Construction of Dynamic Alloy Interfaces for Uniform Li Deposition in Li-Metal Batteries

It is well accepted that a lithiophilic interface can effectively regulate Li deposition behaviors,but the influence of the lithiophilic interface is gradually diminished upon continuous Li deposition that completely isolates Li from the lithiophilic metals.Herein,we perform in-depth studies on the creation of dynamic alloy interfaces upon Li deposition,arising from the exceptionally high diffusion coefficient of Hg in the amalgam solid solution.As a comparison,other metals such as Au,Ag,and Zn have typical diffusion coefficients of 10-20 orders of magnitude lower than that of Hg in the similar solid solution phases.This difference induces compact Li deposition pattern with an amalgam substrate even with a high areal capacity of 55 mAh cm^(-2).This finding provides new insight into the rational design of Li anode substrate for the stable cycling of Li metal batteries.

Multi-dimensional hybrid flexible films promote uniform lithium deposition and mitigate volume change as lithium metal anodes

Lithium metal is the ultimate anode material for next-generation high-energy batteries.Yet,the practical application of lithium metal anodes is limited by the formation of Li dendrites and large volume changes.Herein,an effective multi-dimensional hybrid flexible film(MD-HFF)composed of iodine ion(0 dimension),CNTs(1 dimension)and graphene(2 dimensions)is designed for regulating Li deposition and mitigating volume changes.The multi-dimensional components serve separate roles:(1)iodine ion enhances the conductivity of the electrode and provides lithiophilic sites,(2)CNTs strengthen interlaminar conductance and mechanical strength,acting as a spring in the layered structure to alleviate volume changes during Li plating and stripping and(3)graphene provides mechanical flexibility and electrical conductivity.The resulting MD-HFF material supports stable Li plating/stripping and high Coulombic efficiency(99%)over 230 cycles at 1 mA cm^(-2) with a deposition capacity of 1 mAh cm^(-2).Theoretical calculations indicate that LiI contributes to the lateral growth of Li on the MD-HFF surface,thereby inhibiting the formation of Li dendrites.When paired with a typical NCM811 cathode,the assembled MD-HFF‖NCM811 cell exhibit improved capability and stable cycling performance.This research serves to guide material design in achieving Li anode materials that do not suffer from dendrite formation and volume changes.

Lithium-Ion Charged Polymer Channels Flattening Lithium Metal Anode

The concentration difference in the near-surface region of lithium metal is the main cause of lithium dendrite growth.Resolving this issue will be key to achieving high-performance lithium metal batteries(LMBs).Herein,we construct a lithium nitrate(LiNO_(3))-implanted electroactiveβphase polyvinylidene fluoride-co-hexafluoropropylene(PVDF-HFP)crystalline polymorph layer(PHL).The electronegatively charged polymer chains attain lithium ions on the surface to form lithium-ion charged channels.These channels act as reservoirs to sustainably release Li ions to recompense the ionic flux of electrolytes,decreasing the growth of lithium dendrites.The stretched molecular channels can also accelerate the transport of Li ions.The combined effects enable a high Coulombic efficiency of 97.0%for 250 cycles in lithium(Li)||copper(Cu)cell and a stable symmetric plating/stripping behavior over 2000 h at 3 mA cm^(-2)with ultrahigh Li utilization of 50%.Furthermore,the full cell coupled with PHL-Cu@Li anode and Li Fe PO_(4) cathode exhibits long-term cycle stability with high-capacity retention of 95.9%after 900 cycles.Impressively,the full cell paired with LiNi_(0.87)Co_(0.1)Mn_(0.03)O_(2)maintains a discharge capacity of 170.0 mAh g^(-1)with a capacity retention of 84.3%after 100 cycles even under harsh condition of ultralow N/P ratio of 0.83.This facile strategy will widen the potential application of LiNO_(3)in ester-based electrolyte for practical high-voltage LMBs.

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.

