A layered multifunctional framework based on polyacrylonitrile and MOF derivatives for stable lithium metal anode

Composite Li metal anodes based on three-dimensional(3D) porous frameworks have been considered as an effective material for achieving stable Li metal batteries with high energy density.However,uneven Li deposition behavior still occurs at the top of 3D frameworks owing to the local accumulation of Li ions.To promote uniform Li deposition without top dendrite growth,herein,a layered multifunctional framework based on oxidation-treated polyacrylonitrile(OPAN) and metal-organic framework(MOF) derivatives was proposed for rationally regulating the distribution of Li ions flux,nucleation sites,and electrical conductivity.Profiting from these merits,the OPAN/carbon nano fiber-MOF(CMOF) composite framework demonstrated a reversible Li plating/stripping behavior for 500 cycles with a stable Coulombic efficiency of around 99.0% at the current density of 2 mA/cm~2.Besides,such a Li composite anode exhibited a superior cycle lifespan of over 1300 h under a low polarized voltage of 18 mV in symmetrical cells.When the Li composite anode was paired with LiFePO_(4)(LFP) cathode,the obtained full cell exhibited a stable cycling over 500 cycles.Moreover,the COMSOL Multiphysics simulation was conducted to reveal the effects on homogeneous Li ions distribution derived from the above-mentioned OPAN/CMOF framework and electrical insulation/conduction design.These electrochemical and simulated results shed light on the difficulties of designing stable and safe Li metal anode via optimizing the 3D frameworks.

锂金属负极的挑战与改善策略研究进展

锂金属由于其高比容量和低电极电势等优点被认为是下一代高比能量电池体系中最有潜力的负极材料。然而由于锂金属的高活性,锂负极在循环过程中会产生大量的枝晶,导致SEI(solid-electrolyte interphase)破裂,并且枝晶增加了电极与电解液的接触面积,使得副反应进一步增加。此外,脱落的枝晶形成死锂,从而降低电池的充放电库仑效率。并且不可控的锂枝晶持续生长会刺穿隔膜引发电池短路,伴随着电池热失控等安全问题。本综述基于锂负极存在的主要挑战,结合理解锂枝晶的成核生长模型等机理总结并深度分析近些年来在液态和固态电解质体系中改善锂金属负极的主要策略及其作用机理,为促进高比能量锂金属电池的应用提供借鉴参考作用。

Research progress on construction and energy storage performance of MXene heterostructures

MXenes are a family of two-dimensional (2D) transition metal carbides, carbonitrides/nitrides with superior physical and chemical properties, which have attracted extensive attention since the discovery in 2011. The impressive electrochemical activity of MXene makes it one of the most potential electrode materials in rechargeable batteries and supercapacitors. However, single-component MXene electrodes are difficult to achieve high specific capacity, efficient ion/electron transport, and high stability compatibility in an electrochemical environment. Studies have shown that it is an effective method to introduce nanomaterials between MXene layers to construct heterostructures and to improve the electrochemical performance through the synergistic effect among the components in the heterostructures. The introduction of nanomaterials can effectively suppress the restacking of MXene nanosheets, shorten the diffusion path of ions and promote the electrolyte transport, which is beneficial to enhance the rate performance of MXene;moreover, the excellent mechanical flexibility of MXene can reduce the volume expansion of nanomaterials during charge/discharge, thereby effectively protecting the integrity of the electrode structure and improving the cycling stability. Therefore, in this review, combined with theoretical calculations, we summarize the recent advances of MXene heterostructures in terms of synthesis strategies and energy storage applications, including supercapacitors, metal-ions batteries (Li, Na, K, Mg, Zn, Al) and metal anode protection. Furthermore, potential challenges and application perspectives for MXene heterostructures are also outlined.

Recent advances based on Mg anodes and their interfacial modulation in Mg batteries

Magnesium(Mg)batteries(MBs),as post-lithium-ion batteries,have received great attention in recent years due to their advantages of high energy density,low cost,and safety insurance.However,the formation of passivation layers on the surface of Mg metal anode and the poor compatibility between Mg metal and conventional electrolytes during charge-discharge cycles seriously affect the performance of MBs.The great possibility of generating Mg dendrites has also caused controversy among researchers.Moreover,the regulation of Mg deposition and the enhancement of battery cycle stability is largely limited by interfacial stability between Mg metal anode and electrolyte.In this review,recent advances in interfacial science and engineering of MBs are summarized and discussed.Special attention is given to interfacial chemistry including passivation layer formation,incompatibilities,ion transport,and dendrite growth.Strategies for building stable electrode/interfaces,such as anode designing and electrolyte modification,construction of artificial solid electrolyte interphase(SEI)layers,and development of solid-state electrolytes to improve interfacial contacts and inhibit Mg dendrite and passivation layer formation,are reviewed.Innovative approaches,representative examples,and challenges in developing high-performance anodes are described in detail.Based on the review of these strategies,reference is provided for future research to improve the performance of MBs,especially in terms of interface and anode design.

