Dynamic Octahedral Breathing in Oxygen-Deficient Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) Perovskite Performing as a Cathode in Intermediate-Temperature SOFC.

Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) outperforms as a cathode in solid-oxide fuel cells (SOFC), at temperatures as low as 700-750 °C. The microscopical reason for this performance was investigated by temperature-dependent neutron powder diffraction (NPD) experiments. In the temperature range of 25-800 °C, Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) shows a perfectly cubic structure (a = a0), with a significant oxygen deficiency in a single oxygen site, that substantially increases at the working temperatures of a SOFC. The anisotropic thermal motion of oxygen atoms considerably rises with T, reaching B(eq) ≈ 5 Å(2) at 800 °C, with prolate cigar-shaped, anisotropic vibration ellipsoids that suggest a dynamic breathing of the octahedra as oxygen ions diffuse across the structure by a vacancies mechanism, thus implying a significant ionic mobility that could be described as a molten oxygen sublattice. The test cell with a La(0.8)Sr(0.2)Ga(0.83)Mg(0.17)O(3-δ) electrolyte (∼300 µm in thickness)-supported configuration yields a peak power density of 0.20 and 0.40 W cm(-2) at temperatures of 700 and 750 °C, respectively, with pure H2 as fuel and ambient air as oxidant. The electrochemical impedance spectra (EIS) evolution with time of the symmetric cathode fuel cell measured at 750 °C shows that the Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) cathode possesses a superior ORR catalytic activity and long-term stability. The mixed electronic-ionic conduction properties of Ba(0.9)Co(0.7)Fe(0.2)Nb(0.1)O(3-δ) account for its good performance as an oxygen-reduction catalyst.

Band engineering enhances the electrochemical properties by constructing TiO2 NRs-MoS2 NSFs flexible electrode.

Research and development of flexible electrodes with high performance are crucial to largely determine the performance of flexible lithium-ion batteries (FLIBs) to a large extent. In this work, a flexible anode (TiO2 NRs-MoS2 NSFs/CC) is rationally designed and successfully constructed, in which TiO2 nanorods arrays (NRs) vertically grown on CC as a supporting backbone for MoS2 nanosheets flowers (NSFs) to form a TiO2 NRs-MoS2 NSFs heterostructure. The backbone can not only serve as a mechanical support MoS2 and improve its electronic conductivity, but also limit the dissolution of polysulfides issue during cycling. The density functional theory (DFT) analysis manifests that the obvious interaction between O and S at the interface for the TiO2 NRs-MoS2 NSFs heterostructure changes the electronic structure and reduces the band gap of TiO2 NRs-MoS2 NSFs. The small band gap and high electron state at the Fermi level are both beneficial to the transport of electrons, enhancing the kinetics, and giving the long cycling stability at high density and excellent rate capacity. Furthermore, the assembled TiO2 NRs-MoS2 NSFs/CC//NCM622 full cell delivers superior rate capacity and good cycling stability. Meanwhile, the soft-packed cell shows good mechanical flexibility, which can be lighted up successfully and keep brightness when folding with different angles. This result illustrates that it is a highly potential strategy for constructing flexible electrodes with the controlled electronic structure through band engineering to not only improve the electrochemical performance, but also possibly meet the requirements of high-performance FLIBs.

Zinc Single-Atom-Regulated Hard Carbons for High-Rate and Low-Temperature Sodium-Ion Batteries.

Hard carbons, as one of the most commercializable anode materials for sodium-ion batteries (SIBs), have to deal with the trade-off between the rate capability and specific capacity or initial Columbic efficiency (ICE), and the fast performance decline at low temperature (LT) remains poorly understood. Here, a comprehensive regulation on the interfacial/bulk electrochemistry of hard carbons through atomic Zn doping is reported, which demonstrates a record-high reversible capacity (546 mAh g-1 ), decent ICE (84%), remarkable rate capability (140 mAh g-1 @ 50 A g-1 ), and excellent LT capacity (443 mAh g-1 @ -40 °C), outperforming the state-of-the-art literature. This work reveals that the Zn doping can generally induce a local electric field to enable fast bulk Na+ transportation, and meanwhile catalyze the decomposition of NaPF6 to form a robust inorganic-rich solid-electrolyte interphase, which elaborates the underlying origin of the boosted electrochemical performance. Importantly, distinguished from room temperature, the intrinsic Na+ migration/desolvation ability of the electrolyte is disclosed to be the crucial rate-determining factors for the SIB performance at LT. This work provides a fundamental understanding on the charge-storage kinetics at varied temperatures.

Electronic synergy to boost the performance of NiCoP-NWs@FeCoP-NSs anodes for flexible lithium-ion batteries.