A Single-Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth,but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low-piezoelectricity polymer as employed.Herein,by combining PVDF-HFP and ferroelectric BaTiO_(3),we develop a homogeneous,single-layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength.As squeezed by local protrusion,the polarized PVDF-HFP/BaTiO_(3)composite separator generates a local voltage to suppress the local-intensified electric field and further deconcentrate regional lithium-ion flux to retard lithium deposition on the protrusion,hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF-HFP separator,especially at high rates.Remarkably,the homogeneous incorporation of BaTiO_(3)highly improves the piezoelectric performances of the separator with residual polarization of 0.086 pC cm^(-2)after polarization treatment,four times that of the pure PVDF-HFP separator,and simultaneously increases the transference number of lithium-ion from 0.45 to 0.57.Beneficial from the prominent piezoelectric mechanism,the polarized PVDF-HFP/BaTiO_(3)composite separator enables stable cyclic performances of Li||LiFePO_(4)cells for 400 cycles at 2 C(1 C=170 mA g^(-1))with a capacity retention above 99%,and for 600 cycles at 5 C with a capacity retention over 85%.

Boron-doping induced lithophilic transition of graphene for dendrite-free lithium growth

Li metal,possessing advantages of high theoretical specific capacity and low electrochemical potential,is regarded as the most promising anode material for next-generation batteries.However,despite decades of intensive research,its practical application is still hindered by safety hazard and low Coulombic efficiency,which is primarily caused by dendritic Li deposition.To address this issue,restraining dendrite growth at the nucleation stage is deemed as the most effective method.By utilizing the difference of electronegativity between boron atoms and carbon atoms,carbon atoms around boron atoms in boron-doped graphene(BG)turn into lithiophilic sites,which can enhance the adsorption capacity to Li^(+)at the nucleation stage.Consequently,an ultralow overpotential of 10 mV at a current density of 0.5 mA/cm^(2) and a high average Coulombic efficiency of 98.54%over more than 140 cycles with an areal capacity of 2 mAh/cm^(2) at a current density of 1 m A/cm^(2) were achieved.BG-Li|LiFePO_(4) full cells delivered a long lifespan of480 cycles at 0.5 C and excellent rate capability.This work provides a novel method for rational design of dendrite-free Li metal batteries by regulating nucleation process.

A 3D conducting scaffold with in-situ grown lithiophilic Ni_(2)P nanoarrays for high stability lithium metal anodes

Lithium(Li)metal is the most potential anode material for the next-generation high-energy rechargeable batteries.However,intrinsic surface unevenness and‘hostless’nature of Li metal induces infinite volume effect and uncontrollable dendrite growth.Herein,we design the in-situ grown lithiophilic Ni_(2)P nanoarrays inside nickel foam(PNF).Uniform Ni_(2)P nanoarrays coating presents a very low nucleation overpotential,which induces the homogeneous Li deposition in the entire spaces of three-dimensional(3D)metal framework.Specifically,the lithiophilic Ni_(2)P nanoarrays possess characteristics of electrical conductivity and structural stability,which have almost no expansion and damage during repeating Li plating/stripping.Therefore,they chronically inhibit the growth of Li dendrites.This results in an outstanding Coulombic efficiency(CE)of 98% at 3 mA cm^(-2) and an ultra long cycling life over 2000 cycles with a low overpotential.Consequently,the PNF-Li||LiFePO_(4) battery maintains a capacity retention of 95.3% with a stable CE of 99.9% over 500 cycles at 2 C.

Stable lithium metal anode enabled by a robust artificial fluorinated hybrid interphase

