Lithium (Li) metal is one of the most promising anodes for next-generation energy storage systems. However, the Li dendrite formation and unstable solid-electrolyte interface (SEI) have hindered its further application. Lithium nitrate (LiNO₃) is extensively used as an effective electrolyte additive in ether-based electrolytes to improve the stability of lithium metal. Nevertheless, it is rarely utilized in carbonate electrolytes due to its low solubility. Here, a novel gel polymer electrolyte (GPE) consisting of poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA), poly(ethylene oxide) (PEO) with LiNO₃ additive is proposed to solve this issue. In this GPE, polyether-based PEO serves as a matrix for dissolving LiNO₃ which can be decomposed into a fast Li-ion conductor (Li₃N) in conventional carbonate electrolytes to enhance the stability and Li⁺ conductivity of the SEI film. As a result, dendrite formation is effectively suppressed, and a significantly improved average Coulombic efficiency (CE) of 97.2% in Li-Cu cell is achieved. By using this novel GPE coupled with Li anode and LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532), excellent capacity retention of 94.1% and high average CE of over 99.2% are obtained after 200 cycles at 0.5 C. This work presents fresh insight into practical modification strategies on high-voltage Li metal batteries.

Graphite as a positive electrode material of dual ion batteries (DIBs) has attracted tremendous attentions for its advantages including low lost, high working voltage and high energy density. However, very few literatures regarding to the real-time observation of anion intercalation behavior and surface evolution of graphite in DIBs have been reported. Herein, we use in situ atomic force microscope (AFM) to directly observe the intercalation/de-intercalation processes of PF₆^- in graphite in real time. First, by measuring the change in the distance between graphene layers during intercalation, we found that PF₆^- intercalates in one of every three graphite layers and the intercalation speed is measured to be 2 μm·min^-1. Second, graphite will wrinkle and suffer structural damages at high voltages, along with severe electrolyte decomposition on the surface. These findings provide useful information for further optimizing the capacity and the stability of graphite anode in DIBs.