Capone Isaac, Hurlbutt Kevin, Naylor Andrew J, Xiao Albert W, Pasta Mauro
Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.
Department of Chemistry-Ångström Laboratory, Uppsala University, Box 538, SE-75121 Uppsala, Sweden.
Energy Fuels. 2019 May 16;33(5):4651-4658. doi: 10.1021/acs.energyfuels.9b00385. Epub 2019 Apr 9.
Red phosphorus (RP) is a promising candidate as an anode for sodium-ion batteries because of its low potential and high specific capacity. It has two main disadvantages. First, it experiences 490% volumetric expansion during sodiation, which leads to particle pulverization and substantial reduction of the cycle life. Second, it has an extremely low electronic conductivity of 10 S cm. Both issues can be addressed by ball milling RP with a carbon matrix to form a composite of electronically conductive carbon and small RP particles, less susceptible to pulverization. Through this procedure, however, the resulting particle-size distribution of the RP particles is difficult to determine because of the presence of the carbon particles. Here, we quantify the relationship between the RP particle-size distribution and its cycle life for the first time by separating the ball-milling process into two steps. The RP is first wet-milled to reduce the particle size, and then the particle-size distribution is measured via dynamic light scattering. This is followed by a dry-milling step to produce RP-graphite composites. We found that wet milling breaks apart the largest RP particles in the range of 2-10 μm, decreases the Dv90 from 1.85 to 1.26 μm, and significantly increases the cycle life of the RP. Photoelectron spectroscopy and transmission electron microscopy confirm the successful formation of a carbon coating, with longer milling times leading to more uniform carbon coatings. The RP with a Dv90 of 0.79 μm mixed with graphite for 48 h delivered 1354 mA h g with high coulombic efficiency (>99%) and cyclability (88% capacity retention after 100 cycles). These results are an important step in the development of cyclable, high-capacity anodes for sodium-ion batteries.
红磷（RP）因其低电位和高比容量，是钠离子电池阳极的一个有潜力的候选材料。它有两个主要缺点。首先，在 sodiation 过程中它经历490%的体积膨胀，这导致颗粒粉碎并大幅降低循环寿命。其次，它的电子电导率极低，仅为10 S cm。通过将RP与碳基体进行球磨以形成电子导电碳和小RP颗粒的复合材料，可以解决这两个问题，这种复合材料不易粉碎。然而，通过这个过程，由于碳颗粒的存在，所得RP颗粒的粒度分布难以确定。在此，我们首次通过将球磨过程分为两个步骤来量化RP粒度分布与其循环寿命之间的关系。首先对RP进行湿磨以减小颗粒尺寸，然后通过动态光散射测量粒度分布。接着进行干磨步骤以制备RP-石墨复合材料。我们发现湿磨会使2-10μm范围内最大的RP颗粒破碎，将Dv90从1.85μm降至1.26μm，并显著提高RP的循环寿命。光电子能谱和透射电子显微镜证实成功形成了碳涂层，研磨时间越长，碳涂层越均匀。Dv90为0.79μm的RP与石墨混合48小时后，在高库仑效率（>99%）和循环性能（100次循环后容量保持率88%）下，提供了1354 mA h g的电量。这些结果是开发用于钠离子电池的可循环、高容量阳极的重要一步。
