Sarang Kasturi T, Zhao Xiaofei, Holta Dustin, Radovic Miladin, Green Micah J, Oh Eun-Suok, Lutkenhaus Jodie L
Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, USA.
Department of Material Science & Engineering, Texas A&M University, College Station, TX 77843, USA.
Nanoscale. 2020 Oct 22;12(40):20699-20709. doi: 10.1039/d0nr06086k.
Silicon anodes are promising for high energy batteries because of their excellent theoretical gravimetric capacity (3579 mA h g-1). However, silicon's large volume expansion and poor conductivity hinder its practical application; thus, binders and conductive additives are added, effectively diluting the active silicon material. To address this issue, reports of 2D MXene nanosheets have emerged as additives for silicon anodes, but many of these reports use high MXene compositions of 22-66 wt%, still presenting the issue of diluting the active silicon material. Herein, this report examines the question of what minimal amount of MXene nanosheets is required to act as an effective additive while maximizing total silicon anode capacity. A minimal amount of only 4 wt% MXenes (with 16 wt% sodium alginate and no carbon added) yielded silicon anodes with a capacity of 900 mA h gSi-1 or 720 mA h gtotal-1 at the 200th cycle at 0.5 C-rate. Further, this approach yielded the highest specific energy on a total electrode mass basis (3100 W h kgtotal-1) as comapared to other silicon-MXene constructs (∼115-2000 Wh kgtotal-1) at a corresponding specific power. The stable electrode performance even with a minimal MXene content is attributed to several factors: (1) highly uniform silicon electrodes due to the dispersibility of MXenes in water, (2) the high MXene aspect ratio that enables improved electrical connections, and (3) hydrogen bonding among MXenes, sodium alginate, and silicon particles. All together, a much higher silicon loading (80 wt%) is attained with a lower MXene loading, which then maximizes the capacity of the entire electrode.
硅阳极因其出色的理论重量容量（3579 mA h g-1）而在高能量电池领域颇具前景。然而，硅的大量体积膨胀和低导电性阻碍了其实际应用；因此，需添加粘结剂和导电添加剂，这有效地稀释了活性硅材料。为解决此问题，二维MXene纳米片作为硅阳极添加剂的相关报道不断涌现，但许多此类报道使用的MXene含量高达22 - 66 wt%，仍存在稀释活性硅材料的问题。在此，本报告探讨了在使硅阳极总容量最大化的同时，作为有效添加剂所需的最小MXene纳米片量这一问题。仅4 wt%的最小量MXene（与16 wt%的海藻酸钠混合且不添加碳）在0.5 C倍率下的第200次循环时产生了容量为900 mA h gSi-1或720 mA h gtotal-1的硅阳极。此外，与其他硅 - MXene结构（在相应比功率下约为115 - 2000 Wh kgtotal-1）相比，这种方法在总电极质量基础上产生了最高的比能量（3100 W h kgtotal-1）。即使MXene含量极低，电极性能仍保持稳定，这归因于几个因素：（1）由于MXene在水中的分散性，硅电极高度均匀；（2）高MXene纵横比有助于改善电连接；（3）MXene、海藻酸钠和硅颗粒之间的氢键作用。总体而言，以较低的MXene负载量实现了更高的硅负载量（80 wt%），从而使整个电极的容量最大化。
