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Lithium carbonate (Li2CO3), either as a product of a conversion reaction or as an important component of the solid-electrolyte interphase (SEI) layer on the anode of a lithium ion (Li-ion) battery, is known to be chemically inactive in both reducing and oxidizing atmospheres. No sufficient evidence has shown that Li2CO3 can be reduced, let alone recognize its reduction products. Here we clarify that Li2CO3, as a product of a conversion reaction of cobalt carbonate (CoCO3) upon Li insertion, can indeed be further reduced/converted to lithium carbide (Li2C2) and lithium oxide (Li2O), based on spectroscopic and transmission electron microscopic analyses. These findings will have important guidance to designing electrode (materials) with more stable cycling performances, finding ways to convert some inert compounds into useful electrode materials, and search for electrode materials with higher specific capacities, as well as understanding the excess reversible capacity of some electrode reactions.

Perovskite lithium lanthanum titanate (LLTO) was synthesized using sol–gel method. It shows a reversible capacity of 145 mA h g−1 and moderate cycling performance between 0.01 and 2.00 V. Cyclic voltammetry and X-ray diffraction results demonstrate a two-step solid–solution reaction behavior in the voltage range of 0.00–3.00 V upon lithium insertion/extraction. A stable solid electrolyte interphase (SEI) layer is formed on the surface of LLTO after the initial discharge. Carbon coating by chemical vapor deposition improves its cycling performance significantly. Keywords: Lithium lanthanum titanate, Lithium storage mechanism, SEI formation, Carbon coating

The lithium storage mechanism of carbon-coated nano-CeO2 was studied by in situ X-ray diffraction. It is found that the CeO2 stores lithium by a solid solution reaction. Due to the catalytic effect of the nano-CeO2, electrolyte decomposition occurs above 1.10 V during discharge and the solid electrolyte interphase (SEI) layer decomposes below 2.50 V during recharge. These findings help to understand the lithium storage mechanism in nano-CeO2 and demonstrate its potential applications as a room-temperature electro-catalyst. Keywords: CeO2, Lithium storage mechanism, Solid solution reaction, SEI, Catalyst

Highly ordered mesoporous crystalline MoSe2 is synthesized using mesoporous silica SBA-15 as a hard template via a nanocasting strategy. Selenium powder and phosphomolybdic acid (H3PMo12O40) are used as Se and Mo sources, respectively. The obtained products have a highly ordered hexagonal mesostructure and a rod-like particle morphology, analogous to the mother template SBA-15. The UV-vis-NIR spectrum of the material shows a strong light absorption throughout the entire visible wavelength region. The direct bandgap is estimated to be 1.37 eV. The high surface area MoSe2 mesostructure shows remarkable photocatalytic activity for the degradation of rhodamine B, a model organic dye, in aqueous solution under visible light irradiation. In addition, the synthesized mesoporous MoSe2 possess a reversible lithium storage capacity of 630 mAh g1 for at least 35 cycles without any notable decrease. The rate performance of mesoporous MoSe2 is much better than that of analogously synthesized mesoporous MoS2, making it a promising anode for the lithium ion battery.

Transition metal sulfides are regarded as another type of high-performance anode materials following the transition metal oxides for lithium ion batteries. However, the lithium storage mechanisms of these sulfides are complicated. This work is intended to evaluate the electrochemical performances of molybdenum disulfide (MoS 2 ) and find out its lithium storage mechanism at different lithium insertion stages. It is found that although the MoS 2 shows excellent cycling stability in different voltage ranges, its structural transition is irreversible in the initial cycling. In contrast to the traditional beliefs, metallic Mo is found inert and Li 2 S/S is the redox couple in a deeply discharged MoS 2 /Li cell (0.01 V vs. Li/Li + ). The metallic Mo nanoparticles are believed to be responsible for the enhanced cycling stability of the cell and act as the electronically conducting phase in the capacitive energy storage on the interfaces or grain boundaries of Mo/Li 2 S x nanocomposite. In addition, the Mo/Li 2 S nanocomposite can be used as a cathode material for lithium–sulfur batteries.

The most-popular strategy to improve the cycling stability and rate performance of the sulfur electrode in lithium-sulfur (Li-S) batteries is to astrict the sulfur in a conducting medium by using complicated chemical/physical processing. Lithium sulfide (Li(2)S) has been proposed as an alternative electrode material to sulfur. However, for its application, it must meet challenges such as high instability in air together with all of the drawbacks of a sulfur-containing electrode. Herein, we report the feasibility of using Li(2)S, which was obtained by electrochemical conversion of commercial molybdenum disulfide (MoS(2)) into Li(2)S and metallic molybdenium (Mo) at low voltages, as a high-performance active material in Li-S batteries. Metallic Mo prevented the dissolution of lithium polysulfides into the electrolyte and enhanced the conductivity of the sulfide electrode. Therefore, the in situ electrochemically prepared Li(2)S/Mo composite exhibited both high cycling stability and high sulfur utilization.

Ordered mesoporous tungsten-doped MoO(2) was synthesized by a nanocasting method. The Li storage performance of mesoporous MoO(2) is significantly improved by tungsten doping, which exhibits a reversible capacity of 700 mA h g(-1), better cycling and rate performance. This material combines the advantages of the high theoretical capacity of MoO(2) and the better electroactivity of WO(2).