Application Of Porous Current Collectors Prepared By Phase Inversion Method In Lithium Metal Batteries

Lithium(Li)metal has an ultra-high theoretical specific capacity(3860 mA h g-1)and the lowest redox potential(-3.04 V,vs.SHE),so it is considered to be the optimal anode material for high-energy-density batteries.However,problems such as side reactions,Li dendrite growth and large volume change,severely hinder its practical application.Designing electrode structures such as using porous current collectors is an effective strategy to inhibit dendritic growth and stabilize Li metal anodes.The porous current collector can accommodate the deposited Li,restrict the formation and growth of dendrites,relieve volume change,and reduce the practical current density on the surface.However,porous current collectors reported are mainly composed of random pores and have a high tortuosity.Li metal prefers to deposit on the top surface and has poor uniformity.Based on the study of the mechanism of dendrite growth and the principle of SEI films formation,this paper takes various aspects into consideration,such as optimizing the pore structure of the current collector,reducing the practical current density of the surface,improving the surface lithiophilicity as well as reinforcing the SEI film,and finally design an effective electrode structure to inhibit Li dendrite growth and promote uniform deposition.The main research content is divided into the following five parts:1)The second chapter adopted first principles to calculate the adsorption energy of Li on the surface of various current collector and modification materials such as Cu,Ni,carbon,etc.It was found that the adsorption energies of Li on the surfaces of Cu,Ni and C were-0.46,-0.87 and-1.15 eV,respectively,and the adsorption energy of Cu2O,CuO,NiO,ZnO,Ag and Au were-2.92,-3.67,-3.44,-3.24,-2.03 and-2.53eV,respectively.After systematic comparison,Cu and Ni were selected as the substrate materials of current collectors,and Cu2O,CuO and NiO were selected as lithiophilic modification materials.2)The third chapter prepared porous Cu by a phase inversion method,which serves as a current collector for Li metal anode.It can be seen that,when Li metal was first deposited,the Li metal layer was relatively uniform and dense,and there was still no dendrite after 30 cycles.In a Li-Li symmetric battery,porous Cu can maintain a stable voltage and low polarization within 2200 hours at a capacity of 1 mA h cm-2 and a current density of 2 mA cm-2.In the Li-Cu half cell,the porous Cu exhibited a coulombic efficiency as high as 97.6%under the conditions of 2 mA h cm-2 and 2 mA cm-2.It could be found that the interfacial resistance and charge transfer resistance of porous Cu decrease with cycling.The full cell with porous Cu had a capacity retention rate of 89.9%after 200 cycles at 2C,and a discharge capacity of 65 mA h g-1 at 10C,promising for the practical application of Li metal anodes.3)In the fourth chapter,on the basis of the porous Cu current collector prepared by phase inversion method,an oxide layer was modified on the surface(denoted as CuOx@Cu)by thermal oxidation method,to study the performance improvement of Li metal battery.CuOx has excellent "lithiophilicity" according to the calculations,which can significantly reduce the nucleation overpotential of Li.Meanwhile,the Li2O formed by the reaction with Li can reinforce the SEI films and homogenize Li ion flow.Therefore,the modified CuOx@Cu current collector had a further improvement in performance compared to the original porous Cu.In half cell,CuOx@Cu showed a Coulombic efficiency as high as 98.8%for 525 cycles under 1 mA cm-2,while the coulombic efficiency of the original porous Cu fell below 80%at 300 cycles.CuOx@Cu exhibited lower polarization and longer lifespan in symmetric cell,and both the interfacial impedance and charge transfer impedance were reduced.In full cell,CuOx@Cu also greatly enhanced cycling stability and rate capability,better than the unmodified porous Cu.4)The fifth chapter prepared porous Ni current collector by phase inversion tape casting method,and hydrothermally synthesized NiO nanoarrays on the surface,and studied the electrochemical performance of the corresponding cells.Both Ni and NiO have good "lithiophilicity" according to calculations,which can reduce the energy barrier for Li nucleation.The nanoarray can also greatly increase the specific surface area and nucleation sites.Meanwhile,the Li2O generated by the reaction with Li can enhance the Li ion conductivity of the SEI films and inhibit the growth of dendrites.Therefore,the current collector exhibited excellent performance in Li metal batteries,with a nucleation overpotential as low as 3 mV;under the conditions of 4 mAh cm-2 in the half-cell mode,the coulombic efficiency of 180 cycles was as high as 99.1.%;the cycle life of the symmetric cells was up to 2000 hours;in full-cell mode,it had excellent cycling stability and rate performance,which were better than unmodified porous Ni and commercial Cu foil current collector.5)The sixth chapter explored the application of molten Li infusion method to pre-store Li in a porous current collector.When molten Li contacted with lithiophilic CuOx@Cu,Li would quickly fill the inner space to realize the controllable preparation of the composite anode.The mass specific capacity and volume specific capacity of the prepared composite anode were about 550 mA h g-1 and 1480 mA h cm-3,respectively,both higher than those of graphite.In symmetric-cell mode,the composite anode had a lifespan of up to 850 hours,which was significantly improved compared to Li foil.Even in ester electrolytes,it still had good stability.In full cell,the capacity retention after 1000 cycles at 5C was 90.1%,thus promoting the commercialization of Li metal batteries.