摘要/Abstract
钴锰氧化物（CMO）具有安全无毒、价格便宜、活性位点多等优点，是极具潜力的锌离子电池正极材料.目前，充放电过程中电极材料溶解造成的结构坍塌成为限制其发展的瓶颈问题.本工作提出了一种原位碳包覆的方法来缓解CMO的溶解问题，在提高材料容量的基础上成功地延长了其循环寿命.通过简单的一步水热方法，成功制备了纳米碳（nC）包覆的钴锰氧化物（CMO@C）材料，X射线衍射（XRD）、X射线光电子能谱（XPS）、拉曼光谱（Raman）等表征证明，nC包覆层的引入并没有改变CMO材料的基本组分结构.而且，相较于CMO，CMO@C的电荷转移阻力更小，离子扩散更快，表现出更优异的电化学性能.在0.5 A·g-1的电流密度下，CMO@C显示出271.9 mAh·g-1的比容量，且经过1000圈循环后，材料的比容量没有发生衰减，性能大大优于CMO对比样品（103.7 mAh·g-1；130圈失效）.由此可见，纳米碳包覆层可同时提升CMO的储锌容量和循环寿命.本工作为双金属氧化物正极材料的优化改性提供了新的策略.
关键词: 锌离子电池, 原位包覆, 碳, 锰基材料, 长寿命
The cobalt manganese oxide (CMO), with the advantages of high safety, non-toxicity, easy to obtain, multiple active sites, holds great potential in constructions of Zn-ion batteries (ZIBs). Yet, the dissolution of electrode materials into the electrolyte usually causes the structural collapse during repeated charge/discharge courses, which greatly limits the lifespan of ZIBs and thus restricts their further development. Herein, an in-situ coating method is developed to address this issue. Via a simple one-step hydrothermal method, a nanoscale carbon layer (denoted as nC) is introduced onto the surface of CMO (CMO@C) to prolong its cycling stability. Specifically, 30 mmol NH4F and 75 mmol CO(CH2)2 are first dissolved in 100 mL deionized water. Then, 11.25 mmol Mn(CH3COO)2 and 3.75 mmol Co(CH3COO)2 are added and stirred until the solid completely dissolves. Finally, 0.5 g glucose is dissolved in the solution and stirred for 5 min. The precursor solution is transferred into the 25 mL Teflon-lined stainless-steel autoclave and heated at 125℃ for 6 h in the oven. The as-obtained powder is washed three times by water and then dried at 60℃ overnight. The CMO@C sample is obtained after annealing the powder in air at 450℃ for 1 h. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectra (Raman) characterizations demonstrate that the introduction of the nC coating layer does not alter the composition and structure of CMO. Moreover, taking advantages of the superior conductivity of the carbon coverage, the CMO@C possesses a smaller charge transfer resistance and higher Zn ion diffusion capability compared with the CMO counterpart. The quicker charge transfer and faster ion exchange characteristics are both beneficial to the electrochemical performance optimization, both for the capacity enlargement and for the lifespan extension. As a proof of concept, at the current density of 0.5 A·g-1, the CMO@C shows a high specific capacity of 271.9 mAh·g-1 and no capacity loss is detected after 1000 cycle tests, which substantially outstrip those of the CMO (103.7 mAh·g-1 and 130 cycle lifespan). The work sheds light on the rational design of bimetal oxides as high-performance cathodes for ZIBs assembly.
Key words: Zn-ion battery, in-situ coating, carbon, manganese-base materials, long-term lifespan
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