Study On Fine Interfacial Structure Modulation Of Lithium Metal And Introduction Of High Fluorine Components To Inhibit Lithium Dendrites

Due to the extremely high theoretical specific capacity(3861 m Ah/g)and the lowest electrochemical potential(-3.04 V vs SHE),the lithium(Li)metal has been considered to be an ideal anode material for next generation of high energy battery.Thus,the Li metal batteries(LMBs)based on Li metal anode have received more and more attention.However,the consecutive and uncontrollable growth of Li dendrites virtually restrain the development of LMBs.The formation of Li dendrites could aggravate the consumption of electrolyte and Li moieties,leading to electrochemical performance fading of LMBs.And it may even penetrate the separator,causing a safety hazard such as thermal runaway.Furthermore,the volume change of Li metal during deposition/stripping would lead to the breakage of intrinsic unstable solid electrolyte interface(SEI)layer and the fragmentation of lithium dendrite,which would result in the accumulation of“dead Li”at the interface,the decrease of Coulombic efficiency(CE)and even the failure of cells.Therefore,it is essential to effectively inhibit dendritic growth and improve the stability and safety of Li metal anode for the realization of high specific energy LMBs.Herein,we have significantly improved the interfacial stability of Li metal anode and effectively inhibit the Li dendrite growth by regulating the deposition behavior and kinetics of Li metal at the anode/electrolyte interface to achieve refined modulation of Li metal interfacial structure and by introducing rich-F compounds to regulate the composition and structure of SEI layer.The main work includes:(1)An ultrathin polydopamine(PDA)layer was coated on the Cu current collector through a rapid polymerization and deposition of dopamine trigged by CuSO₄/H₂O₂ to modulate the deposition kinetics and nanostructure of Li metal at the anode interface,therefore effectively inhibiting the growth of Li dendrites.The high binding energy(>3e V)between the abundant functional groups(catechol,amine and imine)of PDA and Li ions endows PDA@Cu current collector with superior lithiophilicity.The interaction between PDA and Li ions could reduce the nucleation overpotential,homogenize the Li-ion flowing and Li-mass electroplating,and enhance the charge-transfer kinetics of Li ions at anode interface,thereby improving the interfacial stability of the Li metal anode and achieving more stable cycling performance.The asymmetric cell based on PDA@Cu current collector can stabilize for at least 300 cycles with high CE(98%)and low voltage polarization(?20 m V)at current density of 1 m A/cm².Even at higher current densities of 5 and 10 m A/cm²,the cycling stability for PDA@Cu electrode can still be maintained for 180 and 100 cycles,respectively.And the PDA layer can regulate the deposition morphology of Li metal.Under the influence of PDA,the nanostructure of Li metal evolve from initial column-like Li grains to cross-linked vertical Li nanosheets and then to dense Li deposition layer with reduction of nanosheets size and porosity shrinkage.It is found that robustness heterogeneity of Li metal is highly related to the dynamic evolution of deposition morphology of Li metal.(2)The dual modulation strategy of consecutive nucleation and confined growth of Li metal was realized by using the metal-organic-framework(MOF)derivative porous structure with in-built lithiophilic Au or Co O_x nanoparticles to effectively alleviate the volume expansion and dendritic growth of Li metal.Firstly,The lithiophilic 3D c-Au@ZIF-8 material with core-shell structure was obtained via etching of Au@ZIF-8 with in-built Au nanoparticles by tannic acid(TA)and following carbonization,which enables the induced nucleation and confinement modulation towards Li plating.Due to the excellent lithiophilicity of Au,these Au nanoparticles can serve as heterogeneous nucleation sites of Li deposition,thus eliminating the nucleation overpotential and promoting the inward injection of Li metal into the abundant cavities in host.The 3D carbon shell with high mechanical stability can further protect the Li metal deposited inside,which substantially alleviates the volume change of Li metal and the formation of dendritic or dead Li.Such modulation is favorable for the interfacial stability of Li metal anode.As a result,the asymmetric cell with c-Au@ZIF-8 