Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.
Nano Lett. 2013 Jun 12;13(6):2485-9. doi: 10.1021/nl400543y. Epub 2013 May 22.
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 nanocomposites 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 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 (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.
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。不稳定的原因包括多硫化物中间体的溶解以及在充放电循环过程中电极膜的体积变化引起的机械不稳定性。在本文中，我们报告了一种新型的石墨烯-硫-碳纳米纤维（G-S-CNFs）多层和同轴纳米复合材料，用于 Li-S 电池的阴极，具有增加的容量和显著改善的长循环稳定性。用这种纳米复合材料制成的电极在 0.1C 时能够提供 694 mA h g(-1)的可逆容量，在 2C 时能够提供 313 mA h g(-1)的可逆容量，这两个容量都远远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。由 G-S-CNFs 制成的初始容量为 745 mA h g(-1)的阴极，在 1C 的高倍率下经过 1500 次充放电循环后，仍能保持约 273 mA h g(-1)的容量，其衰减率极低（1500 次循环后每循环 0.043%）。相比之下，没有石墨烯包裹的电极的容量在 10 倍高倍率下（200 次循环后每循环 0.40%）急剧衰减。这些结果表明，同轴纳米复合材料作为高倍率可充电 Li-S 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 CNFs 的贡献使电极具有改善的导电性、更好的捕获可溶性多硫化物中间体的能力以及在反复充放电循环过程中容纳硫的体积膨胀/收缩的能力。