Research and development of flexible lithium-ion batteries (LIBs) with high energy density and long cycle life for portable and wearable electronic devices has been a cutting-edge effort in recent years. In this paper, a novel flexible self-standing anode for LIBs is fabricated successfully, in which NiCoP nanowires (NWs) coated with FeCoP nanosheets (NSs) to form core-shell heterostructure arrays are grown on carbon cloth (CC) (designated as NiCoP-NWs@FeCoP-NSs/CC). The obtained NiCoP-NWs@FeCoP-NSs/CC anode integrates the merits of the one-dimensional (1D) NiCoP-NW core and two-dimensional (2D) FeCoP-NS shell and the CC to show a high lithium-ion storage capacity with long-term cycling stability (1172.6 mA h g-1 at 1 A g-1 up to 300 cycles with a capacity retention of 92.6%). The kinetics studies demonstrate that the pseudocapacitive behavior dominates the fast lithium storage of this anode material. For fundamental mechanistic understanding, density functional theory (DFT) analysis is carried out, and manifests that electronic synergy can boost the superior performance of the NiCoP-NWs@FeCoP-NSs/CC anode. The assembled LiFePO4//NiCoP-NWs@FeCoP-NSs/CC full battery gives a discharge capacity of 469.9 mA h g-1 at 0.5 A g-1 after 500 cycles, and even at 2 A g-1, it still can retain 581.5 mA h g-1. Besides, the soft pack full battery can keep the LED lit continuously when it is folded at different angles and maintain brightness for a period of time, highlighting the large application potential of this flexible LIB for wearable electronic devices. This work provides an idea for the design and construction of advanced metal phosphide flexible electrodes for LIBs.

Carbon-Decorated Na3V2(PO4)3 as Ultralong Lifespan Cathodes for High-Energy-Density Symmetric Sodium-Ion Batteries.

In this work, several carbon-decorated Na3V2(PO4)3 materials (NVP@C-750/800/850) are successfully fabricated using a sol-gel approach and subsequent heat treatment. When NVP@C-800 is used as a cathode, it shows an ultralong cycle life (2000 cycles) at a high rate of 10C, which is superior to the other two electrodes and those of reported NVP@C cathodes in the literature. The excellent results of NVP@C-800 are attributed to its nanostructure and the well-defined conductive carbon layer. The symmetric sodium (Na)-ion battery (SIB) with NVP@C-800 as both a cathode and an anode shows a high capacity at 40 mA g-1 with a voltage plateau of about 1.79 V and energy density of 113 W h kg-1, revealing that NVP@C is of great application prospect.

Rational Design and in-situ Synthesis of Ultra-Thin ß-Ni(OH)2 Nanoplates for High Performance All-Solid-State Flexible Supercapacitors.

The all-solid-state flexible supercapacitor (AFSC), one of the most flourishing energy storage devices for portable and wearable electronics, attracts substantial attentions due to their high flexibility, compact size, improved safety, and environmental friendliness. Nevertheless, the current AFSCs usually show low energy density, which extremely hinders their practical applications. Herein, ultra-thin ß-Ni(OH)2 nanoplates with thickness of 2.4 ± 0.2 nm are in-situ grown uniformly on Ni foam by one step hydrothermal treatment. Thanks to the ultra-thin nanostructure, ß-Ni(OH)2 nanoplates shows a specific capacitance of 1,452 F g-1 at the scan rate of 3 mV s-1. In addition, the assembled asymmetric AFSC [Ni(OH)2//Activated carbon] shows a specific capacitance of 198 F g-1. It is worth noting that the energy density of the AFSC can reach 62 Wh kg-1 while keeping a high power density of 1.5 kW kg-1. Furthermore, the fabricated AFSCs exhibit satisfied fatigue behavior and excellent flexibility, and about 82 and 86% of the capacities were retained after 5,000 cycles and folding over 1,500 times, respectively. Two AFSC in series connection can drive the electronic watch and to run stably for 10 min under the bending conditions, showing a great potential for powering portable and wearable electronic devices.

V2O5 Nanowire Composite Paper as a High-Performance Lithium-Ion Battery Cathode.

Ultralong, as long as ∼1 mm, orthorhombic vanadium pentoxide (V2O5) nanowires were synthesized using a hydrothermal method. Free-standing and binder-free composite paper was prepared on a large scale by a two-step reduction method using free-standing V2O5 nanowires as the skeleton and reduced graphene oxide (rGO) nanosheets as the additive. Such a free-standing V2O5/rGO composite paper as a cathode for lithium ion batteries possesses both structural integrity and extraordinary electrochemical performance. The reversible specific areal capacity of the V2O5/rGO composite paper electrode is 885 µAh/cm2 at 0.09 mA/cm2, much higher than that of the pure V2O5 nanowire paper electrode (570 µAh/cm2). It also shows excellent cycling performance at high rates with 30.9% loss of its initial capacities after 1000 cycles at a current rate of 0.9 mA/cm2. The excellent performance was attributed to the improved electronic conductivity and Li+ ion transport from the rGO addition.