Investigation Of The Temperature Effects On The Deposition Behaviors Of Lithium Anode

Metallic lithium?Li?has been regarded as the most promising anode for next-generation secondary Li metal batteries due to its lowest reduction potential?-3.04 V?,small density(0.59 g cm^-3)and highest theoretical specific capacity(3860 mAh g^-1).Previous studies have shown that factors such as electrolyte systems,electrolyte additive current density,deposition capacity are closely related to the Li deposition behaviors.However,Temperature as a key kinetic parameter could affect any electrochemical/chemical reaction processes that may occur during lithium deposition including electrolyte decomposition,electrolyte-Li interface formation,lithium nucleation and growth,etc.So far the influence of temperature on the Li deposition kinetics under different electrolyte systems,current density and deposition capacity has not been systematically studied.Therefore,two typical electrolyte systems?ester electrolyte 1 M LiPF₆ EC/DMC/EMC and ether electrolyte 1 M LiTFSI DOL/DME+1 wt%LiNO₃?was specially selected to further investigate the unique nucleation and growth behaviors of lithium within temperature ranging from-20 ^oC to 60 ^oC The relationships between temperature and coulombic efficiency upon Li plating/stripping was explored in details,and the universality of this relationship was further verified even different current densities and deposition capacities were set.Finally,Scanning Electron Microscope,Cyclic Voltammetry,X-ray photoelectron spectroscopy,Electrochemical Impedance Spectroscopy and other characterization techniques were employed to elucidate the possible reasons underneath for the performance differences under high and low temperature.Results demonstrate that:?1?Li shows similar deposition behavior in both ester and ether electrolytes where a smaller nucleation density plus a larger nucleate radius are achieved due to a higher temperature;?2?As current density rises,the initial coulombic efficiency?ICE?increases at a high temperature of 60 ^oC and decreases at a low temperature of 25 ^oC.With the increase of deposition capacity,the ICE and cycling stability of Li-Cu cells tested at high temperature are much superior to that at low temperature though ICE of cells at both high and low temperature gradually increases;?3?the main reason for the performance divergence in different temperature may be related to the varied chemical composition and mechanical properties of SEI film.As the temperature increases,a relatively larger amount of electrolyte participates in the initial decomposition for SEI formation,resulting in a more dense and compact SEI film.owing to much increased reaction activity and ion transfer.Besides,the SEI formed under high temperature possesses a comparatively better ion conductivity and mechanical flexibility enabled by the higher proportion of ionic-conductive and flexible components within the SEI.These properties contribute to the good stability of SEI layer which favors the mitigation of Li/electrolyte consumption,leading to a better ICE and lifespan under high temperature.