Conjugated phthalocyanine-based framework as artificial SEI for over 400 Wh kg^-1 lithium-metal battery

High-voltage lithium-metal batteries (HVLMBs) are appealing candidates for next-generation high-energy rechargeable batteries, but their practical applications are still limited by the severe capacity degradation, attributed to the poor interfacial stability and compatibility between the electrode and the electrolyte. In this work, a 2D conjugated phthalocyanine framework (CPF) containing single atoms (SAs) of cobalt (CoSAs-CPF) is developed as a novel artificial solid-electrolyte interphase (SEI) in which a large amount of charge is transferred to the CPF skeleton due to the Lewis acid activity of the Co metal sites and the strong electron-absorbing property of the cyano group (-CN), greatly enhancing the adsorption of the Li⁺ and regulating the Li⁺ distribution toward dendrite-free LMBs, which are superior to most of the reported SEI membranes. As a result, the Li||Li symmetrical cell with CoSAs-CPF-modified Li anodes (CoSAs-CPF@Li) exhibits a low polarization with an area capacity of 1.0 mAh cm^-2 over 3500 h. The LiFePO₄ (LFP) ||CoSAs-CPF@Li (LFP: 20 mg cm^-2) delivers an ultra-long cycling life of ≤1000 cycles with a high capacity retention of 98.6%. Remarkably, the high-voltage LiNi_0.8Co_0.1Mn_0.1O₂||Li@CoSAs-CPF (NCM811: 10 mg cm^-2) demonstrates a long cycling life of >800 cycles with a high capacity retention of 80%. Meanwhile, in situ ultrasonic transmission technology confirms the admirable ability of artificial CoSAs-CPF SEI to stabilize the Li-anode interface in pouch cells during cycling. Remarkably, the NCM811||Li@CoSAs-CPF pouch cell exhibits an energy density of 421 Wh kg^-1 and keeps 130 cycles with a low electrolyte/capacity ratio of 2.5 g Ah^-1. The strategy of constructing the CoSAs-CPF-reinforced Li anode provides a promising direction for high-energy-density HVLMBs with long cycling stability.