Study On Functional Polymer Modified Cu Current Collector To Suppress Lithium Dendrite Of Lithium Metal Secondary Battery

Nowadays,lithium secondary batteries have been applied to all aspects of people's lives.However,with the demand for lithium secondary batteries with long endurance,the development of lithium-ion batteries has been in a bottleneck and it's urgent to develop higher energy density lithium metal secondary batteries.Lithium metal is considered as the ultimate anode candidate due to its highest theoretical capacity(3860mAh g^-1),extra-low theoretical density(0.534 g cm^-3)and the lowest electrochemical potential?-3.04 V relative to the standard hydrogen electrode?.However,there are still many problems in applying lithium metal anode to practical applications.Such as the safety and efficiency problems of cells caused by the uneven growth of lithium dendrite and infinite volume expansion,which limits its application in the field of energy storage.In order to solve these problems in lithium metal batteries,functional polymer layer was introduced into Cu current collector to suppress lithium dendrite and stabilize lithium anode.The main research contents are as follows:Firstly,a functional polydopamine?PDA?layer inspired by nature is introduced to the surface of Cu foil,which is used as a current collector to suppress lithium dendrite here.During depositing of lithium,lithium ions will firstly react with the hydroxyl groups of PDA layer,yielding uniformly distributed lithium complexing carbonyl groups which can work as nucleation sites and is favorable for uniform and stable deposition of lithium metal on the current collector,thus effectively suppress dendrite formation and growth.As a result,lithium metal batteries with PDA modified current collectors exhibit high coulombic efficiency of above 97%for 100 cycles at 0.5 mA cm^-2 and its interface impedance is small,and the interface impedance is about 89.1?after one cycle?original Cu foil:195.7??.The Li/Li symmetric cells show more than 800 h stable repeated lithium plating and stripping.The LiFePO₄/Li batteries with the modified current collectors show extended cycle life?more than 150 cycles?.This work provides a novel way to address the problems of lithium metal anode.Secondly,a robust and stable inorganic-organic hybrid interface layer is proposed to suppress lithium dendrite.The advantages of using silane-treated alumina nanoparticles?ST-Al₂O₃?as the inorganic hosts are as follows:?1?Al₂O₃ can work as a physical barrier for lithium dendrite growth due to its high Young's modulus,which will suppress the dendrite growth.?2?Al₂O₃ as a Lewis acid can react with lithium salt anions,reduce the lithium salt ion pair and increase the lithium ions conductivity.Polyethylene oxide?PEO?with high ionic conductivity and high stability to metallic lithium is used as a binder between the inorganic particles.High molecular weight PEO has good viscosity and elasticity,which helps to improve the interface properties between the interface layer and the electrode.Also,the flexible of PEO can accommodate the volume change of the electrode during Li plating/stripping.Therefore,a rigid and flexible interface with inorganic particles as main body and polymer as binder is constructed,which can also ensure the transmission of lithium ions.Combining the above advantages,the Li-Cu cells with inorganic-organic hybrid layer modified Cu current collectors exhibit higher coulombic efficiency,the coulombic efficiency remains more than 90%after 120 cycles at a current density of 0.5 mA cm^-2.The electrode morphology of the battery during the cycle was observed by scanning electron microscopy?SEM?.It's obvious that after the introduction of the inorganic-organic hybrid interface layer,the surface of the current collector was extremely flat and dense after 50 cycles,no dendrites can be found.However,the surface structure of the original copper foil was rough and its thickness varies greatly.According to electrochemical impedance test,after 10 cycles of Li plating/stripping,the cells with inorganic-organic hybrid layer modified Cu current collectors have smaller changes in interface impedance than the cells with pristine Cu foils.?inorganic-organic hybrid layer modified Cu current collectors:from 172.5?to 136.9?;pristine Cu foils:from196?to 150.5??.It also indicates that inorganic-organic hybrid layer can effectively suppress lithium dendrite growth.