Porous polymer electrolytes for long-cycle stable quasi-solid-state magnesium batteries

The development of applicable electrolytes is the key point for high-performance rechargeable magnesium batteries(RMBs).The use of liquid electrolyte is prone to safety problems caused by liquid electrolyte leakage.Polymer-based gel electrolytes with high ionic conductivity,great flexibility,easy processing,and high safety have been studied by many scholars in recent years.In this work,a novel porous poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)membrane is prepared by a phase inversion method.By immersing porous PVDF-HFP membranes in MgCl2-AlCl3/TEGDME(Tetraethylene glycol dimethyl ether)electrolytes,porous PVDF-HFP based electrolytes(PPEs)are formed.The PPE exhibits a high ionic conductivity(4.72×10^(-4) S cm-1,25℃),a high liquid electrolyte uptake of 162%,as well as a wide voltage window(3.1 V).The galvanostatic cycling test of Mg//Mg symmetric cell with PPE reveals that the reversible magnesium ion(Mg^(2+))plating/stripping occurs at low overpotentials(~0.13 V).Excellent long cycle stability(65.5 mAh g^(-1) over 1700 cycles)is achieved for the quasisolid-state RMB assembled with MoS2/C cathode and Mg anode.Compared with the liquid electrolyte,the PPE could effectively reduce the side reactions and make Mg^(2+)plating/stripping more uniformly on the Mg electrode side.This strategy herein provides a new route to fabricate high-performance RMB through suitable cathode material and polymer electrolyte with excellent performance.

Carbon dioxide adsorption of two-dimensional carbide MXenes

Two-dimensional carbide MXenes(Ti_3C_2T_x and V_2CT_x)were prepared by exfoliating MAX phases(Ti_3AlC_2 and V_2AlC)powders in the solution of sodium fluoride(NaF)and hydrochloric acid(HCl).The specific surface area(SSA)of as-prepared Ti_3C_2T_x was 21 m^2/g,and that of V_2CT_x was 9 m^2/g.After intercalation with dimethylsulfoxide,the SSA of Ti_3C_2T_x was increased to 66 m^2/g;that of V_2CT_x was increased to 19 m^2/g.Their adsorption properties on carbon dioxide(CO_2)were investigated under 0–4 MPa at room temperature(298 K).Intercalated Ti_3C_2T_x had the adsorption capacity of 5.79 mmol/g,which is close to the capacity of many common sorbents.The theoretical capacity of Ti_3C_2T_x with the SSA of 496 m^2/g was up to 44.2 mmol/g.Additionally,due to high pack density,MXenes had very high volume-uptake capacity.The capacity of intercalated Ti_3C_2T_(x )measured in this paper was 502 V·v^(–1).This value is already higher than volume capacity of most known sorbents.These results suggest that MXenes have some advantage features to be researched as novel CO_2 capture materials.

Integration of homogeneous and heterogeneous nucleation growth via 3D alloy framework for stable Na/K metal anode

Sodium/Potassium(Na/K)metal anodes have been considered as the promising anodes for next-generation Na/K secondary batteries owing to their ultrahigh specific capacity,low redox potential and low cost.However,their practical application is still hampered due to unstable solid electrolyte interphase,infinite volume change,and dendrite growth.Herein,we design a 3D-Na_(3)Bi/3D-K_(3)Bi alloy host which enables the homogeneous and heterogeneous nucleation growth of Na/K metal.The unique structure with periodic alternating of electron and ion conductivity improves the mass transfer kinetics and prevents the volume expansion during cycling.Meanwhile,the sodiophilicity of Na_(3)Bi/potassiophilicity of K_(3)Bi framework can avoid dendritic growth.Cycling lifespans over 700 h with 1 mAh cm^(−2)for 3D-Na_(3)Bi@Na electrode and about 450 h with 1 mAh cm^(−2)for 3D-K_(3)Bi@K electrode are achieved,respectively.3D-Na_(3)Bi@Na||Na_(3)V_(2)(PO_(4))3 full battery shows sustainable cycle performance over 400 cycles.This design provides a simple but effective approach for achieving safety of sodium/potassium metal anodes.

Constructing MOF-derived CoP-NC@MXene sandwich-like composite by in-situ intercalation for enhanced lithium and sodium storage

The development of dual-function anode materials for lithium-ion batteries(LIBs)and sodium-ion batteries(SIBs)is exceedingly essential.Herein,with rationally designed hierarchical metal-organic framework(MOF)@MXene as a precursor,a novel sandwich-like CoP-NC@Ti_(3)C_(2)T_(x) composite has been successfully fabricated by the following phosphorization reaction.As anode material for LIBs,the CoPNC@Ti_(3)C_(2)T_(x) composite exhibits remarkable electrochemical performance with high-rate capability(147.8 mAh g^(-1) at 2000 mA g^(-1);245.6 mAh g^(-1) at 100 mA g^(-1))and ultralong cycling life(2000 cycles with a capacity retention over 100%).For SIBs,it delivers a discharge capacity of 101.6 mAh g^(-1) at a current density of 500 mA g^(-1) after 500 cycles.The well-designed sandwich-like composite effectively supports the easy access to electrolyte,facilitate the Li/Na ion transportation,and protect the active material from pulverization upon long cycling.In addition,the electrochemical reaction kinetics and Li-migration kinetics of the CoP-NC@Ti_(3)C_(2)T_(x) composite have been pioneeringly illuminated by pseudocapacitive behavior calculation and density functional theory(DFT)computations,respectively.This work sheds light on the rational design and development of MOF/MXene-derived dual-function anode materials for Li/Na-storage.