Mitigated reaction kinetics between lithium metal anodes and electrolytes by alloying lithium metal with low-content magnesium

Lithium(Li)metal is regarded as a promising anode candidate for high-energy-density rechargeable batteries.Nevertheless,Li metal is highly reactive against electrolytes,leading to rapid decay of active Li metal reservoir.Here,alloying Li metal with low-content magnesium(Mg)is proposed to mitigate the reaction kinetics between Li metal anodes and electrolytes.Mg atoms enter the lattice of Li atoms,forming solid solution due to the low amount(5 wt%)of Mg.Mg atoms mainly concentrate near the surface of Mg-alloyed Li metal anodes.The reactivity of Mg-alloyed Li metal is mitigated kinetically,which results from the electron transfer from Li to Mg atoms due to the electronegativity difference.Based on quantitative experimental analysis,the consumption rate of active Li and electrolytes is decreased by using Mgalloyed Li metal anodes,which increases the cycle life of Li metal batteries under demanding conditions.Further,a pouch cell(1.25 Ah)with Mg-alloyed Li metal anodes delivers an energy density of 340 Wh kg^(-1)and a cycle life of 100 cycles.This work inspires the strategy of modifying Li metal anodes to kinetically mitigate the side reactions with electrolytes.

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.

Liquid metal as an efficient protective layer for lithium metal anodes in all-solid-state batteries

Lithium metal batteries with inorganic solid-state electrolytes have emerged as strong and attractive candidates for electrochemical energy storage devices because of their high-energy content and safety.Nonetheless,inherent challenges of deleterious lithium dendrite growth and poor interfacial stability hinder their commercial application.Herein,we report a liquid metal-coated lithium metal(LM@Li)anode strategy to improve the contact between lithium metal and a Li6PS5Cl inorganic electrolyte.The LM@Li symmetric cell shows over 1000 h of stable lithium plating/stripping cycles at 2mA cm^(-2) and a significantly higher critical current density of 9.8 mAcm^(-2) at 25°C.In addition,a full battery assembled with a high-capacity composite LiNbO3@-LiNi_(0.7)Co_(0.2)Mn_(0.1)O_(2)(LNO@NCM721)cathode shows stable cycling performance.Experimental and computational results have demonstrated that dendrite growth tolerance and physical contact in solid-state batteries can be reinforced by using LM interlayers for interfacial modification.

The roles of MXenes in developing advanced lithium metal anodes

Lithium(Li) metal has emerged as the most promising anode for rechargeable Li batteries owing to its high theoretical specific capacities, low negative electrochemical potential, and superior electrical conductivity. Replacing the conventional graphite anodes with Li metal anodes(LMAs) provides great potential to exceed the theoretical limitations of current commercial Li-ion batteries, leading to nextgeneration high-energy–density rechargeable Li metal batteries(LMBs). However, further development of LMAs is hindered by several inherent issues, such as dangerous dendrite growth, infinite volume change, low Coulombic efficiency, and interfacial side reactions. MXenes, a family of two-dimensional(2 D) transition metal carbides and/or nitrides, have recently attracted much attention to address these issues due to their 2D structure, lithiophilic surface terminations, excellent electrical and ionic conductivity, and superior mechanical properties. Herein, an overview of recent advances in the roles of MXenes for stabilizing LMAs is presented. In particular, strategies of utilizing MXenes as the Li hosts, artificial protection layers, electrolyte additives, and for separator modifications to develop stable and dendrite-free LMAs are discussed. Moreover, a perspective on the current challenges and potential outlooks on MXenes for advanced LMAs is provided.

A bifunctional ethylene-vinyl acetate copolymer protective layer for dendrites-free lithium metal anodes

Lithium metal batteries are strongly considered as one of the most promising candidates for nextgeneration high-performance battery systems.However,the uncontrollable growth of lithium dendrites and the highly reactive lithium metal result in the severe safety risks and the short lifespan for highenergy-density rechargeable batteries.Here,we demonstrate a hydrophobic and ionically conductive ethylene-vinyl acetate(EVA)copolymer layer can not only endow lithium metal anodes with an air-stable and anti-water surface,but also efficiently suppress the lithium-dendrites growth during the electrochemical cycling process.Therefore,the introduction of the EVA copolymer as a bifunctional protection layer simultaneously improves the anti-water/air performance and electrochemical cycling stability of lithium metal anode.

