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

Abstract

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, LiFePO 4 /Li–Sn–Sb(50 μm) full cells can sustain twice longer cycle life than LiFePO 4 /Li BCC (50 μm) cells. When pairing Li–Sn–Sb anode against high-areal-capacity LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and LiCoO 2 (LCO) cathodes, the cell life is significantly improved compared to lithium metal batteries. In particular, a ~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→Li 22 Sn 5 ) into several milder ones (Sn→Li 2 Sn 5 →LiSn→Li 22 Sn 5 ) by nano features. While the Li-carrying ability of Li 22 Sn 5 is similar to that of Li BCC , 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. Self-supporting Li–Sb–Sn foils are prepared by metallurgically alloying 5 wt%Sb-95 wt%Sn with Li BCC to substitute pure Li BCC foil. During full-cell cycling with an industrial level of lean electrolyte, Li–Sn–Sb can sustain twice longer cycle life than Li BCC due to the smaller apparent electrode thickening and slower electrolyte degradation. In particular, ~6 mAh cm −2 LCO/Li–Sb–Sn pouch cell can deliver an initial high energy density of 1073 Wh L −1 . Needle piercing experiments proved Li–Sb–Sn has less thermal runaway and better safety than Li BCC anode. • A self-supporting Li-Sb-Sn foil is prepared by metallurgically alloying 5wt%Sb-95wt%Sn and Li BCC foils. • The full-cell performance of Li-Sb-Sn is highly competitive against Li BCC , exhibiting slower electrolyte degradation. • Li-Sn-Sb has lower volume expansion, better cycling stability and safety than Li BCC metal foil. • Doping Sb suppresses large porosity and long crack formation due to abundant GBs and PBs relieving stress more adequately. • Doping Sb changes reaction kinetics and breaks down Sn→Li 22 Sn 5 into Sn→Li 2 Sn 5 →LiSn→Li 22 Sn 5 .