Electrode architecture of carbon-coated silicon nanowires through magnesiothermic reduction for lithium-ion batteries
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Research Letter
Electrode architecture of carbon-coated silicon nanowires through magnesiothermic reduction for lithium-ion batteries Young Gyu Nam, Mohammad Humood, Haejune Kim, and Andreas A. Polycarpou, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, USA Address all correspondence to Andreas A. Polycarpou at [email protected] (Received 17 June 2017; accepted 25 September 2017)
Abstract Carbon-coated silicon nanowires (C-Si NWs) were prepared as anodes for lithium-ion batteries (LIBs). The C-Si NWs were synthesized using a simple and effective fabrication strategy via magnesiothermic reduction. The synthesis sequence of carbon coating before the chemical etching of the reduced Si NWs/MgO composite was found to be critical for improved battery performance. In addition, carbon coating was found to help to stabilize the solid electrolyte interphase layer during battery cycling, which is important to realize the benefits of Si-based LIBs. This synthesis method provides an efficient route to synthesizing high-performance Si electrodes via magnesiothermic reduction.
Introduction Lithium-ion batteries (LIBs) have received considerable attention as the most advanced secondary batteries, because of their high-energy densities per volume and per weight. Over the past two decades, there has been significant research on LIBs to improve the energy density, cycle performance and rate capability for high-power and high-energy applications such as power tools, mobile electronics, and electric vehicles.[1] In addition, LIBs are favorable candidates for various stationary power storage applications such as renewable energy.[2] The performance of LIBs is mostly dependent on the characteristics of the electrode materials. Silicon (theoretical capacity is 4200 mAh/g based on Li4.4Si compared with 372 mAh/g for graphite[3]) is the most promising anode materials that could replace the current graphite electrodes. However, the increased Li richness in Si anodes during cycling processes results in breaking the Si-Si bonds due to large volume changes of Si up to 400%.[4,5] This repeated volume changes in the process of lithiation/delithiation causes pulverization and short battery life. For the same reason, as the cycle progresses, the solid electrolyte interphase (SEI) films on the surface of the electrodes become unstable and increase in thickness. The thick SEI films increase the Li diffusion resistance, and consumption of a large amount of cathode’s Li-ions.[6] Unless these technical issues are overcome, the realization of the benefits of Si-based LIBs will continue to be elusive. Progress in nanofabrication and nanomaterials have made significant breakthroughs to tackle the challenges of Si-based LIBs. Recent experimental and theoretical studies suggest several advantages of nanostructured electrode materials. These include: (1) increased surface area, resulting in higher
lithium-ion flux across the electrode/electrolyte interface, (2) better resilience to mechanical failure, and (3) higher l
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