In situ generation of Li_(3)N concentration gradient in 3D carbon-based lithium anodes towards highly-stable lithium metal batteries

The uncontrolled dendrite growth of lithium metal anodes(LMAs)caused by unstable anode/electrolyte interface and uneven lithium deposition have impeded the practical applications of lithium metal batteries(LMBs).Constructing a robust artificial solid electrolyte interphase(SEI)and regulating the lithium deposition behavior is an effective strategy to address these issues.Herein,a three-dimensional(3D)lithium anode with gradient Li_(3)N has been in-situ fabricated on carbon-based framework by thermal diffusion method(denoted as CC/Li/Li_(3)N).Density functional theory(DFT)calculations reveal that Li_(3)N can effectively promote the transport of Li^(+)due to the low energy barrier of Li^(+)diffusion.As expected,the Li_(3)N-rich conformal artificial SEI film can not only effectively stabilize the interface and avoid parasitic reactions,but also facilitate fast Li^(+)transport across the SEI layer.The anode matrix with uniformly distributed Li3N can enable homogenous deposition of Li,thus preventing Li dendrite propagation.Benefiting from these merits,the CC/Li/Li_(3)N anode achieves ultralong-term cycling for>1000 h at a current density of 2 m A cm^(-2)and dendrite-free Li deposition at an ultrahigh rate of 20 m A cm^(-2).Moreover,the full cells coupled with LiFePO4cathodes show extraordinary cycling stability for>300 cycles in liquidelectrolyte-based batteries and display a high-capacity retention of 96.7%after 100 cycles in solid-state cells,demonstrating the promising prospects for the practical applications of LMBs.

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.

Recent advances in quantifying the inactive lithium and failure mechanism of Li anodes in rechargeable lithium metal batteries

Lithium metal is considered as the ultimate anode material for the next generation of high-energy density batteries.However,non-uniform lithium dendrite growth,serious electrolyte consumption,and significant volume changes during lithium deposition/stripping processes lead to sustained accumulation of inactive lithium and poor cycling reversibility.Quantifying the formation and evolution of inactive lithium under different conditions and fully evaluating the complex failure modes are the key issues in this challenging field.This article comprehensively reviews recent research progress on the quantification of formation and evolution of inactive lithium detected by different quantitative techniques in rechargeable lithium metal batteries.The key research challenges such as failure mechanism,modification strategies and operando characterization of lithium metal anodes are systematically summarized and prospected.This review provides a new angle of view to understand failure mechanism of lithium metal anodes and inspiration and guidance for the future development of rechargeable lithium metal batteries.

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.

Interfacial engineering of perfluoroalkyl functionalized covalent organic framework achieved ultra-long cycled and dendrite-free lithium anodes

The finite lithium-ion utilization,short cycling life,and lower capacity retention caused by irreversible dendrite growth become the maximum dilemma in lithium metal batteries’(LMBs’)commercialization.Herein,a perfluoroalkyl-functionalized covalent organic framework(COF-F6)equipped with high stability and supernal proton conduction is introduced as an artificial solid electrolyte interface to stable the lithium metal anode.Benefiting from the strong electron-withdrawing effect of perfluoroalkyl,Li^(+)will be freed more by the competition of electronegative fluorine(F)and bis(trifluoromethanesulphonyl)imide anion(TFSI^(-)).The dissociation of LiTFSI and process of Li^(+)desolvation are easier to achieve.In addition,high electronegative fluorine can also regulate local electron-cloud density to induce the fast immigration of Li^(+).All the above roles contribute to improving the Li^(+)transfer number(0.7)and achieving the goal of inhibiting Li dendrite.As a result,the perfluoroalkyl COF-F6 modified LMB presents outstanding cycling stability.The symmetric batteries accomplish an overlong life-span of more than 5000 h with a lower hysteresis voltage(11 mV)at 5 mA·cm^(-2).Also,no dendrites are observed when using an in-situ optical microscope to learn the process of Li deposition.Therefore,this dendrite-free protection tactic holds broad prospects for the practical application of Li metal anodes.

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.

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.

