SiO 2 is one of the most abundant materials on Earth. It is costeffective and also environmentally benign when used as an energy material. Although SiO 2 was inactive to Li, it was engineered to react directly by a simple process. It exhibited a strong potential as a promising anode for Li-ion batteries.

Nanosized Sn 4 P 3 with a layered structure was synthesized by a mechanochemical method, and electrochemical and local structural characteristics of tin phosphide during charge/discharge were studied for its use as an anode material for lithium secondary batteries. As the amount of lithium insertion increased, tin phosphide was converted into lithium phosphides followed by lithiumtin alloy formation, which was confirmed by differential capacity plots and X-ray absorption spectroscopic ͑XAS͒ analysis. Based on X-ray diffraction, XAS, and electrochemical data, a three-step reaction mechanism of Sn 4 P 3 with lithium was suggested. Tin phosphide showed a good cyclability and retained a fairly large capacity of 370 mAh/g up to 50 cycles when cycled within a limited voltage window.

Re-deposition of manganese compounds on LiMn 2 O 4 electrode after Mn dissolution and its impact on the positive electrode performances are studied by a control experiment, in which the spinel electrode is stored in its charged state at elevated temperature (60 • C) to accelerate Mn dissolution. Upon storage with Li foil, the re-deposition of manganese species is marginal since the dissolved Mn 2+ ions move to the Li foil to be deposited. When stored without Li foil, however, under which the chance for re-deposition of Mn species on the spinel electrode is rather high, the dissolved Mn 2+ ions are deposited as oxide and fluoride. The depth-profiling X-ray photoelectron spectroscopy and transmission electron microscope studies illustrate that Mn-O species are deposited in the earlier period of storage, whereas the Mn-F compounds (MnF 2 ) in the later stage. Due to the deposition of highly resistive MnF 2 phase, the electrode stored for a longer period of time shows a severe cell polarization and capacity loss.Since the reversible lithium intercalation/de-intercalation was reported with the lithium manganese oxide (LiMn 2 O 4, LMO hereafter) in the mid-1980s, this spinel-structured material has been extensively studied as the positive electrode for lithium-ion batteries (LIBs). At present, the LIBs adopting this 4 V positive electrode are widely used as the power source for small electronic devices, and their consumer market seems to be expanded in the near future for electric vehicles (EVs) since this material satisfies the most-demanding requirements for EVs applications; cost, high power and safety characteristics. [1][2][3][4][5][6][7] The high power performance stems from its three-dimensional Li + diffusion channels, whereas the better safety characteristics from its superior thermal stability. That is, LMO is considered as a safer positive electrode as the onset temperature for oxygen release at its charged state is higher than that for the other positive electrode materials. 8 One critical shortcoming for this material is, however, the poor cycle stability that is mainly associated with Mn dissolution during extended cycling. 9 The Mn dissolution has been considered as the most crucial aging mechanism for LMO. Obviously, the Mn dissolution leads to a loss of active material itself from the electrode layer. Many complicated aging mechanisms are also induced by Mn dissolution; an increase in cell polarization, unwanted structural and phase changes, and formation of surface films on negative and positive electrodes. 10-18 Mn dissolution is known to degrade the negative electrode when the graphitic carbons are assembled with LMO positive electrode. Dissolved manganese ions move to the negative electrode to be deposited in the metallic state, which is accompanied by the self-discharge of lithiated graphite. The metallic Mn, which is incorporated into the solid electrolyte interphase (SEI) layer on the negative electrode, is known to induce additional electrolyte decomposition. [19][20][21] It is also known that ...

In this study we embed phase pure natural cubic-FeS 2 (pyrite) in a stabilized polyacrylonitrile (PAN) matrix. The PAN matrix confi nes FeS 2 's electroactive species (Fe 0 and S n 2− ) for good reversibility and effi ciency. Additionally, the stabilized PAN matrix can accommodate the 160% volume expansion of FeS 2 upon full discharge because it is not fully carbonized. At room temperature, our PAN-FeS 2 electrode delivers a specifi c capacity of 470 mAh g −1 on its 50th discharge. Using high-resolution transmission electron microscopy (HRTEM) we confi rm that FeS 2 particles are embedded in the PAN matrix and that FeS 2 's mobile electroactive species are confi ned during cycling. We also observe the formation of orthorhombic-FeS 2 at full charge, which validates the results of our previous all-solid-state FeS 2 battery study.The energy density of conventional Li-ion batteries with LiMO 2 (M = transition metal) cathodes and graphitic anodes is approaching a practical upper limit after two decades of optimization. In order to improve the energy density of Li-ion batteries further, new cathodes must be developed with capacities that compare to those of advanced anodes such as Si. [ 1 ] The FeS 2 conversion chemistry is a promising candidate to replace the LiMO 2 intercalation chemistry because FeS 2 is inexpensive, energy dense, and environmentally benign. The four electron reduction of cubic-FeS 2 (pyrite) with lithium (FeS 2 + 4Li + + 4e −

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