While T-NbO has been frequently reported to display an exceptionally fast rate of Li-ion storage (similar to a capacitor), the detailed mechanism of the energy storage process is yet to be unraveled. Here we report our findings in probing the nature of the ultrafast Li-ion storage in T-NbO using both experimental and computational approaches. Experimentally, we used in operando Raman spectroscopy performed on a well-designed model cell to systematically characterize the dynamic evolution of vibrational band groups of T-NbO upon insertion and extraction of Li ions during repeated cycling. Theoretically, our model shows that Li ions are located at the loosely packed 4g atomic layers and prefer to form bridging coordination with the oxygens in the densely packed 4h atomic layers. The atomic arrangement of T-NbO determines the unique Li-ion diffusion path topologies, which allow direct Li-ion transport between bridging sites with very low steric hindrance. The proposed model was validated by computational and experimental vibrational analyses. A comprehensive comparison between T-NbO and other important intercalation-type Li-ion battery materials reveals the key structural features that lead to the exceptionally fast kinetics of T-NbO and the cruciality of atomic arrangements for designing a new generation of Li-ion conduction and storage materials.

In this study, the reaction mechanism and electrochemical properties of carbon-supported PtSn nanomaterials including nanoparticles and nanowires (NWs) toward the oxygen reduction reaction (ORR) have been investigated computationally and experimentally.

In this study, we have investigated the oxygen reduction reaction (ORR) activity and durability on Co-based alloys mechanistically. CoPt/C catalysts with Pt loading of 7 wt % and Au modification have been prepared and shown excellent ORR performance. The various as-prepared CoPt/C and CoPtAu/C catalysts have about 2.6-9.2 times higher mass activity than commercial Pt/C. The mechanistic insight investigated by density functional theory calculations has found that the enhanced activity is attributable to that Co-based catalysts can easily dissociate surface O2* without the high-barrier protonation step and efficiently remove the dissociated O*. The improved stability, 1000 th decay = 14.6%, corresponds to that the core Au can resist the shrinkage of surface Pt during accelerated durability test.Au in the inner core of CoPt/C can effectively stabilize its structure during the stability test of oxygen reduction reaction.

Inadequate capacity and poor durability of MnO 2 based pseudocapacitive electrodes have long been stumbling blocks in the way of their commercial use. Though layered δ-MnO 2 has higher potential to be used due to its proton-free energy storage reactions, its durability is still far away from carbon based electrodes associated with structure deformation caused by interlayer spacing change and Jahn−Teller effect. Here we report an effective approach to dramatically enhance not only the stability but also the capacity of δ-MnO 2 based electrode through a simple incorporation of exotic cations, hydrated Zn 2+ , in the tunnel of the material. Even at a very fast charge/discharge rate (50 A g −1 ), the capacity of the electrode is gradually increased from 268 to 348 F g −1 after ∼3,000 cycles and then remains relatively constant in the subsequent ∼17,000 cycles, which means ∼128% of the initial capacity is maintained after 20,000 cycles. In contrast, the capacity of bare δ-MnO 2 electrode without modification is degraded gradually along the cycling, retaining only ∼74% of the initial value after 20,000 cycles. To reveal the basic chemistry between them, synchrotron X-ray diffraction and Raman spectroscopy were performed to explore the structural evolution of the modified δ-MnO 2 during cycling; DFT computation was used to estimate the energetics and vibration modes associated with the hydrated Zn 2+ . The performance enhancement is attributed largely to the preaccommodation of [Zn (H 2 O) n ] 2+ , which effectively suppresses the interlayer spacing change during cycling and thus benefits the stability. KEYWORDS: pseudocapacitor, layered δ-MnO 2 /Na 0.55 Mn 2 O 4 , tunnel structure modification/preaccommodation of exotic ions, in situ Raman, DFT computation