School of Metallurgy and Environment , Central South University , Changsha 410083 , China.
State Key Laboratory of Environmental Friendly Energy Materials , Southwest University of Science and Technology , Mianyang 621010 , China.
ACS Appl Mater Interfaces. 2019 Feb 27;11(8):8556-8566. doi: 10.1021/acsami.8b21621. Epub 2019 Feb 14.
Graphene has been implemented as a desirable additive to improve the electrochemical performance of Ni-rich cathode materials. However, it is not only hard to ensure the intimate interaction between them in practice, which may affect the surface electronic conductivity of the composite, but also a challenge to fabricate cathodes with uniform graphene coating because of its two-dimensional planar structure. Besides, the graphene coating layer is easily peeled off from the cathode material during the cycling process, especially at the upper cutoff voltage. Therefore, we introduced a double-functional layer synergistically modified strategy to facilitate the electrochemical properties of LiNiCoMnO cathode materials. In the designed architecture, the LiNiCoMnO particles were uniformly enwrapped by a functional reduced graphene oxide (RGO)-KH560 polymer composite layer which consists of an inner high-flexibility epoxy-functionalized silane (KH560) layer and an outer RGO layer with high electronic conductivity. The KH560 layer, in the structural system, is especially critical in connecting the layer of outer RGO and the inner surface of the active material, which brings about the perfect and complete double-functional coating layer and in turn fully expresses the modification effect of both KH560 and RGO in the improvement of electrochemical performance. Consequently, higher capacity retention, better rate, and improved high-temperature performances (55 °C) at the upper cutoff voltage (4.5 V) of this composite are identified when compared with the RGO-coated and pristine samples. In particular, the cathode with RGO (0.5%)-KH560 (0.5%) coating exhibits capacity retentions of 95.2 and 81.5% after 150 cycles at 1 C, 4.5 V at room and high temperatures, respectively.
石墨烯已被用作一种理想的添加剂，以提高富镍阴极材料的电化学性能。然而，在实际应用中，不仅很难确保它们之间的紧密相互作用，这可能会影响复合材料的表面电子导电性，而且由于其二维平面结构，制造具有均匀石墨烯涂层的阴极也是一个挑战。此外，在循环过程中，石墨烯涂层层很容易从阴极材料上剥落，特别是在上截止电压处。因此，我们引入了一种双重功能层协同改性策略，以改善 LiNiCoMnO 阴极材料的电化学性能。在设计的结构中，LiNiCoMnO 颗粒被均匀地包裹在功能化还原氧化石墨烯（RGO）-KH560 聚合物复合层中，该复合层由内层高柔韧性环氧官能化硅烷（KH560）层和外层具有高导电性的 RGO 层组成。在结构体系中，KH560 层在连接外 RGO 层和活性材料内表面方面起着至关重要的作用，从而形成了完美和完整的双重功能涂层，并充分发挥了 KH560 和 RGO 在改善电化学性能方面的改性效果。因此，与 RGO 涂层和原始样品相比，该复合材料在较高截止电压（4.5 V）下具有更高的容量保持率、更好的倍率性能和改善的高温性能（55°C）。特别是，具有 RGO（0.5%）-KH560（0.5%）涂层的阴极在室温下和高温下分别以 1 C、4.5 V 循环 150 次后，容量保持率分别为 95.2%和 81.5%。
