Alloying anode materials are candidates for replacing graphite in lithium-ion batteries, offering increases in energy and power, but suffer from rapid pulverization-induced degradation upon cycling due to large volume changes from (de)lithiation. Many composite material and nanostructural approaches have been employed to accommodate these volume changes, though the effective design of long-lived anodes has been hindered by a lack of in operando characterization. In this dissertation, x-ray diffraction-based strain measurement techniques are used to characterize the strain evolution of silicon, Ni3Sn 2 and SnO2 nanostructured anodes in operando during lithiation—delithiation cycling, measuring both the average and distribution of strains. Plasticity and damage processes leading to capacity fade are revealed, enabling the bulk measurement of degradation occurring at the nanoscale.
Examining the strain evolution a nickel-supported silicon inverse opal anode, a clear relationship between lithiation, average strain and strain distribution is observed, with increasing lithiation inducing compressive mismatch stresses up to 230 ± 40 MPa (Ni) and simultaneously increasing the strain distribution up to 0.54 ± 0.05 %. A two-step (de)lithiation mechanism is observed, with a second, more gradual change in strain suggesting plasticity occurs in the anode upon both lithiation and delithiation.
Employing the same methodology towards a nickel supported Ni3Sn 2 inverse opal anode, (de)lithiation again induces compressive mismatch strains and an increase in the strain distribution proportional to lithiation extent; similar mechanisms for lithiation exist between the two systems. However, the deformation of the Ni3Sn2 anode is much lower than the Si anode, with linear changes in strain upon (de)lithiation suggesting that inelastic deformation is caused by damage processes in this system.
When these techniques are applied to a SnO2@Cu foam anode, with a different structure and chemistry, the strain behavior observed is very similar to previous studies on inverse opal anodes, demonstrating the versatility of these techniques and the similarity of responses within the alloying family of anodes. Twenty-seven in operando cycles are probed, with both intra- and inter-cycle analysis revealing ratcheting changes in strain evolution with cycle number. These changes point towards conductive pulverization and/or delamination as the primary mechanical failure mode(s).
|Advisor:||Dunand, David C.|
|Commitee:||Faber, Katherine, Hersam, Mark, Okasinski, John S.|
|Department:||Materials Science and Engineering|
|School Location:||United States -- Illinois|
|Source:||DAI-B 77/05(E), Dissertation Abstracts International|
|Subjects:||Energy, Materials science|
|Keywords:||Alloying anodes, In operando, Lithiation strain, Lithium ion batteries, Silicon anodes, Tin anodes|
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