Abstract
The electrochemical performance of novel nano-silicon/biogas-derived carbon nanofibers composites (nSi/BCNFs) as anodes in lithium-ion batteries was investigated, focusing on composition and galvanostatic cycling conditions. The optimization of these variables contributes to reduce the stress associated with silicon lithiation/delithiation by accommodating/controlling the volume changes, thus preventing anode degradation and therefore improving its performance regarding capacity and stability. Specific capacities up to 520 mAh g−1 with coulombic efficiency > 95% and 94% of capacity retention are achieved for nSi/BCNFs anodes at electric current density of 100/200 mA g−1 and low cutoff voltage of 80 mV. Among the BCNFs, those no-graphitized with fishbone microstructure, which have a great number of active sites to interact with nSi particles, are the best carbon matrices. Specifically, a nSi:BCNFs 1:1 weight ratio in the composite is the optimal, since it allows a compromise between a suitable specific capacity, which is higher than that of graphitic materials currently commercialized for LIBs, and an acceptable capacity retention along cycling. Low cutoff voltage in the 80–100 mV range is the most suitable for the cycling of nSi/BCNFs anodes because it avoids formation of the highest lithiated phase (Li15Si4) and therefore the complete silicon lithiation, which leads to electrode damage.
Highlights
In the last decades, the market of lithium-ion batteries (LIBs) has increased enormously due to, mainly, the vertiginous growth of the portable electronic devices that use them
A nSi:biogas-derived carbon nanofibers (BCNFs) 1:1 weight ratio in the composite is the optimal, since it allows a compromise between a suitable specific capacity, which is higher than that of graphitic materials currently commercialized for LIBs, and an acceptable capacity retention along cycling
Respecting anode materials, silicon has emerged as a promising alternative due to the high theoretical specific capacity, the relatively low working potential, the abundance in earth crust and the existence of an industrial manufacturing process [3,4,5,6]
Summary
The market of lithium-ion batteries (LIBs) has increased enormously due to, mainly, the vertiginous growth of the portable electronic devices (mobile phones, tablets, laptop computers, etc.) that use them These batteries are an attractive and feasible alternative for the development of massive electric energy storage systems to allow the implementation of renewable energy sources, as well as the electric vehicle, contributing to the transition from an energy model based on fossil fuels to other more sustainable. Intensive research is being carried out to improve the overall performance of LIBs by increasing both the energy density and power and extending the lifetime, which are all largely governed by the electrode materials In this respect, the development of new electrode materials to replace graphite and LiCoO2 , traditionally used in anodes and cathodes of LIBs, respectively, is receiving worldwide attention by researchers [1,2]. The lithiation of Si causes successive expansions of its internal structure, leading to particles’ fracture and consequent loss of electric contact between them, as well as a continuous formation–breaking–formation of the
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