Li2ZrF6-based electrolytes for durable lithium metal batteries

Abstract

Lithium (Li) metal batteries (LMBs) are promising for high-energy-density rechargeable batteries1–3. However, Li dendrites formed by the reaction between highly active Li and non-aqueous electrolytes lead to safety concerns and rapid capacity decay4–7. Developing a reliable solid–electrolyte interphase is critical for realizing high-rate and long-life LMBs, but remains technically challenging4,8. Here we demonstrate that adding excess m-Li2ZrF6 (monoclinic) nanoparticles to a commercial LiPF6-containing carbonate electrolyte of LMBs facilitates the release of abundant ZrF62– ions into the electrolyte driven by the applied voltage, converting to t-Li2ZrF6 (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-Li2ZrF6-rich solid–electrolyte interphase markedly enhanced Li-ion transfer and suppressed the growth of Li dendrites. As a result, LMBs assembled with LiFePO4 cathodes (areal loading, 1.8/2.2 mAh cm−2), three-dimensional Li–carbon anodes (50-µm-thick Li) and Li2ZrF6-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 Li2ZrF6-based electrolyte for durable LMBs under practical high-rate conditions. Adding excess m-Li2ZrF6 (monoclinic) nanoparticles to a commercial LiPF6-containing carbonate electrolyte forms a stable interphase rich in t-Li2ZrF6 (trigonal), enhancing Li-ion transfer, suppressing dendrite growth and considerably improving the cycling stability of high-rate lithium metal batteries.