A resilient MXene/CNT nano-accordion framework for anode-free sodium-metal batteries with exceptional cyclic stability

초록

Anode-free sodium-metal batteries are considered one of the most promising alternatives for developing high-end batteries due to their high theoretical capacity, low cost, and high natural abundance. However, they have severe drawbacks in the form of inferior long-term cyclic stability. We engineered mechanically resilient MXene/CNT nano-accordion frameworks (NAFs) to host significant Na without dendrite development, even at high currents. The microcellular structures of MXene/CNT-NAFs possess numerous micro-sized pores and sodium nucleation sites. The synergetic effects of strong adhesion and charge transfer between MXene and CNT reduce overpotential during plating/stripping and facilitate uniform Na deposition. Resilient nano-accordion structures are compressed by capillary of Na nucleation during plating and expand during stripping, allowing long-term plating/stripping with little volume change. These benefits allow the MXene/CNT-NAFs/Na asymmetric cell to maintain its average CE at 99.7 % with capacities of 1.0 mAh⋅cm−2 at 1.0 mA⋅cm−2 for 900 h. Furthermore, MXene/CNT-NAFs symmetric cell exhibits a very low overpotential of 12.0 mV after 1,500 h with a capacity of 3.0 mAh⋅cm−2 at 3.0 mA⋅cm−2 and stores high capacities of 20.0 mAh⋅cm−2 at 5.0 mA⋅cm−2 for 1,200 h. The anode-free MXene/CNT-NAFs//Na3V2(PO4)3@C full-cell demonstrates exceptional long-term cyclic stability over 5,000 cycles at 5.0 C and 10.0 C without cell failure.

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