Large-scale sodiophilic/buffered alloy architecture enables deeply cyclable Na metal anodes

The application of Na metal anodes is hindered by the formation of dendrites, which evolves from the initial heterogeneous nucleation. The construction of sodiophilic pure metal layers on substrates can partly improve Na deposition behavior, but huge volume change during the repetitive alloy/dealloy process renders their rapid failure, especially under the high depth of discharge. Inspired by the assets of alloy anodes compared with monometallic anodes in Li/Na ion batteries, a Cu6Sn5 alloy layer is constructed on commercial Cu foils with a huge size of 850 mm x 650 mm via a facile electroless Sn plating approach. The sodiophilic Sn phase can alloy with Na and contribute to an ultralow nucleation overpotential as well as dendrite-free morphology. Meanwhile, the inactive Cu phase acts as buffer media to mitigate the internal stress and volume change induced by the alloy reaction, which prevents the alloy layer from peeling. Based on these synergetic effects, the Cu6Sn5 alloy coated Cu current collector gives rise to a highly prolonged Coulombic efficiency (99.84%) for 2000 cycles and 600 h lifetime under an ultrahigh depth of discharge (80%), which is superior to those of single Sn metal-coated Cu current collector. Furthermore, the full cells coupled with FeS2 cathode can stably operate for 1500 cycles with a decent capacity retention of ~ 95%.