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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]

Development of three-dimensional self-assembled hollow nanoarchitectures combining functional shells and inner voids is an important approach for realizing high-rate and long-life battery electrodes. As a potential high-performance anode for sodium-ion batteries (SIBs), (1 1 0)-bridged nanoblocks self-assembled VS 4 hollow microspheres (PNBH-VS 4) are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure constructs the Na+ conducting channels and e− transfer paths among nano-grains and nanoblocks, and the self-assembled hollow structure presents the double space physical entrapment effect for the excessive volume change of nanoblocks, which synergistically improve the Na+ storage kinetics and structure stability. When employed as an anode for SIBs, PNBH-VS 4 electrode exhibits the superior rate capability and long cycling life, outperforming those of the ever-reported VS 4 -based anode materials. At 0.2, 0.5, 1.0 and 2.0 A g−1, the capacity can reach 629, 564, 428 and 400 mAh g−1 after 250, 200, 350 and 700 cycles, respectively. Even at 5.0 A g−1, the capacity can still stabilize at 309 mAh g−1 after 1000 long cycles. In addition, it is revealed that PNBH-VS 4 electrode undertakes the insertion and conversion reaction in the potential range of 0.50–3.00 and 0.05–0.50 V, respectively, where the main capacity contribution originates from the insertion reaction. Meanwhile, PNBH-VS 4 electrode exhibits better insertion reversibility at lower current densities and conversion reversibility at higher current densities during cycling, respectively. [ABSTRACT FROM AUTHOR]