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