Self-assembled, highly-lithiophilic and well-aligned biomass engineered MXene paper enables dendrite-free lithium metal anode in carbonate-based electrolyte

Lithium metal anode is the ideal candidate for high-energy–density rechargeable batteries.However,uncontrolled dendrite growth hampers its commercialization.Herein,a dendrite-free composite Li metal anode is realized by a flexible,freestanding,well-aligned and highly-lithiophilic MXene paper designed by a facile electrostatic self-assembly of the exfoliated MXene nanosheets and natural polysaccharidechitosan (MX@CS).The MX@CS paper gets a well-aligned layered-3D structure with a micro-crumpled surface that can effectively decrease the local current density,guide even Li plating and suppress dendritic Li growth.More importantly,surface-adsorbed chitosan endows enhanced lithiophilicity for MXene substrate and thus reduces the Li nucleation overpotential,which is confirmed by the density functional theory calculations.Abundant lithiophilic groups on MX@CS surface provide highconcentration Li^(+)anchoring site promoting Li nucleation and laterally inducing uniform Li deposition,which effectively avoids the formation of dendritic Li.As a result,the MX@CS-Li anode with a dendrite-free Li morphology shows a significantly improved cycling life in commercial carbonatebased electrolyte.When coupled with LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)cathode,the full cell exhibits a low capacity decay and steady ultrahigh Coulombic efficiency of 99.6%at a current density of 5C.These findings develop a new approach for designing high-performance metal-based rechargeable batteries.

Electrolyte and current collector designs for stable lithium metal anodes

With the increasing demand for high energy-density batteries for portable electronics and large-scale energy storage systems,the lithium metal anode(LMA)has received tremendous attention because of its high theoretical capacity and low redox potential.However,the commercial application of LMAs is impeded by the uncontrolled growth of lithium dendrites.Such dendrite growth may result in internal short circuits,detrimental side reactions,and the formation of dead lithium.Therefore,the growth of lithium metal must be controlled.This article summarizes our recent efforts in inhibiting such dendrite growth,decreasing the detrimental side reactions,and elongating the LMA lifespan by optimizing the electrolyte structure and by designing appropriate current collectors.After identifying that the unstable solid electrolyte inter-face(SEI)film is responsible for the potential dropping in carbonate electrolytes,we developed LiPF_(6)-LiNO_(3) dual-salt electrolyte and lithium bis(fluorosulfonyl)imide(LiFSI)-carbonate electrolyte to stabilize the SEI film of LMAs.In addition,we achieved controlled lithium depos-ition by designing the structure and material of the current collectors,including selective lithium deposition in porous current collectors,lithio-philic metal guided lithium deposition,and iron carbide induced underpotential lithium deposition in nano-cavities.The limitations of the cur-rent strategies and prospects for future research are also presented.

Effects of nanopores and sulfur doping on hierarchically bunched carbon fibers to protect lithium metal anode

Studies on three-dimensional structured carbon templates have focused on how to guide homogeneous lithium metal nucleation and growth for lithium metal anodes(LMAs).However,there is still insufficient evidence for a key factor to achieve their high electrochemical performance.Here,the effects of nanopores and sulfur doping on carbon-based nanoporous host(CNH)electrode materials for LMAs were investigated using natural polymer-derived CNHs.Homogeneous pore-filling behaviors of lithium metal in the nanopores of the CNH electrode materials were first observed by ex situ scanning electron microscopy analysis,where the protective lithium metal nucleation and growth process led to significantly high Coulombic efficiency(CE)of~99.4%and stable 600 cycles.In addition,a comparison study of CNH and sulfurdoped CNH(S-CNH)electrodes,which differ only in the presence or absence of sulfur,revealed that sulfur doping can cause lower electrochemical series resistance,higher CE value,and better cycling stability in a wide range of current densities and number of cycles.Moreover,S-CNH-based LMAs showed high electrochemical performance in full-cell Li-S battery tests using a sulfur copolymer cathode,where a high energy density of 1370Wh kgelectrode−1 and an excellent power density of 4120Wkgelectrode−1 were obtained.

