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Two kinds of reduced graphene oxide are successfully synthesized by hydrothermal reduction and ascorbic acid reduction and further employed as high-performance electrode material for supercapacitors. These two kinds of reduced graphene oxide exhibit excellent properties as they possess large specific surface and highly reduced state. The structure, morphology, vibrational response, and thermal stability are performed using XRD, SEM, TEM, Raman spectroscopy, and thermo-gravimetric analysis, respectively. While the specific surface area and pore size are carried out via BET surface area technique, the capacitive behaviors of electrode materials are investigated in a three-electrode system at room temperature. The hydrothermal reduced graphene oxide (HT RGO) electrode delivers high specific capacitance of 341 F g−1 at a current density of 1 A g−1 and exhibits excellent cycling stability with 91.58% retention ratio after 5000 cycles, much better than that of ascorbic acid-reduced graphene oxide (AA RGO). This can primarily be ascribed to the larger specific surface area and higher degree of reduction of HT RGO. This work underlines the potential of green approaches to prepare reduced graphene oxide electrode material for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

To improve the stability and performance of the cathode materials, an ionic conductor layer was coated successfully on the surface of Li1.2Mn0.54Ni0.13Co0.13O2 (LMNC) microspheres. The structural analysis confirmed that LiV3O8 coating did not change the basic structure of LMNC, and all obtained materials are solid solutions with a good-layered structure and a good crystallinity. The microscopy measurement showed that the thickness of the coating layer for the LV-3 sample is about 2.5 nm. This appropriate layer is helpful for improving the surface stability of LMNC and the diffusion of lithium, leading to an obvious enhancement of the electrochemical performance. Our result confirmed that the average discharge specific capacities for LV-3 sample at 0.1 C, 0.2 C, 0.5 C, 1 C, and 3 C are respectively 265.9, 219.1, 188.0, 156.3, and 121.5 mAh g−1, which are much larger than the values of other samples. After 50 cycles at a 1 C rate, the capacity retentions for different samples are 60.7%, 74.0%, 87.6%, and 70.4%, indicating that LV-3 sample exhibits the best performance. Furthermore, EIS measurements showed that the diffusion coefficient for LV-3 sample is calculated to be 1.26 × 10−15 cm2 s−1, which is also the largest value among all considered samples. Our experiments identified that coating an ionic conductive layer on the cathode material surface will significantly improve their rate capacity and cycling stability. [ABSTRACT FROM AUTHOR]

Rechargeable lithium-ion batteries (LIBs) are considered as one of the most promising power sources for energy storage system for a wide variety of applications such as personal electronic devices and large-format storage devices. The anode material usually plays a key role in the determination of the safety and cycling stability of LIBs. Among all anode materials, lithium zinc titanate (Li2ZnTi3O8) has been considered as one the most promising anode candidates because it has high theoretical capacity (227 mAh g−1), low working plateau, and excellent thermal and structure stability. However, Li2ZnTi3O8-based batteries always suffer from severe capacity deterioration due to the poor conductivity. Hence, it is necessary to systematically and comprehensively summarize the progress in understanding and modifying Li2ZnTi3O8 anode from various aspects. In this review, we present a general overview of the structural features and the electrochemical behavior of Li2ZnTi3O8. We then offer a comprehensive review of the recent advancements of the breakthroughs in the past decade in the synthesis, doping, and surface coating of Li2ZnTi3O8. At last, we highlight the critical challenges facing us today and future perspectives for further development of Li2ZnTi3O8-based anodes. [ABSTRACT FROM AUTHOR]

