Recent Progress of Conductive Metal-Organic Frameworks for Electrochemical Energy Storage

The development of reliable and low-cost energy storage systems is of considerable value in using renewable and clean energy sources,and exploring advanced electrodes with high reversible capacity,excellent rate performance,and long cycling life for Li/Na/Zn-ion batteries and supercapacitors is the key problem.Particularly because of their diverse structure,high specific surface area,and adjustable redox activity,electrically conductive metal-organic frameworks(c-MOFs)are considered promising candidates for these electrochemical applications,and a detailed overview of the recent progress of c-MOFs for electrochemical energy storage and their intrinsic energy storage mechanism helps realize a comprehensive and systematic understanding of this progress and further achieve highly efficient energy storage and conversion.Herein,the chemical structure of c-MOFs and their conductive mechanism are first introduced.Subsequently,a comprehensive summarization of the current applications of c-MOFs in energy storage systems,namely supercapacitors,LIBs,SIBs,and ZIBs,is presented.Finally,the prospects and challenges of c-MOFs toward much higher-performance energy storage devices are presented,which should illuminate the future scientific research and practical applications of c-MOFs in energy storage fields.

Dual-modification of manganese oxide by heterostructure and cation pre-intercalation for high-rate and stable zinc-ion storage

Zinc-ion batteries(ZIBs)possess great advantages in terms of high safety and low cost,and are regarded as promising alternatives to lithium-ion batteries(LIBs).However,limited by the electrochemical kinetics and structural stability of the typical cathode materials,it is still difficult to simultaneously achieve high rates and high cycling stability for ZIBs.Herein,we present a manganese oxide(Sn_(x)Mn O_(2)/Sn O_(2))material that is dual-modified by Sn O_(2)/Mn O_(2)heterostructures and pre-intercalated Sn;cations as the cathode material for ZIBs.Such modification provides sufficient hetero-interfaces and expanded interlayer spacing in the material,which greatly facilitates the insertion/extraction of Zn^(2+).Meanwhile,the“structural pillars”of Sn^(4+) cations and the“pinning effect”of SnO_(2)also structurally stabilizes the Mn O_(2)species during the repeated Zn^(2+) insertion/extraction,leading to ultra-high cycling stability.Due to these merits,the Sn_(x)MnO_(2)/SnO_(2)cathode exhibits a high reversible capacity of 316.1 m Ah g^(-1) at 0.3 A g^(-1),superior rate capability of 179.4 m Ah g^(-1) at 2 A g^(-1),and 92.4%capacity retention after 2000 cycles.Consequently,this work would provide a promising yet efficient strategy by combining heterostructures and cations preintercalation to obtain high-performance cathodes for ZIBs.

High-capacity,high-rate,and dendrite-free lithium metal anodes based on a 3D mixed electronic-ionic conductive and lithiophilic scaffold

Lithium metal anode possesses a high theoretical capacity and the lowest redox potential,while the severe growth of Li dendrite prevents its practical application.Herein,we prepared a structure of Li_(3)P nanosheets and Ni nanoparticles decorated on Ni foam(NF)as a three-dimensional(3 D)scaffold for dendrite-free Li metal anodes(Li-Li_(3)P/Ni@Ni foam anodes,shortened as L-LPNNF)using a facile melting method.The LiP nanosheets exhibit excellent Li-ion conductivity as well as superior lithiophilicity,and the 3 D nickel scaffold provides sufficient electron conductivity and ensures structure stability.Therefore,symmetric cells assembled by L-LPNNF possess lowered voltage hysteresis and improved long cycle stability(a voltage hysteresis of 104.2 mV after 500 cycles at a high current density of 20 mA cm^(-2) with a high capacity of 10 mA h cm^(-2)),compared with the cells assembled with Li foil or Li-NF anodes.Furthermore,the full cells with paired L-LPNNF anodes and commercial LiFePOcathodes suggest a specific capacity of 124.6 mA h gand capacity retention of 90.8%after 180 cycles with the Coulombic efficiency(CE)of~100%at a current rate of 1 C.This work provides a potentially scalable option for preparing a mixed electronic-ionic conductive and lithiophilic scaffold for dendrite-free Li anodes at high current densities.