High-Performance Freestanding Lithium-Ion Battery Si Anode by Weakening the Current-Collector Constraint

Lithium-ion batteries (LIB) with both high volumetric and gravimetric specific capacities are desirable for power sources in microsystems. Si is a promising anode material for the above LIBs. However, its huge volume change combined with strict constraint by the bulky current collector (and/or the substrate) during lithiation/delithiation causes a severe stress and thus rapid capacity fading. Strategies in the literatures help suppress the capacity fading but degrade the anode initial Coulombic efficiency and specific capacities. This work presents a freestanding Si anode with an ultrathin current collector. Unlike those in the literatures whose current collector (and/or the substrate) accounts for the main part, the Si film dominates in this freestanding anode. This causes weak constraint from the current collector, therefore, the Si film can expand/shrink easily and stress induced by Si volume change can be effectively released, thus resulting in good anode cyclability (98.6% retention over 150 cycles). Moreover, the dominant role of the Si film in this anode ensures the anode to have high volumetric (6989 mAh cm −3 ) and gravimetric (2107 mAh g −1 ) specific capacities even when both the Si and current collector are included for calculations. This freestanding anode also displays a high initial Coulombic efficiency of 92.8% due to its small surface area.