Cu-N Synergism Regulation to Enhance Anionic Redox Reversibility and Activity of Li- and Mn-Rich Layered Oxides Cathode.

Anionic redox chemistry enables extraordinary capacity for Li- and Mn-rich layered oxides (LMROs) cathodes. Unfortunately, irreversible surface oxygen evolution evokes the pernicious phase transition, structural deterioration, and severe electrode-electrolyte interface side reaction with element dissolution, resulting in fast capacity and voltage fading of LMROs during cycling and hindering its commercialization. Herein, a redox couple strategy is proposed by utilizing copper phthalocyanine (CuPc) to address the irreversibility of anionic redox. The Cu-N synergistic effect of CuPc could not only inhibit surface oxygen evolution by reducing the peroxide ion O2 2- back to lattice oxygen O2-, but also enhance the reaction activity and reversibility of anionic redox in bulk to achieve a higher capacity and cycling stability. Moreover, the CuPc strategy suppresses the interface side reaction and induces the forming of a uniform and robust LiF-rich cathode electrolyte, interphase (CEI) to significantly eliminate transition metal dissolution. As a result, the CuPc-enhanced LMRO cathode shows superb cycling performance with a capacity retention of 95.0% after 500 long-term cycles. This study sheds light on the great effect of N-based redox couple to regulate anionic redox behavior and promote the development of high energy density and high stability LMROs cathode.

Rechargeable Aqueous Zinc-Halogen Batteries: Fundamental Mechanisms, Research Issues, and Future Perspectives.

Aqueous zinc-halogen batteries (AZHBs) have emerged as promising candidates for energy storage applications due to their high security features and low cost. However, several challenges including natural subliming, sluggish reaction kinetics, and shuttle effect of halogens, as well as dendrite growth of the zinc (Zn) anode, have hindered their large-scale commercialization. In this review, first the fundamental mechanisms and scientific issues associated with AZHBs are summarized. Then the research issues and progresses related to the cathode, separator, anode, and electrolyte are discussed. Additionally, emerging research opportunities in this field is explored. Finally, ideas and prospects for the future development of AZHBs are presented. The objective of this review is to stimulate further exploration, foster the advancement of AZHBs, and contribute to the diversified development of electrochemical energy storage.

Ultrahigh-energy sodium ion capacitors enabled by the enhanced intercalation pseudocapacitance of self-standing Ti2Nb2O9/CNF anodes.

In order to increase the capacity and improve the sluggish Na+-reaction kinetics of anodes as sodium ion capacitors (SICs), a Ti2Nb2O9/CNF self-standing film electrode comprised of Ti2Nb2O9 nanosheets and carbon nanofibers has been fabricated via electrospinning HTiNbO5 nanosheets with PAN and subsequent carbonization treatment. The as-prepared Ti2Nb2O9/CNF film electrode possesses fast Na-ion intercalation kinetics and high conductivity during Na-ion storage, and it displays a high reversible capacity of 324 mA h g-1 at 0.1 A g-1. Additionally, it also delivers a superior rate capability of 204 mA h g-1 at a high current density of 4 A g-1, as well as an excellent cycling stability of 97% retention after 2000 cycles at 1 A g-1 in a half-cell test. A prototype Ti2Nb2O9/CNF//AC SIC full device was assembled by employing the presodiated Ti2Nb2O9/CNF anode and AC cathode, and it exhibits an high energy density of 129 W h kg-1 at a power density of 75 W kg-1 and a high power density (7560 W kg-1 with 63 W h kg-1), a good cycling performance of 85% capacitance retention after 10 000 cycles at 1 A g-1, suggesting that the Ti2Nb2O9/CNF electrode with excellent performance would be a very promising candidate as the anode for high-performance SICs.

Ultra-Large Sized Siloxene Nanosheets as Bifunctional Photocatalyst for a Li-O2 Battery with Superior Round-Trip Efficiency and Extra-Long Durability.