Driving lithium to deposit inside structured lithium metal anodes:A phase field model

Lithium metal anode is one of the most important anode materials for next-generation high-specificenergy secondary batteries.Structured lithium metal anodes have received extensive attention in the development of practical lithium metal batteries.Methods of driving lithium metal to deposit inside the pores of structured lithium metal anodes have always been one of the most concerned issues,especially for highly conductive frameworks.An electrochemical phase field theory with galvanostatic lithium plating process is employed in this work,the mechanism that illustrates the preference of lithium metal to deposit at the top of the framework structure has been revealed,and through the simulation analysis of various regulating strategies,the strategies that can efficiently drive lithium to deposit inside structured pores are summarized.This work presents the theoretical calculation and analysis methods that can be used for the rational design of lithium metal batteries.

Review on lithium metal anodes towards high energy density batteries

Lithium metal anode(LMA) is a promising candidate for achieving next-generation high-energy-density batteries due to its ultrahigh theoretical capacity and most negative electrochemical potential. However, the practical application of lithium metal battery(LMB) is largely retarded by the instable interfaces, uncontrolled dendrites, and rapid capacity deterioration. Herein, we present a comprehensive overview towards the working principles and inherent challenges of LMAs. Firstly, we diligently summarize the intrinsic mechanism of Li stripping and plating process. The recent advances in atomic and mesoscale simulations which are crucial in guiding mechanism study and material design are also summarized. Furthermore, the advanced engineering strategies which have been proved effective in protecting LMAs are systematically reviewed, including electrolyte optimization, artificial interface, composite/alloy anodes and so on. Finally, we highlight the current limitations and promising research directions of LMAs. This review sheds new lights on deeply understanding the intrinsic mechanism of LMAs, and calls for more endeavors to realize practical Li metal batteries.

Freestanding polypyrrole nanotube/reduced graphene oxide hybrid film as flexible scaffold for dendrite-free lithium metal anodes

Lithium metal anode is the most potential anode material for the next generation high-energy rechargeable batteries owing to its highest specific capacity and lowest redox potential.Unfortunately,the uneven deposition of Li during plating/stripping and the formation of uncontrolled Li dendrites,which might cause poor battery performance and serious safety problems,are demonstrating to be a huge challenge for its practical application.Here,we show that a flexible and free-standing film hybriding with polypyrrole(PPy) nanotubes and reduced graphene oxide(rGO) can significantly regulate the Li nucleation and deposition,and further prohibit the formation of Li dendrites,owing to the large specific surface area,rich of nitrogen functional groups and porous structures.Finally,the high Coulombic efficiency and stable Li plating/stripping cycling performance with 98% for 230 cycles at 0.5 mA cm^(-2) and more than 900 hours stable lifespan are achieved.No Li dendrites form even at a Li deposition capacity as high as4.0 mA h cm^(-2).Besides,the designed PPy/rGO hybrid anode scaffold can also drive a superior battery performance in the lithium-metal full cell applications.

Bottom-up lithium growth guided by Ag concentration gradient in 3D PVDF framework towards stable lithium metal anode

Three-dimensional(3 D)frameworks have received much attention as an effective modification strategy for next-generation high-energy-density lithium metal batteries.However,the top-growth mode of lithium(Li)on the 3 D framework remains a tough challenge.To achieve a uniform bottom-up Li growth,a scheme involving Ag concentration gradient in 3 D PVDF framework(C-Ag/PVDF)is proposed.Ag nanoparticles with a concentration gradient induce an interface activity gradient in the 3 D framework,and this gradient feature is still maintained during the cycle.As a result,the C-Ag/PVDF framework delivers a long lifespan over 1800 h at a current density of 1 mA cm^(-2) with a capacity of 1 mAh cm^(-2),and shows an ultra-long life(>1300 h)even at a high current density of 4 mA cm^(-2) with a capacity of 4 mAh cm^(-2).The advantage of concentration gradient provides further insights into the optimal design of the 3 D framework for stable Li metal anode.

A two-dimension laminar composite protective layer for dendrite-free lithium metal anode

Lithium(Li)metal anodes with the high theoretical specific capacity(3860 mAh g^(-1))and most negative reduction potential(-3.04 V vs.standard hydrogen electrode)have been considered as an ultimate choice for energy storage devices with high energy density[1-4].However,the practical applications of Li metalbased batteries(LMBs)are confronted with two tough issues:Li dendrite growth induced by uneven Li depositions and unstable solid electrolyte interphase(SEI)(Fig.1a)[5,6].