One of the key challenges for achieving stable lithium(Li) metal anode is the construction of the rational solid electrolyte interphase(SEI),but its realization still faces enormous challenges.In this work,a robust artificial fluorinated hybrid interphase consisting of lithium-bismuth(Li3Bi) alloy and lithium-fluoride(LiF) was designed to regulate Li deposition without Li dendrite growth.The obtained hybrid interphase showed the high Li+diffusion rate(3.5 × 10^(-4)S cm^(-1)),high electron resistivity(9.04 × 10^(4)Ω cm),and high mechanical strength(1348 MPa),thus enabling the uniform Li deposition at the Li/SEI interface.Specifically,Li3Bi alloy,as a superionic conductor,accelerated the Li+transport and stabilized the hybrid interphase.Meanwhile,LiF was identified as a superior electron-blocker to inhibit the electron tunneling from the Li anode into the SEI.As a result,the modified Li anode showed the stable Li plating/stripping behaviors over 1000 cycles even at 20 mA cm^(-2).Moreover,it also enabled the Li(50 μm)‖LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(4.4 mA h cm^(-2)) full cell to achieve an average Coulombic efficiency(CE) of 99.6%and a high-capacity retention of 79.2% after 100 cycles,whereas the bare Li anode only exhibited a low-capacity retention of 8.0%.This work sheds light on the internal mechanism of Li+transport within the hybrid interface and provides an effective approach to stabilize the interface of Li metal anode.

Improving Li reversibility in Li metal batteries through uniform dispersion of Ag nanoparticles on graphene

Li metal is the most attractive and promising anode material for next-generation high-energy batteries.However,uncontrolled Li dendrite growth during cycling remains a highly challenging drawback.To solve this problem,silver-coated graphene(Ag/GH)was prepared via a simple liquid-phase reduction method.The effect of Ag/GH on Li deposition behavior was investigated by adjusting the dispersion of Ag nanoparticles(Ag NPs).Subsequently,a composite electrode was fabricated via uniform deposition of metallic Li on Ag/GH.Ag was used as a lithiophilic nucleating agent to ensure uniform deposition of Li and inhibit the growth of Li dendrites on the anode.The prepared composite anode showed a significantly improved performance compared to the unmodified electrode.The symmetric cell comprising this composite electrode exhibited a stable cycling performance with a low hysteresis of~40 mV and a lifetime of>2000 h at a current density of 0.5 mA·cm^(-2).Meanwhile,the discharge capacity reached 0.5 mAh·cm^(-2).In addition,Ag/GH was found to be amenable to large-scale synthesis.Thus,the composite Ag/GH anode exhibited improved performance and the preparation method showed significant potential for application in the manufacture of Li metal batteries.

Polybenzimidazole functionalized electrolyte with Li-wetting and self-fluorination functionalities for practical Li metal batteries

Rough Li plating,low ionic conductivity,and low thermal stability of conventional electrolytes post-primary challenges for achieving reliable high-capacity rechargeable lithium batteries,for which lithiummetal is frequently proposed as themost promising anode material.Conventional low-polarity commercial polypropylene/polyethylene separators fail to support the application of high-energy-density Li anodes due to their rigid physicochemical properties and the high reactivity of Li metal,leading to fatal dendrite formation and vigorous exothermic reaction with electrolytes.Herein,we develop a Li-wetting,flame-retardant binary polymer electrolyte by functionalizing poly(vinylidene fluoride)(PVDF)separators with nonflammable polybenzimidazole(PBI)to build safe room-temperature solid-state electrolyte membranes.A dendrite-free LiFePO4 cell with the solid polymer electrolyte(SPE)delivers a discharge capacity of 127 mAh g^(-1) at 25℃ with a capacity retention of 87.5%after 500 cycles at 0.5℃(0.15 mA cm^(-2)).Phase-field simulations and density functional theory calculations demonstrate that the negatively charged benzimidazole chains of PBI own superior affinity to lithium bis(trifluoromethanesulfonyl)imide(LiTFSI),and shares overlapping electron density with Li anode,giving rise to accelerated Li^(+)conduction at room temperature and uniform Li electrodeposition at the electrolyte/Li metal interface.The SPE is also flame-retardant since heat-resistant polytetrafluoroethylene and a dense,heat-blocking graphitized carbon layer are formed in intense heat throughdehydrogenation/fluorination of PVDF under the catalysis of Lewis base imidazole rings and the decomposition of benzimidazole rings in PBI.No such fire-resistant mechanism is ever reported in conventional electrolytes.