TY - GEN
T1 - Development of novel electrode materials for rechargeable batteries
AU - Jakobsen, Christian Lund
PY - 2022/11/9
Y1 - 2022/11/9
N2 - In this thesis, four different materials, with promising aspect as positive electrode
materials for rechargeable Li- or Na-ion batteries, are investigated with focus on their
structural changes during ion-intercalation. The bearing methodology of the thesis has
been operando powder X-ray diffraction and pair distribution function experiments
analyzed through Rietveld and real-space refinement to obtain structural models
describing the atomic scale of the electrodes and their changes during charge and
discharge.Oxide-based materials are among the best well-performing intercalation
electrodes. In this thesis two oxides have been subject of investigation. One of these,
rutile/pyrolusite β-MnO2, has proven to accommodate at >2 Li-ions during the first
discharge. However, the ion-intercalation induces significant structural disorder. The
structure of the disordered state is revolved herein to consists of nano-domains of a
spinel-like LixMnO2 phase. The other oxide-material, NaCrO2, has been studied in
great detail herein to elucidate both the crystalline-to-crystalline and order-disorder
transitions occurring during charge and discharge. The material goes through several
phase transition upon charge resulting in continuous expansion of the interlayer
distance as opposed to very discrete two-phase transition during discharge.
Furthermore, a previously missed charge-intermediate has been discovered in this
study. As more than 60% Na is extracted from the as-synthesized material NaCrO2,
long-range order is lost as Cr migrates irreversibly to the vacant Na layers forming a
disordered O3-phase.As the oxides undergoes significant structural changes, the benefits of the more
stable polyanionic frameworks are quite appealing. Herein lies the very attractive
phosphates of which two have been studied in this thesis. The orthorhombic
polymorph β-LiVOPO4 shows core-shell formation, which block Li-migration but can
be removed via high-energy ball milling. The material follows a two-phase reaction
during charge and discharge but unexpected solid solution behavior in the Li-poor
phase (β-VOPO4) was revealed. Finally, this thesis combines the advantages of layered
XII
structure with the stability from the polyanions through a layered sodium iron
phosphate, Na3Fe3(PO4)4 which can accept both Li- and Na-ions reversibly. The
material reacts as a solid-solution upon intercalation, where the intercalation of Na
occurs in the cavities between the two iron-sites, causing cell-expansion. As the
material has time to relax after discharge, the intercalated Na migrates to the Na layers,
causing a contraction of the cell.In this thesis, profound new knowledge has been presented for four materials that
has a possible future as positive electrode in rechargeable batteries. The understanding
of structural disorder in these materials during ion (de)intercalation has thoroughly
been analyzed via state of the art characterization techniques. The discoveries in the
thesis can hopefully provide knowledge to predict behaviors of more complex
materials, as material compositional tuning will be imminent for the future of
rechargeable batteries.
AB - In this thesis, four different materials, with promising aspect as positive electrode
materials for rechargeable Li- or Na-ion batteries, are investigated with focus on their
structural changes during ion-intercalation. The bearing methodology of the thesis has
been operando powder X-ray diffraction and pair distribution function experiments
analyzed through Rietveld and real-space refinement to obtain structural models
describing the atomic scale of the electrodes and their changes during charge and
discharge.Oxide-based materials are among the best well-performing intercalation
electrodes. In this thesis two oxides have been subject of investigation. One of these,
rutile/pyrolusite β-MnO2, has proven to accommodate at >2 Li-ions during the first
discharge. However, the ion-intercalation induces significant structural disorder. The
structure of the disordered state is revolved herein to consists of nano-domains of a
spinel-like LixMnO2 phase. The other oxide-material, NaCrO2, has been studied in
great detail herein to elucidate both the crystalline-to-crystalline and order-disorder
transitions occurring during charge and discharge. The material goes through several
phase transition upon charge resulting in continuous expansion of the interlayer
distance as opposed to very discrete two-phase transition during discharge.
Furthermore, a previously missed charge-intermediate has been discovered in this
study. As more than 60% Na is extracted from the as-synthesized material NaCrO2,
long-range order is lost as Cr migrates irreversibly to the vacant Na layers forming a
disordered O3-phase.As the oxides undergoes significant structural changes, the benefits of the more
stable polyanionic frameworks are quite appealing. Herein lies the very attractive
phosphates of which two have been studied in this thesis. The orthorhombic
polymorph β-LiVOPO4 shows core-shell formation, which block Li-migration but can
be removed via high-energy ball milling. The material follows a two-phase reaction
during charge and discharge but unexpected solid solution behavior in the Li-poor
phase (β-VOPO4) was revealed. Finally, this thesis combines the advantages of layered
XII
structure with the stability from the polyanions through a layered sodium iron
phosphate, Na3Fe3(PO4)4 which can accept both Li- and Na-ions reversibly. The
material reacts as a solid-solution upon intercalation, where the intercalation of Na
occurs in the cavities between the two iron-sites, causing cell-expansion. As the
material has time to relax after discharge, the intercalated Na migrates to the Na layers,
causing a contraction of the cell.In this thesis, profound new knowledge has been presented for four materials that
has a possible future as positive electrode in rechargeable batteries. The understanding
of structural disorder in these materials during ion (de)intercalation has thoroughly
been analyzed via state of the art characterization techniques. The discoveries in the
thesis can hopefully provide knowledge to predict behaviors of more complex
materials, as material compositional tuning will be imminent for the future of
rechargeable batteries.
U2 - 10.21996/hb4x-qm42
DO - 10.21996/hb4x-qm42
M3 - Ph.D. thesis
PB - Syddansk Universitet. Det Naturvidenskabelige Fakultet
ER -