Abstract
Silicon (Si) and composites thereof, preferably with carbon (C), show favorable lithium (Li) storage properties at low potential, and thus hold promise for application as anode active materials in the energy storage area. However, the high theoretical specific capacity of Si afforded by the alloying reaction with Li involves many challenges. In this article, we report the preparation of small-size Si particles with a turbostratic carbon shell from a polymer precoated powder material. Galvanostatic charge/discharge experiments conducted on electrodes with practical loadings resulted in much improved capacity retention and kinetics for the Si/C composite particles compared to physical mixtures of pristine Si particles and carbon black, emphasizing the positive effect that the core–shell-type morphology has on the cycling performance. Using in situ differential electrochemical mass spectrometry, pressure, and acoustic emission measurements, we gain insights into the gassing behavior, the bulk volume expansion, and the mechanical degradation of the Si/C composite-containing electrodes. Taken together, our research data demonstrate that some of the problems of high-content Si anodes can be mitigated by carbon coating. Nonetheless, continuous electrolyte decomposition, particle fracture, and electrode restructuring due to the large volume changes during battery operation (here, ∼170% in the voltage range of 600–30 mV vs Li+/Li) remain as serious hurdles toward practical implementation.
Highlights
The demands imposed on battery materials with respect to energy storage capacity, durability, cost, and so forth are ever increasing
After polymerization details of which are given in the Experimental Section the precursor material, containing ≈20 wt % Si (see thermogravimetric analysis (TGA) in Figure S1), was heated under an argon atmosphere at temperatures of 700, 800, or 900 °C to convert the organic shell into carbon
We have demonstrated the successful preparation of small-size Si/C composite particles from a novel polymercoated precursor material
Summary
The demands imposed on battery materials with respect to energy storage capacity, durability, cost, and so forth are ever increasing. A direct result of the large volume changes of Si during Li insertion/extraction with cycling is particle fracture and anode self-pulverization, both of which can be studied by acoustic emission (AE) measurements To this end, half-cells with the LP57 electrolyte using the Si/C composite-containing electrode were built and cycled for five cycles. Hits were detected more or less over the entire potential range, with the highest rate close to the upper cut-off potential
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