He Jiarong, Tao Tao, Yang Fan, Sun Zhipeng
School of Materials and Energy, Guangdong University of Technology, Guangzhou, 510006, P. R. China.
ChemSusChem. 2022 Aug 5;15(15):e202200817. doi: 10.1002/cssc.202200817. Epub 2022 Jun 20.
Although lithium-ion batteries (LIBs) are promising towards high energy density and superior safety energy storage systems (ESS), severe depletion of Li reserve cannot meet the ever-growing demand for LIBs due to the uneven distribution and limited amount of Li resource. Li-free polyanionic cathodes, such as Na V (PO ) (NVP) and Na (VOPO ) F (NVOPF), show intriguing electrochemical performances with prospective future for LIBs due to their appropriate crystallographic sites, robust host structure, and abundant Na resource. In this work, NVP and NVOPF were systematically investigated as cathodes for LIBs using different voltage windows of 2.5-4.3, 2.0-4.3, and 1.5-4.8 V, along with their electrochemical mechanisms, cathode electrolyte interphase properties, and electrode morphologies for comparison. Ex-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy, and post-mortem scanning electron microscopy revealed that their mechanisms shifted from a predominant Na intercalation/deintercalation in the first charging/discharging to a mixed Li /Na intercalation/deintercalation at the subsequent cycling. Due to the residual Na acting as pillar in the structure, NVP and NVPF could serve as robust host framework, providing appropriate crystallographic sites for repeated Li /Na intercalation/deintercalation. NVP electrode delivered a higher discharge capacity of 107.6 mAh g with superior capacity retention of 84.3 % after 1000 cycles (2.5-4.3 V, 100 mA g ) than NVOPF electrode (97.3 mAh g , 68.8 %). Electrode polarization and kinetic analysis manifested one energetically similar and two energetically nonequivalent crystallographic Na sites within the R c and I4/mmm polyanionic structure of NVP and NVOPF. This work comprehensively demonstrates the feasibility and prospect of sodium-based NVP and NVOPF polyanions serving as advanced Li-free cathodes for LIBs, which provides novel insights into seeking Li-free candidates as prospective cathodes for LIBs towards a more sustainable society and a cost-effective battery manufacturing system.
尽管锂离子电池（LIBs）在实现高能量密度和卓越安全性能的储能系统（ESS）方面前景广阔，但由于锂资源分布不均且储量有限，锂储备的严重枯竭无法满足对LIBs不断增长的需求。无锂聚阴离子阴极，如NaV(PO)（NVP）和Na(VOPO)F（NVOPF），因其合适的晶体学位点、坚固的主体结构和丰富的钠资源，展现出引人注目的电化学性能，在LIBs领域具有潜在的未来前景。在这项工作中，系统研究了NVP和NVOPF作为LIBs阴极在2.5 - 4.3、2.0 - 4.3和1.5 - 4.8 V不同电压窗口下的性能，以及它们的电化学机制、阴极电解质界面性质和电极形态以作比较。非原位X射线衍射、非原位X射线光电子能谱和事后扫描电子显微镜表明，它们的机制从首次充电/放电时主要的钠嵌入/脱嵌转变为后续循环中的锂/钠混合嵌入/脱嵌。由于残余的钠在结构中起支柱作用，NVP和NVPF可作为坚固的主体框架，为锂/钠的反复嵌入/脱嵌提供合适的晶体学位点。NVP电极在1000次循环（2.5 - 4.3 V，100 mA g）后提供了107.6 mAh g的较高放电容量和84.3 %的优异容量保持率，优于NVOPF电极（97.3 mAh g，68.8 %）。电极极化和动力学分析表明，在NVP和NVOPF的R c和I4/mmm聚阴离子结构内存在一个能量相似和两个能量不等价的晶体学钠位点。这项工作全面证明了基于钠的NVP和NVOPF聚阴离子作为LIBs先进无锂阴极的可行性和前景，为寻找无锂候选材料作为LIBs的潜在阴极以实现更可持续的社会和具有成本效益的电池制造系统提供了新的见解。
