Cryogenic Mechanical Prelithiation Reduces Porosity and Improves Battery Performance of an Alloy Foil Anode

Anode prelithiation could dramatically improve the initial Coulombic efficiency and battery life. Roll-to-roll mechanical prelithiation (MP) is an attractive option for achieving prelithiation in minutes. While our previous work on metallic-foil prelithiation revealed that an external pressure is necessary to achieve MP in a timely fashion, too high an applied pressure will cause severe damages in the form of porosity and cracking. Thus, gentler MP under smaller pressure, and surprisingly, cryogenic temperatures, while prepositioning prolific grain boundaries as lithium diffusion paths is critical. To this end, first, we developed an accumulative roll bonding (ARB) method to refine the grain size of Sn-5Sb foil for denser grain boundaries. After ARB of 12 cycles (ARB-12), the grain size of Sn-5Sb foil decreased from 20-50 to 0.5-1.5 μm. Then, MP was performed under a mild condition of 0.5 MPa and -20 °C. Thereby, the porosity of prelithiated ARB-12 was reduced to 1.8% from thickness measurement, significantly minimizing the prelithiation damage. As a result, due to grain refinement, we achieved lower interface impedance and better rate performance. The ARB-12 Sn-5Sb foil with a proper prelithiation design exhibited 180 and 110 stable cycles when pairing with commercial LFP and NCM811 cathodes. Furthermore, it also depletes less electrolyte and keeps higher capacity retention under -10 °C than that of the graphite anode.