Advanced characterisation techniques for battery safety assessment

The need to shift to cleaner energy sources is imperative. Battery technology is considered a highly promising technology to successfully bring about this shift. It has already been implemented in numerous ways and features in our day-to-day lives; from mobile phones to homes. Recently, concerns regarding their safety have increased and as a result, governments have boosted research efforts in this area, with the added urge to work collectively with industry partners and regulatory bodies. These cells are prone to undergo catastrophic failures as a result of a series of exothermic reactions (thermal runaway) that can be triggered by several methods. Many research efforts have been made to understand this phenomenon from various perspectives: material selection, mechanical design, mitigation or preventative measures. This thesis shows how we can begin to comprehend this complexity and apply it to advancing existing battery safety assessment techniques. Through thermal analyses and multi-scale X-ray CT imaging, the correlations between heat generation and battery architecture are addressed. In this work, for the first time, differential scanning calorimetry was used to measure heat signals from full cells, high aspect ratio battery samples were imaged and a custom-built calorimeter chamber was developed to provide operando images and heat measurements of cells undergoing thermal failure. The results obtained from the methodologies and techniques established in this work have advanced our understanding of how various battery material morphologies and architectures behave under certain stresses. In turn, these findings can aid not only in the development and manufacture of safer lithium-ion batteries but also in the standardisation of testing standards, and improvement of failure mitigation strategies

X-ray Computed Tomography for Failure Mechanism Characterisation within Layered Pouch Cells

Lithium-ion battery (LIB) safety is a multi-scale problem: from the whole-cell architecture to its composite internal 3D microstructures. Substantial research is required to standardise failure assessments and optimise cell designs to reduce the risks of LIB failure. In this work, the failure response of a 1 Ah layered pouch cell with a commercially available NMC cathode and graphite anode at 100 % SOC (4.2 V) is investigated. The mechanisms of two abuse methods; mechanical (by nail penetration) and thermal (by accelerating rate calorimetry) are compared by using a suite of post-mortem analysis methods. Post-mortem whole-cell architectural changes and electrode layer deformations were analysed for both mechanisms using non-invasive X-ray computed tomography. Furthermore, changes to electrode surfaces, bulk microstructures and particle morphologies are compared by following a proposed cell disassembly and post-mortem sample preparation methodology. Building on the insights into critical architectural weak points, electrode behaviours and particle cracks, the reliability of X-ray computed tomography as a guide for LIB failure assessment is demonstrated

Thermal Runaway of Li-Ion Cells: How Internal Dynamics, Mass Ejection, and Heat Vary with Cell Geometry and Abuse Type

Thermal runaway of lithium-ion batteries can involve various types of failure mechanisms each with their own unique characteristics. Using fractional thermal runaway calorimetry and high-speed radiography, the response of three different geometries of cylindrical cell (18650, 21700, and D-cell) to different abuse mechanisms (thermal, internal short circuiting, and nail penetration) are quantified and statistically examined. Correlations between the geometry of cells and their thermal behavior are identified, such as increasing heat output per amp-hour (kJ Ah-1) of cells with increasing cell diameter during nail penetration. High-speed radiography reveals that the rate of thermal runaway propagation within cells is generally highest for nail penetration where there is a relative increase in rate of propagation with increasing diameter, compared to thermal or internal short-circuiting abuse. For a given cell model tested under the same conditions, a distribution of heat output is observed with a trend of increasing heat output with increased mass ejection. Finally, internal temperature measurements using thermocouples embedded in the penetrating nail are shown to be unreliable thus demonstrating the need for care when using thermocouples where the temperature is rapidly changing. All data used in this manuscript are open access through the NREL and NASA Battery Failure Databank

Metallized Plastic Current Collectors

Metallized plastic current collectors are an innovation patented by the Soteria Battery Innovation Group with the promise of isolating active material involved in an internal short by vaporizing and isolating the short from the rest of the cell electrode jellyroll or stack. Partnering with NREL, UCL, Coulometrics, and Soteria, NASA is leading a research effort into demonstrating the merits and understanding the phenomena of this safety innovation using prototype 18650 cylindrical cells vs control cells with standard metal foil current collectors. Cells with and without the plastic collector, with and without the on-demand internal short circuit device, and with polymer or cellulose separators were made. Safety evaluations were done with driving cells into thermal runaway (TR) with thermal and nail penetration triggers while inside our TR calorimeter and with ultra high speed X-ray videography provided at Synchrotrons. Preliminary results suggests that the thermally unstable plastic current collector innovation has great promise for preventing TR or reducing the severity of the TR output

Health status, difficulties, and desired health information and services for veterans with traumatic brain injuries and their caregivers: A qualitative investigation.

Traumatic brain injury (TBI) is considered the signature injury among military service member and Veterans who served in Operation Iraqi Freedom and Operation Enduring Freedom with over 360,000 individuals sustaining a first-time TBI in the military. These service members and Veterans, and their caregiver(s), must navigate multiple health systems and find experts across many fields of expertise to recover and optimize functionality. Twenty-two individuals, 10 caregivers of Veterans with TBI, 12 Veterans with TBI, participated in semi-structured interviews. Responses were coded using NVivo. Participants from both groups reported difficulties finding community supportive services (support groups) in local communities. Most participants identified the need for an advocate or point-person to help guide them to needed services and provide ongoing support in the post-acute health care recovery phase. Caregivers and Veterans desired a more personalized recovery plan from their medical professionals. When describing their ideal health information and services model most identified interactivity and twenty-four-hour availability as essential components. To provide Veterans and caregivers with optimal support and resources to navigate a complicated health services system, advocates and personalized care plans are needed. Future research should examine the feasibility and cost-effectiveness of these services

Prevention of lithium-ion battery thermal runaway using polymer-substrate current collectors

International audienceIsolating electronically conducting material from internal short circuits is a promising way to prevent the onset of thermal runaway within lithium-ion cells. Here, a metal-coated polymer current collector, which is designed to disconnect internal short circuits by withdrawing from the heating region, is tested in 18650 cells. In addition to having lower mass and manufacturing costs, cells with metal-coated polymer current collectors demonstrate a reduced risk of thermal runaway during nail penetration. High-speed synchrotron X-ray radiography of 18650 cells during nail-penetration testing, in tandem with pre- and post-mortem X-ray computed tomography, provides insights into the function of the current collectors. The results are compared with those of 18650 cells with standard commercial aluminum and copper current collectors. Cells with aluminum-coated polymer current collectors demonstrated 100% success in thermal runaway prevention during nail penetration, retaining a cell voltage >4.00 V, while standard cells consistently experienced thermal runaway