Silicon Nanotubes on Copper Films: Additive-Free Anode Material for Lithium-Ion Batteries.
Authors: DeWees Rachel , Thapa Arjun , Jasinski Jacek Bogdan , Sunkara Mahendra 
Published: September 2023

Thedevelopment of lightweight, long-lasting Li-ion batteries is of great technological importance for critical applications, including but not limited to aerospace and power grid applications. Increasing the specific capacity of the electrodes is the most direct strategy to increase the energy density of the battery. Currently, batteries with silicon anode materials have been commercially available only on a small scale or at a low composition of silicon. Great impact will be made when 100% silicon anode material can be fabricated at large scale. Specifically, the electric vehicle industry will experience disruption when a silicon solution enters the market which can offer durability as it delivers the expected high capacity.
Silicon-based anode materials have a theoretical capacity an order of magnitude beyond the currently implemented graphitic materials- 3579 mAh/g when fully lithiated at room temperature to Li4Si15, as compared with 372 mAh/g. Silicon incorporates lithium into its microstructure as an alloying process as opposed to direct intercalation, like graphite; as such, a volume change of 300% causes mechanical degradation upon cycling if conventional processing is used. Nanoscale 0-D and 1-D materials have been shown to withstand volume expansion and enable Li-intercalation and de-intercalation reactions to occur; recent effective strategies include nanowires, nanoparticles embedded in polymeric matrices, and yolk-shell morphologies with carbon. [1-4]
The abundance of silicon on earth is second only to oxygen; it makes up 28% by mass of the earth’s crust. The natural abundance, non-toxicity, extremely high specific capacity, low cost, chemical stability, and low average delithiation potential of silicon make it an ideal energy material. [5] Research interest has only increased over the last 15 years, as many simultaneous attempts are made at solving the challenges of nanoscale silicon- the successful execution of which will make large scale manufacturing of silicon anode materials possible. [6]
The combination of nanosizing and engineering porosity within the silicon anode are the chief strategies to bring the cycle life necessary for commercialization. We report fabrication of anode material which consists of an additive free layer of silicon nanotubes bonded to copper foil, which has exhibited durability over 100 cycles. This promising novel silicon anode material has areal capacity of >2mAh·cm-2.
[1] Keller, C., et al., Effect of Size and Shape on Electrochemical Performance of Nano-Silicon-Based Lithium Battery. Nanomaterials (Basel), 2021. 11(2). [2] Yang, K., et al., 3D growth of silicon nanowires under pure hydrogen plasma at low temperature (250 degrees C). Nanotechnology, 2021. 32(6): p. 065602. [3] Shi, J., et al., A surface-engineering-assisted method to synthesize recycled silicon-based anodes with a uniform carbon shell-protective layer for lithium-ion batteries. J Colloid Interface Sci, 2021. 588: p. 737-748. [4] Xiao Hua Liu, L.Z., Shan Huang, Scott X. Mao, Ting Zhu, and Jian Yu Huang, Size-Dependent Fracture of Silicon Nanoparticles During Lithiation. ACS Nano, 2012. 6(2): p. 1522-1531. [5] Naoki Nitta, F.W., Jung Tae Lee, and Gleb Yushin, Li-ion battery materials: present and future. Materials Today, 2015. 18(5). [6] Jaramillo-Cabanzo, D.F., et al., One-dimensional nanomaterials in lithium-ion batteries. Journal of Physics D: Applied Physics, 2021. 54(8).

Fig. 1. Micro and nanostructure. Areal capacity.

Figure 1