New insights into the formation of silicon-oxygen layer on lithium metal anode via in situ reaction with tetraethoxysilane

Lithium metal-based secondary batteries are very promising for next generation power battery due to their high energy density.However,lithium anodes suffer from poor electrochemical reversibility in organic electrolytes due to Li dendrites and instability of the solid electrolyte interphase.Recent research demonstrated that the problem can be alleviated via tetraethoxysilane(TEOS)treated lithium metal to form a silicon oxide layer on the lithium surface,however,its reaction mechanism is controversial.Herein,we deeply explore the reaction mechanism between TEOS and Li and propose:Fresh Li can directly react with TEOS even though no lithium hydroxide exists on the lithium surface,and the participation of water will accelerate the reaction process.Moreover,it was found that the silicon oxide layer can promote the uniform deposition of lithium ions by providing lithiophilic nucleation sites,thereby achieving a long cycle life of Li metal batteries.

Synthetic poly-dioxolane as universal solid electrolyte interphase for stable lithium metal anodes

Lithium (Li) metal is a promising anode for the next generation high-energy–density batteries. However, the growth of Li dendrites, low coulombic efficiency and dramatic volume change limit its development. Here, we report a new synthetic poly-dioxolane (PDOL) approach to constructing an artificial 'elastic' SEI to stabilize the Li/electrolyte interface and the Li deposition/dissolution behavior in a variety of electrolytes. By coating PDOL with optimized molecular weights and synthetic routes on Li metal anode, the 'elastic' SEI layer could be maintained on top of the Li metal anode to accommodate the Li deposition/dissolution. No dendrite formation was observed during the cycling process, and the interfacial side reactions were reduced significantly. Consequently, we successfully achieved 330 cycles with a CE of 98.4% in ether electrolytes and 90 cycles with a CE of 94.3% in carbonate electrolytes. Simultaneously, the Li-metal batteries with LiFePO_(4) as cathodes also exhibited improved cycling performance. This strategy could promote the development of dendrite-free metal anodes toward high-performance Li-metal batteries.

Lithiophilicity: The key to efficient lithium metal anodes for lithium batteries

Lithium metal anode of lithium batteries,including lithium-ion batteries,has been considered the anode for next-generation batteries with desired high energy densities due to its high theoretical specific capacity(3860 mA h g^(-1))and low standards electrode potential(-3.04 V vs.SHE).However,the highly reactive nature of metallic lithium and its direct contact with the electrolyte could lead to severe chemical reactions,leading to the continuous consumption of the electrolyte and a reduction in the cycle life and Coulombic efficiency.In addition,the solid electrolyte interface formed during battery cycling is mainly inorganic,which is too fragile to withstand the extreme volume change during the plating and stripping of lithium.The uneven flux of lithium ions could lead to excessive lithium deposition at local points,resulting in needle-like lithium dendrites,which could pierce the separator and cause short circuits,battery failure,and safety issues.In the last five years,tremendous efforts have been dedicated to addressing these issues,and the most successful improvements have been related to lithiophilicity optimizations.Thus,this paper comprehensively reviewed the lithiophilicity regulation in lithium metal anode modifications and highlighted the vital effect of lithiophilicity.The remaining challenges faced by the lithiophilicity optimization for lithium metal anodes are discussed with the proposed research directions for overcoming the technical challenges in this subject.

Plating current density distribution of lithium metal anodes in pouch cells

The uniformity of current density distribution upon electrodes is one of the most important factors determining the lithium dendrites growth and cycling performance of lithium metal batteries(LMBs). Herein,current density distributions of lithium metal anodes induced by various engineering factors, consisting of uneven cathode, electrolyte distribution, and different tab positions, and their effects on the electrochemical performance are investigated theoretically and experimentally in pouch cells. The deviation of current density in lithium metal anodes ranges from 2.47% to 196.18% due to the different levels of uneven cathode materials. However, the deviation is just 13.60% for different electrolyte thicknesses between cathodes and anodes, even a ten-layer separator in some positions. The maximum deviation for variational tab positions is only 0.17%. The nonuniformity in current density distribution results in severe dendrite growth issues and poor electrochemical performance of LMBs. This work not only confirms the direct correlation between the uneven current density distribution and lithium deposition behaviors, but also points out the decisive effects of cathode surface roughness on current distribution of anodes, to which more attentions should be paid in practical applications of LMBs.

