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.

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.

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.

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.

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.

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.

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.

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.

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.

Recent Advances of Electroplating Additives Enabling Lithium Metal Anodes to Applicable Battery Techniques

Lithium(Li)metal batteries have long been deemed as the representative high-energy-density energy storage systems due to the ultrahigh theoretical capacity and lowest electrochemical potential of Li metal anode.Unfortunately,the intractable dendritic Li deposition during cycling greatly restrains the large-scale applications of Li metal anodes.Recent advances have been explored to address this issue,among which a specific class of electrolyte additives for electroplating is deeply impressive,as they are economic and pragmatic.Different from the conventional additives that construct solid electrolyte interphase(SEI)layer on anodes,they make dendrite-free Li metal anodes feasible through altering Li plating behavior.In this research news article,the interlinked principles between industrial electroplating and Li deposition are firstly illustrated.The featured effects of electroplating additives on regulating Li plating morphology are also summarized and mainly divided into three categories:co-deposition with Li cation,coordination with Li cation,and leveling effect of Li films.Furthermore,the mechanism exploration or derivative use of electroplating additive for dendrite suppression and potential research directions are proposed,with emphasizing that industrial electroplating might enable Li metal anode to scalable battery techniques and spread to metal battery systems beyond Li.

Constructing nanoporous Ni foam current collectors for stable lithium metal anodes

Lithium metal,as the most ideal anode material for high energy density batteries,has been researched for several decades.However,the dendrite formation and large volume change during repetitive lithium plating/stripping lead to a serious safety issue and impede the practical application of lithium metal anode.Herein,a nanoporous Ni foam current collector with high surface area and surface flaws is constructed via a facile oxidation-reduction method.The inherent macropore structure of Ni foam can partly accommodate the volume variation during Li plating/stripping.The well-distributed nanopores on the skeleton of Ni foam can effectively reduce the local current density,regulate the uniform lithium nucleation and deposition with homogenous distribution of Li^(+) flux.Moreover,the surface flaws induce the formation of ring Li structures at initial nucleation/deposition processes and concave Li metal spontaneously formed based on the ring Li structures during cycling,which can direct the even Li plating/stripping.Therefore,highly stable Coulombic efficiency is achieved at 1 mA cm^(-2) for 200 cycles.The symmetrical cell,based on the nanoporous Ni foam current collector,presents long lifespans of 1200 and 700 h respectively at different current densities of 0.5 and 1 mA cm^(-2) without short circuit.In addition,the LiFePO4 full cell,with the Li metal anode based on the nanoporous Ni foam current collector,shows excellent cycling performance at 1 C for 300 cycles and rate performance.

Regulating electrodeposition behavior through enhanced mass transfer for stable lithium metal anodes

Electrode process kinetics is a key part that determines the morphology of metal electrodeposition.However,the liquid-phase mass transfer process and its effect on lithium(Li)metal electrodeposition are still poorly understood.Herein,the effect of mass transfer on the electrodeposition behavior of Li metal is explored.Experiments and COMSOL Multiphysics simulations reveal that the enhanced mass transfer,which is induced by ultrasonic wave,can homogenize the ion flow on the surface of electrode to obtain uniform Li nucleation.Meanwhile,the rapid mass transfer of Li^(+)provides sufficient cations around the germinated Li to avoid preferential growth of Li in a specific direction.Based on the simultaneous regulation of nucleation and growth behavior,a smooth and compact Li deposits can be achieved,which exhibit a small polarization voltage during repeated Li plating/striping and a considerably enhanced cyclability.This work enriches the fundamental understanding of Li electrodeposition without dendrite structure and affords fresh guidance to develop dendrite-free metal anodes for metal-based batteries.

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.

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.

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.

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 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.

Constructing a fluorinated interface layer enriched with Ge nanoparticles and Li-Ge alloy for stable lithium metal anodes

Lithium metal batteries(LMBs)based on metallic Li exhibit high energy density to be competent for advanced energy storage applications.However,the unstable solid electrolyte interphase(SEI)layer due to continuous decomposition of electrolytes,and the attendant problem of Li dendrite growth frustrate their commercialization process.Herein,a hybrid SEI comprising abundant LiF,lithiophilic Li-Ge alloy,and Ge nanoparticles is constructed via a simple brush coating method.This fluorinated interface layer with embedded Ge-containing components isolates the Li anode from the corrosive electrolyte and facilitates homogenous Li nucleation as well as uniform growth.Consequently,the modified Li anode exhibits remarkable stability without notorious Li dendrites,delivering stable cycling lives of more than 1000 h for symmetric Li||Li cells and over 600 cycles for Li||Cu cells at 1 mA·cm^(−2).Moreover,the reinforced Li anodes endow multiple full-cell architectures with dramatically improved cyclability under different test conditions.This work provides rational guidance to design an artificial hybrid SEI layer and would stimulate more ideas to solve the dendrite issue and promote the further development of advanced LMBs.