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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigating Particle Cracking in Single- and Polycrystalline Nickel-Rich Cathodes using In Situ Impedance Spectroscopy

Sjödin, Mattias January 2021 (has links)
State-of-the-art Li-ion cathode materials are based on LiMO2 (M=Ni, Mn, Co) layered transition metal oxides (denoted NMC) with Ni-rich composition because of their high specific capacity. Yet, these materials suffer from poor capacity retention due to crack formation during de-/lithiation cycling. Particle cracking leads to exposure of new electrode surface which leads to Li-inventory loss, increased side reactions, and electric disconnection. Quantification of the extent of cracking is therefore desirable, especially during in situ whilst cycling of the Li-ion cell. Herein, we evaluate and improve an analytical methodology based on electrochemical impedance spectroscopy (EIS) in order to estimate the changes in electrochemically active surface area of both poly- and single-crystalline Ni0.8Mn0.1Co0.1(NMC811) active materials. A transmission-line model (TLM) applied to both non-blocking and blocking electrode condition was utilized in order to deconvolute and interpret the acquired experimental data. Fits of the complex TLM equivalent-circuits to the impedance spectra was facilitated by developing a global stochastic iterative function based on local multivariate optimization. Impedance analysis during short- term cycling showed that the single-crystalline NMC811 suffered from less particle cracking and side reactions compared to polycrystalline NMC811, which was also confirmed from post-mortem gas adsorption analysis. A novel approach to estimate the extent of particle cracking in commercial Li-ion cells by utilizing an empirically strong positive correlation between the charge-transfer capacitance and resistance was proposed. The work presented herein demonstrates the unique prospects of the EIS methodology in the development and research of future rechargeable batteries

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