Redox-Active Metaphosphate-Like Terminals Enable High-Capacity MXene Anodes for Ultrafast Na-Ion Storage
Redox-Active Metaphosphate-Like Terminals Enable High-Capacity MXene Anodes for Ultrafast Na-Ion Storage
复制标题
氧化还原活性磷氧端子支持高容量 MXene 阳极用于超快钠离子存储
DOI：
10.1002/adma.202108682
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发表时间：
2022-03-03
影响因子：
29.4
通讯作者：
Feng, Xinliang
中科院分区：
文献类型：
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作者：
Sun, Boya;Lu, Qiongqiong;Feng, Xinliang
二维过渡金属碳化物和/或氮化物，即所谓的MXenes，被认为是理想的快速充电阳离子插入电极材料，但其比容量有限。本文报道，构建氧化还原活性的磷氧末端可以成为Nb4C3 MXenes显著提高其超快Na+存储比容量的一种有吸引力的策略。结果表明，具有PO2-化学计量公式的氧化还原活性末端显示出类似偏磷酸盐的结构，每个P原子维持三个P-O键和一个P(sic)O悬空键。与传统的o型末端相比，偏磷酸盐类末端使Nb4C3（记为PO2-Nb4C3）的载流子密度显著增加（4倍），电导率提高（300 K时提高12.3倍），氧化还原活性位点增加，Nb氧化还原深度增加，Na+扩散能力不下降，并且在Na+插入/脱插过程中缓冲内应力。因此，与o端Nb4C3相比，PO2-Nb4C3具有双倍的Na+存储容量（221.0 mAh g(-1)），保持良好的快速充电能力（80%容量保留时4.9分钟），显着提高了循环寿命（超过2000次循环的不退化容量），并且证明了组装能量-功率平衡的Na离子电容器的可行性。这项研究揭示了MXene终端的分子水平设计为同时开发高容量和快速充电电极提供了机会，减轻了储能设备典型的能量-功率权衡。
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(sic)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.