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NAERINGSPH-Nærings-phd

Carbon-coated Silicon Nanoparticles for long-life, high rate, and high capacity anodes

Alternative title: Karbonbelagte silicon nanopartikler for anoder med lang levetid, høy hastighet og høy kapasitet

Awarded: NOK 2.1 mill.

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Project Number:

304644

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Project Period:

2019 - 2023

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Lithium based energy storage devices are one of the modern world's most important products. With billions of portable devices such as mobile phones currently in use, as well as a strongly growing electric vehicle market, demand is higher than ever. This market growth requires the development of new technologies that increase the power, charge rate, safety and life time of lithium based energy storage devices. Silicon has recently attracted interest as a storage medium for lithium ion batteries (LIBs) and lithium ion capacitors (LICs) due to its ~10-fold increase in storage capacity compared to the conventionally used graphite. However, as silicon stores lithium within its structure it swells up to 320%, which causes problems such as electrode cracking and excess formation of impurities. This project studied the use of Si-P alloys for faster charge/discharge of Si cells. The results showed that the inclusion of P in Si is promising for high-power Si batteries. Analytical techniques developed during the course of this project allow for faster and more accurate analysis of Si data. This allows Si researchers to speed up development of Si batteries. EIS studies on Si half cells revealed the complex relationship between Si and Li. This has allowed for more nuanced interpretations of Si data, and gives insights not only into how Si behaves during cycling, but also how to mitigate the issues faced by commercial actors.

This project studied the use of Si-P alloys for faster charge/discharge of Si cells. The results showed that the inclusion of P in Si is promising for high-power Si batteries. Analytical techniques developed during the course of this project allow for faster and more accurate analysis of Si data. This allows Si researchers to speed up development of Si batteries. EIS studies on Si half cells revealed the complex relationship between Si and Li. This has allowed for more nuanced interpretations of Si data, and gives insights not only into how Si behaves during cycling, but also how to mitigate the issues faced by commercial actors. As of today, development has begun for commercialization of LIBs incorporating the methods and information used here.

The purpose of the PhD project will be to 'make viable' the use of Silicon Nanoparticles (SiNPs) in energy storage devices. The anodes in energy storage devices currently use graphite as the intercalation agent for lithium ions on the anode. While graphite can stably accept and release lithium ions many times, the total amount of lithium ions it can store is limited, with a theoretical capacity of 372mAh/g. In contrast, silicon can store a much larger amount of lithium, giving it a theoretical capacity of 3600mAh/g. This large increase in capacity is the ‘holy grail’ of anode design, and promises to pave the way for more energy dense, and higher rate anodes. However, the alloying of silicon gives rise to a number of problems, mainly the problem of swelling of the silicon as the lithium atoms alloy with the silicon. The difference in size of the pure to alloyed silicon is 320%. This can lead to disintegration of the anode and the cracking of the solid-electrolyte formation (SEI), both of which drastically lower the lifetime of an anode. The main solution to anode fracturing when using silicon is to use silicon nanoparticles instead of bulk silicon, as the nanoparticles can sustain the strain imposed on them during swelling and shrinking. However, the increased surface area increases the cracking of the SEI film, which in turn leads to excess SEI formation. In order to decrease the cracking of the SEI film and reduce anode disintegration, this PhD project proposes to explore the use of / and develop various surface coatings on SiNPs to not only create a more stable barrier against SEI formation, but also to reduce strain on the anode due to swelling and shrinking.

Publications from Cristin

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NAERINGSPH-Nærings-phd