Department of Materials Science and Engineering, Advanced Institute of Science and Technology Korea 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
Department of Chemical and Biological Engineering, Sookmyung Women's University Cheonpa-ro 47-gil 100, Yongsan-gu, Seoul 04310, Republic of Korea.
Sci Rep. 2016 May 5;6:25555. doi: 10.1038/srep25555.
Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp(2) nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g.
在锂-硫氧化还原电池的阴极中放电时产生的多硫化锂很重要，但在每个氧化还原循环中，它们从阴极溶解到电解质中会导致循环寿命缩短。在此，我们使用原位光谱电化学测量来证明纳米晶金属有机骨架-867（nMOF-867）中的有机配体中的 sp(2)氮原子能够将多硫化锂封装在 nMOF-867 的微笼中，从而有助于防止它们在放电/充电循环中溶解到电解质中。通过观察 C=N 和 C-N 键的傅里叶变换红外光谱（FTIR）谱图、nMOF-867 的 Li-N 键的 X 射线光电子能谱（XPS）谱图以及可视化方法，进一步证实了锂化/脱锂多硫化物的封装机制，证明 nMOF-867 可以防止锂多硫化物溶解在电解质中。实际上，使用 nMOF-867 制备的阴极在 500 次放电/充电循环的长循环寿命中表现出出色的容量保持率，在 835 mA/g 的高电流速率下，从 788 mAh/g 的放电容量开始，每个循环的容量损失约为 0.027%。
