Interconnected Two‐dimensional Arrays of Niobium Nitride Nanocrystals as Stable Lithium Host

Abstract

The cycle life of rechargeable lithium (Li)‐metal batteries is mainly restrained by dendrites growth on the Li‐metal anode and fast depletion of the electrolyte. Here, we report on a stable Li‐metal anode enabled by interconnected two‐dimensional (2D) arrays of niobium nitride (NbN) nanocrystals as the Li host, which exhibits a high Coulombic efficiency (>99 %) after 500 cycles. Combining theoretical and experimental analysis, it is inferred that this performance is due to the intrinsic properties of interconnected 2D arrays of NbN nanocrystals, such as thermodynamic stability against Li‐metal, high Li affinity, fast Li+ migration, and Li+ transport through the porous 2D nanosheets. Coupled with a lithium nickel–manganese–cobalt oxide cathode, full Li‐metal batteries were built, which showed high cycling stability under practical conditions – high areal cathode loading ≥4 mAh cm−2, low negative/positive (N/P) capacity ratio of 3, and lean electrolyte weight to cathode capacity ratio of 3 g Ah−1. Our results indicate that transition metal nitrides with a rationally designed structure may alleviate the challenges of developing dendrite‐free Li‐metal anodes.

V2CTx MXene Artificial Solid Electrolyte Interphases toward Dendrite-Free Lithium Metal Anodes

“…Increasing the high rate to 10 mA cm –2 , the Li||V 2 CT x -Cu half-cell still exhibits a CE of 96.9% after 250 cycles (Figure f), indicating the greatly improved Li-ion transport kinetics with the assistance of the V 2 CT x artificial SEI. The CE of Li||V 2 CT x -Cu has surpassed most of the previously reported LMAs in comprehensive consideration of cumulative capacity and current density (Figure g). ,,,,− ,− ,,,− ,,,, Here, the cumulative capacity is the total capacity of Li deposited on each cycle before cell failure or sharply decreased CE of cells . Instead of a comparison of cycle number, cumulative capacity is an aggregative indicator including both capacity and cycle life, better reflecting the superiority of various methods for the LMAs.…”

“…The CE of Li|| V 2 CT x -Cu has surpassed most of the previously reported LMAs in comprehensive consideration of cumulative capacity a n d c u r r e n t d e n s i t y ( F i g u r e 2g). 1,7,9,10,[13][14][15][17][18][19]21,23,[32][33][34]37,41,65,66 Here, the cumulative capacity is the total capacity of Li deposited on each cycle before cell failure or sharply decreased CE of cells. 8 Instead of a comparison of cycle number, cumulative capacity is an aggregative indicator including both capacity and cycle life, better reflecting the superiority of various methods for the LMAs.…”

“…A routine approach is to adopt new electrolytes − or introduce sacrificial additives − in conventional electrolytes to increase the stability of the SEI. The in situ formed SEI improves the CEs of LMAs but is hardly sustained over a long time due to constant consumption of the electrolyte and insufficient Young’s modulus of the SEI. ,, Another strategy has adopted an ex situ artificial SEI layer such as flexible polymers − and rigid inorganics. − Although the artificial SEI layer with the high mechanical property has extended the cycling life of LMAs to 200 cycles, the essential problems of nonuniform nucleation resulting in inhomogeneous Li + flux and vertical growth of Li have been unresolved especially under deep stripping/plating conditions (>2 mA h cm –2 at 2 mA cm –2 ). ,, Under such conditions, the greatly increased volume change from a capacity ≥4 mA h cm –2 and severe concentration polarization due to nonuniform Li + flux at a high rate ≥4 mA cm –2 accelerate cracking of the SEI severely. Therefore, designing a stable artificial SEI, which enables uniform nucleation and horizontal-orientated growth rather than vertical growth of Li, is expected to resolve the abovementioned issues and achieve stable Li stripping/plating even under deep test conditions (≥4 mA h cm –2 at 4 mA cm –2 ).…”

“…38−40 Although the artificial SEI layer with the high mechanical property has extended the cycling life of LMAs to 200 cycles, the essential problems of nonuniform nucleation resulting in inhomogeneous Li + flux and vertical growth of Li have been unresolved especially under deep stripping/plating conditions (>2 mA h cm −2 at 2 mA cm −2 ). 8,11,41 Under such conditions, the greatly increased volume change from a capacity ≥4 mA h cm −2 and severe concentration polarization due to nonuniform Li + flux at a high rate ≥4 mA cm −2 accelerate cracking of the SEI severely. Therefore, designing a stable artificial SEI, which enables uniform nucleation and horizontal-orientated growth rather than vertical growth of Li, is expected to resolve the abovementioned issues and achieve stable Li even under deep test conditions (≥4 mA h cm −2 at 4 mA cm −2 ).…”

Polypyrrole Nanotube Sponge Host for Stable Lithium-Metal Batteries under Lean Electrolyte Conditions

“…3,12,15,24 To achieve the target energy density (350 W h kg −1 ) for practical batteries, the practical test conditions should meet the high areal cathode loading (≥4 mA h cm −2 ), lean electrolytes (E/C < 10 μL mA h −1 ), and N/P as low as possible. 15,24,25 Under the constrained conditions, repetitive SEI buildup/crack because of Li dendritic growth rapidly depletes the electrolyte and Li which is much faster than that under mild conditions, 26,27 resulting in extreme difficulty to obtain long lifespan of practical Li-metal batteries. In addition, according to the opinion of Wang, et al, 16 introducing lithiophilic sites could change Li + ion transfer behavior, which effectively increases homogeneous Li deposition.…”