자료유형  

 학위논문

Control Number  

0017162840

International Standard Book Number  

9798382739823

Dewey Decimal Classification Number  

540

Main Entry-Personal Name  

Fuhst, Mallory R.

Publication, Distribution, etc. (Imprint  

[S.l.] : University of Michigan., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

81 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

General Note  

Advisor: Kurdak, Cagliyan;Siegel, Donald J.

Dissertation Note  

Thesis (Ph.D.)--University of Michigan, 2024.

Summary, Etc.  

요약Improving the safety of rechargeable Li-ion batteries is needed given their widespread and growing use. Of particular concern are failures involving thermal runaway, a key contributor of which is the buildup of gaseous species in the cell. Gases develop from the degradation of the liquid electrolyte, potentially facilitated by interactions with the electrode surfaces. The first portion of this dissertation investigates these processes by using first principles calculations to model the interactions of a common electrolyte solvent molecule with a cathode surface. These materials are thought to be electrochemically stable, but renormalization of the electrolyte window at the cathode surface may lead to side reactions even within normal battery operating conditions. Our work finds that the undercoordinated Co ions on the (1014) low energy surface of LiCoO2 are in an intermediate spin state that makes them more receptive to electrostatic coordination with EC. The barrier for the decomposition of EC into CO2 and acetaldehyde is 2.1 eV, which suggests a kinetically limited reaction pathway at nominal operating temperature. This barrier is expected to decrease as the cathode is delithiated during charging.Another strategy for increasing the safety of rechargeable batteries is to switch to a solid-state electrolyte (SSE). SSEs are more stable, but struggle to match a liquid's high ionic conductivity. One avenue for increasing the conductivity of an SSE is the paddlewheel effect: coordinated motion between a rotating anion group and a migrating cation. First reported for the high temperature (HT) polymorph of Li2SO4, the existence of this phenomena has been the subject of debate for decades. The second component of this dissertation uses aiMD to model dynamics associated with Li migration in high- and low-temperature (LT) Li2SO4. Analysis of the rotational dynamics of the anions reveals that the SO4 anions reorient in the HT polymorph but not the LT polymorph, even at temperatures above the phase transition. Likewise, the simulations identify numerous Li migration events in the HT phase but none in the LT polymorph. These observations are consistent with experimental measurements. Analysis of Li displacements and anion rotations in the HT phase indicate that cation hops and anion reorientations are correlated in space and in time. Additional evidence supporting correlated behavior derives from the similar the energy barrier for Li migration, 0.48 eV, and anion reorientation, 0.40 eV.To further probe the mechanisms associated with paddlewheel dynamics, the third portion of this dissertation draws comparisons with other alkali-metal-based sulfates, Na2SO4 and K2SO4. These solids exhibit structural transformations similar to that of Li2SO4, yet are not reported to be ionic conductors in their HT phases. Consistent with experiments, aiMD simulations exhibit limited cation mobility in these phases. Nevertheless, anion rotations are present in both HT Na2SO4 and K2SO4. Given that anion rotations are present in all of the HT polymorphs studied, why is Li2SO4 the only phase that is ionically-conductive? The crystal structure of the HT polymorphs appears to be the answer. HT-Li2SO4 adopts an FCC lattice that contains occupied Li tetrahedral sites and vacant octahedral sites, which mediate Li migration. HT Na2SO4 and K2SO4 are hexagonal and contain no empty cation sites. We conclude that the presence of anion rotations alone is insufficient to impart high ionic conductivity - cation mobility also requires a sufficient defect concentration.

Subject Added Entry-Topical Term  

Chemistry.

Subject Added Entry-Topical Term  

Physics.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Applied physics.

Index Term-Uncontrolled  

Battery

Index Term-Uncontrolled  

Li-ion battery

Index Term-Uncontrolled  

Density Functional Theory

Index Term-Uncontrolled  

Solid electrolyte

Index Term-Uncontrolled  

Paddlewheel effect

Index Term-Uncontrolled  

Electrolyte gassing

Added Entry-Corporate Name  

University of Michigan Applied Physics

Host Item Entry  

Dissertations Abstracts International. 85-12B.

Electronic Location and Access  

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Control Number  

joongbu:658012