In Situ Reaction Fabrication of a Mixed-Ion/Electron-Conducting Skeleton Toward Stable Lithium Metal Anodes

Lithium metal batteries are emerging as a strong candidate in the future energy storage market due to its extremely high energy density.However,the uncontrollable lithium dendrites and volume change of lithium metal anodes severely hinder its application.In this work,the porous Cu skeleton modified with Cu_(6)Sn_(5)layer is prepared via dealloying brass foil following a facile electroless process.The porous Cu skeleton with large specific surface area and high electronic conductivity effectively reduces the local current density.The Cu_(6)Sn_(5)can react with lithium during the discharge process to form lithiophilic Li_(7)Sn_(2)in situ to promote Li-ions transport and reduce the nucleation energy barrier of lithium to guide the uniform lithium deposition.Therefore,more than 300 cycles at 1 mA cm^(−2)are achieved in the half-cell with an average Coulombic efficiency of 97.5%.The symmetric cell shows a superior cycle life of more than 1000 h at 1 mA cm^(−2)with a small average hysteresis voltage of 16 mV.When coupled with LiFePO_(4)cathode,the full cell also maintains excellent cycling and rate performance.

Elucidating the suppression of lithium dendrite growth with a void-reduced anti-perovskite solid-state electrolyte pellet for stable lithium metal anodes

Solid-state lithium-metal batteries,with their high theoretical energy density and safety,are highly promising as a next-generation battery contender.Among the alternatives proposed as solid-state electrolyte,lithium-rich anti-perovskite(Li RAP)materials have drawn the most interest because of high theoretical Li^(+)conductivity,low cost and easy processing.Although solid-state electrolytes are believed to have the potential to physically inhibit the lithium dendrite growth,lithium-metal batteries still suffer from the lithium dendrite growth and thereafter the short circuiting.The voids in practical Li RAP pellets are considered as the root cause.Herein,we show that reducing the voids can effectively suppress the lithium dendrite growth.The voids in the pellet resulted in an irregular Li^(+)flux distribution and a poor interfacial contact with lithium metal anode;and hence the ununiform lithium dendrites.Consequently,the lithium-metal symmetric cell with void-reduced Li_(2)OHCl-HT pellet was able to display excellent cycling performance(750 h at 0.4 m A cm^(-2))and stability at high current density(0.8 m A cm^(-2)for 120 h).This study provides not only experimental evidence for the impact of the voids in Li RAP pellets on the lithium dendrite growth,but also a rational pellet fabrication approach to suppress the lithium dendrite growth.

Full-chain enhanced ion transport toward stable lithium metal anodes

The dendrite growth that results from the slow electrode process kinetics prevents the lithium(Li) metal anode from being used in practical applications. Here, full-chain enhanced ion transport for stabilizing Li metal anodes is proposed. Experimental and theoretical studies confirm that full-chain enhanced ion transport(electrocrystallization, mass transport in the electrolyte and diffusion in solid electrolyte interphase) under magnetoelectrochemistry contributes to a homogeneous, dense, and dendrite-free morphology. Specifically, the enhanced electrocrystallization behavior promotes the Li nucleation;the enhanced mass transport in the electrolyte alleviates the ion concentration gradient at the electrode surface, which helps to inhibit dendrite growth;and the enhanced diffusion in the solid electrolyte interphase further homogenizes the Li deposition behavior, obtaining regular and uniform Li particles.Consequently, the Li metal anode has exceptional cycling stability in both symmetric and full cells,and the pouch cell performs long cycles(170 cycles) in practice evaluation. This work advances fundamental knowledge of the magneto-dendrite effect and offers a new perspective on stabilizing metal anodes.

