature annealing in the atmosphere of Ar and NH3. The choice of titanium source has an impact on the Li4Ti5O12 surface morphology as well as electrochemical properties. N-doped TiO2 can lead to the generation of uniform N-doped C-coating layer, resulting in improved electrochemical performances at high current rate. The N-doped C-coating Li4Ti5O12 obtained by using Anatase TiO2 produces a serrated thin carbon layer, showing the best electrochemical behaviors with the discharge capacity of 100 mAh g−1 at high rate of 24 C and 92.2% of initial capacity after 800 cycles at 12 C, which should be one of the promising anode materials for hybrid electric vehicles.

Effect of Molecular Weight and Degree of Substitution of a Sodium-Carboxymethyl Cellulose Binder on Li4Ti5O12 Anodic Performance

This paper presents a detailed investigation of the influence of molecular weight (MW) and degree of substitution (DS) of sodium-carboxymethyl cellulose (CMC) used as binder of Li4Ti5O12 (LTO) anodes. CMC MW and DS were in the range of 90 000 to 700 000 and 0.7 to 1.2, respectively. As demonstrated by coin cell tests, the LTO electrode that contained relatively low MW and high DS CMC showed excellent cyclic performance above 150 mAh g–1 even after 100 cycles. Unlike typical electrodes, the adhesion strength of the LTO electrodes was not a critical factor for cell performance. On the contrary, low coverage of CMC on the surface of LTO, which leads to weak adhesion, was more favorable to the cell performance than strong adhesion caused by high coverage. Both an increase in the DS and a decrease in the MW of CMC gave rise to low charge transfer resistance, high ion conductivity, good wettability with the electrolyte, and good lithium ion mobility owing to a relatively large amount of LTO exposed to directly ...

Gassing in Li(4)Ti(5)O(12)-based batteries and its remedy.

Destructive gas generation with associated swelling has been a major challenge to the large-scale application of lithium ion batteries (LIBs) made from Li4Ti5O12 (LTO) anodes. Here we report root causes of the gassing behavior, and suggest remedy to suppress it. The generated gases mainly contain H2, CO2 and CO, which originate from interfacial reactions between LTO and surrounding alkyl carbonate solvents. The reactions occur at the very thin outermost surface of LTO (111) plane, which result in transformation from (111) to (222) plane and formation of (101) plane of anatase TiO2. A nanoscale carbon coating along with a stable solid electrolyte interface (SEI) film around LTO is seen most effective as a barrier layer in suppressing the interfacial reaction and resulting gassing from the LTO surface. Such an ability to tune the interface nanostructure of electrodes has practical implications in the design of next-generation high power LIBs.

Study of Surface Reaction of Spinel Li4Ti5O12 during the First Lithium Insertion and Extraction Processes Using Atomic Force Microscopy and Analytical Transmission Electron Microscopy

Spinel lithium titanate (Li(4)Ti(5)O(12), LTO) is a promising anode material for a lithium ion battery because of its excellent properties such as high rate charge-discharge capability and life cycle stability, which were understood from the viewpoint of bulk properties such as small lattice volume changes by lithium insertion. However, the detailed surface reaction of lithium insertion and extraction has not yet been studied despite its importance to understand the mechanism of an electrochemical reaction. In this paper, we apply both atomic force microscopy (AFM) and transmission electron microscopy (TEM) to investigate the changes in the atomic and electronic structures of the Li(4)Ti(5)O(12) surface during the charge-discharged (lithium insertion and extraction) processes. The AFM observation revealed that irreversible structural changes of an atomically flat Li(4)Ti(5)O(12) surface occurs at the early stage of the first lithium insertion process, which induces the reduction of charge transfer resistance at the electrolyte/Li(4)Ti(5)O(12) interface. The TEM observation clarified that cubic rock-salt crystal layers with a half lattice size of the original spinel structure are epitaxially formed after the first charge-discharge cycle. Electron energy loss spectroscopy (EELS) observation revealed that the formed surface layer should be α-Li(2)TiO(3). Although the transformation of Li(4)Ti(5)O(12) to Li(7)Ti(5)O(12) is well-known as the lithium insertion reaction of the bulk phase, the generation of surface product layers should be inevitable in real charge-discharge processes and may play an effective role in the stable electrode performance as a solid-electrolyte interphase (SEI).

Effects of different carbon sources on the electrochemical properties of Li4Ti5O12/C composites

Li4Ti5O12/C composites have been synthesized via a solid state reaction with TiO2-anatase, Li2CO3 and different carbon sources, such as conductive graphite KS-6 and sucrose, as the starting materials. It was found that the carbon layer from sucrose was homogeneously coated on the Li4Ti5O12 surface and the KS-6 was embedded among the Li4Ti5O12 particles as a conductive bridge without affecting the spinel structure of Li4Ti5O12. Moreover, it was demonstrated that the sucrose and KS-6 played different roles in improving the electrochemical properties of Li4Ti5O12/C composite. Compared with samples prepared by solely KS-6 or sucrose as the carbon source, the Li4Ti5O12/C composite (LTO-1) with KS-6 and sucrose as carbon sources together revealed the optimal electrochemical performance. It showed a high initial specific capacity of 152.5 mAh g−1 at 0.2 C and an excellent cycling performance with 96.8% capacity retention after 1000 cycles at 25 °C at 1 C. Furthermore, the (LTO-1)/LiMn2O4 full battery demonstrated a good cycling performance at 55 °C and could pass the 5 C–20 V overcharge test, external short-circuit and nail-puncture test. Therefore, it is believed that the Li4Ti5O12/C might be a promising anode material for large-scale lithium ion batteries of electric vehicle (EV), hybrid electric vehicle (HEV) and energy storage devices for solar or wind energy.