The thermodynamic stability is a very important quantity for the electrode materials, because it is not only related to the electrochemical performances of the materials but also the safety issue of the cells. To evaluate the thermodynamic stability of LiNiMnO ( x = 0, 1), the formation enthalpies from elemental phases and oxides were obtained. The values for LiNiMnO were calculated to be −1341.10 and −141.84 kJ mol, while those for NiMnO were −949.11 and −49.21 kJ mol. These values are much more negative than those of LiCoO and LiNiO compounds, indicating that the thermodynamic stability of LiNiMnO is better than the two classic compounds. To clarify the microscopic origin, the density of states, magnetic moments, and bond orders were systematically investigated. The results showed that the excellent thermodynamic stability of LiNiMnO is attributed to the absence of Jahn-Teller distortions, strong electrostatic interactions of Li-O ionic bond, and strong Ni-O/Mn-O ionic-covalent mixing bonds. After lithium extraction, the disappearance of the pure Li-O bonds leads to an increase of formation enthalpy, indicating a decreasing thermodynamic stability for NiMnO with respect to LiNiMnO. [ABSTRACT FROM AUTHOR]

LiMnNiO is synthesized by a sol-gel method and the intercalation kinetics as positive electrode for lithium-ion batteries is investigated by EIS. LiMnNiO particles prepared via sol-gel process possess spinel phase with Fd-3m space group. The charge-transfer resistance, the exchange-current density and the solid-phase diffusion are found as a function of temperature. The apparent activation energy of the exchange current, the charge transfer, and the lithium diffusion in solid phase are also determined, respectively. This result indicates that the effect of the temperature on the cell capacity and the current dependence of the capacity results mainly from the enhancement of the lithium diffusion at elevated temperatures. It can be concluded that LiMnNiO cell has a bad rate cycling performance at elevated temperatures before any modification due to the high diffusion apparent activation energy. The relevant theoretical elucidations thus provide us some useful insights into the design of novel LiMnNiO-based positive-electrode materials. [ABSTRACT FROM AUTHOR]

LiMn2O4 (LMO) is a very attractive choice as cathode material for power lithium-ion batteries due to its economical and environmental advantages. However, LiMn2O4 in the 4-V region suffers from a poor cycling behavior. Recent research results confirm that modification by coating is an important method to achieve improved electrochemical performance of LMO, and the latest progress was reviewed in the paper. The surface treatment of LMO by coating oxides and nonoxide systems could decrease the surface area to retard the side reactions between the electrode and electrolyte and to further diminish the Mn dissolution during cycling test. At present, LiMn2O4 is the mainstreaming cathode material of power lithium-ion battery, and, especially the modified LMO, is the trend of development of power lithium-ion battery cathode material in the long term. [ABSTRACT FROM AUTHOR]

LiAl x Mn2 − x O4 and LiAl0.05Mn1.95O4 − y F y spinel have been successfully synthesized by citric acid-assisted sol–gel method. The structure and physicochemical properties of this as-prepared powder were investigated by electronic conductivity test, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test in detail. The electronic conductivity decreases with increasing of the content of doped Al. XRD patterns show that the diffraction of LiAl0.05Mn1.95O4 − y F y samples is similar, with all the peaks indexable in the Fd3 m space group, and a little impurity appears in the LiAl0.05Mn1.95O3.8F0.2 sample. SEM reveals that all LiAl0.05Mn1.95O4 − y F y powders have the uniform, nearly cubic structure morphology with narrow size distribution which is less than 500 nm. Galvanostatic charge–discharge test indicates that LiAl0.05Mn1.95O4 has the highest discharge capacity and electrochemical performance among all LiAl x Mn2 − x O4 samples after 50 cycles, and the initial discharge capacity of LiAl0.05Mn1.95O4 − y F y ( y = 0, 0.02, 0.05, 0.1) is 123.9, 124.6, 124.9, and 125.0 mAh g−1, respectively, and their capacity retention ratios are 94.2%, 94.9%, 91.7%, and 89.9% after 50 cycles, respectively. EIS indicates that LiAl0.05Mn1.95O3.98F0.02 have smaller charge transfer resistance than that of LiAl0.05Mn1.95O4 corresponding to the extraction of Li+ ions. [ABSTRACT FROM AUTHOR]