Intrinsically Safe Materials for Impact-Resistant Lithium-ion Batteries

Lithium-ion batteries (LIBs) are extensively employed in various applications, including powering electronics, mobile phones, laptops, and tablets. They are also used in electric vehicles, and in the storage of renewable energy produced from intermittent sources like solar and wind powers. However, they face a significant safety challenge: thermal runaway triggered by mechanical abuse, which poses a risk of catastrophic consequences. It highlights the urgent need to develop intrinsically safe materials to prevent thermal runaway when subjected to mechanical abuse. In this thesis, three impact-resistant components have been developed to reinforce the safety of LIBs. They include shear thickening electrolyte, Kevlar electrodes, and Kevlar separator, all of which enhance the battery’s resilience to mechanical abuse while maintaining electrochemical performance.

In the first work, a novel shear thickening electrolyte (STE) has been produced for impact-resistant LIBs. It is realised by integrating poly(ethylene oxide) (PEO) with silica nanoparticles within a common liquid electrolyte. This STE features low viscosity, high ionic conductivity, long-term stability, and impact resistance. Silica particles interact with polymer chains to facilitate the formation of hydroclusters for shear thickening effect at a relative low weight percentage (2.2 wt%) of filler. This low viscosity STE, with the added benefit of lightweight, holds the potential to realise impact-resistant and lightweight LIBs.

In the second work, a highly impact-resistant Kevlar-based LIBs has been developed to mitigate thermal runaway against mechanical abuse. Kevlar electrodes are fabricated by coating active materials onto metallic Kevlar fabrics. Their compatibility with liquid electrolyte and STE enables them to achieve comparable electrochemical performance to foil-based electrodes. These electrodes can effectively dissipate impact energy by inheriting the strong mechanical properties of Kevlar fabrics. Their integration with shear thickening electrolytes further improves the impact resistance by leveraging the induced shear thickening effect and increased yarn to yarn friction between Kevlar fabrics. This integration resembles the configuration as liquid body armour.

In the third work, a porous Kevlar separator has been developed for impact-resistant LIBs. This is achieved by introducing a porogen into the aqueous precursor solution through a non-solvent evaporation and vacuum-assisted filtration technique. The porogen has a high boiling point which allows sufficient time for the formation of a porous structure within the cross-linked polymer network when evaporating the solvent. The resulting Kevlar separator exhibits high ionic conductivity, excellent thermal stability, flame retardancy, and good electrolyte wettability. Its efficiency is evidenced by the delivered excellent electrochemical performance and good impact resistance.

In summary, three key components including shear thickening electrolyte, the mechanically strong Kevlar electrodes and Kevlar separator, have been explored to reinforce the impact resistance of LIBs. This research work systematically investigates their impact resistance and electrochemical performance to pave a new path in the development of safe LIBs.