Asymmetric N,O-Coordinated Single Atomic Co Sites for Stable Lithium Metal Anodes

Lithium metal has been considered one of the most promising anodes for next-generation rechargeable batteries,but its practical application is largely hindered by the uncontrollable dendrite growth and infinite volume change.Here,inspired by superior catalytic effects of single-atom catalysts,carbon-supported single atomic Co with asymmetric N,O-coordination(Co-N/O)is developed for Li metal battery.Experimental results and theoretical calculations indicate that single atomic Co atoms with asymmetric N,O-coordination present enhanced binding ability toward Li in comparison with N-coordinated atomic Co site and isolated O site,enabling uniform Li plating/stripping.Moreover,the asymmetric N,O-coordination around Co atoms induces co-activation effects,lowering the energy barriers toward Li^(+)to Li^(0)conversion and largely promoting the deposition kinetics.When used as a Li deposition host,the Co-N/O achieves a high average coulombic efficiency of 98.6%at a current density of 1 mA cm^(-2)and a capacity of 2 mAh cm^(-2),long cycling life of 2000 h in symmetrical cells,and excellent rate performance(voltage hysteresis of 23 mV at 8 mA cm^(-2)).This work provides a comprehensive understanding of single atomic metals with asymmetric heteroatom coordination in the design of Li metal anode.

Sulfur-doped hard carbon hybrid anodes with dual lithium-ion/metal storage bifunctionality for high-energy-density lithium-ion batteries

Bifunctional hybrid anodes(BHAs),which are both a high-performance active host material for lithium-ion storage as well as a guiding agent for homogeneous lithium metal nucleation and growth,exhibit significant potential as anodes for next-generation high-energy-density lithium-ion batteries(LIBs).In this study,sulfur-doped hard carbon nanosphere assemblies(S-HCNAs)were prepared through a hydrothermal treatment of a liquid organic precursor,followed by high-temperature thermal annealing with elemental sulfur for application as BHAs for LIBs.In a carbonate-based electrolyte containing fluoroethylene carbonate additive,the S-HCNAs showed high lithium-ion storage capacities in sloping as well as plateau voltage sections,good rate capabilities,and stable cyclabilities.In addition,high average Coulombic efficiencies(CEs)of~96.9%were achieved for dual lithium-ion and lithium metal storage cycles.In the LIB full-cell tests with typical NCM811 cathodes,the S-HCNA-based BHAs containing~400 mA h g^(−1) of excess lithium led to high energy and power densities of~500Wh kg^(−1) and~1695Wkg^(−1),respectively,and a stable cycling performance with~100%CEs was achieved.

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.

Gas‐phase fluorination of conjugated microporous polymer microspheres for effective interfacial stabilization in lithium metal anodes

Lithium(Li)metal anodes have attracted extensive attention due to their ultrahigh theoretical capacity and low potential.However,the uneven deposition of Li near the unstable electrode/electrolyte interfaces leads to the growth of Li dendrites and the degradation of active electrodes.Herein,we directly fluorinate alkyne-containing conjugated microporous polymers(ACMPs)microspheres with fluorine gas(F_(2))to introduce a novel fluorinated interlayer as an interfacial stabilizer in lithium metal batteries.Using density functional theory methods,it is found that as-prepared fluorinated ACMP(FACMP)has abundant partially ionic C–F bonds.The C–F bonds with electrochemical lability yield remarkable lithiophilicity during cycling.The in situ reactions between the active C–F bonds and Li ions enable transfer of lithium fluoride microcrystals to the solid electrolyte interphase(SEI)layers,guaranteeing effective ionic distribution and smooth Li deposition.Consequently,Li metal electrodes with the fluorinated interlayers demonstrate excellent cycling performances in both half-batteries and full cells with a lithium bis(trifluoromethanesulfonyl)imide electrolyte as well as a nonfluorinated lithium bis(oxalate)borate electrolyte system.This strategy is highly significant in customizable SEI layers to stabilize electrode interfaces and ensure high utilization of Li metal anodes,especially in a nonfluorinated electrolyte.

