First-principles Study On The Corrosion Of Impurities On Copper Current Collector In Electrolyte For Lithium-ion Batteries

The copper current collector is an important component for lithium-ion batteries,the corrosion of impurities on it in the electrolyte will impact the performance of li-ion batteries.Water,the impurity in electrolyte,will deepen the reaction between Cu and electrolyte and form an oxide surface.LiPF6 is widely used as electrolyte in lithium-ion batteries.It will react with water and produce HF,PF5 and so on.The formed PF5 is a strong Lewis acid.HF will corrode the copper surface,and PF5 may promote the corrosion.The reactions can reduce the performance of lithium ion batteries and affect the utility safety property.However,due to the limitations of experiments,the microscopic mechanism of the corrosion process on the surface of Cu foil is not fully described.Therefore,in this dissertation,the micro reaction mechanism of H2O,HF and PF5 on the surface of Cu foil were analyzed and discussed by the first-principles calculations method based on the density functional theory from the bond,density of states,electron density and energy barrier and so on.The simulation results are expected to provide a theoretical basis for controlling the corrosion of the impurities on lithium ion batteries.The major work and results are as follows:Adsorption and dissociation of H2O on Cu(111)surface were calculated and analyzed.The related geometry,energy barrier,density of states and so on were computed by Dmol3 module of the Materials Studio package.The results indicated that the most stable adsorption sites of H2O on a clean and a pre-adsorbed O atom Cu(111)are both top sites,and H2O preferred the molecular adsorption.The analysis on the density of states showed that the orbital hybridization between O 2p and Cu 3d states is quite strong for H2O adsorption on pre-adsorbed O surface,and the hybridization is weak on the clean surface.The energy barrier for H2O dissociation on the clean Cu(111)surface was 148.54 KJ/mol,while the dissociating energy decreases obviously to 92.73 KJ/mol with the aid of the O atom.This revealed that the pre-adsorbed O atom can promote the dissociation of H2O on Cu(111)surface.The reaction mechanism of HF dissociation on the Cu(111)surface and the effect of biaxial strains on the reaction were studied.The results show that surface energy of Cu(111)surface increases with increasing compressive strain,while the surface energy decreases under the increasing tensile strain.The adsorptions of H,F and HF on fcc site are favorable on Cu(111).The energy barrier for HF dissociation on Cu(111)surface decreases or increases under tensile or compressive strain nearly linearly as the magnitude of strain.Linear fitting processing was implemented in Origin software.The curve is an accurate analytical description of the energy barriers for HF dissociation under the applied strains.The rate coefficient increases along with the strain value increasing.The reaction mechanism of HF and PF5 which are generated by decomposition and reaction of LiPF6 and the impurity of H2O on the Cu(111)surface was studied.The schematic drawing of HF,H2O and PF5 adsorbed on Cu(111)and the changes of the geometric parameters showed that H2O and PF5 can promote the dissociation reaction of HF.The promoting effect of PF5 is greater than that of H2O.When H2O and PF5 exist together,the promotion is further improved.PF5 also has a promoting effect on the physical adsorption of H20 on Cu(111)surface.The energy barriers of HF dissociation on a clean Cu(111)surface and a surface with pre-adsorbed O atom were calculated.It reveals the pre-adsorbed O atom can promote the dissociation reaction of HF.Further analysis of electronic density of states and electron density shows that the chemical bond formed by F atom and Cu atom is ionic bond.According to the bond length and the bond angle of the reaction product,CuF2 molecule is indentified.