Study On The Regulation Mechanism Of Lithium Deposition Interface Based On Self-assembled Molecular Interface Modification

With the rapid development of smart electric devices,the development of safe and reliable high-energy-density lithium batteries is of great importance to the development of smart electric devices.The current lithium-ion battery technology cannot meet the growing energy density requirements of smart electric devices.Due to their ultra-high energy density,lithium metal batteries have become the preferred energy supply device for future high-energy-density requirements.By changing the structural system of lithium metal batteries,their energy density can be further improved.A lithium battery with a non-lithium negative electrode structure,using the positive electrode material as a source of lithium and a current collector without active materials as the negative electrode,can further improve the energy density of the battery.However,this type of lithium battery has inherent disadvantages,with main challenge being the formation of dendritic lithium metal during the charging and discharging cycles due to various physical and chemical reactions.To address these problems,this paper significantly improves the stability of the lithium deposition interface from the perspective of stabilizing the negative solid electrolyte interface（SEI）by grafting a layer of regularly arranged polar functional group molecules on the collector using a magnetron sputtering process as well as a simple reagent immersion method.The main study is divided into two aspects as follows:Firstly,a preliminary verification of the improvement of the interfacial stability of lithium metal deposition by a collector containing molecules modified with polar functional groups has been carried out.By modifying the collector at the nanoscale,the electrochemical performance of the cell can be greatly enhanced while maximising the energy density of the cell.The SiO_x-APTES collector can be obtained by grafting a layer of APTES molecules on the surface of copper foil by magnetron sputtering and a simple immersion method.First-principles calculations show that APTES molecules can promote the decomposition of fluoride in the electrolyte during the initial cycle of the cell,resulting in the formation of a lithium fluoride-rich SEI layer on the deposited lithium metal surface,and the grafted molecules can reduce the lithium nucleation overpotential on the collector surface to stabilize the lithium deposition interface and reduce lithium dendrite formation.With the SiO_x-APTES collector as the working electrode and Li Co O₂（LCO）as the positive electrode,the capacity retention rate reached over 88.8%after 150 charge/discharge cycles at 0.2 C.Secondly,the effect of different polar functional group molecules on the lithium deposition interface is compared,and the grafting of carboxylated polar functional group molecules can further stabilize the lithium deposition interface,which can be better used in future lithium-free anode battery systems.The succinic acid molecule containing the carboxyl group was grafted on the collector（SiO_x-COOH collector）and the succinamic acid molecule containing the amino group was grafted on another collector（SiO_x-NH₂collector）by the same method.The prepared collectors were assembled into half cells,and after the initial charge/discharge cycles,the SiO_x-COOH collector had a higher Li F content on the surface,formed a more stable SEI,and had a flatter and denser surface with fewer voids at the lithium deposition interface.The full cell with the SiO_x-COOH collector and LFP as the anode still had a capacity of 135.4m Ah/g after 200 cycles at 0.5 C with a capacity retention rate of 86%.The above experiments demonstrate the good prospects of polar molecule-modified collectors in practical applications.