Ultrathin and Air-Stable Lithium Metal Anodes with Superlong Cycling Life in Ether/Ester-Based Electrolytes

Ultrathin and air-stable Li metal anodes hold great promise toward high-energy and high-safety Li metal batteries(LMBs).However,the application of LMBs is technically impeded by existing Li metal anodes with large thickness,high reactivity,and poor performance.Here,we developed a novel and scalable approach for the construction of a 10-μm-thick flexible and air-stable Li metal anode by conformally encapsulating Li within a multifunctional VN film.Specifically,the highly lithiophilic VN layer guides a uniform deposition of Li,while abundant and multilevel pores arising from assembly of ultrathin nanosheets enable a spatially confined immersion of metallic Li,thus ensuring an ultrathin and sandwiched Li anode.More impressively,the strong hydrophobicity of VN surface can effectively improve the stability of anode to humid air,whereas the highly conductive framework greatly boosts charge transfer dynamics and enhances Li utilization and high-rate capability.Benefiting from such fascinating features,the constructed Li-VN anode exhibits ultrastable cycling stability in both ether(2500 h)and carbonate(900 h)electrolytes,respectively.Moreover,even exposed to ambient air for 12 h,the anode still can retain~78%capacity,demonstrating excellent air-defendable capability.This work affords a promising strategy for fabricating high-performance,high-safety,and low-cost LMBs.

V-MOF-derived V_(2)O_(5) nanoparticles-modified carbon fiber cloth-based dendrite-free anode for high-performance lithium metal batteries

At present,commercial Li-ion batteries are hardly to satisfy the growing demand for high energy density,for this purpose,lithium metal batteries have attracted worldwide attention in recent years.However,its practical applications are hindered by the formation of Li dendrites and volume effect during Li plating/stripping process,which leads to a lot of safety hazards.Herein,we first employed MOF-derived V_(2)O_(5) nanoparticles to decorate the carbon fiber cloth(CFC)backbone to acquire a lithiophilic 3D porous conductive framework(CFC@V_(2)O_(5)).Subsequently,the CFC@V_(2)O_(5) skeleton was permeated with molten Li to prepare CFC@V_(2)O_(5)@Li composite anode.The CFC@V_(2)O_(5)@Li composite anode can be stably cycled for more than 1650 h at high current density(5 mA·cm^(-2))and areal capacity(5 mA·h·cm^(–2)).The prepared full cell can initially maintain a high capacity of about 143 mA·h·g^(-1) even at a high current density of 5 C,and can still maintain 114 mA·h·g^(-1) after 1000 cycles.

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.

Viability of all-solid-state lithium metal battery coupled with oxide solid-state electrolyte and high-capacity cathode

Owing to the utilization of lithium metal as anode with the ultrahigh theoretical capacity density of 3860 mA h g^(-1)and oxide-based ceramic solid-state electrolytes(SE),e.g.,garnet-type Li7La_(3)Zr_(2)O_(12)(LLZO),all-state-state lithium metal batteries(ASLMBs)have been widely accepted as the promising alternatives for providing the satisfactory energy density and safety.However,its applications are still challenged by plenty of technical and scientific issues.In this contribution,the co-sintering temperature at 500℃is proved as a compromise method to fabricate the composite cathode with structural integrity and declined capacity fading of LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM).On the other hand,it tends to form weaker grain boundary(GB)inside polycrystalline LLZO at inadequate sintering temperature for LLZO,which can induce the intergranular failure of SE during the growth of Li filament inside the unavoidable defect on the interface of SE.Therefore,increasing the strength of GB,refining the grain to 0.4μm,and precluding the interfacial defect are suggested to postpone the electro-chemo-mechanical failure of SE with weak GB.Moreover,the advanced sintering techniques to lower the co-sintering temperature for both NCM-LLZO composite cathode and LLZO SE can be posted out to realize the viability of state-of-the-art ASLMBs with higher energy density as well as the guaranteed safety.

The origin of sulfuryl-containing components in SEI from sulfate additives for stable cycling of ultrathin lithium metal anodes

In the light of wireless and non-fossil society based on portable electronics, electric vehicles, and smart grids, secondary batteries with higher energy density, faster charge, and safer operation are pursued persistently [1]. Nowadays, commercial lithium(Li)-ion batteries have been practically applied in our daily life. However,the energy density of Li-ion batteries based on intercalation chemistry is approaching to the theoretical value due to the limited specific capacity of graphite anode(372 mA h g-1) [2].

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.