Fabrication of laminated solid electrolytes with compressive surface stresses for lithium batteries

Thesis

The use of solid-state electrolyte (SSE) for all-solid-state batteries (ASSB) has long been touted to be the next big step for rechargeable lithium-ion batteries. Inorganic oxide SSE was thought to be able to mitigate the Li dendriting problem in such batteries, owing to the high Young’s modulus of this class of SSE. However, this is not the case, with a recent discovery showing that dendrites can still penetrate through by propagating cracks through the brittle oxide SSE. Therefore, should it be possible that the SSE be made more resistant to crack propagation, it should also inhibit the dendriting phenomenon. One main idea by which this can be achieved is by introducing residual compressive stress to the SSE. A question then arises: Is it possible for compressively stressed SSE, induced by means of a symmetrically laminated structure, be fabricated and if it is how will it affect the conductivity and dendrite resistance of said laminated SSE? This thesis presents that such laminated SSE is possible.

Perovskite-type Li3/8Sr7/16Ta3/4Zr1/4O3 (LSTZ) and differently doped garnet type (Al,Ga,Ta)y - LixLa3ZrzO12 (LLZO) SSEs were synthesized using solid-state method, with an optimized calcining regime. It was found that 10% Li excess and 12.5% Li excess was needed for LSTZ and LLZO respectively, to compensate for lithium loss during calcination. After sintering, the resulting pellets show good conductivity, in the order of 10-4 S cm-1. Elastic properties of the pellets were also measured and presented.

Having verified that the synthesized powders are conductive, an innovative sintering technique to co-sinter Ta-doped and Al-doped LLZO was presented. Al-LLZO – Ta-LLZO – Al-LLZO laminated pellets with surface compressive residual stresses were successfully sintered and was demonstrated to be twice as conductive compared to the constituent’s monolithic pellets. CCD cycling suggests that the laminate can withstand higher current compared to similarly prepared monolithic Al-LLZO.

Authors: Tannesia, L

• DOI: 10.5287/ora-azaknq8kr
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: laminated; solid state electrolyte
• Subjects: Battery industry; Materials