Significantly Improved Long-Cycle Stability in High-Rate Li-S Batteries Enabled by Coaxial Graphene Wrapping over Sulfur-Coated Carbon Nanofibers
Significantly Improved Long-Cycle Stability in High-Rate Li-S Batteries Enabled by Coaxial Graphene Wrapping over Sulfur-Coated Carbon Nanofibers
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DOI：
10.1021/nl400543y
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发表时间：
2013-06-01
期刊：
影响因子：
10.8
通讯作者：
Liu, Jie
中科院分区：
文献类型：
--
作者：
Lu, Songtao;Cheng, Yingwen;Liu, Jie
与其他二次电池相比，Li-S电池的长期不稳定性是其主要缺点之一。不稳定性的原因包括多硫化物中间体的溶解和充放电循环期间体积变化引起的电极膜的机械不稳定性。本文报道了一种新型的石墨烯-硫-碳纳米纤维（G-S-CNFs）多层共轴纳米复合材料，用于锂硫电池的正极，具有更高的容量和更好的长循环稳定性。用这种纳米复合材料制成的电极能够在0.1C下提供694 mA h g（-1）的可逆容量，在2C下提供313 mA h g（-1）的可逆容量，这两者都显著高于没有石墨烯包裹的电极。更重要的是，石墨烯包裹显著提高了长循环稳定性。用初始容量为745 mA h g（-1）的G-S-CNF制成的阴极即使在1C的高速率下1500次充电-放电循环后也能够保持类似于273 mA h g（-1），这表示极低的衰减速率（1500次循环后每个循环0.043%）。相比之下，在没有石墨烯包裹的情况下组装的电极的容量以10倍的高速率急剧衰减（类似于200次循环后每循环0.40%）。这些结果表明，同轴纳米复合材料作为高倍率可充电锂硫电池的阴极具有很大的潜力。这种改进的倍率性能和循环稳定性可归因于纳米复合材料的独特同轴结构，其中石墨烯和CNF的贡献使电极具有改进的电导率、更好的捕获可溶性多硫化物中间体的能力以及在重复充电/放电循环期间适应硫的体积膨胀/收缩。
Long-term instability of Li-S batteries is one of their major disadvantages compare to other secondary batteries. The reasons for the instability include dissolution of polysulfide intermediates and mechanical instability of the electrode film caused by volume changes during charging/discharging cycles. In this paper, we report a novel graphene-sulfur-carbon nanofibers (G-S-CNFs) multilayer and-coaxial nanocomposite for the cathode of Li-S batteries with increased capacity and significantly improved long cycle stability. Electrodes made with such nanocornposites were able to deliver a reversible capacity of 694 mA h g(-1) at 0.1C and 313 mA h g(-1) at 2C, which are both substantially higher than electrodes assembled without graphene wrapping. More importantly, the long cycle stability was significantly improved by graphene wrapping. The cathode made with G-S-CNFs with a initial capacity of 745 mA h g(-1) was able to maintain similar to 273 mA h g(-1) even after 1500 charge-discharge cycles at a high rate of 1C, representing an extremely low decay rate (0.043% per cycle after 1500 cycles). In contrast, the capacity of an electrode assembled without graphene wrapping decayed dramatically with a 10 times high rate (similar to 0.40% per cycle after 200 cycles). These results demonstrate that the coaxial nanocomposites are of great potential as the cathode for high-rate rechargeable Li-S batteries. Such improved rate capability and cycle stability could be attributed to the unique coaxial architecture of the nanocomposite, in which the contributions from graphene and CNFs enable electrodes with improved electrical conductivity, better ability to trap soluble the polysulfides intermediate and accommodate volume expansion/shrinkage of sulfur during repeated charge/discharge cycles.