Study On The Charge-discharge Behavior And The Interface Of Metal Anodes(Lithium/Zinc) In Organic Electrolytes

The development of energy storage batteries is of great significance for society to achieve the green and low-carbon transition.Due to the low theoretical specific capacity of the graphite anodes,the improvement of the energy density of lithium-ion batteries is restricted.Metal anodes,which have the advantages of high theoretical specific capacity and low electrochemical potential,are regarded as the ideal anode candidates.However,the metal anodes suffer from severe challenges,such as dendrite growth,interface instability,and large volume change during cycling,resulting in low Coulombic efficiency and short cycle life.Meanwhile,the understanding of the electrode-electrolyte interface and the deposition/stripping behavior of metal anodes is still insufficient,which seriously hinders the development of metal batteries.Lithium metal anode is a hot spot in the research of metal anodes.Because of the high reactivity,a solid electrolyte interphase(SEI)will be formed on the surface of lithium metal,whose properties have a great impact on the deposition/stripping behavior of lithium metal.Moreover,the electrolyte directly determines the structure and composition of SEI,so the investigation of the interfacial properties of lithium metal and its deposition/stripping behavior in different electrolytes is helpful to understand the structure-function relationship.In addition,zinc metal anode is considered as one of the most promising metal anodes.However,the development of zinc metal anode in conventional aqueous electrolytes is impeded by the severe interfacial side reactions,dendrite growth,and hydrogen evolution,and there is no indepth understanding of the growth mechanism of zinc metal.To solve the above problems,this thesis takes lithium metal anode and zinc metal anode as the research objects,and uses atomic force microscopy(AFM)and other various characterization techniques to study the charge-discharge behavior and the interfacial properties of metal anodes in different electrolyte systems.The main research works are as follows:1.AFM is used to study the correlation between the reversibility of lithium metal anode and the deposition morphology in the selected four electrolyte systems.Since the specific surface area of particle-like deposits is much smaller than that of strip-like deposits,the amount of active Li consumed by the parasitic side reactions between Li and the electrolyte are greatly reduced,which facilitates higher CE.Moreover,the processes of SEI formation and Li deposition in both carbonate and ether electrolytes were observed in situ by electrochemical AFM.The results indicate that the SEI formed in these two electrolytes vary widely.Compared with the thin and loose SEI in the carbonate electrolyte,the SEI formed in the ether electrolyte is thicker and uniform,which can promote lithium metal to grow into spherical particles,therefore achieving high Coulombic efficiency.The results reveal the important influence of the properties of SEI on the lithium metal deposition behavior.2.The lithium anode in lithium-sulfur batteries suffers from more complicated interfacial reactions which are caused by the shuttle effect of soluble polysulfides formed during cycling.And the cycling of lithium anode in lithium sulfur batteries starts from stripping.Therefore,we systematically studied the stripping behavior of lithium metal in the lithium polysulfide-containing electrolytes.It is found that the lithium polysulfide can aggravate the uneven stripping of lithium metal,which shows the clear contributing effects toward the failure of the lithium metal anode.By analyzing the test results including AFM mechanical test,it is revealed that an uneven lithium sulfide(Li2S)passivation layer is formed on the lithium surface because of the chemical reaction of lithium metal and lithium polysulfide,and due to the low ionic conductivity of Li2S,lithium dissolution preferentially takes place at areas without Li2S deposition,thus leading to the nonuniform stripping.When a carbon nanotube(CNT)interlayer is used on the cathode side to suppress the shuttle effect of lithium polysulfides,the nonuniform stripping phenomenon is effectively mitigated and the cycling performance of lithium sulfur battery is enhanced.3.A low-cost and green nonaqueous electrolyte,2 M zinc acetate(Zn(OAc)2)dimethyl sulfoxide(DMSO),is developed in this work.Due to the good intrinsic stability of Zn metal in the aprotic solvent DMSO,and the Cu-Zn alloy in situ formed on the Cu which can reduce the diffusion barrier of Zn atoms and induce the uniform and dense deposition of Zn metal,a highly reversible zinc metal anode is realized.In situ EC-AFM is used to directly track the morphological evolution of Zn plating/stripping at the nanoscale,revealing the layer-by-layer growth and the edge-tocenter stripping behavior of Zn metal.Moreover,the Zn‖Mo6S8 full cells exhibit excellent cycling stability,demonstrating the application potential of this electrolyte.