SOLID-STATE NMR INVESTIGATION OF STRUCTURE AND DYNAMICS OF SOLID ELECTROLYTES AND COATINGS FOR LI-ION BATTERY APPLICATIONS

Li-ion batteries have revolutionised energy storage in portable electronics. 30 years later, batteries are in the process of electrifying ground-based transport. For batteries to replace fossil fuels completely, it is paramount to decrease the inherent safety risks of current flammable electrolytes and avoid large battery fires. Potential solutions include solid state batteries in which the organic solvent is replaced by a polymer or inorganic solid electrolyte. Cubic Li7La3Zr2O12 (LLZO) is a solid electrolyte of interest due to its high Li-ion conductivity for an oxide ceramic and expected stability against Li metal. Dopants (e.g. Ga, Al, Ge, Ta) are required to stabilize the faster conducting cubic phase, but the position and overall influence of the dopants is still debated, even though some dopants lead to higher increases in conductivity. In this work, solid-state nuclear magnetic resonance (NMR) has been used to obtain an improved understanding of the local Al and Ga dopant environments. Combined with NMR shift calculations, the unusual 27Al and 71Ga-NMR spectra obtained for doped LLZO were explained and the two high frequency signals assigned to the same tetrahedral site but with different local environments. NMR based techniques were also used to examine the ion mobility directly, which showed good agreement with bulk conductivity measurements with impedance spectroscopy. Follow up measurements were concerned with the influence of exposure to air and moisture on the ion mobility and provided evidence for a decreased Li-ion mobility. The second part of this thesis focused on protective Al-based coatings for cathode materials like LiCoO2, which can improve cycle life and high voltage stability. The aim was to study the local structure created by an “nano-AlPO4” coating on LiCoO2 and provide structural information to better understand the improvement mechanism. 27Al NMR and complementary techniques were applied to study the migration of Al3+ ions into the LiCoO2 host structure and combined with 31P NMR to clarify the conversion mechanism. The conversion of AlPO4 on LiCoO2 to Li3PO4, ɤ-LiAlO2 and LiAlxCo1-xO2 was proven with NMR for the first time. Overall, multi-nuclear solid-state NMR, and in particular 27Al NMR, was used to study the local structure and dynamics of battery materials. The local structure-property relationships and insight developed in this work for LLZO and Al-based coatings will help enable their use in Li-ion batteries.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2020

Author dc:creator

• Emge, Steffen

Advisor dc:contributor.advisor

• Grey, Clare P

• NMR
• LLZO
• solid electrolyte
• coating

Licence

• https://www.repository.cam.ac.uk/bitstreams/a8a1310e-dc23-4d0e-8b71-908dbc20e5e0/download
• https://creativecommons.org/licenses/by-sa/4.0/

Language dc:language

eng

Author Identifier

0000-0001-8613-9465

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/318497