Huw C. W. Parks

Lithium–sulfur batteries are promising candidates for next‐generation energy storage due to their high theoretical capacity and low cost. However, structural instability, polysulfide shuttling, and sluggish ion transport hinder the development of thick sulfur cathodes with high areal loading. Sulfurized polyacrylonitrile (SPAN) mitigates polysulfide shuttling via a quasi‐solid conversion mechanism; however, volume changes and limited ion transport remain challenging, particularly in thick electrodes. Here, a phase inversion‐engineered polymer scaffold is developed to fabricate mechanically robust, ion‐permeable, high‐loading SPAN cathodes. By tuning polymer crystallinity and pore architecture via temperature‐controlled nonsolvent‐induced phase inversion, a hierarchical, low‐tortuosity transport network is achieved, enabling balanced ionic conduction, electronic percolation, and mechanical integrity. The optimized cathode delivers a specific capacity of 1263.68 mAh/g of sulfur at 2 C with 90.83% capacity retention over 500 cycles and presents an ultrahigh electrode loading of 62.95 mg/cm ² , achieving 12.73 mAh/cm ² . This work demonstrates that phase inversion–enabled scaffold engineering is a scalable strategy for fabricating ultrahigh‐loading electrodes.

Solid‐state batteries (SSBs) are considered a safer alternative to conventional lithium‐ion batteries due to the replacement of flammable liquid electrolytes with solid electrolytes. However, many practical SSB designs incorporate liquid catholytes to reduce interfacial resistance at the cathode. The presence of liquid components introduces potential safety risks during failure events, yet the influence of catholyte formulation on cell safety remains poorly understood. In particular, the effect of catholyte gelation on thermal runaway behavior has not been experimentally evaluated. Here, we investigate the safety characteristics of QSSBs containing catholytes with varying degrees of gelation using nail penetration testing. Tests were performed on 2 Ah pouch cells at 100% SOC, with the surface temperature and video recorded throughout. Cells containing liquid catholytes underwent violent thermal runaway, reaching temperatures exceeding 400°C. In contrast, cells incorporating fully gelled catholytes showed no thermal runaway, with temperatures remaining below 25°C. Intermediate levels of catholyte gelation did not produce intermediate safety responses, with partial gelation failing to significantly mitigate failure severity. These results demonstrate that catholyte gelation can dramatically alter the thermal runaway behavior of QSSBs under internal short‐circuit conditions and highlight the importance of electrolyte formulation when evaluating the safety of SSB systems.

During battery operation, cracking occurs in Nickel Manganese Cobalt (NMC) oxide secondary particles. Cracked particles appear darker in micro‐computed tomography (micro‐CT) images due to the partial volume effect, where voxels containing both void and solid yield intermediate grey‐levels. This work presents an automated method for tracking grey‐level changes caused by this effect in large, statistically meaningful micro‐CT datasets containing over 10 000 individual particles. It extends earlier work using the GREAT algorithm to analyze NMC particles in tomography images. The new GREAT2 algorithm increases processing speed, from around 1,400 particles per day with GREAT to over 10 000 particles in under a minute. Furthermore, this work introduces methods for automated tracking of grey‐level intensity changes in individual particles through different states of charge in an operando experiment. This capability enables temporal analysis of particle degradation mechanisms. Additional data processing methods are presented that extract useful insights. Through this work we show that the large sample sizes, enabled by this method and GREAT2, allow for statistically robust analysis of particle populations. These advances significantly accelerate the tomographic study of cracking in battery electrodes. The GREAT2 algorithm and associated workflows have been made available as the GRAPES Python toolkit.

Operando X-ray imaging of NMC811 electrode revealing a non-linear cracking profile as the particles delithiate.

To understand fracture behaviour in battery materials, X-ray computed tomography (X-ray CT) has become the primary technique for non-destructive particle analysis. Cracking causes performance decline in polycrystalline NMC811 by exposing new surfaces for parasitic electrolyte reactions and disconnecting active material from the electrode matrix. First cycle crack formation has been documented, but definitive electrochemically induced particle fracture is challenging to assess due to complex sample preparation and high-resolution X-ray imaging requirements. Presented here is an operando X-ray CT technique that enables accurate observation of fracture behaviour during de-/lithiation. A non-linear relationship between fracture behaviour and cell voltage was uncovered, and evidence of particle reformation during re-lithiation. Using a grey level analysis algorithm for fracture detection, we expedite damage evaluation in several thousands of particles throughout the electrochemical process, understanding crack initiation, propagation, and closure on a large, statistical scale and give the ability to track any one of the thousands of particles through its individual electrochemical history. Additionally, we explore the effects of continued volumetric hysteresis on particle damage. For the first time, we demonstrate the complex plurality of fracture behaviour in commercial lithium-ion battery materials, aiding in designing mitigation strategies against particle fracture.

Establishing the nature of crack formation is paramount to understanding the degradation modes that govern decline in battery performance. Cracking has several possible origins; however, it can be classified in two general cases: mechanically induced, during manufacturing, or electrochemically induced, during operation. Accurate and repeatable tracking of operational cracking without the convolution of pre-existing cracks is highly challenging; observing these features requires the highest resolutions possible for 3D imaging techniques, necessitating very small sample geometry, while also achieving realistic electrochemical performance. Here, we present a technique in which particle cracking can be completely attributed to electrochemical stimulation via a pseudo in-situ laboratory X-ray nano computed tomography (CT) technique. Observed upon electrochemical delithiation of NMC811, was significant cracking within the core of secondary particles which propagated radially. We also noted that contrary to crystallographic data, which suggests the unit cell volume reduces upon charging, significant volume expansion of the secondary particle occurred.