In Situ Formed Tribofilms as Efficient Organic/Inorganic Hybrid Interlayers for Stabilizing Lithium Metal Anodes

The practical application of Li metal anodes(LMAs)is limited by uncontrolled dendrite growth and side reactions.Herein,we propose a new friction-induced strategy to produce high-performance thin Li anode(Li@CFO).By virtue of the in situ friction reaction between fluoropolymer grease and Li strips during rolling,a robust organic/inorganic hybrid interlayer(lithiophilic LiF/LiC_(6)framework hybridized-CF_(2)-O-CF_(2)-chains)was formed atop Li metal.The derived interface contributes to reversible Li plating/stripping behaviors by mitigating side reactions and decreasing the solvation degree at the interface.The Li@CFO||Li@CFO symmetrical cell exhibits a remarkable lifespan for 5,600 h(1.0 mA cm^(-2)and 1.0 mAh cm^(-2))and 1,350 cycles even at a harsh condition(18.0 mA cm^(-2)and 3.0 mAh cm^(-2)).When paired with high-loading LiFePO4 cathodes,the full cell lasts over 450 cycles at 1C with a high-capacity retention of 99.9%.This work provides a new friction-induced strategy for producing high-performance thin LMAs.

The evolution and failure mechanism of lithium metal anode under practical working conditions

Lithium(Li)metal is regarded as a promising anode material to render the Li batteries with high energy density and therefore satisfy the ever-growing energy demands of high-end storage devices[1].Unfortunately,the dendrite growth accompanied with accumulation of"dead Li"leads to low Coulombic efficiency,poor cycling lifespan,and even severe safety hazards,critically hindering the practical implementation of Li metal batteries[2,3].

In vacuo XPS investigation of surface engineering for lithium metal anodes with plasma treatment

Lithium(Li)metal is an attractive anode material with high capacity(3860 mAh g^(−1))and low potential(−3.04 V vs.standard hydrogen electrode)that shows highly promising for applications requiring high energy density.However,the low electrochemical potential of Li metal makes it extremely reactive and inevitably forming a native oxidized layer in the ambient environment and repeatedly being consumed when exposed to liquid electrolytes.It is therefore beneficial to replace the poorly controlled native passivation layer with a tailored artificial SEI to improve interface management between Li and electrolyte and enhance the stability of Li metal battery.Here,we use an integrated glovebox-atomic layer deposition(ALD)-X-ray photoelectron spectroscopy(XPS)setup to in-situ investigating the pristine Li surface and the surface composition after Ar,H_(2)O_(2),N_(2)and NH_(3)plasma treatment processes.We find that the pristine Li foil is naturally being covered with a native oxidized layer,which is mainly composed of LiOH,Li_(2)O and Li_(2)CO_(3).These investigated plasmas can efficiently remove the oxidized layer from the Li metal surface,in which metallic Li surface is obtained after Ar or H2 plasma treatments,where Ar plasma is more efficient.While O_(2)plasma treatment produces a Li_(2)O layer,and N_(2)or NH_(3)plasma treatment leads to a Li3N(including a certain amount of LiON)layer on the Li surface.When employing the representative metallic Li(by Ar plasma treatment),Li_(2)O layer coated Li(by O_(2)plasma treatment)and Li3N layer coated Li(by N_(2)plasma treatment)foils as electrodes in symmetric Li metal batteries,the Li3N coated Li electrode exhibits much higher stability than that of metallic and Li_(2)O layer coated Li foils.Improved electrochemical performance has also been achieved in LiMn_(2)O_(4)(LMO)||Li full cells using Li anode with Li3N protective coating layer.Our work reveals the detailed process of surface engineering of Li metal anodes with plasma treatments by in vacuo XPS,which may also be extended to other gas-treatment or plasma-treatment for stabilization of high energy density Li metal anodes and other metal-based anodes.