Ultra-firm phthalocyanine-based tetragonal covalent organic framework layer @ nano silicon anode for high durability Li-ion battery

The enormous volume change of silicon (Si) leads to pulverization of Si electrodes and continuous growth of solid-electrolyte-interphase (SEI) layers on the Si surface, for which we report a new Si anode material (PMDA-NiPc@Si) with a homogeneous and tetragonal covalent organic frameworks (COFs) coating on the surface of nano-Si particles. COFs with tetragonal structures have higher stability than other structures, which helps to increase the long cycle life of the electrodes. The strong constraining buffering effect of the coating layer can fully inhibit and buffer the volume change of Si nanoparticles during charging-discharging, reduce the consumption of electrolytes and form a homogeneous, stable and robust, LiF- and LiN-rich SEI film, and ultimately improve the rate performance and long-cycle performance. The pre-lithiation of PMDA-NiPc@Si shows a superior lithium ion conductivity that can enhance the lithium ion transport kinetics of silicon electrodes and significantly improve the initial coulomb efficiency (ICE). PMDA-NiPc@Si exhibits excellent specific capacity and cycling performance, with a capacity retention rate of 93.8 % after 100 cycles, which is 2.7 times higher than that of nano-Si. It also offers a high reversible capacity of 654 mAh/g and a capacity retention rate of 80.4 % after 2000 cycles at 5 A/g. The assembled full battery with PMDA-NiPc@Si anode and NCM811 cathode displayed a specific capacity of 175.8 mAh/g with a retention rate of 85.8 % after 100 cycles at 0.2C. The PMDA-NiPc@Si electrode shows only about 44 % of the expansion rate (21.6 to 31.1 μm), which is only 27.3 % of that of the Si electrode. PMDA-NiPc@Si anodes show significantly enhanced electrochemical performance, which will provide novel ideas for the development of high-performance Li-ion batteries.