Novel manufacturing routes for solid-state batteries

Thesis

Solid-state batteries (SSBs) based on sulphide solid electrolytes (SEs) have the potential to increase safety and energy density compared with lithium-ion batteries (LIBs). However, SSB fabrication is at an immature stage. The thesis describes three novel investigations of materials design and associated manufacturing approaches to SE separators and anode-free SSBs.

A solvent-free processing approach was developed for sulphide separators based on polytetrafluoroethylene binder fibrillation and hot calendering, and the microstructure and performance compared with slurry cast equivalents. Optimized free-standing SE sheets had density ∼ 84 %, pore diameter < 1 µm and ionic conductivity > 1 mS/cm at 60 °C. Dry processed 600 µm thick separators had a critical current density for Li dendrite penetration of 1 mA/cm2 compared with 2 mA/cm2 for slurry cast separators.

Anode-free SSB cells with LiNi0.8Mn0.1Co0.1O2/sulphide hybrid cathodes were fabricated with different ∼ 13 µm spray-printed Ag/C particulate interlayer architectures to promote uniformity of plated metallic Li on charging. Interlayers with increased Ag fraction at the current collector showed improved performance, including an initial discharge capacity of > 190 mAh/g, reduced capacity degradation during cycling and a Coulombic efficiency > 98% after 100 cycles. The greater uniformity of Li plating was revealed by cross-sectional microscopy, and a mechanism proposed.

Building on these findings, two alternative, novel Ag/C interlayer processing techniques for anodefree cells were investigated. Precipitation of Ag nanoparticles onto a carboxymethyl cellulose/C precoating allowed control of Ag diameters (10 - 150 nm), but electrochemical performance was not improved. However, sputtering of ∼ 100 nm thick Ag onto a ∼ 1 µm C pre-coated Cu current collector again facilitated greater uniformity of both Li plating and stripping that was revealed by cross-sectional microscopy, leading to a high performing initial discharge capacity of > 200 mAh/g and an initial Coulombic efficiency of 86 %.

Authors: Metzler, M

• DOI: 10.5287/ora-1418jaomz
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Electrochemistry; Solid state batteries; Processing