"High Tap Density Secondary Silicon Particle Anodes by Scalable Mechanical Pressing for Lithium-ion Batteries "

Dingchang Lin: Zhenda Lu, Po-Chun Hsu, Hye Ryoung Lee, Nian Liu, Jie Zhao,Haotian Wang, Chong Liu and Yi Cui ; Energy & Environmental Science, 06/26/15.

Additional Authors: Zhenda Lu, Po-Chun Hsu, Hye Ryoung Lee, Nian Liu, Jie Zhao,Haotian Wang, Chong Liu and Yi Cui

Abstract:

Much progress has been made in developing high capacity lithium ion battery electrode materials such as silicon anode. With the powerful nanomaterials design approach, cycle life of silicon anodes has been increased significantly. However, nanomaterials have three major issues to be addressed, including severe side reactions due to large surface area, low tap density and poor scalability. Nanostructured Si secondary cluster (nano-Si SC) is promising for reducing side reactions and increasing tap density, yet the scalability and tap density could still be further improved. Here, we propose a mechanical approach for SC fabrication to address all the problems. With the mechanical approach, >20 g of nano-Si SC per batch was produced even at our university lab scale, with >95% yield. Moreover, much denser packing of nanostructures can be achieved (1.38 g cm-3, pellet form), which gives much higher tap density (0.91 g cm-3, powder form) and better electrical contact. Accordingly, over 95% of initial capacity is retained after 1400 cycles at 1C, with average specific capacity ~1250 mAh g-1. Stable cycling with >2 mg cm-2 of areal mass loading (~3.5 mAh cm-2) is obtained. After uniformly integrating carbon nanotubes(CNTs) into SCs, intracluster electrical conductivity is further improved. As a result, notably enhanced rate capability is attained, with high reversible specific capacity ~1140 mAh g-1 and ~880 mAh g-1 at 2C and 4C, respectively.