Lithium-ion batteries have become synonymous with modern consumer electronics and potentially, are the cornerstone to development of integrated electrified infrastructure that can support a clean and renewable national energy grid. Despite the widespread applications due to the favourable performance parameters, recent events have elevated the safety concerns associated with lithium-ion batteries. However, there is great difficulty in rapid diagnostic analysis outside specialised laboratories which can hinder the review of functional safety- and novel energy dense- materials for lithium-ion energy storage.

The dynamic evolution of internal architectures and novel active materials across multiple length scales are investigated in this thesis; with in-situ and operando acoustic spectroscopy (AS) via ultrasonic time of flight (ToF) probing, high speed synchrotron X-ray imaging, computed tomography and fractional thermal runaway calorimetry. The identification of characteristic precursor events such as gas-induced delamination in degradation mechanisms before eventual failure by AS; is correlated with X-ray imaging and post-mortem computed tomography (CT), highlighting the potential for battery management systems. Mitigation and prevention of failure with plasticized current collectors and thermally stable cellulose separators was also investigated at multiple length scales, with the transient mechanical structure compared with their commercial counterparts in cylindrical cells. Further work investigating the robustness of acoustic spectroscopy and polymer current collectors were applied to pure silicon nanowire negative electrodes.

The studies reported in this thesis assess novel materials in lithium-ion batteries, and the potential impact of the work is highlighted. Development of AS via ToF probing offers another unique and field deployable insight allowing more complete and comprehensive understanding of batteries as they continue to evolve in complexity. Lithium-ion failure characterisation techniques and literature have evolved and provided insights into the function of polymer current collectors in different cell formats and chemistries. Findings presented in this thesis are anticipated to augment future inherently safer battery design and characterisation of lithium-ion energy storage thermal runaway.