Developing new optimized bifunctional photocatalyst is of great significant for achieving the high-performance photo-assisted Li-O2 batteries. Herein, a novel bifunctional photo-assisted Li-O2 system is constructed by using siloxene nanosheets with ultra-large size and few-layers due to its superior light harvesting, semiconductor characteristic, and low recombination rate. An ultra-low charge potential of 1.90 V and ultra-high discharge of 3.51 V have been obtained due to the introduction of this bifunctional photocatalyst into Li-O2 batteries, and these results have realized the round-trip efficiency up to 185 %. In addition, this photo-assisted Li-O2 batteries exhibits a high rate (129 % round-trip efficiency at 1 mA cm-2 ), a prolonged cycling life with 92 % efficiency retention after 100 cycles, and the highly reversible capacity of 1170 mAh g-1 at 0.75 mA cm-2 . This work will open the vigorous opportunity for high-efficiency utilization of solar energy into electric system.

Electrospun Nb2O5 nanorods/microporous multichannel carbon nanofiber film anode for Na+ ion capacitors with good performance.

For the disadvantages of both the slow reaction kinetics and the poor conductivity for Nb2O5 electrode materials as sodium-ion capacitors (SICs), Nb2O5 NRs/NMMCNF film electrode with good flexibility and high electrochemical property has been fabricated by electrospinning PAN/PMMA/H2Nb2O6·H2O homogeneous viscous suspension and followed by an annealing treatment, in which the precursor H2Nb2O6·H2O nanorods are obtained by grinding H2Nb2O6·H2O nanowires, and Nb2O5 nanorods are uniformly embedded in nitrogen doped microporous multichannel carbon nanofiber. Benefiting from the multichannel network structure, Nb2O5 NRs/NMMCNF film electrode delivers the fast kinetics of Na+-storage and the superior Na-ion storage performance, it delivers outstanding rate capability (101 mAh g-1 at 4 A g-1) and ultralong lifespan (91% capacity retention after 10,000 cycles at 2 A g-1). A Nb2O5 NRs/NMMCNF//AC SIC based on the Nb2O5 NRs@NMMCNF fiber film anode and the AC cathode is assembled. The energy density of the as-assembled device is as high as 91 Wh kg-1 and its maximum power density is 7499 W kg-1. This work offers a new structure design strategy toward intercalation-type metal oxide electrodes for application in SICs.

Few-layer and large flake size borophene: preparation with solvothermal-assisted liquid phase exfoliation.

The preparation of two-dimensional boron (B) nanosheets, especially for borophene, is still a challenge because of its unique structure and complex B-B bonds in bulk boron. In the present work, a novel preparation technology for borophene with only a few layers and large flake sizes is developed by a solvothermal-assisted liquid phase exfoliation process, consisting of ball milling-thinning, solvothermal swelling, and probe ultrasonic delamination. The exfoliation effect of the bulk B precursors is related to the surface tension and Hildebrand parameter of the selected solvents such as acetone, N,N-dimethyl formamide (DMF), acetonitrile, ethanol, and N-methyl pyrrolidone (NMP), and a relative small surface tension when using solvents is favorable for the exfoliation of bulk B. Four-layer thick borophene and an average lateral size of 5.05 µm can be obtained in acetone as the exfoliating solvent. The surface composition of the exfoliated few-layer borophene with large flake size hardly changes, while the chemical state of B changes to some extent because they are partly oxidized on the surface by contaminates before and after exfoliation. This acetone solvothermal-assisted liquid phase exfoliation technique can be used to prepare high quality borophene with large horizontal sizes, and it will provide the basis to study few-layer borophene with large sizes further.

Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density.

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb2O5 nanoparticles/N-doped graphene hybrid anode (T-Nb2O5/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl5 at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb2O5 nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb2O5/NG were improved by doping nitrogen. The T-Nb2O5/NG anode showed superior rate capability (68 mA h g-1 even at 2 A g-1) and good cycling life (106 mA h g-1 at 0.2 A g-1 for 200 cycles and 83 mA h g-1 at 1 A g-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb2O5/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg-1 at a power density of 100 W kg-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g-1) and showed a promising application for highly efficient energy storage systems.