Nature, Published online: 08 January 2025; doi:10.1038/s41586-024-08294-zAdding 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.