image: (a) Schematic illustration of MSAs-CPF (M = Fe, Co, Ni, Cu). (b) Schematic illustration of the fabrication processes for MSAs-CPF@Li and Li deposition processes for MSAs-CPF@Li in lithium metal batteries. (c) Binding energy of Li atoms on MSAs-CPF and MSAs-CN-CPF. d) The migration energy barriers of Li on CoSAs-CPF, NiSAs-CPF, and CuSAs-CPF.
Credit: ©Science China Press
A two-dimensional conjugated phthalocyanine framework containing single cobalt atoms (CoSAs-CPF), with highly atomically uniformly dispersed of cobalt Lewis’ acid sites, excellent electron-withdrawal properties, good charge-transferring ability, and stretchable flexibility, is used for modified SEI and became an ideal platform for the construction of high-performance HVLMBs. As expected, the capacities, rate capabilities, and especially the cyclic stability of the batteries were significantly enhanced, superior to most of the reported SEI membranes.
Further investigation indicates that the mild synthetic route effectively reduces the agglomeration of MSAs-CPF and guarantees the utilization of the metal sites. More importantly, the Lewis acid activity of the MSAs sites and the strong electron-withdrawing property of the cyano groups promoted a large amount of charge transferred to the CPFs skeleton, which effectively enhanced the adsorption of Li+ and suppressed Li dendrite. Meanwhile, MSAs-CPF-based flexible pack batteries also show longer operating life and higher capacity retention. By calculation, it is found that CoSAs-CPF shows a significant advantage in the adsorption and migration process of lithium ions, which keeps a high consistence with the subsequent experiments.
A Li||Li symmetrical cell with CoSAs-CPF modified Li-anodes exhibited a low polarization with an area capacity of 1.0 mAh cm−2 for 3500 h. The CoSAs-CPF anode endows the high-loading LFP cathode (20 mg cm–2) with a long cycling life of up to 1000 cycles. Notably, the NCM811|CoSAs-CPF@Li cells can deliver a stable cycling life of 800 and 450 cycles with a loading of 10 mg cm–2 and 20 mg cm–2, respectively.
Given the diversity of CPF structures, chemically modifiable functional groups on organic linkers, and functional modulation of CPFs properties, it is believed that the concept of functionalized CPFs-based artificial SEI will push forward the future development of high-energy-density HVLMBs.