Surpassing lithium metal rechargeable batteries with self-supporting Li-Sn-Sb foil anode

摘要

Lithium metal rechargeable batteries (LMBs) degrade rapidly due to morphological instabilities as well as electrolyte consumption. As an alternative to Li-BCC metal foil, in this study, a self-supporting Li-Sb-Sn foil prepared by metallurgically alloying 5 wt%Sb-95 wt%Sn with Li-BCC is used as the anode in full-cell configurations. The electrochemical performance is highly competitive against equal-thickness pure Li-BCC foil, exhibiting much slower electrolyte degradation and less volume expansion: at the same amount of industrial-level electrolyte usage, LiFePO4/Li-Sn-Sb(50 mu m) full cells can sustain twice longer cycle life than LiFePO4/Li-BCC (50 mu m) cells. When pairing Li-Sn-Sb anode against high-areal-capacity LiNi0.5Co0.2Mn0.3O2(NCM523), LiNi0.8Co0.1Mn0.1O2(NCM811) and LiCoO2(LCO) cathodes, the cell life is significantly improved compared to lithium metal batteries. In particular, a similar to 6 mAh cm(-2) LCO/Li-Sb-Sn pouch cell delivers an initial energy density of 1027 Wh L-1. Coulombic inefficiency analysis combined with morphological observations reveals that the excellent full-cell performance of Li-Sn-Sb is correlated with the smaller apparent volume expansion (thickening) and mesoscale features such as amount and type of porosity. Theoretical calculations and experimental measurements affirm doping 5 wt% Sb significantly suppresses porosity and long crack damage, evidenced by the smaller total porosity: 11% of Li-Sn-Sb versus 23% of Li-Sn, right after mechanical prelithiation, due to facile stress relief through the sliding grain boundaries (GBs), nano SnSb phase boundaries (PBs) and the buffering of soft residual Sn. The reaction kinetics and lithiation products of Sn electrode also change after doping Sb, breaking down a huge chemomechanical shock (Sn -> Li22Sn5) into several milder ones (Sn -> Li2Sn5 -> LiSn -> Li22Sn5) by nano features. While the Li-carrying ability of Li22Sn5 is similar to that of LiBm, the low volume expansion, cycling stability, better air stability and safety of Li-Sn-Sb foil mean it comprehensively surpasses Li(BCC )metal foil anode.