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Journal Article

Redox-active metaphosphate-like terminals enable high-capacity MXene anodes for ultrafast Na-ion storage


Feng,  Xinliang       
Department of Synthetic Materials and Functional Devices (SMFD), Max Planck Institute of Microstructure Physics, Max Planck Society;

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Sun, B., Lu, Q., Chen, K., Zheng, W., Liao, Z., Lopatik, N., et al. (2022). Redox-active metaphosphate-like terminals enable high-capacity MXene anodes for ultrafast Na-ion storage. Advanced Materials, 34(15): 2108682. doi:10.1002/adma.202108682.

Cite as: https://hdl.handle.net/21.11116/0000-000A-5B8B-4
2D transition metal carbides and/or nitrides, so-called MXenes, are noted as ideal fast-charging cation-intercalation electrode materials, which nevertheless suffer from limited specific capacities. Herein, it is reported that constructing redox-active phosphorus−oxygen terminals can be an attractive strategy for Nb4C3 MXenes to remarkably boost their specific capacities for ultrafast Na+ storage. As revealed, redox-active terminals with a stoichiometric formula of PO2- display a metaphosphate-like configuration with each P atom sustaining three P−O bonds and one P=O dangling bond. Compared with conventional O-terminals, metaphosphate-like terminals empower Nb4C3 (denoted PO2-Nb4C3) with considerably enriched carrier density (fourfold), improved conductivity (12.3-fold at 300 K), additional redox-active sites, boosted Nb redox depth, nondeclined Na+-diffusion capability, and buffered internal stress during Na+ intercalation/de-intercalation. Consequently, compared with O-terminated Nb4C3, PO2-Nb4C3 exhibits a doubled Na+-storage capacity (221.0 mAh g-1), well-retained fast-charging capability (4.9 min at 80% capacity retention), significantly promoted cycle life (nondegraded capacity over 2000 cycles), and justified feasibility for assembling energy−power-balanced Na-ion capacitors. This study unveils that the molecular-level design of MXene terminals provides opportunities for developing simultaneously high-capacity and fast-charging electrodes, alleviating the energy−power tradeoff typical for energy-storage devices.