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• A core–shell structure polypyrrole coated Cu/Cu 2 O nanowires was synthesized. • Li-storage performance of Cu 2 O can be enhanced by introduction of Cu metal and Ppy. • The high capacity of 401 mAh g−1 is still delivered at 1 Ag−1 after 500 cycles. • A phase transformation is proved to be the main reasons for capacity increase. A core-shell structure polypyrrole coated Cu/Cu 2 O (Cu/Cu 2 O@Ppy) nanowires was synthesized by a facile hydrothermal method. Benefiting from the nanowire morphology, the confinement effect of Ppy shell and the modification of Cu metal, the Cu/Cu 2 O@Ppy as the anode of lithium ion battery exhibits an increased reversible capacity of 787 mAh g−1 under the current density of 0.1 A g−1 after 250 cycles. In addition, a good long-life rate capacity also can be obtained (401 mAh g−1 at 1 A g−1 after 500 cycles). More to the point, the increased capacity of Cu/Cu 2 O@Ppy nanowires is explained by the analysis of capacity differential curve, ex-situ X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. It was demonstrated that the constant formation of solid electrolyte interface film and the transformation of Cu to Cu 2 O lead to the increased capacity in the initial cycles. Furthermore, a phase transformation of host material from Cu 2 O to CuO is proved to be the main reasons for the subsequent cycles of capacity increase. This in-situ phase transformation of electrode material provides a novel perspective for the increased capacity phenomenon of metal compounds in lithium ion battery. [ABSTRACT FROM AUTHOR]

• Fe 2 O 3 "mulberry" architecture, quantum dots and bulk particles were synthesized. • Dominant pseudocapacitive feature of the assembled render fast ionic storage. • Less SEI on surface enables the assembled to realize high coulombic efficiency. Constructing pseudocapacitive materials to combine the battery-level energy density with the cycle life and power density of supercapacitors is a promising energy storage technique. Nanostructuring can greatly induce extrinsic pseudocapacitance, but excessive solid electrolyte interphase (SEI) as the activity surface increases usually results in a poor coulombic efficiency (CE) of battery. Here, we separately investigate the electrochemical properties of self-assembled Fe 2 O 3 "mulberry" architecture, quantum dots and bulk particles. Employed as an anode of lithium ion battery, the mulberry architecture retains a dominant pseudocapacitance behavior and high electrochemical activity. It delivers an initial capacity of 1383.8 mAh g−1, 22.1% higher than Fe 2 O 3 bulk in similar size, in which the pseudocapacitance contribution up to 80.6% at 0.4 mV s−1. Furthermore, the mulberry architecture decreases the activity surface contacted with electrolyte to enable a limited SEI, achieving a higher coulombic efficiency (initial CE: 80.1%, average CE: 98.9%) well above that of individual quantum dots. This work is expected to inspire the design of novel high-performance anode materials. [ABSTRACT FROM AUTHOR]

Constructing polycrystalline structure is an effective strategy to improve the electrochemical performance of electrode materials. To enhance the electroactivity of anisotropic VO 2 (M), polycrystalline VO 2 (M) with well-dispersed crystalline zones is successfully synthesized by a facile one-step hydrothermal method, and then their electrochemical performances as an anode of lithium-ion batteries are systematically explored. Results show that the synergistic effect of crystalline zones and amorphous matrices in polycrystalline structure can dramatically activate the anisotropic VO 2 (M) electrode, which contributes to increasing the electroactive zones and facilitating the charge transfer kinetics. Compared with single-crystal VO 2 (M), polycrystalline VO 2 (M) shows the significantly enhanced electrochemical performance, delivering a high reversible capacity of 476 mAhg−1 at 100 mAg−1 after 150 cycles, which is far superior to the theoretical capacity and the reported mixture of VO 2 (M) and VO 2 (B). This work opens up new insights for the activation of anisotropic electrode materials. • Polycrystalline VO 2 (M) with well-dispersed crystalline zones is synthesized. • Synergistic effect of crystalline zones and amorphous matrices is revealed. • The activity of anisotropic VO 2 (M) electrode is dramatically improved. • Polycrystalline VO 2 (M) shows capacity of 476 mAhg−1 at 100 mAg−1 after 150 cycles. [ABSTRACT FROM AUTHOR]

As an indispensable part of lithium-ion batteries (LIBs), the quality of solid-electrolyte interphase (SEI) influences directly the electrochemical performance. α-FeOOH with superior theoretical capacities, low cost, and environmental friendliness has been regarded as a promising anode of LIBs. In this work, we found that the hydroxyl groups on the surface of α-FeOOH bond with organic electrolytes that forming an inferior SEI layer contained excessive ROCO 2 Li, finally causing a poor Li+ transport. Thus, we construct a novel heterostructure of spindle-like α-FeOOH nanorods embedded in mulberry-like Fe 2 O 3 sphere on reduced graphene oxide sheets (F@F/C) based on the dissolution-recrystallization mechanism to optimize the composition of SEI layers. The content of ROCO 2 Li is decreased as expected in the SEI of F@F/C electrode, which diminish the ionic transfer impedance in the interface and provide more alternative diffusion pathways. As expected, the heterostructural hybrid achieves an excellent electrode performance with a reversible capacity about 1800 mAh g−1 at 0.2 A g−1 after 300 cycles. Even cycled at a high current density of 1 A g−1, the hybrid also remains 1050 mAh g−1 after 600 cycles with a capacity decay rate of only 0.005% per cycle. • A heterostructure of spindle-like α-FeOOH nanorods embed in mulberry-like Fe 2 O 3 sphere is rationally constructed. • Embedded architecture optimizes the proportion of Li 2 CO 3 and ROCO 2 Li in SEI to diminish ionic transfer impedance. • Embedded architecture provides more alternative diffusion pathways to improve ionic diffusion kinetics significantly. [ABSTRACT FROM AUTHOR]