Li2ZrF6-based electrolytes for durable lithium metal batteries

Lithium (Li) metal batteries (LMBs) are promising for high-energy-density rechargeable batteries 1 , 2 , 3 . However, Li dendrites formed by the reaction between highly active Li and non-aqueous electrolytes lead to safety concerns and rapid capacity decay 4 , 5 , 6 , 7 . Developing a reliable solid–electrolyte interphase is critical for realizing high-rate and long-life LMBs, but remains technically challenging 4 , 8 . Here we demonstrate that adding excess m -Li 2 ZrF 6 (monoclinic) nanoparticles to a commercial LiPF 6 -containing carbonate electrolyte of LMBs facilitates the release of abundant ZrF 6 2 – ions into the electrolyte driven by the applied voltage, converting to t -Li 2 ZrF 6 (trigonal) and creating a stable solid–electrolyte interphase in situ with high Li-ion conductivity. Computational and cryogenic transmission electron microscopy studies revealed that the in situ formation of the t -Li 2 ZrF 6 -rich solid–electrolyte interphase markedly enhanced Li-ion transfer and suppressed the growth of Li dendrites. As a result, LMBs assembled with LiFePO 4 cathodes (areal loading, 1.8/2.2 mAh cm −2 ), three-dimensional Li–carbon anodes (50-µm-thick Li) and Li 2 ZrF 6 -based electrolyte displayed greatly improved cycling stability with high capacity retention (>80.0%) after 3,000 cycles (1C/2C rate). This achievement represents leading performance and, thus, delivers a reliable Li 2 ZrF 6 -based electrolyte for durable LMBs under practical high-rate conditions.