Research On Modified Copper Current Collector For High Performance Alkali Metal Battery

Direct utilization of Li/Na metal anode,instead of carbon or alloy-based anode,is highly desired in Li/Na-ion batteries mainly because of its low operating potential and high capacity.Nevertheless,the intractable hurdles of Li/Na dendrite growth and low Coulombic efficiency during repeated plating/stripping process hinder the practical use of Li/Na metal anode for high-energy batteries.Achieving uniform nucleation and constructing a stable and uniform solid electrolyte interphase（SEI）are two effective strategies to address these issues,and it is of practical importance to realize it on commercial Cu current collector as Cu foil is the commonly adopted anode current collector in battery industry.In this paper,facile ways including building lithiophilic surface layers and artificial protective layers are applied to Cu current collector to realize improved Li/Na plating/stripping behavior,providing a new opportunity to stabilize Li/Na metal anode.A nanostructured Ag lithiophilic layer is constructed on Cu foil via an electroless plating process for Li metal current collector.The deposition of lithiophilic Ag particles that are homogeneously distributed on Cu foil can reduce the nucleation overpotential of the electrode,ensuring uniform Li nucleation and subsequent smooth Li plating.As a result,stable cycle stability up to 360 h at a current density of 1 mA cm^-2 and high average Columbic efficiency of 94.5%for100 cycles at 1 mA cm^-2 are achieved on modified Cu current collector.Moreover,Li@CuAg||LiFePO₄ full cells exhibit good cycling performances and low polarization voltage.Dendrite-free Na deposition/stripping can be achieved via constructing a protective PVDF layer on Cu current collector through a facile and scalable doctor blade coating technique.As a result,PVDF@Cu current collector exhibits a stable cycling lifetime for 1200 h with a small overpotential（³5 mV）at 1 mA cm^-2,which is 6 times longer than the bare Cu current collector（²00 h）.Furthermore,PVDF@Cu current collector delivers a high average CE of 99.91%for 2000 h at 1mA cm^-2.The excellent electrochemical performances of PVDF@Cu current collectors are found to arise from the formation of a stable solid electrolyte interphase consisted of Na₂O₂ with high mechanical modulus and rich NaF with a fast Na ion migration（based on the defluorination reaction between PVDF and Na）,which synergistically suppresses Na dendrite growth.An inorganic-organic PNF protective layer where flexible PVDF matrix can endure volume change and NaF particles provide improved mechanical strength and Na⁺diffusion conductivity against dendrite growth is constructed on Cu current collector via a simple blade coating method.Based on these synergetic roles,a prolonged cycle life for more than²100 h at 50%of discharge of depth（DOD）is realized at 1 mA cm^-2,which is longer than tenfold the Cu current collector（¹70 h）.Furthermore,Cu current collector with PNF protective layer also delivers stable voltage profile at high current density(5 mA cm^-2)and ultrahigh DOD（80%）.