Combining Solid Solution Strengthening and Second Phase Strengthening for Thinning Li Metal Foils

Thinlithium (Li) metal foils have been proved to beindispensableyet elusive for practical high-energy-density lithium batteries. Currently,the realization of such thin foils (<50 & mu;m) is impeded bythe inferior mechanical processability of metallic Li. In this work,we demonstrate that the combination of solid solution strengtheningand second phase strengthening, achieved by the addition of silverfluoride (AgF) to Li metal, can substantially enhance both the strengthand ductility of metallic Li. Benefiting from the improved machinability,we succeed in fabricating an ultrathin (down to 5 & mu;m), freestanding,and mechanically robust Li-AgF composite foil. More interestingly,the in situ-formed Li x Ag-LiF skeletonin the composite facilitates Li diffusion kinetics and uniform Lideposition, where the thin Li-AgF electrode displays a prolonged cyclelife over 500 h at 1 mA cm(-2) and 1 mAh cm(-2) in a carbonate electrolyte. Coupled with a commercial LiCoO2 cathode (3.4 mAh cm(-2)), the LiCoO2||Li-AgF cell delivers a notable capacity retention of & SIM;90%over 100 cycles at 0.5 C with a low negative/positive ratio of 2.5.