In situ fabrication of Li4Ti5O12@CNT composites and their superior lithium storage properties

In this paper, Li4Ti5O12@CNT composites are fabricated by a controlled in situ growth of CNTs on the surface of Li4Ti5O12. The formation of coiled CNTs occurs by the electroless loading of Ni–P catalysts on the surface of Li4Ti5O12. Coiled CNTs provide electron bridges interconnecting the Li4Ti5O12 particles to form a nano/micro-structured conductive hyper-network. The electronic conductivity of Li4Ti5O12@CNT composites is better than that of the sample before coating. As a result, Li4Ti5O12@CNT composites show superior lithium storage properties comparable to the pristine Li4Ti5O12. Based on electrochemical analysis, it is obvious that Li4Ti5O12@CNT composites can deliver reversible charge capacities of 149.2, 102.6, 73.3 and 47.5 mA h g−1 at 0.2 C, 10 C, 20 C and 50 C, respectively.

Preparation of a spinel Li4Ti5O12 (1 1 1) surface from a rutile TiO2 single crystal

Spinel Li4Ti5O12 is a very promising material for electrodes in a wide range of Li-ion battery applications because of its unique Li-insertion/extraction properties. Although the bulk properties of Li4Ti5O12 have been studied intensively, there have been few reports about the structure and properties of Li4Ti5O12 surfaces in spite of the importance of solid/electrolyte interfaces. This is because of the difficulty in preparing Li4Ti5O12 samples with accessible flat surfaces suitable for scanning probe microscopy study. To address this, we have successfully prepared a flat Li4Ti5O12 crystal surface by solid state reaction from a rutile TiO2 (111) wafer with LiOH·H2O powder. Out-of-plane X-ray diffraction (XRD) and transmission electron microscopy revealed that a highly oriented and crystallized Li4Ti5O12 (111) film was formed on the TiO2 (111) wafer. Atomic force microscopy observations revealed that an atomically flat Li4Ti5O12 (111) surface was formed on the film with terraces of 200–300nm width and steps of a {111} interplanar height. The formed thin films were also investigated by cyclic voltammetry and galvanostatic experiments, revealing that the films have electrochemical activity as battery electrodes.

Synthesis and Electrochemical Properties of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub>/CuO Anode Material for Li-Ion Batteries

Spinel-type electrode material Li4Ti5O12/CuO was synthesized by a two-step solid state reaction method. Cupric acetate (Cu(Ac)2) was used as raw material mixed into Li4Ti5O12 to coat the surface of Li4Ti5O12 with CuO in order to improve the electrochemical and cycle performances. The samples were characterized by XRD and the grain size analysis was researched by laser particle-size analyzer. The curves of charge/discharge and cycles Li4Ti5O12/CuO were researched. The results showed that the electrochemical properties of the material were improved. Among the three samples investigated, it was found that the Li4Ti5O12/CuO (coating amount was 4wt%) possesses the best electrochemical performance, and the first discharge specific capacity was 224, 173, 165 and 162mAh/g at 0.5C, 1C, 5C and 10C rate, respectively.

Towards understanding the effects of carbon and nitrogen-doped carbon coating on the electrochemical performance of Li4Ti5O12 in lithium ion batteries: a combined experimental and theoretical study

We investigate the effects of carbon coating, with and without nitrogen-dopants, on the electrochemical performance of a promising anode material Li(4)Ti(5)O(12) (LTO) in lithium ion battery applications. The comparative experimental results show that LTO samples coated with nitrogen-doped carbon derived from pyridine and an ionic liquid exhibit significant improvements in rate capability and cycling performance compared with a LTO sample coated by carbon derived from toluene and the pristine LTO sample. For the first time, we construct an atomistic model for the interface between the lithium transition metal oxide and carbon coating layers. Our first-principles calculations based on density functional theory reveal that at this interface there is strong binding between the graphene coating layer and the Ti-terminated LTO surface, which significantly reduces the chemical activity of LTO surfaces and stabilizes the electrode/electrolyte interface, providing a clue to solve the swelling problem for LTO-based batteries. More importantly, electron transfer from the LTO surface to graphene greatly improves the electric conductivity of the interface. Nitrogen-dopants in graphene coatings further increase the interfacial stability and electric conductivity, which is beneficial to the electrochemical performance in energy storage applications.

Research on carbon-coated Li4Ti5O12 material for lithium ion batteries

Carbon-coated Li4Ti5O12 anode materials for the lithium ion battery were synthesized by using sucrose to improve the electrochemical properties of Li4Ti5O12, and the carbon content was then tested. X-ray diffraction (XRD) showed that the coating of carbon does not influence the formation of Li4Ti5O12. Transmission electron microscopy (TEM) and Raman spectroscopy confirmed that carbon content exists on the surface of Li4Ti5O12. Electronic conductivity measurement indicated that the electronic conductivity of the carbon-coated Li4Ti5O12 material was 3.8×10−4 S cm−1, which is higher than that for the primary Li4Ti5O12 material (4.3×10−7 S cm−1). CV results show that carbon-coated Li4Ti5O12 shows a larger diffusion coefficient. Charge and discharge tests show that rate capability and cycle performance were improved because of the carbon coating.