Elongating the cycle life of lithium metal batteries in carbonate electrolyte with gradient solid electrolyte interphase layer

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Artificial solid electrolyte interphase (SEI) protective layer has been widely applied to protect lithium (Li) metal anode. However, few attentions have been paid to interface contact between artificial SEI and Li metal. Here, we develop a polymer-inorganic gradient SEI (PIG-SEI) layer on Li, which consists of the outer polymer rich layer of PEGDA-co-VC and inner inorganic nanoparticles rich layer of LiF, Li3N and Cu. The PIG-SEI protected Li metal anode can not only improve interface contact between PIG-SEI layer and Li metal and the Li-ion conductivity of SEI layer but also increase the flexibility and mechanical strength. As a result, the PIG-SEI protected Li metal anode enable Li || Li symmetric cells to maintain a stable overpotential of 20 mV at a capacity of 2 mAh cm−2 over 2500 h, and enable Li || LiFePO4 and Li || LiNi0.8Co0.1Mn0.1O2 cell to capacity of 122 mAh g−1 and 123 mAh g−1 at 0.5 C for 500 cycles under lean carbon-ate-based electrolyte (Li || Li: 5.0 µL mAh−1, Li || LiFePO4 : 14.3 µL mAh−1, Li || LiNi0.8Co0.1Mn0.1O2 : 14.4 µL mAh−1). It is believed that our gradient-layer protected Li metal anode opens up new idea for the practical applications of next-generation high-energy-density Li metal batteries.