host exhibits an enhanced cycling stability of 430 cycles at 1 m A/cm²and even 210 cycles at 10 m A/cm².Its symmetric cell enables a prolonged lifespan over1200 h with low voltage polarization(<25 m V).Benefiting from the dual effects of c-Au@ZIF-8,the Li anode surface is smooth and flat without Li dendrites after cycling.In addition,the induced Li deposition via lithiophilic nanoparticles can be further extended to conversion-type metal oxides.We synthesized the 3D porous framework harnessed with cobalt oxide nanoparticles through partially etching ZIF-67 by TA,which was applied to modulate the Li metal deposition on the anode interface.The cobalt oxide can react with Li metal,endowing with good lithiophilicity.Therefore,the cobalt oxide nanoparticles can behave as pre-planted seeds to induce selective deposition of Li metal inside the 3D porous host.Such 3D host embedded with cobalt oxide nanoparticles can not only reduce the nucleation overpotential,but also alleviate the volume expansion of Li metal.At the current density of 1 m A/cm²,its asymmetric cell can maintain 310 cycles.And it enables stable cycling performance for 150 cycles at much higher current density of 10 m A/cm².Furthermore,the symmetric cell displays a superior cycling stability of 800 h with narrow voltage hysteresis below 25 m V.The combination of 3D hollow/porous structure and lithiophilic heterogeneous nucleation sites significant inhibits the volume expansion and dendritic growth of Li metal,and improves the cycling stability of Li metal anode.(3)The artificial interfacial layer composed of Sr metal,Li F and Sr F₂ was formed in situ by the addition of strontium trifluoroacetate(Sr(TFA)₂)to the electrolyte,which significantly improved the interfacial stability of Li metal anode.As an electrolyte additive,Sr(TFA)₂ can react with Li metal to form metal Sr,which can alloy with Li metal to enhance the conductivity of SEI layer and promote the migration of Li ions.The increased content of Li F,deriving from F-rich anion,can not only improves the stability of SEI layer,but also enhances the stability of the Li-Sr alloy phase.Moreover,the superficial Sr metal would be fluorinated into Sr F₂.The coexistence of Sr F₂ and Li F on the surface can jointly protect the alloy phase from further fluorination or corrosion by electrolyte,which can improve the stability of the inner alloy phase of SEI layer.Due to the synergistic effect of Sr metal,Sr F₂ and Li F,the stability of anode interface has been greatly improved.Therefore,its Li-Cu asymmetric cell and Li-Li symmetric cell exhibit better plating/stripping behavior.The asymmetric cell with addition of Sr(TFA)₂ can be stabilized for 450 cycles at current density of 0.5 m A/cm².And the symmetric cell shows highly stable long-term cycle performance for 1800 h at 0.5m A/cm².Even at high plating capacity of 6 m Ah/cm²(2 m A/cm²),the symmetric cell enables a stable plating/stripping behavior over 400 h.(4)We have achieved the dual stabilization effect of anode interface and electrolyte by directly constructing an artificial F-rich interfacial layer composed of 1H,1H,2H,2H-perfluoro-1-decanol(HDFD)on Li metal surface,thus significantly enhancing the cycling stability of Li metal anode under ultrahigh current density and capacity,and laying the foundation for ether-based electrolyte to match high-voltage cathode material.The HDFD layer was coated on the Li metal surface by low-temperature melting-cooling method.The interfacial HDFD layer can not only induce the formation of Li F-rich SEI layer to improve the interfacial stability and inhibit dendritic growth,but it can also be partially dissolved in the electrolyte to improve the electrochemical window of the Li TFSI-DOL/DME electrolyte.Benefiting from the synergistic stabilization of interface and electrolyte,the HDFD@Li metal achieves an ultralong cycling lifespan of 3000 and 2000 h at unprecedented high current density of 30 and 50 m A cm^-2 with current density of 5 m Ah cm^-2,respectively.And it can be deeply cycled at 30 m A cm^-2 with an ultrahigh capacity of 30 m Ah cm^-2 for 3000 h.More importantly,the enhanced electrochemical window of Li TFSI-DOL/DME electrolyte,which increases to 4.7 V by dissolved HDFD,enables the ether electrolyte to match high-voltage Li Ni_1/3Co_1/3Mn_1/3O₂(NCM111)cathode.The full cell coupled with NCM111 cathode and ether electrolyte achieves an improved cyclability over 200 cycles at 0.5 C.