Endosymbiotic lithium nitride/cellulose layer prolongs the cycle life of lithium metal negative electrode
A research team led by Li Xianfeng and Zhang Hongzhang at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made new progress in the research of lithium-metal batteries with long cycle life. The findings are published in the German Journal of Applied Chemistry.
Lithium metal has the characteristics of high theoretical capacity density and low electrochemical potential, so it is an ideal negative electrode for a high energy density battery. However, due to the high activity of lithium metal, it is easy to have uncontrollable side reactions with traditional electrolytes, resulting in poor chemical and mechanical stability of the solid electrolyte interface layer (SEI). On the one hand, the repeated fracture of the SEI during the cycle will accelerate the formation of dead lithium and irreversible loss of active lithium/electrolyte. On the other hand, the mechanical properties of solvent-induced SEI are poor, which is not enough to inhibit the growth of lithium dendrite, resulting in dendrite piercing the membrane and battery short circuit.
In this study, the team introduced novel additive nitrocellulose into the electrolyte to construct an endosymbiotic lithium nitride/cellulose bilayer SEI (ES -- DSEI) for use in lithium-metal batteries. ES-DSEI has a unique advantage in the protection of lithium metals. Nitrocellulose reacts with lithium first and builds a polymer/inorganic layer on the lithium surface in one step. The flexible polymer layer of the outer layer can adapt to the volume change of lithium metal during the cycle, and its strong adhesion can also inhibit the peel of the inner layer of inorganic substances. The inorganic layer of the inner layer has the characteristics of high mechanical strength, which can inhibit the growth of dendrite, and the crystalline lithium oxide and lithium nitride layers are also conducive to lithium-ion transport. Using density functional theory simulations, the team demonstrated that nitrocellulose has a lower minimum unoccupied molecular orbital energy compared to lithium anions and solvents. In addition, nitrocellulose groups are more likely to react with lithium metal, forming inorganic species such as LiO2 in the inner layer near lithium, while its main chain is tightly adsorbed on the outer layer of distant lithium by Li-O bond. Compared with the liquid phase without nitrocellulose, the cycle life of the lithium anode in the electrolyte containing nitrocellulose as an additive was increased by 1 time. This work provides a new idea for the design of long-life lithium metal anode.
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