Stabilizing sodium metal anode through facile construction of organic-metal interface

Abstract

Implementation of sodium metal anode is highly desired for sodium batteries due to its high theoretical capacity and low redox potential. Unfortunately, formation of unstable solid electrolyte interphase (SEI) and uncontrollable growth of dendrites during charge/discharge cycles greatly hinder the practical application of sodium metal anode. In this study, an organic-metal artificial layer made of PVdF and Bi was constructed to protect Cu current collector via a facile coating method, leading to smooth and dense sodium plating/stripping, which in retern enables stable cycling and high coulombic efficiency (CE). At 1 mA cm−2, PB@Cu current collector presents extended lifetime of ~2500 h with high sodium utilization of 50%, which is approximately six times higher than Cu current collector. PB@Cu electrode also displays high average CE of 99.92% and 99.95% over 2500 and 1300 cycles at 1 and 2 mA cm−2 respectively, which is in sharp contrast to the low and tremendously fluctuant CE gained from bare Cu electrode. Moreover, stable capacity of > 90 mAh g−1 over 150 cycles is realized for PB@Cu-based full cell assembled with NVP cathode at a low negative-positive capacity ratio of ~3.5, which is significantly higher than 37.2 mAh g−1 obtained from NVP/Cu at 150th cycle. The superior electrochemical performance of PB@Cu current collector is revealed to originate from the alloyed Na3Bi phase with high sodium conductivity and robust mechanical strength as well as the formation of NaF-rich SEI with fast sodium ion migration, which enable dendrite-free morphology during plating/stripping cycles.